Would You Solve the Dirac Equation?

Near the end of the year I was in Brazil I received a letter from Professor Wheeler which said that there was going to be an international meeting of theoretical physicists in Japan, and might I like to go? Japan had some famous physicists before the war—Professor Yukawa, with a Nobel prize, Tomonaga, and Nishina—but this was the first sign of Japan coming back to life after the war, and we all thought we ought to go and help them along.

Wheeler enclosed an army phrasebook and wrote that it would he nice if we would all learn a little Japanese. I found a Japanese woman in Brazil to help me with the pronunciation, I practiced lifting little pieces of paper with chopsticks, and I read a lot about Japan. At that time, Japan was very mysterious to me, and I thought it would be interesting to go to such a strange and wonderful country, so I worked very hard.

When we got there, we were met at the airport and taken to a hotel in Tokyo designed by Frank Lloyd Wright. It was an imitation of a European hotel, right down to the little guy dressed in an outfit like the Philip Morris guy. We weren’t in Japan; we might as well have been in Europe or America! The guy who showed us to our rooms stalled around, pulling the shades up and down, waiting for a tip. Everything was just like America.

Our hosts had everything organized. That first night we were served dinner up at the top of the hotel by a woman dressed Japanese, but the menus were in English. I had gone to a lot of trouble to learn a few phrases in Japanese, so near the end of the meal, I said to the waitress, “Kohi-o motte kite kudasai.” She bowed and walked away.

My friend Marshak did a double take: “What? What?”

“I talk Japanese,” I said.

“Oh, you faker! You’re always kidding around, Feynman.”

“What are you talkin’ about?” I said, in a serious tone.

“OK,” he said. “What did you ask?”

“I asked her to bring us coffee.”

Marshak didn’t believe me. “I’ll make a bet with you,” he said. “If she brings us coffee.

The waitress appeared with our coffee, and Marshak lost his bet.

It turned out I was the only guy who had learned some Japanese—even Wheeler, who had told everybody they ought to learn Japanese, hadn’t learned any—and I couldn’t stand it any more. I had read about the Japanese-style hotels, which were supposed to be very different from the hotel we were staying in.

The next morning I called the Japanese guy who was organizing everything up to my room. “I would like to stay in a Japanese-style hotel.”

“I am afraid that it is impossible, Professor Feynman.”

I had read that the Japanese are very polite, but very obstinate: You have to keep working on them. So I decided to be as obstinate as they, and equally polite. It was a battle of minds: It took thirty minutes, back and forth.

“Why do you want to go to a Japanese-style hotel?”

“Because in this hotel, I don’t feel like I’m in Japan.”

“Japanese-style hotels are no good. You have to sleep on the floor.”

“That’s what I want; I want to see how it is.”

“And there are no chairs—you sit on the floor at the table.”

“It’s OK. That will be delightful. That’s what I’m looking for.”

Finally he owns up to what the situation is: “If you’re in another hotel, the bus will have to make an extra stop on its way to the meeting.”

“No, no!” I say. “In the morning, I’ll come to this hotel, and get on the bus here.”

“Well, then, OK. That’s fine.” That’s all there was to it—except it took half an hour to get to the real problem.

He’s walking over to the telephone to make a call to the other hotel when suddenly he stops; everything is blocked up again. It takes another fifteen minutes to discover that this time it’s the mail. If there are any messages from the meeting, they already have it arranged where to deliver them.

“It’s OK,” I say. “When I come in the morning to get the bus, I’ll look for any messages for me here at this hotel.”

“All right. That’s fine.” He gets on the telephone and at last we’re on our way to the Japanese-style hotel.

As soon as I got there, I knew it was worth it: It was so lovely! There was a place at the front where you take your shoes off, then a girl dressed in the traditional outfit—the obi—with sandals comes shuffling out, and takes your stuff; you follow her down a hallway which has mats on the floor, past sliding doors made of paper, and she’s going cht-cht-cht-cht with little steps. It was all very wonderful!

