Theoretical physicist Eric Verlinde has finally published his much anticipated article on the nature of gravity. In a 2010 New York Times article Verlinde already stated: gravity is an illusion. His theory goes beyond the concept of gravity as envisioned by both Isaac Newton and Albert Einstein. It will be very interesting to see other scientists sink their teeth into this.
Abstract of his article:
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional 'dark' gravitational force describing the 'elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional 'dark gravity force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Heck, I'm not even going to pretend I grok any of this: I shine shoes for a living and just hope that my understanding of gravity-as-we-know-it is sufficient to catch the coins customers drop into my weary hand.
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A physicist is using a theory he advanced to explain how EmDrive could work to explain how dwarf galaxies can be held together without the requirement of dark matter:
British physicist Dr Mike McCulloch, who previously used quantised inertia to explain how the controversial electromagnetic space propulsion technology EmDrive works, says that he has new evidence showing his theory can also explain galaxy rotation, which is one of physics' biggest mysteries. McCulloch, a lecturer in geomatics at Plymouth University's school of marine science and engineering, says he now has even more evidence that his "new physics theory" about quantised inertia works, and that it makes it possible to explain why galaxies are not ripped apart without using theory of dark matter.
[...] There are 20 dwarf galaxies in existence from Segue-1 (the smallest) to Canes Venatici-1 (the largest), and dark matter is only meant to work by spreading out across a wide distance, but it is still used to explain dwarf galaxies, even though this requires dark matter to be concentrated within these systems, which is implausible. Instead, McCulloch asserts that quantised inertia can be used to explain how galaxies rotate without using dark matter, and he has written a paper that has been accepted by the bi-monthly peer reviewed journal Astrophysics and Space Science.
Reprint of the IBT link here.
From the abstract of Low-acceleration dwarf galaxies as tests of quantised inertia (DOI not yet published):
Dwarf satellite galaxies of the Milky Way appear to be gravitationally bound, but their stars' orbital motion seems too fast to allow this given their visible mass. This is akin to the larger-scale galaxy rotation problem. In this paper, a modification of inertia called quantised inertia or MiHsC (Modied inertia due to a Hubble-scale Casimir effect) which correctly predicts larger galaxy rotations without dark matter is tested on eleven dwarf satellite galaxies of the Milky Way, for which mass and velocity data are available. Quantised inertia slightly outperforms MoND (Modied Newtonian Dynamics) in predicting the velocity dispersion of these systems, and has the fundamental advantage over MoND that it does not need an adjustable parameter.
Previously: Study Casts Doubt on Cosmic Acceleration and Dark Energy
Dark Matter Beats its Latest Challenge
Emergent Gravity and the Dark Universe
Space Race 2.0: China May Already be Testing an EmDrive in Orbit
Milky Way is Not Only Being Pulled—It's Also "Pushed" by a Void
The dominant Lambda-CDM model is the standard model of physical cosmology, and it has proved reasonably successful. It does, however, have problems, such as dark matter, whose true nature remains elusive. Dutch physicist Erik Verlinde has, in a recent paper, proposed that gravity might not actually be a fundamental interaction at all, but rather an emergent property of spacetime itself, and as such, what current cosmological theory considers dark matter is really an emergent gravity phenomenon. Sabine Hossenfelder has an article about several recent tests of Verlinde's theory, which show that the idea might have promise.
Physicists today describe the gravitational interaction through Einstein's Theory of General Relativity, which dictates the effects of gravity are due to the curvature of space-time. But it's already been 20 years since Ted Jacobson demonstrated that General Relativity resembles thermodynamics, which is a framework to describe how very large numbers of individual, constituent particles behave. Since then, physicists have tried to figure out whether this similarity is a formal coincidence or hints at a deeper truth: that space-time is made of small elements whose collective motion gives rise to the force we call gravity. In this case, gravity would not be a truly fundamental phenomenon, but an emergent one.
[...] Verlinde pointed out that emergent gravity in a universe with a positive cosmological constant – like the one we live in – would only approximately reproduce General Relativity. The microscopic constituents of space-time, Verlinde claims, also react to the presence of matter in a way that General Relativity does not capture: they push inwards on matter. This creates an effect similar to that ascribed to particle dark matter, which pulls normal matter in by its gravitational attraction.
