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.