Now I'm going to discuss how we would look for a new law. In general, we look for a new law by the following process: first, we guess it, no, don’t laugh, that’s the truth. Then we compute the consequences of the guess, to see what, if this is right, if this law we guessed is right, to see what it would imply and then we compare the computation results to nature or we say compare to experiment or experience, compare it directly with observations to see if it works.
If it disagrees with experiment, it’s wrong! In that simple statement is the key to science. It doesn’t make any difference how beautiful your guess is, it doesn’t make a difference how smart you are, who made the guess, or what his name is… If it disagrees with experiment, it’s wrong. That’s all there is to it.
It is therefore not unscientific to make a guess, although many people who are not in science think it is. For instance, I had a conversation about flying saucers, some years ago, with a layman — because I am scientific I know all about flying saucers! I said “I don’t think there are flying saucers”. So the other...my antagonist said, “Is it impossible that there are flying saucers? Can you prove that it’s impossible?” “No, I can’t prove it’s impossible. It’s just very unlikely”. At that he said, “You are very unscientific. If you can’t prove it impossible then how can you say that it’s unlikely?” But that is the way that is scientific. It is scientific only to say what is more likely and what less likely, and not to be proving all the time the possible and impossible. To define what I mean, I might have said to him, "Listen, I mean that from my knowledge of the world that I see around me, I think that it is much more likely that the reports of flying saucers are the results of the known irrational characteristics of terrestrial intelligence than of the unknown rational efforts of extra-terrestrial intelligence." It is just more likely. That is all, and it is a very good guess. And we always try to guess the most likely explanation, keeping in the back of our minds the fact that if it does not work, then we must discuss the other possiblities.
There was, for instance, for a while, a phenomenon called super-conductivity, there still is the phenomenon, which is that metals conduct electricity without resistance at low temperatures and it was not at first obvious that this was a consequence of the known laws with these particles. Now that it has been thought through carefully enough, it is seen in fact to be fully explainable in terms of our present knowledge.
There are other phenomena, such as extra-sensory perception, which cannot be explained by our knowledge of physics here. However, that phenomenon has not been well established, and we cannot guarantee that it is there. If it could be demonstrated, of course, that would prove that physics is incomplete, and it is therefore extremely interesting to physicists whether it is right or wrong. Many, many experiments exist which show that it doesn't work. The same goes for astrological influences. If it were true that the stars could affect the day that it was good to go to the dentist - in America we have that kind of astrology - then the physics theory would be wrong, because there is no mechanism understandable in principle from these things that would make it go. That is the reason that there is some scepticism among scientists with regard to those ideas.
Now you see of course that with this method we can disprove any definite theory. We have a definite theory, a real guess, from which you can clearly compute consequences which could be compared to experiment and in principle we can get rid of any theory. You can always prove any definite theory wrong. Notice however that we never prove it right.
Suppose you invent a good guess, calculate the consequences, and discover every time that the consequences you have calculated agree with experiment. The theory is then right? No, it is simply not proved wrong.
Another thing I must point out is that you cannot prove a vague theory wrong. If the guess that you make is poorly expressed and rather vague, and the method that you use for figuring out the consequences is a little vague —you are not sure, and you say, “I think everything’s right because it’s all due to so and so, and such and such do this and that more or less, and I can sort of explain how this works...” then you see that this theory is good, because it cannot be proved wrong! Also if the process of computing the consequences is indefinite, then with a little skill any experimental results can be made to look like the expected consequences. You are probably familiar with that in other fields. ‘A’ hates his mother. The reason is, of course, because she did not caress him or love him enough when he was a child. But if you investigate you find out that as a matter of fact she did love him very much, and everything was all right. Well then, it was because she was overindulgent when he was a child! By having a vague theory it is possible to get either result. The cure for this one is the following: if it were possible to state exactly, ahead of time, how much love is not enough, and how much love is over-indulgent, then there would be a perfectly legitimate theory against which you could make tests. It is usually said when this is pointed out--when you are dealing with psychological matters things can’t be defined so precisely. Yes, but then you cannot claim to know anything about it.