Something deeply hidden in the forest

[Philip Thrift]

https://twitter.com/WKCosmo/status/1183381747511300102

Sabine Hossenfelder @skdh

·

If a tree drops in the forest, does it decohere and remain in a mixed state of dropped and non-dropped until I come by and update the wavefunction?

(No, it doesn't. That's why decoherence does not solve the measurement problem of quantum mechanics.)

Will Kinney @WKCosmo

Replying to  @skdh

Unless the mixed state density matrix simply encodes the probabilities of various outcomes, in which case you're fine.

Sabine Hossenfelder @skdh

·

Replying to 

@WKCosmo

Have you suddenly become a fan of hidden variables models? In that case, I am totally on your side.

Will Kinney @WKCosmo

I'm not sure why hidden variables are necessary in a probabilistic theory.

Sabine Hossenfelder

@skdh

Oh, they are not necessary. The other alternative is that you give up on reductionism. Is that what you want to advocate?

Will Kinney @WKCosmo

·

If the theory matches reality, sure. I really fail to understand physicists' attachment to a clockwork universe fully determined by boundary conditions. Nature apparently doesn't work that way.

Sabine Hossenfelder @skdh

I see. That's fine with me as long as you acknowledge that in this case the theory is necessarily incomplete because it lacks an explanation for why you need a second postulate for macroscopic objects if their behavior should be derivable, not an additional assumption.

@philipthrift

[Philip Thrift]

(continued)

Will Kinney

@WKCosmo

·

Replying to 

@WKCosmo

 and 

@skdh

Let me try something out on you and see if you agree, at least a little: Suppose that QM is in fact complete, and there is nothing additional underlying it. Shouldn't this tell us something extremely interesting about gravity, even if we haven't figured out what it is yet?

Sabine Hossenfelder

@skdh

·

Oh :( Sorry, I read this after I was just happy to think we agree that QM isn't complete. Well, there is no supposing here, because that view is just inconsistent, that's what I am saying. It's not an option. It cannot be how nature works, we already know that.

Will Kinney

@WKCosmo

·

Hmm. Why must quantum mechanics be incomplete to be probabilistic?

Sabine Hossenfelder

@skdh

·

If you want to interpret the update of the probability to 100% after observation as a statement about the observer's knowledge, you are implicitly assuming that you cannot calculate "observer's knowledge" from the constituents of the observer.

Ian Wardell

@Interesting_Ian

·

Replying to 

@WKCosmo

 and 

@skdh

Physicists demand that reality conforms to their irrational metaphysical presuppositions i.e contiguous causes, reductionism, the mechanistic conception of reality.

@philipthrift 

[Brent Meeker]

On 10/13/2019 1:55 PM, Philip Thrift wrote:

Sabine Hossenfelder

@skdh

Oh, they are not necessary. The other alternative is that you give up on reductionism. Is that what you want to advocate?

Will Kinney @WKCosmo

·

If the theory matches reality, sure. I really fail to understand physicists' attachment to a clockwork universe fully determined by boundary conditions. Nature apparently doesn't work that way.

I think I'm with Kinney.  I don't even see what accepting a probabilistic interpretation of the density matrix has to do with reductionism.  Reductionism doesn't require that every event have a deterministic cause...that just leads to an infinite regress, or a supernatural first-cause.

The interpretation problem is why should the diagonal terms be given a probability interpretation at all when in some other basis the density matrix is not even approximately diagonal?  And if it is given a probability interpretation, what about the cases in which there are very (arbitrarily) many vanishingly small diagonal terms whose total probability is significant (or hard to prove they are not significant).  In other words can be justify the observed classical world as "typical" or is it an improbable freak?

Brent

[Philip Thrift]

Will Kinney  - http://www.acsu.buffalo.edu/~whkinney/ - is on the right path ! with probabilities (and Sabine H. has always presented a view of probabilities that is something where I don't understand what she is talking about), but what this is all about is Sabine always states and states here):

QM (or the Schrodinger Equation, SE) is incomplete because it does not solve the measurement problem, so there must be a new nonlinear SE, and maybe hidden variables. And BTW, MWI doesn't solve the measurement problem either.

and Will is saying 

If probabilities are integrated in QM, [but somehow there are no hidden variables (whatever they are that Sabine is talking about)] then it's OK.

@philipthrift

[John Clark]

 Philip Thrift <cloud...@gmail.com> wrote:

>Have you suddenly become a fan of hidden variables models? In that case, I am totally on your side.

If you're a fan of hidden variables then, to be consistent with experimental results, you must also be a fan of non-locality, or non-reality, or superdeterminism. 

> QM (or the Schrodinger Equation, SE) is incomplete because it does not solve the measurement problem, 

Many Worlds solves the measurement problem because, unlike every other interpretation, it precisely defines what a measurement is, it's just a change, any sort of change. So what you really have is not a measurement problem but a many worlds problem, and it's only a problem for emotional reasons not scientific reasons, some people are just repelled by the idea that there is more than one version of themselves around; but the universe is not required to be in harmony with individual human desires.

> so there must be a new nonlinear SE, 

And all those proposed wheels within wheels added to the Schrodinger Equation and the massive load of additional mathematical complexity that entails does not improve the modified equation's ability to predict experimental results one iota, it gets rid of many worlds and does absolutely nothing else. It reminds me of a fundamentalist preacher's theory that the world was made in 4004 BC and God put dinosaur bones in the ground at that time that look much older but are not, and God can do that because God can do anything. Making quantum calculations is difficult enough as it is, we should be looking for ways to make it easier not harder. 

And by the way, all those modifications of the Schrodinger Equation involve sticking in random factors, Many Worlds has no need of such random factors, it's contend with the simpler deterministic Schrodinger Equation just as it is now.

John K Clark

[Philip Thrift]

The Many Worlds conferences sound like fun.

On the other hand ...

via http://prce.hu

http://prce.hu/w/preprints/QT7.pdf

Backward causation, hidden variables and the meaning

of completeness

Abstract. Bell’s theorem requires the assumption that hidden variables are independent of future measurement settings. This independence assumption rests on surprisingly shaky ground. In particular, it is puzzlingly time-asymmetric. The paper begins with a summary of the case for considering hidden variable models which, in abandoning this independence assumption, allow a degree of ‘backward causation’. The remainder of the paper clarifies the physical significance of such models, in relation to the issue as to whether quantum mechanics provides a complete description of physical

reality.

...

Here is another possibility. Let us think of the ‘hidden’ reality in terms of Feynman paths, between an initial state (e.g., an electron being emitted by a source) and a final state (e.g, detection of that electron at a particular point on the screen in a two-slit experiment). In Feynman’s path integral approach, calculation of the probability of the outcome in question depends on an integration over the possible individual paths between the given initial state and the given final state, each weighted by a complex number. The fact that the weights associated with individual paths are complex makes it impossible to interpret them as realvalued probabilities, associated with a classical statistical distribution of possibilities.

However, there is no such difficulty at the level of the entire ‘bundle’ of paths which comprise the path integral. If we think of the hidden reality as the instantiation not of one path rather than another but of one entire bundle rather than another, then the quantum mechanical probabilities can be thought of as classical probability distributions over such elements of reality. (For example, suppose we specify the boundary conditions in terms of the electron source, the fact that two slits are open, and the fact that a detector screen is present at a certain distance on the opposite side of the central screen. We then partition the detector screen, so as to define possible outcomes for the experiment. For each element of this partition, there is a bundle Bi of Feynman paths, constituting the path integral used in calculating the probability of outcome Oi . We have a classical probability distribution over the set of such Bi .

Of course, this conception of the hidden reality violates IA. The range of possible bundles depends on all the boundary conditions, including those in the future. However, this is the kind of model we were looking for.

@philipthrift 

[John Clark]

On Mon, Oct 14, 2019 at 9:27 AM Philip Thrift <cloud...@gmail.com> wrote:

> Abstract. Bell’s theorem requires the assumption that hidden variables are independent of future measurement settings.

Yes, Bell assumes hidden variables are local, not non-local as backward causality would be.

 John K Clark

[Brent Meeker]

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don't.

Brent

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[Philip Thrift]

https://arxiv.org/abs/quant-ph/9602020 :

Construed as an argument against hidden variable theories, Bell's Theorem assumes that hidden variables would be independent of future measurement settings. This Independence Assumption (IA) is rarely questioned. Bell considered relaxing it to avoid non-locality, but thought that the resulting view left no room for free will. However, Bell seems to have failed to distinguish two different strategies for giving up IA. One strategy takes for granted the Principle of the Common Cause, which requires that a correlation between hidden variables and measurement settings be explained by a joint correlation with some unknown factor in their common past. The other strategy rejects the Principle of the Common Cause, and argues that the required correlation might be due to the known interaction between the object system and the measuring device in their common future. Bell and most others who have discussed these issues have focussed on the former strategy, but because the two approaches have not been properly distinguished, it has not been well appreciated that there is a quite different way to relax IA. This paper distinguishes the two strategies, and argues that the latter is considerably more appealing than the former.

@philipthrift 

[Philip Thrift]

On Monday, October 14, 2019 at 1:20:39 PM UTC-5, Brent wrote:

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don't.

Brent

In the single-particle double-slit experiment*, an observer could see a dot appear anywhere on a screen where path interference does not reduce the probability to zero. So with the literal many-world-branching theory, how many different worlds are produced, each on with its own observer seeing a dot on the screen?

* https://sciencedemonstrations.fas.harvard.edu/presentations/single-photon-interference

In this demonstration we perform the double-slit interference experiment with extremely dim light and show that even when the light intensity is reduced down to several photons/sec, the audience can see the familiar Young's double-slit interference pattern build up over a period of time. This addresses the question of how can single photons interfere with photons that have already gone through the apparatus in the past, or with those that will go through in the future, or with themselves.

@philipthrift

[John Clark]

On Mon, Oct 14, 2019 at 2:20 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

> Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed,

It's not assumed its concluded based on overwhelming experimental evidence and the fact that Gleason's theorem tells us that in 3 spatial dimensions the Born Rule is the only way probability can be unitary. 

 

> If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions

But it can be the probability that something similar to me as I am right now will see Moscow in one second, I say "similar" because the me that might see Moscow in one second would not be exactly the same as the me of right now because that me would see Moscow and I don't right now.

> So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness 

I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

 John K Clark

[Brent Meeker]

On 10/14/2019 12:00 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 2:20 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

> Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed,

It's not assumed its concluded based on overwhelming experimental evidence

But in the theory that's just adding the Born rule on empirical evidence.  For the same reason it implies that only one world is realized.

and the fact that Gleason's theorem tells us that in 3 spatial dimensions the Born Rule is the only way probability can be unitary.

Given unitary evolution you mean.  Probability can be conserved just by renormalizing as in CI, whatever the rule.

 

> If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions

But it can be the probability that something similar to me as I am right now will see Moscow in one second, I say "similar" because the me that might see Moscow in one second would not be exactly the same as the me of right now because that me would see Moscow and I don't right now.

OK, how similar does that something have to be.  Does it have to be conscious?  have memories?  Why can't it exist in a superposition of states?  Remember, being in Moscow or being in Washington is a superposition is some other basis.

> So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness 

I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

But according to MWI it will also take a picture of Washington.  The Born rule isn't part of MWI...it has to derived (or more often just borrowed from CI).  Suppose the camera is triggered by the decay of a radioactive atom and it is taking a picture of a clock.  What time will it have on its film?  Must we suppose there are an uncountable infinity worlds with different times recorded?

Brent

Brent

[Bruce Kellett]

On Tue, Oct 15, 2019 at 5:38 AM Philip Thrift <cloud...@gmail.com> wrote:

On Monday, October 14, 2019 at 1:20:39 PM UTC-5, Brent wrote:

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don't.

Brent

In the single-particle double-slit experiment*, an observer could see a dot appear anywhere on a screen where path interference does not reduce the probability to zero. So with the literal many-world-branching theory, how many different worlds are produced, each on with its own observer seeing a dot on the screen?

According to MWI, an infinite number. Each world will have the dot at a different place on the screen.

Bruce

[Bruce Kellett]

On Tue, Oct 15, 2019 at 7:05 AM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 10/14/2019 12:00 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 2:20 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

> Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed,

It's not assumed its concluded based on overwhelming experimental evidence

But in the theory that's just adding the Born rule on empirical evidence.  For the same reason it implies that only one world is realized.

and the fact that Gleason's theorem tells us that in 3 spatial dimensions the Born Rule is the only way probability can be unitary.

Given unitary evolution you mean.  Probability can be conserved just by renormalizing as in CI, whatever the rule.

Also in MWI. You still have to renormalise the probability once you see the result --  know which branch you are in. Exactly as you have to renormalize the energy according to the result you get. Where is this requirement encoded in the SWE?

Bruce

[Bruce Kellett]

Yes, given MWI. Deutsch even requires an infinite number of parallel worlds, with "shadow" photons, even for the simple two-slit experiment.

Bruce 

[John Clark]

On Mon, Oct 14, 2019 at 4:05 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

>> It's not assumed its concluded based on overwhelming experimental evidence

> But in the theory that's just adding the Born rule on empirical evidence. 

In physics empirical evidence is the only reason you add anything.

> For the same reason it implies that only one world is realized.

How does the empirical evidence from the 2 slit experiment imply there is only one world?    

> Given unitary evolut Probability can be conserved just by renormalizing as in CI, whatever the rule.

But given the fact that the Schrodinger Equation is 100% deterministic what is the physical reason we must deal with probabilities at all? MWI can help us understand why.

 

>> If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions

 

> But it can be the probability that something similar to me as I am right now will see Moscow in one second, I say "similar" because the me that might see Moscow in one second would not be exactly the same as the me of right now because that me would see Moscow and I don't right now.

 

> OK, how similar does that something have to be.

42. How similar does Moscow have to be to be counted as Moscow?

 

 > Does it have to be conscious? 

NO!

>> I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

> But according to MWI it will also take a picture of Washington. 

Yes. That's why the Born Rule can only give probabilities. Under the right circumstances you might be able to say the developed picture will probably be Moscow, but some version of you will see Washington, and there is a non zero probability a electron can tunnel through a energy barrier that it could never do if classical physics was true. Nobody is claiming the MWI allows predictions to be made with total certainty.

> The Born rule isn't part of MWI...it has to derived

This is physics not mathematics, the Born rule isn't derived it's observed, and it's observed to work.

> (or more often just borrowed from CI).

The CI doesn't own the Born Rule, neither does the MWI. All modern interpretations of quantum mechanics are compatible with the Born Rule, they had better be! If one wasn't nobody would be foolish enough to be talking about it today.

 

 > Suppose the camera is triggered by the decay of a radioactive atom and it is taking a picture of a clock.  What time will it have on its film? 

I can't give you a certain answer, only a probability.

> Must we suppose there are an uncountable infinity worlds with different times recorded?

Carroll admits in his book that it isn't clear if there are a denumerably infinite number of worlds or a larger infinity, in fact there may not be a infinite number of worlds at all, there might only be an astronomical number to a astronomical power of them. 

I like Many Worlds because it gives me a little intuitive understanding why we can only make probabilistic predictions even though the underlying mathematics is completely deterministic, and I like it because it gives a precise definition of "measurement". Of course just because I like it doesn't mean it can't be dead wrong. But I would bet money on one thing, if the MWI is wrong then something even stranger is true. 

 John K Clark

 

[Brent Meeker]

On 10/14/2019 2:50 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 4:05 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

>> It's not assumed its concluded based on overwhelming experimental evidence

> But in the theory that's just adding the Born rule on empirical evidence. 

In physics empirical evidence is the only reason you add anything.

But then MWI can't claim to be simpler and "purer" than CI. 

> For the same reason it implies that only one world is realized.

How does the empirical evidence from the 2 slit experiment imply there is only one world?    

> Given unitary evolut Probability can be conserved just by renormalizing as in CI, whatever the rule.

But given the fact that the Schrodinger Equation is 100% deterministic what is the physical reason we must deal with probabilities at all? MWI can help us understand why.

 

>> If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions

 

> But it can be the probability that something similar to me as I am right now will see Moscow in one second, I say "similar" because the me that might see Moscow in one second would not be exactly the same as the me of right now because that me would see Moscow and I don't right now.

 

> OK, how similar does that something have to be.

42. How similar does Moscow have to be to be counted as Moscow?

 

 > Does it have to be conscious? 

NO!

>> I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

> But according to MWI it will also take a picture of Washington. 

