Re: Why are laws of physics stable?

[smitra]

On 04-07-2021 08:38, Bruce Kellett wrote:
> On Sun, Jul 4, 2021 at 2:59 PM smitra <smi...@zonnet.nl> wrote:
>
>> On 02-07-2021 06:46, Bruce Kellett wrote:
>>>
>>> No, I am not tracing out anything. I am looking at whether an
>>> interference pattern is formed or not. I don't have to detect the
>> IR
>>> photons in order for the interference to be destroyed.
>>
>> You choose to look at an interference pattern involving only part of
>> the
>> relevant degrees of freedom and then you find that there is no
>> interference pattern.
>
> That does not make sense.

You are not observing the IR photons, there is still an interference
pattern in the many particle state involving all the relevant particles.

>
>> That's equivalent to replacing the pure state by
>> tracing out the IR photons and considering the density matrix
>> describing
>> the reduced state.
>
> No, that is not what is going on. I am not "tracing out" the IRphotons
> -- I don't even know what that might mean. I can observe the photons,
> or choose not to observe them, that will make no difference. It is the
> existence of the IR photons with sufficient resolution to determine
> 'which way' information at the slits, that is relevant. If such
> photons exist, whether or not they are ever observed, the interference
> pattern vanishes. This is a simple matter of the fact that the
> interference depends on coherence at the slits. If there is some way
> that one could determine which slit the buckyballs went through, then
> there is no interference - the determination has decohered the paths,
> destroying the possibility of interference. This happens whether the
> IR photons are observed or not -- it is merely a matter of their
> existence: an 'in principle' determination of which way information.
>
> So it is not a matter of 'tracing over' any degrees of freedom at all.
> There is no reduced density matrix involved. I do not consider the
> situation when the ball went through the left slit compared with the
> situation in which the ball went through the right slit. There is no
> "splitting into worlds according to paths" here. As stated, it is not
> even necessary to use the IR photons to make a path determination --
> their mere existence is all that is required to inhibit the
> interference at the downstream screen.

You need to consider the many particle interference pattern where you
use different screens for each photon and a screen for the balls. You
consider the number of balls on the screen for the balls as a function
the position on this screen for fixed positions of dots on the screen
for the corresponding IR photons. For every such fixed position of the
dots made by the IR photons there will be a different interference
pattern of the balls. If you don't observe the IR photons in this way,
then the pattern for the balls will be the integral over all the
interference patters, which means that the interference pattern will be
washed out.

>
>>>>
>>>> It's implausible that escaping IR photons should be relevant for
>> the
>>>> question of what an observer is, what observations are etc.
>>>
>>> How is it implausible? It is the inevitable existence of the IR
>>> photons that ensures that the measurement process is irreversible.
>> It
>>> is the formation of permanent (irreversible) records in the
>>> environment that determines the existence of a measurement. If no
>> such
>>> records are made then no measurement has been made.
>>>
>> While IR photons and permanent records are associated with
>> macroscopic
>> observers making observations, these things cannot play a
>> fundamental
>> role in the measurement process if we assume that QM is indeed a
>> fundamental theory that also describes observers.
>
> The formation of permanent records is as much a fully quantum process
> as anything else.
>
Permanent records only arise in the classical limit of QM which is a
degenerate limit, i.e. the classical limit is no longer consistent with
QM, which proves that permanent records are unphysical and cannot
therefore explain observations.

>> If QM is exactly true
>> then one cannot make an essential part of the theory dependent on a
>> degenerate limit of this theory that is in violation of this theory.
>
> The formation of records is not a violation of QM. It is not a
> degenerate limit of the theory. It does not depend on the existence of
> a separate classical realm, although the formation of permanent
> records of experimental outcomes may be an important part of the
> emergence of the classical from the quantum substrate. Nothing in
> what I have said about the buckyball experiments depends on the
> existence of a classical limit.
>
Interference in the buckyball still exists when doing an appropriate
multi-particle experiment. Of course, such experiments are extremely
difficult to do, but it would not violate the laws of physics to perform
such an experiment. The difficulty is, of course, that there are a very
large number of IR photons being emitted and you have to use a screen
for each photon. But nothing in the laws of physics says that this is
forbidden. This would only truly become impossible if there were an
infinite number of IR photons. Suppose we consider approaching this
impossibility as a limit where more and more IR photons are emitted.
Conservation of energy would then imply that the average energy of these
IR photons would have to tend to zero. The wavelength of the IR photons
then also increases, and if this becomes of the order of the separation
between the splits they don't reduce the visibility of the interference
pattern, so these photons then would not count. To get to an infinite
number of relevant IR photons, one then also has to increase the
distance between the slits as the number of IR photons is increased an
their energy is decreased.

Clearly, you are only going to get a truly invisible interference
pattern in the classical limit where the size of the system consisting
of the slits, the screen etc. tends to infinity, and an infinite number
of photons with infinitesimal energy are emitted. Only in this
degenerate limit does there exist no interference pattern at all, not
just one that one can measure in practice, but also none that in
principle exist involving any finite number of the emitted photons.



>> QM is reversible there are no such things as irreversible records,
>> IR
>> photons escaping from a system don't cause the system to evolve from
>> a
>> pure state to a mixed state.
>
> Can you prove that? There certainly are irreversible records in the
> environment. And the irreversibility is 'in principle' it does not
> just depend on the involvement of an intractably large number of
> degrees of freedom, which would just be FAPP irreversibility. The laws
> of physics forbid the recovery of escaping photons. And the formation
> of any record, even writing a result in a lab boo, inevitably involves
> the escape of irrecoverable photons. According to the laws of
> thermodynamics, any physical interaction will generate some heat. Heat
> causes IR photons, and these easily escape to infinity. They are not
> recoverable, so they lead to permanent irreversibility.
>
> I suspect that this irreversibility actually leads from the pure state
> to a mixed state. This is not covered by the Schrodinger equation,
> which would suggest that since the evolution is unitary, there is
> always a unitary matrix that will restore the original state. But this
> misses the fact that no unitary process can avoid the limitations of
> the speed of light. Your whole case relies on an inappropriate use of
> pre-relativistic physics. This is one of the fundamental problems with
> MWI: it does not reflect the actual situation in the physical world --
> it relies on arbitrary simplifications that are simply not true. The
> theory does not replicate the actual physical situation -- it does not
> explain the observed world.
>

As I said before in a previous posting on this thread, you are seeking
to explain what should be fundamental concepts using certain messy
macroscopic aspects of a theory which are not universal. This cannot
possibly work well because the things you invoke like IR photons
escaping at the speed of light and being unrecoverable in principle
would have to be rigorously true and it would have to apply in each and
every case. For example, one may object by invoking that the universe is
filled with a plasma and that the IR photons travel at a speed slightly
below the true vacuum speed of light.


>>>
>>> Says you. The laws of physics, principally the limitation of the
>> speed
>>> of light, means that the state cannot be restored, even in
>> principle.
>>
>> One can have a system locked up in a finite volume with the outer
>> walled
>> cooled arbitrarily close to absolute zero and with many layers of
>> inner
>> walls such that everything from the interior is absorbed or
>> reflected
>> well before reaching the outer limits of the system.
>
> No such system is ever perfectly isolated. And besides, that is not
> the situation for the majority of laboratory experiments that do give
> results, and for which permanent records are easily made.
>

Interference between the different records in the different sectors
involving all the particles never vanishes. That we in practice cannot
see this does not mean that it does not exist.

Saibal

> Bruce+
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[Bruce Kellett]

On Mon, Jul 5, 2021 at 2:23 PM smitra <smi...@zonnet.nl> wrote:

On 04-07-2021 08:38, Bruce Kellett wrote:
> On Sun, Jul 4, 2021 at 2:59 PM smitra <smi...@zonnet.nl> wrote:
>
>> On 02-07-2021 06:46, Bruce Kellett wrote:
>>>
>>> No, I am not tracing out anything. I am looking at whether an
>>> interference pattern is formed or not. I don't have to detect the
>> IR photons in order for the interference to be destroyed.
>>
>> You choose to look at an interference pattern involving only part of the
>> relevant degrees of freedom and then you find that there is no
>> interference pattern.
>
> That does not make sense.

