We met to discuss quarks, a “down-to-earth” approach to theoretical physics, experimental attempts to prove supersymmetry, and much more. Enjoy!
Theoretical physicist, Mikhail Shifman, explains the interaction between quarks as well as the various ways physicists have attempted to explain this unique interaction. Dr. Shifman, an advocate for supersymmetry, comments on his thoughts on the experimental attempts to prove supersymmetry. He discusses his “down-to-earth” approach to his abstract field of theoretical physics. Follow along as Ida Cohen Fine Professor of Theoretical Physics, William I. Fine Theoretical Physics Institute, and University of Minnesota professor, Mikhail Shifman talks with Dr. Jed Macosko, academic director of AcademicInfluence.com and professor of physics at Wake Forest University.
We are not gods and not prophets, that's my attitude. We are…we are humans, we are humans, we have limited abilities, let's see what happens.” – Dr. Mikhail Shifman
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(Editor’s Note: The following transcript has been lightly edited to improve clarity.)
Jed Macosko: Hi, this is Dr. Jed Macosko, at Academic Influence and Wake Forest University, and today we have a very special guest coming to us from the University of Minnesota, Professor Shifman, who is a physicist. So, Professor Shifman, we understand that you do what used to be called Particle Physics and High Energy Physics.
Can you just tell us a little bit about what you are most known for in theoretical physics?
Mikhail Shifman: Okay. My career in theoretical physics, because of some reasons, it can be split in several parts which are connected, but not that closely connected. When I was a young man, at the graduate school, and shortly after school, when I was a type of postdoc and few years after that, I was working on the newly created theory, mostly the theory is called Quantum Chromodynamics, and it describes basically all matter we see around. Like in the 1930s, nuclear physics have been developed with lots of practical and not so practical applications.
But later in the late 1960s, early 1970s, people realized that in fact, protons, neutrons and other similar strongly interacting particles, they’re not elementary, that was one of the reasons why the name Elementary Particle Physics was abandoned. They, in turn, consists of some smaller and more fundamental objects which are called quarks and gluons. Quarks are the carriers of matter and gluons, you see the name comes from the name of glue. Gluons glue them together.
These quarks are much, much smaller than strongly interacting formerly elementary particles. But they’re glued forever, glued together forever. You see, you cannot take one quark and separate it from the other two, because the force between a quark and anti-quark, the energy when you try to split them into parts, it grows linearly with the energy.
So this is a totally new phenomenon, never heard of in theoretical physics because in physics usually if you have two objects, the farther away they are from each other, the weaker is the interaction. Like the farther away we are from Sun, the weaker is the Sun’s attraction and so on. And it’s normal because of this pattern of behavior, only universe can exist, stars, planets and us. If we were glued together everything, and the Earth, you see glued together, you couldn’t separate one piece of it. But the quarks have a very, very unusual feature that they’re glued together to their partners for life. And only in quantum chromodynamics, which was born in 1973 when I was in the beginning of my grad school, there are means and ideas how to describe this special type of behavior.
So that’s what I was working on, this very unusual pattern of interaction for... Well, 1973... Maybe for about 20 years. But during this 20 years, it was realized that the problem is very difficult, full theoretical description of this strong interaction is extremely difficult. And during the subsequent 20 years, from ’73 to ’93, it was realized that the full solution escapes, so far, it’s elusive, but there were many corridors in this subject which were... Or many islands in the solution which have been explained and understood and I’m happy that I have this opportunity to explore, for the first time, some of them.
But when I came to the United States even a little bit before I was... I managed to come, which was not an easy decision, it’s not that I just decided then came to the United States; it took the Soviet Union to collapse for me to be able to come here. So shortly before I decided to go to the... Well, I start thinking about this and then I also start thinking of some other areas of particle physics, which were also very interesting, quite new, partly explored, but not completely explored.