Yes. That's why the Born Rule can only give probabilities. Under the right circumstances you might be able to say the developed picture will probably be Moscow, but some version of you will see Washington, and there is a non zero probability a electron can tunnel through a energy barrier that it could never do if classical physics was true. Nobody is claiming the MWI allows predictions to be made with total certainty.

> The Born rule isn't part of MWI...it has to derived

This is physics not mathematics, the Born rule isn't derived it's observed, and it's observed to work.

But then MWI can't claim to be simpler and "purer" than CI.  I has to add a prescription about how to deviate from simple unitary evolution.

> (or more often just borrowed from CI).

The CI doesn't own the Born Rule, neither does the MWI. All modern interpretations of quantum mechanics are compatible with the Born Rule, they had better be! If one wasn't nobody would be foolish enough to be talking about it today.

 

 > Suppose the camera is triggered by the decay of a radioactive atom and it is taking a picture of a clock.  What time will it have on its film? 

I can't give you a certain answer, only a probability.

> Must we suppose there are an uncountable infinity worlds with different times recorded?

Carroll admits in his book that it isn't clear if there are a denumerably infinite number of worlds or a larger infinity, in fact there may not be a infinite number of worlds at all, there might only be an astronomical number to a astronomical power of them. 

I like Many Worlds because it gives me a little intuitive understanding why we can only make probabilistic predictions even though the underlying mathematics is completely deterministic, and I like it because it gives a precise definition of "measurement".

What is this precise definition of which you write?  That your consciousness becomes correlated with an eigenvalue of some Hermitean operator?  Does MWI define when a measurement has taken place or not?

Brent

Of course just because I like it doesn't mean it can't be dead wrong. But I would bet money on one thing, if the MWI is wrong then something even stranger is true. 

 John K Clark

 

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[Brent Meeker]

There's a technical reason MWI needs an infinite number of branches.  It's only in the statistical limit that one can guarantee that the sample probabilities agree with the Born rule.

Brent

[Philip Thrift]

But Sean Carroll would have to say in his book tour that if he was watching the dots appear on the screen one by one there would literally be an infinite number of actual worlds, each one with their very own own Sean Carroll seeing (and remembering) a different temporal dot process than all the other Seans.

@philipthrift

[Brent Meeker]

On 10/14/2019 3:33 PM, Philip Thrift wrote:

On Monday, October 14, 2019 at 5:24:54 PM UTC-5, Brent wrote:

On 10/14/2019 2:50 PM, Bruce Kellett wrote:

On Tue, Oct 15, 2019 at 7:05 AM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 10/14/2019 12:00 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 2:20 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

> So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness 

I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

But according to MWI it will also take a picture of Washington.  The Born rule isn't part of MWI...it has to derived (or more often just borrowed from CI).  Suppose the camera is triggered by the decay of a radioactive atom and it is taking a picture of a clock.  What time will it have on its film?  Must we suppose there are an uncountable infinity worlds with different times recorded?

Yes, given MWI. Deutsch even requires an infinite number of parallel worlds, with "shadow" photons, even for the simple two-slit experiment.

There's a technical reason MWI needs an infinite number of branches.  It's only in the statistical limit that one can guarantee that the sample probabilities agree with the Born rule.

I wondered about that.  In fact the resolution of photographic film (and CCDs) is finite.  The silver iodide molecule and the photon only have to be within a few de Broglie wavelenths for the photon to be absorbed.

Brent

[Lawrence Crowell]

What you say may open up a bit of a hole or snag in MWI. This is something I have been pondering some since Carroll's popularization. If MWI fundamentally preserves unitarity by splitting off worlds then localization of a measurement is an illusion.Consider a particle measured somewhere on a path from x and x'.  The path integral and the nonlocality of paths is a sum over all possible measurements in all space containing x and x', then there must be a continuum of possible worlds splitting off. If the operator has a continuum of eigenvalues x|x> = x|x> there must then be a continuum of possible worlds if there is indeed no fundamental localization with a measurement. This is not just infinite, but uncountably infinite.

This is different from how decoherence maintains unitarity and conserves qubits. There a local interaction occurs that induces quantum phase to enter into a set of ancillary states or reservoir of states. Then we can consider quantum states as finite, but unbounded from above, so that local observations and measurements are possible. 

This does seem to run into some oddities that either need to be worked out or that might indicate some gap in MWI. The persistence of nonlocality in MWI is interesting for possible quantum gravitation work. In that case I can think of maybe a way around this, where this uncountably infinite set of g_{ij} configurations, or Ψ[g_{ij}], can be identified with "exotic" manifolds that are removed. It is less clear how this can happen with ordinary quantum fields that have local realizations.

LC

[Philip Thrift]

To mix an analysis (or a theory) of the path integral with an analysis (or a theory) of MWI is mixing two fundamentally contradictory frameworks that only leads to confusion.

@philipthrift 

[Lawrence Crowell]

I am thinking of a path integral as most physicists do, which is an action principle that is a sum over amplitudes or histories. You are thinking according to the quantum interpretation of Dowker and others, which has auxiliary postulates or assumptions.

LC 

[Philip Thrift]

Path integrals or histories are  not eve brought up in Sean Carroll's book (a search of the text shows).

So they not present in any way in MWI.

MWI (in Sean's mathematical formulation) is contrary to the path integral, because histories (as you mention above) are simply not worlds (in Sean's formulation).

@philipthrift 

[Philip Thrift]

Also see Feynman's Meaning of Probabilities in QM paper.

But there are no probabilities in MWI.

You can't take a probabilistic theory and gloss it onto MWI.

(like putting lipstick on a pig)

@philipthrift 

[Lawrence Crowell]

Path integrals are just methods. Three is nothing any different from QM or QFT without them other than a methodology. Dowker et al are jumping off into an interpretation based on path integrals.

LC 

[Lawrence Crowell]

Carroll and Sebens who a consistency with Born rule and MWI. Born rule is about a spectrum of observable according to probability amplitudes. MWI just does not assign a local probability of a measurement in quite the way a collapse type interpretation does.

LC 

[Brent Meeker]

On 10/15/2019 4:08 AM, Philip Thrift wrote:
>
> Also see Feynman's Meaning of Probabilities in QM paper.
>
> But there are no probabilities in MWI.

There are, but you have to put them in there essentially by slipping the
Born rule in the back door.

Brent

[Philip Thrift]

There is no interpretation outside of methods.

Physicists who pursue "interpretations" without method (without useful application) are wasting their time in  fantasyland, as Sean Carroll is doing.

See:

https://arxiv.org/abs/1807.10749 :

Quantum Supremacy Is Both Closer and Farther than It Appears

Our algorithms can be characterized as Schrödinger-Feynman hybrids.

Our simulator combines highly-optimized Schrödinger-style simulation within each

qubit block and simulates xCZ gates with Feynman-style path summation, to limit memory use. Unlike in Feynman-style simulation, runtime scales with the number of xCZ gates, which is very limited in planar qubitarray architectures with nearest-neighbor gates. Unlike traditional Schrödinger-style simulation, the resulting algorithms are depth-limited, and supercomputer simulations may hold some advantage for very deep circuits. However, near-term quantum computers rely on noisy gates that also limit circuit depth.

@philipthrift

 

[Philip Thrift]

Carroll himself said if you want a stochastic theory, then one world will do.

There is no probability theory that applies to Many Worlds that isn't nonsense.

@philipthrift 

[Philip Thrift]

There is no "no nonsense" way to assign probabilities to worlds in MWI.

May to the bubble worlds of cosmic inflation, but that's a totally different domain.

@philipthrift 

[Philip Thrift]

Or: I have yet to see any Many Worlds (Carroll's, Everett's, ...) used in the actual programming in quantum modeling software.

Where is it? (Surprise me.)

@philipthrift

[Brent Meeker]

On 10/15/2019 10:46 AM, Philip Thrift wrote:
>
> Or: I have yet to see any Many Worlds (Carroll's, Everett's, ...) used
> in the actual programming in quantum modeling software.
>
> Where is it? (Surprise me.)

Curiously, Deutsch used a quantum computer in a thought experiment to
prove multiple worlds.

Brent

[Philip Thrift]

Not the same thing though as a repository of source code (with a Many Worlds algorithms library). 

@philipthrift

[John Clark]

On Mon, Oct 14, 2019 at 6:22 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote: 

>>This is physics not mathematics, the Born rule isn't derived it's observed, and it's observed to work.

> But then MWI can't claim to be simpler and "purer" than CI. 

CI says the laws of physics work one way if a system is not observed and another way if it is observed, and it never makes clear what observed means. The MWI says the laws of physics only work one way and it makes crystal clear what observed means. And I don't know about purer but MWI is certainly simpler than interpretations that are compelled to add extra terms to Schrodinger's Equation that, other than get rid of other worlds, do nothing but complicate a already hideously complicated calculation.

 

>> I like Many Worlds because it gives me a little intuitive understanding why we can only make probabilistic predictions even though the underlying mathematics is completely deterministic, and I like it because it gives a precise definition of "measurement".

 

> That your consciousness becomes correlated with an eigenvalue of some Hermitean operator?

No.

 

 > Does MWI define when a measurement has taken place or not?

It does.

> What is this precise definition of which you write? 

Oh for christ sake! As I've said over and over, in Many Worlds a change, any change, is equivalent to a measurement and it doesn't make the slightest difference if that change involves consciousness or not. If Brent Meeker flips a coin and it comes out heads then obviously that Brent Meeker is not living in the world where it came out tails. In the same way if you do the two slit experiment and the photon goes through slit A then you are not living in the world where it went through slot B, but the 2 slit experiment can be a little different from
the simple coin toss example.

If after the photon makes its decision on which of the 2 slits to go through it then hits a photographic plate then both photons in both universes are destroyed and thus there is no longer any difference between the two, so the universes will merge back together. So in that newly re-merged universe there will be ambiguity about which slit the photon actually went through which is why that photon will contribute to  the interference pattern that shows up on the photographic plate. The important thing is that the photographic plate destroys the photon in both universes so you could replace the plate with a brick wall and the same thing would happen, it would just be harder to tell that something funny was going on.

However if you had a detector next to each slit and sent information on which slit the photon went through to your computer then there would still be a physical difference between universes even though the photon no longer exists in either, one universe would have computer in it with a few magnetic spots on its disk drive indicating the photon went through slot A but in the other universe the magnetic spots would be in a slightly different place indicating slot B, so the universes remain different, so they don't remerge, so there is no ambiguity in either universe, so neither universe will see a interference pattern.  

Universes don't usually merge back together because the differences between them usually accelerates so it's astronomically unlikely they will ever become identical again, however a skilled experimenter can make the change to be very small and then can gently nudge them back together.  If you got rid of the film (or the brick wall) and let the photon head out into infinite space after it passed the slits then the universes, and you, will split and never recombine, and so of course you will see no interference effect. The beautiful part of the theory is that it doesn't have to explain what an observer is and that's why a brick wall will work just as well as a photographic plate.

John K Clark

[John Clark]

On Tue, Oct 15, 2019 at 1:50 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

> Curiously, Deutsch used a quantum computer in a thought experiment to prove multiple worlds.

He did indeed, I read about it 30 years ago in Deutsch's book "The Ghost In The Atom" and that was when I started to take the MWI seriously. Deutsch's test would be very difficult to perform but the reason it's so difficult is not the Many World's fault, the reason is that the conventional view says conscious observers obey different laws of physics, Many Worlds says they do not, so to test who's right we need a mind that uses quantum properties. Quantum Computers have advanced enormously over the last 30 years so I wouldn't be surprised if it or something very much like it is actually performed in a decade or two.

An intelligent quantum computer shoots photons at a metal plate one at a time that has 2 small slits in it, and then the photons hit a photographic plate. Nobody looks at the photographic plate till the very end of the experiment. The quantum mind has detectors near each slit so it knows which slit the various photons went through. After each photon passes the slits but before they hit the photographic plate the quantum mind signs a document saying that it has observed each and every photon and knows which slit each photon went through. It is very important that the document does NOT say which slit any photon went through, it only says that they went through one slit and only one slit  and the mind has knowledge of which one. There is a signed document to this effect for every photon it shoots.

Now the mind uses quantum erasure to completely destroy its memory of which slit any of the photons went through; the only part remaining in the universe is the document which states that each photon went through one and only one slit and the mind (at the time) knew which one. Now develop the photographic plate and look at it. If you see interference bands then the Many World interpretation is correct. If you do not see interference bands then there are no worlds but this one and the conventional quantum interpretation is correct.

This works because in the Copenhagen interpretation when the results of a measurement enters the consciousness of an observer the wave function collapses, in effect all the universes except one disappear without a trace so you get no interference. In the Many Worlds model all the other worlds will converge back into one universe because information on which slit the various photons went through was the only thing that made one universe different from another, so when that was erased they became identical again and merged, but their influence will still be felt, you'll see ambiguous evidence that the photon went through slot A only and ambiguous evidence it went through slot B only, and that's what causes the interference pattern.

John K Clark

[Brent Meeker]

On 10/15/2019 2:14 PM, John Clark wrote:

On Tue, Oct 15, 2019 at 1:50 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

> Curiously, Deutsch used a quantum computer in a thought experiment to prove multiple worlds.

He did indeed, I read about it 30 years ago in Deutsch's book "The Ghost In The Atom" and that was when I started to take the MWI seriously. Deutsch's test would be very difficult to perform but the reason it's so difficult is not the Many World's fault, the reason is that the conventional view says conscious observers obey different laws of physics, Many Worlds says they do not, so to test who's right we need a mind that uses quantum properties. Quantum Computers have advanced enormously over the last 30 years so I wouldn't be surprised if it or something very much like it is actually performed in a decade or two.

An intelligent quantum computer shoots photons at a metal plate one at a time that has 2 small slits in it, and then the photons hit a photographic plate. Nobody looks at the photographic plate till the very end of the experiment. The quantum mind has detectors near each slit so it knows which slit the various photons went through. After each photon passes the slits but before they hit the photographic plate the quantum mind signs a document saying that it has observed each and every photon and knows which slit each photon went through. It is very important that the document does NOT say which slit any photon went through, it only says that they went through one slit and only one slit  and the mind has knowledge of which one. There is a signed document to this effect for every photon it shoots.

Now the mind uses quantum erasure to completely destroy its memory of which slit any of the photons went through; the only part remaining in the universe is the document which states that each photon went through one and only one slit and the mind (at the time) knew which one. Now develop the photographic plate and look at it. If you see interference bands then the Many World interpretation is correct.

But as Scott Aaronson noted the interference had to happen in one world.

If you do not see interference bands then there are no worlds but this one and the conventional quantum interpretation is correct.

This works because in the Copenhagen interpretation when the results of a measurement enters the consciousness of an observer the wave function collapses,

That was von Neumann's (and briefly Wigner's) interpretation, but Bohr, Heisenberg, and others always held that any macroscopic instrument would collapse the wf.  The development of decoherence theory has made that more well defined.

Brent

in effect all the universes except one disappear without a trace so you get no interference. In the Many Worlds model all the other worlds will converge back into one universe because information on which slit the various photons went through was the only thing that made one universe different from another, so when that was erased they became identical again and merged, but their influence will still be felt, you'll see ambiguous evidence that the photon went through slot A only and ambiguous evidence it went through slot B only, and that's what causes the interference pattern.

John K Clark

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[Bruce Kellett]

On Wed, Oct 16, 2019 at 7:47 AM John Clark <johnk...@gmail.com> wrote:

Oh for christ sake! As I've said over and over, in Many Worlds a change, any change, is equivalent to a measurement and it doesn't make the slightest difference if that change involves consciousness or not. If Brent Meeker flips a coin and it comes out heads then obviously that Brent Meeker is not living in the world where it came out tails. In the same way if you do the two slit experiment and the photon goes through slit A then you are not living in the world where it went through slot B, but the 2 slit experiment can be a little different from
the simple coin toss example.

If after the photon makes its decision on which of the 2 slits to go through it then hits a photographic plate then both photons in both universes are destroyed and thus there is no longer any difference between the two, so the universes will merge back together. So in that newly re-merged universe there will be ambiguity about which slit the photon actually went through which is why that photon will contribute to  the interference pattern that shows up on the photographic plate. The important thing is that the photographic plate destroys the photon in both universes so you could replace the plate with a brick wall and the same thing would happen, it would just be harder to tell that something funny was going on.

However if you had a detector next to each slit and sent information on which slit the photon went through to your computer then there would still be a physical difference between universes even though the photon no longer exists in either, one universe would have computer in it with a few magnetic spots on its disk drive indicating the photon went through slot A but in the other universe the magnetic spots would be in a slightly different place indicating slot B, so the universes remain different, so they don't remerge, so there is no ambiguity in either universe, so neither universe will see a interference pattern.  

