Without endorsing it, and presenting it here without comment, http://physicsfromtheedge.blogspot.com/ http://physicsfromtheedge.blogspot.com/ has explanations o

Without endorsing it, and presenting it here without comment, http://physicsfromtheedge.blogspot.com/ http://physicsfromtheedge.blogspot.com/ has explanations of the theory preferred there (which I think can be labeled an entropic theory of inertia, or perhaps an information-theory-based theory of inertia) that might be an ELI5. The following is my attempt at casting McColloch's idea as an ELI5. McColloch's idea is that inertia is a result of asymmetric Unruh radiation pressure resulting from acceleration causing the Hubble horizion sphere around the accelerated body to not be symmetrically spherical. The idea is that when you accelerate, then the Hubble horizon "behind" you gets much closer to you, which then disallows some Unruh radiation behind you, thus causing there to be more Unruh radiation pressure in front of you. A more fundamental idea underlying this is that Unruh radiation emanating from the Hubble (and, indeed, any) horizon has every possible discrete wavelength that would fit between the horizon and the particle surrounded by that horizon, so as the distance to the horizon changes, so does the longest wavelength that could be visible -that could exist-. Now, as accelerations tend to zero, the idea is that the number of Unruh waves that are disallowed by the horizon behind is much smaller than at higher accelerations, and therefore inertia drops at lower accelerations, leading to gravity feeling stronger. I believe all entropic gravity/inertia theories are at least as controversial as dark matter theories or more so. McColloch's has the benefit of having a physical explanation that can be explained, if not to a 5-year old, then to a 10-year old. However, keep in mind that it could be a simple explanation that is just wrong.