Episode 5 Transcript: Our Quantum Complex Universe
Introduction (00:03): Great science and engineering often begin with a singular hypothesis. But how does a lone spark of innovation become popular science? From Caltech, this is The Lonely Idea.
Rich Wolf, host (00:16): This is your host, Rich Wolf. Joining me for this episode is Maria Spiropulu. Maria is an experimental physicist at Caltech who is building a detector to advance her quest to find evidence of supersymmetry. Supersymmetry proposes that each fundamental particle has a yet to be discovered partner particle, which could explain a number of current mysteries in physics, including the existence of dark matter. Maria, welcome to The Lonely Idea.
Maria Spiropulu, guest (00:41): Thank you for having me. It's exciting.
Wolf (00:45): So Maria, we will get to concepts like supersymmetry, and your time at Fermilab, and your time at CERN, and your involvement in detecting the Higgs particle—and, more importantly, your specific research and your contributions. But before we do that, I'd love to know a little bit about you. Why don't we start with growing up in Macedonia and let's find our way to physics from there?
Spiropulu (01:10): Yeah. This is an interesting start. Thank you for digging into that and bringing me back to my homeland. I grew up, indeed, in West Macedonia. This is in Greece. And I was a terror of a child because I was taking apart everything, just like all engineers and physicists and inventors. I come from a family that they're more artists, designers, and military people rather than scientists. So that was a surprise to my parents, that I was very determined to follow a scientific path in any way, form, or shape, or an engineering path. Initially, I really wanted to be an astronaut, like if you are in West Macedonia, what else would you want to be? An astronaut.
Wolf (02:09): Of course.
Spiropulu (02:09): And a fighter pilot. And in those times, and I was keeping this up together with the science ideas, but I felt that I would go through the route of space. And of course it wasn't possible because I was the wrong gender, still, at that time, to get into the air force academy. The air force academy in Greece was not accepting women at the time that I graduated from high school. So that's the short summary of being brought up in Macedonia. And I went to school in Macedonia to do undergraduate in the Aristotle University of Thessaloniki, where I went into physics. And that was the only school that I applied to. There, I spent five years, one year was a thesis year. I was in the nuclear lab, but also being the terror that I was, I was visiting CERN as a technical student in the technical assistance two group [TA2 under Ettore Rosso].
Spiropulu (03:08): I visited for six months as an exchange technical student in Berlin, at a single drum laboratory. And I did material science characterization of silicon nitride, et cetera. So I got a broad experience in experimental science while, at the same time, I did what we call phenomenology. In other words, I was trying to invent [modelling and] theories about what I was seeing in the data, which was unusual for a college kid to be doing in Greece at that time. And, for me, a very, very exciting endeavor to be doing my experiments and then sitting alone with my lonely idea to compete with some [superstar] theorist in Israel at the time, who was doing theory for the interpretation of this data. And I felt this was a thrilling experience, that I was trying to put the theory on the data.
Wolf (04:09): Well, let's go back because there's an interesting nexus there between wanting to be an adventurer, wanting to be an astronaut, wanting to be a fighter pilot, and also somebody who was a tinkerer who wanted to understand how things work. The notion of you tinkering with things and wanting to understand how they work while also wanting to do crazy far out adventuresome stuff, and now how do we get from there to being at a university where you suddenly think, "I want to divine the theories that explain why I'm seeing what I'm seeing"? And before we get very concrete on anything, there's something innate about you that led you to that. And what do you think that is?
Spiropulu (04:54): Well, it's either the innate thing or the environment with the innate thing, that you feel free, you feel the freedom to explore phenomena in nature and to tinker it without being in a silo of traditional sort of education and how you do research. In other words, I had the tools, or I made it such that the tools were available to me so that I can go to the labs day and night, so that I can irradiate samples in the medical school laboratories. So, I made it such. I constructed my reality such that I can do all these things. And with this, I explored the freedoms of the system that I had in Greece at the university to start with.
