Barry Barish: Gravitational Waves and the Most Precise Device Ever Built | Lex Fridman Podcast #213

Lex Fridman 0:00 The following is a conversation with Barry Barish, a theoretical physicist at Caltech, and the winner of the Nobel Prize in physics for his contributions to the LIGO detector and the observation of gravitational waves. LIGO, or the Laser Interferometer Gravitational-Wave Observatory, is probably the most precise measurement device ever built by humans. It consists of two detectors with four kilometer-long vacuum chambers situated 3,000 kilometers apart, operating in unison to measure motion that is 10,000 times smaller than the width of a proton. It is the smallest measurement ever attempted by science, a measurement of gravitational waves caused by the most violent and cataclysmic events in the universe, occurring over tens of millions of light years away. To support this podcast, please check out our sponsors in the description. This is the Lex Fridman Podcast, and here is my conversation with Barry Barish.

Lex Fridman 1:08 You've mentioned that you were always curious about the physical world, and that, uh, an early question you remember stood out where you asked your dad, "Why does ice float on water?" And he couldn't answer, and this was very (laughs) surprising to you. Uh, so you went on to learn why. Maybe you can speak to what are some early questions in math and physics that, uh, really sparked your curiosity?

Barry Barish 1:31 Yeah. Th- that, that memory is, uh, um, kind of something I use to illustrate, uh, something I think that's common in science, is that people that do science somehow have maintained, um, maintain something that kids always have. Uh, well, a small kid, eight years old or so, uh, asks you so many questions usually, typically, that you consider them pests, you tell them to stop asking so many questions. Um, and, uh, somehow our system manages to kill that in most people. Uh, so, in school we make people do s- study and w- do their things, but not to pester them by asking too many questions. And, uh, um, I think not just myself, but I think it's typical of scientists like myself, that, uh, uh, have somehow escaped that. Maybe we're still children or maybe we somehow didn't get it beaten out of us. But I think it's, uh... I teach in college level and it's, to me, uh, one of the biggest deficits is the lack of curiosity, if you want, that we've beaten out of them, 'cause I think it's an innate human quality.

Lex Fridman 2:47 Is there some advice or insights you can give to how to keep that flame of curiosity going?

Barry Barish 2:51 I think it's a problem of both parents and, and, uh, that parents should be, should realize that's a great quality we have, that you're curious and that's good. Instead we have s- we have expressions like, "Curiosity killed the cat."

Lex Fridman 3:05 (laughs)

Barry Barish 3:06 And, and, uh, and then more. But I mean that basically it's not, not thought to be a good thing. You get i- curiosity killed the cat means if you're too curious you get in trouble. And, uh, it can lead to trouble.

Lex Fridman 3:18 I don't like cats anyway, so maybe it's a good thing. (laughs)

Barry Barish 3:20 Yeah. Yeah. That to me needs to be solved really in education and in homes, that, uh, realization that there's certain human qualities that we should try to build on and not destroy, one of them is curiosity. Anyway, back to me and curiosity. I was a pest and asked a lot of questions, my father generally could answer them, uh, at that age. And the first one I remember that he couldn't answer, uh, was not a very original question, but basically that, uh, ice is made out of water, and so why does it float on water? Uh, and, uh, he couldn't answer it. And it may not have been the first question, it's the first one that I remember. And, uh, and that was the first time that I realized that to learn and answer your own curiosity or questions, there's various mechanisms. In this case it was going to the library and, or asking people who know more and so forth. But eventually you do it by what we call research. But, but it's, um, driven by if you're... uh, hopefully you ask good questions. If you ask good questions and you have the mechanisms to solve them, then you do what I do in life basically. Not necessarily physics but, uh, s- and it's a great quality in humans and we should nurture it.

Lex Fridman 4:46 Do, do you remember any other kind of, in high school, maybe early college, more basic physics ideas that sparked your curiosity? Or mathematics or science in general?

Barry Barish 4:57 I, I wasn't really into science until I got to college-

Lex Fridman 5:01 Yes.

Barry Barish 5:01 ... to be honest with you. But just staying with water for a minute, I remember, uh, that I was curious, uh, why, uh, what happens to water? You know, it rains and there's water, and a wet pavement and then the pavement dries out, what happened to this water that came down? And I, you know, I didn't know that much. And then l- eventually I learned in chemistry or something that water's made out of hydrogen and oxygen, those are both gases, so how the heck does it make this substance, this liquid? Uh...

