Interview with Leonid Grishuk

0:00 See, I think so. And I'll say that it's the 18th of May, 2000, at 11am, and I'm speaking with Leonard Grisha. So, well, as you know, the general, very general topic of my study is the sociology of the community of theoretical physicists interested in some way or another in gravitational wave detection. And I know that you're particularly interested in the detection of gravitational motion in the early universe. And I guess I wanted to start by asking how you got interested in that, in that topic. Um, in some sense, many topics in my career were based on a controversy, on something what I believed should be different from other people say, and even they claim that it is well established. so actually the beginning of my career was an argument with Livshitz, Halatnikov and indirectly with Landau because they were referring to Landau very often and it was about singularity theorems and there was some interval of time when even theory of fields was rewritten by Livshitz because they incorporated their result where they claimed that general solution to Einstein equations does not and I was a student, I was working on exactly the same topic using a simplified model of a matter which is pressureless with dust-like matter and it was always coming out of my calculations that it does have a singularities in most general solution to Einstein equation, most general means maximum number of arbitrary functions which can be so it was a great battle and I believe that I am right before did not receive enough credit but nevertheless they rewritten their book again and they actually referred to their own work but they eventually came to the conclusion that not everything was explored and even for which they were considering there is a general solution similar happened with

2:30 gravitational waves because by that time everybody knew that gravitons cannot not be created in homogeneous isotropic universe there was a consideration of conformal invariance and all authorities including my former teacher or indirect In fact, teachers, Lidovich, they were saying explicitly in the literature that neutrinos, gravitons, photons cannot be quantum mechanically generated because if you write their equations, they turned out to be conformally invariant and matter is conformally flat and so on. So there was Parker, there was Penrose, Strabinski especially was active in trying to prove that I was wrong and claiming that no, it cannot be true. so I really insisted and I realized that Einstein equations when they are reduced to linearized forms they are not conformally invariant that there is clear physical mechanism which I later called super adiabatic amplification there is a coupling and this coupling is different from other fields so it was first of all the desire to to come to the truth and to to show that no it should be different but later of course gradually almost during the same intervals of your paper 74 somewhere in 77 I have written a paper on graviton creation in the early universe and actually its manifestations it in Texas meeting, which again was qualified even in the introduction to this volume, that esoteric paper something, people did not understand, they could not even understand what I'm talking about. But gradually of course it became more and more clear that it is so general and fundamental mechanism that we are relying practically only on general relativity and basic principles of quantum field theory. We do not require anything. Then there was a period of this noise and excitement

5:00 and crying, inflation, inflation, inflation, inflation, which is simply a subclass of what I was doing I was doing for arbitrary power law dependent scale factors deriving form of the spectrum of rally gravitons and energy density and so on and inflation what was known by that time is simply one particular case so among all parametrization which is already present in my work there was no warped inflation but all the formulas and all these spectral indices were already there so then there was the second interval of my excitement and interest because then it was claimed that inflation now specifically in tension not quantum mechanics in general activity create density perturbations And moreover, the density perturbations were claimed until now that they have orders of magnitude, higher amplitude, and effectively, when you look in this analytical formula, this amplitude goes to infinity for most interesting inflationary case, which is spectral index in present notations, n equal 1. so and this was something what I could not agree with altogether because I knew the mechanism I knew main physical principles I knew that there is no mystery behind this it is again the same type of parametrically excited oscillator so I actually I have re-derived everything and And I proved that they do under extra conditions, because for density perturbations you need some assumptions about this scalar field and so on. But if they are satisfied, then equations are almost identically the same. For power law, scale factors, which I was always working on, they're exactly the same. And so the results should be the same. So I showed you my gradually growing interest, but now this interest is even larger than before,

7:30 because now there is this tremendous conflict where the rest of the community, they believe in the so-called standard results. So there is one more controversy, which I hope this time might result only observational. but for me I'm going in a slightly different manner I say that now we may determine the spectral index and something from observations because I know that they do influence microwave background in isotropies and this is why I'm determining actually the parameters of this model which initially was simply a set of models with arbitrary parameters arbitrary power scale power low scale factors and this is why I believe that now observations tells us something about the spectral index about what was happening in the beginning if everything is right and if what we see indeed of quantum to mechanical parametric origin, and then I believe that these gravity waves do exist, that they contribute significantly to microwave background and isotropies. And then extrapolating and applying this theory to intervals tested by ground-based and space-based interferometers, I am simply giving concrete predictions. I am saying that this is what you should see. So this is why I think that my interest is growing, and I indeed believe that this is how it will be and will be proven someday. I don't know, maybe I will not be alive by that time, but this is roughly the origin of my interest and the reason why this interest continues and in some sense is even increasing. Which of the various types of detectors or detectors, whether the initial ground-based detectors or just like all the advanced ones or space-based detectors, do you think are most likely to provide? If I'm right, then of course everything follows from the formalism, from formulas. And then it turns out that the spectral shape, so it is in characteristic unisex,

10:00 characteristic wave amplitude, there is some number. So we are considering this number as a function of frequency. But then this number is going down as a function of frequency. clear reasons of those shorter waves they spend shorter time in amplifying regime and this is why by now they have smaller amplitude and so on so it is not surprising but if so then the lower frequency we are considering the better for us so this is why i believe that in microwave background and isotopes which simply already see them because then their amplitude to the minus 5 and this is what is of the order of delta T over T which we see on the sky. In the space-based interval it will be 10 to the minus 20 something like that 10 to the minus 21 or 22 but this is something what Lisa can measure whereas in the ground-based interferometers 10 to minus 26 which 25 which is below their sensitivity curves there is still hope so if you have several detectors and if you integrate for a long time and you're fighting with instrumental noises you still can do this however if among this range of models which still I believe are viable, there are optimistic and there are something what I believe we cannot go beyond then in the most optimistic case which even I consider as the limit of applicability to the entire theory, then it could be done by advanced LIGO in one year, by two instruments in one year integration time take this other side then we will need Lisa at the signal to noise level of the order of C or maybe even something like a follow-up mission after Lisa because then for ground-based interferometers it goes much below so you need two stages of future you know improvements whereas for space basis amplitude is simply higher there