We went into my room and the guy who arranged everything got all the way down, prostrated, and touched his nose to the floor; she got down and touched her nose to the floor. I felt very awkward. Should I touch my nose to the floor, too?

They said greetings to each other, he accepted the room for me, and went out. It was a really wonderful room. There were all the regular, standard things that you know of now, but it was all new to me. There was a little alcove with a painting in it, a vase with pussywillows nicely arranged, a table along the floor with a cushion nearby, and at the end of the room were two sliding doors which opened onto a garden.

The lady who was supposed to take care of me was a middle-aged woman. She helped me undress and gave me a yukata, a simple blue and white robe, to wear at the hotel.

I pushed open the doors and admired the lovely garden, and sat down at the table to do a little work.

I wasn’t there more than fifteen or twenty minutes when something caught my eye. I looked up, out towards the garden, and I saw, sitting at the entrance to the door, draped in the corner, a very beautiful young Japanese woman, in a most lovely outfit.

I had read a lot about the customs of Japan, and I had an idea of why she was sent to my room. I thought, “This might be very interesting!”

She knew a little English. “Would you rike to see the garden?” she asked.

I put on the shoes that went with the yukata I was wearing, and we went out into the garden. She took my arm and showed me everything.

It turned out that because she knew a little English, the hotel manager thought I would like her to show me the garden—that’s all it was. I was a bit disappointed, of course, but this was a meeting of cultures, and I knew it was easy to get the wrong idea.

Sometime later the woman who took care of my room came in and said something—in Japanese—about a bath. I knew that Japanese baths were interesting and was eager to try it, so I said, “Hai.”

I had read that Japanese baths are very complicated. They use a lot of water that’s heated from the outside, and you aren’t supposed to get soap into the bathwater and spoil it for the next guy.

I got up and walked into the lavatory section, where the sink was, and I could hear some guy in the next section with the door closed, taking a bath. Suddenly the door slides open: the man taking the bath looks to see who is intruding. “Professor!” he says to me in English. “That’s a very bad error to go into the lavatory when someone else has the bath!” It was Professor Yukawa!

He told me that the woman had no doubt asked do I want a bath, and if so, she would get it ready for me and tell me when the bathroom was free. But of all the people in the world to make that serious social error with, I was lucky it was Professor Yukawa!

That Japanese-style hotel was delightful, especially when people came to see me there. The other guys would come in to my room and we’d sit on the floor and start to talk. We wouldn’t be there more than five minutes when the woman who took care of my room would come in with a tray of candies and tea. It was as if you were a host in your own home, and the hotel staff was helping you to entertain your guests. Here, when you have guests at your hotel room, nobody cares; you have to call up for service, and so on.

Eating meals at the hotel was also different. The girl who brings in the food stays with you while you eat, so you’re not alone. I couldn’t have too good a conversation with her, but it was all right. And the food is wonderful. For instance, the soup comes in a bowl that’s covered. You lift the cover and there’s a beautiful picture: little pieces of onion floating in the soup just so; it’s gorgeous. How the food looks on the plate is very important.

I had decided that I was going to live Japanese as much as I could. That meant eating fish. I never liked fish when I was growing up, but I found out in Japan that it was a childish thing: I ate a lot of fish, and enjoyed it. (When I went back to the United States the first thing I did was go to a fish place. It was horrible—just like it was before. I couldn’t stand it. I later discovered the answer: The fish has to be very, very fresh—if it isn’t, it gets a certain taste that bothers me.)

One time when I was eating at the Japanese-style hotel I was served a round, hard thing, about the size of an egg yolk, in a cup of some yellow liquid. So far I had eaten everything in Japan, but this thing frightened me: it was all convoluted, like a brain looks. When I asked the girl what it was, she replied “kuri.” That didn’t help much. I figured it was probably an octopus egg, or something. I ate it, with some trepidation, because I wanted to he as much in Japan as possible. (I also remembered the word “kuri ” as if my life depended on it—I haven’t forgotten it in thirty years.)

