Information conservation and irreversibility

[Alan Grayson]

I assume information conservation depends on irreversibility. How solid is the latter assumption? AG

[Alan Grayson]

I meant to write that information conservation depends on reversibility! How solid is that assumption? AG

[Jason Resch]

On Thu, Aug 4, 2022, 5:23 AM Alan Grayson <agrays...@gmail.com> wrote:

> I meant to write that information conservation depends on reversibility! How solid is that assumption? AG

I think it is pretty good.

I think reversibility is part of it. Certainly in a reversable Newtonian kind of physics (no GR and no QM, full determinism), reversability would imply an inability to destroy information.

In reversible computers, information can't be deleted, only shuffled around, so in this simplistic model, reversibility (in a Turing machine) implies conservation of information.

In GR, matter falling into black holes was originally thought to be an irreversible process. This led to the "black hole war".

https://en.wikipedia.org/wiki/The_Black_Hole_War which was eventually settled by concluding information isn't destroyed in a black hole, therefore the pattern of black hole radiation must somehow indicate or encode what has fallen in to it.

In QM, wave function collapse was thought to be an example of an irreversible process. Yet from the global view of all the branches and many world's it is not.

But moreover, despite the apparent irreversibility if collapse from the confines of any one branch, the information available within any single branch still seems to be conserved (just as matter and energy are). This lead to a kind of: energy-matter-information equivalence. https://en.wikipedia.org/wiki/Holographic_principle#Energy,_matter,_and_information_equivalence

This question, I think, probes at the very deepest levels of physics. I have some more thoughts on this written here:

https://alwaysasking.com/why-does-anything-exist/#Information_as_Fundamental

Jason

[Alan Grayson]

I recall Bruce giving an example of an irreversible process, but I can't recall the details. AG

[smitra]

On 04-08-2022 17:41, Alan Grayson wrote:
> I recall Bruce giving an example of an irreversible process, but I
> can't recall the details. AG
>

Probably a FAPP irreversible process.

Saibal

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[John Clark]

On Thu, Aug 4, 2022 at 11:47 AM smitra <smi...@zonnet.nl> wrote:

On 04-08-2022 17:41, Alan Grayson wrote:

>> I recall Bruce giving an example of an irreversible process, but I can't recall the details. AG

> Probably a FAPP irreversible process.

If states X and Y can both produce  Z then it's irreversible because if you look at Z you have no way of knowing if the previous state was X or Y.  A good example of that would be Conway's Game of Life, it's completely deterministic but it's not reversible. 

John K Clark    See what's on my new list at  Extropolis

nrr

[Brent Meeker]

If a photon is emitted into an infinite universe it is irreversible in
principle, not just FAPP.  But it doesn't mean the physical theory is
irreversible.  The arrow of time comes from the boundary condition.

Brent

[spudb...@aol.com]

This group of essays led by Strominger at Harvard, a few years ago, implies the storage and reversibility of all data axiomatically, via the interaction of gravity, and infrared photons. That is my understanding of it. Now, if someone doesn't think this is right they can always falsify it with observation, if they can? Here was George Musser's op appearing in FXQI back in 2019. I haven't followed validation or devalidation since then, really?

https://fqxi.org/community/articles/display/233

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[Alan Grayson]

So what's the bottom line; are physical processes reversible or not? Does the answer depend on whether the universe is infinite, that is, without a boundary condition, or not? TY. AG

[Dirk Van Niekerk]

What do the physicists and engineers on the list think of Zurek's idea the quantum measurements become irreversible, in principle, once a record of the quantum measurement is made?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5990664/#RSTA20170315C9

Dirk 

[Jesse Mazer]

Why do you say it's irreversible in principle? Wouldn't the time-reverse of that just be a photon traveling towards an atom and being absorbed, which is permitted by the laws of physics given a different set of initial boundary conditions?

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[Brent Meeker]

That's why I wrote, "The arrow of time comes from the boundary condition."

Brent

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[Jesse Mazer]

But when physicists say that a given system's dynamics are "reversible" doesn't this generally involve an appeal to different initial boundary conditions? (The end conditions with all the velocities reversed and treated as a new system's initial conditions, for example.) Are you using reversible/irreversible in a more colloquial sense?