You are not observing the IR photons, there is still an interference
pattern in the many particle state involving all the relevant particles.

The only interference pattern of relevance is that on the screen hit by the buckyballs. Of course, for there to be such a pattern, many balls have to be sent through the slits. But that is the case for any interference experiment. Otherwise, I do not understand your comment.

What on earth are you talking about? There is no screen for the photons; and only one photon needs to be emitted by each ball sent through the slits. Observing that photon on a screen is like firing it into the wall -- such an operation does not recover the which way information for the balls. You would have to use a microscope suitable for IR photons (if such exists?). That would enable one to overcome diffraction limits in order to determine where the photon came from -- from a ball through the left or right slit, for example.

I don't think this is actually done in the experiment. What is observed is the presence or absence of the interference pattern on the screen where the balls hit. The photons are not detected. But if, in principle, they are of suitable wavelength to resolve the slit difference, then the interference pattern vanishes. The experiment is convincing in that they start wil cold buckyballs which show a clear interference pattern. They then gradually heat the balls so that the typical wavelength of the photons decreases. This gradually washes out the interference pattern. (Because at lower temperatures, the wavelength distribution of the IR photons is such that a few of them have shorter wavelengths.) As the temperature is increased so that most IR photons have short enough wavelengths, the interference pattern disappears completely. The paper by Hornberger et al. is at

     arXiv:quant-ph/0412003v2

You
consider the number of balls on the screen for the balls as a function
the position on this screen for fixed positions of dots on the screen
for the corresponding IR photons. For every such fixed position of the
dots made by the IR photons there will be a different interference
pattern of the balls. If you don't observe the IR photons in this way,
then the pattern for the balls will be the integral over all the
interference patters, which means that the interference pattern will be
washed out.

This is not what happens. Read the paper referenced above.

You have failed to understand what the experiment is about.

But nothing in the laws of physics says that this is
forbidden. This would only truly become impossible if there were an
infinite number of IR photons. Suppose we consider approaching this
impossibility as a limit where more and more IR photons are emitted.
Conservation of energy would then imply that the average energy of these
IR photons would have to tend to zero. The wavelength of the IR photons
then also increases, and if this becomes of the order of the separation
between the splits they don't reduce the visibility of the interference
pattern, so these photons then would not count. To get to an infinite
number of relevant IR photons, one then also has to increase the
distance between the slits as the number of IR photons is increased an
their energy is decreased.

Clearly, you are only going to get a truly invisible interference
pattern in the classical limit where the size of the system consisting
of the slits, the screen etc. tends to infinity, and an infinite number
of photons with infinitesimal energy are emitted. Only in this
degenerate limit does there exist no interference pattern at all, not
just one that one can measure in practice, but also none that in
principle exist involving any finite number of the emitted photons.

This is all totally irrelevant to the actual experiment in question.

These considerations do apply to each and every case. I mentioned the buckyball experiment because it makes things obvious. But the general principle is always true. Experiments that produced recorded results are not reversible. Because, for example, they are not thermally isolated, and IR photons can always escape to infinity and be irretrievable.

For example, one may object by invoking that the universe is
filled with a plasma and that the IR photons travel at a speed slightly
below the true vacuum speed of light.

What difference would that make. The IR photons are still faster than any material object sent after them to capture them. They will always escape. And because the universe is expanding, they will eventually pass over the Hubble horizon and be forever lost from sight!

>>>
>>> Says you. The laws of physics, principally the limitation of the
>> speed of light, means that the state cannot be restored, even in
>> principle.
>>
>> One can have a system locked up in a finite volume with the outer
>> walled cooled arbitrarily close to absolute zero and with many layers of
>> inner walls such that everything from the interior is absorbed or
>> reflected well before reaching the outer limits of the system.
>
> No such system is ever perfectly isolated. And besides, that is not
> the situation for the majority of laboratory experiments that do give
> results, and for which permanent records are easily made.
>

Interference between the different records in the different sectors
involving all the particles never vanishes. That we in practice cannot
see this does not mean that it does not exist.

The fact that it is not physically relevant means that your physics has failed to capture some important fact about the universe. Experiments with recorded results are generally irreversible. If your theory does not accommodate this fact, then your theory is deficient.

Whether this means that the off-diagonal terms of the density matrix (in the appropriate basis) do actually vanish, or if this is achieved by some other means, your theory has to adapt to the reality of irreversibility or your theory does not describe the real world. It is clear that for many reasons, pure Everettian QM, based solely on the Schrodinger equation, fails to explain many important features of the world we observe.

Bruce

[smitra]

This is then what I said previously, what you denied, i.e. that you are
only considering part of the system which is defined by the reduced
density matrix. The complete system of buckyball plus photons will show
interference, even if the wavelength is small enough to resolve the
slits provided you perform the right sort of measurement on the balls
and photons.

>
>> You
>> consider the number of balls on the screen for the balls as a
>> function
>> the position on this screen for fixed positions of dots on the
>> screen
>> for the corresponding IR photons. For every such fixed position of
>> the
>> dots made by the IR photons there will be a different interference
>> pattern of the balls. If you don't observe the IR photons in this
>> way,
>> then the pattern for the balls will be the integral over all the
>> interference patters, which means that the interference pattern will
>> be
>> washed out.
>
> This is not what happens. Read the paper referenced above.

It's not what happens in that experiment, but you can in principle
demostrate an interference pattern also when photons are emitted by the
balls.

But that's irrelevant for the main issue here, i.e. that interference
can in principle always be denonstrated, no matter how far the system
has decohered.

And that experiment is in turn irrelevant to the question of whether or
not a real superposition actually exist. You can always perform a
measurement involving more particles where an interference has vanished,
that only demonstrates that the reduced density matrix described a mixed
state, the entire system is still in a pure state.

Even if IR photons always escape to infinity, the complete quantum state
of the entire system is still a pure state. There is still a
superposition between the balls going through one and the other slit.

>
>> For example, one may object by invoking that the universe is
>> filled with a plasma and that the IR photons travel at a speed
>> slightly
>> below the true vacuum speed of light.
>
> What difference would that make. The IR photons are still faster than
> any material object sent after them to capture them. They will always
> escape. And because the universe is expanding, they will eventually
> pass over the Hubble horizon and be forever lost from sight!
>

But the observations on the balls will be completed long before that, so
how is this relevant for the existence of parallel worlds?

Which would mean that QM cannot be correct as a fundamental theory.

Saibal

> Bruce

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[Bruce Kellett]

On Mon, Jul 5, 2021 at 7:39 PM smitra <smi...@zonnet.nl> wrote:

On 05-07-2021 09:00, Bruce Kellett wrote:
> On Mon, Jul 5, 2021 at 2:23 PM smitra <smi...@zonnet.nl> wrote:
>
> I don't think this is actually done in the experiment. What is
> observed is the presence or absence of the interference pattern on the
> screen where the balls hit. The photons are not detected. But if, in
> principle, they are of suitable wavelength to resolve the slit
> difference, then the interference pattern vanishes. The experiment is
> convincing in that they start wil cold buckyballs which show a clear
> interference pattern. They then gradually heat the balls so that the
> typical wavelength of the photons decreases. This gradually washes out
> the interference pattern. (Because at lower temperatures, the
> wavelength distribution of the IR photons is such that a few of them
> have shorter wavelengths.) As the temperature is increased so that
> most IR photons have short enough wavelengths, the interference
> pattern disappears completely. The paper by Hornberger et al. is at
>      arXiv:quant-ph/0412003v2

This is then what I said previously, what you denied, i.e. that you are
only considering part of the system which is defined by the reduced
density matrix. The complete system of buckyball plus photons will show
interference, even if the wavelength is small enough to resolve the
slits provided you perform the right sort of measurement on the balls
and photons.

