The world with its quarks and chromosomes, its distant lands and spiral nebulae, is like a vast computer in a black box, forever sealed except for its input and output registers. These we directly observe, and in the light of them we speculate on the structure of the machine, the universe. Thus it is that we think up the quarks and chromosomes, the distant lands and the nebulae; they would account for the observable data. When an observation turns out unexpectedly, we may try modifying our theory of that structure at one or another point. When an observation shows that a system of beliefs must be overhauled, it leaves us to choose which of those interlocking beliefs to revise this important fact has come up repeatedly. The beliefs face the tribunal of observation not singly but in a body. But note now that the observation sentence itself the sentence that reports or predicts a present or imminent observation, is peculiar on this score. It does face the tribunal singly, in the usual case, and simply stands or falls with the observation that it reports or predicts. And, standing or falling, it sustains or lets down the system of beliefs that implied it.

We don't know how it works, we only see the inputs and outputs and must extrapolate hypotheses from what we see.

One way, that's kind of a fun analogy in trying to get some idea of what we're doing in trying to understand nature, is to imagine that the gods are playing some great game like chess, let's say, and you don't know the rules of the game, but you're allowed to look at the board, at least from time to time, in a little corner, perhaps, and from these observations you try to figure out what the rules of the game are, what the rules of the pieces moving are. You might discover after a bit, for example, that when there's only one bishop around on the board that the bishop maintains its color. Later on you might discover the law for the bisohp as it moves on the diagonal which would explain the law that you understood before--that it maintained its color--and that would be analogous to discovering one law and then later finding a deeper understanding of it. Then things can happen, everything's going good, you've got all the laws, it looks very good and then all of a sudden some strange phenomenon occurs in some corner, so you begin to investigate that--it's castling, something you didn't expect. We're always, by the way, in fundamental physics, always trying to investigate those things in which we don't understand the conclusion. After we've checked them enough, we're okay.

Physics is like attempting to figure out the rules of chess by watching games being played.