Both have been criticized for the lack of any experimental data. Now, one might be made or broken by a test. We are talking about the two theories of quantum gravity String Theory and Loop Quantum Gravity – and the latter is all set to be tested. A French team intends to test the correctness of Loop Quantum Gravity (LQG) by simulating the expected signatures of the evaporation of a black hole.
The Difficult Job
The main problem in testing these two theories lies in the fact that one has to probe Planck scale physics and the high energy associated with that. However, Monte Carlo simulations show the way out, or so thinks the team of A.Barrau, T. Cailleteau, X.Cao, J.Diaz-Polo and J.Grain, whose paper appeared in Physical Review Letters.
The plan is daunting. They plan to observe black holes evaporating via the Hawking radiation mechanism and this should reveal critical signatures, if LQG is true. Also, bigger black holes and smaller ones give different signatures. The paper presents the simulations that they have done and what signatures in the radiation pattern they expect to see.
The tough job comes after that. LQG predictions indicate features in the black hole evaporation spectrum, but in order to get that one needs to look at a large number of black holes, so that the energy reconstruction can be done with as little error as possible.
Barrau’s team is also looking at signatures of LQG in the cosmic background radiation. But, that’s another story.