Re: Conservation of information (was Re: Revised Kansas
Thu, 19 Aug 1999 21:36:04 +0000


I did not know that Dembski believed that information was conserved.
Remember Maxwell's demon from Thermo class? Thermodynamics predicts that
you can't get energy out of a heat reservoir that is not above or below the
ambient temperature. THis is because a difference in temperature is
required to get useful work out of the system. Maxwell proposed a demon
that stood at a door between two chambers of air which were at the same

| A |B |
| | |
| \ | \ is the door where the demon stands.

When the demon sees a molecule coming at the door which is moving faster
than average (hot) in Chamber B, he opens the door and lets it into chamber
A. And when he sees a molecule moving slower than normal in chamber A,
coming towards the door, he opens the door and lets the slow (cool) molecue
into chamber B. After a while the demon has moved the hot molecules into A
and the cold molecules into B. Now there is a temperature difference which
can be used to gain useful work. And this demon violates the claims of the
laws of thermo. Unchecked the demon would allow for a perpetual motion
machine. That paradox is solved by the fact that the demon must expend
entropy to gain information about the particles coming to him at the door.

"The kinship with the computer memory now begins to shine through. In a
computer each ofthe possible logical states is represented by a certain
configurationn in the hardware--each of n logical states has its physical
representation in the hardware. And when the computer memory of n bits is
cleared, the number of 2^n possible states is reduced to 1--an increase in
information which must be balanced by an increase in entropy in the
computer's environment, in compliance with the conservation law.
"It is thus the forgetting that is thermodynamically costly. And that is
why a computer, indeed, any cognitive entity, cannot skirt the Second Law.
This solution to Maxwell's perennial riddle finally came in recent years
through a penetrating inquiry into the energy requirements of digital
computers by the mathematicians Rolf Landauer and Charles Bennett. It is
the resetting of the memory register where the unavoidable thermodynamic
price is paid." Werner R. Lowenstein, The Touchstone of Life, (New York:
Oxford University Press, 1999), p.13

Information is gained at the cost of an increase in entropy for the
universe. So information is not constant. It can be increased. But there is
a price to pay. I would also be interested in David Bowman's comments on
this aspect of information theory.


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