This is a discussion of the FQXi Podcast from April 30, 2012
FQXi April 30, 2012 Podcast
2 months later
[deleted]
Table-Top Test of Quantum Gravity: Response to Sabine Hossenfelder's Critique
In response to the critique of Sabine Hossenfelder I would like to make the following comments that hopefully clarify the motivation and the analysis behind聽our paper.
1) It is incorrect that we assume that the centre of mass degree of freedom is given as a linear (or any other) sum of momenta of individual constituents. We do not need to make any such assumption. The centre of mass degree of freedom of the mirror is defined operationally: it is the degree of freedom with which light interacts in the experiment and has been confirmed in numerous experiments thus far. How this degree of freedom arises from the fundamental degrees of freedom of constituting particles is an interesting and as Sabine Hossenfelder mentioned still open theoretical question, but not decisive for our argument (we do mention in the Appendix that if the centre of mass degree of freedom is given as a linear sum of momenta of individual constituents - anticipating all the problems that Hossenfelder mentions - and the deformation applies to individual constituents, then the predicted effect would be smaller, with the exact amount depending on the underlying theory used.)
2) The proposed experiment can achieve a very high sensitivity, and it can easily compete in the precision of measuring violations of Lorentz invariance that are typically only considered in astronomical observations. But, even if the latter could have better bounds in some ranges of parameters, astronomical observations and other tests of possible consequences of quantum gravity are mostly performed in the domain of validity of classical physics. We think that direct measurements of the non-commutativity of canonical observables on quantum states has its own explanatory power that does not rely on any particular assumed transition from quantum to classical. The latter is not trivial and might be modified in presence of quantum gravity effects.
3) We do not have a theory with a consistent description of the composite system. The theories of commutator deformations do not precisely specify in which domain they would be applicable, or to which degree of freedom, and it is up to experiments to probe any possibility. It might be that the deformation increases with mass until some maximal mass and then saturates or decreases, such that it is not observable in the classical domain. Honestly, nobody knows what the correct theory would be. Our experiment can test the deformation in the particular range of the experiment which we precisely define in the paper.聽 In this respect it is also important to note that in our setup the predicted effect due to some of the considered deformations of the commutation relation actually decreases with the mass as 1/m. That means that the effect would be larger, the lighter the particle is, provided the interaction with the particle can be realized as required in our paper.
Caslav Brukner (one of the authors of the paper)
University of Vienna
5 years later
Here is a good view on thre origin of mass, see article attached.Attachment #1: Advanced_Relativity_and_formula_Emc2.pdf