On the left-hand side of the field equation we may add the fundamental tensor guv, multiplied by a universal constant, -λ, at present unknown, without destroying the general covariance.

Truth is what stands the test of experience.

When the Special Theory of Relativity began to germinate in me, I was visited by all sorts of nervous conflicts... I used to go away for weeks in a state of confusion.

People are like bicycles. They can keep their balance only as long as they keep moving.

Heroism on command, senseless violence, and all the loathsome nonsense that goes by the name of patriotism - how passionately I hate them!

I regard class differences as contrary to justice and, in the last resort, based on force.

The thinking it took to get us into this mess is not the same thinking that is going to get us out of it.