Lex Fridman 5:36 (laughs)

Barry Barish 5:36 (laughs)

Lex Fridman 5:37 Yeah. It's, uh, but... So that has to do with states of matter. You've, uh, I know perhaps LIGO and all, all, uh, the, the thing for which you've gotten the Nobel Prize and the things much of your life work m- m- perhaps was a happy accident in some sense in the early days. But is, is there a moment where you looked up to the stars and also, the same way you wondered about water, wondered about some of the things that are out there in the universe?

Barry Barish 6:03 Oh, yeah. I think everybody's looks and is in awe, and is curious about what, what it is out there. And it, you know, and as I learned more, I learned, of course, that we don't know very much about what's there. And the more we learn, the more we know we don't know. I mean, we don't know what the majority of anything is out there. It's all what we call dark matter or dark energy, and that's one of the big questions 20 year, when I was a student, those weren't questions. So we even know less in a sense the more we, uh, the more we look. So of, of course, I think that's one of the areas that, um, almost it's universal. People see the sky, they see the stars and they're beautiful, and, and see it looks different on different nights, and it's a, a curiosity that we all have.

Lex Fridman 6:55 What are some questions about the universe th- that in the same way that you felt about the ice, that today, you mentioned to me offline you're teaching, um, a course on the frontiers of science, frontiers of physics.

Barry Barish 7:09 Yeah.

Lex Fridman 7:10 What are some questions, outside the ones we'll probably talk about, that kind of, yeah, f- fill you with, uh, get your flame of curiosity up in the, firing up, uh, you know, fill you with awe?

Barry Barish 7:26 Well, first, I'm a physicist not an astronomer, so I'm interested in physic-, the physical phenomenon really. So the question of, of, uh, dark matter and dark energy, which we probably won't talk about are rec-, are recent. They're the last 20, 30 years for certainly dark energy. Dark energy is a complete puzzle. It, it goes against what I'll, will, what you will ask me about, which is general relativity and Einstein's general relativity, it basically takes something that he thought was, uh, what he, what he called a constant, which isn't, and, and, uh, um, and if that's even the right theory and it represents most of the universe, and then we have something called dark matter, and there's good reason to believe it might be an exotic form of particles. Um, and that is something I've always worked on, on particle accelerators and so forth. And it's a big puzzle what it is. It's a bit of a cottage industry in that there's lots and lots of searches, um, but it may be a little bit like, you know, looking for a treasure under rocks or something, you don't, it's hard to ha- uh, we don't have really good guidance except that we have very, very good information that it's pervasive and it's there.

Lex Fridman 8:48 Mm-hmm.

Barry Barish 8:48 And that it's probably particles, small, that, that evidences all of those things. But then the most, uh, logical solution doesn't seem to work, something called super symmetry.

Lex Fridman 9:01 Mm-hmm. And do you think the answer could be something very complicated?

Barry Barish 9:08 You know, I like to hope that, think that most things that appear complicated are actually simple if you really understand them, and I think we just don't know at the present time and it isn't something that affects us. It does affect, it affects how the stars go around each other and so forth, 'cause we detect that there's missing gravity, but, uh, but it doesn't affect everyday life at all. I tend to think and expect maybe, and that the answers will be simple and we just haven't found it yet.

Lex Fridman 9:45 Do you think those answers might change the way we see other sources of gravity, black holes, the way we see the parts, uh, of the universe that we do study?

Barry Barish 9:56 It's, it's conceivable. Uh, the black holes that we found in our experiment and how we are trying now to understand the origin of those, it's conceivable but not, doesn't seem the most likely that they are pre-mort, primordial. That is, they were made at the beginning, and they, in that sense, they could represent at least part of the dark matter. So there can be connections. Dark, uh, black holes or how many there are, how much of the mess they encompass is still root pretty primitive, we don't know.

Lex Fridman 10:28 So before I talk to you more about black holes, let me take a step back to-

Barry Barish 10:31 Yeah.

Lex Fridman 10:32 I was, actually went to high school in Chicago and would go to, uh, take, uh, classes at Fermilab, uh, watch the Buffalo and so on.