That is false.

>
> This is not what happens. Read the paper referenced above.

It's not what happens in that experiment, but you can in principle
demostrate an interference pattern also when photons are emitted by the
balls.

Provided the  wavelength of the IR photons is too large to resolve the inter-slit distance. When you heat the balls further, the interference disappears.

>
> This is all totally irrelevant to the actual experiment in question.
>

And that experiment is in turn irrelevant to the question of whether or
not a real superposition actually exist. You can always perform a
measurement involving more particles where an interference has vanished,
that only demonstrates that the reduced density matrix described a mixed
state, the entire system is still in a pure state.

Of course real superpositions exist. The experiment shows that decoherence need not involve large numbers of degrees of freedom.

>
> These considerations do apply to each and every case. I mentioned the
> buckyball experiment because it makes things obvious. But the general
> principle is always true. Experiments that produced recorded results
> are not reversible. Because, for example, they are not thermally
> isolated, and IR photons can always escape to infinity and be
> irretrievable.

Even if IR photons always escape to infinity, the complete quantum state
of the entire system is still a pure state. There is still a
superposition between the balls going through one and the other slit.

Maybe that is not what is observed. That superpostion has decohered.

>
>> For example, one may object by invoking that the universe is
>> filled with a plasma and that the IR photons travel at a speed
>> slightly below the true vacuum speed of light.
>
> What difference would that make. The IR photons are still faster than
> any material object sent after them to capture them. They will always
> escape. And because the universe is expanding, they will eventually
> pass over the Hubble horizon and be forever lost from sight!
>

But the observations on the balls will be completed long before that, so
how is this relevant for the existence of parallel worlds?

I think it is relevant to the question of reversibility.

>
> Whether this means that the off-diagonal terms of the density matrix
> (in the appropriate basis) do actually vanish, or if this is achieved
> by some other means, your theory has to adapt to the reality of
> irreversibility or your theory does not describe the real world. It is
> clear that for many reasons, pure Everettian QM, based solely on the
> Schrodinger equation, fails to explain many important features of the
> world we observe.
>
Which would mean that QM cannot be correct as a fundamental theory.

It is very probable the QM, in its current form, is not the correct fundamental theory.  In the history of science it is never the case that the dominant theory at one time survives unaltered into the future. The negative induction against scientific realism is that all scientific theories are ultimately shown to be false.

Bruce

[smitra]

This is easy to see. Denote the buckyball state of a buckball moving
through the left slit by |L> and moving through the right slit by |R>.
Suppose that a photon is emitted by the by the buckyballs such that the
ball moving through the left slit emits a photon in a state |PL> that
will be orthogonal to the state |PR> of the photon emitted by the ball
moving through the right slit . The state of the system after the ball
passes the slits is then:

|psi> = 1/sqrt(2) [|L>|PL> + |R>|PR>]

This state then evolves under unitary time evolution, we can write the
state just before the ball hits the screen as:

|psi_s> = 1/sqrt(2) [|L_s>|PL_s> + |R_s>|PR_s>]

There is then no interference patter on the screen for the buckyballs
because |PL_s> and |PR_s> are orthogonal, the unitary time evolution
preserves the orthogonality of the initial states. The probability to
observe a buckyball on position x on the screen is:

P(x) = ||<x|psi_s>||^2 = 1/2 [|<x|L_s>|^2 + |<x|R_s>|^2] + Re[<x|L_s>
<x|R_s>* <PR_s|PL_s>]

And the last interference term is zero because <PR_s|PL_s> = 0

But if we also observe the photon on another screen and keep the joint
count for buckyballs landing on spot x on the buckyball screen and for
photons landing on spot y on the photon screen as a function of x and y,
then we do have an interference pattern as a function of x for fixed y.
If we de note by U the unitary time evolution for the photons until they
hit their screen, and put |PL_t> =U|PL_s> and |PR_t> = U|PR_s>, then the
probability distribution is:

P(x,y) = |<x,y|U|psi_s>|^2 = 1/2 [|<x|L_s>|^2|<y|PL_t>|^2 +
|<x|R_s>|^2|<y|PR_t>|^2] +Re[<x|L_s> <x|R_s>* <y|PL_t><y|PR_t>*]

The interference term Re[<x|L_s> <x|R_s>* <y|PL_t><y|PR_t>*] does not
vanish as it involves evaluating the components of the buckyball and
photon states in the position basis and so there is no inner product
involved anymore. For fixed y the quantity <y|PL_t><y|PR_t>* will have
some value that will be nonzero in general, so if we keep y fixed then
there will be an interference term.

So, we can conclude that invoking escaping IR photons does not male any
sense in this discussion because all it does is it scrambles the
interference pattern to make it invisible in a way that allows it to be
recovered in principle using measurements on those IR photons. You can,
of course, erase the interference patter by measuring the observable for
the photons that has |PR> and |PL> as its eigenstates. But even in that
case the information will still be there in the state of all the atoms
of the measurement apparatus for the photons. But if you don't perform
any measurement then the information will simply continue to exists in
the escaping photons.

So, in general we can conclude by generalizing this to any large number
of particles that even with what we consider to be permanent records,
you don't get rid of the theoretical possibility of interference between
the sectors where those records are different. So, the existence of
parallel worlds cannot be made fully 100% irrelevant if QM is rigorously
correct, and we cannot therefore argue that QM is exactly equivalent to
an alternative theory that leaves out parallel worlds. Even though the
difference may be almost 100% insignificant FAPP, it's not exactly 100%
even in the macroscopic realm.

The argument against the existence of parallel worlds by invoking
decoherence that makes superposition hard to detect for complex systems
is thus analogous to the defense of creationists when they invoke a God
of ever smaller gaps of things that have not yet been fully explained.

Saibal

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[Bruce Kellett]

It is a shame that your fancy analysis is contradicted by the actual experimental results. I leave it as an exercise for you to determine where your mistake is. But I suggest that you actually reads the paper quant-ph/0412003.

The argument against the existence of parallel worlds by invoking
decoherence that makes superposition hard to detect for complex systems
is thus analogous to the defense of creationists when they invoke a God
of ever smaller gaps of things that have not yet been fully explained.

My dear, you really have lost the plot, haven't you Saibal?

[smitra]

The analysis is 100% rigorous, based on standard QM. The results of the
paper quant-ph/0412003 are irrelevant as they don't measure the joint
interference pattern. In that case the interference pattern of the balls
will vanish due to the photon states being orthogonal, as I've shown
above.

>
>> The argument against the existence of parallel worlds by invoking
>> decoherence that makes superposition hard to detect for complex
>> systems
>> is thus analogous to the defense of creationists when they invoke a
>> God
>> of ever smaller gaps of things that have not yet been fully
>> explained.
>
> My dear, you really have lost the plot, haven't you Saibal?
>

I'm sticking to QM, your position depends on some unproven effect that
would make pure states evolve into mixed states.

Saibal

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[Bruce Kellett]

On Tue, Jul 6, 2021 at 11:41 PM smitra <smi...@zonnet.nl> wrote:

On 06-07-2021 14:10, Bruce Kellett wrote:
>
> It is a shame that your fancy analysis is contradicted by the actual
> experimental results. I leave it as an exercise for you to determine
> where your mistake is. But I suggest that you actually reads the paper
> quant-ph/0412003.

The analysis is 100% rigorous, based on standard QM. The results of the
paper quant-ph/0412003 are irrelevant as they don't measure the joint
interference pattern.

It is only your confused notion that even considers such a thing to be relevant. Hornberger et al. give a complete and detailed quantum analysis of their experiment and show that their results are in complete accordance with quantum theory. The thing is that you have to take their experiment results, particularly as shown in Fig 8 of the paper, seriously. They show that the interference fringes are gradually washed out as the temperature of the balls increases. I quote their abstract:

"We study C_70 fullerene matter waves in a Talbot-Lau interferometer as a function of their temperature. While the ideal fringe visibility is observed at moderate molecular temperatures, we find a gradual degradation of the interference contrast if the molecules are heated before entering the interferometer. A method is developed to assess the distribution of the micro-canonical temperature of the molecules in free flight. This way the heating-dependent reduction of the interference contrast can be compared with the predictions of quantum theory. We find that the observed loss of coherence agrees quantitatively with the expected decoherence rate due to the thermal radiation emitted by the hot molecules."

