I now turn to another kind of principle or idea, and that is that there is no sense in
calculating the probability or the chance that something happens after it happens. A lot of
scientists don't even appreciate this. In fact, the first time I got into an argument over this
was when I was a graduate student at Princeton, and there was a guy in the psychology
department who was running rat races. I mean, he has a T-shaped thing, and the rats go,
and they go to the right, and the left, and so on. And it's a general principle of
psychologists that in these tests they arrange so that the odds that the things that happen
happen by chance is small, in fact, less than one in twenty. That means that one in twenty
of their laws is probably wrong. But the statistical ways of calculating the odds, like coin
flipping if the rats were to go randomly right and left, are easy to work out. This man had
designed an experiment which would show something which I do not remember, if the
rats always went to the right, let's say. I can't remember exactly. He had to do a great
number of tests, because, of course, they could go to the right accidentally, so to get it
down to one in twenty by odds, he had to do a number of them. And its hard to do, and he
did his number. Then he found that it didn't work. They went to the right, and they went
to the left, and so on. And then he noticed, most remarkably, that they alternated, first
right, then left, then right, then left. And then he ran to me, and he said, "Calculate the
probability for me that they should alternate, so that I can see if it is less than one in
twenty." I said, "It probably is less than one in twenty, but it doesn't count." He said,
"Why?" I said, "Because it doesn't make any sense to calculate after the event. You see,
you found the peculiarity, and so you selected the peculiar case."
For example, I had the most remarkable experience this evening. While coming in here, I
saw license plate ANZ 912. Calculate for me, please, the odds that of all the license
plates in the state of Washington I should happen to see ANZ 912. Well, it's a ridiculous
thing. And, in the same way, what he must do is this: The fact that the rat directions
alternate suggests the possibility that rats alternate. If he wants to test this hypothesis, one
in twenty, he cannot do it from the same data that gave him the clue. He must do another
experiment all over again and then see if they alternate. He did, and it didn't work.
Mislim, da njegove poante ne razumem najbolje, zato bi prosil za kakšno pojasnitev.