Emergent Gravity and the Dark Universe

https://arxiv.org/abs/1611.02269

by mrreelmo • 10 years ago

209 80 10 years ago

arxiv.org

mrreelmo• 10 years ago

An explanation by the author: https://www.youtube.com/watch?v=ynRVnIh6wq4

supermatou• 10 years ago

Also, a simple explanation for the layman: http://www.alphagalileo.org/ViewItem.aspx?ItemId=169788&Cult...

freelancezombie• 10 years ago

Wow, contrast on that text... Fail.

nealabq• 10 years ago

Same text: http://phys.org/news/2016-11-theory-gravity-dark.html

geo101101• 10 years ago

Thanks for the layman link... I started reading and encountered a concept I didn't understand so I googled it. Then, I encountered another concept I didn't understand and google that, again and again, until I was several pages deep and only on the second sentence of the paper's description. TIL I don't know as much as I thought.

pmontra• 10 years ago

Thanks for the link (+1) but it's very far from being an explanation for the layman.

In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.

It doesn't explain how gravity emerges from bits of information. I'd love to understand how those bits make apples move from trees to the ground, the equivalence between gravity and acceleration and the weightless free fall experience. That should be one paragraph for the general principle and one for each example. Then it's for the layman, and me too :-)

aurora72• 10 years ago

Gravity might have a lot to do with the electro-magnetism force. I've written "electro" separately on purpose because gravity and electromagnetic force might fundamentally be the same forces caused by the same electrons. Remember both magnetic and gravity forces act vertically. The gravity might be just an EM force on the pull mode.

ajcarpy2005• 10 years ago

It's funny how scientists always reference time in relation to gravity and yet separate out gravity from other forces of motion when the implicate order would be to have gravity always playing a role in motion whatever the axis or motion of travel.

The other thing to know is that for a wave, there are more motions of travel than upon a triune 3-dimensional axis. The common thought process of a pondering individual is to simply add singular 3-dimensional particles to a 4, 5 or more dimensional time-space environment and try to peer into the behaviors of a hyperspatial-capable environment.

This is ridiculous because in a hyperspatial environment, so-called objects have a tendency to be in more of a wave-like state and even more-so than the waves of an ocean. These waves would be more like a fine-cotton tuft which is being pulled by electrostatic strands in multiple directions at once and wherein the "identities" of each may out of behavior dynamics be considered as singular with multiple locations because of a tendency to collapse at the same time or leave one the strongest through a matrix interconnections consisting of concepts of "Tensegrity." <wiki it.

Then you have photons which are thought to be low-mass or perhaps even zero or negative in mass. This seems to correlate nicely with their high-speed velocities.

In a Universe which has hyper-spatial dimensions not only overlaying reality but also underpinning it via multiple directions (like the gravity of multiple stars, planets, and moons affecting each planetary body), the hyper-spatial arenas would seem to be more elastic and able to slip and slide over and around the greater reality. Mystics and even scientists talk about these other dimensions as a deeper reality but it might be fair to take it with a grain of salt and see our current average reality as the "deeper reality."

So gravity is the "sums" of multiple affecting bodies. The datastreams coming in from the Sun, Moon, and other planets all affect life on Earth. The Moon mostly contributes to water while other elements likely have greater response to other planetary bodies, depending on their molecular and nuclear composition. (although this has not been published in the traditional manuscripts of current science)

Anyway, to answer the question in the way I think of it, gravity is related more closely to time than the way in which science usually connects time to gravity. Scientists usually act like a photon travels at the 299 792 458 m / s rate.

It would seem that whatever forces of information flow (entropy...and some would say proto-consciousness) are behind gravity - are also interrelated with time itself.

Here's the kicker. People assume everything falls to Earth. Why? Because most things do? What about balloons filled with Helium? What about light which reflects to the astronauts in space? What about the electrical currents flowing to the Sun and back in the chains of ions? How much mass is held in those ions?

And that's just talking "vertically" without reference towards the hyper-spatial dimensions which the common man has even less experience with - even though we are experiencing the interactions with these dimensions all the time.

Let me make an important note before I forget: Electromagnetic forces may very well be different enough from "gravity forces" to be differentiated but there may also certainly be some overlap at various scales or in high-voltage or highly-sophisticated quantum situations.

Whichever ways in which time is generated/observed/transmitted, both gravity and electromagnetic forces are bound to be related with the flow & effects. If information is practically as important as energy and gravity, how much information leaves Earth through light or ionic currents which flow to the Sun (or other stars?)