Universes don't usually merge back together because the differences between them usually accelerates so it's astronomically unlikely they will ever become identical again, however a skilled experimenter can make the change to be very small and then can gently nudge them back together.  If you got rid of the film (or the brick wall) and let the photon head out into infinite space after it passed the slits then the universes, and you, will split and never recombine, and so of course you will see no interference effect. The beautiful part of the theory is that it doesn't have to explain what an observer is and that's why a brick wall will work just as well as a photographic plate.

I think an equivalent experiment has been done. It is the quantum eraser work of Zeilinger and associates:

https://en.wikipedia.org/wiki/Quantum_eraser_experiment

This also illustrates delayed choice, since the decision to erase the "welcher weg"  information can be made after the photons have been recorded on the screen. Ingenious variations of this have been done using polarised photons as carriers of the "which way" information, using rotated polarisers to erase the information or not.

I don't think anyone has seen many worlds emerge from these experiments. They have straightforward interpretation in any quantum interpretation.

Bruce

[Brent Meeker]

On 10/15/2019 1:46 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 6:22 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote: 

>>This is physics not mathematics, the Born rule isn't derived it's observed, and it's observed to work.

> But then MWI can't claim to be simpler and "purer" than CI. 

CI says the laws of physics work one way if a system is not observed and another way if it is observed, and it never makes clear what observed means. The MWI says the laws of physics only work one way and it makes crystal clear what observed means. And I don't know about purer but MWI is certainly simpler than interpretations that are compelled to add extra terms to Schrodinger's Equation that, other than get rid of other worlds, do nothing but complicate a already hideously complicated calculation.

 

>> I like Many Worlds because it gives me a little intuitive understanding why we can only make probabilistic predictions even though the underlying mathematics is completely deterministic, and I like it because it gives a precise definition of "measurement".

 

> That your consciousness becomes correlated with an eigenvalue of some Hermitean operator?

No.

 

 > Does MWI define when a measurement has taken place or not?

It does.

> What is this precise definition of which you write? 

Oh for christ sake! As I've said over and over, in Many Worlds a change, any change, is equivalent to a measurement and it doesn't make the slightest difference if that change involves consciousness or not. If Brent Meeker flips a coin and it comes out heads then obviously that Brent Meeker is not living in the world where it came out tails.

Any change??  What about the world in which a K40 atom in JKC's blood stream decayed compared to one in which it didn't? What about the one were this N2 molecule bounced left instead of right on colliding with that CO2 molecule?

In the same way if you do the two slit experiment and the photon goes through slit A then you are not living in the world where it went through slot B, but the 2 slit experiment can be a little different from
the simple coin toss example.

If after the photon makes its decision on which of the 2 slits to go through it then hits a photographic plate then both photons in both universes are destroyed and thus there is no longer any difference between the two, so the universes will merge back together. So in that newly re-merged universe there will be ambiguity about which slit the photon actually went through which is why that photon will contribute to  the interference pattern that shows up on the photographic plate. The important thing is that the photographic plate destroys the photon in both universes so you could replace the plate with a brick wall and the same thing would happen, it would just be harder to tell that something funny was going on.

However if you had a detector next to each slit and sent information on which slit the photon went through to your computer then there would still be a physical difference between universes even though the photon no longer exists in either, one universe would have computer in it with a few magnetic spots on its disk drive indicating the photon went through slot A but in the other universe the magnetic spots would be in a slightly different place indicating slot B, so the universes remain different, so they don't remerge, so there is no ambiguity in either universe, so neither universe will see a interference pattern.  

Universes don't usually merge back together because the differences between them usually accelerates so it's astronomically unlikely they will ever become identical again, however a skilled experimenter can make the change to be very small and then can gently nudge them back together. 

Well in practice he has to measure them in an orthogonal basis in order to erase the welcher weg.

Brent

If you got rid of the film (or the brick wall) and let the photon head out into infinite space after it passed the slits then the universes, and you, will split and never recombine, and so of course you will see no interference effect. The beautiful part of the theory is that it doesn't have to explain what an observer is and that's why a brick wall will work just as well as a photographic plate.

John K Clark

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[Philip Thrift]

But the path integral is both interpretation of quantum computing - https://arxiv.org/abs/quant-ph/0607151 (2006) - and algorithm for the Google quantum computer simulator - https://arxiv.org/abs/1807.10749 (2018). The Google quantum computer paper does not mention "many worlds".

@philipthrift 

[John Clark]

On Tue, Oct 15, 2019 at 6:01 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

>> Oh for christ sake! As I've said over and over, in Many Worlds a change, any change, is equivalent to a measurement and it doesn't make the slightest difference if that change involves consciousness or not. If Brent Meeker flips a coin and it comes out heads then obviously that Brent Meeker is not living in the world where it came out tails

> Any change?? 

Yes any change, and if you don't like it don't complain to me complain to Schrodinger's Equation.

 

> What about the world in which a K40 atom in JKC's blood stream decayed compared to one in which it didn't?

What about it?

> What about the one were this N2 molecule bounced left instead of right on colliding with that CO2 molecule?

I repeat, what about it?

> Well in practice he has to measure them in an orthogonal basis in order to erase the welcher weg.

I don't quite see how but apparently you think that will result in there being a difference between the two universes and thus you predict no interference pattern will be seen when the photographic plate is developed, but David Deutsch thinks bands of interference will be on that plate. I'm not certain who is right but I'd give 2 to 1 odds that it's Deutsch. Well know for sure before 2050, maybe much sooner.

John K Clark

[Lawrence Crowell]

No it is not. I have worked a derivation of a path integral here before. If I have to I will do it again. There is nothing in a path integral outside of plain vanilla QM or QFT. Dowker and others start to assign ontological meaning to paths and the rest and launch into interpretation.

LC 

[Brent Meeker]

On 10/15/2019 4:10 PM, John Clark wrote:

On Tue, Oct 15, 2019 at 6:01 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

 

>> Oh for christ sake! As I've said over and over, in Many Worlds a change, any change, is equivalent to a measurement and it doesn't make the slightest difference if that change involves consciousness or not. If Brent Meeker flips a coin and it comes out heads then obviously that Brent Meeker is not living in the world where it came out tails

> Any change?? 

Yes any change, and if you don't like it don't complain to me complain to Schrodinger's Equation.

 

> What about the world in which a K40 atom in JKC's blood stream decayed compared to one in which it didn't?

What about it?

Does it produce another world?

> What about the one were this N2 molecule bounced left instead of right on colliding with that CO2 molecule?

I repeat, what about it?

> Well in practice he has to measure them in an orthogonal basis in order to erase the welcher weg.

I don't quite see how but apparently you think that will result in there being a difference between the two universes

No, I think (and know from experiments) that the measurement in an orthogonal basis is necessary to have an interference pattern appear.  If you just leave welcher weg information encoded somewhere there won't be interference.   Didn't you read Carroll's example of quantum erasure?

Brent

and thus you predict no interference pattern will be seen when the photographic plate is developed, but David Deutsch thinks bands of interference will be on that plate. I'm not certain who is right but I'd give 2 to 1 odds that it's Deutsch. Well know for sure before 2050, maybe much sooner.

John K Clark

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[Bruce Kellett]

In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there. So decoherence has set in, and any parallel universes have necessarily become different in some ways. According to your interpretation, therefore, there can then be no interference, because the worlds cannot come back together. But we can restore the interference pattern by quantum erasing the which way information (e.g., by measuring in an orthogonal basis). So it is not a matter of whether there are differences between parallel universes -- it is whether or not the which way information still exists in some form or the other. Deutsch simply got the explanation of interference in terms of interactions between parallel universes wrong.

Bruce

[Philip Thrift]

That's not what the two arXiv papers linked to above suggest.

And as the first one points out, there is the version of QM based on state vectors and the wave function.  But saying these exist (in an interpretation of quantum computing) is as "outlandish" as positing paths or histories as the basic ingredients.

@philipthrift

[Bruno Marchal]

On 14 Oct 2019, at 20:20, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Ot to Mechanism, as Everett already suggested.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don’t.

The others happen too, but are not suited for mechanism to develop. There is no preferred base in the MWI, but only those on which consciousness can stabilise and allow first person plural reality to make sense can be seen by machine.

With Everett, quantum mechanics becomes exactly the physics expected from mechanism: a statistics on relative indexical first person (plural) experience.

Bruno

PS I agree that hidden variable reintroduces 3p indeterminacy, non locality, or threaten physical realism (which is impose by mechanism, btw).  Also, making the SWE non linear demolish the QM prediction, without making the “parallel histories” disappearing. According to Steve Weinberg, it allows interaction in between the “parallel” branches of the superposition, and eventually contradict both thermodynamic and special relativity.

Brent

On 10/14/2019 4:36 AM, John Clark wrote:

 Philip Thrift <cloud...@gmail.com> wrote:

>Have you suddenly become a fan of hidden variables models? In that case, I am totally on your side.

If you're a fan of hidden variables then, to be consistent with experimental results, you must also be a fan of non-locality, or non-reality, or superdeterminism. 

> QM (or the Schrodinger Equation, SE) is incomplete because it does not solve the measurement problem, 

Many Worlds solves the measurement problem because, unlike every other interpretation, it precisely defines what a measurement is, it's just a change, any sort of change. So what you really have is not a measurement problem but a many worlds problem, and it's only a problem for emotional reasons not scientific reasons, some people are just repelled by the idea that there is more than one version of themselves around; but the universe is not required to be in harmony with individual human desires.

> so there must be a new nonlinear SE, 

And all those proposed wheels within wheels added to the Schrodinger Equation and the massive load of additional mathematical complexity that entails does not improve the modified equation's ability to predict experimental results one iota, it gets rid of many worlds and does absolutely nothing else. It reminds me of a fundamentalist preacher's theory that the world was made in 4004 BC and God put dinosaur bones in the ground at that time that look much older but are not, and God can do that because God can do anything. Making quantum calculations is difficult enough as it is, we should be looking for ways to make it easier not harder. 

And by the way, all those modifications of the Schrodinger Equation involve sticking in random factors, Many Worlds has no need of such random factors, it's contend with the simpler deterministic Schrodinger Equation just as it is now.

John K Clark

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[Bruno Marchal]

On 15 Oct 2019, at 00:22, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 10/14/2019 2:50 PM, John Clark wrote:

On Mon, Oct 14, 2019 at 4:05 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

>> It's not assumed its concluded based on overwhelming experimental evidence

> But in the theory that's just adding the Born rule on empirical evidence. 

In physics empirical evidence is the only reason you add anything.

But then MWI can't claim to be simpler and "purer" than CI. 

MWI, that is NON-collapse, is “purer” in the sense that it does not invoke another theory to explain measurement, except mechanism and its “trivial” first person indeterminacy.

Then the real problem is that it has to extract the wave itself from arithmetic, given that arithmetic realise all computations (including all quantum computations). We have to explain why the quantum computation win the “measure battle”, and the logic of self-reference suggest in a precise and testable way how this happens.

Bruno

> For the same reason it implies that only one world is realized.

How does the empirical evidence from the 2 slit experiment imply there is only one world?    

> Given unitary evolut Probability can be conserved just by renormalizing as in CI, whatever the rule.

But given the fact that the Schrodinger Equation is 100% deterministic what is the physical reason we must deal with probabilities at all? MWI can help us understand why.

 

>> If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions

 

> But it can be the probability that something similar to me as I am right now will see Moscow in one second, I say "similar" because the me that might see Moscow in one second would not be exactly the same as the me of right now because that me would see Moscow and I don't right now.

 

> OK, how similar does that something have to be.

42. How similar does Moscow have to be to be counted as Moscow?

 

 > Does it have to be conscious? 

NO!

>> I'll be damned if i can see what consciousness has to do with it. The Born rule would also give the probability a film camera with a automatic one second timer will take a picture that when developed will turn out to be a picture of Moscow.

> But according to MWI it will also take a picture of Washington. 

Yes. That's why the Born Rule can only give probabilities. Under the right circumstances you might be able to say the developed picture will probably be Moscow, but some version of you will see Washington, and there is a non zero probability a electron can tunnel through a energy barrier that it could never do if classical physics was true. Nobody is claiming the MWI allows predictions to be made with total certainty.

> The Born rule isn't part of MWI...it has to derived

This is physics not mathematics, the Born rule isn't derived it's observed, and it's observed to work.

But then MWI can't claim to be simpler and "purer" than CI.  I has to add a prescription about how to deviate from simple unitary evolution.

> (or more often just borrowed from CI).

The CI doesn't own the Born Rule, neither does the MWI. All modern interpretations of quantum mechanics are compatible with the Born Rule, they had better be! If one wasn't nobody would be foolish enough to be talking about it today.

 

 > Suppose the camera is triggered by the decay of a radioactive atom and it is taking a picture of a clock.  What time will it have on its film? 

I can't give you a certain answer, only a probability.

> Must we suppose there are an uncountable infinity worlds with different times recorded?

Carroll admits in his book that it isn't clear if there are a denumerably infinite number of worlds or a larger infinity, in fact there may not be a infinite number of worlds at all, there might only be an astronomical number to a astronomical power of them. 

I like Many Worlds because it gives me a little intuitive understanding why we can only make probabilistic predictions even though the underlying mathematics is completely deterministic, and I like it because it gives a precise definition of "measurement".

What is this precise definition of which you write?  That your consciousness becomes correlated with an eigenvalue of some Hermitean operator?  Does MWI define when a measurement has taken place or not?

Brent

Of course just because I like it doesn't mean it can't be dead wrong. But I would bet money on one thing, if the MWI is wrong then something even stranger is true. 

 John K Clark

 

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[Bruno Marchal]

“Many-worlds” is synonymous with “no collapse”. The worlds are the terms in any superposition, written in any base. 

That some base are better for consciousness to stabilise is no more strange that some planet configuration are better for life to develop.

No need to take the word “world” to much seriously, those are only computations, which exists already in all models of any theory of natural numbers in which you can define addition and multiplication.

Bruno

@philipthrift 

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[Philip Thrift]

On Wednesday, October 16, 2019 at 7:23:53 AM UTC-5, Bruno Marchal wrote:

On 14 Oct 2019, at 20:20, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Ot to Mechanism, as Everett already suggested.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don’t.

The others happen too, but are not suited for mechanism to develop. There is no preferred base in the MWI, but only those on which consciousness can stabilise and allow first person plural reality to make sense can be seen by machine.

With Everett, quantum mechanics becomes exactly the physics expected from mechanism: a statistics on relative indexical first person (plural) experience.

Bruno

PS I agree that hidden variable reintroduces 3p indeterminacy, non locality, or threaten physical realism (which is impose by mechanism, btw).  Also, making the SWE non linear demolish the QM prediction, without making the “parallel histories” disappearing. According to Steve Weinberg, it allows interaction in between the “parallel” branches of the superposition, and eventually contradict both thermodynamic and special relativity.

In this theory, each world branch would have its own population of consciousnesses, branched off from a parent world, a multiplicity of selves: Bruno-.0, then Bruno-0.0, Bruno-0.1, Bruno-0.00, Bruno-0.10, Bruno-0.01, Bruno-0.11, ... no one self anymore.

@philipthrift

[John Clark]

On Tue, Oct 15, 2019 at 7:55 PM 'Brent Meeker' <everyth...@googlegroups.com> wrote:

>>> What about the world in which a K40 atom in JKC's blood stream decayed compared to one in which it didn't?

 

>> What about it?

 

> Does it produce another world?

Do I really have to spell this out? I have said over and over that if Many Worlds is true then ANY change produces another world, a K40 atom in my bloodstream decaying is obviously a change, so obviously another world is produced.

> I think (and know from experiments) that the measurement in an orthogonal basis is necessary to have an interference pattern appear.  If you just leave welcher weg information encoded somewhere there won't be interference.  

That's nice, and that is also obviously true. If the which way information is encoded then obviously the worlds will be different, so obviously they will not merge, so obviously there will be no ambiguity about the photon's path, so obviously there is no interference. But in Deutsch's proposed exparament where is that which way information encoded?? And what exactly is your prediction anyway? There can be only 2 possibilities, at the end of the experiment when the photographic plate is developed will there be interference bands on it or will there not be? When Deutsch's experiment is actually performed, and someday it will be, I have already said I would give 2 to 1 odds that there WILL be interference bands on that all important photographic plate, so now it's your turn to put your money where your mouth is as I have done. How would you place your bet?