In that case the interference pattern of the balls
will vanish due to the photon states being orthogonal, as I've shown
above.

>
>> The argument against the existence of parallel worlds by invoking
>> decoherence that makes superposition hard to detect for complex
>> systems is thus analogous to the defense of creationists when they invoke a
>> God of ever smaller gaps of things that have not yet been fully explained.
>
> My dear, you really have lost the plot, haven't you Saibal?
>

I'm sticking to QM, your position depends on some unproven effect that
would make pure states evolve into mixed states.

Your idea of QM is sadly flawed. The real professional quantum analysis given in the quoted paper shows how the observed effects are completely consistent with quantum mechanics. The emission of thermal radiation by the heated balls leads to a clear and evident loss of coherence. Your pseudo-analysis has nothing to do with either quantum mechanics or the actual set-up of this buckyball experiment.

Bruce

[Brent Meeker]

In the Bucky Ball experiment there's no interference pattern when the
photons have long wave length. So it's not just a question of the states
being orthogonal.

> the unitary time evolution preserves the orthogonality of the initial
> states. The probability to observe a buckyball on position x on the
> screen is:
>
> P(x) = ||<x|psi_s>||^2 = 1/2 [|<x|L_s>|^2 + |<x|R_s>|^2] + Re[<x|L_s>
> <x|R_s>* <PR_s|PL_s>]
>
> And the last interference term is zero because <PR_s|PL_s> = 0
>
> But if we also observe the photon on another screen and keep the joint
> count for buckyballs landing on spot x on the buckyball screen and for
> photons landing on spot y on the photon screen as a function of x and
> y, then we do have an interference pattern as a function of x for
> fixed y. If we de note by U the unitary time evolution for the photons
> until they hit their screen, and put |PL_t> =U|PL_s> and |PR_t> =
> U|PR_s>, then the probability distribution is:
>
> P(x,y) = |<x,y|U|psi_s>|^2 = 1/2 [|<x|L_s>|^2|<y|PL_t>|^2 +
> |<x|R_s>|^2|<y|PR_t>|^2] +Re[<x|L_s> <x|R_s>* <y|PL_t><y|PR_t>*]
>
> The interference term Re[<x|L_s> <x|R_s>* <y|PL_t><y|PR_t>*] does not
> vanish as it involves evaluating the components of  the buckyball and
> photon states in the position basis and so there is no inner product
> involved anymore. For fixed y the quantity <y|PL_t><y|PR_t>* will have
> some value that will be nonzero in general, so if we keep y fixed then
> there will be an interference term.

The position operators are projections and include decoherence. I don't
think having fixed y will recover the interference pattern, but I'm not
clear on what y is measuring?  Are there just two spots on the y-screen
corresponding to L and R slits?

>
> So, we can conclude that invoking escaping IR photons does not male
> any sense in this discussion because all it does is it scrambles the
> interference pattern to make it invisible in a way that allows it to
> be recovered in principle using measurements on those IR photons. You
> can, of course, erase the interference patter by measuring the
> observable for the photons that has |PR> and |PL> as its eigenstates.
> But even in that case the information will still be there in the state
> of all the atoms of the measurement apparatus for the photons. But if
> you don't perform any measurement then the information will simply
> continue to exists in the escaping photons.

And per the first sentence of the paragraph the interference will be
eliminated by the escaping IR photons.  Are you contradicting this in
the last sentence?  The experiment showed the interference  disappeared
as the IR photon wave length decreased. It said nothing about them being
observed or escaping into space.

Brent

[smitra]

None of this contradicts what I wrote.

>> In that case the interference pattern of the balls
>> will vanish due to the photon states being orthogonal, as I've shown
>>
>> above.
>>
>>>
>>>> The argument against the existence of parallel worlds by invoking
>>>> decoherence that makes superposition hard to detect for complex
>>>> systems is thus analogous to the defense of creationists when
>> they invoke a
>>>> God of ever smaller gaps of things that have not yet been fully
>> explained.
>>>
>>> My dear, you really have lost the plot, haven't you Saibal?
>>>
>>
>> I'm sticking to QM, your position depends on some unproven effect
>> that
>> would make pure states evolve into mixed states.
>
> Your idea of QM is sadly flawed. The real professional quantum
> analysis given in the quoted paper shows how the observed effects are
> completely consistent with quantum mechanics. The emission of thermal
> radiation by the heated balls leads to a clear and evident loss of
> coherence. Your pseudo-analysis has nothing to do with either quantum
> mechanics or the actual set-up of this buckyball experiment.

As I said, what I wrote is 100% consistent with their results. The fact
that you can't see this implies that you have forgotten basic QM and are
unqualified to continue this discussion. I remember from a while back on
this list that you claimed that in two slit experiment, if the
wavefunctions of the particle moving through the left slit is orthogonal
to that of the right slit, then there would be no interference. This is
obviously wrong, and there was a long discussion where you kept on
repeating your flawed point.

Saibal

>
> Bruce

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[smitra]

If there are many photons, then you have large number of inner products
between the unobserved photon states and the interference pattern then
gets suppressed as well.

Y is measuring the position at which the photon is landing on the screen
for the photon. When you measure y and x then there is an interference
in the joint probability distribution. For every fixed y, the function
P(x,y) will show interference as a function of x. You can also say that
measuring y destroys the which way information present in the photon
states.

>
>
>>
>> So, we can conclude that invoking escaping IR photons does not male
>> any sense in this discussion because all it does is it scrambles the
>> interference pattern to make it invisible in a way that allows it to
>> be recovered in principle using measurements on those IR photons. You
>> can, of course, erase the interference patter by measuring the
>> observable for the photons that has |PR> and |PL> as its eigenstates.
>> But even in that case the information will still be there in the state
>> of all the atoms of the measurement apparatus for the photons. But if
>> you don't perform any measurement then the information will simply
>> continue to exists in the escaping photons.
>
> And per the first sentence of the paragraph the interference will be
> eliminated by the escaping IR photons.  Are you contradicting this in
> the last sentence?  The experiment showed the interference 
> disappeared as the IR photon wave length decreased. It said nothing
> about them being observed or escaping into space.
>
> Brent

I don't disagree with that, if you don't measure y then there is no
interference pattern. And even if you do measure y, you would then have
to count the number of buckyballs on the screen only when the photon
lands on some specific position. If you just consider the total numbers
of buckyballs irrespective of where the photon is detected then the
interference pattern will vanish again, because you are then integrating
over the term <y|PL_t><y|PR_t>* which yields the inner product between
the photon states which was assumed to be zero.

Saibal

[Bruce Kellett]

On Wed, Jul 7, 2021 at 5:26 PM smitra <smi...@zonnet.nl> wrote:

On 07-07-2021 01:17, Bruce Kellett wrote: 

>
> Your idea of QM is sadly flawed. The real professional quantum
> analysis given in the quoted paper shows how the observed effects are
> completely consistent with quantum mechanics. The emission of thermal
> radiation by the heated balls leads to a clear and evident loss of
> coherence. Your pseudo-analysis has nothing to do with either quantum
> mechanics or the actual set-up of this buckyball experiment.

As I said, what I wrote is 100% consistent with their results.

Your analysis, as I understand it, suggests that if the IR photons are not observed, no interference pattern is seen. This seems to overlook the fact that the photons are emitted only probabilistically -- there need not be any photons at all, and yet the experiment sees a buckyball interference pattern at the lower temperatures. This pattern is gradually washed out as the temperature of the balls is increased. No photons are ever detected in that experiment.

Do you dispute that that is what the paper by Hornberger et al. says?

