Wednesday, January 27, 2010

Entropic Everything

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. Is this because I am conservative or lack imagination or too narrow minded? If it were not for the author, I would have rated it as pure crackpottery. But maybe I am missing something. Today, there were three follow-up papers dealing with cosmological consequences (the idea being roughly that Verlinde uses the equipartition of energy between degrees of freedom each getting a share of 1/2 kT which is not true quantum mechanically at low temperatures as there the system is in the ground state with the ground state energy. As in this business temperature equals acceleration a la Unruh this means the argument is modified for small accelerations which is a modification of MOND type).

Maybe later I try once more to get into the details and might have some more sensible comments then but right now the way different equations from all kinds of different settings (Unruh temperature was already mentioned, E=mc^2, one bit per Planck area, etc) are assembled reminds me of this:


Pope Maledict XVI said...

I am getting seriously depressed about the way theoretical physics is going. Last year's fad was Lifshitz gravity; that wasn't a very good idea, but it was worth half a dozen cites or so. Instead it has over 200. Now this demented thing... I bet it will hit 100 cites by July 2010.

Is it time to give up on physics?

Anonymous said...

Blame the job market. There is so much incentive to get quick results in order to get tenure, and you end up with lots of dubious fads (aka citation count padders).

The older, most promising leads at this point requires so much effort to get anywhere with and the easy calculations have already been done and redone.

Anonymous said...

I don't think it's just the job market. Even people with secure positions are getting desperate because nothing sensible is going on.

Meanwhile, the prize for nonsense^2 goes to the first paper to *combine* Horava with Verlinde:

Or is this a joke? Somebody please say yes!

Blake Stacey said...

My background in this corner of physics is admittedly weak, but I'm having a hard time understanding what the "entropic force" papers are trying to accomplish. I mean, yes, given some relationship X, we could rewrite X in a form which looks like it involves some kind of entropy, but that doesn't mean X is entropic in origin. Even if the logic isn't circular (maybe it's just my head spinning), it might be running in the wrong direction.

Robert said...

the ns^2 paper is really amazing. Could somebody please explain why it seems that in particular the Chinese seem to pick up on the Entropic Gravity idea?

I don't think it's only the job market. As far as I know Eric has a good position and even without this paper it shouldn't have been too hard from him to get another one.

Blake: AFAIK this is exactly the idea of the Verlinde paper: Everybody knows that gravity leads to thermodynamic behaviour, but this paper turns it around.

Anonymous said...

I refuse to believe that *most* of the people involved in writing papers on Horava gravity, unparticle physics and Entropic goobledygook, actually genuinely think these things have anything to do with nature.

At least in the case of Unparticles, they're kind of fun to draw consequences and to exercise the brain a little bit (even if the odds are completely tiny to be realized in nature). Otoh the other two just seem so manifestly wrong to me, that I can't believe its anything other than a rather cynical means to catch the hype train while its still producing citations.

Maybe I just lack imagination.

Pope Maledict XVI said...

To be fair, at least these ideas are interesting, even if they are silly. [Unparticles are different --- that idea is not obviously wrong, though it is so ugly that it was a relief to realise eventually that it was crap]. Look at the arxiv these days: what you see is almost unrelieved *boredom*. This is certainly the most boring era in physics since the first half of the 19th century! People are even making jokes about this in their papers: for example, a group of very well-known people recently began a very long and exceedingly boring paper with the words

"Since the dawn of time, humankind has wondered, what is the potential on the Coulomb
branch of the conifold gauge theory, and what are the consequences for models of D-brane
inflation? In this paper, we continue this quest."

I think that there is a real longing out there for something interesting to work on, and this unparticle/Lifshits/entropy rubbish is the consequence.

Anonymous said...

"what I don't understand, must be wrong"

Mitchell said...

I'm seeing serious overreaction here. Go back decades in any major journal of theoretical physics and look at the papers. You will find people writing about the fashionable topics of the day.

The culture of physics - intellectual, institutional, technological, its relationship to culture at large - changes every decade, but there is always something good happening, even in lean times. Identifying decadence and excesses is only useful as a step towards finding where the good stuff is. Don't wallow in despair.

Sabine Hossenfelder said...

Robert: Incidentally, I had a similar reaction when I read the paper, but I admittedly haven't thought about it very much (because I can't figure out what it's good for). I'd be interested to learn about your opinion. It smells to me like a reformulation of the usual flux-through-surface argument that gives you Newton's law (or Coulomb's law for that matter). All you really need is a conserved charge and a long range interaction. (And then the potential depends on the number of spatial dimensions as Verlinde also mentions.) It doesn't really matter much whether you optimize the action or the entropy or if you talk about flux or temperature. Or am I missing something here? Stehe auf dem Schlauch. Gruesse,


Anonymous said...

I agree that Verlinde's paper is sign of desperation in the pop physics community. It represents the culmination of person-years of wasted effort by physicists to find the next "big idea" without any real effort to fully define relationships between mathematics and physical observation.

However, I would not give up hope; the central thesis driving almost all physics research to date is that gravity has a relationship to ignorance brought on by our partitioning methodology. Whether we can really develop an understanding of gravity hinges on our ability (or inability) to understand mathematical concepts such as the continuum hypothesis.

The fundamental issue is that for the last 25 years, physicists have been working at the 100,000 ft level and not at the 100 or 10 ft level. Verlinde's paper is a symptom, not a disease.

Anonymous said...

I admit that in Verlinde's paper one can find many questionable assupmtions and some circular logics. But, Padmanbahan and others also did similar works more rigorously and support this kind of idea.

I think the most important thing
a sound physics theory should have is predictability.
At least theories in this field provide some predictions which can be compared with observations soon.
How about string theory?
Lots of geniuses? are spending their talents for meaningless study.
I think Verlinde's theory is, albeit humble, much physical than string theory.
This is a 20th century physics, which is found in 21st century!

TheDLK said...

YES --- and since everything = TIME... Everything by nature must be evil ACCORDING TO YOUR LOGIC PROFESSOR (((Ha-Ha))). 4---Real--True UNDERSTANDING OF THIS CONSCIOUSNESS Thermal Rift!!!

Unknown said...

No guts no glory!