Barry Barish 10:41 Yeah. (laughs)

Lex Fridman 10:43 (laughs) So let me ask about the, you mentioned that Enrico Fermi was somebody who was inspiring to you in a certain kind of way. Um, why is that? Can you speak to that?

Barry Barish 10:52 Sure. He was amazing actually. Uh, he's the last, th- this is not the re-, I'll come to the reason in a minute, but the, he had a big influence on me at a young age. Uh, he, he, uh, but he was the onl-, the last physicist of note that was both an experimental physicist and a theorist at the same time, and he did two amazing things within months. I- in 1933, he, w- it was, we didn't really know what the nucleus was, what, uh, radioactive decay was, what beta decay was when electrons come out of a nucleus, and in th- near the, near the end of 1933, um, he, the neutron had just been discovered, and that meant that we knew a little bit more about what the nucleus is, that it's made out of neutrons and protons. The neutron wasn't discovered till 1932, and then once we discovered that there was a neutron and proton and they made the nucleus and then there are electrons that go around, the basic ingredients were there, and he, uh, wrote down not only just the theory, a theory, but a theory that lasted decades and has only been improved on, uh, of beta decay, that is the radi- radiation. He did this w-... came out of nowhere, and it was a fantastic theory. He, uh, submitted it to Nature Magazine, which was the primary, uh, pla- best place to publish even then, and it got rejected as being too, uh, speculative. And so, he went back to his, uh, drawing board in Rome, where he was, added some to it, made it even longer, uh, 'cause it's really a classic article, and then published it in the local Italian, uh, journal for physics and the German one. At the same time, in 19- January of 1932, Giulio and Curie for the first time s- div- uh, saw artificial radioactivity. This was an important discovery because radioactivity had been discovered much earlier. And, you know, we'd... They had X-rays, and you shouldn't be using them, but they- there was radioactivity. People knew it was useful for medicine. But radioactive materials were hard to find, and so it wasn't prevalent. But if you could make them, then they had great use. And Giulio and Curie were able to bombard, uh, aluminum or something with alpha particles and f- find that they excited something that decayed and gave, uh, decayed and ga- had some half-life and so forth, meaning it was an artificial version, or let's call it a, not, not a natural version, an induced version of radioactive, uh, uh, materials. And, uh, Fermi somehow had the insight, and, uh, I still can't see where he got it, that the right way to follow that up was not using charged particles, like alphas and so forth, but use, use these newly discovered neutrons as the bombarding particle. Seemed impossible. They barely had been seen. Uh, it was hard to get very many of them. But it had the advantage that they don't, um, they're not charged, so they go right into the, to the nucleus, and, uh, that turned out to be the experimental work that he did that, uh, won him the Nobel Prize. And it was the first step in fission, uh, uh, discovery of fission. And that's... He did this, two completely different things. Uh, an experiment that was a great idea, and, uh, tremendous implementation because how do you get enough neutrons?

Lex Fridman 14:57 Mm-hmm.

Barry Barish 14:57 And then he learned quickly that not only do you want neutrons, but you want really slow ones. Uh, and he, he learned that experimentally, and he learned how to make slow ones, and then they were able to make... uh, go through the periodic table and make lots of, uh, particles. He missed on fission at the moment, but he had the basic information, and th- and then fission followed soon after that.

Lex Fridman 15:22 Forgive me for not knowing, but wha- is the birth of the idea of bombarding with nu- uh, neutrons, is that, uh, is that an experimental idea? Was it born out of an experiment, he just observed something? Or is this an Einstein-sty- style idea where you come up from basic intuition?

Barry Barish 15:40 I think, I think, I think, uh, that took a combination because he realized that neutrons had a characteristic that would allow them to go all the way into the nucleus when we didn't really understand what the, you know, what, how, what the structure was of all this. So, that took, uh, an understanding or recognition of the physics itself of how a neutron interacts compared to, say, an alpha particle that Giulio and Curie had used. And then he had to invent a way to have enough neutrons and, uh, uh, you know, uh, he had a team of associates and p- and he pulled it off quite quickly. So, you know, it was pretty astounding.

Lex Fridman 16:22 And probably, maybe you can speak to it, his ability to put together the engineering aspects of great experiments and doing the theory, they probably fed each other. I wonder, can you speak to why we don't see m- more of that? Is that just really difficult to do?