Bruce

[smitra]

I don't dispute these results. The buckyballs are coming from a thermal
reservoir at some finite temperature. We can avoid working with mixed
states by simply considering the interference pattern for each pure
state separately and then summing over the probability distribution over
the pure states. But for this discussion we want to focus on what the
interference pattern will be if all the buckyballs are in the same
exited state. If we put the entire system ina finite volume then we have
a countable set of allowed k-values for the photon momenta. We then have
a set of allowed states for the photons defined by the allowed momenta
and a polarization. We can then label these photon states using a number
and then specify an arbitrary state for the photons by specifying how
many photons we have in each state, and these numbers can then be equal
to zero. If they are all zero then no photons are present.

If only the right slit is open, the state of the buckyball and the
photons just before the screen is hit can be denoted as:

|Right> = sum over n1, n2,n3,...|R(n1,n2,n3,...)>|n1,n2,n3,......>

where |R(n1,n2,...)> denotes the quantum state of the buckyball if it
emits n1 photons in state 1, n2 photons in state 2 etc. The state of the
photons is then denoted as |n1,n2,n3,......>


If only the left slit is open, the state of the buckyball and the
photons just before the screen is hit can be denoted as:

|Left> = sum over n1, n2,n3,...|L(n1,n2,n3,...)>|n1,n2,n3,......>

where |R(n1,n2,...)> denotes the quantum state of the buckyball. Here we
note that the state of the photons will pick up a phase factor relative
to the case of only the right slit being open, but we can then absorb
this phase factor in |L(n1,n2,n3,...)>.

With both slits open, we'll then have a state of the form:

|psi> = 1/sqrt(2) [|Right> + |Left>]

The inner product of |psi> with some position eigenstate |x>, <x|psi> is
then a state vector for the photon states, the squared norm of that
state vector is the probability of finding the buckyball at position x,
because this is the sum over the probabilities for photons over all
possible photon states. So, the probability is then:

P(x) = ||<x|psi>||^2 = 1/2 [||<x|Right>||^2 + ||<x|Left>||^2] +
Re[<Left|x><x|Right>]


We can then evaluate the interference term as follows:

Re[<Left|x><x|Right>] = Re sum over n1, n2,n3,...m1,m2,m3
<x|L(m1,m2,m3,...)>*<x|R(n1,n2,n3,...)><m1,m2,m3,...|n1,n2,n3,......>

Using that <m1,m2,m3,...|n1,n2,n3,......> = 0 unless m_j = n_j for all
j, in which case this inner product equals 1, we then have:

Re[<Left|x><x|Right>] = Re sum over n1, n2,n3
<x|L(n1,n2,n3,...)>*<x|R(n1,n2,n3,...)> =


Re[<x|L(0,0,0...)>*<x|R(0,0,0,...>] +
Re[<x|L(1,0,0...)>*<x|R(1,0,0,...>] + ..... (1)

As explained above when there are photons present then we've absorbed
the phase factor due to translation of the photon states in the states
|L(n1,n2,n3...)>. For each wave vector k there is a factor for each
photon with that wavevector of exp(i k dot r) where r is the position of
the left slit w.r.t. the right slit. So, the total phase factor will be:

Product over j of exp(i kj nj dot r)

In the experiment there is then an additional summation over the pure
states of the buckyballs. If the temperature is low then the summation
will consist of states for which |R(0,0,0,..> and |L(0,0,0,..> are the
dominant terms, as most of the time no photons will be emitted. At
higher temperatures the typical states there will be contributions from
different numbers pf photons, so the interference pattern will be a sum
of many different terms in (1) with comparable norms, they come with
different phase factors due to the different numbers of photons with
different momenta. So, the interference pattern will be washed out.

Saibal

[Bruce Kellett]

This analysis contradicts what you said in your first analysis. In the first analysis, you claimed that no interference would be seen if the IR photons were not detected. You seem to have dropped this notion in the above. You now say that there is interference when no photons are present, but this is washed out when there are different numbers of photons.

I think you are making the same basic mistake that you made when we previously discussed  two-slit interference: You are analysing the two slit case as a sum over single slit patterns, and assuming the emission of independent photons from the ball through each slit. The trouble is that there are not two balls, one for each slit. The same ball goes through both slits and there is only one ball emitting (or not emitting) photons.

Neither of your analyses actually explain the observed behaviour.

Bruce

[Bruno Marchal]

You are right. Some people invoke their personal ontological commitment, which is invalid in this setting.

To make a parallel world disappearing is impossible as long as 2+2=4.

Bruno

> To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/68ed0f821281a93b3044ee78e31a5c89%40zonnet.nl.

[Jason Resch]

This conversation brought to mind Feynman's question: what happens in the limit of going from 2 slits to infinite slits, such that the wall disappears?

Jason

[smitra]

In that case I considered a simple model where one photon would be
emitted such that the state of that photon emitted from the ball moving
through one slit would be orthogonal to that of the state of the photon
emitted by the ball moving through the opther slit.

You seem to have dropped this notion in
> the above.

In the derivation above I work in the momentum basis for the photons.
Obviously, exp(i k dot r) and exp(i k dot (r+u)) are not orthogonal, but
then one needs to consider a superposition of such momentum eigenstates
as I do above.

You now say that there is interference when no photons are
> present, but this is washed out when there are different numbers of
> photons.
>

Yes, the above derivation captures more of the details.

> I think you are making the same basic mistake that you made when we
> previously discussed two-slit interference: You are analysing the two
> slit case as a sum over single slit patterns, and assuming the
> emission of independent photons from the ball through each slit. The
> trouble is that there are not two balls, one for each slit. The same
> ball goes through both slits and there is only one ball emitting (or
> not emitting) photons.

I agree that there are no two balls for each slit, the derivation
involves only one ball and treats the superposition in the usual way.

>
> Neither of your analyses actually explain the observed behaviour.

It does so, otherwise the experiment would have proven that QM is
invalid.

Saibal

[Brent Meeker]

On 7/10/2021 1:19 AM, Bruno Marchal wrote:
> So, in general we can conclude by generalizing this to any large number of particles that even with what we consider to be permanent records, you don't get rid of the theoretical possibility of interference between the sectors where those records are different.

We can if the universe is expanding faster than light beyond the Hubble
radius.

Brent

[smitra]

The expansion of the universe is irrelevant. The information needed to
see the interference pattern continues to exist outside the horizon when
it isn't accessible to us anymore. And this is irrelevant for the
discussions about observations in quantum mechanics. If an observer
performs a measurement and the claim is that this is a unitary process
with the observer evolving into a superposition, while the objection
against this claim is that infrared photons are escaping and will
eventually move beyond the Hubble volume, then these photons will still
not have escaped beyond the Hubble horizon by the time the observer is
aware of the results of the experiment. So, whether or not the photons
will eventually no longer be accessible, cannot be relevant.

Saibal

> Brent

[Bruce Kellett]

Once the photons escape from the immediate environs of the experiment, they are not recoverable. Try shining a torch at night to illuminate a tree. Now try to stop the illumination already present. You can stop future illumination by covering the torch, or switching it off. But once the tree is illuminated it is not reversible. The expansion of the universe, and the existence of the Hubble horizon, just makes the irreversibility more obvious.

Bruce

[Bruce Kellett]

So, in your opinion, the quantum mechanical analysis given in the paper is wrong.

Bruce

[smitra]

This is only true in practice, not in principle because the escaping
photons be captured and detected in principle. It's also irrelevant,
because the photons that escape continue to exist, the information
contained in the photons continues to exist, even if it were true that
they could not be recovered. Then if we were to conduct an interference
experiment with the balls then we wouldn't see an interference pattern.
But if we write down where each balls lands on the screen then this
information together with information that could be obtained by
performing certain measurements on the escaping photons emitted by each
ball would still yield an interference pattern.

> Bruce
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[smitra]

It is correct, it's just that your conclusion about the MWI based on
that paper is incorrect. Escaping infrared photons and the decoherence
this causes are totally irrelevant. Whether or not an interference
pattern can be detected is not relevant to the question of whether or
not a superposition exists when we know that it exist and it has no
decohered. It's just that you then can't reproduce one particular line
of evidence for the validity of quantum mechanics in that particular
experiment.

