W: With me is Professor Sergei Kopeikin from the Department of Physics and Astronomy. And Dr. Kopeikin is studying cosmology. He is an astrophysicist. He is well known for his work in general relativity and the theory of gravity. And Dr. Kopeikin has kindly agreed to answer some of my questions here.
So, Sergei, when I was preparing some questions, things I wanted to know about the field and about you, actually, I let my mind drift back when I started astronomy and I was thinking that back then cosmology was just a fledgling science. There was some work out there but it was not a serious field of study, perhaps, only a few people partook of it. Now of course some major discoveries have been made in cosmology. So I was wondering if you cast your mind back to when you started studying over the past 40 years, what are the discoveries that have excited you most or have surprised you most? Or maybe just one?
S: Well, my decision to start studying astrophysics and cosmology in particular was based on the impression I got from being a student at Moscow State University, which included such people like Lev Landau, Yakov Zel’dovich and Vitaly Ginzburg, two of them actually got the Nobel Prize and Zel’dovich was, or is, considered as the father of modern cosmology. Discovery of cosmic microwave background radiation was definitely well known at that time and it stimulated great development of cosmology about 40-50 years ago. At the same time Kip Thorne as American scientist was very much interested in ideas, which were proposed by Zel’dovich so Kip Thorne used to go to Moscow University particularly to our group to discuss these ideas with Zel’dovich. So I got acquainted and became a friend with Kip Thorne already and all that impressed me very much. And this is why I’m doing cosmology so far.
W: Is there anything in particular since you, after you graduated, any particular discovery that shook your outlook so to speak?
S: Yeah, one discovery that particularly affected my next career and this was the discovery of binary pulsar by Hulse and Taylor in 1974. In 1979 they detected what we call emission of gravitational waves. But that detection was not quite direct. It was indirect detection of gravitational wave. Gravitational waves take away energy and then get momentum from the binary system and because of the orbital period of the binary system is decreasing. And this is what Hulse and Taylor were able to observe. And the decrease in the orbital period of the binary pulsar was with very high accuracy equal to the prediction made on the basis of the general theory of relativity.
So Zel’dovich was very much interested in proving theoretical prediction made by Einstein but in a different way. Not by making use of the assumption that gravitational wave exist but the assumption that you have equations of motion and these equations of motion have some break in force radiation of reaction force which actually decelerates orbital motion of the pulsar and its companion, and this is why we can see the decrease in the orbital field. And so I was asked to do a PhD on this subject. This is how it determined my whole life.
W: Excellent, excellent. You became famous for actually measuring something that very few people think about in everyday life, and that is you actually measured the speed of gravity. I don’t know if you can say in a few words for people at my level that don’t have a good grasp of all these equations involved. Could you maybe say how you can even possibly measure the speed of gravity, because to us it’s just you drop something and it’s instantaneous. How can you measure it? Can you maybe say something about how you did that?
S: Right. Electromagnetic waves propagate at the speed of light. We have known already for quite a long time. The speed of light was measured by Hertz at the end of the nineteenth century. The prediction about finite speed of propagation of electromagnetic wave is based on the Maxwell’s equations. Now we are in the realm of gravitational fields. General theory of relativity also predicts like Maxwell’s theory that there are waves, but these waves are not waves of light but waves of gravitational field. These waves are also propagating at the speed of light. This is prediction of the general theory off relativity. This prediction is quite nice, but at the same time we have to have some experimental proof that gravity is propagating at the speed of light. So in order to conduct such an experiment you have to find out some situation in which you will have light body moving in non-stationary gravitational field. One of such bodies can be considered like a light particle itself. So you propagate light in the field of gravity, which is changing. So I was thinking about the solar system. In the solar system it is really difficult to find gravitational field which changes quite rapidly. But I found such a body; it’s Jupiter.
Jupiter moves in the sky with light speed. The ratio of b or of c, velocity of Jupiter to the speed of light is 410 to the -5, which means the Jupiter moves around sun at speed of ten kilometers per second. Then you take a source of light and this is a physical source of light, you propagate light through the gravitational field of Jupiter so when light propagates toward a viewer on Earth, Jupiter is moving slowly through the sky, so gravitational field is changing. In principle, you can detect with which speed that gravitational field changes. So it must be the speed of light. It must be the same as the speed of light as in the Maxwell theory, but I’m talking about the speed of gravity.
