Tryggth’s Blog

Have been incredibly busy with work and prepping for leading a multi-day training class. So this is just going to be a brief update on what has been going on with respect to Verlinde’s paper.

First of all, the paper continues to generate interest at a healthy rate as indicated by the SPIRES citation index. The index is not complete since the indexing relies on the format of citations, but the rate continues to be about one paper a day.

Two of the pre-prints (here and here) argue that Verlinde’s entropic derivation of gravity is logically flawed. I haven’t had a chance to look closely at these papers and have no opinion yet.

Also, Nobel laureate George Smoot (et al) have put up a pre-print with a very Verlinde-ish flavor. The abstract reads:

To accommodate the observed accelerated expansion of the universe, one popular idea is to invoke a driving term in the Friedmann-Lema\^{i}tre equation of dark energy which must then comprise 70% of the present cosmological energy density. We propose an alternative interpretation which takes into account the temperature intrinsic to the information holographically stored on the screen which is the surface of the universe. Dark energy is thereby obviated and the acceleration is due to an entropic force naturally arising from the information storage on a surface screen. We consider an additional quantitative approach based upon the entropy and surface terms usually neglected in General Relativity and show that this leads to the entropic accelerating universe.

They aren’t the first to suggest that dark energy (sorry, no reference for this statement) has an “entropic” origin. And though I suspect in the end the ontology will change, the whole approach of considering dark energy as the “Hawking radiation of the cosmic horizon” has some truth to it.

In an interesting interview T. Padmanabhan has a couple of things to say about Verlinde’s paper:

Verlinde’s paper has two logical parts. One part derives Einstein’s equations from thermodynamic arguments. This is not new, and I had done this a long time ago. In the second part, and this is the part he seems most excited by, he has derived Newton’s law of motion out of entropic considerations. Unfortunately, I do not agree with this part, and I think it involves faulty, circular reasoning. Nevertheless, it has generated popular interest in this work. Hopefully, it will spur more work in the area, but in the right direction.

It will take some time but hopefully a future post will dive into:

• Looking closely at the assumptions being used in discussion (axiomization and physics ontology)
• The duality of the holographic principle (vis-a-vis operationalism and why there is confusion about ‘emergence’)
• Causal Dynamic Triangulation (CDT), the successor of the ‘regge calculus‘ – the angle of the jangle
• And the one-parameter group of automorphisms which arise with some noncommutative mathematical objects

UPDATE: Today an interesting blog post showed up where the author went through Verlinde’s paper (aided by some discussions with Verlinde) and broke down some of the underlying assumptions. Its worth a read. The author collected the notes taken while reviewing Verlinde’s pre-print in this pdf.