Barry Barish 16:38 It's difficult to do. Yeah, I think i- in, in both theory and experiment in physics anyway was, uh, it was conceivable if you had an- the right person to do it, and no one's been able to do it since. So, I had the dream that that-

Lex Fridman 16:54 (laughs)

Barry Barish 16:54 ... was what I was gonna be like Fermi. But...

Lex Fridman 16:56 So, you love both sides of it, the theory and experiment?

Barry Barish 16:58 Yeah, yeah. I never liked the idea that you did experiments without really understanding the theory or the theory should be related very closely to experiments. And so, I've always done experimental work that was closely related to the theoretical ideas.

Lex Fridman 17:15 I think I told you I'm Russian, so I'm gonna ask some romantic questions. Uh, but is- (laughs)

Barry Barish 17:20 Yeah.

Lex Fridman 17:20 Is it tragic to you that he's seen as the architect of the nuclear age? That some of his creations led to potentially some of his work has, has led to potentially still the destruction of the human species? Some of the most destructive weapons-

Barry Barish 17:39 Yeah. Uh, I think even more general than him, I, I, I, I gave you all the virtues of curiosity a few minutes ago. There's an interesting book called The Ratchet of Curiosity. You know, a ratchet is something that goes in one direction. And that, that, it's written by a guy who's probably a sociologist or a philosopher or something, and he, he picks on this particular problem, but other ones, and that is the, the danger of knowledge basically. You know, you're curious, you learn something. So, it's a little bit like curiosity killed the cat.

Lex Fridman 18:12 (laughs)

Barry Barish 18:12 You have to be worried about whether you can handle new information that you get. So, in this case, the new information had to do with really understanding nuclear physics.... and that information, maybe we didn't have the sophistication to know how to keep it under control. Uh, and Fermi himself was a, a very apolitical person, so he wasn't very driven by... Or at least, he appears in all of his writing, the writing of his wife, the interactions that others had with him is, either he avoided it all (laughs) or he was pretty apolitical. I mean, he just saw s- the world through kind of the lens of a scientist. But you asked if it's tragic? Uh, the, uh, the bomb was tragic certainly on Japan, and he had a role in that. So I wouldn't want it as my legacy, for example.

Lex Fridman 19:07 I mean that... But broader to the human species that it's the ratchet of curiosity that we, (sighs) uh, we do stuff just to see what happens. That, that curiosity, that, uh, in sort of my area of artificial intelligence, that's been a, a concern. They're kind... On a small scale, on a silly scale perhaps currently, there's constantly s- unintended consequences, that you create a system and you put it out there and you have intuitions about how it will work. You have hopes how it will work, but you put it out there just to see what happens.

Barry Barish 19:44 Yeah. Th-

Lex Fridman 19:45 And, uh, in most cases because artificial intelligence is currently not super powerful, it doesn't create, uh, large-scale negative effects. But that same curiosity as it progresses might lead to something that destroys the human species, and the same may be true for bioengineering. There's people, uh, that, p- you know, engineer viruses to protect us from viruses, to see, you know, how do... Uh, how close is this to mutating so it can jump to humans? Or, or going, you know... Or engineering, uh, defenses against those. And it seems exciting and the application, the positive applications are really exciting at this time, but we don't think about how that runs away in decades to come.

Barry Barish 20:34 Yeah. And I think it's the same idea as this little book, The Ratchet of, of Science.

Lex Fridman 20:39 Yeah.

Barry Barish 20:40 The, the, uh, ratchet of curiosity. I mean, whether you pursue... You take curiosity and let artificial intelligence or machine learning run away with having its, uh, solutions to whatever you want, or we do it, is, I think a similar consequence.

Lex Fridman 20:59 I think, uh, from what I've read about, uh, Enrico Fermi, he, he became a little bit cynical about the human species towards the end of his life, about having observed what he observed.

Barry Barish 21:13 Well, he didn't write much. Uh, I mean, he died young. He died d- soon after World W- the World War. Uh, there was already, you know, the work by Teller to develop the hydrogen bomb, and I think he was a little cynical of that, you know, pushing it even further and, uh, rising tensions between the Soviet Union and the US, and looked like an endless thing, so. But he didn't say very much, uh, but a little bit as you said that-

Lex Fridman 21:39 Yeah, there's a few clips. This j-

Barry Barish 21:41 Yeah.

