Weekend Reading: Richard Feynman: Math and Science
Richard Feynman: Math and Science: "I’m going to describe to you how Nature is—and if you don’t like it, that’s going to get in the way of your understanding it...
...It’s a problem that physicists have learned to deal with: They’ve learned to realize that whether they like a theory or they don’t like a theory is not the essential question. Rather, it is whether or not the theory gives predictions that agree with experiment. It is not a question of whether a theory is philosophically delightful, or easy to understand, or perfectly reasonable from the point of view of common sense. The theory of quantum electrodynamics describes Nature as absurd from the point of view of common sense. And it agrees fully with experiment. So I hope you can accept Nature as She is—absurd.
I’m going to have fun telling you about this absurdity, because I find it delightful. Please don’t turn yourself off because you can’t believe Nature is so strange. Just hear me all out, and I hope you’ll be as delighted as I am when we’re through.
How am I going to explain to you the things I don’t explain to my students until they are third-year graduate students? Let me explain it by analogy:
The Maya Indians were interested in the rising and setting of Venus as a morning “star” and as an evening “star”—they were very interested in when it would appear. After some years of observation, they noted that five cycles of Venus were very nearly equal to eight of their “nominal years” of 365 days (they were aware that the true year of seasons was different and they made calculations of that also).
To make calculations, the Maya had invented a system of bars and dots to represent numbers (including zero), and had rules by which to calculate and predict not only the risings and settings of Venus, but other celestial phenomena, such as lunar eclipses.
In those days, only a few Maya priests could do such elaborate calculations. Now, suppose we were to ask one of them how to do just one step in the process of predicting when Venus will next rise as a morning star—subtracting two numbers. And let’s assume that, unlike today, we had not gone to school and did not know how to subtract.
How would the priest explain to us what subtraction is? He could either teach us the numbers represented by the bars and dots and the rules for “subtracting” them, or he could tell us what he was really doing:
Suppose we want to subtract 236 from 584. First, count out 584 beans and put them in a pot. Then take out 236 beans and put them to one side. Finally, count the beans left in the pot. That number is the result of subtracting 236 from 584.
You might say, “My Quetzalcoatl! What tedium—counting beans, putting them in, taking them out—what a job!”
To which the priest would reply:
That’s why we have the rules for the bars and dots. The rules are tricky, but they are a much more efficient way of getting the answer than by counting beans. The important thing is, it makes no difference as far as the answer is concerned: we can predict the appearance of Venus by counting beans (which is slow, but easy to understand) or by using the tricky rules (which is much faster, but you must spend years in school to learn them).
To understand how subtraction works—as long as you don’t have to actually carry it out—is really not so difficult. That’s my position: I’m going to explain to you what the physicists are doing when they are predicting how Nature will behave, but I’m not going to teach you any tricks so you can do it efficiently. You will discover that in order to make any reasonable predictions with this new scheme of quantum electrodynamics, you would have to make an awful lot of little arrows on a piece of paper. It takes seven years—four undergraduate and three graduate—to train our physics students to do that in a tricky, efficient way.
That’s where we are going to skip seven years of education in physics: By explaining quantum electrodynamics to you in terms of what we are really doing, I hope you will be able to understand it better than do some of the students!
Taking the example of the Maya one step further, we could ask the priest why five cycles of Venus nearly equal 2,920 days, or eight years. There would be all kinds of theories about why, such as, “20 is an important number in our counting system, and if you divide 2,920 by 20, you get 146, which is one more than a number that can be represented by the sum of two squares in two different ways,” and so forth. But that theory would have nothing to do with Venus, really. In modern times, we have found that theories of this kind are not useful. So again, we are not going to deal with why Nature behaves in the peculiar way...
Richard Feynman (1985): QED: The Strange Theory of Light and Matter (Princeton: Princeton University Press: 0691024170) <http://amzn.to/2iXkx5Z>