If I prepare the state of a particle in a superposition and let this
interact in a certain way, then we know how this state will evolve. If
this evolution involves interactions with many particles, then the
system will decohere. Then it may be true that we cannot distinguish the
state of the system from being in a pure or mixed state in practice due
to not being able to conduct an interference experiment involving a very
large number of particles, but quantum mechanics still tells us that
the superposition exists and that if we were to conduct the right sort
of interference experiment, we would see an interference that would
prove that the state is not a mixed state.

Then given that we don't have any experimental evidence to doubt the
validity of quantum mechanics, saying that the superposition does not
really exists in such a a case, is just silly.

Saibal
>
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[Brent Meeker]

But does it exist if part of the information has crossed the Hubble
boundary?  Then there is no experiment, even in principle, that would
prove the state is not a mixed one.

Brent

[Bruce Kellett]

Not true. You can;t ever catch up with the escaping photons to capture them.

It's also irrelevant,
because the photons that escape continue to exist, the information
contained in  the photons continues to exist, even if it were true that
they could not be recovered. Then if we were to conduct an interference
experiment with the balls then we wouldn't see an interference pattern.
But if we write down where each balls lands on the screen then this
information together with information that could be obtained by
performing certain measurements on the escaping photons emitted by each
ball would still yield an interference pattern.

This is where you go seriously wrong. Simply recording where the photons land does not quantum erase the information they carried. Once the photons carry off the which way information, the interference pattern is restored only if the information carried by the photons is quantum erased. Simply running the photons into a screen (or the wall), even if you record where they land, is not quantum erasure. See, for example, the paper arXiv:1206.6578 on quantum erasure. In this paper they say "the presence of path information anywhere in the universe is sufficient to prohibit any possibility of interference. In other words, the atoms' path states alone are not in a coherent superposition due to the atom-photon entanglement." This transfers directly to the buckyball experiment under discussion. Running the photons into a screen, or the wall, does not destroy the ball-photon entanglement.

Bruce

[Bruce Kellett]

On Sun, Jul 11, 2021 at 10:36 AM smitra <smi...@zonnet.nl> wrote:

On 11-07-2021 01:05, Bruce Kellett wrote:
> On Sun, Jul 11, 2021 at 1:18 AM smitra <smi...@zonnet.nl> wrote:
>
>> On 10-07-2021 07:58, Bruce Kellett wrote:
>>>
>>> Neither of your analyses actually explain the observed behaviour.
>>
>> It does so, otherwise the experiment would have proven that QM is
>> invalid.
>
> So, in your opinion, the quantum mechanical analysis given in the
> paper is wrong.

It is correct, it's just that your conclusion about the MWI based on
that paper is incorrect. Escaping infrared photons and the decoherence
this causes are totally irrelevant. Whether or not an interference
pattern can be detected is not relevant to the question of whether or
not a superposition exists when we know that it exist and it has no
decohered.

The question is not whether or not there is a superposition. The question is whether or not the superposition is coherent. If the balls are entangled with photons that have escaped, the superposition has decohered and is no longer coherent. Loss of coherence means that there can be no interference pattern. It is not just that it is not visible -- it simply no longer exists. Coherence can only be restored if the escaping information is quantum erased. The escaping photons are part of the total system. If you ignore this entanglement, the remaining system is a mixed state.

Bruce

[smitra]

The theories that tell you that there is such a thing like a Hubble
boundary, also tell you that information does not vanish. We can now
detect photons from galaxies that have always receded from us faster
than light. So, that's information we're that has leaked away from those
galaxies that does objectively exists. To prove that a state is a pure
state one can just point to the way the state was prepared and invoke
quantum mechanics. It's not necessary to demonstrate interference to
prove that quantum mechanics is still valid.

Saibal

> Brent
>

[smitra]

On 11-07-2021 00:59, Bruce Kellett wrote:

Nothing stops you from doing the experiment in a closed volume with
mirrors at the boundary. Since what we measure in a experiments is
determined by the laws of physics which are local in nature, the sort of
we impose boundary conditions on photons far away is irrelevant. Whether
or not an observer measuring the z-component of a spin that was
polarized in the positive x-direction ends up in a superposition where
there are objectively both outcomes being realized or only one outcome
does not depend on whether or not all the escaping infrared photons can
actually be captured and be made part of a giant interference experiment
to demonstrate an interference to prove that the superposition indeed
exists.

The existence of the superposition depends on the validity of quantum
mechanics for large systems. One can prove or disprove that in suitable
experiments. Once that's done and, say, collapse theories are ruled out
then it's not necessary to prove this over and over again for each and
every case. As things stand now, we can't rule out that an objective
collapse can happen, but this would require a violation of quantum
mechanics.

> Bruce
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[smitra]

Yes, so you need a combined measured on the balls and the photons to
demonstrate interference. But whether or not we actually do this is then
irrelevant to the question of whether or not in a superposition both
sectors of that superposition actually exist, unless one would doubt the
validity of quantum mechanics and would want to test the quantum
mechanical prediction. If we assume that quantum mechanics is valid then
we assume that both sectors objectively exist, regardless of whether or
not you could actually perform the required interference experiment.

Saibal


> Bruce
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[Philip Benjamin]

[Philip Benjamin]
Confusion worse confounded? Permanent records? Theoretical possibility of different sectors interfering? Quarks and electrons are different sectors with "permanent records". Will they not just "whizz around", at least say at some "beginnings" (the imaginary Big Bang). How do they eventually form "protons" and "neutrons" and remain separate from "electrons"? How do these "protons" (and neutrons) remain "bound" together to form a nucleus of an atom, with electrons in "permanent records of energy levels" orbiting around but not falling into the nucleus? From whence comes the "permanent record" that an atom may combine with another atom according to "permant records of the Laws of Chemistry? From whence comes the "permanent record" that there will be atoms of inert gases with a "stable" duet or octet of "electrons"? Will there be any universe at all without these "permanent records", CopenPagan Interpretation notwithstanding?
Philip Benjamin

.

[smitra]

They can be reflected back using mirrors. One can therefore at least in
principle do experiments that rule out collapse theories for large
systems that are large enough to include observers. And once collapse
theories are ruled out in a few experiments it follows that in a
superposition all the sectors where observers find different results
objectively exist, regardless of whether or not in those particular
situations one could have done the same sorts of experiments that ruled
out collapse theories.

Recording where the photons land on the screen is enough, this is very
easy to see. Let's consider an interference experiment where the
particle gets entangled with another particle that carries away the
which way information. If we work in the position representation then we
have a wavefunction:

psi(x,y) = 1/sqrt(2) [psi_1(x,y) + psi_2(x,y)] (1)

where x is the position of particle 1 just before it hits the screen and
y the position of the other particle at that time, and psi_1(x,y) is the
wavefunction when only slit 1 is open while psi_2(x,y) the wavefunction
with only slit 2 open. We also assume that particle 2 carries the which
way information, this means that psi_1(x,y) and psi_2(x,y) for x kept
fixed and considered as a function of y are eigenfunctions with
different eigenvalues of an observable that corresponds to extracting
the which way information from the second particle. This then implies
that psi_1(x,y) and psi_2(x,y) are orthogonal for every x:

Integral psi_1(x,y)*psi_2(x,y)d^3y = 0 (2)

So, if we compute the probability of observing particle 1 at some
position x, while we don't measure the position of particle 2, we find
by taking the modulus squared of (1) and integrating over y:

Integral |psi(x,y)|^2 d^3y = 1/2 Integral |psi_1(x,y)|^2 d^3y + 1/2
Integral |psi_2(x,y)|^2 d^3y

+ Re Integral psi_1(x,y)*psi_2(x,y) d^3y

And the last term vanishes due to (2), so we don't detect interference.
But now suppose that we perform a simultaneous measurement of the
positions of both particles. The probability of detecting particle 1 at
position x and particle 2 at position y is:

|psi(x,y)|^2 = 1/2 |psi_1(x,y)|^2 y + 1/2 |psi_2(x,y)|^2 + Re
psi_1(x,y)*psi_2(x,y)

So, there now clearly an interference term. If we keep y fixed the
probability distribution of x will show interference., This requires one
to count the dots on the screen for particle 1 for the cases where
particle 2 ends up within some narrow range for some fixed y. If we
don't keep track of y and just add up all the dots at the positions on
the screen for particle 1, then that amounts to integrating the
interference term over all y, which will make it vanish die to
orthogonality.

