 It's a great pleasure for me today to be here talking to Giorgio Parisi, the 2021 Nobel laureate for physics for his groundbreaking work in several aspects of physics actually. And it's with me today is my colleague, Professor Antan Arlos Cardicchio, who has in fact collaborated with Giorgio and it's a pleasure for me as a theoretical physicist that Giorgio is among the people who has been an important figure in my field. He has made deep and far-reaching contributions to a wide variety of topics in theoretical physics ranging from the evolution equations for the constituents of nuclear matter then to spin glasses and complex systems. And I think this breadth of his scientific work and this open-ended quality I would say is reminiscent of the great Renaissance physicist Enrico Fermi in the finest traditions of Italian physics. So it's a pleasure for me to welcome Giorgio. Thank you. So maybe I can start with your work, which became known as Altarelli-Parisi Equation because you started your life so to speak in high energy physics to begin with. So maybe do you want to say what led to your interest in quantum promo dynamics and the physics that led to the Altarelli-Parisi Equation? Well, the things was clear. In physics in those days there essentially were two schools. One school, which essentially was a school of bootstrap or S-metrics. Everything was done by everythings. The only things you have to find are self-consistent solutions of some kind of questions that were not clearly written, but the idea was essentially to take a lot of things that come from quantum field theory, like dispersion relations, turn out to the model of quantum field theory, remaining with dispersion relations, and try to find a democratic solution to the... Nuclear democracy. ...in which all particles had the same role and therefore anything can be understood in terms of also other things. There was no fundamental sense in particle physics and so on. And this was in America, something that started mainly in the United States, but yes, people going around all the world. The only thing that was missing for this picture was electromagnetism, because in electromagnetism and also with interaction, electromagnetism, we have a local object where the current we have all these kinds of things that really can be understood in field theory. And this was not so clear to put this hard object in this bootstrap stuff and so on. Therefore, there was another school, the one that was constructed around problem understanding and weak interaction, which was very strong in Europe. And there was a lot of meetings, for example, there were sometimes younger meetings between Rome, Paris, Utrecht, and there were led in Rome by Nicolaus Biberi, Luciano Magliani. There was a very strong school in Paris by Prenki, Iriopoulos, Bouchard, and Philippe Meier. And there was the Utrecht school, sorry, with a first teeny belt man, and then around these things, there was the idea that field theory was important, was not only something that you take some prediction and you throw away. And therefore, it was natural in that thing to discuss things in terms of quantum field theory. Indeed, one of the two papers that I have written, I mean, most of the work was done by the older author, was the Kebibopavici test on the plus and minus of this, making the relation with the total procession with some quirks and deep and elastic scattering. And the idea was that to try to understand how you can get the pattern idea of Feynman using field theory. And now from that point of view, after that you start to understand quantum field theory in deep and elastic scattering, Bjorken-Lohr, in a way that is neglecting some hard interaction between patterns, it asks now the problem of what happens in patterns in a certain other way. If patterns interact in that way, Bjorken-Lohr is not satisfied. You have a relation of Bjorken-Lohr and so on, and so on, which can be computed in some theory, but you don't know the theory, but you can get some try to compute things in the theory. And this I realized that there was an experimental fact that in some regions of X, X, the things was increasing, X equal to 1, this was decreasing. And this type of behavior was exactly what we predicted by correlation of scaling law because the integral should be constant between randomization. So we were very interested in these things. So Nicola was interested in, for other reasons, for electrodynamics in understanding well how to fast compute processing quantum electrodynamics, there was a Watzkeke-Williams, but the Watzkeke-Williams could be extended to discuss what happens if electrons inside a gamma, and that was also the type of computation that Nicola was doing. For Nicola, remember in 1975 or 1976, 75 maybe, he wrote a paper with Watzke that was never published on these things, and in the moment Watzke-Williams for electrons and so on. I was working on this business from a field theory argument of you starting from more abstract setting, and therefore one day with Artarelli, Artarelli proposed, but why we do not write some paper which is clear, which will put all the type of scaling relation during computations from scratch using the infinite momentum, and therefore written the paper. However, the paper was very interesting, I think because it was a change of perspective. And now this change of perspective to put the accent on the fact that there are effective group or pattern distribution which are q-square dependent, it was just a starting point to be able to compute all other cross sections that were later on fundamental for doing prediction for x, discovery at the large scale collider. Okay, so you and Artarelli collaborated in Rome or in Paris now? In Paris, in Paris. Guido was joking that Artarelli-Pérycy was the most cited French