John K Clark

[spudb...@aol.com]

My focus (not yours!!!) is ponder the crossing over from universe to universe, which I believe you hold, as impossible. QC universes was Deutsch's spec, on quantum computing and the principle behind it. Good fortune to us all, if we can successfully harness QC. Let is do it to enhance human survival and quality of life. If all it turns out to be merely, a code breaker, then, from my pov. meh!

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[John Clark]

On Tue, Oct 15, 2019 at 8:00 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there.

No. In the delayed choice experiment the decision on if to erase the information about which slit the photon went through can be made after the photon passes through the slit, even billions of years after, but it must be made while the photon still exists and is inflight not after it hits the screen.

 John K Clark

[scerir]

"In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there. So decoherence has set in, and any parallel universes have necessarily become different in some ways. According to your interpretation, therefore, there can then be no interference, because the worlds cannot come back together. But we can restore the interference pattern by quantum erasing the which way information (e.g., by measuring in an orthogonal basis). So it is not a matter of whether there are differences between parallel universes -- it is whether or not the which way information still exists in some form or the other. Deutsch simply got the explanation of interference in terms of interactions between parallel universes wrong.
Bruce"

Zeilinger et al. wrote:
"It is a general feature of delayed-choice experiments
that quantum effects can mimic an influence of future
actions on past events. However, there never emerges
any paradox if the quantum state is viewed only as `catalogue
of our knowledge' (Schroedinger, 1935) without any
underlying hidden variable description. Then the state is
a probability list for all possible measurement outcomes
and not a real physical object. The relative temporal order
of measurement events is not relevant, and no physical
interactions or signals, let alone into the past, are necessary
to explain the experimental results. To interpret
quantum experiments, any attempt in explaining what
happens in an individual observation of one system has
to include the whole experimental configuration and also
the complete quantum state, potentially describing joint
properties with other systems. According to Bohr and
Wheeler, no elementary phenomenon is a phenomenon
until it is a registered phenomenon (Bohr, 1949; Wheeler,
1984). In light of quantum erasure and entanglement
swapping, one might like to even say that some registered
phenomena do not have a meaning unless they are
put in relationship with other registered phenomena (Ma
et al., 2012)." https://arxiv.org/abs/1407.2930

[Brent Meeker]

I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

Brent

[Philip Thrift]

This ("you can erase the information after the photon has hit the screen") can be shown to be possible in Many Worlds theory?

What page of the book? (I'll get a copy and check it out.)

@philipthrift

 

[Brent Meeker]

He's posted it on his blog https://www.preposterousuniverse.com/blog/ almost word-for-word.

Brent

@philipthrift

 

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[John Clark]

On Wed, Oct 16, 2019 at 4:49 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

> I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

If you wait to erase the which way information until after the photon has hit the screen then the experiment would be much easier to perform, but the results of it are obvious and rather dull, you would see interference bands because there would be ambiguity over which slit the photon went through. The more interesting thing to do is to make the decision on whether to erase the which way information or not to erase it until after the photon passes the slits but before it hits the screen; it turns out that if you decide to not erase the information then you don't get a interference pattern, but if you decide to erase it then you do get a interference pattern. And that exparament has already been performed and yes the results are weird because the decision to erase or not to erase the information was made long after, even billions of years after, the photon passed the slits so you might think it would make no difference as far as the picture on the screen is concerned, but it does.

And I think all of this is super interesting, but it is not the experiment Deutsch proposed. And you still haven't told me what your best guess is that Deutsch will find when he develops that all important photographic plate; will he see interference bands or no interference bands? I've already told you how I'd place my money.

 John K Clark

[Brent Meeker]

On 10/16/2019 2:50 PM, John Clark wrote:

On Wed, Oct 16, 2019 at 4:49 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

> I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

If you wait to erase the which way information until after the photon has hit the screen then the experiment would be much easier to perform, but the results of it are obvious and rather dull, you would see interference bands because there would be ambiguity over which slit the photon went through.

Here's Carroll's description from his blog...which is more interesting that just erase or not erase:

When we measured the recording spin in the vertical direction, the result we obtained was entangled with a definite path for the traveling electron: [↑] was entangled with (L), and [↓] was entangled with (R). So by performing that measurement, we knew that the electron had traveled through one slit or the other. But now when we measure the recording spin along the horizontal axis, that’s no longer true. After we do each measurement, we are again in a branch of the wave function where the traveling electron passes through both slits. If we measured spin-left, the traveling electron passing through the right slit picks up a minus sign in its contribution to the wave function, but that’s just math.

By choosing to do our measurement in this way, we have erased the information about which slit the electron went through. This is therefore known as a “quantum eraser experiment.” This erasure doesn’t affect the overall distribution of flashes on the detector screen. It remains smooth and interference-free.

But we not only have the overall distribution of electrons hitting the detector screen; for each impact we know whether the recording electron was measured as spin-left or spin- right. So, instructs our professor with a flourish, let’s go to our computers and separate the flashes on the detector screen into these two groups — those that are associated with spin- left recording electrons, and those that are associated with spin-right. What do we see now?

Interestingly, the interference pattern reappears. The traveling electrons associated with spin-left recording electrons form an interference pattern, as do the ones associated with spin-right. (Remember that we don’t see the pattern all at once, it appears gradually as we detect many individual flashes.) But the two interference patterns are slightly shifted from each other, so that the peaks in one match up with the valleys in the other. There was secretly interference hidden in what initially looked like a featureless smudge.

Adapted from Wikipedia

In retrospect this isn’t that surprising. From looking at how our quantum state Ψ was written with respect to the spin-left and -right recording electrons, each measurement was entangled with a traveling electron going through both slits, so of course it could interfere. And that innocent-seeming minus sign shifted one of the patterns just a bit, so that when combined together the two patterns could add up to a smooth distribution.

You professor seems more amazed by this than you are. “Don’t you see,” she exclaims excitedly. “If we didn’t measure the recording photons at all, or if we measured them along the vertical axis, there was no interference anywhere. But if we measured them along the horizontal axis, there secretly was interference, which we could discover by separating out what happens at the screen when the recording spin was left or right.”

You and your classmates nod their heads, cautiously but with some degree of confusion.

“Think about what that means! The choice about whether to measure our recording spins vertically or horizontally could have been made long after the traveling photons splashed on the recording screen. As long as we stored our recording spins carefully and protected them from becoming entangled with the environment, we could have delayed that choice until years later.”

Sure, the class mumbles to themselves. That sounds right.

“But interference only happens when the traveling electron goes through both slits, and the smooth distribution happens when it goes through only one slit. That decision — go through both slits, or just through one — happens long before we measure the recording electrons! So obviously, our choice to measure them horizontally rather than vertically had to send a signal backward in time to tell the traveling electrons to go through both slits rather than just one!”

After a short, befuddled pause, the class erupts with objections. Decisions? Backwards in time? What are we talking about? The electron doesn’t make a choice to travel through one slit or the other. Its wave function (and that of whatever it’s entangled with) evolves according to the Schrödinger equation, just like always. The electron doesn’t make choices, it unambiguously goes through both slits, but it becomes entangled along the way. By measuring the recording photons along different directions, we can pick out different parts of that entangled wave function, some of which exhibit interference and others do not. Nothing really went backwards in time. It’s kind of a cool result, but it’s not like we’re building a frickin’ time machine here.

The more interesting thing to do is to make the decision on whether to erase the which way information or not to erase it until after the photon passes the slits but before it hits the screen; it turns out that if you decide to not erase the information then you don't get a interference pattern, but if you decide to erase it then you do get a interference pattern. And that exparament has already been performed and yes the results are weird because the decision to erase or not to erase the information was made long after, even billions of years after, the photon passed the slits so you might think it would make no difference as far as the picture on the screen is concerned, but it does.

And I think all of this is super interesting, but it is not the experiment Deutsch proposed. And you still haven't told me what your best guess is that Deutsch will find when he develops that all important photographic plate; will he see interference bands or no interference bands? I've already told you how I'd place my money.

I haven't because I'd have to re-read Deutsch's thought experiment, I don't remember how he proposed to erase the which-way.

Brent

[Philip Thrift]

On Wednesday, October 16, 2019 at 4:47:43 PM UTC-5, Brent wrote:

On 10/16/2019 2:05 PM, Philip Thrift wrote:

On Wednesday, October 16, 2019 at 3:49:12 PM UTC-5, Brent wrote:

On 10/16/2019 8:22 AM, John Clark wrote:

On Tue, Oct 15, 2019 at 8:00 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there.

No. In the delayed choice experiment the decision on if to erase the information about which slit the photon went through can be made after the photon passes through the slit, even billions of years after, but it must be made while the photon still exists and is inflight not after it hits the screen.

I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

Brent

This ("you can erase the information after the photon has hit the screen") can be shown to be possible in Many Worlds theory?

What page of the book? (I'll get a copy and check it out.)

He's posted it on his blog https://www.preposterousuniverse.com/blog/ almost word-for-word.

Brent

Yes, there it is:

https://www.preposterousuniverse.com/blog/2019/09/21/the-notorious-delayed-choice-quantum-eraser/

But as he says: alas, not everyone is an Everettian. 

So either one is an Everettian, or one is something even more outlandish (according to Sean Carroll). 

@philipthrift

 

[John Clark]

On Wed, Oct 16, 2019 at 6:10 PM 'Brent Meeker' v <everyth...@googlegroups.com> wrote:

>> you still haven't told me what your best guess is that Deutsch will find when he develops that all important photographic plate; will he see interference bands or no interference bands? I've already told you how I'd place my money.

 

> I haven't because I'd have to re-read Deutsch's thought experiment

Then I'd strongly suggest you do so.

 John K Clark

[Bruce Kellett]

The quantum erasure-delayed choice experiments that have been done, and discussed by Carroll (in his book and on his blog) are entirely equivalent to Deutsch's thought experiment. The decision to erase or not erase the welcher weg information until after the photons have hit the screen was a central feature of these experiments -- making the results more significant than if the information was erased *before* the photons hit the screen.

Exercise: Explain why the experimenters took trouble to do it *after* the photons hit the screen!

I think the interesting fact is that in the experiments (see Wikipedia), and in Carroll's account and explanation, the assumption of many worlds plays an entirely insignificant role -- the explanation of delayed choice and quantum erasure goes through just as well in a single world as in many worlds. Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds. The existing experiments show this conclusively. The effect is real, but do not require many worlds.

Bruce 

[John Clark]

On Wed, Oct 16, 2019 at 7:53 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> The quantum erasure-delayed choice experiments that have been done,

True.

 

and discussed by Carroll (in his book and on his blog)

True.

> are entirely equivalent to Deutsch's thought experiment.

Bullshit. Where is the intelligent quantum computer? Where is the signed document saying the mind has observed each and every photon and knows which slit each photon went through but not mentioning which slit that is? Where is the fact that the very last step in Deutsch's experiment is not erasing the which way information but is looking at the developed photographic plate?  

> The decision to erase or not erase the welcher weg information until after the photons have hit the screen was a central feature of these experiments

NO!! Deutsch made it clear you erase the which way information AFTER the photons have passed the slits but BEFORE the photons hit the screen! I know this for a fact because 30 years ago when I first heard about his idea I specifically asked him about this very point and he said the erasure must be BEFORE anything hits the screen.

 

>Explain why the experimenters took trouble to do it *after* the photons hit the screen!

After? Took the trouble? After would be easy, and pointless. It is much more difficult to erase the which way information after the photons hit the slits but before they hit the screen, it would also be far more informative.

 

> Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds.

Actually Deutsch didn't say that, he said his experiment would test Many Worlds not prove it correct. When the exparament is actually performed for all I or Deutsch knows it could prove that the Many Worlds idea is dead wrong. I've already told you what my best guess on the outcome so what is your prediction? When that photographic plate is developed will there be interference bands on it or not?

 John K Clark

[Bruce Kellett]

On Thu, Oct 17, 2019 at 11:41 PM John Clark <johnk...@gmail.com> wrote:

On Wed, Oct 16, 2019 at 7:53 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> The quantum erasure-delayed choice experiments that have been done,

True.

 

and discussed by Carroll (in his book and on his blog)

True.

> are entirely equivalent to Deutsch's thought experiment.

Bullshit. Where is the intelligent quantum computer? Where is the signed document saying the mind has observed each and every photon and knows which slit each photon went through but not mentioning which slit that is? Where is the fact that the very last step in Deutsch's experiment is not erasing the which way information but is looking at the developed photographic plate?  

I see, Deutsch was testing the idea that it was consciousness that collapsed the wave function. But, apart from a few flirtations with the idea, none has ever taken that seriously. It is certainly not part of the Copenhagen Interpretation. The Only place I know of that idea being worked out is in the SciFi novel "Quarantine" by Greg Egan.

> The decision to erase or not erase the welcher weg information until after the photons have hit the screen was a central feature of these experiments

NO!! Deutsch made it clear you erase the which way information AFTER the photons have passed the slits but BEFORE the photons hit the screen! I know this for a fact because 30 years ago when I first heard about his idea I specifically asked him about this very point and he said the erasure must be BEFORE anything hits the screen.

Deutsch may have thought it important, but it is not. It is reason is similar to the need to test EPR correlations with the measurements at space-like separations -- given SR, there can be no signal informing one observer of the other's results. In the quantum earless case, if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there. The reason for erasing or not *after* the signal photons hit the screen is to eliminate this possibility -- any signal to the screen would have to be backwards in time. Although some suggested this possibility, it has never been taken seriously.

>Explain why the experimenters took trouble to do it *after* the photons hit the screen!

After? Took the trouble? After would be easy, and pointless. It is much more difficult to erase the which way information after the photons hit the slits but before they hit the screen, it would also be far more informative.

I think you have misunderstood the experiments. The interference pattern is present  if the welcher weg information is erased, whether the erasure takes place before or after the photons hit the screen. If the information is not erased, no interference pattern is seen, even if the idler photons drift off to infinity.

> Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds.

Actually Deutsch didn't say that, he said his experiment would test Many Worlds not prove it correct.

OK. But the alternative that Deutsch seems to have been testing was that only a conscious observer could collapse the wave function. As I have said, this has never been a serious scientific position.

When the exparament is actually performed for all I or Deutsch knows it could prove that the Many Worlds idea is dead wrong. I've already told you what my best guess on the outcome so what is your prediction? When that photographic plate is developed will there be interference bands on it or not?

If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

Bruce

[Brent Meeker]

On 10/17/2019 2:35 PM, Bruce Kellett wrote:

I think you have misunderstood the experiments. The interference pattern is present  if the welcher weg information is erased, whether the erasure takes place before or after the photons hit the screen. If the information is not erased, no interference pattern is seen, even if the idler photons drift off to infinity.

> Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds.

Actually Deutsch didn't say that, he said his experiment would test Many Worlds not prove it correct.

OK. But the alternative that Deutsch seems to have been testing was that only a conscious observer could collapse the wave function. As I have said, this has never been a serious scientific position.

When the exparament is actually performed for all I or Deutsch knows it could prove that the Many Worlds idea is dead wrong. I've already told you what my best guess on the outcome so what is your prediction? When that photographic plate is developed will there be interference bands on it or not?

If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

In Carroll's version of the experiment, which has been performed  arXiv:quant-ph/9903047 v1 13 Mar 1999, the experimenter who arranged that each electron has its welcher weg recorded by a spin UP (left slit) or spin DOWN (right slit) particle does, at the end of the experiment, knows there's a record of which slit each electron went thru, and he can sign an affadavit that says that information is known.   But he doesn't know it consciously; it's recorded by all the spin particles, but not in his memory that he can bring to consciousness.  We know what happens if he signs such an affadavit or if he doesn't, it's the same: if the recording spin particles are measured in a left/right basis the information is erased and the interference pattern can be discerned by considering only particles that measured left or only those measuring right.

So Deutsch was proposing to test whether the conscious AI which could have the recording particles as part of it's memory and presumably be conscious of the up/down spins before they were erased would produce a different result.

But I wonder what happens in Carroll's experiment if, after measuring in the left/right basis and noting that two different interference patterns can then be discerned by considering either those due to left spin recording particles or considering right spin particles, one measures the recording particles again in the up/down basis.  The overall pattern is the same, it's just that  you've relabeled spots on the screen according to whether the second measurement of recording particles assigned them to UP or to DOWN.  Now you can consider the subset labeled UP (or DOWN).  This should be a superposition of ensembles randomly selected from the left and right ensembles and in that case would not show an interference pattern...but the information has certainly been erased (twice)?

