4 current QG theories are singled out as not meeting a “quantum covariance criterion.”
Quantum gravity’s split personality: multiverse vs. universe
A paper on quantum gravity says a suitable Heisenberg Generalized Uncertainty Principle should be local, covariant, and tied to a “quantum covariance criterion” for physically-admissible spacetimes. It also says that most current QG theories — including string theory, Geometrodynamics, loop quantum gravity, GUP and minimum-length-theories — are framed in a multiverse representation of spacetime, while an alternative universe representation is described as using a variational tensor field different from the unique background metric tensor.
Gobble's Take: The paper’s real provocation is simple: not every elegant quantum-spacetime story gets past the gatekeeper.
Source: Perplexity Search
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