[...] So, it's a promising idea and it has recently been put to test in a number of papers.
[...] Another paper that appeared two weeks ago tested the predictions from Verlinde's model against the rotation curves of a sample of 152 galaxies. Emergent gravity gets away with being barely compatible with the data – it systematically results in too high an acceleration to explain the observations.
A trio of other papers show that Verlinde's model is broadly speaking compatible with the data, though it doesn't particularly excel at anything or explain anything novel.
[...] The real challenge for emergent gravity, I think, is not galactic rotation curves. That is the one domain where we already know that modified gravity – at last some variants thereof – work well. The real challenge is to also explain structure formation in the early universe, or any gravitational phenomena on larger (tens of millions of light years or more) scales.
Particle dark matter is essential to obtain the correct predictions for the temperature fluctuations in the cosmic microwave background. That's a remarkable achievement, and no alternative for dark matter can be taken seriously so long as it cannot do at least as well. Unfortunately, Verlinde's emergent gravity model does not allow the necessary analysis – at least not yet.
Previously:
Emergent Gravity and the Dark Universe
(Score: 2) by The Mighty Buzzard on Thursday November 10 2016, @12:34AM
I like the hypothesis but at the end of the day I'm just glad it keeps working, illusion or no.
My rights don't end where your fear begins.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @12:56AM
This is what I care about: Run a solar system simulation with this model that includes a propagation time for gravity. Can it be done?
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @12:59AM
No. Simulations are unable to account for entropy displacement, it leads to memory errors which can only be reconciled through a subspace string.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @02:47AM
Too bad then.
(Score: 2) by Kell on Thursday November 10 2016, @06:37AM
Eh? What stops you from using identical techniques to wave propagation simulations?
Scientists ask questions. Engineers solve problems.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @06:41AM
Usually what happens using non-instantaneous gravity is that after not too long the planets will fly off every which way. Try it.
(Score: 1) by khallow on Thursday November 10 2016, @09:32AM
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @01:47PM
Yes, it is angular momentum that is usually the culprit.
(Score: 2) by lgw on Thursday November 10 2016, @04:03PM
This is what I care about: Run a solar system simulation with this model that includes a propagation time for gravity. Can it be done?
Not sure what you mean. Gravity propagates at the speed of light. Of course, everything is already where it is, so it's changes to net gravitational force that propagate as things move relative to one another. The Sun attracts the Earth towards where we see it, not towards where it was 8 minutes ago.
(Score: 2) by frojack on Thursday November 10 2016, @01:01AM
Yeah, I don't understand it either but I just read about it yesterday.
Illusion is probably not the right word. But the other words don't help much either: [dailymail.co.uk]
His controversial suggestion says gravity is not a fundamental force of nature at all, but rather an 'emergent phenomenon'.
This can be thought of as the same way temperature is an emergent phenomenon, arising from the movement of microscopic particles.
The new theory, called 'emergent gravity', suggests gravity comes as a side-effect of the entropy of the universe.
Professor Verlinde's took the entropy of the universe and used it to adapt a theory called the holographic principle.
He says gravity emerges from the changes of fundamental bits of information, stored in the structure of spacetime.
Now isn't that a lot clearer? I thought so.
No, you are mistaken. I've always had this sig.
(Score: 3, Interesting) by Thexalon on Thursday November 10 2016, @01:47AM
Well, if the math works, and it holds up under tests, that sure sounds like the beginnings of a Grand Unified Theory (uniting the physics of very small things, i.e. quantum mechanics, and the physics of very large things, i.e .relativity) that stumped Einstein, Bohr, and a lot of other very smart physicists. I can understand Verlinde wanting to explore along those lines.
On the other hand, a bit early to go to the press with it when you're still in the hypothesis stage, eh? It sure seems like you're fishing for a Nobel there.
"Think of how stupid the average person is. Then realize half of 'em are stupider than that." - George Carlin
(Score: 2) by frojack on Thursday November 10 2016, @01:53AM
But the dark matter math works out too, no?
(Other than all that missing dark matter, mumble mumble).
No, you are mistaken. I've always had this sig.
(Score: 3, Interesting) by lgw on Thursday November 10 2016, @04:07PM
I'm quite skeptical of this because is claims to explain one part of what dark matter explains without explaining the rest. Immediately my crackpot alarms sound.