paper in this subject. The French, because the Otto had the French institutions, both of the Otto's. But there was also, I mean simultaneously at different times actually, right? And Dr. Schitzer and Gribbov-Lipoto discovered this in the, I mean in the Soviet Union. Okay, at that time, well, did you learn about it? Well, I mean, I learned by previous papers that no one quotes that, previous to all that, that it's a paper by Poliakov, because Poliakov also introduced the some idea or effective part on distribution. So the idea, if you want, of effective part on distribution was, I think, and also Leo Saskin wrote something. Indeed, in some paper we quote Poliakov, maybe Saskin or Saskin was quoted in another paper. Not the one you mentioned, because that was, I think, that they were mostly unknown to us. But the point, the real point was that, the real point of the paper was, first in the case, look to QCD, while other things were not looking QCD. Second, put the computation that were already known, already done for QCD on one side, the one done on the simple way on the infinity frame, and check that the two things were the same. So the two languages were exchangeable. And, first, the short distance expansion was something that could not be useful, be useful, for example, to compute other processes, like, for example, young and so on. Therefore, it's clear that one has to live in the short distance expansion. And indeed, what finally happened, they got the Petronso Amati, not Petronso Veneziano, Formanschi, got this factor, general factorization theorem that for all abstractions and so on, you have everything factorized in one part, which is scaling relation, which is logarithmically dependent, log dependence, with perturbative computations that can be done with the alpha running. And therefore, these things that essentially, what was done at the end, what could be done only after this type of work that we did with Altarelli, indeed, it was immediately done after. So, as you have just shown answering the question by Atish, the first part of your career, you did a lot of contributions in high-energy physics. And then, at a certain point, if I understand correctly, in order to understand better the replica you started studying, this was the part of entry into the study of complexity, of spin glasses, and then what became complexity. Can you tell us the story? Well, first of all, I was interested in statistical mechanics, in first transition, at the same point that I was interested in, at that moment I was interested in high-energy physics, because what was interesting to me, scaling variance, and we have a scaling variance for ocean energy physics, or approximate scaling variance, and scaling variance in two-dimensional phase transitions. The scaling variance was the thing that was joined the two things. Also, the other thing that was very interesting was the fact that one could use statistical mechanics for lattice case theory, and that was something that was interesting. But the technical point for which I went to spin glasses was the following. We were working with Duff and Nicola to understand the high-temperate expansion for lattice case theory. Before you have a lattice case theory, a lattice case theory you can have a high-temperate expansion, and what if you look, you can re-sum the term, so high-temperate expansion, and if you say high-temperate, so what happens in the lattice case theory, the surface is very rigid, and it does not soften. So the interesting thing was if we could find some way to understanding the softening of the surface. What is this discovery that re-summing the leading diagram of high energy of perturbation theory, sorry, of high-temperate expansion, that there was something like, for the main phenomenon that was served in perturbation in this expansion, was something like a formation of a particle which must, something like a group ball, whose mass was going to zero, and it was becoming something like a tecion. Now this was something that probably one should need some kind of better understanding with respect to summing all the leading terms. So this thing looks like some kind of, in reality, some kind of interacting polymer. So the force of model of interacting polymer, so I looked on the lattice, and I found a paper on Lubenski on interacting polymer, and also many other problems on which they were using this replica trick. This replica trick was introduced a few years ago, but from that years I was not reading the things in high energy, only high energy physics, and I was, and I ever want to understand better the replica trick, and I noticed that it did not escape my attention. One paper that says that the replica tricks get wrong result in the case of the Sherwin-Tontipatic model. So now if you know that something gives the wrong result in one case, you'll have to understand why it gives in that case before using by yourself. So I took books, made a lot of photocopies, at the time there was a period of photocopy, carried home and learned some books, took some books from the library, and I started to study the problem, and the problem was quite difficult. At the end I discovered that I arrived at the fault should be of some kind, of some kind. I found that Kosterlitz et al. put the finger on that point, and therefore there was a problem of some assumption that was not correct, some asymmetric solution was unstable. Ever once that you know the symmetric solution is unstable, you have to find the right direction, so the right way to break the symmetry. And there was a few things, there was a paper by Bray, there was another paper by Blondin and others in France, I think Blondin, and after I looked at these type of things, and they did similar computation, but the computation was doing something that did not give