If anyone could talk about physics enthusiastically, passionately and passionately, it was Richard Feynman. The American's lectures are world famous. As a physicist, he further expanded the newly developed quantum theory with quantum electrodynamics. Kennislink asked the flamboyant physicist if he wanted to explain this in a 'fictional interview'.
A child prodigy, a brat, a Nobel Prize winner and a national hero:Richard Feynman (1918 – 1988) was it all. His contributions to physics – in the field of the interactions between the smallest particles in existence – were of great value. He had an unconditional love for physics and could talk about it with passion.
Feynman was brimming with ideas and amused many with his lively appearance. He was also a safecracker, a bongo player and a womanizer. The "playboy scholar" collaborated on the Manhattan Project and unraveled the Challenger explosion. He was very willing to talk to Kennislink about his impressive career.
Mr. Feynman, what an honor to speak to you! We should just ignore the lady who just left your hotel room? “Haha, oh well, It is well known by now that I have had many adventures in my life. The "playboy scholar" they called me jokingly during my time at Cornell University. I got into dubious clubs in Las Vegas, where science professors never went. Women did go home regularly, yes, I've had a lot of love relationships. But now that I'm married to Gweneth (his third wife, ed. ) my life is peaceful. My first and only really great love was Arline. She died much too early, of tuberculosis.”
Your greatest passion has always been science after all. Where does that passion come from? “I got that from my father Melville. He was all about science. When my mother Lucille was pregnant with me, he already said:“If it's a boy, he'll become a scientist.” He did his best for that, haha (laughs broadly, red. ). He taught me everything about how nature works and what is behind phenomena.
He often took me to the museum, read to me from the Encyclopedaedia Britanica and during walks he showed all kinds of things in nature. My father never pressured me to become a scientist, but his pleasant conversations motivated me for science. And it just so happened that I was best at physics (he says with a grin, ed. ). I got that humor from my mother."
You were good at physics in school? “Yes, in high school I already took algebra lessons of the highest class in first grade. I was greatly stimulated to gain knowledge and to solve problems. I was very curious even then. At home I looked at critters under the microscope or tinkered with devices. The pleasure I had in it was my drive to discover the world.
In my senior year of high school, I was taught by Abram Bader. After one of his lessons, he called me over and said he wanted to tell me something interesting. He gave me an advanced math book and told me about the principle of minimal action. That has always fascinated me and formed the basis of my work on quantum electrodynamics (QED)."
The "strange theory of light and matter," as you called it. Can you tell us how you got started? “I was doing my PhD at MIT and my supervisor John Wheeler presented me – as he often did – with a problem. But this time I had a lot of trouble with it. It was about how an electron interacts with itself. That problem was relevant, because at that time people were looking for a quantum theory for electricity and magnetism. Look, Maxwell had the classic . with his equations situation described of electromagnetism. But now that quantum mechanics had just been born in the 1920s - and it had become apparent that particles such as electrons and protons adhere to completely different laws than we thought - people were looking for a way to put Maxwell's electromagnetism in a 'quantum jacket':the quantum electrodynamics.
And how does the problem of an electron interacting with itself fit into this? “Patience, patience. I explain. My great hero Paul Dirac had taken a first step towards the QED in 1928. He had devised an equation – the Dirac equation – with which you could describe the interaction of charge with electromagnetic fields, but in such a way that it satisfied Einstein's special theory of relativity and the Schrödinger equation, say the basic formula for quantum particles. The problem was that "infinities" appeared in some solutions of the Dirac equation. For example, the electrical force exerted by an electron on another particle is inversely proportional to its distance from that particle. But in the electron itself - we describe electrons as a 'point' - the distance is zero and the force goes to infinity! We couldn't, so according to Dirac we needed a 'radically new idea' for the interaction of an electron with itself."