Spiropulu (05:43): But also thinking about Caltech, Caltech gives you also this freedom and also the freedom to cross barriers, among traditional disciplines. So I told you, when I explained what I was doing, is I was jumping and crossing disciplines and applying what I learned in one to my thinking on how I conduct the other. And in fact, this emerges right now that we are talking about it—I never thought about this before, but one of the most spectacular things that students observe when they work with me is that I push them to cross barriers and learn more than just one particular field of expertise.
Wolf (06:29): Well, and it also sounds like you think of theory and experiments in a continuous loop, which some people don't. There's some people that think, particularly in physics, that the theory is hard enough to do, and the theory and the mathematics postulates something. And then there's a whole other group of people that go out and they try to design experiments to match that theory. LIGO [The Laser Interferometer Gravitational-Wave Observatory] is an example of that, in many ways, although, fortunately we had some theorists who really wanted to get their hands dirty with the experiments in that one too. But it sounds like in your case, you liked the idea of observing something in nature or through an experiment, then thinking about the theory, going back and conducting another experiment, having that help design more theories, and that continuous loop is something that you think only works when you have a lot of intellectual freedom. Actually I want to call it brain freedom, where your brain can just kind of run. That's fabulous. You mentioned your students. How do you do that for your students? What do you do in your lab to enable that brain freedom?
Spiropulu (07:32): Right. So the first thing that I am explaining to students is that physics is an experimental science and theory is part of the scientific method. So I want them to both have the fundamentals and the experience in the experimental instrumentation part. The engineering part is part of physics. There's no question about that in my mind. But then I want them to be thinking outside the box and question all the theories that we have up to now because all the theories find some complementarity and they need to be pushed in order to get to the frontiers. And because my science, the place I operate in science, is always close to the frontiers, they kind of get attuned to this kind of thinking, that it's not just enough to build the experiment, that it's actually fun for them to think and not to just take ready thinking and just trying to apply it. I think students, especially the students of Caltech, and the reason why I'm at Caltech is the students. The students recruited me. I was a staff member at CERN. Students are the glue and the core and [during] the time they are operating to do their undergraduate thesis or their graduate thesis, they are in a position to have all the freedom in the world. They are not bound by anything.
Wolf (09:05): I want to come back to students later in the segment because there are a couple of particular stories that I would love to revisit with you, ones that I know. But I want to touch on something else that you just raised, which is the environment and creating the environment and being in a place where you have the freedom to do something. Let's go back to Thessaloniki and you mentioned a competitive program going on in Israel. Let's get a little deeper and talk about what were you specifically do doing, what was the science and what was the competitive program?
Spiropulu (09:34): Right. So the competitive program was a theorist who was taking the data, our experimental data from the experiments, that was thermoluminescent experiments that we were doing in the nuclear lab in the Aristotle University of Thessaloniki, and he was devising theories. And he was not an experimentalist. And I was building the experiment, taking the data, and also I was thinking of better interpretations. In other words, putting a better theoretical model [to it]. So now imagine, I was 19 or 20. So, when I put the paper out with the experimental data, but also with a new way of describing the theory, everybody was very surprised because, you know, where did that come from? It was surprising. And where I came from is that I was studying a little bit ahead of my time, quantum mechanics and entanglement and how we do superposition in some stuff. So I threw some ideas [in] there, that were not integrated in the previous theories and people were very surprised, my teachers and others. And so, it was quite rewarding, even if it was a little bit out there.
Wolf (10:51): And, what was the nature of the result that you found?
Spiropulu (10:56): So the result was the characterization of some particular solids and how did they respond to various kinds of radiation: alpha, beta, and gamma radiation. So it was, let's say, a nuclear kind of problem for which the theoretical description was very standard over the years. And I was observing phenomena that were showing additional contributions, let's say, that the theoretical model was not [completely] describing then.