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[Bruce Kellett]

On Sat, Aug 6, 2022 at 7:54 AM Jesse Mazer <laser...@gmail.com> wrote:

Why do you say it's irreversible in principle? Wouldn't the time-reverse of that just be a photon traveling towards an atom and being absorbed, which is permitted by the laws of physics given a different set of initial boundary conditions?

The laws of physics are invariant under the time-reversal operation. That does not imply that irreversible processes are impossible. Brent has pointed out that sending a photon out into an expanding universe is a process that is irreversible in principle. The time invariance of the laws means that a photon coming in from outer space is consistent with the laws. But that cannot be the same photon. The idea that you can surround everything with a perfectly reflecting mirror, so that all emitted photons are returned, is just a fanciful diversionary tactic -- no such reflective surrounds exist. Besides, reflecting photons back is not a process reversal in an expanding universe. The red shift induced by the expansion means that the returning photon inevitably has lower energy than the emitted photon.

Bruce

[Jesse Mazer]

"The time invariance of the laws means that a photon coming in from outer space is consistent with the laws. But that cannot be the same photon."

But "reversibility" as physicists define it has nothing to do with actually causing the same system to reverse itself, it's a more abstract notion that you could have a different system obeying the same dynamical laws whose behavior over time would be a perfectly time-reversed mirror of the first system's behavior. If you think it's about a single system evolving one way for some period of time and suddenly reversing itself so that its subsequent behavior looks like a reversed version of its initial behavior, that's just a misunderstanding of the concept.

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[Bruce Kellett]

On Sat, Aug 6, 2022 at 9:29 AM Jesse Mazer <laser...@gmail.com> wrote:

"The time invariance of the laws means that a photon coming in from outer space is consistent with the laws. But that cannot be the same photon."

But "reversibility" as physicists define it has nothing to do with actually causing the same system to reverse itself, it's a more abstract notion that you could have a different system obeying the same dynamical laws whose behavior over time would be a perfectly time-reversed mirror of the first system's behavior. If you think it's about a single system evolving one way for some period of time and suddenly reversing itself so that its subsequent behavior looks like a reversed version of its initial behavior, that's just a misunderstanding of the concept.

You are talking about the time-reversal invariance of the laws of physics. That is one thing, but when people ask whether irreversible processes are possible, then the emphasis is on the process, not the underlying laws. So the issue is whether there are individual processes that cannot be reversed, not whether there can exist separate processes that look like the original process in reverse.

This is important in the context of unitary evolution in quantum mechanics. Unitary time evolution obeys time symmetric laws, but the emission of a photon into an expanding universe, while consistent with unitary evolution, is not a reversible process.

Bruce

[Brent Meeker]

I'm pointing out that in some cases creating the reverse boundary conditions is impossible in principle because they are at infinity.

Brent

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[Jesse Mazer]

But reversibility as understood by physicists isn't about whether you could "create" the appropriate type of system with advanced technology or whatever, it's about the abstract question of whether the time-reversed version is a valid solution to the same dynamical laws of physics. One could imagine a god who can create multiple universes, with the only constraint that they all obey the same laws of physics--if the laws and dynamics are reversible, that implies that for any given universe, the god can also create a distinct universe that behaves like a time-reversed version of the first one.

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[Jesse Mazer]

Are you defining "process" as a *pattern* of behavior which can be duplicated with different bits of matter, or as something that refers to some specific bits of matter, so that reversing a process would require doing it to the same bits of matter that underwent the original process? I think if a physicist talked about a "process" being reversible or not, they would be referring to the pattern-based notion. For example, take the process of a rogue planet coming close to a planetary system and getting captured by its gravitational interactions with the star and the planets in the system. With a pattern-based notion of process, that process is reversible in the sense that one could have a different star and different planets with identical masses, where the initial conditions were such that the planet got ejected from the system in a perfect time-reversed version of the behavior of the first system.

