Which theory do you think is right—-General relativity or Quantum mechanics and why?
It’s not so much that GR is wrong–it’s correct within it’s domain of applicability, which encompasses all experiments that ever have been (and maybe ever will be) performed. Ultimately, GR is probably going to be superceded by a quantum field theory of some sort (every other force is, and there’s no reason to think gravity is special). We haven’t figured out the exact form of that theory. We have effective theories that can reproduce GR as a classical limit, but they have divergences. String theory is one possibility that works very nicely. The trouble with quantum gravity is that gravity doesn’t reveal its quantum nature at energies we can access (or possibly ever will access) experimentally. If you know some quantum field theory, a good book is Feynman’s “Lectures on Gravitation”. It builds up a simple quantum field theory to model gravity, shows how GR is reproduced, and discusses the infinite-energy problems that crop up.
