Experience alone can decide on truth.

Whether or not you can observe a thing depends upon the theory you use. It is the theory which decides what can be observed.

The relativity principle in connection with the basic Maxwellian equations demands that the mass should be a direct measure of the energy contained in a body; light transfers mass. With radium there should be a noticeable diminution of mass. The idea is amusing and enticing; but whether the Almighty is laughing at it and is leading me up the garden path -- that I cannot know.

Only a monomaniac gets anything done.

The intellect has little to do on the road to discovery. There comes a leap in consciousness, call it Intuition or what you will, the solution comes to you and you don't know how or why.

Man would indeeded be in a poor way if he had to be restrained by fear of punishment and hope of reward after death.

I know little about nature and hardly anything about men.