Saibal

> Bruce
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[Philip Benjamin]

[spudb...@aol.com]

I am guessing that the reason physics is stable or the mechanism for this is the quantum weirdness observations of old as taught by Schrodinger, Heisenberg, Wigner, Wheeler, and Bell, all typified by repeated Stern - Gerlach experiments. 

https://www.forbes.com/sites/startswithabang/2021/07/09/ask-ethan-is-there-a-hidden-quantum-reality-underlying-what-we-observe/?sh=43131f4fef72

Somehow reality is crystalized by some "observer" and things may be programmed to generate a result. This doesn't answer the next question but it is a summary how the cosmos behaves. Why it is programmed in such a manner or how it is open to conjecture. This question needs a big project budget.

-----Original Message-----
From: Jason Resch <jason...@gmail.com>
To: Everything List <everyth...@googlegroups.com>
Sent: Sat, Jul 10, 2021 7:01 am
Subject: Re: Why are laws of physics stable?

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.

[Brent Meeker]

?? I think that's a contradiction.

> So, that's information we're that has leaked away from those galaxies
> that does objectively exists. To prove that a state is a pure state
> one can just point to the way the state was prepared and invoke
> quantum mechanics. It's not necessary to demonstrate interference to
> prove that quantum mechanics is still valid.

So, then you agree with Bruce that so long as the which-way information
exists in those outgoing photons, the interference pattern will show up?

Brent

>
> Saibal
>
>> Brent
>>
>

[Bruce Kellett]

It's worse than that -- it's gibberish.

> So, that's information we're that has leaked away from those galaxies
> that does objectively exists. To prove that a state is a pure state
> one can just point to the way the state was prepared and invoke
> quantum mechanics. It's not necessary to demonstrate interference to
> prove that quantum mechanics is still valid.

So, then you agree with Bruce that so long as the which-way information
exists in those outgoing photons, the interference pattern will show up?

I think you might have meant that as long as the which-way information exists (has not been quantum erased), then no interference is visible.

Bruce

[Bruce Kellett]

On Mon, Jul 12, 2021 at 3:44 AM smitra <smi...@zonnet.nl> wrote:

On 11-07-2021 02:46, Bruce Kellett wrote:
> On Sun, Jul 11, 2021 at 10:21 AM smitra <smi...@zonnet.nl> wrote:
>>>
>> This is only true in practice, not in principle because the escaping
>>
>> photons be captured and detected in principle.
>
> Not true. You can;t ever catch up with the escaping photons to capture them.

 

They can be reflected back using mirrors.

You can't decide to put mirrors in place after the photons have been emitted.

Of course, you could always decide in advance to perform all experiments in reflecting boxes, but that is not what is done in practice. So the general rule is that escaping photons are not recoverable.

This is the same mistake that you have routinely made in all of these discussions. You calculate for particles through each slit independently. But if that is the case, then no interference can ever be seen. The possibility of interference relies on coherence between the amplitudes at the two slits. In your calculations, you have never allowed for this coherence -- the amplitudes at the two slits are not independent.

Bruce

[Bruce Kellett]

To see this in more detail, we can go through your original argument.

You write : denote the buckyball moving through the left slit by |L> and the right slit by |R> and the photons by |PL> and |PR>. Now the states |R> and |L> are coherent; thus correlated; and the overlap <L|R> does not vanish. Writing

     |psi> = (|L>|PL>  +  |R>|PR>) 

is the same as assuming that the photons are emitted from the slits if they detect a ball passing through that slit. This is a direct "which-way" measurement, and since the photon states are independent, they are, as you say, orthogonal, and there can be no interference if such measurements are made at the slits. This is the essential loss of coherence.

Your claim then is that if we observe the photons on another screen and keep track of the ball positions on their screen for photons that arrive at the same point on this other screen, then the interference pattern is restored. This is wrong, because the photons emitted from the slits if and when they detect a ball passing through the corresponding slit are still independent. The fact that they might arrive at the same point on a further screen is irrelevant. The photon states are still independent. In fact, there can only ever be one photon for each buckyball, so there can be no case in which two photons arrive at the photon screen at the same time. So the photon states are necessarily always independent and orthogonal, and your overlap function

      <y|PL_t><y|PR_t> = 0,  always.

Consequently, your joint detection of photons does not restore the interference. Decoherence, once present, destroys coherence. And this coherence cannot be restored simply by observing the which-way photons. You have to quantum erase the which-way information. And this is not easy for this particular set-up. Quantum erasure essentially requires a measurement of a conjugate variable, measurement of which means that the original state cannot be recovered. For example, measurement of photon polarization at 45 degrees will quantum erase a horizontal/vertical polarization state.

Going back to the original buckyball experiment, the balls are laser heated and this puts them in an excited state. The state then decays by IR emission. This happens after the balls have passed the initial slits, so it is not a direct which-way measurement. It is only as the temperature increases, and the emitted photons have shorter wavelengths, that the wavelength is such that the photon can discriminate between the slits, that which-way information can be recovered from the IR photons. Letting the photons go undisturbed to infinity, or detecting them on some other screen, does not destroy the which-way information that they carry. As long as these photons are created, the interference pattern of the balls is lost. The photon information could be quantum-erased, I suppose, but I have no idea how that might be achieved.

Your analyses, neither the first nor subsequent analyses, come anywhere near explaining this observed behaviour.

Bruce

[smitra]

On 12-07-2021 00:43, Bruce Kellett wrote:
> On Mon, Jul 12, 2021 at 3:44 AM smitra <smi...@zonnet.nl> wrote:
>
>> On 11-07-2021 02:46, Bruce Kellett wrote:
>>> On Sun, Jul 11, 2021 at 10:21 AM smitra <smi...@zonnet.nl> wrote:
>>>>>
>>>> This is only true in practice, not in principle because the
>> escaping
>>>>
>>>> photons be captured and detected in principle.
>>>
>>> Not true. You can;t ever catch up with the escaping photons to
>> capture them.
>
>> They can be reflected back using mirrors.
>
> You can't decide to put mirrors in place after the photons have been
> emitted.
> Of course, you could always decide in advance to perform all
> experiments in reflecting boxes, but that is not what is done in
> practice. So the general rule is that escaping photons are not
> recoverable.

If in one experiment with mirrors they are recoverable and therefore
interference can be detected in principle, then that proves that the
other sectors do objectively exist. Since the objective existence of
these sectors does not depend on whether or not one uses mirrors in the
experiment, one can conclude that they exist in general.

No that's not what I did.

But if that is the case, then no interference can ever
> be seen. The possibility of interference relies on coherence between
> the amplitudes at the two slits. In your calculations, you have never
> allowed for this coherence -- the amplitudes at the two slits are not
> independent.
>

No, I really think you need to refresh you knowledge of quantum
mechanics.