Brent

[Bruce Kellett]

On Fri, Oct 18, 2019 at 10:05 AM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

But I wonder what happens in Carroll's experiment if, after measuring in the left/right basis and noting that two different interference patterns can then be discerned by considering either those due to left spin recording particles or considering right spin particles, one measures the recording particles again in the up/down basis.  The overall pattern is the same, it's just that  you've relabeled spots on the screen according to whether the second measurement of recording particles assigned them to UP or to DOWN.  Now you can consider the subset labeled UP (or DOWN).  This should be a superposition of ensembles randomly selected from the left and right ensembles and in that case would not show an interference pattern...but the information has certainly been erased (twice)?

If I understand you, what you are suggesting is that either the left polarized, or right polarized, are measured again in the up-down direction. I think that if you do this second measurement, you will simply reduce the intensity by a factor of two. The welcher weg information was permanently erased by the first left-right measurement.

Bruce

[Brent Meeker]

No.  You just partitioning the spots on the screen in a different way, so there are the same number of spots.  After the first measurement of the recording particles spins, in the left/right basis, you labeled the spots on screen according to left or right.  And when you looked only at the left labeled spots they showed an interference pattern.  And necessarily the right labeled spots were the complement relative to the no-interference pattern. So there are two implicit complementary interference patterns hidden in the no-interference pattern.  But on the second measurement of the recording particles in the up/down basis each one should be up or down with probability 1/2.  So all those measuring UP is just a random selection of the overall ensemble, the ensemble that showed no interference.  So yes it's intensity is reduce (only half the spots end up labeled UP) but it's a no-interference pattern. 

The welcher weg information was permanently erased by the first left-right measurement.

Right.  So why doesn't the interference pattern persist after the second measurement of the recording particles?  I suppose the answer is that it does, we just don't have the information necessary to pick it out anymore.  Still it seems curious that we can erase the which-way once and, by looking at the results, find the interference pattern.  But if we erase twice we can't find it.

Brent

[Bruce Kellett]

Are you suggesting that we lose the original left-right labels? I thought that if you select 'left', then re-measure just those photons in the up-down basis, you still get the 'left' interference pattern, with the spots now randomly labelled 'up' or 'down'. If you put both the 'left' and 'right' photons through the second measurement, and lose the original labels, then the interference pattern may vanish, and you get randomly scattered 'up' and 'down' spots. But that is because you forgot the original separation -- it is still there, you just labelled things differently.

Or am I still missing your point?

Bruce

[Philip Thrift]

So, in the end,  it seems that reading Carroll's book is a huge waste of time after all, if his "explanation" leads to confusion.

@philipthrift

[Brent Meeker]

I was thinking of the second, in which you do the two measurements in succession, like one SG after another so that you never looked at or recorded the first measurement result.  But that would mean you'd have to put the beams back together between the measurements.  In that case the second measurement would be just like the first hadn't happened, and you'd be able to discern an interference pattern.

Brent

[Bruce Kellett]

OK. If you recombine the beams before decoherence, you effectively erase the first erasing measurement. In which case the interference pattern disappears, and the second up-down measurement doesn't do anything except but show the diffraction patterns from each slit separately. (up-down distinguishes the L-R slits -- you know which-way!)

Bruce

[Philip Thrift]

e.g. What Sean proposes is a middle decoherence [from his blog]:

The trickiness relies on the fact that by becoming entangled with a single recording spin rather than with the environment and its zillions of particles, 

         the traveling electrons only became kind-of decohered. 

With just a single particle to worry about observing, we are allowed to contemplate measuring it in different ways. If, as in the conventional double- slit setup, we measured the slit through which the traveling electron went via a macroscopic pointing device, we would have had no choice about what was being observed. True decoherence takes a tiny quantum entanglement and amplifies it, effectively irreversibly, into the environment. In that sense the delayed-choice quantum eraser is a useful thought experiment to contemplate the role of decoherence and the environment in measurement.

In terms of Many Worlds, it sounds like a Middle World.

@philipthrift 

[Bruce Kellett]

Even in Sean's analysis it is clear that delayed choice has nothing to do with many worlds: you get the same analysis in single world or collapse theories, such as GRW.

Bruce

[Philip Thrift]

It seems his book is pointless then.

@philipthrift 

[John Clark]

On Thu, Oct 17, 2019 at 5:35 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> I see, Deutsch was testing the idea that it was consciousness that collapsed the wave function. But, apart from a few flirtations with the idea, none has ever taken that seriously. It is certainly not part of the Copenhagen Interpretation. [...] given SR, there can be no signal informing one observer of the other's results.

I see.... no I take that back  I don't see. You used a very odd word in the above that I don't understand at all, the word is "observer".

 

> if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there.

So you admit it. If you continue to insist Many Worlds do not exist then to explain an experiment that has been performed many times you must postulate new physics and mess with Schrodinger's Equation. 

 

> The reason for erasing or not *after* the signal photons hit the screen is to eliminate this possibility -- any signal to the screen would have to be backwards in time.

If you decide to erase or not to erase after the photon passes the slits but before it hits the photographic plate then to explain the results you've either got to embrace Superdeterminism, backward causality or Many Worlds. If you erase the information after the photon hits the photographic plate then you don't have to embrace anything because the experiment would tell you nothing. It's called The Wheeler Delayed Choice Experiment but it was actually first proposed in 1926 by Gilbert Lewis (he also coined the word "photon"), but it remained just a thought exparament for 81 years and was not actually performed until 2007.

Experimental realization of Wheeler’s delayed-choice GedankenExperiment

Why do you suppose that is, why the big delay between thought experiment and real experiment? Because although it's simple in concept it's very difficult to actually perform, you need super fast electronics and a very good random number generator to make the split second decision to erase or not to erase in the ultra short amount time between the photon passing the slit and it hitting the photographic plate. If you could take your time and wait until after it hit the plate Lewis could have not just talked about it but actually done the exparament in 1926 and he wouldn't have needed advanced electronics; steam powered, or even horse powered, machinery would have been good enough.
 

>> After? Took the trouble? After would be easy, and pointless. It is much more difficult to erase the which way information after the photons hit the slits but before they hit the screen, it would also be far more informative.

  The interference pattern is present  if the welcher weg information is erased,

Yes,

 

> whether the erasure takes place before or after the photons hit the screen.

Yes but you can't expect to learn anything if you look at the developed photograph and then decide whether to erase the which way information or not. If you decide to erase the information do you imagine you will see the photograph change before your eyes??

> If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

If that's the way the exparament turns out and a interference pattern exists but Many Worlds does not exist then how do you explain the existence of a signed document testifying that somebody observed the photon going through one and only one slit and the he knew which one? Inquiring minds want to know.  

John K Clark

[Philip Thrift]

That appears right and that Sabine Hossenfelder would agree.

So if there just just One World, what does that tell you?

@philipthrift

[Brent Meeker]

On 10/18/2019 7:39 AM, John Clark wrote:

Yes but you can't expect to learn anything if you look at the developed photograph and then decide whether to erase the which way information or not. If you decide to erase the information do you imagine you will see the photograph change before your eyes??

It will change before your eyes when you partition the points into those whose erasure measurement was left rather than right.  Didn't you read Carroll's blog explication of the experiment?  Many worlds are irrelevant to the phenomenon.

> If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

If that's the way the exparament turns out and a interference pattern exists but Many Worlds does not exist then how do you explain the existence of a signed document testifying that somebody observed the photon going through one and only one slit and the he knew which one? Inquiring minds want to know.  

I want to know how the AI did the measurement and the erasure, and what consciousness had to do with it?  We could easily connect a computer to the array of particles whose spin is used to record the welcher weg.  But how would the AI of the computer "know" those values.  I think it would have to interact with them so as to create classical records, in which case the interference would be wiped out.  On the other hand if the AI is only required to know that the array of particles recorded the welcher weg and then were quantum-erased by a measurement in the orthogonal basis, it can sign the affadavit and the interference pattern will be there implicit in the partition of the film spots according to the result of the erasure experiment...just as Carroll describes.  But the existence of this affadavit is not mysterious.  A human experimenter who knows and understands the setup could sign an affadavit saying the welcher weg was known and then erased.

Brent

[John Clark]

On Fri, Oct 18, 2019 at 3:39 PM 'Brent Meeker' <everyth...@googlegroups.com> wrote: 

> I want to know how the AI did the measurement

The same way a human does.

 

> and the erasure,

The same way Lewis and then Wheeler said.

and what consciousness had to do with it? 

The AI's consciousness, which it claims to have, has just as much to do with it as your consciousness has, which you also claim to have. And that would be zero, which is also exactly as much evidence I have that either of your claims of being conscious are true. And Brent there is one more thing, you're dead wrong about the information being erased after the photograph is made, and I think deep down you've come to realize that.

John K Clark

[Bruce Kellett]

On Sat, Oct 19, 2019 at 1:39 AM John Clark <johnk...@gmail.com> wrote:

On Thu, Oct 17, 2019 at 5:35 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> I see, Deutsch was testing the idea that it was consciousness that collapsed the wave function. But, apart from a few flirtations with the idea, none has ever taken that seriously. It is certainly not part of the Copenhagen Interpretation. [...] given SR, there can be no signal informing one observer of the other's results.

I see.... no I take that back  I don't see. You used a very odd word in the above that I don't understand at all, the word is "observer".

And you dishonestly deleted all the intervening explanatory text.

> if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there.

So you admit it. If you continue to insist Many Worlds do not exist then to explain an experiment that has been performed many times you must postulate new physics and mess with Schrodinger's Equation. 

Not at all. The results of the experiment are easily explained within the structures of conventional quantum mechanics, whatever interpretation one wishes to adopt. There is nothing mysterious here.

> The reason for erasing or not *after* the signal photons hit the screen is to eliminate this possibility -- any signal to the screen would have to be backwards in time.

If you decide to erase or not to erase after the photon passes the slits but before it hits the photographic plate then to explain the results you've either got to embrace Superdeterminism, backward causality or Many Worlds.

No, you have got it wrong here. No need for any of this.

If you erase the information after the photon hits the photographic plate then you don't have to embrace anything because the experiment would tell you nothing. It's called The Wheeler Delayed Choice Experiment but it was actually first proposed in 1926 by Gilbert Lewis (he also coined the word "photon"), but it remained just a thought exparament for 81 years and was not actually performed until 2007.

Experimental realization of Wheeler’s delayed-choice GedankenExperiment

Why do you suppose that is, why the big delay between thought experiment and real experiment? Because although it's simple in concept it's very difficult to actually perform, you need super fast electronics and a very good random number generator to make the split second decision to erase or not to erase in the ultra short amount time between the photon passing the slit and it hitting the photographic plate. If you could take your time and wait until after it hit the plate Lewis could have not just talked about it but actually done the exparament in 1926 and he wouldn't have needed advanced electronics; steam powered, or even horse powered, machinery would have been good enough.

The decision to erase or not to erase is made at a space-like separation from the screen in the experiment you cite. This was done, presumably, to eliminate the possibility of unknown physics informing the photons in-flight, or at the screen, about what choice was made. Delaying the choice until after the photons hit the screen achieves the same end. Why do you think it is called "delayed choice" after all?

>> After? Took the trouble? After would be easy, and pointless. It is much more difficult to erase the which way information after the photons hit the slits but before they hit the screen, it would also be far more informative.

  The interference pattern is present  if the welcher weg information is erased,

Yes,

 

> whether the erasure takes place before or after the photons hit the screen.

Yes but you can't expect to learn anything if you look at the developed photograph and then decide whether to erase the which way information or not. If you decide to erase the information do you imagine you will see the photograph change before your eyes??

Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob.

I think you should go back and read Sean Carroll's account of this (on his blog, or in his book) a bit more carefully. You could even go the the Wikipedia page on this:

https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

to see how it works. 

> If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

If that's the way the exparament turns out and a interference pattern exists but Many Worlds does not exist then how do you explain the existence of a signed document testifying that somebody observed the photon going through one and only one slit and the he knew which one? Inquiring minds want to know.

The signed document is irrelevant because it does not contain the welcher weg information. Many worlds has nothing to do with it. I am assuming that when you say the information was erased from the QC memory, then you mean completely erased, no traces left anywhere. Failure to completely erase the information, even if it is not easily accessible, will result in loss of the interference patterns.

I really do think that you have to do a bit more work in order to understand what is going on here.

Bruce 

[Brent Meeker]

On 10/18/2019 1:04 PM, John Clark wrote:

On Fri, Oct 18, 2019 at 3:39 PM 'Brent Meeker' <everyth...@googlegroups.com> wrote: 

> I want to know how the AI did the measurement

The same way a human does.

In that case it would not be erasable because a human being is big and hot and decoherence would be statistically irreversible.  The point of imaging a conscious AI in a quantum computer was that the quantum AI could "know" things yet still quantum erase them.

 

> and the erasure,

The same way Lewis and then Wheeler said.

and what consciousness had to do with it? 

The AI's consciousness, which it claims to have, has just as much to do with it as your consciousness has, which you also claim to have. And that would be zero, which is also exactly as much evidence I have that either of your claims of being conscious are true.

I agree it should have nothing to do with it.  But I think it was an essential point for Deutsch because he wanted to test whether consciousness collapsed the wf.  However, as I wrote, it's been a long time since I read Deutsch's experiment.  What I was referring to in my post was Carroll's blog description of the delayed erasure experiment.

And Brent there is one more thing, you're dead wrong about the information being erased after the photograph is made, and I think deep down you've come to realize that.

I don't know what you're talking about.  It's explicit in Carroll's blog that the welcher weg is erased after the many particles have hit the screen a at low rate (one per hour). 

Brent

John K Clark

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[Bruno Marchal]

On 16 Oct 2019, at 15:45, Philip Thrift <cloud...@gmail.com> wrote:

On Wednesday, October 16, 2019 at 7:23:53 AM UTC-5, Bruno Marchal wrote:

On 14 Oct 2019, at 20:20, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

Part of the dislike of the MWI is that its proponents assume a purity that is not an evident virtue of the intepretation.  For example, interpreting the squared amplitudes as probabilities seems to be assumed, along with the existence of the preferred basis in which the amplitudes are defined.  Together these are almost the same as CI.  If you ask "probabilities of what?" in MWI the answer can't be probability of existing because MWI has committed to all solutions, however improbable, existing.  So it becomes probability of finding yourself in a particular world...which depends on a theory of consciousness and seems to regress to von Neumann and Wigner.

Ot to Mechanism, as Everett already suggested.

Zurek's envariance attempts to answer these questions and provide a justification for preferred bases and what probability refers to.  But notice that to the extent he succeeds he is justifying taking a simple probabilistic view and saying one of those preferred states happens and the others don’t.

The others happen too, but are not suited for mechanism to develop. There is no preferred base in the MWI, but only those on which consciousness can stabilise and allow first person plural reality to make sense can be seen by machine.

With Everett, quantum mechanics becomes exactly the physics expected from mechanism: a statistics on relative indexical first person (plural) experience.

Bruno

PS I agree that hidden variable reintroduces 3p indeterminacy, non locality, or threaten physical realism (which is impose by mechanism, btw).  Also, making the SWE non linear demolish the QM prediction, without making the “parallel histories” disappearing. According to Steve Weinberg, it allows interaction in between the “parallel” branches of the superposition, and eventually contradict both thermodynamic and special relativity.

In this theory, each world branch would have its own population of consciousnesses, branched off from a parent world, a multiplicity of selves: Bruno-.0, then Bruno-0.0, Bruno-0.1, Bruno-0.00, Bruno-0.10, Bruno-0.01, Bruno-0.11, ... no one self anymore.

No one unique, or no one one with a unique life. Yes. 

It is a consequence of mechanism, but it it is not clear to me if a non mechanist theory can evacuate easily this self-multiplication, except by adding some absolute unicity axiom. But how to test it? Such theory would make both Mechanism wrong, and Quantum Mechanics wrong.

Bruno

@philipthrift

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[Bruno Marchal]

On 16 Oct 2019, at 17:16, spudboy100 via Everything List <everyth...@googlegroups.com> wrote:

My focus (not yours!!!) is ponder the crossing over from universe to universe, which I believe you hold, as impossible. QC universes was Deutsch's spec, on quantum computing and the principle behind it. Good fortune to us all, if we can successfully harness QC. Let is do it to enhance human survival and quality of life. If all it turns out to be merely, a code breaker, then, from my pov. meh!

The QC can also find a needle in a haystack more quickly (but not exponentially more quickly) than a classical computer. And diverse other things, so it might be that some day it will just enhance classical computing.

In a sense, even today’s laptop’s existence is a quantum phenomenon, as it is an exploitation of a quantum phenomenon which explains how work electronics and transistors and allows their impressive miniaturisation. 

We might pass continuously from classical computing to quantum computing without most user noticing it. People will not be more aware of what the machine does than they are aware today.