Also, to the person who also answered here and said electromagnetism can never be related with gravity, how do they imagine ions are moving through a wire or exchanged in an electrolyte solution of a battery or a hydrogen-production system? Again, to change the angle to "vertical" rather than horizontal is a weird way to classify an entirely different force.

Oh...as I was saying, :) it's all about the timing. In a coherent stream of information like a flow of photonic light or the flow of electrons in an electromagnetic current, the forces of motion are resistant to changes in the flow of time within their area of influence. Next move your attention to the heat we can "see" radiating from the smokestack of a semi tractor. This thermal emission is a form of energy which is slightly more disordered and "dispersed" than the kinds of "motion" we "see" elsewhere.

One would possible assume that if we get so close to Earth where we are essentially at "ground-level" and we allow the gravity well to exert its influence on an object, that the strong effect we see is because there is a very "unified" pull of forces. But this is just as false as if we get closer to a cable being weaved from dozens of smaller diameter threads. We begin 'seeing' the smaller threads are spread further apart as we change our perspective to a smaller and closer entity.

Why do we see water swirling different rotations into a drain on different places upon Earth? All to due with the nature of time, gravity, and space itself being shaped and molded by a force which is positional and situational and thus inherently "proto-conscious."

Link: Implicate Order: http://www.bizint.com/stoa_del_sol/plenum/plenum_3.html

justifier• 10 years ago

i think at the scale of a tree and an apple such insight would be a clear revolution stead essentially a whitepaper

but from the perspective of the paper i think this answers your initial question:

It doesn't explain how gravity emerges from bits of information.

resides on large scales, infored bu flattening of rotational curves, and entanglement entropy(o)

there is a known relation, inequality, between entanglement entropy, a subsequent of quantum information, and large scale gravitational considerations

should one interpret the relation as 'emergent' or 'coincidence' it would seem a viable avenue of investigation

from the paper:

1.3 Hints from observations: the missing mass problem
...The observed flattening of rotation curves, as well as many other observations of dark matter phenomena, indicate that they are controlled by the Hubble acceleration scale a0, as first pointed out by Milgrom...
...Consider a spherical region with boundary area A(r) = 4πr2 that contains matter with total mass M near its center...
...The appearance of the cosmological acceleration scale a0 in galactic dynamics is striking and gives a strong hint towards an explanation in terms of emergent gravity, as envisaged in [38].
To make this point more clear let us rewrite the above inequality as SM = 2πM/ha0 < A(r)/4Gh (1.4)
The quantity on the left hand side represents the change in the de Sitter entropy caused by adding the mass M, while the right hand side is the entropy of a black hole that would fit inside the region bounded by the area A.
Our goal is to give a theoretical explanation for why the emergent laws of gravity differ from those of general relativity precisely when the inequality (1.4) is obeyed.
We will find that this criterion is directly related to the presence of the volume law contribution to the entanglement entropy.
At scales much smaller than the Hubble radius gravity is in most situations well described by general relativity, because the entanglement entropy is still dominated by the area law of the vacuum.

that last quote seems to reference the apple

(o) https://en.wikipedia.org/wiki/Entropy_of_entanglement

hammock2• 10 years ago

Gravitons always struck me as a goofy half-baked concoction (even though we've supposedly observed them now), and so did dark matter. Emergent gravity theories are very interesting.

wbhart• 10 years ago

Observing gravitational waves is not really the same as observing individual gravitons. It's unlikely we can observe gravitons with any equipment we can actually build.

hammock2• 10 years ago

You are right, we have detected gravitational waves not gravitons. Thanks for clarifying

wanda• 10 years ago

even though we've supposedly observed [gravitons] now

Source? Or are you saying that the existence of gravitational waves constitute a proof of the existence of gravitons, due to wave/particle duality?

I'm not a physicist, but all I thought we had detected were gravitational waves.

TeMPOraL• 10 years ago

the existence of gravitational waves constitute a proof of the existence of gravitons, due to wave/particle duality

I always thought this is the case. But IANAP either. Could anyone with actual knowledge chime in?

maverick_iceman3• 10 years ago

Gravitons are simply quanta of gravitational waves. They arise in the same way as photons in electromagnetism. There's nothing goofy about them.

theptip• 10 years ago

Goofy in what way? All other known forces are carried by particles, so why not gravity?

raattgift3• 10 years ago

Gravitons appear in several different families of theory.

We have not observed any of them; the interaction cross-section is so small (because gravity is so weak) that we have no hope of observing a single graviton, or failing to observe an expected one, any time soon.

