Two of the greatest scientific achievements of the last century were the establishment of the theories of Quantum Mechanics and General Relativity, both of which have withstood continual experimental scrutiny. However, a problem remains. The two theories seem to be at odds with each other.
Researchers, for decades, have sought a theory that would combine the two realms – the large-scale gravity fields, and the tiny quantum scales – while Einstein himself spent the latter part of his life searching for just such a theory.
Source: Red Orbit. Read full article. (link)