No man really becomes a fool until he stops asking questions.

Scientific theories need reconstruction every now and then. If they didn't need reconstruction they would be facts, not theories. The more facts we know, the less radical become the changes in our theories. Hence they are becoming more and more constant. But take the theory of gravitation it has not been changed in four hundred years.

I have succeeded in getting my actual work down to thirty minutes a day. That leaves me eighteen hours for engineering.

Electricity is doing for the distribution of energy what the railroads have done for the distribution of materials.

Money is a stupid measure of achievement, but unfortunately it is the only universal measure we have.

From a mathematical standpoint it is possible to have infinite space. In a mathematical sense space is manifoldness, or combinations of numbers. Physical space is known as the 3-dimension system. There is the 4-dimension system, the 10-dimension system.

The mercury light doesn't show red. It makes the blood in your skin look blue-black. But see how splendidly it brings out the green in the plants.

Take the rose—most people think it very beautiful: I don’t care for It at all. I prefer the cactus, for the simple reason that it has a more interesting personality. It has wonderfully adapted itself to its surroundings! It is the best illustration of the theory of evolution in plant life.

As for my memory, I have a particularly good one. I never keep any record of my investigations or experiments. My memory files all these things away conveniently and reliably. I should say, though, that I didn’t cumber it up with a lot of useless matter.

No evidence or proof of the existence of a God has been found in the phenomena of nature, based on experience.