How do you reconcile classical quantum mechanics with general relativity?

In may, in fact, not be possible to do this at all, however there are a growing number of theoretical physicists who believe they are on the verge of finding a 'Theory of Everything' that does just this.

The problem is that quantum mechanics is a non-local theory involving wave functions. General relativity is a classical theory of fields that has nothing to say about the behavior of wave functions, or the structure of matter. It says nothing about how the gravitational field is generated by matter and energy, and it is a global theory of space-time, not a local theory of space-time. One can scarcely imagine two great theories that have less to say to one another than quantum mechanics and general relativity!

Physicists are convinced that the general relativistic treatment of gravity must be replaced by one in which the gravitational force is replaced by one dealing with a quantum field theory. The prototypes are the quantum field theories for the other three forces in nature which have proven to be very successful in the 'Standard Model'. It is a very vexing challenge, however, to find the right mathematics to bridge the conceptual gap between classical gravity and space-time, and a quantum description of gravity and space-time.

Still, in the last 10 years there have been many 'miraculous' theories that have shown that under certain circumstances this gap can be bridged. It remains to see whether any experiments can be devised to prove which of the many prototypical theories are correct.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.