The dynamical casimir effect tells that an accelerating mirror should produce photons. Due to equivalence principle a mirror in uniform gravitational field also should produce photons. So, should a planet covered with mirror radiate and if so, where the energy should come from?
1 Answer
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From the abstract of Fulling & Davies paper from 1976 (it is cited in Wikipedia article linked in the OP):
A uniformly accelerating mirror does not radiate.
So a static mirrored planet also would not be radiating.