VIA lecture by Prof. Elias Okon "Is the equivalence principle valid in a quantum context?" took place on 24.10.2014.

It's record is in VIA library

http://viavca.in2p3.fr/lias_okon.html

The following comments and questions were put in Discussion:

Shantanu: I didn't understand why quantum particles with spin do not follow geodesics. Does that mean neutrinos do not propagate along geodesics? My understanding is that from SN 1987A we have evidence that neutrinos follow the same geodesics as photons, but maybe you can point me to the reference

Nauenberg: a reminder: neutrinos have mass

Shantanu: well that shouldn't matter for relativistic neutrinos, but let's discuss at the end.

Eolo: Quick question: can you exhibit a non-trivial configuration of a homogeneous gravitational field (e.g. one which is not Minkowski space-time)?

Emmanuel Saridakis: What about alternative theories of gravity that do not need the EP (although they can accept it)? For instance teleparallel gravity?

Shantanu: so coming back to my question.. From SN1987A we know that neutrinos and photons travel on the same geodesics within 0.2%. The reference for that is http://adsabs.harvard.edu/abs/1988PhRvL..60Q.173L and in response to Mike Nauenberg's question. The Shapiro delay for massive neutrinos has also been calculated and can be found at http://adsabs.harvard.edu/abs/1988PhRvD..38.2335B. So my question is whether this is consistent with Papepoutrou's paper from 50s and a follow up question to this. What about spin-2 particles (gravitons)? This is again important from experimental point of view for people doing coincident GW-EM searches. What about spin-2 particles?

Dirk Puetzfeld: Thank you for this interesting talk. Just a note: I may add to the initial question regarding the non-geodesic motion of (classical) test bodies, that the so-called "problem of motion" in GR has a very long and rich history. Without going into detail, alongside the work of Papapetrou (1951) also the much earlier work of Mathisson (1937) should be mentioned. The concepts introduced by these authors were later on developed by many others in the context of GR, most notably by Dixon starting in 1964, who completed the program of Mathisson in a series of works from 1970 to 1974. In the context of more general gravity theories, in particular also covering intrinsic spin as well as nonminimal coupling, I may point interested readers to some recent works of Y.N. Obukhov and myself (please see, e.g., Phys. Rev. D 90 (2014) 084034 and references therein).

Eolo: Another quick one: in a classic reference (Ehlers-Pirani-Schild '72), the authors prove that the presence of privileged trajectories (universal, free-fall trajectories of test particles) equip a generic manifold with at least a projective/path structure. then, if one adds a conformal structure, the Riemannian structure naturally follows from some compatibility/integrability conditions. what is your take on this result, and how/if you think it agrees with your "no-geometrisation" idea of EP1.

Eolo: ok, seems a bit clearer now. thank you.

Shantanu: I presume the COW (Collella-Overhauser-Werner ) experiment tests EP2? in quantum context? Can I ask about the COW experiment measures?

Shantanu: thank you. That answers my question also

Dirk Puetzfeld: May I ask for the reference regarding the just described experiment. I mean the Stanford experiment.

Nauenberg: I hope I was not too emphatic but I completely disagree with Elias about mass dependence in quantum mechanics. His views, which are shared by others in the literature is based on a misunderstanding on the role of scales such as a m for mass in physics as simple exercise is to change the scales for length l and time t in Schrodingers equation Then you find that l^2/t which is the scale for acceleration the parameter m drops out, as the ancients use to say QED.

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