Emergent Gravity Disproved

kdawson writes "A paper up on the ArXiv claims to disprove the gravity-from-entropy theory of Erik Verlinde, which we discussed soon after he introduced the idea in a symposium late in 2009. Archil Kobakhidze says that experiments measuring the effect of gravity on quantum particles (neutrons in this case) match results expected from classical Newtonian gravity, not Verlindian entropic gravity. Here is Kobakhidze's paper (PDF)."

Comments

Here we go again

[Anonymous Coward]

Kdawson, could you please try to have the first clue about something that you submit? This is a non-peer-reviewed article, fresh on the arXiv. It's a followup to an earlier article which was widely criticized within the community as being full of holes, and the arguments in this article are very very weak. At best it's an argument against entropic gravity, but it is a LONG way from a proof that entropic gravity is wrong.

The way that neutron states are treated here is questionable - see http://arxiv.org/abs/1104.4650 for a summary of what's wrong with them.

Disclaimer: I am a gravitational theorist. I think gravity ISN'T entropic. However this paper is nowhere near sufficient to show that. I'd wait a LOT longer for the dust to settle on this one before making a strong statement one way or the other.

Re:Here we go again

[Zedrick]

> I am a gravitational theorist.

I don't even understand what that title means, but it sounds very cool.

Re:Here we go again

[patlabor]

> I am a gravitational theorist.

I don't even understand what that title means, but it sounds very cool.

He attracts a lot of ideas...

Re:Here we go again

[Freddybear]

For more discussion of Kobakhidze's paper, and for criticism of the paper by Chaichian cited above, go here:
http://motls.blogspot.com/2011/08/once-more-gravity-is-not-entropic-force.html

Motl also responds directly to Verlinde here:
http://motls.blogspot.com/2010/01/erik-verlinde-why-gravity-cant-be.html
The discussion of a two-slit interference experiment in a gravitational field is clear enough that even I can almost understand it. ;)

Re:Here we go again

[bcrowell]

Kdawson, could you please try to have the first clue about something that you submit?

There's no reason to be so rude. In fact, I would consider the summary pretty accurate, although maybe not the title.

This is a non-peer-reviewed article, fresh on the arXiv.

Totally irrelevant. New research typically appears on arxiv first. That doesn't mean it's wrong.

It's a followup to an earlier article which was widely criticized within the community as being full of holes, and the arguments in this article are very very weak.

I'm not a specialist in this field (my specialty is experimental nuclear physics), but the impression I get as an outsider is that this is inaccurate. Actually many people in the field seem to find Kobakhidze's arguments very strong. I think the most fair summary would be that right now, the whole thing is controversial. Verlinde never claimed that he had a worked-out theory. It's always just been a rough heuristic. Even if it's right, it's wrong. What I mean by that is that it's at best a provisional picture (historically analogous to the Bohr atom) which needs to be reworked into a real theory (analogous to quantum mechanics). Just as there were no clear criteria for judging whether the Bohr model was a good idea or a dead end in 1915, there are no clear criteria for judging whether this idea is good or a dead end in 2011.

Motl comments

[Sara Chan]

Lubo Motl has some additional, supportive, thoughts on his blog:
Once more: gravity is not an entropic force

Gravity again?

[The Creator]

I thought that we decided to go with intelligent falling?