Wolf (11:28): And this is going to play very nicely into our discussion of the standard model later in the session. But how did you come up with a way of doing an experiment that would show that these materials acted differently? You thought of something. What was that?
Spiropulu (11:46): Yeah, so I thought of doing the experiment with various metrics that people were not doing as a function of time, as a function of response, as a function of the energy. So I kind of looked at more than one axis of how things were being done up to then with characterizing this kind of solid, this kind of materials. So it was just curiosity and it was just a fresh mind getting in there and saying, "Why don't we look at this, as a function of that and that and that and that?", instead of doing the same thing that was done before. And this is why students are the path to progress, because they come with their fresh minds and they ask questions and they shake what was done before.
Wolf (12:37): But someone at Thessaloniki must have said, "Let her do this, let her run." And you've obviously taken that now and you let your students run.
Spiropulu (12:45): That's right.
Wolf (12:45): Who was that person?
Spiropulu (12:48): So it was the professor of the nuclear lab, the director of the nuclear lab. And he said, "Whatever ideas you have, go and run with them." And then the other professors there, they gave me the keys, and they taught me how to do the experiments the way they were doing it. And I took it upon myself then to start amending and doing measurements and trying to figure out the interpretations. I mean, this was not groundbreaking, right? This was a part of research that was not like when I arrived at Fermilab and we discovered the top quark. That was groundbreaking. It was like a seismic event. Or the Higgs, even more so. But it was the way I entered into science and the way I exercised my freedom. And this is what I want to see in the students here, although my students now, everything they do is on the groundbreaking frontier.
Wolf (13:53): In many ways, and it's the reason I wanted to focus on it, it was groundbreaking. Because it's what enabled you to go on and do those other experiments. So that obviously led you to go and do your PhD. And let's now fast forward to the year 2000. You finished your PhD and now you're really ready to kick it into high gear in terms of engaging in this loop between experimentation and theory. What did you do next?
Spiropulu (14:23): Well, so the whole PhD was kicking the tires in order to find new methodologies to discover supersymmetry. So, my PhD was seven years and 22 days. It was a long PhD.
Wolf (14:37): And let's back up just a second. If you were explaining to a lay person supersymmetry, how would you explain supersymmetry?
Spiropulu (14:47): Right, so supersymmetry would be saying that we double the particles, the elementary states that make up the universe. We double them. And not for a bad reason, but for the reason of understanding quantum corrections to the Higgs mass, which we didn't know at the time. But we were narrowing it down to be in a place that it needed the quantum corrections from particles like supersymmetric particles. And so supersymmetry has been and still is, as a theoretical model, the most compelling model to solve the theoretical problem, at the time, of the Higgs corrections, of the Higgs mass corrections.
Wolf (15:38): If these subatomic particles didn't have basic relationships with one another, we would have a major problem. The universe couldn't be held together if they don't have these basic relationships. And you're trying to figure out what these relationships are.
Spiropulu (15:50): That's right. And now nature gave us a curve ball because we discovered the Higgs and we discovered it at a mass that is super peculiar and we haven't discovered supersymmetry to protect the mass of the Higgs from the quantum corrections. So we're scratching our heads since 2012, that we discovered the Higgs, on the question, why haven't we discovered supersymmetry. It must, it has to be there. So something else is going on and this is where we are gearing now, to figure out which kind of extended supersymmetry, different supersymmetry, or what kind of new states are there that protect the Higgs mass from quantum corrections. Otherwise we have to toss quantum field theory out of the window and figure out what is going on.
Wolf (16:44): Wow. So we've now, just by actually discovering this particle, which we never even knew we could discover and would exist...
Spiropulu (16:53): Correct. Correct.
Wolf (16:53): ...an enormous amount of work that went into that. We've now opened up an entirely new field and we have to start looking for examples of supersymmetry in nature. Let's go back to the Higgs particle discovery and just particle theory in general.