There were some areas, it’s called supersymmetry. Supersymmetry is a new symmetry, which was discovered in 1972, which relates to each other, bosons and fermions. It’s hard to explain, but bosons are particles like, for instance, the light quantum is a boson, particle of integer spins and they like to aggregate with each other. The more such particles you push towards each other to some, one single state, the more they’re alike. So they’re extreme communists, so to say, everyone behaves in the same way as everyone else. And another type of particles is called fermions, they have half integer spins, the simplest fermion is electron.
And they hate... Hate to behave... There is, in our universe, there is not a single electron which is exactly like any other electron. So they’re extreme individualists. They never congregate. Even two of them cannot be in the same state. They can be in close states, but not the same.
So at first sight, what could be further away than the distance between bosons and fermions? However, it was discovered in 1972, ’73, that there is a very special symmetry which relates them, what’s called supersymmetry. For many years, it was a hope that a breakthrough... The supersymmetry was searched at the highest energy accelerators from 1980s till these days. Unfortunately experimentally, it’s not confirmed so far, so it’s elusive too; maybe higher energies are needed. But theory went a very large distance from zero as it was in early 1970s till today. And I’m also happy to be able to say a few new words in this exciting area.
Jed: I’m so glad you’ve been able to contribute.
So you would say that you are a proponent of supersymmetry, and were you one of the ones that was most disappointed by the things that came out of the Superconducting Super Collider in CERN, or were you not so disappointed?
I don't go as far as to say that the theory of everything can be worked out, and we are like gods at a certain point in time, at a certain moment of time, we will be able to understand anything.” – Dr. Mikhail Shifman
Mikhail: Of course I was disappointed, but I was not as disappointed as string theorists because string theory requires, in a sense, requires supersymmetry. I personally, I personally more down-to-earth theorist. I don’t go as far as to say that the theory of everything can be worked out, and we are like gods at a certain point in time, at a certain moment of time, we will be able to understand anything. So I take it easy. I think, okay, it was not this discovered experiment. I tell you okay, next time, when larger accelerators, that’s not be very soon because accelerators are very, became very, very expensive. Now, modern accelerators are huge and diverse and extremely expensive, and can be built only by a global effort.
So maybe in 20 years. Of course, at that time, I will be already retired, but okay. Younger people, they need some luck too to go into this breakthrough area. [chuckle] And still there are... Yeah? Go ahead.
Jed: You’re one of the ones who thinks that the Large Hadron Collider was not big enough, and we just need a bigger one, and then we will find supersymmetry. Are you of that opinion?
…all beautiful things, all beautiful theories, they materialize in nature this way or that way.” – Dr. Mikhail Shifman
Mikhail: Well, I think, in my experience, all beautiful things, all beautiful theories, they materialize in nature this way or that way. But of course, it’s a limited experience of... But it lasts for 50 years and in my lifetime, beautiful ideas... Even take, say for instance, Yang-Mills theories, they were not invented for... They are the modern theory of this standard model and quarks and gluons. They were invented in 1954 for totally different purposes. And they were never found or realized in this area of questions for which they were invented.
It took 15 years to realize that they are still beautiful theories because they found their place at the level of quarks and gluons, not... Of which people couldn’t even anticipate this in 1954. It was... Took another 15, 14, 15 years of development before it became clear. So my attitude is something about like this. There is a beautiful theory. It surely will find the range of phenomena where it is important, where it is basic, where it is foundational. When it happens and in which particular area, I don’t know. Unfortunately, it didn’t come at LHC. Okay, this happens. We’re not gods, and not prophets. That’s my attitude.
Jed: That’s a great attitude. [chuckle]
Mikhail: Yeah. We’re humans. We’re humans. We have limited abilities. Let’s see what happens.
Jed: So it’s just maybe that the ideas of supersymmetry might find their way into something else, and you might not even be around to see it come to pass, but you really do think that since it’s such a beautiful theory, it must come about somehow.
Is that what you’re saying?
