On 09.02.2012 07:49 meekerdb said the following:

> There's an interesting paper by Bennett that I ran across, which
> discusses the relation of Shannon entropy, thermodynamic entropy, and
>  algorithmic entropy in the context of DNA and RNA replication:
> http://qi.ethz.ch/edu/qisemFS10/papers/81_Bennett_Thermodynamics_of_computation.pdf
> Brent

I have browsed the paper. It is nice indeed. A couple of comments.

1) Reversible computation

The author seems not to reject the idea of reversible computation. This, in my view, shows that the first statement from the paper

"Computers may be thought of as engines for transforming free energy into waste heat and mathematical work."

just does not work literally. If reversible computation is possible, then we do not have any thermodynamic limits in this respect. What is left is just a thermal noise in form of kT.

2) Maxwell demon

I have never understood a problem with the Maxwell's demon. Why it is not enough to say that it does not exist? Why for example Maxwell's demon touches the imagination of physicists and engineers and the idea of the God not?

3) Reversible chemical reactions and reversible thermodynamic processes

I think that the author misuses the term reversible in a sense that the word has completely different meaning in thermodynamics and in chemistry. In thermodynamics, the reversible process implies that the entropy of the system and surrounding does not change (the entropy of the Universe remains constant). In chemistry, a term reversible reaction means we have two reactions (forward and backward) running in parallel. Thereafter, by playing with conditions we could transform A to B and then B back to A. However, when a reversible chemical reaction takes place it is impossible to implement it as a reversible thermodynamic process. Hence a reversible chemical reaction is not thermodynamically reversible.

4) Algorithmic entropy

I have missed the point on the connection between the algorithmic entropy and thermodynamic entropy. Here would be good to be back to the Jason's example from about his work on secure pseudo-random number generators


What a thermodynamic system should be considered at all here?

In my view, the algorithm is independent of implementation details. It seems that this is one of the points at this list when people claim that it could be possible to make a conscious robot. Yet, how then the thermodynamic entropy could be connected with the algorithmic entropy?

5) DNA, RNA and information

I have recently read

Barbieri, M. (2007). Is the cell a semiotic system? In: Introduction to Biosemiotics: The New Biological Synthesis. Eds.: M. Barbieri, Springer: 179-208.

and below there is a quote. It is quite a different viewpoint on the processes in the cell.

"At this point, we can summarize all the above concepts by saying that in protein synthesis:

(1) Organic information is the sequence used by a copymaker during a copying process.

(2) An organic sign is the sequence used by a codemaker during a coding process.

(3) An organic meaning is the sequence produced by a codemaker during a coding process.

(4) Organic information, organic signs and organic meaning are neither quantities nor qualities. They are a new kind of natural entities which are referred to as nominable entities.

(5) Organic information, organic signs and organic meaning have the same scientific status as physical quantities because they are objective and reproducible entities which can be defined by operative procedures.

(6) Organic information, organic signs and organic meaning have the same scientific status as fundamental physical quantities because they cannot be reduced to, or derived from, simpler entities."


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