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.

Logic will get you from A to B. Imagination will take you everywhere.

My only refuge, as a serious young man, from the despair of my financial burden to my family, is that I did everything I could to never permit myself any amusements or diversions except those afforded by my studies.

You cannot prevent and prepare for war at the same time.

If you can't explain what you are doing to a nine-year-old, then either you still don't understand it very well, or it's not all that worthwile in the first place.

A conviction akin to religious feeling of the rationality or intelligibility of the world lies behind all scientific work of a high order.

I believe that whoever tries to think things through honestly will soon recognize how unworthy and even fatal is the traditional bias against Negroes. What can the man of good will do to combat this deeply rooted prejudice? He must have the courage to set an example by words and deed, and must watch lest his children become influenced by racial bias.