12:30 it even in this conservative case I believe that it is enough for me they will be able to distinguish a signal signal to noise ratio of the order of three then it could happen that Lisa will see So this is why it is better to go to lower frequencies under all other conditions the same. Of course, if somebody could say that in higher frequencies your amplitude is lower, but my instrument is so much better, its noises are much, much smaller than because of cosmic environment or whatever it is, in principle, objection to do this in laboratory, in ground-based. But the reality is that we are using essentially the same type of technique. It is lasers or microwave responders, and the same type of noises and limits. So this is why I really think that realistically we will need to wait until laser. So, you were saying that on the basis of the, I guess, the COBE observations, already you think there's evidence for… Yes. Yes, this is an absolutely independent statement, because there is something what I am saying as a theory. So I am guaranteeing and in conflict with many of, you know, this inflation, at least, when I am saying that simply as a purely theoretical level, let's agree that we play the same game. We want to start from what we all believe was zero-point quantum fluctuation, something. what we will represent as some minimal amplitude which is unavoidable on quantum mechanical grounds and so on. And then we drag through all these amplification errors and we want to calculate what will be happening today. So on purely theoretical grounds I am saying that if I stay on this position, then theoretically under the same model gravitational wave contribution must be a little bit larger than density perturbation.

15:00 So this is what I am predicting, and I stated this in the form of a single phrase, which was the abstract of my paper in 1993. If microwave background and isotropies are caused by cosmological perturbations of quantum mechanical origin, then they are most likely gravitational waves rather than density perturbations or rotation perturbation. One sentence. Why? Because it was based on this theoretical conclusion. A different thing is that everything can be wrong or you know maybe this coefficient not as I'm saying 2 maybe it is 1.5 or something like that. So now we are returning back to what people analyze and how they do this in microwave ground in these atoms unfortunately they were so misled by this inflationary noise I mean noise in the literature they immediately concluded and are doing all their processing under the assumptions of gravity waves are zero they say this because this inflationary prediction is arbitrarily large amplitude so it is almost Then they divide one by another, and they say that gravity waves should go to zero, because they divide gravity waves, which are finite and small, to density perturbations, which theoretically go to infinity. So this is why this ratio becomes equal to zero. So there is this complete confusion. But unfortunately, it resulted in all these derivations based on these density perturbations only. Of course, they forgot by that time that inflationary is predicting a large amplitude. They simply say that, well, we will simply take Harrison-Zildovic spectral index, which indeed will follow if the initial stage was the sitter or almost the sitter. And then they process and derive all these cosmological parameters totally ignoring this. But other people, and only in the recent years, extent under the influence of my insistence and nastiness or independently but what I saw in quite recent paper for fun they processed all this data assuming that there are gravitational waves for

17:30 the first time okay and then they derived the best fit model best fit model which means that you included several parameters in gravity waves also and you try to combine all that in such a manner that you will fit the observed shape including this peak and so on with minimal square root mean square deviations and then it turned out that they derived that the gravitational wave contribution is several times exactly what I'm saying but they do not refer to this moreover they own theoretical grounds they say well this would be what this is what their model says and the processing so it is best fit but they prefer to go to a slightly worse fit but doing all that without gravity waves and then they say that well, we still can do something and then with this contribution, small, being small. This is, so I believe that actually it will be proven that it is of the same order unless everything what we see on the sky has nothing to do with this quantum mechanics and the early universe, which is still a possibility. But for our discussion and for ground-based and space-based interferometers it is important because it is a normalization point if i'm right and if i am placing an observational point at this frequency and i know the spectral slope i know what to say to experimenters in other frequency intervals so if you if you take the kobe data as a as a point on the gravitational as giving you one point in the gravitational yes absolutely this is exactly what i'm doing i'm plotting and this is what i'm deriving so if you now take kobe as i interpret them if you take the spectral index now the spectral index is also going back and forth so this is what i call maximum it is it would be well measurable by lisa but it is what i mentioned before that it is our maximum this is what i'm

20:00 as kind of reasonable estimates, partially supported by observation. And this is what would be a kind of minimum. So suppose within all these ranges of spectral indices which they seemingly determine, suppose we go to the lower side, so this slope is such that it goes sharper and sharper down. then even Lisa will not be sufficient and so if Lisa for instance does see does observe gravitation ways then that would be strong evidence in favor of the interpretation of the COVID strictly speaking it is independent there will be still battle people will say that well what we see here can not necessarily be extrapolated as I want by several orders, many orders of magnitude and to relate with Coby. So logically it is still possible that there is something in Coby and suppose it is even gravitational waves. There is something in Leesa and suppose it is also gravitational waves. But how do you prove that it is the same spectrum, the same origin and so on? So this is why the next round probably will be developed in coming years, because I see that people are getting interested. It is my insistence that if we are serious about this, then this background is not something noisy, it is very specific, it is squeezed quantum states, specific statistical properties and so on. So for me the final proof would be when we could prove that it was indeed of quantum if it were proved and this can be done independently strictly speaking in each of these frequency intervals then I would say you know what it is difficult to imagine that it is two different unrelated pieces both of quantum mechanical origin both pointing to each other and not being simply the consequence of these simple models which were constructed long ago So this would be my position. I would say that if quantum mechanical origin is proven and the squeezing or some other consequence like standing wave pattern, fixed temporal phases and so on, there are features.

22:30 So, you know, it is a signal which, when we say quantum mechanics, we are not joking with quantum mechanics. Quantum mechanics says, okay, if you are serious, take your quantum state, bring it through Schrodinger evolution, you will get a different quantum state, but it is in one-to-one correspondence, it is unitary evolution. You now know everything about this quantum state, all mean values, variances, whatever correlation functions. this background which I'm discussing it is not simply something you know hand waving some zero-point quantum fluctuations it is literally literally one vacuum state evolves in two more squeeze vacuum state with absolutely unique statistical properties if this is shown I think that then I'm a winner when will it happen I don't know so if when gravitational gravitational waves are detected with evidence of being produced by squeezing so that they have some sort of polarization properties then that would be a strong evidence I think that polarization measurements of microwave background are important independently and without whether or not it will prove squeezing It may prove the amount of gravitational waves, first of all, without even going into these more delicate statistical properties. Because something what density perturbations produce or not produce in polarization, gravity waves are different in this respect. So there is signature in polarization. There are many, actually, aspects where they can deviate from each other, multiple distribution and so on. But multiple distribution is not very sensitive. You can always say that, well, I'm changing a little bit my Hubble constant, and then it will be again the same. When you are operating with something which is either zero or non-zero in one of two cases, some particular mode of polarization, then it is convincing.