good results, the things is improving. And now what was clear that at this stage that one has to do something strange, because normally when you do the parameter, you do the computation with some parameter, you have usually, or you have to maximize with respect to the parameter, and you have to minimize, but this is in that computation the things were strange, with some parameter you have to maximize and some parameter you have to minimize. But the result was wrong, so I was not clear what happens. And there was a Meiko 6 conference in 1979 at ICTP, I participated to the conference, I not presented the talk, but I presented the poster. I presented the poster where I said that you should have the computation that people do, and I was to generalize in their computation, we could have it done to maximize with one parameter and to minimize with another one. And I remember that conference at ICTP, a friend in Rome, Mr. came and said, look, it's completely nonsense that you maximize to something and you minimize to the other one. You should follow, I mean, you should do the same thing for all parameters, the free energy. And I talked that the argument had some importance, and therefore I considered another number that was an integer. They said that it could not take away from being an integer to a non-integer, and I maximized with respect to everything, there would be an integer number that finally was non-integer to the other two numbers, I got something that was working much better. And so that's the way, and also the things was quite amazing, the mathematical structure was quite amazing that I start to work on this thing for a long time. So this was the beginning of your work on complexity? Yes, it was the beginning, it was the first paper that I submitted, the first paper was submitted, the referee said the things is completely, it does not make sense, but just because the result is correct, you should publish it. The second part in which I was generalizing the result, and that was the deepest part, I said, that part is not worthwhile, the paper which is written. So I took out that part from the paper. It was kind of a random walk towards new ideas, right? Yes. Maybe since you have worked on so many different fields, now of course you have also done the KPZ and matrix models, which was the most exciting moment of your scientific career, maybe more than one? Well, one of the things that was exciting, that at a certain moment I was looking to, I mean because it was complicating the approach, I was breaking the symmetry once, more, and the symmetry could be broken once more and once more, and therefore I remained with something like an infinite number of parameters to describe the symmetry and I think that at a certain moment I realized that this infinite number of parameters were describing a continuous function. So the real solution should be done in terms of a continuous function. Therefore a continuous function was there. This was, for this point, something very exciting. The other point was very exciting because we fought for three years to understand the meaning of that continuous function and at the end, staying in Paris in 1982, there was some observation that was done to me by Ixinson, called Ixinson, and reflecting on this type of observation, I came out of the interpretation, the found out which was the interpretation of this continuous function and that was very important. The continuous function is the Parisian or the parameter? Yes, the Parisian parameter. And some that you can consider may be an anticlimax, that I remember that I continued to look to the problem and after doing some computation, I arrived at what Gilles Landeguere approved in a rigorous way. That's where the Gilles Landeguere identity. And I looked at the identity and I remember that my thought was that nonsense, the proof must be wrong because it produced. But after some time I convinced that despite all these completely strange identities, the proof could make sense. So in the motivation of the Nobel Prize, it's mentioned your work on complex systems. Yes. What do you see as one of the paths, maybe the path in the research on complex systems, both quantum and classical, over what you want in the future? So what problem in this field would you suggest a young student to look into? Well, I would suggest not to look at the problem, I suggest to them. Because you see, one that worked on a field for a long time is going to see the things with his own spectacle, his own eyes, and therefore he's not able to see things that are new. So that is something that... This is something that probably... I mean, I can see lots of problems that I would like to solve. I would like to better understand quantum physics, to understand quantum twin glasses in more detail, also quantum Earth sphere. And there are lots of problems of a normalization group for Earth spheres. For example, I would say that it would be considered interesting. Also, the problem we have been fighting for nearly 40 years is computing look corrections to construct a normalization group for spin glasses. Maybe this is not a good question. Maybe the good question is something completely new. Also because somebody has tried for many years to push something one direction, to get a new idea from something from scratch or it's difficult to follow all the ideas to... So you're suggesting to young students to talk among themselves and try to figure out by themselves which... Well, let me talk about myself to figure out and let me just tell me something that T. D. Lee said. So the only... T. D. Lee is a famous physicist that won the Nobel Prize, I think, at 29 years, if I'm not wrong. And together with Yang, that was much older, he was 32. And well, the three years difference account. And also especially in Chinese