## Gravity as an Entrophic force

Study matter and its motion through spacetime...

### Gravity as an Entrophic force

Someone started a thread about this topic on the old site. I found it pretty interesting but no one else joined in and the thread died. I'm going to reopen the topic. Here the abstract of the original paper, a free version of which can be found here

Starting from 1st principles and general assumptions Newton's law of grav-
itation is shown to arise naturally and unavoidably in a theory in which space
is emergent through a holographic scenario. Gravity is explained as an entropic
force caused by changes in the information associated with the positions of ma-
terial bodies. A relativistic generalization of the presented arguments directly
leads to the Einstein equations. When space is emergent even Newton's law of
inertia needs to be explained. The equivalence principle leads us to conclude
that it is actually this law of inertia whose origin is entropic.

I personally beleive that entropy could very well be an underling component of all physical theories. All of physics deals with the behavior of a system relative to a set number of degrees of freedom. the Second law on the other hand tells about the number of degrees of freedom a system can possibly have. therefore it is a lower level physical law. So in some sense I feel like we might be able derive or evolve the other physical laws from special instances of the second law. This paper trys to do that with gravity it's interesting and readable but a little hand wavy.
Last edited by Mononoke on Mar 04, 2010 9:02 pm, edited 1 time in total.

Mononoke

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### Re: Gravity as an Entrophic force

Your link is telling me the paper can't be found, any chance it could be a broken link? I'd be really interested in reading the paper.
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Rachel

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### Re: Gravity as an Entrophic force

Rachel wrote:Your link is telling me the paper can't be found, any chance it could be a broken link? I'd be really interested in reading the paper.

Fixed! Try it now

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### Re: Gravity as an Entrophic force

Gravity is a warping of spacetime caused by the presence of mass (mass = energy x c^2). When something is orbiting around something else, it is falling in a straight line around the second object. Newton was great, but his view of gravitation was changed almost 100 years ago. I think it's time that high school physics classes caught up.
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### Re: Gravity as an Entrophic force

num1cubfn wrote:Gravity is a warping of spacetime caused by the presence of mass (mass = energy x c^2). When something is orbiting around something else, it is falling in a straight line around the second object. Newton was great, but his view of gravitation was changed almost 100 years ago. I think it's time that high school physics classes caught up.

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### Re: Gravity as an Entrophic force

I never understood Einstein. For some reason, no one wants to explain all the complicated mumbo jumbo in English
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### Re: Gravity as an Entrophic force

Paul1 wrote:I never understood Einstein. For some reason, no one wants to explain all the complicated mumbo jumbo in English

Which bits do you want explaining?

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### Re: Gravity as an Entrophic force

Mononoke wrote:Someone started a thread about this topic on the old site. I found it pretty interesting but no one else joined in and the thread died. I'm going to reopen the topic. Here the abstract of the original paper, a free version of which can be found here

Starting from 1st principles and general assumptions Newton's law of grav-
itation is shown to arise naturally and unavoidably in a theory in which space
is emergent through a holographic scenario. Gravity is explained as an entropic
force caused by changes in the information associated with the positions of ma-
terial bodies. A relativistic generalization of the presented arguments directly
leads to the Einstein equations. When space is emergent even Newton's law of
inertia needs to be explained. The equivalence principle leads us to conclude
that it is actually this law of inertia whose origin is entropic.

I personally beleive that entropy could very well be an underling component of all physical theories. All of physics deals with the behavior of a system relative to a set number of degrees of freedom. the Second law on the other hand tells about the number of degrees of freedom a system can possibly have. therefore it is a lower level physical law. So in some sense I feel like we might be able derive or evolve the other physical laws from special instances of the second law. This paper trys to do that with gravity it's interesting and readable but a little hand wavy.

DISCLAIMER : I have just finished Smolin's "Life of the Cosmos" and it is pretty much what I know about contemporary physics. If I am talking nonsense, thank you to correct me.

I found the article interesting, although a good part of it flied over my head. If I understood Smolin correctly, one way to look at the law of physics as we know them is that they must be emerging from the physics at the Planck scale, that we know close to nothing about. Two natural hypotheses would be :
- That they are the emergent properties of a complex system.
- That they are statistical properties of a disorganized system.

So the author thinks that gravity is of the second kind ?

A funny thing is that I intended to ask a layman's question about gravity and entropy, but that seems unrelated to that thread. I will soon post it in a new thread.
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### Re: Gravity as an Entrophic force

bookmarked.
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### Re: Gravity as an Entrophic force

palindnilap wrote:
I found the article interesting, although a good part of it flied over my head. If I understood Smolin correctly, one way to look at the law of physics as we know them is that they must be emerging from the physics at the Planck scale, that we know close to nothing about. Two natural hypotheses would be :
- That they are the emergent properties of a complex system.
- That they are statistical properties of a disorganized system.

So the author thinks that gravity is of the second kind ?

A funny thing is that I intended to ask a layman's question about gravity and entropy, but that seems unrelated to that thread. I will soon post it in a new thread.

I've only skimmed the paper, but yes, it seems to be postulating that gravity can be described as a force which is in some way a result of statistical physics. An intresting way of thinking of it. I need to read it in more detail - it looks like he's taken many very different areas of physics - classical thermodynamics, black hole entropy formulae, holographic principles, relativity, and combined them to "derive" Newton's and Einstein's gravity. I'm not sure what to make of it yet...
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### Re: Gravity as an Entrophic force

Hmm, I tried to read the paper but most of it over my head - I've done stat mech and relativity and such but I can't really follow it.

If I'm understanding this correctly, he derives Newton's gravity first then goes on to Einstein. I'd have thought that it would be more fundamental to just go straight to Einstein and not bother with Newton. That'd be more fundamental, wouldn't it?
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### Re: Gravity as an Entrophic force

Rachel wrote:If I'm understanding this correctly, he derives Newton's gravity first then goes on to Einstein. I'd have thought that it would be more fundamental to just go straight to Einstein and not bother with Newton. That'd be more fundamental, wouldn't it?

I must say that it surprised me as well. Einstein isn't Newton plus a corrective factor, is it ?
palindnilap
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### Re: Gravity as an Entrophic force

If anyone's interested, Lubos Motl has written a critique of the Verlinde arguments here

Motl has very strong opinions on theoretical physics and isn't afraid to voice them. There are often some quite heated (but usually quite high quality) discussions on his blog.
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