Spiropulu (17:08): When you get the particles to collide, you get many more debris out of the particles, all of the initial states that collide. And then you go to reconstruct all the energy you put in the collision, whether you created a new state, a heavier state. And this is how we discovered the top quark, and this is how we discovered the Higgs. And the phenomenon that is happening in the collision is not just in the simple analogy of a bag with stuff that are in because there is quantum transformations. So the Higgs does not contain particles that it decays to. There is a quantum phenomenon that happens that the Higgs decays to two new ones. The Higgs not have two zed [Z] particles or form new ones. The Higgs does not contain anything. It's a quantum state that has this ability of mutating into new forms of matter. And that's how collisions in general work and how decays of particles work.
Wolf (18:08): Well, I remember you once saying to me, one of the other analogies you gave was, imagine inside the Large Hadron Collider, the LHC, we were slamming Volkswagens against one another and every now and then after millions...
Spiropulu (18:21): Comes a Porsche...
Wolf (18:24): Comes a Porsche.
Spiropulu (18:24): Yes, that's exactly right.
Wolf (18:24): A Porsche comes flying out.
Spiropulu (18:28): A Porsche comes flying out after the two Volkswagens collide or a Tesla comes out.
Wolf (18:31): So, you manage to do this, you and obviously many, many others managed to do this in 2012. And the problem is, while you solved one major problem, you created a whole mess of other problems for yourself.
Spiropulu (18:46): Huge, huge, huge. How are we going to now write down the equations of the quantum corrections to this particular Higgs mass? It's 125 GeV [gigaelectronvolts]. That's what it is. It's neither here nor there. We didn't expect it to be there. We expected it either a little lower or a little higher. We have the additional problem that supersymmetry was giving an answer to the dark matter problem perfectly well. We have a problem with the Higgs, and we have a problem with dark matter, a very significant problem with dark matter, because we know from gravitational phenomena that dark matter is there in the universe. And so the whole field of gravitational physics from the point of view of the theory, namely space-time, generation of space-time, quantum gravity, dark matter, and dark energy. All of these are connected with gravity. We were hoping that supersymmetry, which has a super gravity component, which has something that is giving you the right candidate for dark matter, is not discovered.
Spiropulu (19:53): So we are left with some very big puzzles to solve. And this is why we are driven to study very carefully the Higgs, study self-propelling quantities because the Higgs gives mass to all the other particles, but who gives much to the Higgs itself? So we need to understand how it does that because that will tell us how the Higgs potential, how we describe the Higgs potential. It will tell us something about which kind of criticality do we have in the universe. And it's telling us something [fundamental]. We have to figure out something about Higgs and dark matter and its connections, if dark matter is interacting with [matter] via the Higgs.
Wolf (20:39): Is it necessary to identify examples of supersymmetry in nature in order to make that connection between the Higgs and dark matter?
Spiropulu (20:45): Well, yeah, it is absolutely necessary to discover it. So supersymmetry, up until the time that I was in school, in graduate school, we were teaching it as if it is for sure the answer. We were teaching it as if we had discovered it. But no, supersymmetry is a theory, unlike the standard model that is a theory of the world as we know it, experimentally proven. Supersymmetry is only a theory, and by the way, a fantastic theory, like an amazing theory, but we haven't discovered it. This theory is an unproven theory.
Wolf (21:22): What are some of the things that you're working on to try to discover examples of supersymmetry in nature?
Spiropulu (21:29): So the way we are approaching it now is we're trying to find...since the prompt supersymmetry, in other words, the two Jettas giving you a Porsche, and the Porsche is coming exactly at the point where the two Jettas collided. Now imagine that I collide two Jettas and the Porsche appears far away from the collision. So it flew before I saw it. So there is this parameter of the phase space for supersymmetry in dark matter of what we call delayed states. This is a departure from the vanilla supersymmetry, from the let's say classical supersymmetry if you want, that has been going on for 40 years. Now we're doing exotic supersymmetry if you want. And we're trying also to figure out if this kind of delayed particles can be candidates for dark matter. And in order to do that, you have to have more detectors that make precise measurements of the time that this particle arrived in a detector. So we're building some exquisite "time of flight" detectors that measure the time of arrival of a particle with the resolution of 30 picoseconds. And this was something that I proposed in 2012 when I arrived at Caltech, and it was approved a couple of years ago. It's a long process to build new detectors, and all my students are working on one aspect of this or another, and the staff and my group.