society account. Anyhow, T. D. Lee was saying that in order to be very good, to do a very important discovery, you must be very cultivated or very little cultivated. Because if you are just medium cultivated, you get a new idea and you look into the literature and you say, well, this is excluded by other things and so on. If you are not too cultivated, you don't bother what is written in the literature and you go on. If you are highly cultivated, you are right that what's written in the literature on that thing is wrong. And never can ask him which of the two categories was considered himself. But... So, George, you also received the 1919 Diraq Medal from ICTP. Yes. Then you have been now on the Diraq Medal Selection Committee and you have many collaborators here. So you have a long association with ICTP. Maybe do you have some experience and memories of visiting here? Well, ICTP is a wonderful place. It's a wonderful place, not only because it is in a wonderful place. I mean, it's around a wonderful place. But this idea of Salam or constructing a bridge between the developed country and the undeveloped country and having a first-class science done in that place because it's easy to construct a bridge but not having the first-class science done. But you do first-class science in a given place. On the same type, you have people coming from different parts of the world that are exposed to science with colloquial course and so on. It's a wonderful idea and I think that it's extremely important for the development of science in the rest of the world as we know by the incredible number of students that... Which is the number here? We have something like 5,000 scientists, not students, but 5,000 scientists. Exactly, which is... Visitors, visiting scientists... Which is an incredible number. It means that everybody who has nearly 20, every working day, nearly 20 people arrive. Including Christmas. This is something that is incredible and it's something that has been useful, something that has been a great thing from Italy, first of all because it allows Italy to be known in the world, to have people who may learn Italian, may have a familiarity with Italian colleagues and so on and also because the ACTP, also with the work of Budinich, it was the starting point of CISA because Budinich was vice director of ACTP which, if I understand correctly, all bureaucratic things went to Budinich and the high level things were done by CELAM so Budinich was a real strong vice director which meant they had all the connection with local government discussion with local... And also this was the starting of the science area for CES because the CISA, which was also funded by Budinich when it was... ACTP was going well and it did not do its work and also the all the electric stuff and so on, the area on... Padricciano, yes. And exactly the fall was crucial and this is very important for CES because CES, from the viewpoint of Italy, is just on the little corner of Italy so having something which is related to science is one of the main vocations of CES and this vision idea of Budinich I mean, incarnated in the first time then ACTP and with incredible success and ACTP is a wonderful avant-garde of modern science towards the Balkans and indeed this project of West Balkans as is discussed at extremely high level and the European Commission and so on I think that this West Balkan project will go on with the idea maybe having the center, the headquarter of the project should be likely to... should be interested because this is the best place to be done so ACTP has been the starting point of everything here. Yeah, I think what you say is correct that first of all in ACTP of this 5,000 scientists to come half of them are from the developing countries and ACTP funds them but so on one hand it benefits the world at large but it's also that it internationalizes Italian science as you said and it has developed this Trieste Science System which has become sort of the center for further development and let me add that the director after Salam Miguel Virasoro was very important in expanding the ACTP that was only from energy species including climate science, statistical mechanics of this group so the influence of Miguel Virasoro which commemorated today is... which have commemorated today has been extremely important with ACTP because it expanded the scope after the retro the stone still expanded the scope but the break with the monoculture of Salam that was an important breaking point because one could be intimidated by the memory of Salam and the institute should be... Only one high-energy physics, SS Salam time So we were speaking about large numbers one large number is the number of collaborators you had in your career which is several hundreds Well, the people I did the computation three years ago and three years ago there were 317 collaborators and they did a nice posture with all names I think their names and now it's all the 340, 315 they're doing a new posture with the new names Yes, I'm looking forward to see that You were one of them I was one of them, yes, already three years ago, yes So how much do you value collaboration in physics? Well, collaboration in physics is extremely important It's all because if you work very hard on yourself it's tiring I mean, it's... I mean, it's when I was more young when I was, sorry, young When I was young, many of the people were not written by collaborators I did many paper written by myself but I found it's very important in that case to ask people around and say, look, hear what I'm doing because I mean, speaking with people because it helps you to be clear to understand better that if you have to explain something you have to understand well and if you don't speak with other people you understand maybe... You think you understand