I remember reading about the groundbreaking experiment by Nesvizhevsky (et al. 2001) some 12 years ago using ultra-cold neutrons which showed the first experimental evidence of quantum gravity. It is my understanding that these experiments has been repeated since then in labs around the world and similar results observed(neutrons bouncing off the reflector in a discrete set of quantized energy states rather than varying continuously)and more recently by Kobakhizde(2010), who was testing Erik Verlinde's "entropy theory of gravity". Am I correct about the reproducibility of Nesvizhevsky's results? If so, these experiments seem to suggest that gravity is indeed an actual force after all and not simply an emergent property as posited by GR. But do any of the results of these experiments conflict with the weak/strong equivalence principles? Someone on Yahoo! answers with the handle OzoneGuy claimed that the observations were explainable simply by diffraction. But this could be tested by positioning the diffraction grating to be parallel to the neutron reflector.So it is simply diffraction? Or is there actual evidence of quantum gravity?
I wouldn't describe Nesvizhevsky's work as groundbreaking. It's a refinement on a type of experiment that was first carried out 38 years ago (Colella 1975). For a recent review article, see Abele 2012.
It also isn't a probe of quantum gravity. By the equivalence principle, this type of experiment is equivalent to simply accelerating the apparatus in a region where there is no gravitational field.
Quantum gravity becomes relevant at the Planck scale, and nothing in this experiment got anywhere close to the Planck scale.
Abele, 2012, http://iopscience.iop.org/1367-2630/14/5/055010
Colella, Overhauser, and Werner, Phys. Rev. Lett. 34 (1975) 1472
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