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
On Thursday, August 4, 2022 at 3:10:47 PM UTC-6 [email protected] wrote: > 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 > >> > >> -- > >> You received this message because you are subscribed to the Google > >> Groups "Everything List" group. > >> To unsubscribe from this group and stop receiving emails from it, send > >> an email to [email protected]. > >> To view this discussion on the web visit > >> > https://groups.google.com/d/msgid/everything-list/1c5ab1b8-fef6-4a5c-bd88-fb7b24d0e4b8n%40googlegroups.com > > >> > >> [1]. > >> > >> > >> Links: > >> ------ > >> [1] > >> > https://groups.google.com/d/msgid/everything-list/1c5ab1b8-fef6-4a5c-bd88-fb7b24d0e4b8n%40googlegroups.com?utm_medium=email&utm_source=footer > > >> > > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/ce37f695-fa3e-4603-a5b1-9ee4e9ecbaffn%40googlegroups.com.
