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posted by Fnord666 on Wednesday March 01 2017, @05:21PM   Printer-friendly
from the seemed-like-a-hack-anyway dept.

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


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  • (Score: 2) by HiThere on Thursday March 02 2017, @12:40AM (1 child)

    by HiThere (866) Subscriber Badge on Thursday March 02 2017, @12:40AM (#473639) Journal

    Popper hasn't, and can't be "debunked". You can argue with how he uses words, or whether his domains are properly specified..and at times I would, but this is far from being debunked. That's like saying Newton was debunked. I'll admit I've never read Lakatos, but you can be pretty sure that he, also, did not say the last word on the subject. He may cover a wider field than does Popper (who really only properly covers experimental sciences that have readily replicated experiments).

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  • (Score: 0) by Anonymous Coward on Thursday March 02 2017, @03:20AM

    by Anonymous Coward on Thursday March 02 2017, @03:20AM (#473704)

    Falsifiability doesn't work as a criterion. The only reason it seemed to work is because scientists before that knew what they were doing and predicted something precise. Now we have NHST where everyone tries to predict whether A is correlated with B (the vaguest thing possible). That aint science, because an insane number of explanations can be easily put forward for such vague observations. Such predictions, and "tests" of them, do not help distinguish between the theories.

    As lakatos put it, every theory grows in a "sea of anomalies". They are born and live falsified. It is all about making one/few precise predictions that otherwise have low prior probability.