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[Bruce Kellett]

On Sat, Aug 6, 2022 at 12:10 PM Jesse Mazer <laser...@gmail.com> wrote:

Are you defining "process" as a *pattern* of behavior which can be duplicated with different bits of matter, or as something that refers to some specific bits of matter, so that reversing a process would require doing it to the same bits of matter that underwent the original process? I think if a physicist talked about a "process" being reversible or not, they would be referring to the pattern-based notion. For example, take the process of a rogue planet coming close to a planetary system and getting captured by its gravitational interactions with the star and the planets in the system. With a pattern-based notion of process, that process is reversible in the sense that one could have a different star and different planets with identical masses, where the initial conditions were such that the planet got ejected from the system in a perfect time-reversed version of the behavior of the first system.

I think I was drawing a distinction between time reversible laws and  processes as things that happen to particular "bits of matter". The laws might be time reversal invariant, but particular processes might not be reversible. It makes little sense to restrict one's attention to reversible laws when one is asked whether a particular process can be reversed or not. There are clearly processes that cannot be reversed, in principle and not just FAPP. The emission of photons into an expanding universe is just one example, even though the emission process might be governed by reversible laws. The emitted photon cannot be caught and returned. That is all that is meant by saying that it is not reversible. This is relevant to the question as to whether a quantum measurement is reversible or not. Quantum evolution is unitary, but generally the process of measurement is not reversible, even in principle. Take the spin measurement of a spin-half particle. Given an "up" result for instance, one cannot reverse this to determine the spin state of the particle prior to the measurement. Many worlds do not help here, because one has no access to other worlds.

Bruce

[Alan Grayson]

Can't your argument be extended to the question of whether time is irreversible FAPP,  or IRREVERSIBLE IN PRINCIPLE. For example, consider a gas at some temperature in an enclosure which is cooling. We might conclude the time is irreversible FAPP,  but quantum theory does not give any information about the direction of the emitted thermal photons. So I conclude, based on present theory, that time is strictly irreversible, that is, IRREVERSIBLE IN PRINCIPLE. AG

[John Clark]

On Fri, Aug 5, 2022 at 6:47 PM Jesse Mazer <laser...@gmail.com> wrote:

> But when physicists say that a given system's dynamics are "reversible" doesn't this generally involve an appeal to different initial boundary conditions?

If at the time of the Big Bang the universe was it in an extremely low entropy state then even if the laws of physics were 100% deterministic and even if X and Y always produced Z and nothing except X and Y could produce Z the second law of thermodynamics would still insist that things are irreversible because there are an astronomical number to an astronomical power more ways for something to have high entropy than low entropy.

John K Clark    See what's on my new list at  Extropolis

2le

[Jesse Mazer]

The question of whether a process happening to particular bits of matter can be reversed in those same bits of matter may be an interesting one worth thinking about, but I think it creates unnecessary confusion to use the term "reversibility" to talk about this, since that isn't what physicists mean by reversibility. They're talking about whether, if you have a solution to the equations of motion, the reversed version is also a solution--the identity of the bits of matter involved isn't relevant, and there's no notion of a single time-evolution where the system evolves a certain way for the first half, then there's some kind of intervention and the subsequent evolution for the second half looks like a reversed version of the first half.

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[Jesse Mazer]

Physicists may distinguish between time-reversibility of the dynamics, also called "microscopic reversibility" at https://en.wikipedia.org/wiki/Microscopic_reversibility , vs. "macroscopic" or "thermodynamic" irreversibility, which as you say is ultimately thought to be a statistical consequence of the low-entropy conditions at around the time of the Big Bang. But from the dynamical point of view you could have a valid solution with a universe that's been eternally contracting towards a Big Crunch, with a low-entropy state near the Big Crunch, which would be the time-reverse of our universe's evolution. Huw Price's book Time's Arrow and Archimedes' Point has a good discussion of the issues surrounding microscopic reversibility vs. thermodynamic irreversibility, and the role of low-entropy boundary conditions.