Gravitational waves have spin 2 symmetry and are massless. A straightforward quantization of a gravitational wave leads to gravitons as a spin 2 massless gauge boson. Conversely, in almost any gauge theory that admits a massless spin 2 particle, that particle mediates a force almost exactly like gravitation, and is amenable to analysis under the Paramaterized Post-Newtonian Formalism.

Indeed, when gravity is weak, such theories essentially exactly reproduce General Relativity. It's only in strong gravity that non-negligible differences appear, and in this case strong gravity is when the quantum uncertainty in curvature distorts distances in ways that can't be worked around e.g by a change of basis or system of coordinates. Alternatively, gravity is strong when you have multiple loops of gravitons in a Feynman diagram.

So in the type of quantization above, the problem is that the momentum carried by an individual graviton is much much much much smaller than that carried by an individual low frequency photon. For example, a near-infrared photon has a momentum-energy on the order of about 1 eV/c^2, a 100 MHz photon has an energy on the order of 10^-7 eV/c^2, and a graviton will be less than 10^-22 eV/c^2 (LIGO collab., https://arxiv.org/abs/1602.03837, about six paragraphs before section VIII).

In other words, even the extremely weak signals LIGO's detected represent waves comprising huuuuuuge numbers of gravitons. But each graviton is so weak (or equilvalent long-wavelengthed) that we have no hope of detecting it individually. Think of how much fun you would have trying to isolate with your fingers an individual molecule of water in a surfers-beware ocean wave -- that'd be easier than isolating a graviton from a presently-detectable GW.

auntienomen• 10 years ago

Gravitons are basically unavoidable. They may not be fundamental particles, but they'll always show up in the long-wavelength approximation of any theory of quantum gravity that extends general relativity.

eloff• 10 years ago

I love this, it feels cleaner and more elegant a solution than dark matter particles. However, nature doesn't care what we like, so that doesn't make it more likely to be true.

eli_gottlieb3• 10 years ago

I agree that it sounds elegant, especially since it puts entropy/information into the core ontology so as to explain the arrow of time and thermodynamic behavior as part of the same theory that can account for Einsteinian space-time.

I just wish I understood enough physics to tell this paper from elegant-sounding word salad!

Avshalom• 10 years ago

Dark matter is hilariously clean.

It's literally just

"Hey you know how there's like a bunch of particles that don't interact with EM forces?"

"Yeah"

"Well what if there's like a BUNCH of particles that don't interact with EM forces?"

"...oh hey that makes this math way easier"

mrfusion• 10 years ago

Like others have mentioned I'm not sure what happens now to the gravity waves we've detected.

ars8• 10 years ago

I'm not convinced we have in fact detected gravity waves. From our point of view merging black holes would not move due to time dilation, but the waves detected are modeled after black holes without time dilation.

Although it's possible we detected a wave from a different source, not a black hole.

empath753• 10 years ago

While we can never see them merging completely, we can see them asymptotically approach a merger, which does in fact take about 1/5th of a second to get most of the way there.

jpm_sd• 10 years ago

I'm currently reading The Confusion [0] and just got through Leibniz's explanation of monadology [1][2]. Summarized very very briefly, the idea is that every particle in the universe is a sort of computational device, and their actions/reactions are determined by their "perception" of all the other particles in the universe.

Does this research suggest that he may have been semi-correct??

[0] https://en.wikipedia.org/wiki/The_Confusion [1] https://en.wikipedia.org/wiki/Monadology [2] https://quantummoxie.wordpress.com/2014/09/09/neal-stephenso...

tpeo2• 10 years ago

Frankly, I'd be surprised if anything ever suggested that Leibniz's colorful metaphysics was correct, even or incorrect.

Leibnizian monads are unextended and unable to act on one another (from §1 and §7 of the Monadology), which is to say that they're non-physical. On the other hand, as they're somehow supposed each to have a complete picture to the world (§56), they imply some form of non-locality. Which is to say that they're some very spooky things.

The thing that comes closest to Leibniz's monadology is the idea that the world is a simulation running inside a computer. But Leibniz's idea was more like that there is an arbitrarily large number of computers running the same simulation, while some of them also run artificial intelligences which just watch the simulation unfold.

Which is an idea I think can be fairly described as "completely nuts".

wcoenen• 10 years ago

But Leibniz's idea was more like that there is an arbitrarily large number of computers running the same simulation, while some of them also run artificial intelligences which just watch the simulation unfold.