Lex Fridman 21:41 ... sort of, uh, maybe picked on a bad mood, but in, in a sense-

Barry Barish 21:45 (laughs) .

Lex Fridman 21:46 ... that, uh, almost like a sadness, a m- melancholy sadness to, um, a hope that waned a little bit about that, uh-

Barry Barish 21:54 Yeah.

Lex Fridman 21:55 ... perhaps we can do, like, s- th- the scie- this curious species can find the way out.

Barry Barish 22:01 Well, especially, I think people who worked like he did at Los Alamos and spent years of their life, somehow had to convince themselves that dropping these bombs would bring lasting peace-

Lex Fridman 22:12 Yes, and it didn't.

Barry Barish 22:13 ... and, and that it didn't. Yeah.

Lex Fridman 22:17 As a small interesting aside, it'd be intere- interesting to hear if you have opinions

Lex Fridman 22:22 on this. His name is also attached to the Fermi Paradox, which asks if there's, uh, you know, which formu-

Barry Barish 22:30 Yeah, yeah.

Lex Fridman 22:30 .... it's a very interesting question-

Barry Barish 22:31 Yeah, yeah.

Lex Fridman 22:31 ... which is... If... It does seem if you sort of reason basically that, that there should be a lot of alien civilizations out there. If the human species... If Earth is not that unique by basic... No matter the values you pick, uh, it's likely that there's a lot of alien civilizations out there, and if that's the case, why have they not at least obviously visited us or sent us loud signals that everybody can hear?

Barry Barish 23:00 Fermi's quoted as saying, sitting down at lunch, I think it was with, uh, Teller?

Lex Fridman 23:07 Mm-hmm.

Barry Barish 23:07 And Herb York, who was kind of the f- one of the fathers of the atomic bomb, and he sat down and he says something like, "Where are they?"

Lex Fridman 23:16 Yeah. Yeah.

Barry Barish 23:17 (laughs) Which meant where are these-

Lex Fridman 23:19 Yeah.

Barry Barish 23:19 ... other... And, um, b- and then he did some numerology where he calculated, you know, how many... What they knew about how many, uh, galaxies there are and how many stars and how many planets then are like the Earth and blah, blah, blah.

Lex Fridman 23:36 Yep.

Barry Barish 23:36 That's been done much better by somebody named Drake, uh, and so people usually refer to the Dr- I don't know whether it's called the Drake formula or something, but it has the same conclusion. The conclusion is it would be a miracle if there weren't other, you know... Uh, there's... The statistics are so high that how can we be singular and separate? Uh, th- that... So probably there is l- well, there's almost certainly life somewhere, maybe there was even life on Mars a while back. But, uh, intelligent life, probably. Why are we so... So, you know, the statistics say that. Communicating with us? I think that it's harder than people think (laughs) . Uh, we might not know the right way to expect the communication, uh, but-... all the communication that we know about travels at the speed of light and we d- we don't, we don't think anything can go faster than the speed of light. That limits the problem quite, quite a bit, and it, uh, makes it difficult to have any back and forth communication. You could send signals, like we try to or look for, but to have any communication, it's pretty hard when you... it has to be close enough that the speed of light, uh, would mean we could communicate with each other. And I, I think, and we didn't even understand that. I mean, it's, we're an advanced civilization but we didn't even understand that a little more than 100 years ago.

Lex Fridman 25:12 Yeah.

Barry Barish 25:13 So, uh, are we just not advanced enough? Maybe.

Lex Fridman 25:19 Yeah.

Barry Barish 25:20 Uh, to know something about that's the speed of light, maybe there's some other way to communicate that isn't based on electromagnetism. I don't, I don't know. Gravity seems to be also this, have the same speed. That was a principle that Einstein had and something we've measured actually.

Lex Fridman 25:36 So is, is it possible... I mean, so w- we'll talk about gravitational waves and it, in some sense there's, um, there's a brainstorming going on which is like, how do we detect the signal? Like what would a signal look like and how would we detect it? And that's true for gravitational waves, that's true for basically any physics phenomena. You have to predict that that signal should exist, you have to have some kind of theory, a model why that signal should exist.

Barry Barish 26:03 Right.

Lex Fridman 26:03 I mean, is it possible that aliens are communicating with us via gravity? Like, why not?

