"One thing I have learned in a long life: that
all our science, measured against reality, is primitive and childlike -- and yet it is the most
precious thing we have."
From before 1920 until his death in 1955, Einstein struggled to find laws of
physics far more general than any known before. In his theory of relativity,
the force of gravity had become an expression of the geometry of space and time.
The other forces in nature, above all the force of electromagnetism, had not
been described in such terms. But it seemed likely to Einstein that electromagnetism
and gravity could both be explained as aspects of some broader mathematical
structure. The quest for such an explanation -- for a "unified field" theory
that would unite electromagnetism and gravity, space and time, all together
-- occupied more of Einstein's years than any other activity.