>I heard about that. But why would you want to have quantum field theory of gravity? Why can't you just consider gravity to be only about the shape of space-tim

>I heard about that. But why would you want to have quantum field theory of gravity? Why can't you just consider gravity to be only about the shape of space-time in which everything including quantum field theories of everything else happen? No, because it turns out that curved space-time is actually incompatible with quantum field theory in certain extreme parameter regimes, in a way that it actually makes it impossible to make predictions on scales where both gravitational and quantum effects are very strong (e.g. neutron stars). We want a quantum field theory of gravity as then it will "play nice" with other quantum field theories. >Does GR really describe fundamental interactions? For me it seem that it only describes shape of space-time where all the fundamental interactions take place. I think it is quite fundamental that energy curves space-time and that it affects the paths of objects (even light), but yes maybe I wouldn't call it a fundamental interaction in the same sense as quantum field theories, particularly because it isn't quantised so it isn't really a single "thing" being exchanged (like a gauge boson). Most physicists do call it an interaction or a force though. I mean that it describes nature on a fundamental and indivisible level (at least so far as our current/most popular understanding) >Isn't it just because we lack data from systems where gravity is extremely strong and systems are small/isolated enough to show any quantum effects? How can we be sure that we need quantum gravity? Why it's not enough to calculate QFT in curved spacetime instead of flat spacetime? Of course we lack this data, which is why measurements of, for example, the aforementioned neutron star equation of state will give us more understanding. We can't be sure that we need a quantum theory of gravity, it could be that it is actually just impossible to describe both gravity and QFT at the same time. QFT in a curved spacetime is only a first approximation of general relativity and doesn't capture all of the effects of GR (see here for example https://en.wikipedia.org/wiki/Quantum_field_theory_in_curved_spacetime https://en.wikipedia.org/wiki/Quantum_field_theory_in_curved...). I don't really know much about quantum gravity, but I don't believe that QFT in curved space-time is sufficient, at the very least it doesn't solve the cosmological constant problem (https://en.wikipedia.org/wiki/Cosmological_constant_problem https://en.wikipedia.org/wiki/Cosmological_constant_problem) > And I argue we shouldn't be able to because I believe it's completely different thing from a real force It's worth considering that what we call a force in quantum field theory is very different from what Newton would have considered a force! Probably in fact the gravitational "force" due to curved space-time would seem more like a force to him, certainly QFT is much weirder than GR after all...