The belief in an external world independent of the perceiving subject is the basis of all natural science. Since, however, sense perception only gives information of this external world or of "physical reality" indirectly, we can only grasp the latter by speculative means. It follows from this that our notions of physical reality can never be final. We must always be ready to change these notions - that is to say, the axiomatic basis of physics - in order to do justice to perceived facts in the most perfect way.

In one's youth every person and every event appear to be unique. With age one becomes much more aware that similar events recur. Later on, one is less often delighted or surprised, but also less disappointed than in earlier years.

I do not believe that a man should be restrained in his daily actions by being afraid of punishment after death or that he should do things only because in this way he will be rewarded after he dies. This does not make sense. The proper guidance during the life of a man should be the weight that he puts upon ethics and the amount of consideration that he has for others.

We owe a lot to the Indians, who taught us how to count, without which no worthwhile scientific discovery could have been made.

About God, I cannot accept any concept based on the authority of the Church... As long as I can remember. I have resented mass indoctrination. I cannot prove to you there is no personal God, but if I were to speak of him, I would be a liar. I do not believe in the God of theology who rewards good and punishes evil. His universe is not ruled by wishful thinking, but by immutable laws

The difference between what the most and the least learned people know is inexpressibly trivial in relation to that which is unknown.

If [quantum theory] is correct, it signifies the end of physics as a science.