Mikhail: Yeah, I want to make a little bit more accurate statement. It’s not that they, all this, what, 40 years of development, or 45 years of development, where and when, because there are already some applications of supersymmetry which are of paramount importance. They are not experiment... It’s not experimentally confirmed, but you see, supersymmetry turned out to be a very powerful tool in dealing with theories with strong interactions, with strongly coupled theories. And not even... Not only in high energy physics, but even in condensed matter, something is helped.
And in this case, for this purpose, it’s already very useful. There were quite a number of new solutions, new methods developed, new discoveries made, so it’s just... So it’s very... A very successful theory, very useful, just not that it’s as universal, for the time being, it’s not as universal as it had been anticipated in 1980s.
Jed: Well, do you think that because of your background, both in the former Soviet Union and also your parents being of Jewish origin, that you have adopted a more humble attitude towards what humans can discover about the universe?
Mikhail: I don’t know. Yeah, my background in the Soviet Union, of course, was very pressing and in some instances, depressing even. Life was not easy but I’m not sure that it had an impact on my scientific views. I think it’s just how I developed. I like problems which are more down to earth. I used to like... Even to love problems which at the end of the day allow you to get some numerical predictions, which you can go to your experimental colleagues, and say, "Look, I have these and these numbers, can you tell me what you’ll see in your setup, your measurements, what this number is?" The first 20 years in my career I worked on that and I liked it and I miss it, even now after 20 or 30 more years in more abstract areas. I always try to be as close as I can to our real world, although of course, I’m doing now more abstract things, less related to experiment, but the reason for that is only because the experiments become scarce. They are not so... In my area experiments don’t occur every day, not even every year. So it’s just a response to changing the environment, that’s all.
Jed: But you’re still having a lot of fun these last 30 years with this more abstract area.
Mikhail: Yeah. Undeniably, undeniably.
Jed: And how would you describe this newer area, these last 30 years to somebody who doesn’t really know theoretical physics?
Mikhail: Well, there is certainly... Well, it depends on... Theoretical physics is very broad. It encompasses many areas starting from High Energy Physics, Astrophysics is the second area, Astrophysics and Cosmology, and then Condensed Matter is the third huge area, and then areas related to material sciences, nanotechnology... So there are many areas in Theoretical Physics.
If you look back in time in all these four basic branches which I told you about, there were enormous developments. But now, today, the pace of developments sort of changed relatively to each other. Cosmology and Astroparticle Physics is still developing very rapidly because... And in the first place, because there are lots of new experimental data coming from experiment.
In the structure of galaxies, dark matter is a huge discovery, a huge revolution in our understanding of how the world is structured, turns out that 27% of our world is not visible to NASA and we know nothing about this 25%, a quarter of our matter is not understood, not visible.” – Dr. Mikhail Shifman
For instance, the discovery of the gravitational waves, it’s probably the largest discovery of this century, experimental discovery of this century. There were some other discoveries of this type in Astroparticle Physics. In the structure of galaxies, dark matter is a huge discovery, a huge revolution in our understanding of how the world is structured, turns out that 27% of our world is not visible to NASA and we know nothing about this 25%, a quarter of our matter is not understood, not visible.
So that’s why this area grows. Condensed Matter grows intensely because there are needs from material sciences, Graphene came into being, now technologies are being... Our area which is related to High Energy Physics still continues to develop, but not at that pace as it used to be 30 or maybe 40 years ago, which is natural because that happens all the time in sciences. In basic sciences, one branch goes a little faster, develops, grows faster, another a little less faster, and then this second branch which is not that fast to grow gives another offspring, another branch, which outpaces everybody else. So there is nothing out of ordinary, I would say in Theoretical Physics, it’s still the theory of the matter at the very fundamental level, at the most fundamental level.
Jed: Well, we’re really glad that you could explain sort of the big picture of Theoretical Physics, and we’re so glad that you got your start in the very beginning of this new phase and that you’ve continued on and that you’ve had a chance to tell us about it today. Thank you very much. We really appreciate you taking the time with us today.
Mikhail: Thank you for having me with you.