Did you have such a 'radically new idea'? “Well, (looks away uncomfortably, red. ) actually. I assumed that an electron exerts no influence on itself, but only on other charges. That in turn led to other problems that are now too far-reaching to explain. All in all, it made me let go of the concept of an electromagnetic field. I formed the image that one charge exerts a force on another charge, with no field in between. A force 'at a distance' so to speak. Do you still get it? It's hard, I know, but hang in there!
I did the math with my supervisor John and we discovered that our idea of a force at a distance can be formulated in terms of 'action' - that says something about how much a movement costs in energy. If a charge exerts a force on another particle, this always happens with the minimum action, the principle of the minimum action is called that. It turned out that the minimal action of a charged particle is always exactly the movement that Maxwell's equations predict. In other words, we had made a new description of classical electrodynamics, but not in terms of fields, but in terms of forces at a distance."
Aha, so now it was important to make a 'quantum version' of this? “Exactly, very good ! That wasn't easy, because because I had a different, unconventional description, I couldn't apply the 'normal' rules for quantization either. A 1933 Dirac article got me started. This described a mathematical function that says how a quantum state changes, or what the motion of a particle is, for example. Because the function is just about the total movement was of a particle, and not just about the position at one particular moment, I could use this.
The function gives a probability for how a quantum state changes, so what is the probability that a particle takes a certain path. The action is hidden in that probability. Do you remember that term? Now, note:you can say something about the total motion of a particle — say, between two points — if you add up the probabilities for each possible route between those points. I designed a mathematical way to do that, the path integral. Now the joke is:in the classical situation, the path integral calculates the movement with the minimum action. In the 'quantum situation' you get the chance that a particle will make a certain movement. The formula is equivalent to the Schrödinger equation and it is also easier to calculate!"
Let's let it sink in. You also had to let go of the subject after your PhD, because of the Manhattan project. In our series, Albert Einstein and Niels Bohr said they wanted as little to do with the Manhattan Project as possible. You cooperated fully. Tell me about that period. “Actually, I didn't want to participate when Robert Wilson asked me to do a secret investigation into the atomic bomb. I wanted to concentrate on my dissertation and Arline had become very ill. But when I thought about the idea that the Germans would develop an atomic bomb, I hated it so much that I decided to join in.
I moved to Los Alamos in March 1943. By the way, I have a nice story about that. We were advised not to buy a train ticket at the station in Princeton. After all, many boxes with equipment and instruments had already been sent to Los Alamos from there and we didn't want to run the risk that too much attention was drawn to this - insignificant - place. But I thought:if everyone adheres to that, I can buy my ticket in Princeton without any problems. To which the woman behind the counter there said to me:'Oh, then all that material is yours!'
Anyway, I put Arline in a hospital in Alberquerque, about 150 kilometers from Los Alamos. I visited her every weekend and sent letters every day. That was a nice distraction from work. My work in Los Alamos was diverse:making calculations and models and assembling or repairing machines. I also found a challenge in detecting weaknesses in the organization of the project. I made a sport of breaking open safes, which soon made me known as a burglar!"
In the summer of 1945, the Trinity Test takes place, the successful test of your atomic bomb. Were you there? “Yes, but just in time. Arline had sadly passed away a month before. I was on vacation, but when Hans Bethe (the leader of his department, red. ) heard 'that the child would be born' I immediately traveled back to Los Alamos. We took a bus to a point – point zero – to watch the explosion. Everyone put on sunglasses except me. I hid behind the jeep. Thus I could see with the naked eye the huge orange sphere and the flashes of light from the center.
This test was the first moment to see if our predictions were correct. The discharge was enormous. Relieved that our work hadn't been in vain. I couldn't resist beating a tambourine exuberantly, the tension had almost become too much!"
Didn't you hate what you built? “At that time I was really excited that the test had passed, but when I saw the result in Japan I was very sad. I suffered from it for a long time. I imagined what the consequences would be if such a bomb fell on New York, terrible.”
