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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

#91

Post by flufluflufluffy »

meindnoch wrote: post #49
prof-dr-ir wrote: post #36

Earlier quoted context omitted.

Good question. You are absolutely right that entropy is always fundamentally a way to describe are our lack of perfect knowledge of the system [0]. Nevertheless there is a distinct "reality" to entropic forces, in the sense that it is something that can actually be measured in the lab. If you are not convinced then you can look at: https://en.wikipedia.org/wiki/Entropic_force and in particular the example that is alw…

Sure, I'm not denying that entropy exists as a concept, that can be used to explain things macroscopically. But like you said, it's origins are statistical. To me, temperature is also a similar "made up" concept. We can only talk about temperature, because a sufficiently large group of particles will converge to a single-parameter distribution with their velocities. A single particle in isolation doesn't have a tempe…

Yes, exactly. The model is based on (in the first approach) a “lattice” of some type of undiscovered particle-like thing (what they refer to as “qubits” in the article, which is unfortunate because it is NOT the same “qubit” from quantum computing) permeating space time. Or maybe more aptly, it is that lattice from which spacetime emerges. And what we observe as the force of gravity emerges from the entropic forces happening in this lattice.

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

#92

Post by cwharris »

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.

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

#93

Post by bavell »

hackinthebochs wrote: post #85
sat_solver wrote: post #69

Earlier quoted context omitted.

You're thinking of information entropy, which is not the same concept as entropy in physics. An ice cube in a warm room can be described using a minimum description length as "ice cube in a warm room" (or a crystal structure inside a fluid space), but if you wait until the heat death of the universe, you just have "a warm room" (a smooth fluid space), which will have an even shorter mdl. Von Neuman should never have…

Maxwell's demon thought experiment implies they are the same concept. Given a complete knowledge of every particle of gas you can in principle create unphysical low entropy distributions of the particles. This[1] goes into more detail. [1] https://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_...

A fun visual explanation: https://youtu.be/8Uilw9t-syQ?si=D9sR2YAm40SPFG3a

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

#94

Post by IAmBroom »

aurareturn wrote: post #58
logicchains wrote: post #22

Earlier quoted context omitted.

Entropy isn't a function of imperfect knowledge. It's a function of the possible states of a system and their probability distributions. Quantum mechanics assumes, as the name implies, that reality at the smallest level can be quantised, so it's completely appropriate to apply entropy to describing things at the microscopic scale.

If we knew the exact state of all particles in an enclosed system, we can calculate what future states will be exactly. No need to calculate possible states.

Since that's not possible in any physical system of one or more particles, it's irrelevant.

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

#95

Post by IAmBroom »

brador wrote: post #42

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.

Vacuums don't suck; high pressure repels.

Similarly, umbrellas aren't places to stand under when it's not raining.

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

#96

Post by [deleted] »

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…

[deleted]

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

#97

Post by westurner »

lewdwig wrote: post #71
JPLeRouzic wrote: post #68

Earlier quoted context omitted.

Please, how is the article related to MOND's theories?

In general, they’re not. But if the only thing emergent theories predict is Newtonian dynamics and General Relativity then that’s a big problem for falsifiability. But if they modify Newtonian dynamics in some way, then do we have something to test.

From https://news.ycombinator.com/item?id=43738580 :

> FWIU this Superfluid Quantum Gravity [SQG, or SQR Superfluid Quantum Relativity] rejects dark matter and/or negative mass in favor of supervaucuous supervacuum, but I don't think it attempts to predict other phases and interactions like Dark fluid theory?

From https://news.ycombinator.com/item?id=43310933 re: second sound:

> - [ ] Models fluidic attractor systems

> - [ ] Models superfluids [BEC: Bose-Einstein Condensates]

> - [ ] Models n-body gravity in fluidic systems

> - [ ] Models retrocausality

From https://news.ycombinator.com/context?id=38061551 :

> A unified model must: differ from classical mechanics where observational results don't match classical predictions, describe superfluid 3Helium in a beaker, describe gravity in Bose-Einstein condensate superfluids , describe conductivity in superconductors and dielectrics, not introduce unoobserved "annihilation", explain how helicopters have lift, describe quantum locking, describe paths through fluids and gravity, predict n-body gravity experiments on earth in fluids with Bernoulli's and in space, [...]

> What else must a unified model of gravity and other forces predict with low error?

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

#98

Post by bravesoul2 »

MaxikCZ wrote: post #21
bravesoul2 wrote: post #9

Earlier quoted context omitted.

> particle B will have a slightly higher statistical chance of randomly jumping closer to it, Why? Also how do you explain acceleration due to gravity with that model. How do you explain solid objects?

My guess would be the answer is right in the part before you quote? If theres more "space" (imagining more space coordinates possible) for me on the left than on the right, me jumping to a random location would statistically move me left. Repeating results in movement, getting closer to the object intensifies this effect, results in acceleration. Solid objects are products of electric charge preventing atoms/particle…

I don't understand the more space thing then. Is this more space due to spacetime curvature or something else.

E.g. if we have earth and moon:

    O   o
Why is there more space from the moon towards earth than away?

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

#99

Post by gus_massa »

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, "…

> 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,

I agree.

> and that the global and exquisitly weak force of gravity emerges from that theory as a sort of accounting error.

Nah, it's probably just another weird family of bosons, just like the other forces.

From the article:

> Entropic gravity is very much a minority view. But it’s one that won’t die, and even detractors are loath to dismiss it altogether.

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

#100

Post by kgwgk »

tsimionescu wrote: post #83
kgwgk wrote: post #74

Earlier quoted context omitted.

The same microstate will have different probabilities depending on what are the constraints or measurements used in _your_ description of the system. If you choose to describe the system using its microstate - and you know it - there are no probabilities anywhere. You can of course know something and choose to ignore it - the entropy is still a reflection of the uncertainty (actual or for the sake of a lower-resoluti…

But the point is that, regardless of how you choose to describe or even measure the system, it will need exactly as much heat to raise its temperature by 1 degree (or it will need as much kinetic energy to increase the average velocity of the constituents by the same amount, in the microstate framework). So there is some objective nature to entropy, it's not merely a function of subjective knowledge of a system. Or,…

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 experimental constraints and measurements.

If we relate entropy to work that can be extracted someone with a better understanding of the state of the system and operational access to additional degrees of freedom can extract additional work.

Thermodynamics assumes the state variables provide a complete description of the system. Statistical mechanics assumes the state variables provide an incomplete description of the system - and work out what that entails.

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