25:00 And finally, if you are proving that it is still not squeezing, and finally if you are proving that it is squeezed, then I think that it is convincing proof that we were right in calculating, in dragging, in models, and this is how we will deduce what was happening in the early universe. because now if I prove that, then I think that I don't know what was happening there, what was the rate of expansion and Hubble parameter and all that. If I remember correctly, in regard to detection by, of gravitational waves by LIGO-lisa type detectors, there was a claim made of a while back that maybe it wouldn't be possible to see any kind of polarization arising and squeezing in the Earth universe because too much time had elapsed? It is a very area which is under investigation at the moment, so you will see many conflicting reports. For instance, there was a paper which was arguing with me, agreeing with me that if generated then they will be very specific it will be so called non-stationary signal but questioning the possibility of distinguishing this in laboratory environment but then in conflict with themselves they would say that in something else nevertheless it can be done so there is some argument which looks like a very convincing and then they will counter-argue to themselves that in this frequency range it is impossible but in another frequency range it can still be possible and this work continues so my position is the same for many years I am saying that since the amplitude is larger for longer waves and this squeeze parameter as I say is larger is much more enhanced if you go to the longer and longer waves than simply almost by definition if you go to that region, you're in a better

27:30 environment, in a better situation. Unfortunately everything should be compared with instrumental noises. So you go there but then periods are becoming billions of years, you know, not rely on something that you see one phase another phase then it is astronomical observations rather than laboratory observations and so on but theoretically speaking if the rest if there is no noises if there is no limits on my you know experimental abilities then signal as such response in terms of squeezing is better for longer weeks so whatever now technique which can reveal this if this technique is noiseless then this response would be better there in reality we always compare the response with the instrument noise or astronomical noise so I don't know whether it will indeed be this is actually one of topics that we continue to work I don't know the result but it is obvious that it will not be easy because polarization first of all as such is one order of magnitude lower under most favorable assumptions than variations in temperature as such so if delta where it is 10 to the minus 6, and you are measuring with your instrument the limits of your norm, then expected polarization is 10 to the minus 7, or much less. So this is what requires even more effort. So it will never be easy, but nevertheless, who knows, if you speak about Planck and Planck being 10 times more, future plan, second plan ten times better then these estimates predictions and their capabilities do much and it becomes potentially possible. I personally think that we will find sophisticated means of doing this in laboratories so what we explored so far indeed does not seem to provide a concrete working scheme

30:00 as this statistics and squeezing is present it is there it is matter of finding a variable or correlation function or something how to reveal it yes this is what i don't know at the moment but i do not exclude that this will be done and because it is in laboratory under your control and you have many period many cycles and it will depend because everything is periodically dependent then it can happen that we will find a better way and it will be done simply with ground-based interferometers when they will reach the level to detect the signal first and then to explore its statistical properties. I was curious if you have an opinion as to why many of the cosmologists working on microgrid background and the way you've described seem to be resistant to including gravitational waves? I believe that it is this harm which was inflicted by this community of dirty and quick theorists because there was a time where if you wanted to be promoted and to receive a job you should have included world inflation in your paper and to refer to all other inflationists And then you will be immediately published, and then you compile a list of publications which is much better than in your neighbor, and then you apply and get a position. I seriously believe that there was great damage because of this change of attitude to what is admissible or not. so what happened when you hear from everywhere that there is something standard which produces zero for gravity or almost zero for gravity weight they will never say that it produces infinity so this is why it is zero it is not zero because it is calculable I calculated this long ago before all these inflationary noises you know so it is a calculable quantity something else which is many orders of magnitude higher then they divide this quantity to that and then they say that the ratio goes to zero which is true, ratio goes to zero but not because gravity waves go to zero but because your

32:30 denominator goes to infinity this created this general feeling I had really vigorous discussions with Lassenby for instance who is doing this, and he's a professional guy, but he's working with general theories as such. I mean, he's not simply an observer. I would say that he's partially theorist as well. But he was so polarized, he heard this everywhere, that for him it is still not a matter of principle, it is a matter of inclusion of extra parameters. He said, OK, in my future processing I may include, because I'm also planning to include a deviation of two sorts of neutrinos from three sorts of neutrinos. So for him it is at the same footing, it is some little extra something which we can include or could not include. While if you stay on these fundamental positions, it is the main thing, it is not small deviation. that it was a result of this existing environment. People have already claimed so many times they are rejecting my papers systematically. Once I will show you for a sociological study which is the level of incompetence and rudeness and how people want to prevent something from publication because it threatens their prosperity, literally. I believe that there is no any other explanation because if you talk about science then you should compare formulas, you should argue that this may be not right or that people refer to that Grishuk is the only one in the world who believes that gravity wave contributes significantly so this is why this paper and it was shown many times by many people that it is wrong So you cannot question something well established. Then you are in a position where this is interesting for you because, of course, in the history of science it was happening billions of times. So if you say that it is not the sun which rotates around the earth but vice versa, of course, you will be killed or something like that.

