“Entanglement” is the current buzzword of physics, here are two new stories featuring this:
Back in 2013 one could read lots of claims in the media that “Hard evidence for the multiverse” had been found, based on “effects of quantum entanglement between our horizon patch and others”. These claims were discussed on this blog (with a response from the authors here). A new paper by Will Kinney has now been published in JCAP, including the following conclusion about such claims:
It is worthwhile to discuss in general the “concrete predictions” originally claimed by the authors of refs. [1,2], since several key claims do not survive even cursory scrutiny. For example, the discontinuity in the effective potential claimed to be correlated with voids and the CMB cold spot does not appear to in fact exist: for all physically relevant values of the parameters V0, λ, and b, the modulation F(φ) is a smooth function, with no characteristic discontinuities which would explain features in the power spectrum. Perhaps more importantly, the form of the effective potential resulting from landscape entanglement is completely dependent on the choice of inflationary potential V(φ), which is itself an arbitrary free function. One could just as consistently choose the underlying inflationary potential in the absence of landscape corrections to be the same as the effective potential (2.7)! In this sense, the landscape model is no more (or less) predictive than single-field inflation itself, and most of the claimed predictions of the entanglement model turn out not to have been
predictions at all. However, any considerations of theoretical consistency are a moot point: even if one takes the claimed predictions at face value, almost all of them are ruled out by Planck. Experiment always supersedes theory, and the model does not match the data.
Another entanglement story that is getting some press attention this week is this paper by Erik Verlinde, with its associated press release, explaining that we may be “on the brink of a scientific revolution”. I’ll have to avoid trying to give an explanation of the physical argument of the paper, on the grounds that I don’t understand it, partly because there seems to be no underlying physical model here. The basic idea is stated as replacing dark matter by
an elastic response due to the volume law contribution to the entanglement entropy in our universe.
but someone else will have to explain exactly what that means. Maybe I’m missing it, but I don’t see anywhere in the paper a suggested experimental test of the theory. Someone much more expert than me is needed to explain whether the picture of this paper is consistent with the known astrophysical and cosmological evidence usually interpreted as dark matter/dark energy.