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[smitra]

No, we perform a detection at a point y on the photon screen, the
product of these amplitudes are not zero, it only becomes zero if you
integrate this over y. The rest of your argument does not apply

Saibal

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[smitra]

It's a correct statement, see https://doi.org/10.1071/AS03040 page 101
section 3.3:

"The most distant objects that we can see
now were outside the Hubble sphere when their comoving
coordinates intersected our past light cone. Thus, they
were receding superluminally when they emitted the photons
we see now. Since their worldlines have always been
beyond the Hubble sphere these objects were, are, and
always have been, receding from us faster than the speed
of light.3"

Saibal

>
>>> So, that's information we're that has leaked away from those
>> galaxies
>>> that does objectively exists. To prove that a state is a pure
>> state
>>> one can just point to the way the state was prepared and invoke
>>> quantum mechanics. It's not necessary to demonstrate interference
>> to
>>> prove that quantum mechanics is still valid.
>>
>> So, then you agree with Bruce that so long as the which-way
>> information
>> exists in those outgoing photons, the interference pattern will show
>> up?
>
> I think you might have meant that as long as the which-way information
> exists (has not been quantum erased), then no interference is visible.
>
> Bruce
>

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[Brent Meeker]

Interesting.  I shall read it carefully.  But it doesn't affect the point that in the Bucky Ball double slit experiment the photons can either hit the walls or escape to infinity and in either case the interference pattern will be washed out.  Even your citation says,  "No observer ever overtakes a light beam and all observers measure light locally to be travelling at c."

Brent

Saibal

So, that's information we're that has leaked away from those

galaxies

that does objectively exists. To prove that a state is a pure

state

one can just point to the way the state was prepared and invoke
quantum mechanics. It's not necessary to demonstrate interference

to

prove that quantum mechanics is still valid.

So, then you agree with Bruce that so long as the which-way
information
exists in those outgoing photons, the interference pattern will show
up?

I think you might have meant that as long as the which-way information
exists (has not been quantum erased), then no interference is visible.

Right.  That's what I meant to write.

In quantum erasure double-slit experiments the which-way photons must be focused to the same point regardless of which slit they indicate...that's the "erasure".

Brent

[Bruce Kellett]

On Mon, Jul 12, 2021 at 1:48 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

On 7/11/2021 7:57 PM, smitra wrote:

It's a correct statement, see https://doi.org/10.1071/AS03040 page 101 section 3.3:

"The most distant objects that we can see
now were outside the Hubble sphere when their comoving
coordinates intersected our past light cone. Thus, they
were receding superluminally when they emitted the photons
we see now. Since their worldlines have always been
beyond the Hubble sphere these objects were, are, and
always have been, receding from us faster than the speed
of light.3"

Interesting.  I shall read it carefully.  But it doesn't affect the point that in the Bucky Ball double slit experiment the photons can either hit the walls or escape to infinity and in either case the interference pattern will be washed out.  Even your citation says,  "No observer ever overtakes a light beam and all observers measure light locally to be travelling at c."

Brent

The situation is confusing because the Hubble radius expands with time, so objects (and light) that were once beyond the Hubble horizon can enter it and be seen now. I think the important point is "The particle horizon can be larger than the event horizon, although we cannot see events that occur beyond our current event horizon, we can still see many galaxies that are beyond our current event horizon by light they emitted long ago."

This does not alter the fact that light that we emit now and that passes out beyond our Hubble horizon is lost from us forever. And events that now occur beyond our Hubble horizon are forever hidden from us. In other words, the photons escaping in the buckyball experiment are lost beyond possibility of recovery. So the which-way information they carry still exists somewhere, and the interference is washed out, as Brent says.

Bruce

[Bruce Kellett]

On Mon, Jul 12, 2021 at 1:48 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

So, then you agree with Bruce that so long as the which-way
information
exists in those outgoing photons, the interference pattern will show
up?

I think you might have meant that as long as the which-way information
exists (has not been quantum erased), then no interference is visible.

Right.  That's what I meant to write.

In quantum erasure double-slit experiments the which-way photons must be focused to the same point regardless of which slit they indicate...that's the "erasure".

Maybe that is what Saibal is getting at with his observation of the photons at some point on a second screen. His notation is for a mechanism at each slit which emits a photon if the ball went through that slit. If the photons emitted from either slit are observed at the same point on the photon screen, then you can't tell from which slit they originated -- hence the "erasure". That makes sense, but it did not seem to be what Saibal was saying. And it bears little relation to the actual setup in the buckyball experiment. There is no mechanism to register which slit the ball went through -- the photn(s), if any, are emitted downstream as the heated ball transitions to a lower energy state.

Bruce

[Bruce Kellett]

On Mon, Jul 12, 2021 at 12:44 PM smitra <smi...@zonnet.nl> wrote:

On 12-07-2021 00:43, Bruce Kellett wrote:
>
> You can't decide to put mirrors in place after the photons have been emitted.
> Of course, you could always decide in advance to perform all
> experiments in reflecting boxes, but that is not what is done in
> practice. So the general rule is that escaping photons are not
> recoverable.

If in one experiment with mirrors they are recoverable and therefore
interference can be detected in principle, then that proves that the
other sectors do objectively exist. Since the objective existence of
these sectors does not depend on whether or not one uses mirrors in the
experiment, one can conclude that they exist in general.

The point of measurement is to get a definite permanent result. Escaping photons (IR or other) are secondary to this endeavour. They just represent one universal way in which information can escape from an experiment and contribute to the overall decoherence. If you recover all these photons, and reverse all other records of the particular experimental result, then you have effectively not made a measurement. Measurement being defined by the formation of permanent records of a result. If there are no such records, then no measurement has been made. That may well be the case. But that does not demonstrate the objective existence of other sectors, or other worlds in which different results were obtained. There was no measurement in that case, so no results were obtained anywhere. Showing that some particular experiment is (or was) reversible, does not actually prove anything other than that the laws of physics are reversible. Which we knew anyway, and is not relevant for measurement.

Bruce

[Bruno Marchal]

> On 10 Jul 2021, at 21:41, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:
>
>
>
> On 7/10/2021 1:19 AM, Bruno Marchal wrote:
>> So, in general we can conclude by generalizing this to any large number of particles that even with what we consider to be permanent records, you don't get rid of the theoretical possibility of interference between the sectors where those records are different.

I did not write this, and out of context, I don’t know if I agree or not with this.

>
> We can if the universe is expanding faster than light beyond the Hubble radius.

How do you a physical being to singularise its consciousness?

The term “physical universe” is no more an ontological being if we assume Digital Mechanism. It is an appearance, a phenomenological reality, not an ontology.

Bruno



>
> Brent

>
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[Philip Benjamin]

[Philip Benjamin]
Mathematics is a tool of science to solve problems, not reality itself , though it may wrongly or rightly define reality or construct useful representations of reality. The four coordinates of spacetime are non-Euclidian, and merely coordinates. Only Euclidian geometry describes normal life. Mathematical models of reality may not actually have any reflection on actualities of life. For instance, Ptolemaic geocentric mathematical model of the solar system actually produced very accurate predictions, but it has nothing to do with the reality of heliocentrism. Trillions of physical particles are not whizzing around in the universe of real objects, though they may be symbolically or mathematically so presented as zipping around.

This basic aspect is missing in the CopenPagan Interpretation, because Greco-Romo-Eastern pagan mysticism was circularly brought into science by eminent pagan brains with un-awakened consciousnesses capable of reconning and mathematizing infinite numbers, without recognizing that numbers and their manipulations are no more real than any quale or experience thereof such as the color green. There is no aseity, or meaning for numbers. Numbers are just numbers. Equating them with ultimate reality is a CopenPagan absurdity.
Philip Benjamin

[Brent Meeker]

On 7/12/2021 2:38 AM, Bruno Marchal wrote:
>> On 10 Jul 2021, at 21:41, 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:
>>
>>
>>
>> On 7/10/2021 1:19 AM, Bruno Marchal wrote:
>>> So, in general we can conclude by generalizing this to any large number of particles that even with what we consider to be permanent records, you don't get rid of the theoretical possibility of interference between the sectors where those records are different.
> I did not write this, and out of context, I don’t know if I agree or not with this.
>
>
>> We can if the universe is expanding faster than light beyond the Hubble radius.
> How do you a physical being to singularise its consciousness?
>
> The term “physical universe” is no more an ontological being if we assume Digital Mechanism. It is an appearance, a phenomenological reality, not an ontology.

The Hubble radius isn't a "physical universe", it's a 2-surface.

Brent