Scientific tragedy of late
Einstein. He tried hard to unify all fundamental forces in a framework like his
General Relativity. While GR ranks among the greatest achievements of physics, UFT never worked out.
According to
CF von Weizsäcker, Einstein's UFT was far from explaining
sharply separated types of elementary particles, while
Heisenberg's attempts on UFT came a little closer.
It's an unsolved problem to fit
gravitation and
quantum physics into one mathematical framework.