35:00 So this is a reluctance. However, now it is changing. I will be satisfied even if they, without quoting me, but simply will take it properly into account. So Hawking suddenly declared that since gravitational waves do contribute significantly to a microwave background, and he continues. Why he concludes this? From everything what he was doing, and people refer to him, it should follow. He did not say it himself, but other people said that it is partially based on Hawking, the perturbations go to infinity and gravity waves go to zero. Suddenly, without any reference as something taken for granted, he declares that they do contribute. Which I consider a positive, at least if they do not believe me, they may believe Hawking, and then they will start processing with gravitational waves, and I believe that many evaluations will simply change. Will simply change. It'll become possible that for people to take that as a serious part? I think that they should have taken this simply as for security. Suppose you are not a serious, suppose you do not believe you do not take any side, but if you understand that in principle it is possible and nobody denies that this process exists that it does generate actually everything started from gravitational waves this amplification was actually applied to density perturbations later but all the mechanism all the physics was already in gravitational waves so nobody questions that they do exist it was a matter of the number much of each of them. So I think that what these observers, if they were less frightened, apparently it is also a sociological part, people do not want to be in conflict. It is my education and my style allowed me to shout to everyone, you know, to say that you're stupid and so on, which people do not like. They do not like this style of scientific they do not want to be in conflict which is what they hear from everywhere

37:30 and this is why do not process their data they do not want to do something to be accused that you are stupid we showed long ago that there is no gravity waste and he included so whatever he derived must be wrong because he assumes that there is a reasonable contribution of gravity waste and we all know that there must be no So now they started doing, and as I said, Tragmar and Zaldariaga, two very active young guys, they processed all that with gravity waves, and they obtained that most of contribution is actually due to gravity waves. And this is the best fit model, so it is a model which fits the rest in the best way. But then this sociological pressure, then they say, but no. No, it cannot be true. So let's better switch to models which give not so good fit, but which we like theoretically better. So the effect is somehow so strong that even when, in the first instance, people are reluctant to include the gravitational waves into mothling because they figure it doesn't contribute significantly, but then so strong is the effect that even when they do, if it turns out to contribute much then they feel that that must be wrong absolutely this is exactly what is happening so they discovered essentially they discovered the amount which actually fits with theoretical predictions but they are in conflict with others so then they start saying something that it would be in conflict with I don't know generation of primordial black holes or some very strange idea, and then they switch to something else. So it is not only that they did not include it originally because of these prejudices, but even after they have done this, they still try to get rid somehow, because they feel more comfortable to live in this bunch, to discuss whether H is 0.55 or 0.65. for them it seems to be more fundamental and they think that what we are doing is distinguishing two or three sorts of neutrino

40:00 whereas in reality we are only determining most general crude features, we are determining at all what is the main source we will come to these details much later not now because the spectral index can be changing many, many extra, you know, difficulties which will explain all that in a better manner than this. They believe that it is a matter of including 10 physical parameters or 100, calculating 10,000 models or 15,000. They compete with each other in computing 15,000 models versus 10,000 models with all these powerful codes, all in the same framework. They're all in the same framework. They all use the same initial conditions and codes and so on. They simply say that, oh, recent boomerang made this a little bit lower or a little bit larger. so let's see what sort of neutrinos I will do which would be perfectly alright if we were in the position in solid state physics, in laboratory physics this is what people do when they know that they indeed there is no any other you know, big systematic errors then by more and more accurate calculations you are simply determining more and more accurately some of your parameters which would be an absolutely legitimate procedure understanding is that we are so far away from this to begin this because you do not include gravity waves all together and I know that they must exist so this is why I don't believe that it is a productive way of thinking but we will see we will have a new interview with you may have been 10 years the of course within the field of gravitational waves there's been a certain amount of history of controversy as well. Indeed at one time people argued that gravitational waves didn't exist or were emitted by binary stars and so on. My impression is that while this was a common argument in

42:30 Britain and America and some European countries that in Russia there wasn't a similar sort argument going on. Were gravitation waves more widely accepted? Possibly it is true. Possibly it is true. Partially because in Russia it was a period of strong and very pragmatic people. Falk was working on this and Falk became famous through quantum mechanics first of all. So he you want to make Fox space, and so on. So he was doing this in practical manner. He was not speculating as Infeld or, I don't know, Comar or Goldberg, you know, on some theoretical possibilities and why this pseudo-tensor gives that and another pseudo-tensor gives that, something else. He was calculating what followed directly from equations. And when he was calculating and when he was seeing that there is back reaction, that there is change of motion of this binary, and that the amount of this change is in agreement, what would you calculate most naively with all these constructions, then for him there was no question. Landau and Lifshitz also contributed, because they derived what is known as their pseudotensor, still pseudo-tensor, which is not quite satisfactory, but it nevertheless gave exactly the same numerical values which would follow from near zone calculations. And for me, most importantly, and this is why I completely made piece by now, and this is what we recently published with Stas Babak, is that for a long time I am thinking about general relativity in a kind of philosophical manner, so again I try to get rid of something what everybody considers perfectly well known. Everybody knows that space-time is curved, that space-time is vibrating, that space-time is propagating in itself, so gravity In this language, there are ripples of space-time, so you are absorbing ripples and so on and so on, which for me is kind of difficult to understand. I do not say that technically it will be wrong. For me it was simply unpleasant.

45:00 I wanted to proceed in the manner in which people actually tried to proceed. They were saying, okay, there is gravitation, but there was Newtonian gravitation. Now it is relativistic gravitation, so it will be a relativistic field. Okay, it will be a relativistic field. It may be non-linear. Okay, it is a non-linear field. But let's see what comes out of this. And other people, Feynman, they also tried, but their purpose was to show that general relativity kind of naturally follows from this approach which was not sufficient for me i wanted to make a working instrument so if it follows and then let's literally speak everything and describe everything in this language so in this language we will discuss everything although from the very beginning i was doing this as a reformulation of general relativity it is not an alternative theory it is a theory which will give me exactly the same results if you insist that space-time is curved and I insist that actually there is Minkowski space-time and there is a universal non-linear gravitational field but when we will be discussing with you why this measurement gives that and that you will say because it is curved space-time I will be saying no because a field has acted on your propagation and this is what But the last twist was that in this approach you can introduce genuine energy-momentum tensor, so it is not pseudo-tensor anymore. But what we did recently with Stas-Babak, we literally derived this energy-momentum tensor, demonstrating that it satisfies conditions which we are always imposing in the rest of physics. from Lagrangian it is conserved due to equations of motion does not contain higher derivatives is symmetric and so on and so on and is unique unique in the sense that what you derive you prove that you can only modify by a constant what was always possible so for me this controversy does not exist anymore at