W: So, Jupiter would move in front of this very distant quasar and you would follow the bending of the light waves?
S: Yes, and the General Theory of Relativity predicts that gravitational field deflects light. So the position of the quasar in the presence of Jupiter changes and would not be the same as without Jupiter. So the gravitation field of the Jupiter changes the position of Quasar in the sky. That prediction was well known, it was made by Einstein himself already in 1915. But what I discovered was that the motion of Jupiter actually brings about an additional effect. It’s the same deflection of light but not along the radial direction but in the direction tangential to that direction. We were looking for the tangential deflection of light by moving Jupiter, and that tangential deflection is actually proportional to the speed of gravity. And we detected it.
W: That’s very impressive. Was it a little bit of luck that this quasar was just in the right position? Are there so many quasars that you could repeat the experiment?
S: We have quite a lot of quasars but not all of them are bright enough in order to do such an observation. Effectively, if you count all the quasars that are suitable for doing such an experiment, you find that such an experiment can be done approximately once in several years, not more often. So it was not quite luck. We were working hard to find in order to find such quasars, and we found it.
W: Well, it certainly that got noticed. I just saw that the BBC at the time was reporting on it. What are you currently working on? Probably many things. But just before you go to bed, what goes through your mind? What work are you thinking of?
S: Well, right now, a quite interesting question is about the application of atomic quarks to study gravitational field in the solar system and for studying geophysics, actually, and geology. One of the basic problems of modern geology, the science which studies the shape of the earth, is to measure height. So it looks quite obvious concept, height, but to measure height precisely – some mountain for example - scientists should do quite a little work called leveling. So this is what people doing land survey are doing with a special device called theodolite and a rule, you know, you sink with centimeter marks, so they have to work from point to point and measure difference between heights of those points so in order to do this at large distance, people have to walk thousands of kilometers. And this is time consuming and very, very expensive. So imagine you have to know landscape of the whole country, like United States or Russia or Africa. Imagine how many people you have for doing this work. So, it’s very expensive and time-consuming work.
Another idea after the General Theory of Relativity was created is to use atomic clocks. General Relativity predicts that atomic clocks run differently at different gravitational potential. So if you are at different heights, the gravitational potential is different. Modern atomic clocks are able to measure the difference in height of about one centimeter. And…
W: That’s so strange. So a clock measures the difference in height?
S: Yes, so this is very nice. Imagine you have such a clock, you send a person to any point, and they guy immediately can measure the height without doing leveling, so it’s much cheaper. Of course, the atomic clock is very expensive, but as soon as you have it, it’s done. But we need a theory for doing this, so this is what I’m doing now.
W: That’s fascinating. To change topic a little bit. The students in this part of the course they will learn, or will hear the words I should say dark matter and dark energy. And they probably may be a little bit, well, disbelieving of things you cannot see or touch. Do you think we can make any progress in maybe detecting or saying something tangible about dark matter or maybe creating some dark matter here on Earth or make some progress in the field of dark energy research? Do you have anything to say to our students? Do you believe that dark energy and dark matter exist?
S: Yes, I do believe that dark energy and dark matter exist. I prefer … there are two ways to think about this. First way is to believe the general theory of relativity is correct and the matter actually is not quite well known. That matter we call dark matter or dark energy, so they are responsible for creation of the gravitational field of the whole universe, and when we observe motion of stars in our galaxy or motion of our galaxies in the sky, or when we measure temperature of cosmic microwave background radiation, we definitely see that something exists, but that something we can’t say what exactly that something is, so we call it dark matter or dark energy and we are trying to understand the nature of this dark energy or dark matter better. There are good theoretical prospects to understand this, but definitely we need much more experimental data in order to be more convinced in the exact nature of dark matter and dark energy. We don’t know yet the nature.
