How do you reconcile classical quantum mechanics with general relativity?

It 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 theory that describes matter and energy in terms of discrete packets of energy called 'quanta', which move unhindered through space. General relativity, meanwhile, has nothing to say about the structure of matter. It says nothing about how the gravitational field is generated by matter and energy. 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 quanta. 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 on the one hand, and a quantum description of gravity and space-time on the other hand.

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.

Return to Dr. Odenwald's Gravity page at the Astronomy Cafe Blog.