I read an interesting paper from the arxiv today: Quantum-gravity phenomenology, Lorentz symmetry, and the SME by Ralf Lehnert.

In the paper, Lehnert explains that in order to have a quantum theory of gravity me must understand physics at the plank length. He propses one practical way for doing that would be to search for symmetry violations. If we could find direct evidence of a symmetry violation, such as Lorentz Invariance, we would know something about the plank length.

He gives various examples. My favorite is if we could find a particle described by a vector field which has a direction in the ground state we would have a violation since there should be no preferred direction in Lorentz Invariant physics. There are other violations he discusses as well.

So is we could find some "sacred" symmetry breaking it would be wonderful for quantum gravity theories for we could use the violations to probe the plank length and adopt quantum gravity thoeries where such violations are possible and discard the rest.

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