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## Main Question or Discussion Point

Penrose says in “Cycles of Time” that rest mass isn't exactly a Casimir operator of the de Sitter group, so a very slow decay of rest mass isn't out of the question in our universe.

If rest mass is strictly conserved, should it be a Casimir operator of the de Sitter group?

Decay of rest mass is crucial for Penrose's “conformal cyclic cosmology” theory, so how strong is this argument that rest mass isn't exactly a Casimir operator?

thanks

Laura

If rest mass is strictly conserved, should it be a Casimir operator of the de Sitter group?

Decay of rest mass is crucial for Penrose's “conformal cyclic cosmology” theory, so how strong is this argument that rest mass isn't exactly a Casimir operator?

thanks

Laura