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Is gravity just entropy rising? Long-shot idea gets another look

quantamagazine.org

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Re: Is gravity just entropy rising? Long-shot idea gets another look

#121

Post by neuroelectron »

Xcelerate wrote: post #119
steamrolled wrote: post #109

Earlier quoted context omitted.

> Because they are vibrating, a lot of that energy is being wasted in brownian motion. So the denser it is, the more your average vector is going to be toward more dense brownian motion as the particles interact and induce more brownian motion ... Seems pretty intuitive to me. So this is why warm objects weigh more?

Warm objects actually do weigh more than their counterfactual cold versions haha. The stress energy tensor is the quantity to look at here.

I didn't know this, thanks for sharing.

https://herebeanswers.com/things-weigh-heavier-or-lighter-wh...

Re: Is gravity just entropy rising? Long-shot idea gets another look

#122

Post by dawnofdusk »

lewdwig wrote: post #41
pif wrote: post #40

As an experimental physicist, I refuse to get excited about a new theory until the proponent gets to an observable phenomenon that can fix the question.

The problem with emergent theories like this is that they _derive_ Newtonian gravity and General Relativity so it’s not clear there’s anything to test. If they are able to predict MOND without the need for an additional MOND field then they become falsifiable only insofar as MOND is.

Deriving existing theories of gravity is an important test of the theory, it's not a problem at all. It's only a problem if you can only do this with more free parameters than the existing theory and/or the generalized theory doesn't make any independent predictions. Seems like in the article the former may be true but not the latter.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#123

Post by nathan_compton »

mr_mitm wrote: post #53
MathMonkeyMan wrote: post #6

Entropic gravity is a compelling framework. I think that most Physicists admit that it would be nice to believe that the yet unknown theory of everything is microscopic and quantum mechanical, and that the global and exquisitly weak force of gravity emerges from that theory as a sort of accounting error. But there are so many potential assumptions baked into these theories that it's hard to believe when they claim, "…

What are some of the most problematic assumptions in your opinion?

I'm not an expert in this field but I think reproducing realistic gravitational interactions seems to require a lot of fiddly set up with heat baths etc.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#124

Post by dawnofdusk »

dist-epoch wrote: post #4

We all know that life on Earth gets it's energy from the Sun. But we also know that's an approximation we tell kids, really life gets low entropy photons from the Sun, does it's thing, and then emits high entropy infrared waste heat. Energy is conserved, while entropy increases. But where did the Sun got it's low entropy photons to start with? From gravity, empty uniform space has low entropy, which got "scooped up"…

This is just a question about the origins of inhomogeneity in the universe. The prevailing theory is cosmic inflation, I believe: in the early universe a quantum field existed in a high entropy state and then the rapid expansion of space magnified small spatial inhomogeneities in the field into large-scale structures. What we see as "low entropy" structures like stars are actually just high entropy, uniform structures at a higher scale but viewed from up close so that we can see finer-scale structure.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#125

Post by kgwgk »

tsimionescu wrote: post #115
kgwgk wrote: post #100

Earlier quoted context omitted.

There is some objective nature to the operational definition of entropy based on an experimental setup where you fix the volume and measure the temperature or whatever. And this is related to the statistical mechanical definition of entropy based on the value of the corresponding state variables. But it’s not a property of the microstate - it’s a property of the macrostate which makes sense only in the context of the…

> But it’s not a property of the microstate - it’s a property of the macrostate which makes sense only in the context of the experimental constraints and measurements. The same can be said about the wavefunction then, right? You can't directly observe it, you can only use it to predict the statistics of a particular experimental setup. So, at worse, entropy is as real as wavefunction amplitudes. > If we relate entrop…

> Per my understanding

What’s the source of that understanding? You cannot measure the entropy, only changes of entropy - which will be the same (for an ideal gas).

Edit: we already had this discussion, by the way: https://news.ycombinator.com/item?id=42434862

Re: Is gravity just entropy rising? Long-shot idea gets another look

#126

Post by cantor_S_drug »

ajkjk wrote: post #110
cwharris wrote: post #92

This seems backwards. Entropy is a dispersive force — it favors distribution and disorder. But the universe clumps. Planets, stars, galaxies — all of them are low-entropy configurations. So how did scattered dust particles form the planet we’re standing on… through entropy? If gravity is just emergent from entropy, then it should be fighting against planet formation, not causing it. There’s a missing piece here — may…

There is a whole article explaining it... if you don't read the article, how do you expect to know the idea?