Dark matter explains: galaxy/cluster rotation rates and the distribution of matter in the early universe and gravitational lensing where there's no visible matter. Cranks focus on the first, and ignore the other two.
(Score: 1) by khallow on Thursday November 10 2016, @03:36PM
On the other hand, a bit early to go to the press with it when you're still in the hypothesis stage, eh?
Do you think Mr. Verlinde has the experimental apparatus to verify his theory? Going to the press is the next step.
(Score: 3, Interesting) by Gaaark on Thursday November 10 2016, @02:16AM
"emergent phenomenon, arising from the movement of microscopic particles."
This reminds me of Julian Barbour's theory that time and space are separate and that time only exists due to the movement of things in space: time is emergent from movement in space.
Maybe gravity and time only exist because particles move in space: no movement, no gravity, no time.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --
(Score: 2, Insightful) by tftp on Thursday November 10 2016, @04:41AM
Maybe gravity and time only exist because particles move in space: no movement, no gravity, no time.
How would you detect the movement without having time to measure its speed?
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @09:48AM
But how would you define and measure time without processes which involve moving?
Time and movement are just two views of the same thing. By default we used to chose the time as primary view, but relativity suggests we should pick the movement for better understanding of the world.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @02:53PM
Using processes that change some properties of something while staying in place?
(Score: 2) by Nerdfest on Thursday November 10 2016, @02:47AM
Isn't gravity generaly thought of as an emergent property of mass these days anyway? Emergent from entropy is a very different take on it though.
(Score: 2, Informative) by Anonymous Coward on Thursday November 10 2016, @08:52AM
No. Emergent is something different than "caused by" or "coupled to". As an example, the American two-party system is an emergent phenomenon of the US election system: Nowhere in the constitution or elsewhere it is prescribed that there shall be only two big parties. But the way the system works, most of the time only two big parties will emerge.
Neither Newtonian nor Einsteinian gravitation is of that type; in both theories gravitation there is an explicit gravitational field (resp. spacetime curvature) the mass (resp. energy and momentum) couples to. Also in quantum gravitation theories, gravitation usually is explicitly included either as field (mediated by the graviton), or in the form of a quantized curved spacetime (as in loop quantum gravitation).
(Score: 4, Interesting) by RedBear on Thursday November 10 2016, @02:05AM
Coincidentally again, I have something to say on this.
So the last time [soylentnews.org] I commented about this I think nobody noticed, but the time before that [soylentnews.org], it generated a bit of interest, even though both times I was flailing about and probably misusing some terms (like saying "intertia" where I think I should have said "accelleration"). Anyway, long story short, a fellow Soylentil recently posted a link to this blog [blogspot.co.uk] by Mike McCulloch, a UK lecturer in kinematics (apparently that involves the motion of objects in space(?) like stars and galaxies and whatnot). Anyhow, this guy lays out in a relatively straightforward way a simple theory he calls MiHsC or Quantised Inertia (QI) [blogspot.co.uk] that supposedly explains all the weird galaxy rotation stuff that caused the invention of the pixie dust we call "dark matter", and the cosmic expansion stuff that caused us to invent "dark energy", and several other things besides. Seems to me, from my simplistic understanding of this MiHsC theory it is saying exactly the same thing the paper in the summary is saying. That's if I'm chewing through all the technical gobble-de-gook in the summary correctly.
Like the paper in the summary, MiHsC also indicates that gravity is in fact an illusion, or more precisely an "emergent phenomenon" caused by massive objects in space shielding other massive objects from experiencing pressure from Unruh radiation from the Hubble horizon (the edge of the observable universe, if I'm understanding the concept correctly). You'll notice it talks about "Hubble scale" in the summary, and the breakout of MiHsC is "Modified inertia by a Hubble-scale Casimir effect". In other words, MiHsC also says there is no such thing as gravity, objects in space just get "pushed" towards each other by Unruh waves. There is no "pulling" going on, because gravity isn't a real force. The stars at the edge of galaxies that are supposed to go spinning off into space because they're moving too fast are held in place orbiting the galaxy not by some mystical distribution of dark matter that somehow inexplicably condenses into a hollow disk with most of its mass focused near the edge of the galaxy, but rather because the mass of the galaxy blocks the Unruh waves on one side of the star while the unblocked Unruh waves on the other side push the star back toward the galaxy.