I think this was just Leibniz awkward attempt at explaining modal realism. The idea of many possible worlds is much more mainstream now in physics, so I wouldn't call it "completely nuts".

cshreve• 10 years ago

So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe. However, is it just me or does the falsification of this seem a bit sketchy: if we find a dark matter particle...then my theory is false. That's a bit like saying...oh yeah if we find a different way to unify general relativity and quantum mechanics...then String Theory is false. It seems like there should be a 'smaller' way to falsify it.

jcoffland• 10 years ago

I think you will find all the models are false to a degree. A model is only an approximation of the real thing. Quantum mechanics and General relatively cannot both be right. The obvious answer is that they are both wrong.

duaneb• 10 years ago

Isn't that just relativistic quantum field theory?

zamalek• 10 years ago

A thought experiment of mine.

Assume that all possible hypothesis or theories (explanations in general) form part of an "explanation space." Some explanations are good (theories), some have no evidence (hypothesis) and some are false (we are riding a giant turtle). Given the number of false explanations, the overall space is infinite. Hypothesis spaces would be islands within the false explanation space, theories islands within hypothesis and the truth as a single point within one of those theory spaces.

The question is, does that mean that the theory space is infinite? If so, that would mean that it would be impossible to know that we've found the truth (as a single point within this infinite space) - we'd only ever be able to conclude that we've found a closer approximation. Scientists may never run out of work.

maikb• 10 years ago

Remember that these people use a language that might sound similar to common english, but words have different meaning and it is much more precise. No reading between the lines.

He gave an example of what would falsify his theory, that is all.

npgatech• 10 years ago

"So I too love the idea that we don't need dark matter to explain all the gravitational effects we observe in the universe."

It is an attempt to explain. Just like an attempt to explain (prediction) of Higgs Boson. It was only true once we observed it via experimentation.

Falsification makes sense if the theory has been experimentally validated. You can't falsify something that has not been proven.

There is no one claiming String theory or the theory discussed here is true - no experimental evidence has been produced.

slowmovintarget• 10 years ago

In the summary, it says that these theories are "best understood in Anti de Sitter space...". I thought current observations ran against a spacetime that had a negative curvature. Are they just saying the math is easier in that geometry, but that it still applies to flat (or ever-so-slightly-positively curved) spacetime? Or are they arguing in favor of a "saddle-shaped" universe?

empath753• 10 years ago

The ADS in 'ADS/CFT correspondence' stands for 'anti-de Sitter'. Any time you read someone talking about 'information on the boundary' of a bulk space, that's usually what they're working with.

I'm sure there's a way to transform everything to a de Sitter space, but i'm neither a mathematician nor a physicist, so I don't know how it's done...

maverick_iceman3• 10 years ago

Spacetime has a positive cosmological constant, so it's closer to de-Sitter than Anti de-Sitter. It doesn't really have to do with curvature exactly, which is given by the Riemann tensor (so it doesn't make sense to say it's positive/negative).

codethief3• 10 years ago

But you certainly can talk about curvature scalars being positive/negative which are derived from the Riemann tensor.

slicktux• 10 years ago

https://news.ycombinator.com/item?id=12526559

ilostmykeys• 10 years ago

How about Dark Meat? I like Dark Meat.

plank• 10 years ago

Discussion in Dutch: http://www.volkskrant.nl/wetenschap/ineens-klopt-het-univers...

rudolf0• 10 years ago

To what degree does this contradict Einstein's theory of gravity?

teilo• 10 years ago

It does not contradict Einstein's theory of gravity, just as Einstein did not contradict Newton. All three are different models explaining progressively more thorough levels of observation.

Don't think of a theory so much as "what is true" but rather as a set of propositions and equations which are designed to model the way physical processes are observed to occur.

Theories exist within their own provenance of observation. Both Einstein and Newton's theories reflect reality within certain limits, but outside those limits they do not. To allow Einstein's theory to apply at larger scales, we proposed dark matter because Einstein could not account for the behavior of galaxies unless there was some hidden element involved. Thus we proposed dark matter. It is a reasonable accommodation, but one that has defied confirmation.

The emergent theory embraces both Newton and Einstein, eliminates any need for dark matter, and attempts to explain all current observations within a single framework.

Einstein's theory made testable predictions which were later proven to be true. The emergent theory lacks such confirmation, and so time will tell whether it reflects reality.

eli_gottlieb3• 10 years ago

Einstein's theory made testable predictions which were later proven to be true. The emergent theory lacks such confirmation, and so time will tell whether it reflects reality.

The author claims to be making a few novel predictions which, he claims, astronomers can go check. He also retrodicts several things we observe, though I'm not enough of a physicist to say if he's using a simple enough model for that to be interesting.

nedsma• 10 years ago

How does the theory explain unaccountable 96% of the universe which we cannot observe/detect? Is there a thing such as antibaryonic matter?

