Unitary evolution preserves information. It is only through
measurement by an observer that information can be created or
destroyed. Usually, the second law is interpreted as the destruction
of information (anyone observing a closed system will over time know
less information about the system), so it puzzles me that you have the
sign the other way.

Because of the action of the second law, it actually takes a
thermodynamic flux to preserve information - which is why you need to
read your old backup tapes an make copies every few years if you want
to retain access to your data.


On Sun, Apr 09, 2006 at 12:11:52AM -0700, Wei Dai wrote:
> 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 of 
> thermodynamics is a consequence of this. In order to forget anything 
> (decrease entropy), we have to put the information somewhere else (increase 
> 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 perhaps 
> 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 accessible 
> to life before the evolution of intelligence. It may be a good idea to look 
> 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?
A/Prof Russell Standish                  Phone 8308 3119 (mobile)
Mathematics                                    0425 253119 (")
UNSW SYDNEY 2052                         [EMAIL PROTECTED]             
Australia                                http://parallel.hpc.unsw.edu.au/rks
            International prefix  +612, Interstate prefix 02

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