A point McCulloch makes in his blog several times is that dark matter is so goofy that you have to manually fudge a different amount of this invisible stuff for each galaxy in order to try and make the data fit the theory, while MiHsC explains it all without any fudging whatsoever. This is very appealing and seems like an extremely solid empirical (and falsifiable) scientific theory, which is capable of explaining a large number of oddball things in physics, including the mystery of why the EmDrive seems to work (as NASA seems to have just confirmed a few days ago [digitaltrends.com]).
And the only reason I immediately clued in on what the summary was referring to is because somebody already put that exact quote in one of the comments on McCulloch's latest blog entry. Just yesterday as a matter of fact. At the moment it's the last comment on the blog post here, by "qraal": http://physicsfromtheedge.blogspot.co.uk/2016/10/a-test-using-redshift_30.html [blogspot.co.uk]
Seriously, you guys should really take a few minutes and check this blog out. And by all means shoot it down if it doesn't make any sense to you.
This makes me wonder, if these theories are true, doesn't that mean that everyone over the last several decades who has been trying to merge gravity with quantum mechanics to discover the fabled holy-grail "Unified Field Theory" has kind of been wasting their time? If gravity isn't real it would be hard to merge with anything, wouldn't it?
(Score: 2) by Gaaark on Thursday November 10 2016, @03:13AM
" This is a ‘patch’ since it is not predictive: you have to add dark matter 'by hand' to get agreement "
--Reminds me of the , what, 26 imaginary dimensions they've had to create in order for string theory to work, lol.
"MiHsC also predicts that you can’t have a constant velocity, zero acceleration, since the Unruh waves would then be longer than the Hubble scale, and none would fit, so inertia would collapse. This modifies special relativity’s insistence on a speed of light limit, and the predicted (tiny) acceleration agrees with the observed cosmic acceleration, as noted above."
--can anyone explain this? Not really understanding the whole 'constant velocity, zero acceleration' thing as it's pertaining to the speed of light limit... is he saying the should be NO limit to speed/acceleration???
Velly intelesting theory! No magical pull, but an explainable push! I like it!
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --
(Score: 2) by Gaaark on Thursday November 10 2016, @03:20AM
Actually, after re-reading it, he IS saying there should be NO limit!
I always wondered about that:if a particle of light is travelling towards the sun, should it not accelerate as it approaches the sun and then decelerate as it leaves? Light I not massless, because the sun will bend it from it's path.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. I have always been here. ---Gaaark 2.0 --
(Score: 2) by migz on Thursday November 10 2016, @08:16AM
IANAAP
Relativity uses "c", the speed of light as it's "base" unit of measure. If light does change speed then relativity ignores that, since it is using this as a base, the number doesn't change, so the change has to go somewhere else in the equation. This is why space time bends. It might or might not, this is how the model works.
Always remember, the map is not the territory. You can have different types of maps, of different accuracy. Just because a phenomena is on a map, does not mean that it is true in the real world.
As light approaches the sun, it cannot accelerate or decelerate, since by definition c is constant. What happens is spacetime warps.
Of course if you use a different model you could get different results.
Relativity works well, because we can brush a lot of things under the carpet by keeping c constant, and pushing all the wriggly bits into spacetime. Unfortunately you land up with unsatisfactory mismatch with reality which is bodged over with dark matter and dark energy.
Assuming that rather than bending spacetime, we shunt time over to the speed of light side of the equation. In this case we are in very speculative ground. I guess that it would make sense to talk about lighttime accelerating towards the sun leaving the rest in space (including gravity and all the other wriggly bits). In this model space is still bendy, but time is constant on that side of the equation.
What we need from this theory is a testable hypothesis that yields a different result from relativity, that can be tested in the real world. Then we can see who is right. Note more than one model can be "correct". Depending on what you are doing two different maps might be more accurate for what you are doing (e.g. topographical map, vs subway map).
(Score: 1, Informative) by Anonymous Coward on Thursday November 10 2016, @09:05AM
No. Light doesn't gain energy by increasing its speed, but by increasing its frequency (corresppnding to E = h f).
