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
On 8/4/2022 8:47 AM, smitra 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.
Saibal
On Thursday, August 4, 2022 at 6:39:04 AM UTC-6 Jason wrote:
On Thu, Aug 4, 2022, 5:23 AM Alan Grayson <[email protected]>
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
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