47:30 all because before it was based and related with the notion of an energy people did not object to the notion of something wave-like process because it is the consequence of equations you all see that there is something constellation what they were doubting about whether it is somehow related with transfer of energy momentum whether it is real whether it is real gravitational waves or not mathematical artifacts so by now for me this question does not exist at all because all these energetical questions are simply answered by exact equations and simply present them in theoretical manner then you will see how this energy momentum tender participates and how it influences and what form of your equation will be so i think that it is true that first in the no such, you know, seated discussions, although there were. There was a guy, Shirokov, his name, who actually proved, and first I objected, but then I realized that he was perfectly right. He simply said that if you guys believe that pseudo-tensors are good description, then I am proving, and he proved, that for any possible pseudo tensor I'm using T 0 0 tau 0 0 0 0 1 tau 0 2 tau 0 3 which is energy density and flux of energy as my coordinate conditions so he proved that you can always choose such coordinates that for any pseudo tensor in new coordinates tau 0 0 tau 0 1 tau 0 2 tau 0 3 will be equal to zero and And of course, also there was some controversy, battle, but I think that he was formally right. I think that it only emphasizes the defects of these pseudo-tensor constructions. But fortunately it did not lead to any, you know, conclusions like that gravitational waves cannot be measured or we should not develop experimental programs or something like that.

50:00 So this was before and I think that by now I would say, at least from this philosophical position, that for me this question does not exist anymore. I know how to answer all the questions and I believe that simply gravity is non-linear, universal, relativistic field which satisfies equations which are derivable from Lagrangian, which have absolutely clear physical meaning. It is something like d'Alembertian, non-linear d'Alembertian applied to your field variables is equal to energy, momentum, momentum tensor, not combination, not quadratic terms, energy momentum tensor derives from the same Lagrangian in the right hand side. And this is why after having found solutions, I have no doubt that calculated with these solutions flux of energy will be in agreement with motion of bodies. and so no doubt for me that they do exist, they transfer energy and so on and so on. So this is sort of a tensorial description of the energy flux? Yes, of course, conceptually you change your language. First of all, instead of G-menu, which was for us, in geometrical approach, playing a double role, where you put your finger, you say G-menu is metric tensor. On the other hand, if somebody asks you what is gravitational field variables, you are again putting your finger, you are saying G-menu. So in this field theory, it never is like that, because there is Minkowski space-time, and you put your finger to eta-menu or gamma-menu, it is your metric, and you understand that it is flat if all fields are in moon. but then there is some new quantity which you call your field variable so in this field theoretical approach this is exactly what happens you have metric and you have tensor field which satisfies non-linear equations but then after having formalized this and writing a Lagrangian and we want to derive equations or we want to do all the same what we do in the rest of physics then as a byproduct as absolutely necessary

52:30 calculation, which we always do, you derive energy momentum tensor, which is now constructed from your field variables and their first derivatives. That's it. So again, this is something what some parts of communities do quote. People who are dissatisfied with this dominance of geometrical thinking, they do refer to this. Other people are reluctant to face difficulties because every textbook will teach you that Einstein proved which I do not deny, I am simply explaining what Einstein proved Einstein proved this because this gravity gravitational field is universal and it is only for this kind of thing that you can combine now this Minkowski metric with this tensor field call it new letter G-M-E-N-U interpret this as G-menu of curved space-time and then purely formally all your equations all your Lagrangians and so on they will be converted to each other after this identification so it does happen but it happens only because gravitational field is universal which we assume from the very beginning and we assume that it's coupling to the rest of matter is universal So there is strict mathematical formula which symbolizes what we call equivalence principle, universality, and so on. It means that when you are writing a corresponding term in Lagrangian, and if you ask how my field, we put H minu as field, couples to whatever matter is around, we say it couples in the same manner. It is a universal product of something to something. Oh, but if so, then for any matter, if you do the substitution which I mentioned, then everything is being absorbed in this G-menu, what you called matter-energy-momentum-tensor will be not the same as what I call matter-energy-momentum-tensor, but nevertheless everything goes da-da-da-da-da, and identically the same. at the level where it is simply reformulation

55:00 we indeed will agree and I do not object against Einstein I am saying that you can say you can say that if I am sending something and it gets deviated that it was because curved space-time but you should not deny say as we were saying in the rest of physics that it is getting deviated because there was an acting field so if I'm measuring something like triangle and if you want to conclude that your space-time is curved because you see this from measurements ending here there there and so on you're welcome to do this I am simply saying that it is absolutely equivalent to what I would say out of a universal interaction of gravitational field if there is no neutral particles if they did exist then of course i would prove that underlying geometry is flat i do not need any curves underlying geometry so it is not that einstein was wrong i think that what we need to realize that we need to open our mind because as long as it is only different language it is already whereas Feynman said it is power of thought, clearness and power of thought, and it simply helps you to understand. But when we go to other domains, for instance, quantum domain or modifications of Einstein's theory, now I see what to do, I understand what I'm doing, because now when I look at super string theory, which is all formulated in this language, I better see what corresponds to what. But if I am confined to this geometrical picture, what should I associate, g minu, a square root of g minu, or g minu minus it minu, or what is that? You know, gravity is taken like out of the rest of physics, in my opinion. And Pendros says, no. I spoke with Pendros. He says, no, we have different views about what is the rest of physics. So there is another point of view here. Probably thinks that physics should be geometrised. Whereas I think that physics is already normal and gravity should be put in the same framework rather than the rest of physics geometrised.