Bruno

-----Original Message-----
From: John Clark <johnk...@gmail.com>
To: everything-list <everyth...@googlegroups.com>
Sent: Tue, Oct 15, 2019 5:14 pm
Subject: Re: Something deeply hidden in the forest

On Tue, Oct 15, 2019 at 1:50 PM 'Brent Meeker'  <everyth...@googlegroups.com> wrote:

> Curiously, Deutsch used a quantum computer in a thought experiment to prove multiple worlds.

He did indeed, I read about it 30 years ago in Deutsch's book "The Ghost In The Atom" and that was when I started to take the MWI seriously. Deutsch's test would be very difficult to perform but the reason it's so difficult is not the Many World's fault, the reason is that the conventional view says conscious observers obey different laws of physics, Many Worlds says they do not, so to test who's right we need a mind that uses quantum properties. Quantum Computers have advanced enormously over the last 30 years so I wouldn't be surprised if it or something very much like it is actually performed in a decade or two.

An intelligent quantum computer shoots photons at a metal plate one at a time that has 2 small slits in it, and then the photons hit a photographic plate. Nobody looks at the photographic plate till the very end of the experiment. The quantum mind has detectors near each slit so it knows which slit the various photons went through. After each photon passes the slits but before they hit the photographic plate the quantum mind signs a document saying that it has observed each and every photon and knows which slit each photon went through. It is very important that the document does NOT say which slit any photon went through, it only says that they went through one slit and only one slit  and the mind has knowledge of which one. There is a signed document to this effect for every photon it shoots.

Now the mind uses quantum erasure to completely destroy its memory of which slit any of the photons went through; the only part remaining in the universe is the document which states that each photon went through one and only one slit and the mind (at the time) knew which one. Now develop the photographic plate and look at it. If you see interference bands then the Many World interpretation is correct. If you do not see interference bands then there are no worlds but this one and the conventional quantum interpretation is correct.

This works because in the Copenhagen interpretation when the results of a measurement enters the consciousness of an observer the wave function collapses, in effect all the universes except one disappear without a trace so you get no interference. In the Many Worlds model all the other worlds will converge back into one universe because information on which slit the various photons went through was the only thing that made one universe different from another, so when that was erased they became identical again and merged, but their influence will still be felt, you'll see ambiguous evidence that the photon went through slot A only and ambiguous evidence it went through slot B only, and that's what causes the interference pattern.

John K Clark

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[Bruno Marchal]

> On 16 Oct 2019, at 17:43, 'scerir' via Everything List <everyth...@googlegroups.com> wrote:
>
>
> "In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there. So decoherence has set in, and any parallel universes have necessarily become different in some ways. According to your interpretation, therefore, there can then be no interference, because the worlds cannot come back together. But we can restore the interference pattern by quantum erasing the which way information (e.g., by measuring in an orthogonal basis). So it is not a matter of whether there are differences between parallel universes -- it is whether or not the which way information still exists in some form or the other. Deutsch simply got the explanation of interference in terms of interactions between parallel universes wrong.
> Bruce"
>
> Zeilinger et al. wrote:
> "It is a general feature of delayed-choice experiments
> that quantum effects can mimic an influence of future
> actions on past events. However, there never emerges
> any paradox if the quantum state is viewed only as `catalogue
> of our knowledge' (Schroedinger, 1935) without any
> underlying hidden variable description. Then the state is
> a probability list for all possible measurement outcomes
> and not a real physical object. The relative temporal order
> of measurement events is not relevant, and no physical
> interactions or signals, let alone into the past, are necessary
> to explain the experimental results. To interpret
> quantum experiments, any attempt in explaining what
> happens in an individual observation of one system has
> to include the whole experimental configuration and also
> the complete quantum state, potentially describing joint
> properties with other systems. According to Bohr and
> Wheeler, no elementary phenomenon is a phenomenon
> until it is a registered phenomenon (Bohr, 1949; Wheeler,
> 1984). In light of quantum erasure and entanglement
> swapping, one might like to even say that some registered
> phenomena do not have a meaning unless they are
> put in relationship with other registered phenomena (Ma
> et al., 2012)." https://arxiv.org/abs/1407.2930



Quantum erasing occurs already in arithmetic, by amnesia, i.e. classical memory erasing, which fuse the first person experiences. I agree with Zeilinger that the quantum state is just a first person (plural thanks to the tensor product) state description, but the divergence and convergence of the histories leads still to “many-histories” or “many-dreams”, which confirms the many dreams internal interpretation of elementary arithmetic implied by “simple” Mechanism.

Mechanism is mainly “One-Person—Many Dreams” somehow. First person plural is a way for that person to say “hello” to itself in the coherent set of sharable dreams.

Maybe some people have a too much naive conception of God and Universe, which is normal when metaphysics and theology have been taken out of science since so long (to exploit fear and wishful thinking for special interests).

Bruno

>
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[Bruno Marchal]

On 16 Oct 2019, at 23:47, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 10/16/2019 2:05 PM, Philip Thrift wrote:

On Wednesday, October 16, 2019 at 3:49:12 PM UTC-5, Brent wrote:

On 10/16/2019 8:22 AM, John Clark wrote:

On Tue, Oct 15, 2019 at 8:00 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there.

No. In the delayed choice experiment the decision on if to erase the information about which slit the photon went through can be made after the photon passes through the slit, even billions of years after, but it must be made while the photon still exists and is inflight not after it hits the screen.

I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

Brent

This ("you can erase the information after the photon has hit the screen") can be shown to be possible in Many Worlds theory?

What page of the book? (I'll get a copy and check it out.)

He's posted it on his blog https://www.preposterousuniverse.com/blog/ almost word-for-word.

This corroborates with the fact that MWI, i.e. NON-collapse, does not allow neither FTL, nor retro-causality.

My “advise”: if your theory or your interpretation leads to FTL action, change the theory or the interpretation.

Bruno

Brent

@philipthrift

 

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[Bruno Marchal]

On 17 Oct 2019, at 23:35, Bruce Kellett <bhkel...@gmail.com> wrote:

On Thu, Oct 17, 2019 at 11:41 PM John Clark <johnk...@gmail.com> wrote:

On Wed, Oct 16, 2019 at 7:53 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> The quantum erasure-delayed choice experiments that have been done,

True.

 

and discussed by Carroll (in his book and on his blog)

True.

> are entirely equivalent to Deutsch's thought experiment.

Bullshit. Where is the intelligent quantum computer? Where is the signed document saying the mind has observed each and every photon and knows which slit each photon went through but not mentioning which slit that is? Where is the fact that the very last step in Deutsch's experiment is not erasing the which way information but is looking at the developed photographic plate?  

I see, Deutsch was testing the idea that it was consciousness that collapsed the wave function. But, apart from a few flirtations with the idea, none has ever taken that seriously. It is certainly not part of the Copenhagen Interpretation. The Only place I know of that idea being worked out is in the SciFi novel "Quarantine" by Greg Egan.

Well, it has been defended by prominent people, like von Neuman, Wigner, London and Bauer, Walker, and many others. 

I tend to think this view has been shown to be inconsistent by Abner Shimony. 

It makes also no sense in any theory in which the observer does fully obey to quantum mechanics, like in all Mechanist theory of mind (used more or less explicitly by Everett at the start).

With mechanism, there is no collapse of “the wave”, but there is no wave either. The wave described only the relative map on the accessible state, and is (retro)predicted by the fact that first person plural self-reference implies a quantum logic and the quantisation of the observable.

Bruno

> The decision to erase or not erase the welcher weg information until after the photons have hit the screen was a central feature of these experiments

NO!! Deutsch made it clear you erase the which way information AFTER the photons have passed the slits but BEFORE the photons hit the screen! I know this for a fact because 30 years ago when I first heard about his idea I specifically asked him about this very point and he said the erasure must be BEFORE anything hits the screen.

Deutsch may have thought it important, but it is not. It is reason is similar to the need to test EPR correlations with the measurements at space-like separations -- given SR, there can be no signal informing one observer of the other's results. In the quantum earless case, if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there. The reason for erasing or not *after* the signal photons hit the screen is to eliminate this possibility -- any signal to the screen would have to be backwards in time. Although some suggested this possibility, it has never been taken seriously.

>Explain why the experimenters took trouble to do it *after* the photons hit the screen!

After? Took the trouble? After would be easy, and pointless. It is much more difficult to erase the which way information after the photons hit the slits but before they hit the screen, it would also be far more informative.

I think you have misunderstood the experiments. The interference pattern is present  if the welcher weg information is erased, whether the erasure takes place before or after the photons hit the screen. If the information is not erased, no interference pattern is seen, even if the idler photons drift off to infinity.

> Deutsch was simply wrong when he thought that his experiment would "prove" the existence of many worlds.

Actually Deutsch didn't say that, he said his experiment would test Many Worlds not prove it correct.

OK. But the alternative that Deutsch seems to have been testing was that only a conscious observer could collapse the wave function. As I have said, this has never been a serious scientific position.

When the exparament is actually performed for all I or Deutsch knows it could prove that the Many Worlds idea is dead wrong. I've already told you what my best guess on the outcome so what is your prediction? When that photographic plate is developed will there be interference bands on it or not?

If the welcher weg information is quantum erased, then there will be an interference pattern, whether or not it is a conscious observer who is erased.

Bruce

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[Philip Thrift]

On Saturday, October 19, 2019 at 1:06:39 AM UTC-5, Bruno Marchal wrote:

On 16 Oct 2019, at 23:47, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 10/16/2019 2:05 PM, Philip Thrift wrote:

On Wednesday, October 16, 2019 at 3:49:12 PM UTC-5, Brent wrote:

On 10/16/2019 8:22 AM, John Clark wrote:

On Tue, Oct 15, 2019 at 8:00 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> In the delayed choice experiment, the decision whether or not to quantum erase the "which way" information can be made long after the original photons hit the screen and make their marks there.

No. In the delayed choice experiment the decision on if to erase the information about which slit the photon went through can be made after the photon passes through the slit, even billions of years after, but it must be made while the photon still exists and is inflight not after it hits the screen.

I thought you read Carroll's book.  His example shows in what sense you can erase the information after the photon has hit the screen.

Brent

This ("you can erase the information after the photon has hit the screen") can be shown to be possible in Many Worlds theory?

What page of the book? (I'll get a copy and check it out.)

He's posted it on his blog https://www.preposterousuniverse.com/blog/ almost word-for-word.

This corroborates with the fact that MWI, i.e. NON-collapse, does not allow neither FTL, nor retro-causality.

My “advise”: if your theory or your interpretation leads to FTL action, change the theory or the interpretation.

Bruno

Anyone who has an interest in CLP (concurrent logic programming), or SCLP (stochastic CLP) might think of a logical processes (in the CLP sense) version of physics (nature as "billions and billions" of processes). The logical variable would play a role as a hidden variable (the term mentioned in some QM references) because its binding could allow one process to instantly "update" another process separated from it by either space or time (either spacial or temporal nonlocality).

* Two reference for concurrent logic programming:

– Guarded Horn Clauses: Application and Implementation

– The Family of Concurrent Logic Programming Languages

In Stochastic Concurrent Prolog The GHC (guarded Horn clause) is extended to probabilistic GHCs:

Head :- Guard / Probability | Body.

@philipthrift 

[smitra]

On 19-10-2019 00:33, 'Brent Meeker' via Everything List wrote:
> On 10/18/2019 1:04 PM, John Clark wrote:
>
>> On Fri, Oct 18, 2019 at 3:39 PM 'Brent Meeker'
>> <everyth...@googlegroups.com> wrote:
>>

>>> _ > I want to know how the AI did the measurement_

>>
>> The same way a human does.
>
> In that case it would not be erasable because a human being is big and
> hot and decoherence would be statistically irreversible. The point of
> imaging a conscious AI in a quantum computer was that the quantum AI
> could "know" things yet still quantum erase them.

It would be erasable in principle, because of local nature of the laws
of physics (I'm not talking about quantum non-locality here, that's
irrelevant here). When you perform a measurement and are conscious about
the results, this process unfolds in a finite amount of time, therefore
only a finite number of physical degrees of freedom can have become
entangled with the measured quantum system. That number may be
astronomically large, but it's ultimately just a finite number.

This means that the entire process can be simulated by a quantum
computer that has only a finite number of qubits. It doesn't matter that
it cannot be done in practice for the argument that QM (where everything
including observers are described in a unified way) implies the MWI. The
only way to avoid the MWI is to assume that QM is not exactly true. But
note that QM not being exactly true may still lead to a multiverse.

Saibal

[Brent Meeker]

On 10/19/2019 8:49 AM, smitra wrote:
> On 19-10-2019 00:33, 'Brent Meeker' via Everything List wrote:
>> On 10/18/2019 1:04 PM, John Clark wrote:
>>
>>> On Fri, Oct 18, 2019 at 3:39 PM 'Brent Meeker'
>>> <everyth...@googlegroups.com> wrote:
>>>
>>>> _ > I want to know how the AI did the measurement_
>>>
>>> The same way a human does.
>>
>> In that case it would not be erasable because a human being is big and
>> hot and decoherence would be statistically irreversible.  The point of
>> imaging a conscious AI in a quantum computer was that the quantum AI
>> could "know" things yet still quantum erase them.
>
> It would be erasable in principle, because of local nature of the laws
> of physics (I'm not talking about quantum non-locality here, that's
> irrelevant here). When you perform a measurement and are conscious
> about the results, this process unfolds in a finite amount of time,
> therefore only a finite number of physical degrees of freedom can have
> become entangled with the measured quantum system. That number may be
> astronomically large, but it's ultimately just a finite number.

So that would make it just as irreversible as thermodynamics.  But in
fact it's even less reversible, because only a bit of information has to
be carried away at the speed of light, so that it is in-principle
irreversible, to prevent erasure.

>
> This means that the entire process can be simulated by a quantum
> computer that has only a finite number of qubits. It doesn't matter
> that it cannot be done in practice for the argument that QM (where
> everything including observers are described in a unified way) implies
> the MWI. The only way to avoid the MWI is to assume that QM is not
> exactly true.

You mean Everett's QM...whether it's QM is what the question.  QM worked
just fine for 30yrs without Everett.  And QBism is an alternative that
leaves QM exactly true; just interpreted differently.

Personally, I think the long sought theory that merges QM and GR may
modify QM by cutting off small probabilities based on the holographic
principle.

Brent

[John Clark]

On Fri, Oct 18, 2019 at 6:31 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> I see, Deutsch was testing the idea that it was consciousness that collapsed the wave function. But, apart from a few flirtations with the idea, none has ever taken that seriously. It is certainly not part of the Copenhagen Interpretation. [...] given SR, there can be no signal informing one observer of the other's results.

I see.... no I take that back  I don't see. You used a very odd word in the above that I don't understand at all, the word is "observer".

> And you dishonestly deleted all the intervening explanatory text.

I must have inadvertently deleted that "intervening explanatory text" so well that now even I can no longer find it, and that's a pity as it could solve the greatest mystery of the age. Please repeat your explanation of exactly what a "observer" is, a explanation that is different from the one provided by Many Worlds as you don't like that one for some reason.

 

> if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there.

So you admit it. If you continue to insist Many Worlds do not exist then to explain an experiment that has been performed many times you must postulate new physics and mess with Schrodinger's Equation. 

> Not at all. The results of the experiment are easily explained within the structures of conventional quantum mechanics, whatever interpretation one wishes to adopt. There is nothing mysterious here.

There is a lot of mystery here! In 2007 entangled photons were sent 89 miles between La Palma and Tenerife, the decision to erase or not to erase was made in less time than it took for light to travel those 89 miles and hit the detector:

Quantum Spookiness Spans the Canary Islands

The last potential loophole, the freedom of choice loophole, was pretty much closed in April 2018. That loophole says that maybe your measurement settings that chose between erase and don't erase are not really random after all, there might be a deterministic process that makes the choice and misleads us:

Quantum entanglement loophole quashed by quasar light

They state that:

"Arguably the most interesting assumption is that the choice of measurement settings is “free and random,” and independent of any physical process that could affect the measurement outcomes. As Bell himself noted, his inequality was derived under the assumption “that the settings of instruments are in some sense free variables, say at the whim of experimenters, or in any case not determined in the overlap of the backward light cones.”

So to close this loophole they didn't use a standard random number generator to make the choice to erase or not erase the information in the short amount of time it takes light to travel those 89 miles before (yes BEFORE) the photon hit their detector; instead they used the light from a distant quasar to make the decision, so if its a conspiracy to mislead us (as Superdeterminism says) it's a grand conspiracy indeed. They conclude:

"This experiment pushes back to at least 7.8 billion years the most recent time by which any local-realist influences could have exploited the “freedom-of-choice” loophole to engineer the observed Bell violation"

>> If you decide to erase or not to erase after the photon passes the slits but before it hits the photographic plate then to explain the results you've either got to embrace Superdeterminism, backward causality or Many Worlds.