Wolf (23:10): You mentioned a couple of things along the way. SUSY refers to supersymmetry.
Spiropulu (23:14): Correct.
Wolf (23:15): You also mentioned the concept of beyond the standard model, which is something that I think a lot of lay people actually have embraced. I mean, you need only pick up every other Scientific American to try to find out what's the relationship between dark matter and dark energy, and how do all the particles in the universe actually fit together, which, matter in anti-matter asymmetry, neutrino oscillations, all of the things that go into taking us beyond the standard model.
Wolf (23:43): You've picked out this particular area within supersymmetry and you've said, "If we can design a detector that enables us to measure that Porsche when it's way far away, then we'll at least be able to put a stake in the ground." And that stake will go on the ground and say, "Okay, we found the Higgs particle. That makes sense. We know there's evidence, there has to be evidence of dark matter, that has to exist or else nothing makes sense. And now we found examples of supersymmetry." So, before we talk about what's next, let's talk about building that detector because I love the notion that all of your students have to not only be theorists, they also have to be engineers and experimentalists. So let's come back. Let's come back to building that detector, and the exciting aspect of that. What are you going to do now that you have this funded?
Spiropulu (24:31): So the group is operating in three places: at CERN, Fermilab, and here at Caltech. And here we're doing the module assembly of the parts of the detector and we're testing them. We're testing them on laser test-stands, and we're testing them with nuclear sources and we're doing the radiation damage studies. But we have done also the design for the mechanical structures, for the thermal studies, the design of the actual sensors, how you collect the energy, or the light, of the particles. And we have picked out, we have created the blueprint of how this detector will work.
Wolf (25:11): And Maria, are there people out there who are saying this is not the right way to do this, this is not the right way to find examples of supersymmetry in nature?
Spiropulu (25:21): Sure. I mean, nobody disagrees that this is a way that we will probe a parameter of space that was not probed ever before. But some people they have beliefs and they say, "Oh, I don't believe that this would be the answer." Now for me, it's not a matter of belief, what it is, the answer. [My] question is, "Can I look where we haven't looked before and how do I do that?"
Wolf (25:44): Which is incredible. And that is the lonely idea, postulating that if we build this detector and we look for the Porsche way, way, way over here, that will be at least an example. It'll be one data point to get us one step closer to understanding SUSY, supersymmetry.
Spiropulu (25:57): That's right.
Wolf (25:58): How do we get from where we are now to that level of understanding? What's the next thing after it? So let's say we prove that supersymmetry exists, and we see it, we see the Porsche out there, then what's next?
Spiropulu (26:08): If we discover new particles, whether it is supersymmetry or whether it is an extended supersymmetry or whether it is some other theory, we have to study them extremely hard. And then we have to start fitting the puzzle of what is going on with dark matter, how this new theory connects with dark matter. So there is a pinnacle of understanding the standard model, in the context of the physical universe, and that is gravity, how gravity integrates. So this is the famous problem: How do we put quantum mechanics and general relativity together? The standard model of the world, of the universe, will only be the standard model of the universe if we manage to figure it out, figure out the generation of space-time.
