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Emergent Gravity and the Dark Universe
- deleted 10y ago[deleted]
- mrreelmo 10y agoAn explanation by the author: https://www.youtube.com/watch?v=ynRVnIh6wq4 https://www.youtube.com/watch?v=ynRVnIh6wq4
- ghgfhgfhn 10y agoI need to go and find all the reddit threads where I argued for this case and treated like a loon.
- supermatou 10y agoAlso, a simple explanation for the layman: http://www.alphagalileo.org/ViewItem.aspx?ItemId=169788&CultureCode=en http://www.alphagalileo.org/ViewItem.aspx?ItemId=169788&Cult...
- freelancezombie 10y agoWow, contrast on that text... Fail.
- nealabq 10y agoSame text: http://phys.org/news/2016-11-theory-gravity-dark.html http://phys.org/news/2016-11-theory-gravity-dark.html
- geo101101 10y agoThanks 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 10y agoThanks 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 10y agoGravity 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.
- M_Grey 10y agoNot even remotely the case, although I'd be fascinated to see where you got this notion from.
- SomeStupidPoint 10y agoI mean, one could argue that perhaps EM is really a special kind of gravitational ripple (eg, geons might work out in quantum gravity to model electrons and photons, and then the question arises that if all EM is gravity induced and modeled, is EM not part of gravity?), but I don't know that I've heard it the other way. It's also certainly not the mainstream view, as classical geons are extremely unstable.
- M_Grey 10y agoI'm not sure how EM and Gravity could be unified as a single force, especially since the best theory of gravity that's out there describes gravity as curvature in spacetime, not a force.
- hammock 10y agoGravitons 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 10y agoObserving 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.
- hammock 10y agoYou are right, we have detected gravitational waves not gravitons. Thanks for clarifying
- wanda 10y 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.
- deleted 10y ago[deleted]
- TeMPOraL 10y 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?
- ars 10y agoNo, a gravitational wave has mass (carries mass is more accurate), but a graviton does not. They are not two aspects of the same thing.
- eloff 10y agoI 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_gottlieb 10y agoI 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 10y agoDark 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 10y agoLike others have mentioned I'm not sure what happens now to the gravity waves we've detected.
- ars 10y agoI'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.
- empath75 10y agoWhile 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 10y agoI'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 https://en.wikipedia.org/wiki/The_Confusion [1] https://en.wikipedia.org/wiki/Monadology https://en.wikipedia.org/wiki/Monadology [2] https://quantummoxie.wordpress.com/2014/09/09/neal-stephenson-on-leibniz-monads-and-more/ https://quantummoxie.wordpress.com/2014/09/09/neal-stephenso...
- tpeo 10y agoFrankly, 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 10y 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".
- tpeo 10y agoI wasn't previously acquainted with the term "modal realism" (been avoiding contemporary philosophy for a while now), but there doesn't seem to be an immediate connection in this case. There aren't actually many worlds being simulated here, as each computer simulates the same world and they all get the same results. Leibniz does introduce the idea of many possible worlds (§53), but as a set of designs for this whole thing (computers plus the stuff running inside them) from which God draws one particular design to be the actual world. He might be closer to modal realists in other regards, though. I don't know.
- cshreve 10y agoSo 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 10y agoI 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 10y agoIsn't that just relativistic quantum field theory?
- baq 10y agothat's the thing, gravity from GR doesn't quantize well, or actually at all.
- raattgift 10y agoEinstein gravity quantizes remarkably well in the weak field limit; it's called perturbative quantum gravity, and is considered (with good reason) a sound effective field theory (in the Kenneth G Wilson sense of "effective"). One of the results of perturbative quantization is the discovery of the non-renormalization -- by power-set counting -- of gravity and why (very roughly and simply, it's because gravity is a long-range and self-interacting force). However, this only matters in systems where you would need to use Feynman diagrams involving multiple loops of gravitons, which essentially defines strong gravity, and you'll only find that well inside the event horizons of black holes, or in the extremely early big bang universe. Outside the strong gravity limit, perturbative quantization of Einstein gravity exactly corresponds with General Relativity, as indeed any theory seeking to extend or replace General Relativity pretty well must (since GR accords with so much observational and experimental evidence). There is also little reason to expect that we will never arrive at methods other than power-set counting to deal with the explosion of variables in many-loop systems, although that in itself should not preclude investment in other quantum gravity programmes that are very different.
- slowmovintarget 10y agoIn 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?
- empath75 10y agoThe 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_iceman 10y agoSpacetime 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).
- codethief 10y agoBut you certainly can talk about curvature scalars being positive/negative which are derived from the Riemann tensor.
- slicktux 10y agohttps://news.ycombinator.com/item?id=12526559 https://news.ycombinator.com/item?id=12526559
- ilostmykeys 10y agoHow about Dark Meat? I like Dark Meat.
- plank 10y agoDiscussion in Dutch: http://www.volkskrant.nl/wetenschap/ineens-klopt-het-universum-zwaartekrachttheorie-erik-verlinde-in-zes-lekenvragen~a4411221/ http://www.volkskrant.nl/wetenschap/ineens-klopt-het-univers...
- rudolf0 10y agoTo what degree does this contradict Einstein's theory of gravity?
- teilo 10y agoIt 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_gottlieb 10y 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.
- deleted 10y ago[deleted]
- nedsma 10y agoHow does the theory explain unaccountable 96% of the universe which we cannot observe/detect? Is there a thing such as antibaryonic matter?
- 323454 10y 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 10y agoDoes this in any way match with Lipinski's gravity discussion (http://adsabs.harvard.edu/abs/2008AcPPB..39.2823L http://adsabs.harvard.edu/abs/2008AcPPB..39.2823L) that was mentioned here just recently (unifiedgravity.com)?
- zmanian 10y agoDoes entropic gravity explain the lensing phenomenon attributed to dark matter?
- benibela 10y agoI do not understand this stuff, but the connection between gravity and horizont sounds like this [quantized acceleration theory](http://physicsfromtheedge.blogspot.de/ http://physicsfromtheedge.blogspot.de/)
- MrQuincle 10y agoThere 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 https://arxiv.org/abs/1108.4161 + http://physics.stackexchange.com/questions/4289/is-gravity-an-entropic-force-after-all http://physics.stackexchange.com/questions/4289/is-gravity-a... + Lubos Motl: http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-cant-be.html http://motls.blogspot.nl/2010/01/erik-verlinde-why-gravity-c... and http://motls.blogspot.nl/2010/01/erik-verlinde-comments-about-entropic.html 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 10y agoIf 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 10y agoImagining 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 10y 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 10y agoThere 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 https://en.wikipedia.org/wiki/Bullet_Cluster
- zer0gravity 10y agoI 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.