Barry Barish 26:10 Well, i- i- why-

Lex Fridman 26:12 (laughing)

Barry Barish 26:12 Yeah, it's true. Why not? Uh, for us, it's very hard to detect these gravitational effects that have to come from something pretty, that has a lot of gravity like black holes. But we're pretty primitive at, at this stage. Uh, there's, uh, very reputable physicists that look for a fifth force, one that we haven't found yet. Maybe it's the key. So, you know-

Lex Fridman 26:40 It should be.

Barry Barish 26:40 ... it's possible.

Lex Fridman 26:41 What would that look like? What- what would a fifth force of physics look like, exactly?

Barry Barish 26:45 Well usually they think it's probably a long-range for- longer range force than we have now. Um, but, uh, there are reputable phy- colleagues of mine that spend their life looking for a fifth force.

Lex Fridman 26:58 So longer range than gravity? Is it like-

Barry Barish 27:00 Yeah. Yeah.

Lex Fridman 27:01 ... super low?

Barry Barish 27:01 It doesn't fall off like one over R squared, but maybe separately. W- uh, gravity, uh, Newton taught us, goes like w- inversely th- one over the square of the distance apart you are. So it falls pretty fast.

Lex Fridman 27:14 That's... okay, so now we have a theory of what consciousnesses is. It's just the fifth force of, uh, physics.

Barry Barish 27:19 Fifth force. Yeah.

Lex Fridman 27:20 There we go. That's a good hypothesis. Uh... (laughs)

Lex Fridman 27:26 speaking of gravita- uh, of gravity, uh, what are gravitational waves? Let's maybe start from the basics.

Barry Barish 27:34 We learned gravity from Newton, right? You, you when you were young, you were told that if you jumped up, the Earth pulls you down. And when the apple falls out of the tree, the Earth pulls it down. And, um, maybe you even asked your teacher why, but most of us accepted that. That was Newton's picture, the apple falling out of the tree. But Newton's theory never told you why the apple was attracted to the Earth. That was, uh, missing in Newton's theory. Uh, Newton's theory also... Newton recognized at least one of the two problem solves tell you, one of them is, there's more than those, but one is, why does the Earth... what's the mechanism by which the Earth pulls the apple or holds the moon when it goes around, whatever it is? Uh, that's not explained by Newton even though he has a most successful theory of physics ever. Went 200 and some years with nobody ever seeing, uh, violation.

Lex Fridman 28:35 But he accurately describes the movement of an object falling down to Earth, but he's not answering why that, what's the act-

Barry Barish 28:41 Yeah. Yeah. He, he-

Lex Fridman 28:42 ... 'cause it's a distance, right?

Barry Barish 28:43 He gives a formula-

Lex Fridman 28:44 Right.

Barry Barish 28:44 ... which e- which it's a product of the Earth's mass, the apple's mass inversely proportional to the square of the distance between.

Lex Fridman 28:53 Mm-hmm.

Barry Barish 28:53 And then the strength he called capital G. The strength he couldn't determine, but it was determined 100 years later. But no one ever saw a violation to this until a possible violation which Einstein fixed which was very small that has to do with Mercury going around the sun. The orbit being slightly s- wrong if you calculate it by Newton's theory. But, so, um, like most theories then in, in physics, you can have a wonderful one like Newton's theory. It isn't wrong, um, but you have to have a, an improvement on it to answer things that it can't answer. And in this case, Einstein's theory is the next step. We don't know if it's anything like a final theory or even the only way to formulate it either, but he formulated this theory which wa- which he released in 1915. He took 10 years to develop it even though in 1905, he solved three or four of the most important problems in physics in a matter of months, and then he spent 10 years on this problem before he, uh, let it out. And this is called general relativity, it's a new theory of gravity. 1915. And 1916, Einstein, um, wrote a little paper where he did not do some fancy derivation. Instead he did, um, what I would call, used his intuition which he was very good at too. Uh, and that is he noticed that if he form- if he wrote the formulas for general relativity in a particular way, they looked a lot like the formulas for electricity and magnetism.... being Einstein, he then took the leap that electricity and magnetism, we discovered only 20 years before that in the 1880s, uh, have waves. Of course, that's light and electromagnetic rays, radio waves, everything else. So, he said, "If the formulas look similar, then gravity probably has waves too."

