# If gravity doesn't exist,what are the implications?

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I just heard about new theories proposed by Erik Verlinde about the fact that Gravity doesn't exist..or at least it's not a foundamental force. My question is : if this is true what are the implications on current models like string theory , eternal inflation ecc ecc ? what can change in the understanding of our universe ?

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user user27494
Semantics of the first sentence aside, I could read your question as asking if string theory admits models in which gravity is emergent in the sense of Verlinde. Is that it?

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Nikolaj K.
For one, apples would stop falling.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Dimensio1n0
@nick kidman yes exactly

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user user27494
Essentially a duplicate of physics.stackexchange.com/q/4289/2451

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Qmechanic
For something like this, a link to a paper on arxiv would be really helpful. Otherwise how the heck are we going to know what is being discussed? AFAICT this is just a duplicate.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Ben Crowell
@Qmechanic: I disagree that this is a duplicate. This question is asking for the implications. Voting to reopen.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Dimensio1n0

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I take the question being asked to be:-

"If gravity doesn't exist, what are the implications ?"

Ergo, anything to do with Erik Verlinde is irrelevant to the question.

Gravity is one of the two infinite range forces; the other being the Coulomb force between electric charges.

Unlike electric charges, eg proton and electron, if they meet, effectively cancel as far as external fields are concerned. Like electric charges mutually repel, and can only be compressed together by Coulombic forces, outside of them; which in turn requires more outer charges.

Earnshaw's theorem tells us that no stable configuration of electric charges exists, so large amounts of matter cannot be compressed to high density by any static Coulomb field.

Gravity, is the only long range force that pulls instead of pushes (between like objects).

So gravity sucks. Without gravity there would be no stars; and no ground or apples to fall on it.

Doesn't matter a jot why gravity does or does not exist; without it there would be nothing that we would recognize.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user user26165
answered Sep 16, 2013 by anonymous
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You have a few misconceptions here.

# Verlinde's theory does not really say that there is no gravity

Instead, it gives a "mechanical" explanation for (Newtonian) gravity, through some sort of entropy differences, which I do not fully understand.

# Verlinde's theory is not likely to be true, anyway

Verlinde's theory only derives Newtonian Gravity, and it is unlikely that it will be ever consistent with General Relativity, for example,.

While it has been pointed out in the comments by Danu & Jerry Schrimer (and I think I had a very bad memory of what Verlinde's paper was about, looking at the abstract...), the above argument is wrong, I still think the Verlinde paper cannot be right. See for example, these articles by Lubos and this paper by Kobhakidze (whom I initially thought to be Verlinde himself).

Ok, now what about your question? As I said, Verlinde's theory does not agree with even General Relativity, and it's probably not going to be quantised either, so it will never agree with string theory, most likely.

Also, if it were true that gravity didn't exist, apples would stop falling.

answered Sep 16, 2013 by (1,955 points)
A few notes: 1) Verlinde's paper basically assumes the Hawking entropy and spherical symmetry, and then derives the Newtonian force--this is, by happenstance, identical to the GR geodesic equation for radial observers 2) Other entropic approaches have been able to derive the Hilbert action 3) I've always looked at these as arguments that GR is "generic" rather than emergent, anyway.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Jerry Schirmer
Verlinde did actually derive GR using his approach, in the original paper in fact (although I'm entirely ignorant of the details).

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Danu
@DImension10 Maybe i posted the question in the wrong way..For what i understood from Verlinde's theory gravity is not a foundamental force but it just derive from the other ones and it's a form of entropy of the space time..As you saying,if this theory doesn't fit with general relativity,string theory or other models im trying to understand what Verlinde is trying to explain with this assumption

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user user27494
@JerrySchirmer Are you saying that Verlinde's approach doesn't change nothing in current theories but it's just a way to explain gravity ?

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user user27494
@Danu: Hm... Seems you're right. I'll probably fix my answer.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Dimensio1n0
@JerrySchirmer: Ok, let me correct my answer. One minute.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Dimensio1n0
@user27494: No; see the links (Specifically, the first.) in the updated answer. It seems that the theory of entropic gravity doesn't really agree with experiments.

This post imported from StackExchange Physics at 2014-03-12 15:51 (UCT), posted by SE-user Dimensio1n0

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