Another point of view is that you disbelieve in the general theory of relativity. You say that is incorrect, everything is fine, but something is wrong with the gravitational field. I don’t like this point of view. Quite a number of people prefer to think in this way, but I do experimental gravity and I know that the general theory or relativity in all experiments inside the solar system and outside the solar system was confirmed with unparalleled degree of accuracy. This is why I believe the general theory of relativity itself is correct and something is wrong with matter. That wrong is dark matter and dark energy. We need to understand it much better. But the creation on the Earth? In order to create, we have to know the nature of dark energy and I don’t know how to create dark matter or dark energy on Earth. We don’t know the nature.
W: Cause I just read some popular science publications, and their scientists are always very optimistic that somehow maybe in experiments at CERN we will create a little bit of dark matter. Is that possible?
S: It could be. It could be. And I’m also optimistic. We have to work hard and be active. Have good inspiration. Try different things. You know. If we don’t do anything, nothing will happen. So we definitely should do something, you know, and try to interpret what we see. But I’m against explosions. It’s better to do something peaceful.
W: Can I ask you a very strange question?
S: Well, please go ahead.
W: In the course we will also talk about planets and moons and we will focus on maybe the presence of liquid water and maybe the possibility of life forms existing outside of our Earth’s atmosphere. Do you ever think about things like that? Do you ponder whether we are alone in this big universe you’re trying to describe?
S: Well, I personally believe that we are not alone, that there are other civilizations, and that it’s a matter of time to find them. Why not? I don’t see any reason to believe that human kind is specifically exceptional in this universe. It looks like laws of nature are universal, so why should we discard the idea that other civilizations exist? I believe aliens exist. A friend of mine…
W: Is an alien?
S: No, he’s not an alien, but he’s trying to contact aliens. He’s sending messages to aliens in the hope that these messages will reach them. So his task is not to find them in the sky but to deliver a message to the aliens. So even if we are not successful to find them, maybe the aliens will be successful to find us. Some scientists actually disagree with the idea of this friend of mine. They say that this is dangerous. They think aliens can be malicious, can be aggressive civilization, so if we send messages to them, they receive the message, and they can come to us. I think this is kind of crap. May be, but so what? Anybody can be aggressive or peaceful. We don’t know. But we should do something to understand the surrounding universe. I’m not afraid about messaging to aliens.
W: They’re far away. Maybe I can ask you one more question. Suppose a student from this course gets inspired and comes up to you and says, “I want to study what you’re studying,” or “I want to study cosmology in particular.” Would you encourage this student, or would you say it’s much better to get a real job?
In order to work in the field I am working in, the student should be really good in mathematics. So I shall not discourage the student, of course, but after awhile he or she will understand on her own whether it is valuable to continue or not. It takes some time. I cannot say immediately just don’t go into this field. Maybe the student is exceptionally good, who knows? We need some time. But mathematics is important, good skills in mathematics.
W: Part of the reason I asked is your field is so specialized, it’s even very difficult to explain to your colleagues, and therefore it must be very difficult to get the money from governmental organizations to carry out your research.
S: This is true. Funding is not so good in this area. Basically the money allocated from NSF in this country is now focused on gravitational waves, on construction of huge big machines called gravitational wave detectors, so this is where the money goes. And the rest of the money is left for scientists working like in Missouri or other local places. So you have to be part of a big team in order to get good funding. But at the same time we have quite a number of private foundations. The funds they have are not great, but they are sufficient in order to do good research. In this sense, I don’t see too much problem.
W: Okay. Since you brought it up, you mentioned the gravitational wave detector, and we are on record here, do you think the detectors like the LIGO detector in Louisiana will actually detect gravitational waves?
S: I believe that sooner or later they will do it, but I believe that it will be rather later than sooner. We should not be too optimistic. I think this will be very hard. I really have no idea how long it will take, but I hear about detection of gravitational waves already for 40 years, and every time people promise to detect gravitational waves in the next 3 or 5 years, that promise was never fulfilled. So I stopped to believe in these promises. So let’s wait and see, but the idea is right. The idea is absolutely right. Gravitational waves are extremely big and elusive, and this is a problem. There are many other kinds of noises from these we have to extract the signal, a very weak signal. This is a problem. But sooner or later it will be done, and gravitational waves will be detected.
W: Thank you very much for answering my questions. Thanks for coming. Good luck with the research.