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[Brent Meeker]

On 8/6/2022 5:16 AM, Jesse Mazer wrote:
> The question of whether a process happening to particular bits of
> matter can be reversed in those same bits of matter may be an
> interesting one worth thinking about, but I think it creates
> unnecessary confusion to use the term "reversibility" to talk about
> this, since that isn't what physicists mean by reversibility. They're
> talking about whether, if you have a solution to the equations of
> motion, the reversed version is also a solution--the identity of the
> bits of matter involved isn't relevant,

I agree with that, but a solution of the equations of motion depends on
boundary conditions, not just the equations of motion.  So some boundary
are nomologically impossible to realize in reverse and some are only
FAPP impossible to realize in reverse.

Brent

[Brent Meeker]

What you're leaving out is that there are boundary conditions that are impossible to realize, not just because they are too complex, like a high entropy state, but because they require infinite specifications.

Brent

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[Alan Grayson]

That's defining IRREVERSIBLE FAPP.  OTOH, if X and Y produce Z at any time, I don't see any way to reverse the process, so it's IRREVERSIBLE IN PRINCIPLE. Do you agree? AG

[Alan Grayson]

IRREVERSIBILITY is an artifact of the CI, where collapse occurs to an eigenstate of the observable being measured. But if the measuring apparatus is treated quantum mechanically, all processes associated with measurements are unitary and reversible. 

[Alan Grayson]

I was referring to IRREVERSIBLIY IN PRINCIPLE, which is an artifact of the collapse hypothesis of the CI. What remains, for sure, is IRREVERSIBILITY FAPP.  AG

[Alan Grayson]

It's puzzling why Bruce and Clark affirm IR-reversible in principle in the context of the collapse model of the CI, when they should know that this is the source of the error. If the apparatus is treated quantum mechanically, we are left SOLELY with IR-reversible FAPP. But this is still an unproven, and likely unprovable result of decoherence theory. AG

[Lawrence Crowell]

It is the case of a billiard ball impacting another vs a set of racked billiard balls. If I were to take a video of a billiard ball impacting another, framed this in the center of mass of the balls and mask any perception of the rotation of the balls, the video run backwards and forwards would by very similar. There would be nothing to distinguish the forwards and backwards video. It is perfectly time reverse invariant. Now consider the racked balls impacted by the cue-ball. It is pretty easy to see which is forwards in time, as we do not expect balls to rush inwards and align themselves in an ordered set and eject another. However, if the table were "perfect," it had frictionless surface and the balls reflected off the sides perfectly, if we wait long enough it will return to its original state. This is Poincare recurrence. You have to wait a lot longer than the duration of the universe so far. 

The same happens with quantum mechanics. There is a Poincare recurrence, given by the exponential of the Euclideanized action. However, there is an additional phase, which defines the quantum complexity and the recurrence time on that is the exponential of the Poincare recurrence time. Quantum complexity is interesting, and I think it involves the Hilbert-Polya conjecture concerning the Riemann zeta function and the zeros being mapped to the eigenvalues of a Hermitian operator. In this case the recurrence is a vast period of time, as long as the stability of the de Sitter manifold of the cosmos. 

In effect we have limitations on what we can observe and account for, but ultimately the universe may have an accounting of quantum information, at least for unitary systems and quantum gravitation with Petrov types that have Killing vectors. When it comes to the universe at large, that may be a different matter. Such ideas may turn out to be false.

LC

 

[John Clark]

On Sun, Aug 21, 2022 at 7:23 AM Lawrence Crowell <goldenfield...@gmail.com> wrote:

> The same happens with quantum mechanics. There is a Poincare recurrence, given by the exponential of the Euclideanized action. However, there is an additional phase, which defines the quantum complexity and the recurrence time on that is the exponential of the Poincare recurrence time. Quantum complexity is interesting, and I think it involves the Hilbert-Polya conjecture concerning the Riemann zeta function and the zeros being mapped to the eigenvalues of a Hermitian operator. In this case the recurrence is a vast period of time, as long as the stability of the de Sitter manifold of the cosmos. 

But doesn't quantum recurrence and complexity depend on if time and space are continuous or not? 