Lex Fridman 31:08 That's such a big leap, by the way. I mean, maybe you can correct me, but that just seems-

Barry Barish 31:13 So that-

Lex Fridman 31:13 ... that seems like a heck of a leap.

Barry Barish 31:15 Yeah, and so that, and it was considered to be a heck of a leap. So first, that paper was, except for this intuition, was, uh, poorly written, had, had a serious mistake. It had the fa- a factor of two wrong in the strength of gravity, which meant if we used those formulas, we would...

Lex Fridman 31:34 (laughs) .

Barry Barish 31:34 And, uh-

Lex Fridman 31:36 Yeah.

Barry Barish 31:36 ... two years later, he wrote a second paper, and in that paper, it turns out to be important for us because in that paper, he not only fixed his factor of two mistake, which he never admitted. He just wrote it, fixed it like he always did, and, and then he, uh, told us how you make gravitational waves, what, what makes gravitational waves. And you might recall, in electromagnetism, we make electromagnetic waves in a simple way. You take a plus charge, a minus charge, you oscillate like this, and that makes electromagnetic waves. And a physicist named Hertz made a receiver that could detect the waves and put it in the next room. He saw them and moved forward and backward and saw that it was wave-like. So, uh, Einstein said, "It won't be a dipole like that. It'll be a four-pole thing." And that's what it's called a quadrupole moment that gives the gravitational wave. So, he saw that again by insight, not by derivation. That set the table for which you need it to do, to do it. At the same time, in the same year, Schwarzschild, not Einstein said there were things like called black holes. So, it's interesting that that came the same-

Lex Fridman 32:51 So what year was that? So that was-

Barry Barish 32:54 1915.

Lex Fridman 32:55 It, it was in parallel...

Barry Barish 32:57 With-

Lex Fridman 32:57 Uh, d- did I, uh, I sh- I should probably know this, but did Einstein not have an intuition that there should be such things as black holes?

Barry Barish 33:04 That came from Schwarzschild.

Lex Fridman 33:05 Oh, interesting.

Barry Barish 33:07 Yeah. So, Schwarzschild, who was a, a, a German theoretical physicist, that he got killed in the war, I think, in the First World War a year, two years later or so. He's the one that proposed black holes, that there were black holes.

Lex Fridman 33:22 It feels like a natural conclusion of, uh, general relativity, no? Or is that, uh, not-

Barry Barish 33:29 Uh.

Lex Fridman 33:29 ... if you-

Barry Barish 33:29 Well, it may seem like it, but I don't know about a natural conclusion. It is a, it's a result of curved spacetime though.

Lex Fridman 33:36 Right, and it's, but it's such a weird result that you might have to-

Barry Barish 33:40 Yeah. Yeah.

Lex Fridman 33:40 ... uh, it's a, it's a special-

Barry Barish 33:41 Yeah, it's a special case.

Lex Fridman 33:43 Yeah.

Barry Barish 33:43 So, um, I, I don't know. Anyway, Einstein then, an interesting part of the story is that Einstein then left the problem. Most physicists, because it really wasn't, uh, derived, he just made this st- didn't pick up on it or general relativity much, because quantum mechanics became the thing in physics. And Einstein, uh, only picked up this problem again after he immigrated to the US. So, he came to the US in 1932, and I think in 1934 or 5, he was working with another physicist called Rosen, who he did several important works with. And they revisited the question, and they, uh, had a problem that most of us as students always had that study general relativity. General relativity is really hard because it's four-dimensional instead of three-dimensional, and if you don't set it up right, you get infinities which don't belong there. The, we call them coordinate singularities as a name, but it, but if you get these infinities, you don't get the answers you want. And, uh, he was trying to derive now general relativity ou- from general relativity gravitational waves.

Lex Fridman 35:00 Mm-hmm.

Barry Barish 35:01 And in doing it, he kept getting these infinities, and so he wrote a paper with Rosen that he submitted to our most important journal, Physical Review Letters, and, uh, that when it was submitted to Physical Review Letters, it was entitled, "Do Gravitational Waves Exist?" A very funny title to write 20 years after he proposed they exist.

Lex Fridman 35:26 (laughs) .