> No, you have got it wrong here. No need for any of this. 

That's it? That's all you've got to say? If you have a explanation for all the odd stuff coming from the 2 slit experiment that has been bedeviling scientists for a century, a explanation not involving Superdeterminism, backward causality or Many Worlds then please enlighten a poor mortal such as myself.

 

>> why the big delay between thought experiment and real experiment? Because although it's simple in concept it's very difficult to actually perform, you need super fast electronics and a very good random number generator to make the split second decision to erase or not to erase in the ultra short amount time between the photon passing the slit and it hitting the photographic plate. If you could take your time and wait until after it hit the plate Lewis could have not just talked about it but actually done the exparament in 1926 and he wouldn't have needed advanced electronics; steam powered, or even horse powered, machinery would have been good enough.

>The decision to erase or not to erase is made at a space-like separation from the screen in the experiment

Exactly! I guess you're conceding my point. If you take your time and wait until after the photon hits the screen there will be insufficient spacetime separation for the experiment  to produce new meaningful results, so you've got to make the distance between the slit and the screen to be very large, or make the decision to erase or not erase very quickly, or both. The decision to erase or not to erase must be made in less time than it takes for light to move between the slits and the photographic plate to preclude the possibility that a unknown signal of some sort is moving between the slit and the plate influencing things.  

 

> Delaying the choice until after the photons hit the screen achieves the same end.

I guess you're not conceding my point after all and would prefer to embrace logical inconsistency. 

 

> Why do you think it is called "delayed choice" after all?

Because the choice to erase or not to erase is delayed until long after the photon has passed the slit, it could be made a billion years after it passed the slit, and the decision could be made one nanosecond before the photon hit the photographic plate, but it must be before or you will see nothing new or interesting. One might naively think that the photon either passed through one slit or two and whatever you do after it passed the slits can't change that fact, but it can!

As long as the photon is still in transit if you erase the which way information you see a interference pattern and if you don't erase that information there is no interference pattern. And that is seriously weird and seriously interesting. If you wait to make the decision until after the picture is made the results are not weird at all and is in fact dull as dishwater because you'll learn nothing new that Thomas Young didn't discover in 1801 when he performed the 2 slit exparament for the very first time; when Young looked at his screen he also did not have any which way information and that's why he saw a interference pattern.

>>you can't expect to learn anything if you look at the developed photograph and then decide whether to erase the which way information or not. If you decide to erase the information do you imagine you will see the photograph change before your eyes??

> Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob.

Ah Bruce.....in that case you are very obviously erasing the which way information BEFORE it hits the screen or photograph that you're looking at!

>> If that's the way the exparament turns out and a interference pattern exists but Many Worlds does not exist then how do you explain the existence of a signed document testifying that somebody observed the photon going through one and only one slit and the he knew which one? Inquiring minds want to know.

> The signed document is irrelevant because it does not contain the welcher weg information.

The signed document doesn't say which slit but it doesn't need to because it DOES say the photon went through one and only one slit. So if Many Worlds, Superdeterminism and Backward Causality are all wrong and the photons only went through one slit then why on earth is there a interference pattern on that photographic plate? Inquiring minds want to know.

 

> I really do think that you have to do a bit more work in order to understand what is going on here.

I'm not a expert on this so I may be shaky on some subtle point in this experiment, but some things are not subtle and at least I understand the big stuff; and there is nothing bigger than the FACT that the which way information is erased AFTER the photon passed the slits but BEFORE it hits the photographic plate and actually makes a picture. That's Delayed Choice 101, it's the very first thing you've got to understand to make any sense whatsoever about what's going on in this experiment!

John K Clark

[Bruce Kellett]

On Sun, Oct 20, 2019 at 8:32 AM John Clark <johnk...@gmail.com> wrote:

On Fri, Oct 18, 2019 at 6:31 PM Bruce Kellett <bhkel...@gmail.com> wrote:

 

> if you erase or not the welcher weg information 'before' the signal photon hits the screen, then presumably some, presently unknown physics, could send this information to the screen and influence the result there.

So you admit it. If you continue to insist Many Worlds do not exist then to explain an experiment that has been performed many times you must postulate new physics and mess with Schrodinger's Equation. 

> Not at all. The results of the experiment are easily explained within the structures of conventional quantum mechanics, whatever interpretation one wishes to adopt. There is nothing mysterious here.

There is a lot of mystery here! In 2007 entangled photons were sent 89 miles between La Palma and Tenerife, the decision to erase or not to erase was made in less time than it took for light to travel those 89 miles and hit the detector:

Quantum Spookiness Spans the Canary Islands

The last potential loophole, the freedom of choice loophole, was pretty much closed in April 2018. That loophole says that maybe your measurement settings that chose between erase and don't erase are not really random after all, there might be a deterministic process that makes the choice and misleads us:

Quantum entanglement loophole quashed by quasar light

They state that:

"Arguably the most interesting assumption is that the choice of measurement settings is “free and random,” and independent of any physical process that could affect the measurement outcomes. As Bell himself noted, his inequality was derived under the assumption “that the settings of instruments are in some sense free variables, say at the whim of experimenters, or in any case not determined in the overlap of the backward light cones.”

So to close this loophole they didn't use a standard random number generator to make the choice to erase or not erase the information in the short amount of time it takes light to travel those 89 miles before (yes BEFORE) the photon hit their detector; instead they used the light from a distant quasar to make the decision, so if its a conspiracy to mislead us (as Superdeterminism says) it's a grand conspiracy indeed. They conclude:

"This experiment pushes back to at least 7.8 billion years the most recent time by which any local-realist influences could have exploited the “freedom-of-choice” loophole to engineer the observed Bell violation"

It seems that the fundamental problem here is that you are confusing tests of Bell's inequality on entangled particles with delayed choice experiments. These are different things.

 

>> If you decide to erase or not to erase after the photon passes the slits but before it hits the photographic plate then to explain the results you've either got to embrace Superdeterminism, backward causality or Many Worlds.

> No, you have got it wrong here. No need for any of this. 

That's it? That's all you've got to say? If you have a explanation for all the odd stuff coming from the 2 slit experiment that has been bedeviling scientists for a century, a explanation not involving Superdeterminism, backward causality or Many Worlds then please enlighten a poor mortal such as myself.

If you are confused by this, then read the explanations that we have offered, by Carroll or Wikipedia.

[...]

Because the choice to erase or not to erase is delayed until long after the photon has passed the slit, it could be made a billion years after it passed the slit, and the decision could be made one nanosecond before the photon hit the photographic plate, but it must be before or you will see nothing new or interesting.

Exactly what do you think that you will see in that case? and why do you think it uninteresting?

[....]

 

> Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob.

Ah Bruce.....in that case you are very obviously erasing the which way information BEFORE it hits the screen or photograph that you're looking at!

You will have to explain that to me. I pass the photon through the slits and entangle it with some spin state that will be spin-up for the left slit, and spin-down for the right slit. I store these particles for a billion or so years until long after the original photons have hit the screen and have been recorded photographically. I then decide to measure my stored "which-way particles". If I measure them in the up-down basis, I can tell which slit the photon went through, so I do not see any interference. However, if I measure my stored particles in an orthogonal basis, such as the left-right basis, I have quantum erased the which-way information, so I do see interference by selecting either the left- or right- polarized particles. The decision of which to measure was clearly made *after* the original photons hit the screen, so it is not erasing the which-way information *before* they hit the screen.

You say you are not an expert on this.....I think that has become very clear.....

Bruce

[Brent Meeker]

On 10/19/2019 2:31 PM, John Clark wrote:

As long as the photon is still in transit if you erase the which way information you see a interference pattern and if you don't erase that information there is no interference pattern. And that is seriously weird and seriously interesting. If you wait to make the decision until after the picture is made the results are not weird at all and is in fact dull as dishwater because you'll learn nothing new that Thomas Young didn't discover in 1801 when he performed the 2 slit exparament for the very first time; when Young looked at his screen he also did not have any which way information and that's why he saw a interference pattern.

It's new (relative to 1801) that you can record the welcher weg so that the interference pattern doesn't appear on the screen.  But then you can erase it after the pattern is already on the screen, and the interference pattern "reappears" in a sense, which you can see by partitioning the points according to the erasure result.

Brent

[John Clark]

On Sat, Oct 19, 2019 at 5:57 PM Bruce Kellett <bhkel...@gmail.com> wrote

>> Because the choice to erase or not to erase is delayed until long after the photon has passed the slit, it could be made a billion years after it passed the slit, and the decision could be made one nanosecond before the photon hit the photographic plate, but it must be before or you will see nothing new or interesting.

> Exactly what do you think that you will see in that case? and why do you think it uninteresting?

If you decide, one nanosecond BEFORE the photon hits the screen, to erase the information about which slit the photon went through a billion years ago then you will always see a interference pattern, and that indicates a billion years ago the photon must have gone through both slits. But if you decide, one nanosecond BEFORE the photon hits the screen, NOT to erase the information about which slit the photon went through a billion years ago then you will NOT see a interference pattern and you will know that a billion years ago the photon must have gone through one and only one slit. I find that result to be so interesting and surprising that I feel no necessity to spell out why. But if the information is erased after the photon hits the screen then the results are neither interesting or surprising because it wouldn't tell us anything new we didn't discover in 1801.

>>> Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob.

>> Ah Bruce.....in that case you are very obviously erasing the which way information BEFORE it hits the screen or photograph that you're looking at!

> You will have to explain that to me.

If you place a polarizing filter oriented in the left-right direction over one slit and a polarizing filter oriented in the up-down direction over the other slit and shine a light through both slits and onto a screen you will not see a interference pattern on that screen because the filters have encoded information onto the photons about which slit they went through. However if you then place a third polarizing filter, this time oriented at a intermediate 45 degree angle, after the slits but BEFORE the screen then "the interference pattern emerges from the apparent no-interference" because that 45 degree filter has erased the which way information that was encoded on the photons BEFORE any photons hit the screen that you're looking at.

> You say you are not an expert on this.....I think that has become very clear.....

It's perfectly true I'm not a expert on this, but I certainly hope you're not claiming that you're different and are an expert because that would be laughable. You have demonstrated a profound lack of understanding of a basic fact that is taught in the first minute on the first day in a first course on The Delayed Choice. If you don't even understand the basic facts of the experimental setup how in the world can you hope to interpret the results?

 John K Clark

[smitra]

It's not "in principle irreversible", just put the entire system in a
large box with reflecting boundary conditions. How could what we
experience when we do measurements possibly depend on what boundary
conditions are imposed very far away?

>
>>
>> This means that the entire process can be simulated by a quantum
>> computer that has only a finite number of qubits. It doesn't matter
>> that it cannot be done in practice for the argument that QM (where
>> everything including observers are described in a unified way) implies
>> the MWI. The only way to avoid the MWI is to assume that QM is not
>> exactly true.
>
> You mean Everett's QM...whether it's QM is what the question.  QM
> worked just fine for 30yrs without Everett.  And QBism is an
> alternative that leaves QM exactly true; just interpreted differently.
>
> Personally, I think the long sought theory that merges QM and GR may
> modify QM by cutting off small probabilities based on the holographic
> principle.

Cutting off small probabilities will by itself not get rid of "many
worlds". It can have the effect that different sectors become totally
independent. And that can then be invoked by people in debates, they can
leave out the "FAPP" qualifier when arguing that other worlds don't have
any physical effect.

Saibal

[smitra]

On 19-10-2019 23:57, Bruce Kellett wrote:
> On Sun, Oct 20, 2019 at 8:32 AM John Clark <johnk...@gmail.com>
> wrote:
>
>> On Fri, Oct 18, 2019 at 6:31 PM Bruce Kellett
>> <bhkel...@gmail.com> wrote:
>>

>> _> if you erase or not the welcher weg information 'before' the

>> signal photon hits the screen, then presumably some, presently
>> unknown physics, could send this information to the screen and

>> influence the result there._

>>
>> So you admit it. If you continue to insist Many Worlds do not exist
>> then to explain an experiment that has been performed many times you
>> must postulate new physics and mess with Schrodinger's Equation.
>
>> Not at all. The results of the experiment are easily explained
> within the structures of conventional quantum mechanics, whatever
> interpretation one wishes to adopt. There is nothing mysterious here.
>
> There is a lot of mystery here! In 2007 entangled photons were sent 89
> miles between La Palma and Tenerife, the decision to erase or not to
> erase was made in less time than it took for light to travel those 89
> miles and hit the detector:
>

> Quantum Spookiness Spans the Canary Islands [1]

>
> The last potential loophole, the freedom of choice loophole, was
> pretty much closed in April 2018. That loophole says that maybe your
> measurement settings that chose between erase and don't erase are not
> really random after all, there might be a deterministic process that
> makes the choice and misleads us:
>

> Quantum entanglement loophole quashed by quasar light [2]
>
> They state that:
>
> _"Arguably the most interesting assumption is that the choice of

> measurement settings is “free and random,” and independent of any
> physical process that could affect the measurement outcomes. As Bell
> himself noted, his inequality was derived under the assumption “that
> the settings of instruments are in some sense free variables, say at
> the whim of experimenters, or in any case not determined in the

> overlap of the backward light cones.”_

>
> So to close this loophole they didn't use a standard random number
> generator to make the choice to erase or not erase the information in
> the short amount of time it takes light to travel those 89 miles
> before (yes BEFORE) the photon hit their detector; instead they used
> the light from a distant quasar to make the decision, so if its a
> conspiracy to mislead us (as Superdeterminism says) it's a grand
> conspiracy indeed. They conclude:
> "This experiment pushes back to at least 7.8 billion years the most
> recent time by which any local-realist influences could have exploited
> the “freedom-of-choice” loophole to engineer the observed Bell
> violation"
>
> It seems that the fundamental problem here is that you are confusing
> tests of Bell's inequality on entangled particles with delayed choice
> experiments. These are different things.
>
>>>> If you decide to erase or not to erase after the photon passes
>> the slits but before it hits the photographic plate then to explain
>> the results you've either got to embrace Superdeterminism, backward
>> causality or Many Worlds.
>
>>
>

>> _> No, you have got it wrong here. No need for any of this. _

>
> That's it? That's all you've got to say? If you have a explanation for
> all the odd stuff coming from the 2 slit experiment that has been
> bedeviling scientists for a century, a explanation not involving
> Superdeterminism, backward causality or Many Worlds then please
> enlighten a poor mortal such as myself.
>
> If you are confused by this, then read the explanations that we have
> offered, by Carroll or Wikipedia.
>
> [...]
>
>> Because the choice to erase or not to erase is delayed until long
>> after the photon has passed the slit, it could be made a billion
>> years after it passed the slit, and the decision could be made one
>> nanosecond before the photon hit the photographic plate, but it must

>> be BEFORE or you will see nothing new or interesting.

>
> Exactly what do you think that you will see in that case? and why do
> you think it uninteresting?
>
> [....]
>

>>> _> Yes, of course you do: you just select the subsets of photons

>>> that were quantum-erased by passing the left polarizer
>>> (respectively, the right polarizer) to see the interference

>>> patterns emerge from the apparent no-interference blob._

>>
>> Ah Bruce.....in that case you are very obviously erasing the which
>> way information BEFORE it hits the screen or photograph that you're
>> looking at!
>
> You will have to explain that to me. I pass the photon through the
> slits and entangle it with some spin state that will be spin-up for
> the left slit, and spin-down for the right slit. I store these
> particles for a billion or so years until long after the original
> photons have hit the screen and have been recorded photographically. I
> then decide to measure my stored "which-way particles". If I measure
> them in the up-down basis, I can tell which slit the photon went
> through, so I do not see any interference. However, if I measure my
> stored particles in an orthogonal basis, such as the left-right basis,
> I have quantum erased the which-way information, so I do see
> interference by selecting either the left- or right- polarized
> particles. The decision of which to measure was clearly made *after*
> the original photons hit the screen, so it is not erasing the
> which-way information *before* they hit the screen.
>
> You say you are not an expert on this.....I think that has become very
> clear.....
>

Yes, Bruce is right on this point of the interference being detectable
after the photons hitting the screen by transferring the which way
information to the spins of electrons. But John Clark is right about the
main topic this discussion is about. One can construe that also in terms
of realism (I think John did mention this also some tome ago). The
traditional view is that we must abandon realism, but that leads to
paradoxes as it's problematic to then get to realism at the macroscopic
level. In principle the macroscopic world is also described by QM, and
any formalism that assumes non-realism would have to apply there at
well. The MWI solves this problem in a much better way by explaining
non-realism as an artifact of Many-World realism. The different
realities in the different Worlds makes the notion of single World
realism false.