 John K Clark    See what's on my new list at  Extropolis

pqr

[Brent Meeker]

On 8/21/2022 4:22 AM, Lawrence Crowell wrote:

On Friday, August 5, 2022 at 6:14:42 PM UTC-5 Bruce wrote:

On Sat, Aug 6, 2022 at 7:54 AM Jesse Mazer <laser...@gmail.com> wrote:

Why do you say it's irreversible in principle? Wouldn't the time-reverse of that just be a photon traveling towards an atom and being absorbed, which is permitted by the laws of physics given a different set of initial boundary conditions?

The laws of physics are invariant under the time-reversal operation. That does not imply that irreversible processes are impossible. Brent has pointed out that sending a photon out into an expanding universe is a process that is irreversible in principle. The time invariance of the laws means that a photon coming in from outer space is consistent with the laws. But that cannot be the same photon. The idea that you can surround everything with a perfectly reflecting mirror, so that all emitted photons are returned, is just a fanciful diversionary tactic -- no such reflective surrounds exist. Besides, reflecting photons back is not a process reversal in an expanding universe. The red shift induced by the expansion means that the returning photon inevitably has lower energy than the emitted photon.

Bruce

It is the case of a billiard ball impacting another vs a set of racked billiard balls. If I were to take a video of a billiard ball impacting another, framed this in the center of mass of the balls and mask any perception of the rotation of the balls, the video run backwards and forwards would by very similar. There would be nothing to distinguish the forwards and backwards video. It is perfectly time reverse invariant. Now consider the racked balls impacted by the cue-ball. It is pretty easy to see which is forwards in time, as we do not expect balls to rush inwards and align themselves in an ordered set and eject another. However, if the table were "perfect," it had frictionless surface and the balls reflected off the sides perfectly, if we wait long enough it will return to its original state. This is Poincare recurrence. You have to wait a lot longer than the duration of the universe so far. 

The same happens with quantum mechanics. There is a Poincare recurrence, given by the exponential of the Euclideanized action. However, there is an additional phase, which defines the quantum complexity and the recurrence time on that is the exponential of the Poincare recurrence time.

Is that in some thermodynamic limit?  There is no chaos in QM so I would expect the recurrence time to be bounded by that.  Do you have a reference?

Brent

Quantum complexity is interesting, and I think it involves the Hilbert-Polya conjecture concerning the Riemann zeta function and the zeros being mapped to the eigenvalues of a Hermitian operator. In this case the recurrence is a vast period of time, as long as the stability of the de Sitter manifold of the cosmos. 

In effect we have limitations on what we can observe and account for, but ultimately the universe may have an accounting of quantum information, at least for unitary systems and quantum gravitation with Petrov types that have Killing vectors. When it comes to the universe at large, that may be a different matter. Such ideas may turn out to be false.

LC

 

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[Lawrence Crowell]

On Sunday, August 21, 2022 at 2:03:41 PM UTC-5 meeke...@gmail.com wrote:

On 8/21/2022 4:22 AM, Lawrence Crowell wrote:

On Friday, August 5, 2022 at 6:14:42 PM UTC-5 Bruce wrote:

On Sat, Aug 6, 2022 at 7:54 AM Jesse Mazer <laser...@gmail.com> wrote:

Why do you say it's irreversible in principle? Wouldn't the time-reverse of that just be a photon traveling towards an atom and being absorbed, which is permitted by the laws of physics given a different set of initial boundary conditions?

The laws of physics are invariant under the time-reversal operation. That does not imply that irreversible processes are impossible. Brent has pointed out that sending a photon out into an expanding universe is a process that is irreversible in principle. The time invariance of the laws means that a photon coming in from outer space is consistent with the laws. But that cannot be the same photon. The idea that you can surround everything with a perfectly reflecting mirror, so that all emitted photons are returned, is just a fanciful diversionary tactic -- no such reflective surrounds exist. Besides, reflecting photons back is not a process reversal in an expanding universe. The red shift induced by the expansion means that the returning photon inevitably has lower energy than the emitted photon.