The next day I asked a Japanese guy at the conference what this convoluted thing was. I told him I had found it very difficult to eat. What the hell was “kuri ”?

“It means ‘chestnut.’ “ he replied.

Some of the Japanese I had learned had quite an effect. One time, when the bus was taking a long time to get started, some guy says, “Hey, Feynman! You know Japanese; tell ‘em to get going!”

I said, “Hayaku! Hayaku! Ikimasho! Ikimasho! ”—which means, “Let’s go! Let’s go! Hurry! Hurry!”

I realized my Japanese was out of control. I had learned these phrases from a military phrase book, and they must have been very rude, because everyone at the hotel began to scurry like mice, saying, “Yes, sir! Yes sir!” and the bus left right away.

The meeting in Japan was in two parts: one was in Tokyo, and the other was in Kyoto. In the bus on the way to Kyoto I told my friend Abraham Pais about the Japanese-style hotel, and he wanted to try it. We stayed at the Hotel Miyako, which had both American-style and Japanese-style rooms, and Pais shared a Japanese-style room with me.

The next morning the young woman taking care of our room fixes the bath, which was right in our room. Sometime later she returns with a tray to deliver breakfast. I’m partly dressed. She turns to me and says, politely, “Ohayo, gozai masu,” which means, “Good morning.”

Pais is just coming out of the bath, sopping wet and completely nude. She turns to him and with equal composure says, “Ohayo, gozai masu,” and puts the tray down for us.

Pais looks at me and says, “God, are we uncivilized!”

We realized that in America if the maid was delivering breakfast and the guy’s standing there, stark naked, there would be little screams and a big fuss. But in Japan they were completely used to it, and we felt that they were much more advanced and civilized about those things than we were.

I had been working at that time on the theory of liquid helium, and had figured out how the laws of quantum dynamics explain the strange phenomena of super-fluidity. I was very proud of this achievement, and was going to give a talk about my work at the Kyoto meeting.

The night before I gave my talk there was a dinner, and the man who sat down next to me was none other than Professor Onsager, a topnotch expert in solid-state physics and the problems of liquid helium. He was one of these guys who doesn’t say very much, but any time he said anything, it was significant.

“Well, Feynman,” he said in a gruff voice, “I hear you think you have understood liquid helium.”

“Well, yes..

“Hoompf.” And that’s all he said to me during the whole dinner! So that wasn’t much encouragement.

The next day I gave my talk and explained all about liquid helium. At the end, I complained that there was still something I hadn’t been able to figure out: that is, whether the transition between one phase and the other phase of liquid helium was first-order (like when a solid melts or a liquid boils—the temperature is constant) or second-order (like you see sometimes in magnetism, in which the temperature keeps changing).

Then Professor Onsager got up and said in a dour voice, “Well, Professor Feynman is new in our field, and I think he needs to be educated. There’s something he ought to know, and we should tell him.”

I thought, “Geesus! What did I do wrong?”

Onsager said, “We should tell Feynman that nobody has ever figured out the order of any transition correctly from first principles, so the fact that his theory does not allow him to work out the order correctly does not mean that he hasn’t understood all the other aspects of liquid helium satisfactorily.” It turned out to be a compliment, but from the way he started out, I thought I was really going to get it!

It wasn’t more than a day later when I was in my room and the telephone rang. It was Time magazine. The guy on the line said, “We’re very interested in your work. Do you have a copy of it you could send us?”

I had never been in Time and was very excited. I was proud of my work, which had been received well at the meeting, so I said, “Sure!”

“Fine. Please send it to our Tokyo bureau.” The guy gave me the address. I was feeling great.

I repeated the address, and the guy said, “That’s right. Thank you very much, Mr. Pais.”

“Oh, no!” I said, startled. “I’m not Pais; it’s Pais you want? Excuse me, I’ll tell him that you want to speak to him when he comes back.”

A few hours later Pais came in: “Hey, Pais! Pais!” I said, in an excited voice. “Time magazine called! They want you to send ‘em a copy of the paper you’re giving.”

