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.

----- Original Message ----- 
From: "Wei Dai" <[EMAIL PROTECTED]>
To: <>
Sent: Sunday, April 09, 2006 09:11 AM
Subject: why can't we erase information?

> If we consider our observable universe as a computation, it's rather
> atypical in that it doesn't seem to make use of the erase operation (or
> other any operation that irreversibly erases information). The second law
> thermodynamics is a consequence of this. In order to forget anything
> (decrease entropy), we have to put the information somewhere else
> entropy of the environment), instead of just making it disappear. If this
> doesn't make sense to you, see Seth Lloyd's new book "Programming the
> Universe : A Quantum Computer Scientist Takes On the Cosmos" for a good
> explanation of the relationship between entropy, computation, and
> information.
> Has anyone thought about why this is the case? One possible answer is that
> if it were possible to erase information, life organisms would be able to
> construct internal perpetual motion machines to power their metabolism,
> instead of competing with each other for sources of negentropy, and
> intelligence would not be able to evolve in this kind of environment. If
> this is the case, perhaps there is reason to hope that our universe does
> contain mechanisms to erase information, but they are not easily
> to life before the evolution of intelligence. It may be a good idea to
> out for such mechanisms, for example in high energy particle reactions.
> However I'm not sure this answer is correct because there would still be
> competition for raw material (matter and energy) where intelligence can
> still be an advantage. Anyone have other ideas?
> >

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