But quantum gravity works very well. Did you mean: "quantum gravity which should work in my opinion doesn't work"?
-
This Tweet is unavailable.
-
Extra dimensions turn out to be necessary when we quantize the string and impose some constraints resulting from QM. That's very elementary derivation which you can find in any string theory textbook. So yes, extra dimensions are definitely quantum effect.
Yes they are necessary to formulate string theory, however what’s not necessary is the radius of the extra dimensions. The reason they “must” be so small is because the others have been ruled out