[asa] Information and knowledge

Having finally worked my way through the mountain of posts from the last three weeks, I'd like to comment on a couple. There were several references to information, its mass and energy, and its relationship to the genome. Maybe we should remind ourselves of some of the fundamental principles of information.

Claude Shannon was the key pioneer of information theory. Rolf Landauer may have done the most to turn it into a bona fide hard science. Charles Bennett has been a leader in moving Shannon's ideas in the classical realm to the exotic world of quantum theory.

Landauer made a number of key observations:

1. Information is physical
2. Information is independent of its physical embodiment
3. Erasing one bit of information dissipates at least kT/2 of energy

The first point indicates that without mass or energy, there is no information. How much mass is there in information? The old joke is that "my briefcase is so heavy because I downloaded so many books onto my hard drive." This confuses two types of information--the message or meaning that is conveyed vs the basic binary bits underlying that information. A 80GB hard drive contains the same number of bits no matter what is downloaded. They just aren't all intelligible until we rearrange them.

The second point is easily visualized by thinking of a telephone conversation. As the information passes from the mind of person A to the mind of person B, the physical medium that conveys the information changes many times. The information doesn't.

This also leads to an important observation on the 'information' in the genome. Charles Bennett once gently corrected me, saying that technically, the more accurate term is 'complexity' not 'information.' The genetic code conveyed from one cell to its replicated cell is not 'information' as Shannon described. This 'information' is not independent of its physical embodiment. The physical embodiment IS the information. It is never converted from one medium to another. This is really complexity, not information. The supposed notions of conservation of information don't apply to the genetic code. It is not a message conveyed from one agent to another. Information about the genome and its sequence of course is classical information.

Randy

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Received on Sun Apr 8 19:18:02 2007