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Neither of them are theories. If you drop your pint, it won't fall to the ground in theory; it will actually do so, because something is causing it to fall. Whatever the cause of that falling, it is called gravity. Quite how you managed to miss the list of theories about gravity, is a mystery.
Quantum Mechanics is similarly a whole raft of theories to explain why mass, energy, momentum and whatnot come in discrete packets, and not smoothly, as classical physics assumes.
It's General Relativity that can't be combined with QM, because as a classical theory, it assumes that spacetime is smooth. According to QM, nothing is smooth. Most of the alternative theories listed above are inspired by this fact, or at least seek to address it.Philosophy Explorer wrote: ↑Sun Apr 29, 2018 11:17 pmAre they really the same theory or distinct? Why can't they be combined as Einstein and many others have tried to do?