Wolf (27:00): The thing that I love about this is I envision two sides of a bridge being built separately, one being quantum mechanics and the other being general relativity. And we're continuing to add pieces to the bridge and hopefully at some point we'll put that last stone in that'll connect the pieces of the bridge. But each and every experiment you do is one more important pillar, one more important part of the suspension bridge as we get that much closer. There are a million lonely ideas in trying to find each and every component of the bridge and the other part is at least with a bridge, we know we need steel and concrete. In this case, we don't even know what pieces need to go in there. I wanted to close with a little bit of a discussion of your students because when we first met, which is going back 15 years now, I also once asked you about your proudest moment in recent memory of a student. And I wonder if you would share that story as well?
Spiropulu (27:51): Right? So let's start from the student. I had a student, one of my first students at CERN, she was [almost] blind. And she chased me to do a supersymmetry thesis. She was so determined to do data analysis and thesis and to do everything that it takes. And she said, I want you to be my advisor and I want to do a SUSY (supersymmetry ) thesis and I want to do this and that. So she was extremely determined. She and I, we have become good friends and she's a colleague now. She impressed me with her resolve and also with her character. That it doesn't matter, all the adversity of the world, there is a way to actually do what I want to do. And I have picked who I want to do it with, who to advise me. I was stunned. So I said, "all right, let's do that." And she did an excellent thesis. She did a lot of partnerships with theorists, even after we finished the thesis, she's going to conferences and she became a fellow. And she became staff in Taiwan, in the university, and she keeps on with an indomitable spirit. I think it was a great example of a student that really touched me very much, and, of course I, I accepted to be her advisor.
Wolf (29:12): You, you also have gone out of your way to be able to speak different languages so that you can connect with your students and manage their dissertations and theses defense. That's going above and beyond. Why do all of it?
Spiropulu (29:25): So this was, let's say, I want to say this was circumstantial or in some sense, situational. If you are at CERN, you are dealing with engineers and students from France, from Italy, from Germany for sure. And so these people, being lab staff, they use somebody from CERN to be their advisor, but they're writing their thesis in their own language, some people in Danish, et cetera. And so I knew already [some of] these languages. So I was able to communicate with them and advise them in their own language. And it was also rewarding because in everybody's own language, they express their own frustrations about the research. Which if you make them translate it, you don't see where they are, where they're stuck or whether their brain wants something more.
Wolf (30:25): The whole notion that you would go above and beyond to be able to have that connection with your students is just incredible to me. And now as I hear you talk about wanting to be able to give them the freedom, there's a level of interaction that you have with your students that I think not only fosters creativity but also gives them the confidence, "Wow, my thesis advisor wants to learn my language to be able to speak to me. She has that much respect for me that she wants me to do this." And, oh by the way, as you said at Thessaloniki, they gave you the keys to the lab. You give them the keys to the lab. And I think that is such a wonderful model for every faculty member out there, and I'm grateful that you do that for our students at Caltech, Maria.
Spiropulu (31:08): Yes, and I'm grateful to Caltech for having students that are unparalleled to everywhere. I think I told once when I was asked at one of the meetings at Caltech, they asked me something about my experience with Caltech. And it was all, I had to reply, everything about the students because they are so unique, and I have been in many places in the world and many universities. I was at Harvard, University of Chicago, other places, and the Caltech students are so unique.
Wolf (31:36): What an exciting topic and what a great time. I mean it's just such a wonderful time in physics.
Spiropulu (31:42): It is.
Wolf (31:42): There are so many people that came before you that I know wish they could be here to watch you do this set of experiments and build these machines. I can't thank you enough for this time today on The Lonely Idea, Maria. It's been absolutely wonderful taking the time to speak with you and to learn more about your research and also your personal life, and the time that you spend with your students. Thank you again for the time.
Spiropulu (32:02): Thanks everybody. Thanks for doing this podcast. I think it's a very, very useful and it's good to learn about our community even more, and our faculty and our students. Yes. So thank you for doing that.
Conclusion (32:14): The Lonely Idea is produced at Caltech. Learn more about Caltech innovators and their research on our website at www.Caltech.edu or connect with Caltech on Facebook, Twitter, Instagram, and YouTube.