Actually Roger Penrose also had this line of thinking if my memory serves right.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#127

Post by bee_rider »

heyjamesknight wrote: post #106
cwharris wrote: post #92

This seems backwards. Entropy is a dispersive force — it favors distribution and disorder. But the universe clumps. Planets, stars, galaxies — all of them are low-entropy configurations. So how did scattered dust particles form the planet we’re standing on… through entropy? If gravity is just emergent from entropy, then it should be fighting against planet formation, not causing it. There’s a missing piece here — may…

Entropy isn't a force. It doesn't "favor" anything. Its a property of statistics, information, and distributions. Also why does this have that particular ChatGPT social media post rhythm to it? Please, Lord, tell me we haven't reached the point where people are writing HN comments w/ AI.

We’ve definitely reached that point. I’ve seen responses that are essentially,

Well, here’s what ChatGPt has to say:

If folks are doing that, then I assume they are also quoting it without citation—although, I have no idea about this case. It looks sort of rambling for ChatGPT, doesn’t it?

Re: Is gravity just entropy rising? Long-shot idea gets another look

#128

Post by cwharris »

heyjamesknight wrote: post #106
cwharris wrote: post #92

This seems backwards. Entropy is a dispersive force — it favors distribution and disorder. But the universe clumps. Planets, stars, galaxies — all of them are low-entropy configurations. So how did scattered dust particles form the planet we’re standing on… through entropy? If gravity is just emergent from entropy, then it should be fighting against planet formation, not causing it. There’s a missing piece here — may…

Entropy isn't a force. It doesn't "favor" anything. Its a property of statistics, information, and distributions. Also why does this have that particular ChatGPT social media post rhythm to it? Please, Lord, tell me we haven't reached the point where people are writing HN comments w/ AI.

You’re right. the cadence is written by ChatGPT. I’m pretty terrible at keeping my thoughts cohesive, so I often use it as a post processor. I’ll try not to do that.

Because you had the decency to respond, I’ll spent some more time thinking about this and see if I can come up with a more well rounded response that incorporates more of the traditional language of physics. But to your point about entropy not being a “force”, you’re probably right. Someone got to choose what that word means, and I’m probably not using their definition. But let me ask you this… would you rather have a book that explains everything and not know how to read it, or trust your own eyes ears and hands, and not be able to share it?

Re: Is gravity just entropy rising? Long-shot idea gets another look

#129

Post by echelon »

heyjamesknight wrote: post #106
cwharris wrote: post #92

This seems backwards. Entropy is a dispersive force — it favors distribution and disorder. But the universe clumps. Planets, stars, galaxies — all of them are low-entropy configurations. So how did scattered dust particles form the planet we’re standing on… through entropy? If gravity is just emergent from entropy, then it should be fighting against planet formation, not causing it. There’s a missing piece here — may…

Entropy isn't a force. It doesn't "favor" anything. Its a property of statistics, information, and distributions. Also why does this have that particular ChatGPT social media post rhythm to it? Please, Lord, tell me we haven't reached the point where people are writing HN comments w/ AI.

Because it has emdashes and ellipses that Chrome, Firefox, Mac, Linux, and Android text input controls do not natively produce.

I don't know about iPhone.

If you see these artifacts, it was authored in some other software (be it an editor or LLM) and pasted over.

Re: Is gravity just entropy rising? Long-shot idea gets another look

#130

Post by [deleted] »

danparsonson wrote: post #111
neuroelectron wrote: post #105

The speed of light is C, a constant. Mass is composed of these particles that are bound by C. Because they are vibrating, a lot of that speed is being wasted in brownian motion. So the denser it is, the more your average vector is going to be toward more dense brownian motion as the particles interact and induce more brownian motion. The gradient has a natural sorting effect. Seems pretty intuitive to me. The questio…

> Seems pretty intuitive to me OK, but it's nonsense. Apart from whatever-you're-talking-about-with-C, quantum fluctuations are not Brownian motion; Brownian motion is the visible effect of a lot of invisible particles interacting kinetically with macroscopic particles like dust, making those macroscopic particles appear to vibrate of their own accord. Atoms that cannot be seen in a microscope flying around in straig…

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