You are right, however, that light has to gain energy when approaching the sun, and lose it when going away; that is known as gravitational red shift. Also it is true that light is bent by the sun's gravitation, which physically is an acceleration orthogonal to the direction of movement. That is, light can change its velocity, but not its speed. So in a physical sense it can accelerate (= change its velocity), but not in the colloquial sense (= increasing its speed).
Note that the physical meaning of acceleration encompasses the colloquial meanings of acceleration, deceleration and changing direction; only the latter thing is possible.
Also note that the above statement is only true when measuring the speed of light locally; otherwise you will see light to (apparently) slow down when approaching the sun, due to gravitational time dilation (which is, BTW, also another way to understand the gravitational red shift). Indeed, when replacing the sun with a black hole, you'll find that, when looked at from the outside, the light comes to a halt when reaching the event horizon. An observer falling into the black hole will, however, find that the light still goes at the same speed as he falls through the horizon.
(Score: 2, Informative) by Anonymous Coward on Thursday November 10 2016, @03:22AM
Push theories of gravity are as old as Newton's laws: https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitation [wikipedia.org]
If you think carefully about the objections, all of the issues are now accepted by the mainstream for other reasons: weakly interacting particles moving at insane speeds (neutrinos), invisible stuff (dark matter, dark energy), etc. So maybe gravity is a push after all?
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @09:17AM
Neutrinos still are limited by the speed of light. Le Sage theory would require speeds far above the speed of light, which today is much less acceptable than it was back then.
(Score: 3, Informative) by tfried on Thursday November 10 2016, @08:26AM
I won't pretend to understand the least of either of those theories, but from that ignorant perspective they do not seem very similar to me at all.
Like the paper in the summary, MiHsC also indicates that gravity is in fact an illusion, or more precisely an "emergent phenomenon"
Yes. But even without understanding the theory, that apparent similarity can easily be explained as an "emergent phenomenon" of the search for a "Theory of Everything". The whole point of that endeavour is to explain some concepts/forces in terms of the other, or in other words, to "do away" with some concept by explaining them as "emergent". So any physicist participating in that endeavour is hoping to show that Y is an emergent phenomenon of X, or ultimately, that everything is an emergent phenomenon of X. (Cue philosophers pointing out that the next step after that will be to show how X emerges from itself, autopoeitically).
(Score: 2) by fritsd on Thursday November 10 2016, @09:21AM
IANAPhysicist, but what you say sounds a lot like figure 5 in Verlinde's article.
However, as I understand it, he doesn't talk about radiation pressure from the outer edge, but that when a mass exists in the universe, it removes a bit of the universe's entropy, i.e. creates a bit of "quantum information" (Shannon's law? Don't think he mentioned that information = -entropy).
I still don't have a clue about what de Sitter space (or anti-de Sitter space) means.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @03:23PM
Anti-de Sitter space is that part of the room with no chairs.
(Score: 1, Insightful) by Anonymous Coward on Thursday November 10 2016, @04:23AM
Make a prediction or shut the fuck up.
(Score: 2) by fritsd on Thursday November 10 2016, @09:36AM
Hey editors, what happened to my submission?
I was posting basically the same story as Sarasani. I thought it was quite a scoop.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @10:34AM
... and with some Gpogle translate maybe as well for others:
http://www.quantumuniverse.nl/emergente-zwaartekracht-en-het-donkere-heelal/ [quantumuniverse.nl]
The main (very simplified) idea is that information inherent the fabric of time and space (just like temperature and pressure originate from a bunch of molecules, while a single molecule does not have these properties) is the source of the gravity.
Entropy causes a translocation of this information, which generates the gravity.
(Score: 2) by GreatAuntAnesthesia on Thursday November 10 2016, @11:15AM
And on to the big unasked question: Does this new understanding[1] of gravity allow us to do anything with it? Does it open the door for some kind of technological gravity manipulation? Because that would be, you know, pretty cool.
[1] Assuming this hypothesis turns out to be accurate.
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @04:37PM
this is what i wanted to know. will this allow anti-gravity boots, planes, etc.
(Score: 1) by Demena on Friday November 11 2016, @11:05PM
No but MiHSC may
(Score: 0) by Anonymous Coward on Thursday November 10 2016, @03:34PM
By whom?