Quantum Gravitation
We have argued that at the Planck scale we must apply the principles of quantum mechanics to
the gravitational force. But our best theory of gravity is general relativity and
it does not respect the principles of quantum
mechanics (nor does quantum mechanics respect the principles of general relativity).
What is required then is a theory of gravitation that also is
consistent with quantum mechanics. This could be termed a theory of
quantum gravitation.
Unfortunately, no one has yet understood how to
accomplish this very difficult task, and we do not have an internally
consistent theory of quantum gravity (see the discussion of infinities in the right panel).
The most promising present alternative is
called superstring theory, but it is not yet clear whether it can
provide a correct picture of quantum gravitation.