Reality is merely an illusion, albeit a very persistent one.

Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world. In our endeavor to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and the moving hands, even hears its ticking, but he has no way of opening the case. If he is ingenious he may form some picture of a mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility or the meaning of such a comparison.

As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.

One thing I have learned in a long life: All our science, measured against reality, is primitive and childlike — and yet it is the most precious thing we have.