Paul J. Steinhardt, a theoretical physicist who proposed the concept of "quasicrystallines," recalls a report at the California Institute of Technology when he first proposed the quasicrystalline concept, and Feynman came up with his habitual criticism, as he did many years ago. In the story, Steinhardt also recalls the experience of studying with Feynman. If you finished something in front of Feynman and words like "impossible," "ridiculous," "stupid, etc." popped out of his mouth, what did it mean? At the very least, don't get scared!
Written by | Paul J. Steinhardt (Professor of Physics, Princeton University)
Translate | Ren Yu
No way!
These words resounded throughout the great lecture hall. And I've just finished talking about a revolutionary concept of a new type of state of matter, which I co-invented with my graduate student, Dov Levine.
The California Institute of Technology lecture hall is filled with scientists from various departments. The discussion had gone fairly well, but just as the last crowd was pouring out, a familiar, high-pitched voice sounded: "Impossible!" ”
I could also recognize this offbeat, low, hoarse, distinctly New York voice with my eyes closed. Standing in front of me was my scientific icon, the legendary physicist Richard Feynman, with gray shoulder-to-shoulder hair, his usual white shirt, and a sly smile that let his guard down.
Joker – Richard Feynman: Despite richard Feynman's witty humor, he was also extremely blunt. Paul J. Steinhardt remembers giving his own presentation one day, only to see Feynman sitting in the front row, and he was suddenly a little intimidated.
By this time Feynman had already won the Nobel Prize for his pioneering work on developing the first quantum theory of electromagnetic phenomena. Among the scientific community, he is already regarded as one of the greatest theoretical physicists of the twentieth century. And, because of his pivotal role in confirming the cause of the Space Shuttle Challenger accident, as well as his two best-selling books, Surely You're Joking! and What Do You Care What Other People Think?, he eventually earned idol status in the public eye.
He has a particularly mischievous sense of humor and is "notorious" for his elaborate pranks. But when it comes to science, Feynman has always been unapologetically honest and always harshly judged, which makes him a particularly intimidating presence at scientific seminars. Anyone could have expected that as soon as he heard something that seemed unclear or wrong to him, he would simply interrupt and openly challenge the speaker.
So, when Feynman entered the lecture hall before I started my speech and sat in the front row of his habitual seats, I was acutely aware of his presence. Throughout the speech, I kept glancing carefully at him out of the corner of my eye, waiting for any possible outburst. But Feynman never interrupted me or questioned me.
Physical X
After the speech, Feynman came forward to confront me, which I am afraid would scare many scientists. But this is not the first time we have seen each other. Almost a decade ago, when I was an undergraduate at Caltech, I had the privilege of working intimately with Feynman, and I had only admiration and affection for him. Feynman changed my life through his articles, speeches, and coaching.
When I first entered campus as a freshman in 1970, I intended to study biology or math. In middle school, I never had much interest in physics. But I know that every Caltech undergraduate student requires two years of physics.
I soon discovered that, in large part, thanks to that textbook, The Feynman Lectures on Physics (Volume I), the nascent physics was rarely a curse. Rather than a traditional textbook, the book is based on a series of brilliant articles that Feynman famously made in the 1960s on physics reports for freshmen.
Unlike any other physics textbook I've ever been exposed to, Feynman's Lecture Notes on Physics never bothered to explain how to solve problems, which makes trying to complete the difficult after-school assignments time-consuming and laborious. Those articles, though, offer something more valuable—a deep insight into the way Feynman himself thinks about science. Generations have benefited from Feynman's handouts. For me, that experience was a complete enlightenment.
After a few weeks, I felt like I had been brainwashed. I started thinking like a physicist and was passionate about it. Like many scientists in my generation, I am proud to see Feynman as my hero. I dismissed my original plan to study biology and mathematics and decided to go the extra mile to specialize in physics.
I remember a few times during my freshman year that I plucked up the courage to say hello to Feynman before the presentation. It was completely unthinkable to have any other moves at the time. But by the time I was a junior, my roommate and I somehow had the courage to knock on his office door and ask if he could consider teaching an informal course, meeting with undergraduates like us once a week, and answering any questions we might have. We told him that the whole course was informal, with no assignments, no quizes, no grades, and no grade points. We know that he is an outlaw who has no patience for administrative affairs, and we hope that this casual performance will attract him.