57:30 So, in some sense that you think, you know, that the habit of life, the dominance of the geometry, if you point amongst, say, browsers, may create difficulties when they're attempting the same... Definitely. I think that it creates difficulties right now. It is unhealthy, I believe. When people discuss how laser interferometers will work, they say that laser interferometers squeezing of space. So space itself is being changed and this is why arms, arms, it is not that mirrors are moving in your cube, but it is arms which are getting shorter or longer. Of course I understand what they mean, of course I understand that in experimental sense we will come to the same conclusion, but I think that it is misleading because it actually makes it mysterious. So what we are space-time is being squeezed in this direction and being stretched in that direction and my interferometer reacts like that then the question arises if I hit by hand this mirror what will happen if it measuring only the squeezing of space and apparently there is no squeezing I am simply touching it by hand but I know that if I touch by hand will be everything will be exactly the So what gravity wave is doing, you can say that it is squeezing space-time if you are thinking in terms of G-menu, but I'm thinking in terms of H-menu and field, and then what gravity wave is doing is trivial, it is the same what I would be doing by hands or by simply a mass which has tidal, you know, gravitational field. so from time to time this tidal nature and so on it is present in textbooks but at the same time what is present this dominance of geometrical picture which requires from you to acquire everything to the properties of space-time there is not nothing more it is space-time so I think that this clear more clear vision

1:00:00 would be helpful even for today's purposes, for today's purposes, to avoid mysteries because our students, they think that general relativity and gravity, it is something absolutely above their head, they cannot, because you need to know Christophels symbols, covariant derivatives, and it will be always something about coordinates and about space-time and so on. To what extent And is it necessary? It is not necessary. It is actually one frame of thinking. So I am trying to do this at every hour meeting, but it will take some time. I think that we had a discussion recently what future school texts will teach about. And the speaker said that for him it was so obvious that light burns the universe. It was such a visitor. So he made peace in his mind by saying that properties of light are responsible for gravity. and so it is so obvious that he thinks that this is what people will read in school textbooks in the future. Where I objected, I thought that I hope it will not. I hope that they will read about gravity what they already studied in the second, third year. In the second, third year, they are studying Newtonian physics. they study electrodynamics, they study some Lagrangian, Hamiltonians, how they derive. So it is much more natural now to introduce gravitational field by saying, okay, you know all that, now imagine that there is a Lagrangian which is simply non-linear, there is a tender field instead of vector field, and you have one extra index, but you should not bother about your curved space-time it is the same Cartesian coordinates and flat space-time and so on and if you want now to understand why people in the past were thinking that it is somehow related with properties of space-time this is an explanation because if in this field you start measuring something with whatever particles whatever rays

1:02:30 physical systems they are coupled to this gravity universally so there is no way of distinguishing in contrast to electrodynamics in the electrodynamics you have neutral particles you have charged particles so why do we not conclude that electrodynamics is associated with curvature because they also are deviating and if you're measuring with electrons all these triangles they will give you a non-zero why do we say that because we say ah let me send a particle and then it will plot Miminkowski in geometry and this is genuine geometry and this is result of the field interaction. So it is not curvature space-time, it is field. But for gravity it is all the same except that there is no neutral particle. So I think that this approach someday at least will coexist. I do not say that it will replace because there is certain beauty in geometrical thinking, no doubt. But to ignore this and to not to use its advantages, I think that it is unacceptable. So, do you think it's useful to have two different ways of looking at the same? Definitely, definitely, definitely. This is why I am quoting Feynman in his Nobel lecture. He said that even if this alternative approach gives the same experimental predictions, it gives you extra power and clarity of thought and it is important by itself, something like that. So definitely it is like two languages. You speak one language, I speak another language and we discuss some properties of the world. So, clearly, we need to know the vocabulary and to speak, know how to transform, because in my culture, I will be doing something and calling something by the framework that I was guided. I was guided by the idea that it is flat space, but there is a field. then I am raising my own questions. If it's a field, what is energy-momentum-tensor, and so on. In your language, which is geometrical, you are talking, but you say from the beginning, as Mr. Tornviller said, there is no such notion. It is a question, it is an attempt of finding a right answer

1:05:00 to the wrong question, because gravitational field can be removed. You start following an energy, somewhere evaporates, and it doesn't exist. Then they will say that it is locally done, but globally it may exist, that you should average something, and so on and so on. So, to get better knowledge of all that, we at least should understand what each of us is doing. So, I think that, at the very minimum, I would... If I was responsible for textbooks, I would put them in parallel. I would say that this is what follows, how to say, traditionally. This is what Einstein and Poe and Kare wanted. They started, actually, from relativistic generalization of the Newton's law. But later, Einstein went through this geometrical picture. But this is what is equivalent, it has its own beauty and its own defects, and these two pictures are different languages of the same physical things. This is my position, I don't know what other people think about this. I think Kip is gradually changing his position because he now accepts this better than before. I believe that he was pure geometry. My conversations with him were almost no-go at the beginning, but I think that now he is willing to accept at least as an alternative way of thinking. He still will deny that there are advantages, but he at least will say, and partially I believe because he was editor of this new Feynman's book, and Feynman clearly was saying he did not go too far. with his generation. For him it was important to show that general relativity is a beautiful theory. It follows from these principles. But for me it is not a question. For our generation we confirm general relativity from observations and so on. We want to go further. So for us

1:07:30 it is not a matter of fighting, proving that it is elegant, natural and so on. For us it is a matter of showing whether it is useful and how we can develop and what in case if to modify Einstein's theory after all at some moment we will realize that it is not the last word in the truth so how to do this who is in a better position to propose possible modifications I believe that I am in a better position I know something like inclusion of the mass of a graviton which is impossible in geometrical there is no construction in Lagrangian even to do this is trivial and almost inevitable in this field theoretical formulation so if someday somebody convinces me that mass is likely to be generated and those all tiny it is not exactly equal to zero I think that I immediately will say what it corresponds to You mentioned the different languages that arise out in different ways of looking at general education and the difficulty of communicating where two people are speaking a different language. What have you found is the best way to overcome that communication barrier is just that you Do you have to know and be able to speak their language to get anything across to them, or can they sort of absorb? No, I think that my obligation is always to speak the language of somebody. If I want to be useful or to convince somebody, it is my obligation to speak his language. This is why when I am trying to explain something, of course I am changing to framework, position, language. If I know from my framework that something is wrong, for instance, then I am doing this. density and gravitational waves, which I did in old-fashioned manner in synchronous coordinates, which we were doing for ages because we knew that it is always in our hands. But these people, they speak about something gauge invariant. They do not understand that speaking about gauge invariant, if it's gauge invariant, that is also applicable to my gauge, what I'm working. So if you are right, then you simply, in this gauge, you are giving me gauge invariant result, it is also applicable in my gauge but I got a different result and they thought

