Free The Meaning of It All by Richard P. Feynman Page B

Rome. I didn’t find out how they did it, but that’s the crux of the matter.
    The question is whether the cure had anything to do with the process associated with the praying of Mother Seaton. In order to answer a question like that, one would have to gather all cases in which prayers had been given in the favor of Mother Seaton for the cures of various people, in various states of disease. They would then have to compare the success of the cure of these people with the average cure of people for whom such prayers were not made, and so forth. It’s an honest, straightforward way to do it, and there is nothing dishonest and nothing sacriligious about it, because if it’s a miracle, it will hold up. And if it’s not a miracle, the scientific method will destroy it.
    The people who study medicine and try to cure people are interested in every method that they can find. And they have developed clinical techniques in which (all these problems are very difficult) they are trying all kinds of medicines too, and the woman got better. She also hadchicken pox just before she got better. Has that got anything to do with it? So there is a definite clinical way to test what it is that might have something to do with it—by making comparisons and so forth. The problem is not to determine that something surprising happens. The problem is to make really good use of that to determine what to do next, because if it does turn out that it has something to do with the prayers of Mother Seaton, then it is worthwhile exhuming the body, which has been done, collecting the bones, touching many ribbons to the bones, so as to get secondary things to tie on other beds.
    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 somethingwhich 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 it’s 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