from Hacker News

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

by pseudolus on 6/16/25, 12:36 AM with 284 comments

• by abetusk on 6/16/25, 3:48 PM

  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 which gets filled in with peanuts.

  For entropic gravity, the idea is that there's a base density of something (particles? sub-atomic particles?) hitting objects in random ways from all directions. When two large massive objects get near each other, their middle region will have lower density thus being attracted to each other from particles hit with less frequency from the lower density region. They sort of cast a "shadow".

  I'm no physicist but last time I looked into it there were assumptions about the density of whatever particle was "hitting" larger massive objects and that density was hard to justify. Would love to hear about someone more knowledgeable than myself that can correct or enlighten me.

  As an aside, the brazil nut effect is a very real effect. To get the raisins, you shake the raisin bran. To get gifts left from your cat, you shake the kitty litter. It works surprisingly well.

  [0] https://en.wikipedia.org/wiki/Granular_convection

  [1] https://www.youtube.com/watch?v=Incnv2CfGGM

• by MathMonkeyMan on 6/16/25, 7:45 AM

  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, "look, Einstein's field equations."

• by pif on 6/16/25, 9:32 AM

  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.

• by meindnoch on 6/16/25, 8:18 AM

  I don't get it.

  To me, entropy is not a physical thing, but a measure of our imperfect knowledge about a system. We can only measure the bulk properties of matter, so we've made up a number to quantify how imperfect the bulk properties describe the true microscopic state of the system. But if we had the ability to zoom into the microscopic level, entropy would make no sense.

  So I don't see how gravity or any other fundamental physical interaction could follow from entropy. It's a made-up thing by humans.

• by fnordpiglet on 6/17/25, 4:18 AM

  I’ve been a believer in entropic gravity for a long time and believe it’s due to quantum foam. In a region of space with nothing in it the quantum foam in that space would be perfectly uniformly random. With mass and energy the state of the space would be biased and less random. This creates an entropic gradient. Further this doesn’t just explain gravity but explains why the space between galaxies seems to demonstrate negative energy and space expansion. I’m glad to see more research into the idea of entropic gravity as it’s IMO a more reasonable explanation than most other gravity theories I’ve heard.

• by dist-epoch on 6/16/25, 7:28 AM

  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" as the Sun formed.

  EDIT: not sure why this is downvoted, is the explanation Nobel Physics laureate Roger Penrose gives: https://g.co/gemini/share/bd9a55da02b6

• by Caelus9 on 6/16/25, 2:50 PM

  It's a fascinating idea that gravity could be an emergent result of how information works in the universe. I feel like we still don't have that clear piece of evidence where this model predicts something different from general relativity. For now it is one of those theories that are fun to explore but still hard to fully accept.

• by bawana on 6/17/25, 12:06 AM

  the statistical mechanical definition of entropy relies on the number of possible arrangements of particles in a system. In a closed system entropy approaches an equilibrium which has been sensationally described as the 'heat death of the universe'. But since we know our universe is expanding, the number of possible arrangements is also increasing so entropy may never reach equilibrium. If the universe is expanding faster than its components redistribute, then entropy could be decreasing. With this in mind, any theory involving entropy as a component of gravity would suggest a changing gravity over time

• by uticus on 6/18/25, 2:54 PM

  really enjoyed this article from a few years ago. looks like the domain is no longer active but the content is a good intro and most of the external links still work

  https://web.archive.org/web/20211215122133/https://an0maly.c...

• by the__alchemist on 6/17/25, 12:53 PM

  This effect reminds me of the "hydrophobic interactions" used when modelling biological systems. E.g. The tendency for hydrophobic residudes to be on the inside of a protein.

• by raindeer2 on 6/16/25, 5:54 PM

  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

• by deadbabe on 6/16/25, 3:33 PM

  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?

• by hoseja on 6/16/25, 8:17 AM

  Like some sort of buoyancy?

• by colanderman on 6/16/25, 6:09 PM

  See also: emergent fox-treasure gravity in Skyrim: https://www.eurogamer.net/skyrims-myth-of-the-treasure-fox-f...

  TLDR: areas around treasure have higher entropy by a measure relevant primarily to stochastic movement of foxes. Since there are thus on average more ways for a fox to walk toward treasure than away, they tend to gravitate toward treasure.

• by fourthark on 6/16/25, 4:19 PM

  > "The ontology of all of this is nebulous"

• by MintNow on 6/17/25, 6:43 AM

  nice product

• by omeysalvi on 6/16/25, 7:50 AM

  "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

• by metalman on 6/16/25, 8:41 AM

  gravity=time

• by amai on 6/16/25, 5:08 PM

  So entropy can curve spacetime? My fridge locally lowers entropy, does that mean inside my fridge gravity is lower than outside?

• by almosthere on 6/17/25, 12:17 AM

  I think it's magnetism. Been saying this for years. Mostly non-aligned fields, the net effect leans just slightly towards a pull.

• by brador on 6/16/25, 9:42 AM

  Anti matter is created and repulsed and expelled, leaving a vacuum, things get sucked into that vacuum, creating the illusion of gravity, that’s my novel theory.

• by cwharris on 6/16/25, 12:45 PM

  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 — maybe coherence, resonance, or field attraction. But “just entropy”? That doesn’t explain formation. It explains dissolution.

• by john_moscow on 6/16/25, 7:13 AM

  Space exists around things with mass. Also, above-absolute-zero temperatures cause particles to jump around randomly.

  Now if there is "more space" around particle A, particle B will have a slightly higher statistical chance of randomly jumping closer to it, than farther.

  Rinse-repeat. Gravity as we know it.

• by neuroelectron on 6/16/25, 2:06 PM

  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 question remains though, what is this density made of since gravity exists in a vacuum? Quantum fluctuations popping in and out of reality? Does this infer that quantum fluctuations are affected by mass as well? It would seem so since in Bose Einstein Condensate, what is "communicating" the state across the BEC if the particles are no longer interacting?