1:10:00 that it is result because I am working in a specific gauge okay conceptual misunderstanding first of all because if I am working in a particular gauge and your gauge invariant it only means that if I work in a different gauge I would still got the same result as you did because you you seem to be more powerful You know, you are gauge invariant and they think that I am gauge dependent, although the results which we are obtaining, you say that they are gauge invariant, so this is why I changed my language, my approach, I demonstrated in their language, it is on deaf ear, but I demonstrated that if you guys want to do this, so take your gauge invariant quantity zeta, you are right, this zeta is a constant, you are saying, this zeta is a constant from today and back to inflationary beginning, this is what you say okay, now by doing all that you calculate delta rho rho, you get formula and it gives infinitely large, and they agree that it is infinitely large or very large, then I say okay, so then it is your zeta which is related with your delta rho rho And they are numerically equal, so it is the same number. Now, if you want this number to be as large as you want, and if your gauge invariant quantity is constant, as you say, it must have been arbitrarily large from the very beginning. So what kind of vacuum fluctuations you are talking about if you started from this? so some parts of community understood and they are quiet others are still trying to find but I found that it was more convincing instead of saying that you are stupid look I calculated in synchronous coordinates when I changed to this language now I see that some parts of the community are saying we take for granted that density perturbations And they are fine at something like that. So they do not analyze anymore why it happened that it seemingly could be arbitrarily large. They say that we take it for granted.

1:12:30 So clearly, when we have... What I meant in theoretical sense, it was more than language. It was, of course, different conceptual frameworks. But at a smaller level, when we speak really different languages using synchronous coordinates or some other coordinates, I think that it is my responsibility to switch to my opponent's language and to work in his framework otherwise. Unless he is really a very responsible scientist and he will try to understand, most of them try not to do this. say oh no no no it doesn't fit my calculations it might be wrong so this is the importance of the language is it a difficult process for you it is technically difficult technically difficult in case of general relativity it was an opposite way of course I was born and educated in geometrical framework from the year zero definitely but it was growing dissatisfaction and also fight with Logunov in Moscow who actually was saying and repeating the right things. He was a field theorist. By that time my first paper was published, but I gave him his students a copy before it was submitted. It was not published. It was written and ready, but it was not yet published. Anyway, I don't know the story, but what I'm saying is that he was seemingly saying the same words which I agree with that there is full theoretical possibility but he claimed at the same time that because of that general relativity as we know it is wrong it is mathematical and physically inconsistent whereas this approach which he called his own theory in reality it was simply reformulation is the right theory so this was extra motivation for me to clarify this because I was defending general relativity there was no grounds for me to say that

1:15:00 it was wrong or physically or logically inconsistent it is different framework different language it is different concepts but it answers to all physical and experimental questions in exactly the same manner as I do so what did happen of course what happened it was their misinterpretation of the role of coordinates and these coordinate conditions and so on so they stayed at field theoretical positions without recognizing that it is field theoretical positions but of the same theory it is the same theory it is not different theory it is not right theory versus wrong theory it is the same theory so as you see this acquiring different language and speaking can go both ways either you start deviating from your mother language trying to understand other people or if you are criticising them, then you better have to study their language. Okay, I think that I speak too much, unless it is interesting. I mean, is it what you wanted? It is very much of a lot of people, I find it very interesting, but maybe you... No, we can speak a little bit, but probably I am repeating myself, I do not want to take your time. Okay, no, another bit. I find it very interesting, so fine. and I'll just ask a couple of, two or three questions that have come into my mind while we were talking. First, quickly, somebody, and I don't know anything about this subject, but since you mentioned Lagunov, at some point somebody said something to me that Lagunov's work that you just mentioned had some connection with the discriminatory gravitational waves, but I... With what? that, and I may have just misapprehended what somebody said to me, but that there was some, that this controversy that arose about Lagunov's alternative theoretic approach was in some way connected with the controversy over gravitational waves, but is that...? Well, if it was, then in this aspect I believe that he stayed on the right position, actually. they were always emphasizing that from their theory, which, as I said, is exactly general relativity,

1:17:30 but gravitational waves do follow in the way and manner as we understand them. And in this sense, I believe that he would stay on exactly the same positions as, say, I stayed. He was objecting to other things. He was saying that, for instance, when you are measuring Shapiro effect, something like that, then there is one unique expression, which is true, while general relativity gives you several expressions, and this shows general relativity's inconsistency, because you have to choose. Because general relativity does not answer this. So it was misleading, misunderstanding of actually what general relativity says, even in its geometrical formulation. So he was not with his surrounding, which was quite mediocre. They simply did not know properly this material. So he was objecting to this, he was objecting to cosmological models, he was objecting to black holes, which I am also objecting to, but not on the grounds of Einstein's theory. I believe that they do follow a solution. I do not like them, but it is a different matter. But he claims that black holes exist in Einstein's theory and do not exist in his theory, which was simply wrong, because, again, it was misinterpretation of what general relativity says and what is the content of what they call relativistic theory of gravity, which is simply identical plus gauge condition. So, no, I cannot say that he was, you know, wrong, nasty, or behaved incorrectly in this respect. On the contrary, to some extent, he was supporting Braginsky, for instance. Braginsky was a great friend of him, and he received some support from him. There was some controversy, I think in the 50s, over Fock's approach to general relativity, where he said that the harmonic gauge should be treated as a preferred gauge in which to calculate the general relativity.

