Tuesday, May 28, 2013

New Directions in the Foundations of Physics Conference in Washington DC 2013

This year I attended again the “New Directions” conference and yet again there were many interesting talks. I will gradually present what I learned from this year’s conference, with the caveat that I cannot be comprehensive and cover all talks.

Landauer’s Principle

One talk was by James Ladyman on his refutation of John Norton’s rejection of Landauer’s principle.

Landauer’s Principle states that erasure of information in an irreversible computation creates heat (http://en.wikipedia.org/wiki/Landauer's_principle). In prior years, I heard Norton’s talk on rejecting Landauer’s Principle based on his one molecule gas analysis. Refuting Norton’s analysis, Ladyman presented his own arguments, and since Norton was present in the audience, the talk got really interesting in the Q&A session when Norton answered back.

Norton started with a funny joke about a recent Nature paper on this: two identical pieces of paper one which had written a long series of 1s and the other which had a random series of 0 and 1s were burned and the one with the random number generated more heat.

Then he proceeded to find holes in Ladyman’s arguments and rehashed his one molecule gas analysis (which I recalled from prior years). This time there was vigorous disagreement between the audience and Norton was on what constitutes a thermal equilibrium process for a one molecule gas. Basically, Norton’s core argument was that the piston pressing down of a one molecule gas has to be very light and hence it will have violent position fluctuations. In turn this makes a slow compression of the piston impossible and this killed Ladyman's counterarguments.

However, to me the one-molecule gas arguments look flimsy because the arguments hinge on the validity of the thermodynamic limit. And this limit was not proven to my satisfaction. It is highly likely Norton’s arguments will turn to be an artifact of this limit.

Since I am no expert in Landauer’s Principle, I cannot say with certainty who is right and who is wrong. But if I were to bet I’ll put my own money on Landauer’s principle. 

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