Saibal

[scerir]

Il 20 ottobre 2019 alle 17.57 smitra < smi...@zonnet.nl> ha scritto:

Yes, Bruce is right on this point of the interference being detectable

after the photons hitting the screen by transferring the which way

information to the spins of electrons. But John Clark is right about the

main topic this discussion is about. One can construe that also in terms

of realism (I think John did mention this also some tome ago). The

traditional view is that we must abandon realism, but that leads to

paradoxes as it's problematic to then get to realism at the macroscopic

level. In principle the macroscopic world is also described by QM, and

any formalism that assumes non-realism would have to apply there at

well. The MWI solves this problem in a much better way by explaining

non-realism as an artifact of Many-World realism. The different

realities in the different Worlds makes the notion of single World

realism false.

Saibal

"The experimental results demonstrate the possibility of observing both particle-like and wave-like behavior of a light quantum via quantum mechanical entanglement. The which-path or both-path information of a quantum can be erased or marked by its entangled twin even after the registration of the quantum." https://arxiv.org/abs/quant-ph/9903047

As for "realism" I think we need a definition. What is "real"? (Yes, I know the EPR definition.)

s.

 “The probability function, which covered a wide range of possibilities, is suddenly reduced to a much narrower range by the fact that the experiment has led to a definite result, that actually a certain event has happened. In the formalism this reduction requires that the so-called interference of probabilities, which is the most characteristic phenomenon of quantum theory, is destroyed by the partly undefinable and irreversible interactions of the system with the measuring apparatus and the rest of the world.” (Heisenberg, 1958)

[Brent Meeker]

If we're in the perfect reflecting box (with perfectly rigid mirrors)
then we prevent the erasure, unless we can test our selves in an
orthogonal basis.  So it's still irreversible.

>>
>>>
>>> This means that the entire process can be simulated by a quantum
>>> computer that has only a finite number of qubits. It doesn't matter
>>> that it cannot be done in practice for the argument that QM (where
>>> everything including observers are described in a unified way)
>>> implies the MWI. The only way to avoid the MWI is to assume that QM
>>> is not exactly true.
>>
>> You mean Everett's QM...whether it's QM is what the question. QM
>> worked just fine for 30yrs without Everett.  And QBism is an
>> alternative that leaves QM exactly true; just interpreted differently.
>>
>> Personally, I think the long sought theory that merges QM and GR may
>> modify QM by cutting off small probabilities based on the holographic
>> principle.
>
> Cutting off small probabilities will by itself not get rid of "many
> worlds". It can have the effect that different sectors become totally
> independent. And that can then be invoked by people in debates, they
> can leave out the "FAPP" qualifier when arguing that other worlds
> don't have any physical effect.

Or that they are mere metaphysical artifacts of taking mathematics too
seriously.

Brent

[Bruce Kellett]

On Mon, Oct 21, 2019 at 1:19 AM John Clark <johnk...@gmail.com> wrote:

On Sat, Oct 19, 2019 at 5:57 PM Bruce Kellett <bhkel...@gmail.com> wrote

>> Because the choice to erase or not to erase is delayed until long after the photon has passed the slit, it could be made a billion years after it passed the slit, and the decision could be made one nanosecond before the photon hit the photographic plate, but it must be before or you will see nothing new or interesting.

> Exactly what do you think that you will see in that case? and why do you think it uninteresting?

If you decide, one nanosecond BEFORE the photon hits the screen, to erase the information about which slit the photon went through a billion years ago then you will always see a interference pattern, and that indicates a billion years ago the photon must have gone through both slits. But if you decide, one nanosecond BEFORE the photon hits the screen, NOT to erase the information about which slit the photon went through a billion years ago then you will NOT see a interference pattern and you will know that a billion years ago the photon must have gone through one and only one slit. I find that result to be so interesting and surprising that I feel no necessity to spell out why. But if the information is erased after the photon hits the screen then the results are neither interesting or surprising because it wouldn't tell us anything new we didn't discover in 1801.

I may not have been sufficiently clear in what case I was asking about. You claim that nothing interesting is seen if you make the choice between observing which-way information and quantum erasing it after the signal photons have been recorded on the screen. It seems that you think you will just see Young's interference fringes whatever you do *after* the record is made at the screen. But that is false, as has been demonstrated in many experiments. It does not matter whether you make the choice between which-way and quantum erasure before or after the photons hit the screen.

That is what the experiments of Zeilinger and his associates show. These are the experiments where the decision to erase or not were made 144 km away from the lab in which the interference measurement was made. See the original paper at 

https://arxiv.or/abs/1206.6578

>>> Yes, of course you do: you just select the subsets of photons that were quantum-erased by passing the left polarizer (respectively, the right polarizer) to see the interference patterns emerge from the apparent no-interference blob.

>> Ah Bruce.....in that case you are very obviously erasing the which way information BEFORE it hits the screen or photograph that you're looking at!

> You will have to explain that to me.

If you place a polarizing filter oriented in the left-right direction over one slit and a polarizing filter oriented in the up-down direction over the other slit and shine a light through both slits and onto a screen you will not see a interference pattern on that screen because the filters have encoded information onto the photons about which slit they went through. However if you then place a third polarizing filter, this time oriented at a intermediate 45 degree angle, after the slits but BEFORE the screen then "the interference pattern emerges from the apparent no-interference" because that 45 degree filter has erased the which way information that was encoded on the photons BEFORE any photons hit the screen that you're looking at.

That is not the experimental set-up of the Zeilinger et al. assessment of delayed choice. Read the sources I have quoted.......

> You say you are not an expert on this.....I think that has become very clear.....

It's perfectly true I'm not a expert on this, but I certainly hope you're not claiming that you're different and are an expert because that would be laughable.

I can at least read the original papers, and the summary and analysis given by Carroll or on Wikipedia. It seems that you have been unable to understand any of these sources.

Bruce

[Bruce Kellett]

On Mon, Oct 21, 2019 at 4:29 AM 'scerir' via Everything List <everyth...@googlegroups.com> wrote:

Il 20 ottobre 2019 alle 17.57 smitra < smi...@zonnet.nl> ha scritto:

Yes, Bruce is right on this point of the interference being detectable

after the photons hitting the screen by transferring the which way

information to the spins of electrons. But John Clark is right about the

main topic this discussion is about. One can construe that also in terms

of realism (I think John did mention this also some tome ago). The

traditional view is that we must abandon realism, but that leads to

paradoxes as it's problematic to then get to realism at the macroscopic

level. In principle the macroscopic world is also described by QM, and

any formalism that assumes non-realism would have to apply there at

well. The MWI solves this problem in a much better way by explaining

non-realism as an artifact of Many-World realism. The different

realities in the different Worlds makes the notion of single World

realism false.

Saibal

"The experimental results demonstrate the possibility of observing both particle-like and wave-like behavior of a light quantum via quantum mechanical entanglement. The which-path or both-path information of a quantum can be erased or marked by its entangled twin even after the registration of the quantum." https://arxiv.org/abs/quant-ph/9903047

As for "realism" I think we need a definition. What is "real"? (Yes, I know the EPR definition.)

Thanks Serafino. I must admit that I do not understand the reference to "realism" either. The Zeilinger group are careful to enforce Einstein's notion of locality -- by ensuring that the choice about whether to erase or not, the interference itself, and the quantum erasure of welcher-weg information, are all made at space like separations (see arXiv:1206.6578). But I do not see what realism has got to do with it, or what definition of realism is involved.

Bruce

[John Clark]

On Sun, Oct 20, 2019 at 6:24 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> It seems that you think you will just see Young's interference fringes whatever you do *after* the record is made at the screen. But that is false,

Like hell it is! Do you actually think Zeilinger and other experimental physicists claim they can make a photograph change before your eyes AFTER it has been taken like something out of Back To The Future? It was a fun movie but that's not the way things work.

 

> as has been demonstrated in many experiments.

That statement is worse than false, you're talking logical nonsense. The photograph itself contains which way information, if the photo has no interference pattern then you know the photon went through one and only one slit, and if it does have a interference pattern then you know the photon went through both slits. So if you have the ability and really and truly want to destroy the which way information AFTER the photon hits the photographic plate (or screen) then you MUST destroy the photograph too and do so before anybody looks at it. In 1801 Thomas Young was not a fool and that's why he had no desire to destroy his screen BEFORE he looked at it, and that's why he saw a interference pattern; but it's true if he had he would have not seen a interference pattern, he would not see anything at all because there would be no screen to look at because he destroyed it.

> It does not matter whether you make the choice between which-way and quantum erasure before or after the photons hit the screen.

There is one difference and it's a rather large one. If you have no which way information at all (like Thomas Young) or if you make the erase/don't-erase decision AFTER  the photon passes the slits but BEFORE it hits your photographic plate or screen or electronic detector (like Zeilinger and other experimentalists in the 21st century) then your experiment produces data;  BUT if you really insist on erasing all the which way information AFTER the photon hits your photographic plate or screen or electronic detector then your experiment will produce NO data, not one bit of it, because you must destroy your photographic plate or screen or electronic detector. And you can't look at it before you destroy it because then you would have the which way information. 

>That is what the experiments of Zeilinger and his associates show. These are the experiments where the decision to erase or not were made 144 km away from the lab in which the interference measurement was made.

And why do you think the experimenters thought it was so important to make the distance between the slits and their detector that long? Because light is very fast and for practical reasons it takes time for experimenters to make the erase/don't-erase decision and it takes time to actually make the erasure, if the distance was as long as 144 km then even though light moves fast they still had enough time to do all that BEFORE the photons hit their interference measurement detector.  

>> If you place a polarizing filter oriented in the left-right direction over one slit and a polarizing filter oriented in the up-down direction over the other slit and shine a light through both slits and onto a screen you will not see a interference pattern on that screen because the filters have encoded information onto the photons about which slit they went through. However if you then place a third polarizing filter, this time oriented at a intermediate 45 degree angle, after the slits but BEFORE the screen then "the interference pattern emerges from the apparent no-interference" because that 45 degree filter has erased the which way information that was encoded on the photons BEFORE any photons hit the screen that you're looking at.

> That is not the experimental set-up of the Zeilinger et al. assessment of delayed choice. Read the sources I have quoted.......

Yes Bruce you have quoted sources, but I am not at all impressed. I do not believe for one nanosecond you understand anything in them and I doubt if you've spent more than 45 seconds skimming a Wikipedia article about them.

John K Clark

[Brent Meeker]

On 10/21/2019 7:40 AM, John Clark wrote:

On Sun, Oct 20, 2019 at 6:24 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> It seems that you think you will just see Young's interference fringes whatever you do *after* the record is made at the screen. But that is false,

Like hell it is! Do you actually think Zeilinger and other experimental physicists claim they can make a photograph change before your eyes AFTER it has been taken like something out of Back To The Future? It was a fun movie but that's not the way things work.
 

> as has been demonstrated in many experiments.

That statement is worse than false, you're talking logical nonsense. The photograph itself contains which way information, if the photo has no interference pattern then you know the photon went through one and only one slit, and if it does have a interference pattern then you know the photon went through both slits. So if you have the ability and really and truly want to destroy the which way information AFTER the photon hits the photographic plate (or screen) then you MUST destroy the photograph too and do so before anybody looks at it. In 1801 Thomas Young was not a fool and that's why he had no desire to destroy his screen BEFORE he looked at it, and that's why he saw a interference pattern; but it's true if he had he would have not seen a interference pattern, he would not see anything at all because there would be no screen to look at because he destroyed it.

You apparently have still not read Carroll's blog.  He discusses exactly what happens when you erase the welche weg after the photons have hit the screen, and it doesn't involve erasing the photograph.


In figure 3  of the Xiao-song et al paper, Carroll's example is equivalent to noting, in the lower half of the figure which spot  goes with which path, but then not partitioning the spot's into different curves.   They add to a flat line as in the upper figure.   But after the fact you can use the recorded information  to recover the sinusoidal distributions.

Brent

> It does not matter whether you make the choice between which-way and quantum erasure before or after the photons hit the screen.

There is one difference and it's a rather large one. If you have no which way information at all (like Thomas Young) or if you make the erase/don't-erase decision AFTER  the photon passes the slits but BEFORE it hits your photographic plate or screen or electronic detector (like Zeilinger and other experimentalists in the 21st century) then your experiment produces data;  BUT if you really insist on erasing all the which way information AFTER the photon hits your photographic plate or screen or electronic detector then your experiment will produce NO data,

If will if you keep track of the erasure result for each point on the screen.  Although I'm curious about the implicit asymmetry in Carroll's example.

not one bit of it, because you must destroy your photographic plate or screen or electronic detector. And you can't look at it before you destroy it because then you would have the which way information. 

>That is what the experiments of Zeilinger and his associates show. These are the experiments where the decision to erase or not were made 144 km away from the lab in which the interference measurement was made.

And why do you think the experimenters thought it was so important to make the distance between the slits and their detector that long? Because light is very fast and for practical reasons it takes time for experimenters to make the erase/don't-erase decision and it takes time to actually make the erasure, if the distance was as long as 144 km then even though light moves fast they still had enough time to do all that BEFORE the photons hit their interference measurement detector. 

>> If you place a polarizing filter oriented in the left-right direction over one slit and a polarizing filter oriented in the up-down direction over the other slit and shine a light through both slits and onto a screen you will not see a interference pattern on that screen because the filters ha ve encoded information onto the photons about which slit they went through. However if you then place a third polarizing filter, this time oriented at a intermediate 45 degree angle, after the slits but BEFORE the screen then "the interference pattern emerges from the apparent no-interference" because that 45 degree filter has erased the which way information that was encoded on the photons BEFORE any photons hit the screen that you're looking at.

> That is not the experimental set-up of the Zeilinger et al. assessment of delayed choice. Read the sources I have quoted.......

Yes Bruce you have quoted sources, but I am not at all impressed. I do not believe for one nanosecond you understand anything in them and I doubt if you've spent more than 45 seconds skimming a Wikipedia article about them.

John K Clark

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[Bruce Kellett]

On Tue, Oct 22, 2019 at 1:41 AM John Clark <johnk...@gmail.com> wrote:

On Sun, Oct 20, 2019 at 6:24 PM Bruce Kellett <bhkel...@gmail.com> wrote:

> It seems that you think you will just see Young's interference fringes whatever you do *after* the record is made at the screen. But that is false,

Like hell it is! Do you actually think Zeilinger and other experimental physicists claim they can make a photograph change before your eyes AFTER it has been taken like something out of Back To The Future? It was a fun movie but that's not the way things work.
 

> as has been demonstrated in many experiments.

That statement is worse than false, you're talking logical nonsense. The photograph itself contains which way information, if the photo has no interference pattern then you know the photon went through one and only one slit, and if it does have a interference pattern then you know the photon went through both slits. So if you have the ability and really and truly want to destroy the which way information AFTER the photon hits the photographic plate (or screen) then you MUST destroy the photograph too and do so before anybody looks at it. In 1801 Thomas Young was not a fool and that's why he had no desire to destroy his screen BEFORE he looked at it, and that's why he saw a interference pattern; but it's true if he had he would have not seen a interference pattern, he would not see anything at all because there would be no screen to look at because he destroyed it.

All your ranting does nothing to enhance your credibility. I quote from the Xiao-song Ma et al. paper (Zeilinger group): "The authors proposed to combine the delayed-choice paradigm with the quantum erasure concept. Since the welcher-weg information of the atoms is carried by the photons, the choice of measurement of the photons -- either revealing or erasing  the atoms' welcher-weg information -- can be delayed until 'long after the atoms have passed' the photon detectors at the double slit. The later measurement of the photons 'decides' whether the atoms can show interference not even after the atoms have been detected. This seemingly counter-intuitive situation comes from the fact that in a bipartite quantum state the observer correlations are independent of the space-time arrangement of the measurements on the individual systems."

In reference to the 144 km Canary Island experiments, they say: "The other arrangements such that the choice event  happens approximately 450 microseconds after the events I_s (recording of interference or not at the screen) in the reference frame of the source, which puts a record to the amount of delay by more than 5 orders of magnitude to the previously recorded quantum eraser experiment."

There is no doubt that they make the choice of whether or not to erase the welcher-weg information 450 microsecs *after* the photons hit the screen and are irreversibly recorded.

You clearly do not know what your are talking about.....

Bruce