Approaches to Quantum Gravity

Questions and answers• Q - L. Crane - to C. Burgess:Can any of the approximate calculations you describe be used to make anypredictions concerning the long distance interferometry tests which are beingconsidered for QG?– A-C.Burgess:In principle yes, although the prediction is generically that the quantumeffects to be expected are negligibly small. (Of course the details will dependon the precise tests which are of interest.) Although this is disappointing ifthe goal is to detect these quantum effects, it is what justifies the classicalanalyses of these tests which are usually performed.• Q-D.Oriti-toC.Burgess:Assuming one takes your suggested point of view on gravity as an effectivefield theory, and is also re-assured by your explanation of how we can use it satisfactorilyto make predictions at low energy, what if he/she wants to go further,i.e. what if he/she wants to find the fundamental (ultra-)microscopic theory ofspacetime from which GR emerges at low energy? What can the effective fieldtheory point of view teach us about the properties of the fundamental theory, ifit exists? If spacetime and gravity emerge from the unknown microscopic theory(that therefore does not use our familiar notions of space and time) in thesame way as hydrodynamic concepts and field theories emerge in many condensedmatter systems from the underlying quantum (field) theories of “atoms”,how much and what exactly can we deduce about the quantum (field) theoryof fundamental “space atoms” from the effective theory (GR) we know (e.g.symmetries, type of degrees of freedom)?– A-C.Burgess:Unfortunately, this is the hard part! Based on experience with other interactions,the properties of the effective theory can point you to the energy scalesat which the more fundamental theory becomes important, but it does not571