Re: Conservation of information (was Re: Revised Kansas

Arthur V. Chadwick (
Thu, 19 Aug 1999 13:44:32 -0700

At 02:09 PM 08/19/1999 -0700, Brian wrote:

. After all the
>discussion surrounding this hypothesis I was really floored to
>read the following in <Science>:
>#"Basic principles of physics teach that information in
>#the universe is preserved: If you had perfect knowledge
>#of the present, you could, in theory at least, reconstruct
>#the past and predict the future. (Such perfect knowledge
>#is impossible in practice, of course.) Suppose you threw
>#an encyclopedia into a fire, for example; if you had perfect
>#knowledge of the radiation emitted and the ensuing motions
>#of all the atoms and molecules, you could, with infinite
>#attention to the details, reconstruct the knowledge inside
>#the encyclopedia. Physicists refer to their equations as
>#'unitary'--that is, they preserve information."
>#-- Gary Taubes <The Holographic Universe>,
># Science 285:515, 23 July 1999.
>Quite a remarkable statement. I guess the first thing to
>occur to me is that what little I know about info theory
>is in the context either of communication theory (Shannon
>info theory) or complexity theory (algorithmic info theory).
>I was aware that physicists also use the word information,
>perhaps they mean something different by the term? Any
>physicists like to clarify? David Bowman?
>More interesting would be if anyone would like to defend
>that statement. A bad sign is that the author talks about
>the knowledge inside the encyclopedia. The best case scenario
>would be that with "infinite attention to the details" one
>might be able to reconstruct the physical arrangement of
>ink on paper. But this physical arrangement does not itself
>reflect knowledge. But even this ideal case I would say is
>still impossible. It is reminiscent of Laplace's dream,
>which I had thought that most everyone now recognizes as
>a pipe dream. Am I wrong about this?

It not only is impossible, but it is impossible as well. The key phrase is
"If". Uncertainty Principle makes this quite impossible, and the necessity
to know the starting conditions to infinite precision makes this doubly
impossible (if there is such a thing). So even in theory, it would be
quite impossible, since the uncertainty principle is a theory that suggests
otherwise, as does complexity theory.