323454• 10 years ago

The central idea of this paper is that the volume law contribution to the entanglement entropy, associated with the positive dark energy, turns the otherwise “stiff” geometry of spacetime into an elastic medium. We find that the elastic response of this ‘dark energy’ medium takes the form of an extra ‘dark’ gravitational force that appears to be due to ‘dark matter’.

novalis78• 10 years ago

Does this in any way match with Lipinski's gravity discussion (http://adsabs.harvard.edu/abs/2008AcPPB..39.2823L) that was mentioned here just recently (unifiedgravity.com)?

zmanian• 10 years ago

Does entropic gravity explain the lensing phenomenon attributed to dark matter?

benibela• 10 years ago

I do not understand this stuff, but the connection between gravity and horizont sounds like this [quantized acceleration theory](http://physicsfromtheedge.blogspot.de/)

MrQuincle• 10 years ago

There seems to be considerable disagreement in the field. Why is it news (I really would like to know!)?

+ Kobakhidze explaining neutron experiments: https://arxiv.org/abs/1108.4161

+ http://physics.stackexchange.com/questions/4289/is-gravity-a...

+ Lubos Motl: http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-c... and http://motls.blogspot.nl/2010/01/erik-verlinde-comments-abou...

It's nice to see that also experts in these highly specified fields quarrel about what it means to be "entropic" and "irreversible", etc.

taliesinb• 10 years ago

If you're wondering how this isn't some weird form of MOND, which is basically dead as an explanation, here's an important paragraph from the paper:

We like to emphasize that we have not derived the theory of modified Newtonian dynamics as proposed by Milgrom. In our description there is no modification of the law of inertia, nor is our result (7.43) to be interpreted as a modified gravitational field equation. It is derived from an estimate of an effect induced by the displacement of the free energy of the underlying microscopic state of de Sitter space due to matter. This elastic response is then reformulated as an estimate of the gravitational self-energy due to the apparent dark matter in the form of the integral relation (7.40). Hence, although we derived the same relation as modified Newtonian dynamics, the physics is very different. For this reason we referred to the relation (7.43) as a fitting formula, since it is important to make a clear separation between an empirical relation and a proposed law of nature. There is little dispute about the observed scaling relation (7.43), but the disagreement in the scientific community has mainly been about whether it represents a new law of physics. In our description it does not.

spynxic• 10 years ago

Imagining gravitational waves inevitably leads me to believe that gravity is a force that varies (in a cycle) over spacetime. But.. what exactly does it mean to propagate over a cycle in spacetime? (particularly the time aspect confuses me since something propagating in space remains constant in time (either accelerating or decelerating)

mcbits• 10 years ago

According to the holographic principle, all the information in the entire universe can be described on a giant imaginary sphere around it. Verlinde now shows that this idea is not quite correct: part of the information in our universe is contained in space itself.

I thought the holographic principle just said the amount of information in any physical structure (up to the whole universe) was such that it could fit on a 2D surface the size of the event horizon of the structure, not that it actually is contained on the surface. Does this theory change that?

autocorr• 10 years ago

There is a great deal of observational evidence favoring Lambda-Cold-Dark-Matter, ie the status quo of cosmology with dark matter. The bullet cluster [1] is evidence for two colliding galaxy clusters where the luminous matter ran into itself but the dark matter kept going. The total mass (luminous plus dark) can be mapped out with the gravitational lensing of background galaxies and can be done very accurately. This was essentially the nail in the coffin for the leading alternative theory modified newtonian dynamics (MOND).

Dark matter is so deeply embedded into cosmology and modern astrophysics, you would have to explain a host of solidly observed phenomena to be a compelling alternative (baryon acoustic oscillations, the cosmic microwave background, primordial abundances, the evolution of structure or the "cosmic web"). Comparing to those things would probably take man-decades of work and also require computationally expensive cosmological simulations on super computers, so I'm skeptical we will see the kind of theoretical/observational comparison that would make you sit up and take notice.

[1] https://en.wikipedia.org/wiki/Bullet_Cluster

zer0gravity• 10 years ago

I think it helps a lot to try to understand the universe from an engineering perspective, thus by posing the question "How would I build a universe?" The apparent obvious answer is : as an N dimensional matrix where each cell executes some code.

With such a setup, effects like gravity, are more probable to be emergent effects.

Another consideration is that in such a setup the only thing that matters is the state of the matrix, in other words there is no time, just iterations.

So my 2 cents are: gravity should be explained as an emergent phenomenon, and time should be removed from all equations that try to explain the underlying fabric of reality.

Emergent Gravity and the Dark Universe

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