Frank Wilczek on Albert Einstein

“Most scientists are happiest when they are making clear progress, solving some perhaps small but well-defined and significant problems by clever adaptations of known techniques. Most people—perhaps all—feel acutely anxious and unhappy when they are "groping in the dark" or find themselves poised uneasily upon "no firm foundation." We must admire the courage of those rare individuals who, like Einstein, systematically seek out such situations.”

“A clear pattern emerges... he latches on to some perceived fundamental weakness or contradiction in existing physical theory and worries over it for long periods of time—as long as it takes. He is concerned not to exploit existing ideas but to transcend them. This restless style is not necessarily a recipe for success. Einstein did not play a creative role in the development of physics after 1925... The basic difficulty was that Einstein believed he saw difficulties in the basic foundations of quantum theory and that, characteristically, he wished to overhaul the theory rather than to exploit it. While his colleagues were applying quantum theory with great success to elucidate the workings of atoms, nuclei, and bulk matter, Einstein held aloof.”

“It is quite easy to include a weight for empty space in the equations of gravity. Einstein did so in 1917, introducing what came to be known as the cosmological constant into his equations. His motivation was to construct a static model of the universe. To achieve this, he had to introduce a negative mass density for empty space, which just canceled the average positive density due to matter. With zero total density, gravitational forces can be in static equilibrium. Hubble's subsequent discovery of the expansion of the universe, of course, made Einstein's static model universe obsolete. ...The fact is that to this day we do not understand in a deep way why the vacuum doesn't weigh, or (to say the same thing in another way) why the cosmological constant vanishes, or (to say it in yet another way) why Einstein's greatest blunder was a mistake.”