![]() ![]() Image credit: Wikimedia Commons user luca. all do better-or-worse jobs at explaining these rotation curves. The extended rotation curve of M33, the Triangulum galaxy. Emergent gravity gets away with being barely compatible with the data – it systematically results in too high an acceleration to explain the observations.Ī 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. Their conclusion, therefore, is invalid.Īnother paper that appeared two weeks ago tested the predictions from Verlinde’s model against the rotation curves of a sample of 152 galaxies. But they seem not to have taken into account that the equation they are using does not apply on solar system scales. One paper is particularly critical, with the authors claiming that they have ruled out the model by seven orders of magnitude using solar system data. So, it’s a promising idea and it has recently been put to test in a number of papers. Image credit: Supernova Cosmology Project, Amanullah, et al., Ap.J. In emergent gravity, there is only a new type of entropy, responsible for what we perceive as the effects of both dark matter and dark energy. The amount of dark matter and dark energy is determined through independent sources: supernovae, the. In the new emergent gravity model, this relation follows because the apparent dark matter is, in fact, related to the cosmological constant. In modified gravity scenarios, the departure from General Relativity becomes relevant at a particular acceleration scale. That scale turns out to be similar – on the same order of magnitude – to the temperature of de-Sitter space, which is proportional to the (square root of the) cosmological constant. ![]() Second, Verlinde’s idea explains a previously noted numeric coincidence. This solves a serious problem with many modifications of gravity which usually work well on galactic scales but not on solar system scales. On galactic scales however, the modification to General Relativity becomes noticeable, and manifests itself as apparent dark matter. This happens in systems with a comparably high average density, such as solar systems. Therefore, once the additional entropy is entirely depleted, one is left with only the usual, holographic entropy and gets back ordinary General Relativity. However, the new entropy that Verlinde introduces can’t become less than zero. that's affected by the normal, baryonic matter present in space. The dark matter halo around galaxies could be explained, in principle, by a new type of entropy. ![]()
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