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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

#171

Post by prophesi »

cwharris wrote: post #163
prophesi wrote: post #136

Earlier quoted context omitted.

> 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? Maybe use AI to help you understand TFA instead of writing gut reactions to the title.

I... Do... With quite a lot of articles... And I build semiconductors in my garage using what I learn. I just don't see how this particular article would be beneficial, even if it _were_ correct.

Are these the very same semiconductors writing your comments? NGL, a 9 year old account with 0 posts that suddenly starts posting AI-assisted comments is very suspicious.

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

#172

Post by ndriscoll »

abetusk wrote: post #160

Entropic gravity is like the "brazil nut effect" [0] [1]. The idea is that if you shake a glass full of different sized nuts, the large ones will rise to the top. From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts), and because of gravity, there's a cavity left under the brazil nut wh…

Aren't more massive particles smaller though (in terms of de Broglie wavelength, at least), so they'd have a smaller "shadow"? Or do different forces have different cross-sections with different relationships to mass, so a particle's "size" is different for different interactions (and could be proportional to mass for gravity)?

Actually this is currently blowing my mind: does the (usual intro QM) wavefunction only describe the probability amplitude for the position of a particle when using photon interaction to measure, and actually a particle's "position" would be different if we used e.g. interaction with a Z boson to define "position measurement"?

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

#173

Post by ang_cire »

deadbabe wrote: post #153

Couldn’t it be a byproduct of frame dragging? Any massive object that spins is pulling stuff into it by forcing things to rotate in some kind of space time whirlpool? This means if something massive doesn’t spin, it would have no gravity, but isn’t everything large enough to have gravity in space pretty much spinning?

No, many asteroids have detectable, "functional" (e.g. they pull dust towards them) gravitational fields, but are not spinning like planets.

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

#175

Post by tsimionescu »

kgwgk wrote: post #125
tsimionescu wrote: post #115

Earlier quoted context omitted.

> 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

> You cannot measure the entropy, only changes of entropy

You can measure the changes in entropy from a minimal state and integrate - and you'll get the "total" entropy.

And thanks for looking it up! I remembered a very similar conversation and was wondering if you were the same person, but was a bit lazy to search :)

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

#176

Post by franktankbank »

sim7c00 wrote: post #164
abetusk wrote: post #160

Entropic gravity is like the "brazil nut effect" [0] [1]. The idea is that if you shake a glass full of different sized nuts, the large ones will rise to the top. From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts), and because of gravity, there's a cavity left under the brazil nut wh…

but these nuts move by gravity do they not? and what in the universe is exactly up and down? and why would that matter? are all celestial bodies then a local up and 'away from them' down? this analogy hurts my brain. please tell me how to make the hurting stop

No you are right. You can't invoke gravity in an analogy trying to explain gravity.

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

#177

Post by kgwgk »

tsimionescu wrote: post #175
kgwgk wrote: post #125

Earlier quoted context omitted.

> 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

> You cannot measure the entropy, only changes of entropy You can measure the changes in entropy from a minimal state and integrate - and you'll get the "total" entropy. And thanks for looking it up! I remembered a very similar conversation and was wondering if you were the same person, but was a bit lazy to search :)

> You can measure the changes in entropy from a minimal state and integrate - and you'll get the "total" entropy

That doesn’t help with the following (at least if you keep those kinds of gas in gas state):

> if I give you three containers […] you can measure their entropy using thermodynamic experiments and tell which of the three is a mix of the other two because it will have a higher entropy

But you can weight them, it’s much easier.

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

#178

Post by Someone »

abetusk wrote: post #160

Entropic gravity is like the "brazil nut effect" [0] [1]. The idea is that if you shake a glass full of different sized nuts, the large ones will rise to the top. From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts), and because of gravity, there's a cavity left under the brazil nut wh…

> From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts)

That doesn’t make sense to me. If larger objects move slower, don’t they move faster relative to the (accelerating) reference frame of the container?

Also, conventional wisdom has it that shaking (temporarily) creates empty spaces, and smaller objects ‘need’ smaller such spaces to fall down, and thus are more likely to fall down into such a space.

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

#179

Post by bobbylarrybobby »

ndriscoll wrote: post #172
abetusk wrote: post #160

Entropic gravity is like the "brazil nut effect" [0] [1]. The idea is that if you shake a glass full of different sized nuts, the large ones will rise to the top. From what I understand, this is because larger objects have more mass, moving slower when shaked, so as the larger (brazil nuts) don't move as much relative to the smaller ones (peanuts), and because of gravity, there's a cavity left under the brazil nut wh…

Aren't more massive particles smaller though (in terms of de Broglie wavelength, at least), so they'd have a smaller "shadow"? Or do different forces have different cross-sections with different relationships to mass, so a particle's "size" is different for different interactions (and could be proportional to mass for gravity)? Actually this is currently blowing my mind: does the (usual intro QM) wavefunction only de…

The momentum wavefunction (or more properly, the wavefunction in the momentum basis) completely determines the position wavefunction (wavefunction in the position basis). And we can probe the momentum wavefunction with any particle at all, by setting up identical (say) electrons and seeing the momentum they impart on a variety of test particles. That is to say, the probability distribution of momentum of a particle does not depend on what we use to probe it.

As the position wavefunction is now completely determined in a probe-agnostic matter, it would be hard to justify calling a probe that didn't yield the corresponding probability distribution a “position measurement”.

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

#180

Post by raindeer2 »

Wonder if this perspective is compatible with Wolframs physics model based on hypergraphs?

Gravity, in this framework, is an emergent property arising from the statistical behavior of the hypergraph's evolution, suggesting that gravity is an "entropic force" arising from the tendency of the system to minimize its computational complexity

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