On reversibility, there is the observation (I think acredittable to Tom
Toffoli)
that most/all irreversible systems have a reversible subsystem and the
dynamics arrive in that
subsystem after some (finite) time. Thus any system that we observe a
while
after it has started will, with high likelihood, be reversible. In some
sense the
irreversibility dissipates and leaves a reversible core.
Tim
On Apr 10, 2006, at 3:22 AM, Jesse Mazer wrote:
>
> Saibal Mitra wrote:
>
>>
>>
>> How would an observer know he is living in a universe in which
>> information
>> is lost? Information loss means that time evolution can map two
>> different
>> initial states to the same final state. The observer in the final
>> state
>> thus
>> cannot know that information really has been lost.
>
> If he is able to figure out the fundamental laws of physics of his
> universe,
> then he could see whether or not they have this property of it being
> possible to deduce past states from present ones (I think the name for
> this
> property might be 'reversible', although I can't remember the
> difference
> between 'reversible' and 'invertible' laws). For example, the rules of
> Conway's "Game of Life" cellular automaton are not reversible, but if
> it
> were possible for such a world to support intelligent beings I don't
> see why
> it wouldn't be in principle possible for them to deduce the underlying
> rules.
>
> As for the question of why we live in a universe that apparently has
> this
> property, I don't think there's an anthropic explanation for it, I'd
> see it
> as part of the larger question of why we live in a universe whose
> fundamental laws seem to be so elegant and posess so many symmetries,
> one of
> which is time-symmetry (or to be more accurate, CPT-symmetry, which
> means
> the laws of physics are unchanged if you switch particles with
> antiparticles
> and flip the 'parity' along with reversing which direction of time is
> labeled 'the future' and which is labeled 'the past'). Some TOEs that
> have
> been bandied about here say that we should expect to live in a universe
> whose laws are very compressible, so maybe this would be one possible
> way of
> answering the question.
>
> Jesse
>
>
>
> >
>
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