Bruce

It is the case of a billiard ball impacting another vs a set of racked billiard balls. If I were to take a video of a billiard ball impacting another, framed this in the center of mass of the balls and mask any perception of the rotation of the balls, the video run backwards and forwards would by very similar. There would be nothing to distinguish the forwards and backwards video. It is perfectly time reverse invariant. Now consider the racked balls impacted by the cue-ball. It is pretty easy to see which is forwards in time, as we do not expect balls to rush inwards and align themselves in an ordered set and eject another. However, if the table were "perfect," it had frictionless surface and the balls reflected off the sides perfectly, if we wait long enough it will return to its original state. This is Poincare recurrence. You have to wait a lot longer than the duration of the universe so far. 

The same happens with quantum mechanics. There is a Poincare recurrence, given by the exponential of the Euclideanized action. However, there is an additional phase, which defines the quantum complexity and the recurrence time on that is the exponential of the Poincare recurrence time.

Is that in some thermodynamic limit?  There is no chaos in QM so I would expect the recurrence time to be bounded by that.  Do you have a reference?

Brent

Look up Susskind arXiv:1810.11563v1 [hep-th] 27 Oct 2018 .

LC

[spudb...@aol.com]

Ah, LC, your colleague Sabine Hossenfelder has given forth on the autodidactic universe. She doesn't hold with it but still enriches the knowledge base. 

https://time.com/6208174/maybe-the-universe-thinks/

https://groups.google.com/d/msgid/everything-list/2e92f31f-9d08-4ed1-9d90-42c4dfd63ef2n%40googlegroups.com

.

[Lawrence Crowell]

I do not think much of this idea that the universe is sentient.

LC

[John Clark]

On Fri, Aug 26, 2022 at 5:41 AM Lawrence Crowell <goldenfield...@gmail.com> wrote:

> I do not think much of this idea that the universe is sentient.

I think the idea is a bit silly because I don't see any way to prove or disprove it even in theory. And in the entire universe the only thing that I know with absolute certainty is sentient is the 3 pounds of gray goo inside a bone vat that is sitting on my shoulders.   

John K Clark    See what's on my new list at  Extropolis

ibv

 

[spudb...@aol.com]

Now this, I fully expected LC. My point is not a personal sales pitch to yourself, but rather a n acknowledgement that Autodidactic is getting a review. I couldn't even set the parameters on how we'd test this? I like crap like this because it has something more for the serfs, rather than only the doyens of physics and mathematics. I never thought it would thrill you or Dr. Sabine for that matter. 

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[spudb...@aol.com]

Ah! I tend to agree, but I do ponder of intelligence is way different than occurs on planet earth? I mean you love twiddling about Schrodinger & Wigner, and "Observers," so who's to say all observers must apply to earth life? 

Maybe there's something to boltzmann brains, after all? Or not? Mayve.  

-----Original Message-----
From: John Clark <johnk...@gmail.com>
To: everyth...@googlegroups.com
Sent: Fri, Aug 26, 2022 5:52 am
Subject: Re: Information conservation and irreversibility

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[Lawrence Crowell]

The idea is similar to panpsychism, which cannot be tested. If everything is conscious, where is a reference frame without consciousness to test whether consciousness exists? The idea the universe is conscious also would suggest the universe is subMarkovian in some way, which would require a hell of a lot of explaining. It is silly, and it comes down to somebody having a sort of brain-fart that sounded really deep and then writing an article on it.

LC 

[Brent Meeker]

Even if it were sentient its thoughts would be incomprehensible to us.

Brent

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[smitra]

The time evolution operator maps past states of our universe to present
states. So, the present state of the universe, which includes our
conscious experience of the present state was also present in the early
universe in a nonlocal way where there would be no obvious sign of us
existing at all.

Saibal

On 27-08-2022 02:44, Brent Meeker wrote:
> Even if it were sentient its thoughts would be incomprehensible to
> us.
>
> Brent
>
> On 8/26/2022 2:52 AM, John Clark wrote:
>
>> On Fri, Aug 26, 2022 at 5:41 AM Lawrence Crowell
>> <goldenfield...@gmail.com> wrote:
>>

>>> _> I do not think much of this idea that the universe is
>>> sentient._

>>
>> I think the idea is a bit silly because I don't see any way to prove
>> or disprove it even in theory. And in the entire universe the only
>> thing that I know with absolute certainty is sentient is the 3
>> pounds of gray goo inside a bone vat that is sitting on my
>> shoulders.
>>

>> John K Clark See what's on my new list at Extropolis [1]

>>
>> ibv
>>
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>> [2].