but maybe you don't Maybe you don't, you have to fast and so on Working with collaborators is fundamental because collaborators may have a wonderful idea that you don't have Indeed, as I was mentioned before some of the most important paper of spin glasses were written in collaboration with Miguel Miguel and Marc Mezzar some of them wish to lose and Nicolas Soules and they were important because they had in some viewpoint that they were certainly not being able to do because I mean, it's clear that when you do a paper the thing that is very important is the ground because it's not only the technical point it's that you need the similar you need the interpretation and so on and that people with different ground and also the collaboration with Marc Marc Mezzar had an incredible capacity of doing very complex computations I remember that once it was the most difficult computation that we did at that time we were one of us in Paris and the other one in Rome we discussed some way how to do the computation that could be done in two different ways Marc did it in one way I did it in the same different way I mean, there were faxes of ten pages but the final result was the same in spite of them there was a small mistake in the paper that we corrected but not in the difficult part it was in the easy part So I think one of the things that you are becoming interested now from what I hear is I mean this support for fundamental science or let's say curiosity-driven science as opposed to mission-driven science or innovation, the kind of emphasis that is shifting in the terms of policymaking also this was something Salam himself said I think in the 80s that he felt that if he had tried to create something like ICTP in that time he was quite pessimistic that he may not have received the support so in some ways it's important to communicate I don't know how to communicate but how well we know what we know in physics we really understand maximum equations which is somehow not appreciated sufficiently and at the same time there are maybe more speculative ideas like wormholes or something which immediately catch hold of the imagination and so both this what is your feeling about this emphasis on curiosity-driven science I mean curiosity-driven science is important because it just puts the basis for all this type of construction I don't say that you have to also do some science that is driven by which given applied argument but curiosity is extremely important also because curiosity-driven science is something that sometimes lets get applications which are completely unexpected let me think for example one case, number theory if you look with the book of Hardy the Apologies of the Mathematicians it's a wonderful book and they said a wonderful book and they said that one of the things that he was trying was the things he was doing had no application had no application people went on with number theory they started discussion on how to factorize a big number in two things and from these things you discovered now what is used by everybody the way that you can communicate cryptography which opens key cryptography which you exchange information and on the middle cannot intercept anything and this was something that came out not in the right way because long time but it was all the number theory that was put forward by Hardy, Littwood and so on the final arrived to this type of applications another application which I think that was completely unexpected is probably because of not being able to follow directly part of the original paper, Chomsky Chomsky was interested in human grammar in the grammar of human language and he had the idea that grammar should be defined not in a fluid way but should be defined by formula by some kind and therefore he started to define some type of grammar regular grammar I mean with recursion and so on and all these type of things and also to classify this type of grammar it was this wonderful idea that you can construct an automa an automa that reads the text and decide if it is grammatically correct or not correct and depending on the memory on the type of characteristic of the automa they correspond to more and more complex grammar to more and more complex automa this was done for classifying human language and so on however in a very short while Chomsky idea went to the basis of producing automa that they read the computer language so if you open a book of the 60s or the 70s or the 80s on computer language the first thing they teach is the grammar classification of automa and so on how to implement Chomsky automa to understand the format how to go for one formulation the grammar to other one and therefore that was something that was completely I mean I am not sure if Chomsky has in the back his mind that these things can be applied to computer language but that they were born in that time but I don't know but other things for example you know that we have a tunnel microscope tunnel microscope are done with a tip and the people that started to do tunnel microscope had no idea that they could get such incredible accuracy they just want to do some more less deductive tool to show how tunnel is working and the idea is the following there was one they did a conceptual mistake when they did the things well you have to do a tip now if you do a tip it's clear that you have to cut some way and it's very difficult to do a tip that is sharp so the idea is that they could not do a tip that is sharp than 100 atoms so they believed that the resolution was limited to 100 atoms there may be a few 100ms after they started to do they realized that although the tip is cut in some way there is one atom which may conduct everything and the tip now although is cut down in a microscope way there is one atom on the top that makes all the conduction and so the