“Aw!” he says. “Publicity is a whore!”

I was doubly taken aback.

I’ve since found out that Pais was right, but in those days, I thought it would be wonderful to have my name in Time magazine.

That was the first time I was in Japan. I was eager to go back, and said I would go to any university they wanted me to. So the Japanese arranged a whole series of places to visit for a few days at a time.

By this time I was married to Mary Lou, and we were entertained wherever we went. At one place they put on a whole ceremony with dancing, usually performed only for larger groups of tourists, especially for us. At another place we were met right at the boat by all the students. At another place, the mayor met us.

One particular place we stayed was a little, modest place in the woods, where the emperor would stay when he came by. It was a very lovely place, surrounded by woods, just beautiful, the stream selected with care. It had a certain calmness, a quiet elegance. That the emperor would go to such a place to stay showed a greater sensitivity to nature, I think, than what we were used to in the West.

At all these places everybody working in physics would tell me what they were doing and I’d discuss it with them. They would tell me the general problem they were working on, and would begin to write a bunch of equations.

“Wait a minute,” I would say. “Is there a particular example of this general problem?”

“Why yes; of course.”

“Good. Give me one example.” That was for me: I can’t understand anything in general unless I’m carrying along in my mind a specific example and watching it go. Some people think in the beginning that I’m kind of slow and I don’t understand the problem, because I ask a lot of these “dumb” questions: “Is a cathode plus or minus? Is an an-ion this way, or that way?”

But later, when the guy’s in the middle of a bunch of equations, he’ll say something and I’ll say, “Wait a minute! There’s an error! That can’t be right!”

The guy looks at his equations, and sure enough, after a while, he finds the mistake and wonders, “How the hell did this guy, who hardly understood at the beginning, find that mistake in the mess of all these equations?”

He thinks I’m following the steps mathematically, but that’s not what I’m doing. I have the specific, physical example of what he’s trying to analyze, and I know from instinct and experience the properties of the thing. So when the equation says it should behave so-and-so, and I know that’s the wrong way around, I jump up and say, “Wait! There’s a mistake!”

So in Japan I couldn’t understand or discuss anybody’s work unless they could give me a physical example, and most of them couldn’t find one. Of those who could, it was often a weak example, one which could be solved by a much simpler method of analysis.

Since I was perpetually asking not for mathematical equations, but for physical circumstances of what they were trying to work out, my visit was summarized in a mimeographed paper circulated among the scientists (it was a modest but effective system of communication they had cooked up after the war) with the title, “Feynman’s Bombardments, and Our Reactions.”

After visiting a number of universities I spent some months at the Yukawa Institute in Kyoto. I really enjoyed working there. Everything was so nice: You’d come to work, take your shoes off, and someone would come and serve you tea in the morning when you felt like it. It was very pleasant.

While in Kyoto I tried to learn Japanese with a vengeance. I worked much harder at it, and got to a point where I could go around in taxis and do things. I took lessons from a Japanese man every day for an hour.

One day he was teaching me the word for “see.” “All right,” he said. “You want to say, ‘May I see your garden?’ What do you say?”

I made up a sentence with the word that I had just learned.

“No, no!” he said. “When you say to someone, ‘Would you like to see my garden? you use the first ‘see.’ But when you want to see someone else’s garden, you must use another ‘see,’ which is more polite.”

“Would you like to glanceat my lousy garden?” is essentially what you’re saying in the first case, but when you want to look at the other fella’s garden, you have to say something like, “May I observe your gorgeous garden?” So there’s two different words you have to use.

Then he gave me another one: “You go to a temple, and you want to look at the gardens …”

I made up a sentence, this time with the polite “see.”

“No, no!” he said. “In the temple, the gardens are much more elegant. So you have to say something that would be equivalent to ‘May I hang my eyes on your most exquisite gardens?’”

Three or four different words for one idea, because when I’m doing it, it’s miserable; when you’re doing it, it’s elegant.

