So, the equations for general relativity are as follows: $$G (mu, nu) = ĸ T (mu,nu)$$ I was told, that since energy, momentum and other observables are quantum then the stress-energy tensor $T$ is quantum, and therefore the Einstein tensor $G$ must be adapted to it. However, what if we used expected values $\langle T\rangle$ to make the stress-energy tensor "classical" which makes quantum gravity "unnecessary". How would this lead to any problems, and why haven't we tried it?
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$\begingroup$ Possible duplicates: physics.stackexchange.com/q/52211/2451 , physics.stackexchange.com/q/6980/2451 , physics.stackexchange.com/q/10088/2451 and links therein. $\endgroup$– Qmechanic ♦Commented Feb 13, 2022 at 8:29
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$\begingroup$ Using expectation value for T doesn't make quantum gravity unnecessary. $G=8\pi \langle T \rangle$ means that only the matter field is quantized on a classical background space time. It's called the semi classical approximation $\endgroup$– KP99Commented Feb 13, 2022 at 13:39
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