On Sat, Feb 18, 2012 at 04:49:44PM +0100, Evgenii Rudnyi wrote:
> 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.

My understanding is that is possible to perform a reversible
computation with arbitrarily small amounts of energy provided you do
the computation slowly enough. The only way to do it for zero energy
expenditure is to not do it at all.

> 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?

Its a thought experiment. Its quite well-defined (formalisable) whereas
the notion of God is 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.

A reversible computation has the same meaning of reversible as in
thermodynamics. Change of entropy is zero. Information is
conserved. Reversible computations can never erase memory locations,
for instance, or implement assignment.

> 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
> http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
> 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?

That seems like a non-sequitur. Could you expand on your thinking please?

> 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.

I'm afraid semiotics leaves me cold. I've never seen one useful
conjecture come out of it. Apologies to all those Pearceans out there.


Prof Russell Standish                  Phone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Professor of Mathematics      hpco...@hpcoders.com.au
University of New South Wales          http://www.hpcoders.com.au

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