In an experiment by Page and Geilker published in Indirect Evidence for Quantum Gravity, two mases that are connected by a spring are allowed to oscillate inside box if a radioactive material decays (similar idea as in the Schrödinger cat experiment). The differences in the energy-momentum tensor of the masses are recorded in some device outside the box. The experiment supports the hypothesis that

I would like to understand the details and study the math, but I have no access to the document in the PROLA. Does someone know about this and is willing to elaborate?

This experiment excludes semiclassical gravity as the true theory, provided that some additional assumptions on quantum mechanics are accepted. For an approach that does not accept these assumptions, thus making semiclassical gravity viable see http://arxiv.org/abs/gr-qc/0611037
(I apologize to those who do not like my advertisement of the Bohmian approach that offers a possible solution to many fundamental problems in quantum physics.)