Some moments during these lectures we have looked together into one of the rooms of the house called Science. . . . One thing we find throughout the house—there are no locks. There are no shut doors. Wherever we go, there are signs and usually the words of welcome. It is an open house, open to all comers.

The discoveries of science, the new rooms in this great house, have changed the way men think of things outside its walls. We have some glimmering now—the depth in time and the vastness in space of the physical world we live in. An awareness of how long our history, how immense our cosmos—touches us, even in simple earthly deliberations. . . .

What is new, what was not anticipated a half century ago, is that though to an atomic system there was a potential applicability of one or another of these ideas in any real situation, only some of these ways of description could be actual. This is because we need to take into account not merely the atomic system we are studying but the means we use in observing it, and the fitness of these experimental means for defining and measuring selected properties of the system. All such ways of observing are needed for the whole experience of the atomic world. All but one are excluded in any actual experience. . . .

Atomic theory is then in part an account of these descriptions and in part an understanding of the circumstances to which one applies or another or another. And so it is with man's life. He may be any one of a number of things, but he will not be all of them. He may be well versed. He may be a poet. He may be a creator in one, or more than one science. He will not be all kinds of man, or all kinds of scientist even. He will be lucky if he has a bit of familiarity outside that room in which he works.