Friday, May 3, 2019

Entropic Gravity

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Recorded: 4/4/2019 Released: 5/3/2019

Randy and Jim discuss Eric Verlinde's theory of emergent gravity that relies on statistical methods to produce both gravitational attraction and inertial effects.


1. The papers we read for this program:

2. Additional related paper I half-read and we discussed:
3. Related Episodes of Physics Frontiers:

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  1. Really enjoyed listening to this and I learned a lot about the nature of the entropic gravity claim. I wanted ask for your thoughts on a couple of recent news items I've seen that might relate to entropic gravity. First, there have been two reports of galaxies that seem to have no evidence of dark matter -- i.e. the outer bits orbital velocities are consistent with the visible matter. If I read the reports correctly, they're both unusually diffuse galaxies, but either way, this would be a challenge to entropic gravity as it should emerge from from every galaxy. Second, your episode on negative mass/gravitational force at quantum scales would also present a challenge for entropic gravity, since it shouldn't be able to be seen except when lots of quantum particles are bouncing around (i.e. Boyle's law has no definition around a single atom).

  2. There have also been challenges to the theory, such as when attempting to model conservative forces in the general Newtonian case, many physical requirements come to light.(1) It has also been shown that when energy-momentum conservation, cosmological homogeneity, and isotropy requirements are included, entropic gravity has severely limited applications.(2) Finally, testing the theories presented in this paper would require space-based experiments performed at the Lagrangian points within our solar system, which is currently not feasible.

    1. Visser, M. Conservative entropic forces.
    arXiv:1108.5240 [gr-qc, physics:hep-th] (2011)
    2. Wang, T. Modified entropic gravity revisited.
    arXiv:1211.5722 [gr-qc, physics:hep-th] (2012).

    1. Very Interesting! Thanks! I'll look those up!

      When I get time I want to start up WEP again and try to revisit some old episodes and other things I'd like to talk about but Randy doesn't. I'll put those on the list!

      I would only take exception to the last sentence. In fact, that there are experiments that would falsify the theory is _good_, and that they aren't _currently_ feasible is disappointing, but in no way bad. Do you know: which Lagrange points need to be used? And what kind of detector would they need?

      Or would it be an interferometer that uses four out of the five?

    2. Oh, and congrats! That was almost exactly 2 years after the episode was originally published!