Ten years ago or earlier, Feynman taught a similar course, but only for freshmen and only one quarter a year. Now we're asking him to do the same all year, and it's open to all undergraduates, especially third- and fourth-yearrs like us who might ask more in-depth questions. We suggest that this new course be called "Physics X", like his previous course, to make it clear to everyone that it is completely out of the book.
Feynman thought for a moment, and to our surprise, he replied, "Yes!" So for the next two years, my roommate and I, along with some other lucky students, spent a wonderful and memorable afternoon with Feynman every week.
Physical X always opens like this: He enters the lecture hall and asks who has a problem. Occasionally, someone wants to ask a question about which Feynman happens to be an expert. Naturally, his answers to these questions were masterful. At other times, however, it is clear that Feynman had never thought about these issues before. I've always found these times particularly interesting because I've had the opportunity to witness how he thinks and solves a problem head-on.
I distinctly remember asking some questions that I found interesting, even though I was worried that it would seem boring to him. I wondered, "What color is a shadow?" ”
After walking back and forth in front of the lecture hall for a while, Feynman began to peel back the question with great interest. He initiated a discussion about subtle hierarchical changes in shadows, about the properties of light, about the perception of color, about shadows on the moon, about the reflection of the earth on the moon, about the formation of the moon, and so on. I was fascinated.
During my senior year, Dick agreed to be a mentor for my research projects. Now I can get a closer look at his approach. I also experienced his harsh tone when he didn't live up to his expectations. He often used words like "crazy," "nuts," "ridiculous," and "stupid" to criticize my mistakes.
These harsh words were very poignant at first, and I doubted for a while whether I was suitable for studying theoretical physics. But I found that Dick didn't take these harsh criticisms as seriously as I did. Often, he would encourage me to try different approaches and invite me to come back when I was making progress.
One of the most important things Feynman taught me was that some of the most exciting scientific accidents could be found in everyday phenomena. All you have to do is take the time to look at things carefully and ask yourself good questions. He also influenced my belief that there was no need to be confined to a certain field of science under external pressure, as many scientists do. Feynman's words and deeds taught me that if there is curiosity to guide, it is also possible to explore different fields.
locus
During my last semester at Caltech, one of our exchanges was particularly memorable. I'm explaining a mathematical method I've come up with that can be used to predict the motion behavior of super balls. It was a rubber ball with super elasticity that was all the rage of the year.
It's a challenging one because the superball changes direction every time it bounces back. I wanted to predict how the supersphere bounced on a series of planes placed at different angles, which added another layer of difficulty. For example, I calculated its trajectory bouncing from the ground to under the table, to an inclined plane, and then to the wall. These seemingly random movements are completely predictable according to the laws of physics.
I showed Feynman one of my calculations. It predicted that after I threw the superball, after a series of complex bounces, it would come back right back into my hand. I handed him the paper, and he glanced at my formula.
"It's impossible!" He said.
No way? I was startled by the word. It was a new word that popped out of his mouth. It's no longer "crazy" or "stupid" that I sometimes expect.
"Why do you think it's impossible?" I asked nervously.
Feynman pointed out his considerations. According to my formula, if someone releases a super ball from a certain height and lets it spin, the ball will bounce back and bounce to the side at a small angle to the ground.
"It's obviously impossible, Paul," he said.
I looked at my equation and saw that my prediction did indicate that the ball would bounce back and take a very small angle. But I'm not so sure it's impossible, even though it seems counterintuitive.
I've been through a lot of battles now and dare to refute it. "Well," I said, "I've never tried this experiment before, so let's try it right in your office." ”
I pulled a super ball out of my pocket and Feynman stared at me to give it a turn and throw it. With great certainty, the ball bounced out precisely in the direction predicted by my equations, bouncing to the side at a very small angle from the ground, in a way that Feynman found impossible.
In a flash, he knew his mistake. He did not take into account the very high viscosity of the surface of the supersphere, which would alter the effect of rotation on the trajectory of the ball.
"So stupid!" Feynman said out loud, in the exact same tone he sometimes used to criticize me.
After two years of collaboration, I finally knew exactly what I had been suspicious of: "stupidity" was just an expression of Feynman, used for anyone, including himself, as a way to stare at a mistake and not make it again.
