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

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

#191

Post by floxy »

Gravityloss wrote: post #89
mr_mitm wrote: post #57

Earlier quoted context omitted.

You only hear these terms in layman explanations. Physics has precise definitions for these things. When we say "ordered", we mean that a particular macrostate has only few possible microstates. Check this Wikipedia article for a quick overview: https://en.wikipedia.org/wiki/Microstate_(statistical_mechan... Details can be found in any textbook on statistical mechanics.

Exactly. The coin flipping example is a very nice way to put it. It works since the coins are interchangeable, you just count the number of heads or tails. If the coins were of different color and you took that into account, then it wouldn't work. It's not intuitive to me what gravity has to do with entropy though, as it's classically just a force and completely reversible (unlike entropy)? Ie if you saw a video of u…

> Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed.

How does that work with things like black holes? If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video? Even if you take account the gravitational waves?

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

#192

Post by layer8 »

gavinray wrote: post #86
aurareturn wrote: post #61

Earlier quoted context omitted.

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" as the Sun formed. From the Big Bang originally. We don’t know what caused the Big Bang.

The end of the previous Big Bang, a-la Big Bounce ;^) "It's turtles all the way down."

You’d have to explain how the steadily increasing entropy in our universe would revert to a low-entropy state again.

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

#194

Post by FilosofumRex »

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…

This is a better YouTube video describing granular physics and shows the speed (amplitude) of vibrations can cause counterintuitive arrangements of particles.

At lower speeds you get something akin to Newtonian gravity but at higher velocities you get something resembling MOND gravity where galaxies clusters and large voids appear - no dark matter needed.

https://www.youtube.com/watch?v=HKvc5yDhy_4

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

#195

Post by nitwit005 »

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.

But, think of all the fun math we get to do before someone shows it's an unworkable idea.

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

#196

Post by abetusk »

hcarvalhoalves wrote: post #170
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…

In other words, gravity would be explainable by statistical mechanics (like heat)?

That's the allure, that gravity is a derived effect from statistical mechanics. Thus the name 'entropic attraction'.

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

#197

Post by kgwgk »

floxy wrote: post #191
Gravityloss wrote: post #89

Earlier quoted context omitted.

Exactly. The coin flipping example is a very nice way to put it. It works since the coins are interchangeable, you just count the number of heads or tails. If the coins were of different color and you took that into account, then it wouldn't work. It's not intuitive to me what gravity has to do with entropy though, as it's classically just a force and completely reversible (unlike entropy)? Ie if you saw a video of u…

> Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed. How does that work with things like black holes? If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video? Even if you take account the gravitational waves?

If you saw a comet coming from the sun, or a meteorite coming from the moon, etc. you would also find that suspicious.

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

#198

Post by dudeinjapan »

franktankbank wrote: post #176
sim7c00 wrote: post #164

Earlier quoted context omitted.

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.

The same effect could be replicated in a zero-gravity environment using an alternative background force (centrifugal force, vacuum suction, electromagnetism, etc.)

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

#199

Post by abetusk »

FilosofumRex wrote: post #194
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…

This is a better YouTube video describing granular physics and shows the speed (amplitude) of vibrations can cause counterintuitive arrangements of particles. At lower speeds you get something akin to Newtonian gravity but at higher velocities you get something resembling MOND gravity where galaxies clusters and large voids appear - no dark matter needed. https://www.youtube.com/watch?v=HKvc5yDhy_4

Thanks for the link, very interesting. I'll have to check out the paper but just watching the video it seems all these counter intuitive effects can be described from the oscillations being related to the size of the chamber.

For example if I were to roll the chamber at a very low frequency, I would expect the particles to clump on one side, then the other and so on. This is not really so surprising and the frequency will depend on the chamber dimensions.

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

#200

Post by ThinkBeat »

omeysalvi wrote: post #7

"There’s some kind of gas or some thermal system out there that we can’t see directly" - The Ether is back on the menu boys

95% of the Universe is made up of dark matter and dark energy. These are words astronomers have come up with to give a name to the mysterious, invisible side of the Universe
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