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> [3].
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> Links:
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> [1] https://groups.google.com/g/extropolis
> [2]
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[Brent Meeker]

Why do you think the evolution is deterministic of our part of universe?

Brent

[spudb...@aol.com]

It cannot be tested in our age, me thinks, but there are different flavors of panpsychism too. My way of thinking relates more to the philosopher, John Leslie, who wrote often about his version of Panpsychism.  

Works by John Leslie - PhilPapers

or-

John Leslie - Does Cosmology Provide Meaning? - YouTube

and-

John Leslie - Alternative Concepts of God? - YouTube

5 years ago-

John Leslie - Immortality and Personal Consciousness? - YouTube

Nobody has to believe, because we all of us have our own path. Mil atheism is as messed up as mil religions. Reject as desired. It's ok fine. As da' Buddha is quoted, "if you are walking down a path, and the Buddha stands in your way, strike him down!" Meaning, if you got a better way, Rock On!  

My suspicion? The universe acts as a big database. 500 years ago somebody may as asked, "Do you mean an abacus, a ledger??" 

Me? "Not exactly see the mathematicians.." Random standbyer would yell, "Witch! Burn the witch!" 

I am not a follower exclusively of John Leslie. There's Moravec, and Tipler, Turchin and Chernyakov, Prisco. I also have recently acquired the Autodidactic Universe's authors as well. Works for me, and may not work for Thee! 

[2104.03902] The Autodidactic Universe (arxiv.org)

-----Original Message-----
From: Lawrence Crowell <goldenfield...@gmail.com>
To: Everything List <everyth...@googlegroups.com>
Sent: Fri, Aug 26, 2022 7:57 pm
Subject: Re: Information conservation and irreversibility

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.

[smitra]

It's a unitary map, it will evolve the past state into a superposition
of many different states. One may argue that this is meaningless, as one
has to choose a basis. But this is essentially what time evolution
operator does for you. If you work in a particular basis then applying
the time evolution operator amounts to changing that basis into another
basis without affecting the state of the system in any way.

Saibal

[Brent Meeker]

But in the mean time the expansion of the universe has moved lots of
what the wave function of the universe beyond our horizon. And what we
can access is not the unitary evolution of what we could earlier.

Brent

[smitra]

But then you are describing only part of the system using QM. The whole
system includes the universe itself, this is described by a
wavefunctional that assigns amplitudes to entire space-time
configurations and the fields in it.

Saibal

[Brent Meeker]

Exactly.  That's why I wrote "...our part of universe".  Whether the
part of the system that we can never interact with is relevant is a
question for metaphysics.

Brent

[Lawrence Crowell]

I think physics fundamentally constrains causal rules to obey the Church-Turing thesis. That is, computable dynamics are computable on a Turing machine. However, there is some form of axiomatic incompleteness such as Gödel's theorem or Turing's result on universal Turing machines. We have then has a universal form of event horizon, of which the quantum uncertainty principle and spacetime event horizons are examples of. In a full quantum gravitational setting we may then have the CT thesis upheld so there are no physical hypercomputations (I wonder what happened to Phill Thrift?) that skirt the Gödel theorem or Turing's result. 

As a result physics is "Turing computable" with a minimal number of oracle inputs. These oracle inputs could be things such as what we call the collapse of a wave function or the incomplete description of gravitational collapse behind the horizon. Nature just gives these oracle in puts randomly. There is no dynamics behind them that we can ever compute. In other words, chasing after a solution to the so called measurement problem in QM is a fool's errand. 

This universal event horizon goes into our inability to measure anything concerning the nature of things beyond inflation or the quantum gravitational amplitude, or vacuum expected value etc, leading to inflation. Ideas of cyclic cosmologies or the universe comes from a black hole or the multiverse or ... , may simply be unattainable. These may be similar to the interpretations of QM, which are axiomatic input, oracle outputs if you will, that we impose. These things may be fundamentally unobservable and formally undecidable.

LC