This is essentially the standard argument for why we have to quantize gravity.
Sort of. The problem first appears because the LHS of the EFE is a classical tensor, while the RHS is an operator, two different beasts. And using expectation value of the stress energy tensor does not work that well. The cosmological constant problem does not help, either. The MWI ontology just makes the issues starker. That’s why I am surprised that Carroll completely avoids discussing it even though GR is his specialty.
Sort of. The problem first appears because the LHS of the EFE is a classical tensor, while the RHS is an operator, two different beasts. And using expectation value of the stress energy tensor does not work that well. The cosmological constant problem does not help, either. The MWI ontology just makes the issues starker. That’s why I am surprised that Carroll completely avoids discussing it even though GR is his specialty.