1:20:00 Well, yeah, I think that by now it completely has only historical interest. Fogg was using these harmonic coordinates as a technical tool. He was emphasizing all the time that it is a technical tool and that it can be avoided. However, he loved them. He loved them, and from time to time he would say that something becomes clear and Newtonian-looking if you are using this harmonic coordinate. So, they have some special status. And he was also arguing that this special status is related with the fact that, say, at asymptotically large distances, they are related by Lorentz transformations, that they go into asymptotically what we would like in the rest of physics, some kind of words. which i believe is absolutely right and legitimate however when it is very risky to say something that you want to prefer something then all people jumped and they start criticizing that he does not understand the meaning of coordinate conditions that it is only coordinates and other coordinates are possible and all that is true other coordinates are possible but he did this concretely and he came to the final result he was the first actually to do all that why all these other people they were jumping on his not very accurate statement that he prefers this coordinate don't you objectify so it was not a real scientific controversy I believe that he was absolutely right in what he was saying. He was not mystifying this harmonic coordinate. And I would say that this is the other side of the community. And here I remember that many of my American friends, I remember that somebody was very critical. It was Havas or Goldberg or Komar in the Soviet Union. there was companies who was shouting that how folk cannot understand that in general

1:22:30 relativity we can use any coordinates and he says that there is something specific about and preferable about harmonic or of course it is of course there is a in other contexts it is synchronous coordinates which are preferable because they make your equations simpler it depends on the problem which you are solving you you have this freedom and you do this on the list of paper in our world if you are studying something like longitudinal motion it is better to use Cartesian coordinates but if you are using and discussing rotation it turns out that it is better to shift to spherical coordinates of course I will be discussing spherical pendulum in spherical will be reduced to one variable instead of three so it is exactly the role which is played by this harmonic coordinates in general relativity it is a matter of choice which is always in my hands and I want to simplify my life I am not so stupid to interpret them as you know I remember that it is coordinate system some quantities which are coordinate dependent I should not everybody will be measuring or something you should define what how do you move and what you measures and I will answer all your questions but it is something what refers to my coordinate system which again is absolutely the same what was always in physics so extra motivation why is this polarization of minds and mystification of general relativity there is something special oh but it was Geometers are doing this, and the physicists were doing this in laboratories all their lives. They knew that there is freedom and choice of coordinates. So this is my response to so-called controversy with regard to harmonic coordinates. Dean, you mentioned the dominance of the geometric thinking, which certainly I guess is true amongst relativists. amongst, say, people active in cosmology, who obviously also deal with relativity as a big part of their work, does their background tend to mean that they also tend to exhibit geometric thinking?

1:25:00 Of course, no doubt. moreover most of them to say the truth they do not even understand general relativity in this limited aspect they are always tempted to do Newtonian calculations thinking that then you simply extrapolate them so they do actually many mistakes by doing Newtonian cosmology and then pretending that it is applicable to arbitrarily large z and so on but clearly in cosmology it is entirely geometrical because if I ask you why the redshift occurs it is because our universe is expanding so there is some you know there is this concept of geometry and this geometry is changing and so on but you should have asked if I'm on this field theoretical positions and apparently geometry is also a part of fields are and of course it is of course it is also what is cosmology for me for me cosmology is a different type of gravitational wave fields in contrast to isolated systems which have localized fields and going to zero somewhere at infinity cosmological fields are such that they actually do not go to zero to infinity and sometimes they are even growing so when I am explaining redshift why is it being redshifted it propagates in this non-linear evolving gravitational field and it is acted upon by this field as any particle and like everything would be in my laboratory and and this is why it gets red-shifted. Does it mean that I deny expansion, or no? I am saying that, of course, it is the same, and we will find peace after we have come to the same language. But for most of cosmologists, for gravity wave people, field language is much more acceptable. They would agree that there are gravity waves which act which display they will say well maybe it is even useful because from time to time they are using the same language unconscious but for

1:27:30 cosmologists it would be absolutely unacceptable because now I'm saying that well I'm dealing with a different field configuration and even closed world is nothing more than a specific field configuration so when we come to If we are serious, then topology is extra property for both of us, for geometers and for field theories. Topology is not governed by local differential equations. Okay, then you will say something about what you want, and I will say something about what I want, and then it will turn out that we have the same topological properties. But closed world I will be describing as a specific field configuration I feel that when my particle is orbiting at seemingly infinitely large distances, suddenly I'm discovering that it takes a short time for this particle to traverse, which on geometrical language is simpler, because you say, ah, you're on the North Pole and this is a circle and actually it is small. For me, it seems to be more difficult because it's kind of large R. But this is why I need to explain what is happening, how this field is organized, how this field influences my particles, what I will be judging about, lengths, times and so on and so on, extracting them from these physical measurements. And of course, I will also conclude that strangely enough, although it looked like a large R, But in reality, this particle suspiciously goes along very short paths, and I do not exclude that I should identify all the points at infinity and simply to interpret this as a kind of stereographic projection of a sphere, and this answers all the questions. So cosmologists will be the last to step up at this position, Except maybe if we convince them that what we are doing with stars, that possibly gravitational mass is explanation to what we think there is a cosmological constant or something like that.

1:30:00 so if there is something presented in their framework but in geometrical framework but with something what will explain their data better than what they do and then after that if I say that aha you agree with this you like it but now what I told you is simply this field and this field actually the field, and this is the term in this massive field, and this is what is happening, maybe only after that they will be willing to accept this, because I helped them to explain the data. For gravity weight people, I'm helping them simply in framework, I'm not helping to explain the data, they do not have data. For them it is acceptable because they are thinking in the same fashion. Cosmologists are thinking in a different fashion, so it will help. Well, I guess a final quick question. Do you think that Kip should play his one is a bet about protecting gravitational waves before the year 2000 on the basis of the COBE Sorry, Kip has a bet with maybe it's Ostreicher or someone that gravitation waves would be detected before the year 2000, and I forget, there was something excluded from the bet anyway, but do you think that he should claim that the bet is won on the basis of Kobe's observations? I think yes. Whether he will accept this as his argument and especially whether the referee will accept this, I don't know. I think that Kip in some good position because I believe that binary pulsar, although it is not direct observation, but it is so convincing that I would say that for me it was clear manifestation which is simply a continuation of all calculations and I did not have any theoretical difficulties because my framework is exact saying exactly the same so for me I would say that even

1:32:30 binary pulsar already proved this but it is not laboratory detection now my background anisotropies if keep agreed with my position with my calculations If it was proven, which is still not, we still do not know, it is my belief, but I would need, although indirectly, but to demonstrate somehow that these gravity waves do indeed contribute significantly, and otherwise I cannot explain this microwave background data. Then I think that it is also a good argument to claim the win. But I suspect that they probably meant real laboratory type detection, which did not occur and this is why Kiep should lose if he was betting on this. That's all the questions I can think of. Thank you very much. Okay, you're welcome. Let's do it.