17 December 2010

Motl and Jacobson

In a recent post, Lubos Motl discusses a paper from 1995 by Ted Jacobson. That paper makes an important point: gravitation is a consequence of the thermodynamics of space-time. The paper does not explain what the microscopic degrees of freedom are, but it makes the point that gravitation derives from them.

The argument is old and simple. But Lubos cannot live with it, because he believes that gravity is a phenomenon due to higher dimensions and supersymmetry. He has a problem though: there is not a shred of evidence for either assumption. Both assumptions are ideological.

On the contrary, there is a lot of evidence for Jacobson's argument – the entropy of black holes, for example. Worse, Jacobson makes the point that gravity is due to thermodynamics in three space dimensions. Obviously, anybody who makes such patently false statements (:-) makes Lubos's hormones go ballistic. He writes:

 "First of all, the entropy associated with the Rindler horizon is not "objectively real". It only exists relatively to an accelerating observer who decides not to ever see the space behind the horizon. From the viewpoint of the whole spacetime and coordinates that cover the whole spacetime, random areas in the spacetime obviously carry no entropy!"

Here you see what happens when ideology guides reasoning. In other words, if one observer measures something, and another not, obviously the first one is wrong, says Lubos Motl. Following this reasoning, black holes have no "objectively real" entropy, because an observer falling into a black hole does not see a horizon.

But read for yourself and enjoy how the false conviction that an argument in agreement with experiment cannot be correct makes a theoretical physicist go completely bonkers.

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