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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: 1, Insightful) by Anonymous Coward on Wednesday March 01 2017, @08:09PM (6 children)
No, the whole principle behind science is to make observations and construct models to try to understand the workings of physical law. Simplicity is not a requirement; it is a desirement. It is more a philosophically driven attitude than anything else. Given two models where one has symmetric central forces and mathematically beautiful equations, and one that is teetering on stability where you have large offsetting terms barely holding together numerical stability, you go with the first one. Why? A belief that Nature is governed by simple and/or beautiful laws is a big reason, but that is more a philosophical stance than anything else. Plus, history has also shown that large, complicated models break down or become too burdensome (e.g., epicycles), and aren't able to make future predictions.
Back on point, the fact that one cannot understand the mathematics behind something does not imply that something is wrong. Mathematics, and higher level mathematics can be quite beautiful to those who understand it. A lot of string theory work is like that. Forcing your models of physical law to conform to the requirement that they must be expressed at a high school calculus level is what I would consider a theological approach to bend nature to your understanding and not the other way around.
(Score: 0, Disagree) by Anonymous Coward on Wednesday March 01 2017, @08:42PM (1 child)
If you believe the universe is incomprehensible then this effort is misguided.
It isn't a matter of understanding, it is a matter of time/effort. As mentioned, just running a computer program that does the calculations (w/o any understanding) is not something that is done because the model is so damn complicated.
(Score: 3, Informative) by tangomargarine on Wednesday March 01 2017, @09:02PM
If you believe the universe is incomprehensible then this effort is misguided.
He didn't say that.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by HiThere on Thursday March 02 2017, @12:56AM
The very concept of "physical law" is a problem. If you had said "observed regularity" I'd have no problem, but the concept of law involves an implicit assumption that "this is the truth, the whole truth, and nothing but the truth", which is probably impossible, and which I have certainly never seen.
Science is about modeling observed regularities in a way that allows accurate predictions to almost always be made. (When the predictions aren't accurate, you try to refine the model.)
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 1, Flamebait) by aristarchus on Thursday March 02 2017, @07:09AM (2 children)
it is a desirement. It is more a philosophically driven attitude than anything else. Given two models where one has symmetric central forces and mathematically beautiful equations, and one that is teetering on stability where you have large offsetting terms barely holding together numerical stability, you go with the first one. Why? A belief that Nature is governed by simple and/or beautiful laws is a big reason, but that is more a philosophical stance than anything else.
It is called "Ockham's Razor", and it will cut you bad, unless you have an alternative? The most unstable, unlikely, crazy theory is more likely to be the correct one? We call that the "jmorris razor", followed by the "khallow correlary", and further backed up by "Runaway1956". It's just "Runaway", he is a force of confusion all by hisself, without being a razor, a law, or even a corrolary. No, Ockham's razor has stood the test of time, in the face of all the crazy, and was even cited by Jodie Foster in "Contact", co-written by Carl Sagan.
(Score: 1) by khallow on Friday March 03 2017, @03:35PM (1 child)
(Score: 2) by aristarchus on Friday March 03 2017, @04:34PM
I disagree with *your* overly simplistic opinion about my comment!