I also realized that when Feynman used the word "impossible," it didn't necessarily mean "unachievable" or "ridiculous." Sometimes it means, "Wow! There's something magical about this that contradicts what we usually think is right. It's worth figuring out! ”
Quasi-crystalline
So 11 years later, when Feynman approached me with a sly smile after the report and jokingly claimed that my theory was "impossible," I knew exactly what he was referring to. The subject of my report, a completely new form of matter called quasicrystals, clashes with what he believes is the right principle. So it's interesting and also worth figuring out.
I set up an experiment on the table to test the idea, and Feynman stepped forward, pointing at them and demanding, "Show me again!" ”
I toggled the switch to start the demonstration, and Feynman stood motionless. He witnessed, witnessed the explicit violation of one of the most widely known principles of science. This principle is so fundamental that he also describes it in Feynman's lecture notes. In fact, these principles have been taught to every young scientist for nearly 200 years.
But now, here I am, standing before Richard Feynman, to explain that these long-standing norms are wrong.
Crystals are not the only possible forms of matter with ordered atomic arrangements and dot-like diffraction patterns. There is now a new world of possibilities, with its own norms, which we call quasi-crystals.
We chose this name to show how these new materials differ from the usual crystals. Both types of materials contain a set of atoms that are repeated throughout the structure.
A set of atoms in a crystal is repeated at regular intervals, just like five known patterns. In quasicrystals, however, different groups of atoms are repeated at different intervals. We were inspired by a two-dimensional pattern known as penrose tiling. These patterns are extraordinary, they contain two different types of blocks, and are repeated at two irreversible intervals. Mathematicians call such patterns quasiperdiodic. Therefore, we named our theoretical finding "quasiperiodic crystals," or simply "quasicrystals."
The little demo I did for Feynman proved my point, using only a laser beam and a photographic projection of a quasi-periodic pattern. I turned on the laser at Feynman's instructions and aimed the beam so that it was cast on the distant wall through the slide. The laser produces the same effect as X-rays passing through channels between atoms: it produces a diffraction pattern, as shown in the photo below.
I turned off the top light so Feynman could see more clearly the snowflake-like dot patterns on the walls. It's not like any other diffraction pattern Feynman has ever seen.
As I did in my report, I pointed out to him that the brightest points formed concentric rings of ten elements. This is unheard of. We can also see some spots forming pentagons, which reveals a symmetry that is thought to be absolutely forbidden in nature. Closer observation revealed more bright spots between the spots, as well as more and more bright spots.
Feynman asked to look at the slide more closely. I turned on the light, took it off the tray and handed it to him. The image on the slide was so shrunken that it was difficult to see the details, so I also handed him an enlarged version of the puzzle that he could put on the table and look at it in front of the laser.
The next period of time passed in silence. I began to feel like a student again, waiting for Feynman to react to the latest absurd thoughts that came to me. He stared at the enlarged version on the table, recrammed the slide into the tray, and turned on the laser himself. He looked at it, staring at the enlarged plate on the table for a moment, looking up at the laser pattern on the wall for a moment, and then looking down at the enlarged version again.
"Impossible!" Feynman finally said. I nodded in agreement and smiled, because I knew it was one of his highest approvals.
He looked back at the wall and shook his head. "Absolutely impossible! It was one of the most amazing things I've ever seen. ”
Then, without saying anything more, Feynman stared at me excitedly, a sly smile on his face.
About the Author
Paul J. Steinhardt is the Albert Einstein Professor of Science at Princeton University and director of the Princeton Center for Theoretical Sciences, with research interests in particle physics, astrophysics, cosmology, and condensed matter physics. Steinhardt was one of the famous contributors to the cosmic inflation model, and later collaborated on the "circular universe model". In 1983 he and his student Dov Levine proposed the quasicrystalline theory, which subsequently elucidated many of the mathematical and physical properties of this new material structure. In 2009 he led the team to discover the first natural quasicrystal.
This article is translated from What Impossible Meant to Richard Feynman, Nautilus, 2021.11.24, from Paul J. Steinhardt's the book The Second Kind of Impossible: The Extraordinary Quest for a New Form of Matter. Original link: https://nautil.us/issue/108/change/what-impossible-meant-to-richard-feynman