So much for the war, back to quantum physics. You started as a professor at Cornell University and picked up again? “Indeed, I combined my research with teaching – something I really enjoyed! I was just writing an article about my path integrals method when a conference took place in Shelter Island. I have attended many conferences, but none have been as important as this one. Here Willis Lamb and Isidor Rabi presented experiments that showed that Dirac's theory was not quite right on a certain part.
“I knew I could solve this with my method, but I hadn't applied my method to the usual electrodynamics – which is based on fields – before. It took me a few months of hard work and then I had the complete theory on paper. I was also able to explain Lamb and Rabi's new experimental results. I just hadn't published it yet. Unfortunately, it turned out that I was not the only one with a successful solution!”
Who was your competitor? Julian Schwinger, a well-known name at the time – unlike myself – had developed a new formulation of the QED based on the usual field theory. He presented it at a conference in 1948. However, it contained one small flaw and I was so bold to point this out to him. In my theory it was correct. You saw the audience thinking:what does that brat think about the 'great Julian Schwinger'?
I presented my method at a subsequent conference, but I made the mistake of focusing too much on the mathematical aspects. They were just so atypical and not yet completely perfected that the public was not convinced. While:I was able to draw up rules from my theory, with which you could very easily calculate phenomena in the QED, such as interaction between electrons and photons. What I needed was a way to make that clear."
You got help from an unexpected source… “From my colleague Freeman Dyson! He saw that the little drawings I used in my articles – diagrams – were very suitable as a visual representation of the rules I had drawn up. Using these diagrams, anyone could easily calculate QED. Thanks to Dyson, it became known to everyone, he promoted it at every convention! Fortunately, because a third formulation of the QED appeared to be buzzing around, from the Japanese Sinichiro Tomonaga. In the end, the three of us – Schwinger, Tomonaga and I – were awarded the Nobel Prize for our description of the QED.”
Feynman diagrams made it much easier to calculate processes in the QED, such as the influence of a field on a particle. In a diagram, the arrows represent particles and waves, curls or dashes represent the forces. Interaction takes place at the nodes. In the picture on the left the time goes from bottom to top. It describes the process in which two electrons exchange a photon:one electron emits a photon which is absorbed by the other electron.
In addition to your research, you gained international fame for your enthusiastic way of teaching. “Education was a great passion. You know:the lecture hall is a kind of theater and as a professor you are an actor. You have to entertain your audience. But my pleasure was not in making an exciting spectacle, I wanted to convey the love for my profession. Making those youngsters as curious as I am! I was looking for concrete examples. The books often contained definitions that students memorized. But did they understand how to apply it? Well no! You don't learn anything from names and definitions, it's about knowing what something does."
Your method caught on. Your classes at California Institute of Technology (Caltech) will not soon be forgotten. “That was great fun to do. Matthew Sands, a colleague at Caltech, wanted to improve the physics curriculum and asked me to teach a new, modern course for students. In this Lectures on Physics I tried to present it in my own way. The lectures were a show and were able to count on a large audience. I saw it as an experiment. I don't think I succeeded in better preparing students for an exam, but my goal was to make them appreciate the wonders of nature.”
You become a national hero when you serve on the committee that investigates why the space shuttle Challenger crashed so tragically in 1986. How was that? “At first I refused to participate. I never wanted anything to do with the government. But at the urging of my friends and Gweneth, I decided to work for four months anyway. It was not a nice experience. I was confronted with a world full of hypocrisy, lies and dishonest politicians. Fortunately, I was able to get to the core of the problem:the rubber rings that closed the cracks around the rocket motors.
The morning before launch it had been so cold that the rubber was less flexible than usual. During the launch, the rubber could not fill the cracks sufficiently and the extremely hot exhaust gases could come through the cracks. When they came into contact with the rocket fuel, the space shuttle exploded.
During a press conference I was able to demonstrate the principle with a simple experiment for everyone to see. They had wanted to complete the work too quickly to meet the safety requirements. But if technology is to succeed, reality must prevail. You cannot deceive nature."
Finally, you liked to play bongo. Would you like to play a piece for us? “Of course! Here we go…”