We come now to the question: what is a priori certain or necessary, respectively in geometry (doctrine of space) or its foundations? Formerly we thought everything; nowadays we think nothing. Already the distance-concept is logically arbitrary; there need be no things that correspond to it, even approximately.
Albert EinsteinYou do not really understand something unless you can explain it to your grandmother.
Albert EinsteinThe world is an evil place to live in. Not for those who do evil, but for those who sit back and allow evil to occur.
Albert EinsteinThe best that Gauss has given us was likewise an exclusive production. If he had not created his geometry of surfaces, which served Riemann as a basis, it is scarcely conceivable that anyone else would have discovered it. I do not hesitate to confess that to a certain extent a similar pleasure may be found by absorbing ourselves in questions of pure geometry.
Albert Einstein