resolution is one atom but I mean it's something it's something that you could not predict a priori and for example also a Mueller discovered high temperature superconductors he had some idea that these kind of materials could be superconductors but the idea was clearly wrong because after the material were discovered no one was able to do a clear theory of superconductivity for that material nowadays we have something but it's a complete theory therefore it was just by chance that they take the good I mean it was intuition I mean they get the intuition I mean the intuition probably was right but the other part of the theory was wrong so people just do things by chance and a few and both projects on one of them both Mueller project and microscope project if they should go to some committee some panel to be approved they should be put to a lower priority but I mean at IBM I think I was told each research has amount of money $20,000, $30,000 that it can use without having to justifications and that was the possibility of giving this price so you have a lot of things that are done by curiosity you mentioned hardy I mean also Ramanujan's work nowadays has come to play a role in quantum black holes I mean these kinds of connections you cannot I mean there is this unity of science you might say since you have worked on so many that you cannot really put borders where one thing starts and the other thing ends is the unity of science because also you have pointed that science creates metaphor and the metaphor used by other scientists are used also outside the science and this metaphorical communication is something that is very important so the black hole may be very important the black hole may produce some metaphor may be not applied but may create a metaphor for other things for example one of the things there is a computer and biology I mean I speaking of the 50s and computers are divided in one part that is hardware of the computer that we know and the software of the computer that is something more intangible that has a completely different support of the hardware and now the idea that the cells have an hardware that is protein and DNA that is a software is something that was a very important analogy metaphor that was the driving force of all research in the 50s and the 60s this metaphor is computer at the end we understand now that the things are more complex the DNA may modify itself there are more objects in the middle and so on but it was something that therefore the metaphor is very important so you cannot say which kind of which kind of part of the science I'm going to do to go on in another part of science Okay so I have just one last question on my part so we have been discussing about you know technological advances versus fundamental research and how people today you also say during your colloquium that people more easily value technological advances which are brought by science than science itself and that in some countries we might actually see a reduction of the funding and support in general for fundamental science since here at ICTP we are interested in the whole world of science so we were wondering what do you think could be the role of ICTP in fighting against these tendencies where they are present ICTP is I think it's very important just because sometimes the situation in the third world is not so good for science and it's very important there are some regions from which you should things should be done and you should teach things of course it's clear this is important because especially in some region or not to develop a world there are some rest of some kind of magic thinking and so on therefore it is important that you have to bring science of course you have to bring science you must be careful because you must bring things that are relevant for these guys and because otherwise you may bring things that are just like a tree there in the desert let me just tell me a small ameduct that was told by a friend of mine that in some place I don't remember Central Africa they imported cow to produce milk cow yes to produce milk so there was so however after they started producing milk they discovered that milk deteriorates very fast at that temperature at that temperature and you cannot and therefore you don't have a fridge you don't have a refrigeration the templates I saw a friend of mine went to the place where they were having this milk that they cannot produce and teach them to make cheese so if you transform milk into cheese this is something that you can preserve for a long time and so on but I mean they just said that the intervention must be integrated because if you start to do only one thing without considering all the boundaries and for these things it's very important that if you want the contribution of people that live in the place because people live in the place recognize what can be done what cannot be done what is missing and of course the people that live in the place must be educated and therefore this is it is important so ECTP is a wonderful doing a wonderful job and completely fulfilled the mission of UNESCO of the EIA because it goes in the right direction of increasing the knowledge and bringing I mean science bringing knowledge to the third world that is a very important thing and it's very important also because people must be educated in science in order to understand the danger of climate change because if they do not educated in science they do not understand the danger they do not understand the origin they do not understand why one should have to do something which may be painful in some sense therefore it's clear that to have scientific information in the third world is also fundamental in order to have people to do what they should do for climate change Thank you very much Thank you very much