I was learning Japanese mainly for technical things, so I decided to check if this same problem existed among the scientists.

At the institute the next day, I said to the guys in the office, “How would I say in Japanese, ‘I solve the Dirac Equation’?”

They said such-and-so.

“OK. Now I want to say, ‘Would you solve the Dirac Equation?’—how do I say that?”

“Well, you have to use a different word for ‘solve,’ “they say.

“Why?” I protested. “When I solve it, I do the same damn thing as when you solve it!”

“Well, yes, but it’s a different word—it’s more polite.”

I gave up. I decided that wasn’t the language for me, and stopped learning Japanese.

The 7 Percent Solution

The problem was to find the right laws of beta decay. There appeared to be two particles, which were called a tan and a theta. They seemed to have almost exactly the same mass, but one disintegrated into two pions, and the other into three pions. Not only did they seem to have the same mass, but they also had the same lifetime, which is a funny coincidence. So everybody was concerned about this.

At a meeting I went to, it was reported that when these two particles were produced in a cyclotron at different angles and different energies, they were always produced in the same proportions—so many taus compared to so many thetas.

Now, one possibility, of course, was that it was the same particle, which sometimes decayed into two pions, and sometimes into three pions. But nobody would allow that, because there is a law called the parity rule, which is based on the assumption that all the laws of physics are mirror-image symmetrical, and says that a thing that can go into two pions can’t also go into three pions.

At that particular time I was not really quite up to things: I was always a little behind. Everybody seemed to be smart, and I didn’t feel I was keeping up. Anyway, I was sharing a room with a guy named Martin Block, an experimenter. And one evening he said to me, “Why are you guys so insistent on this parity rule? Maybe the tau and theta are the same particle. What would be the consequences if the parity rule were wrong?”

I thought a minute and said, “It would mean that nature’s laws are different for the right hand and the left hand, that there’s a way to define the right hand by physical phenomena. I don’t know that that’s so terrible, though there must be some bad consequences of that, but I don’t know. Why don’t you ask the experts tomorrow?”, -

He said, “No, they won’t listen to me. You ask.”

So the next day, at the meeting, when we were discussing the tau-theta puzzle, Oppenheimer said, “We need to hear some new, wilder ideas about this problem.”

So I got up and said, “I’m asking this question for Martin Block: What would be the consequences if the parity rule was wrong?”

Murray Gell-Mann often teased me about this, saying I didn’t have the nerve to ask the question for myself. But that’s not the reason. I thought it might very well be an important idea.

Lee, of Lee and Yang, answered something complicated, and as usual I didn’t understand very well. At the end of the meeting, Block asked me what he said, and I said I didn’t know, but as far as I could tell, it was still open—there was still a possibility. I didn’t think it was likely, but I thought it was possible.

Norm Ramsey asked me if I thought he should do an experiment looking for parity law violation, and I replied, “The best way to explain it is, I’ll bet you only fifty to one you don’t find anything.”

He said, “That’s good enough for me.” But he never did the experiment.

Anyway, the discovery of parity law violation was made, experimentally, by Wu, and this opened up a whole bunch of new possibilities for beta decay theory, It also unleashed a whole host of experiments immediately after that. Some showed electrons coming out of the nuclei spun to the left, and some to the right, and there were all kinds of experiments, all kinds of interesting discoveries about parity. But the data were so confusing that nobody could put things together.

At one point there was a meeting in Rochester—the yearly Rochester Conference. I was still always behind, and Lee was giving his paper on the violation of parity. He and Yang had come to the conclusion that parity was violated, and flow he was giving the theory for it.

During the conference I was staying with my sister in Syracuse. I brought the paper home and said to her, “I can’t understand these things that Lee and Yang are saying. It’s all so complicated.”

“No,” she said, “what you mean is not that you can’t understand it, but that you didn’t invent it. You didn’t figure it out your own way, from hearing the clue. What you should do is imagine you’re a student again, and take this paper upstairs, read every line of it, and check the equations. Then you’ll understand it very easily.”