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?
On Thu, Aug 4, 2022 at 5:10 PM Brent Meeker
<[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
>>
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