Tryggth’s Blog

Ignore the diagram to the left.

In the previous post I compared Verlinde’s ‘revelation‘ to the hyped proposal of Garret Lisi. I also tried to lay some of the historical groundwork which is context for Verlinde’s paper. Lee Smolin, in his paper building on Verlinde’s result, provides a more concise recounting of the historical context. Check it out.

Erik Verlinde

Verlinde is not a crackpot. A postdoctoral student  and then long term research member of the Institute of Advanced Study, Verlinde has regularly published in the area of string theory. He currently teaches at the Institute for Theoretical Physics at the University of Amsterdam. But his paper has not generated a universal ‘a-ha’ among physicists. One of my favorite reactions is Robert Helling’s:

The latest paper by Eric Verlinde on gravity as an entropic force makes me wonder whether I am getting old: Let me admit it: I just don’t get it.

Helling then goes on to write that Verlinde’s paper reminds him of the following proof:

girls = time * money [obvious, a priori]

time = money [experimentally determined]

girls = money ^ 2 [substitution into line #1]

money = sqrt(evil) [biblical]

money ^ 2 = evil [square of previous line]

girls = evil [transitive property]

I have no problem with that. But I would have thought Helling more sympathetic to Verlinde’s paper. After all, Verlinde’s use of polymer elasticity as an example of ‘entropic force‘ surely would have resonated with Helling’s own investigations into the thermodynamics of protein folding. And Helling, who won a ‘Schlössmann Award’ for describing gravity as an emergent property, can’t possibly be thrown by the dethroning of gravity from the big-4 of forces. Maybe, as he says, he is just ‘getting old’.

I suspect at this stage the uncertainty about Verlinde’s paper has to do with the following:

• The derivation of Einstein’s equations has been done before using roughly the same set of assumptions (see earlier post reference to Jacobson).
• There is an incredible muddle regarding the particulars and degree of gravity emergence. For one thing, the holographic principle in its usual forms has tons of implicit assumptions about the geometry (including dimensionality) of ’space’.
• The Unruh effect/temperature buries within itself a multitude of sins, especially relativistic quantum field theory.
• Most importantly, the paper messes with people’s usual ontology. The pre-geometric physical entities which provide the semantics to an unstated, but implied (since gravity is emergent) reformulation of the holographic principle as well as the dynamics of those essentially information-theoretic entities is pretty alien.

And yet… and yet…

It seems – at this point in time – what Verlinde has done is pointed to a reaxiomization  of some basic physics. Similar to there being several different equally adequate axiomizations (given a set of basic symbols) of propositional logic, Verlinde will focus attention on perhaps redundant underlying assumptions of quantum mechanics, general relativity and thermodynamics.

To be continued…