Barry Barish 35:26 Uh, but it's because he had found these singularities, these infinities, and so, um, the, um, editor at that time, and part of it that I don't know, is peer review. We live and die by peer review as scientists, send our stuff out, and it's p- We don't know when peer review actually started or what it, what peer review Einstein ever experienced before this time. But the editor of Physical Review sent this out for review. Uh, he had a choice. He could take any article and just accept it, he could reject it, or he could send it for review.

Lex Fridman 36:05 Right, I believe the editors used to have much more power.

Barry Barish 36:08 Yeah, yeah. And he was a young man, his name was Tate, and he ended up being editor for years. But, uh, so he sent this for review, uh, to, um, uh, a theoretical physicist named Robertson, who was also in this field of general relativity, who happened to be on sabbatical at that moment at Caltech. Otherwise, his institution was Princeton, where Einstein was.

Lex Fridman 36:33 Mm-hmm.

Barry Barish 36:33 And he saw that the way they set up the problem, the infinities were like I g- make it as a student, because if you don't set it up right in general relativity, you get these infinities. And so he reviewed the article and told-... gave an illustration that if they set it up in what are called cylindrical coordinates, these infinities went away. He-

Lex Fridman 36:57 Nice.

Barry Barish 36:57 ... uh, editor of Physical Review was obviously intimidated by Einstein. He wrote this really ni- not a letter back like I would get saying, you know, "You screwed up in your paper." Instead there, it was kind of, uh, a, "What do you think of the comments of our-"

Lex Fridman 37:15 (laughs)

Barry Barish 37:15 "... referee."

Lex Fridman 37:16 Yeah.

Barry Barish 37:16 Einstein wrote back, and it's a well-documented letter, wrote back a letter to Physical Review saying, uh, "I didn't send you the paper to g- to send it to one of your so-called experts. I sent it to you to publish."

Lex Fridman 37:30 Wow.

Barry Barish 37:30 "I now, I withdraw the paper."

Lex Fridman 37:32 Wow.

Barry Barish 37:33 Uh, and he never published again in the j- in that journal. That was 1936. Instead, he rewrote it with the fixes that were made-

Lex Fridman 37:45 Yeah.

Barry Barish 37:45 ... changed the title, and published it in what was called the Franklin Review, which is the, uh, Franklin Institute in Philadelphia, uh, which is Benjamin Franklin Institute, which doesn't have a journal now, but did at that time. So the article is published, it's the last time he ever wrote about it. It remained controversial. So it wasn't until close to 1960, 1958, where there was a conference in, whi- which brought to- that brought together the experts in general relativity to try to sort out whether there was, uh, um, whether there (laughs) , it was true that there were gravitational waves or not. And there was a very nice derivation by a British, uh, theorist from th- the heart of the theory that gets gravitational waves, uh, and that was number one. The second thing that happened at that meeting is Richard Feynman was there. And Feynman, uh, said, "Well, if there's..." He- typical Feynman, "If there's gravitational waves, they'd need to be able to do something, otherwise they don't exist. So they have to be able to transfer energy." So he made a idea of a Gedankenexperiment, that is just a, a bar with a couple of rings on it. And then, if a gravitational wave goes through, it distorts the bar.

Lex Fridman 39:12 Mm-hmm.

Barry Barish 39:13 Uh, and that creates friction on these little rings.

Lex Fridman 39:16 Yeah.

Barry Barish 39:17 And that's heat and that's energy. So the, that meant that-

Lex Fridman 39:20 Is that a good idea? It sounds like a good idea.

Barry Barish 39:22 Yeah. It means that he showed that with the distortion of spacetime, you could transfer energy.

Lex Fridman 39:29 Mm-hmm.

Barry Barish 39:30 Just by this little idea. And it was shown theoretically. So at that point, it was, uh, believed theoretically then by people that gravitational waves should exist. Th-

Lex Fridman 39:43 No-

Barry Barish 39:43 It-

Lex Fridman 39:44 ... we should be able to detect them, you mean?

Barry Barish 39:45 We should be able to detect them, except, except that they're very, very small. Just-

Lex Fridman 39:50 And, and so what kind of, uh... There's a bunch of questions here, but what kind of events would generate gravitational waves?

Barry Barish 39:58 You have to have this c- what I call quadruple moment. That comes about if I have, uh, for, for example, two objects that go around each other like this, like the Earth arou- the Earth around the Sun, or the Moon around the Earth, or in our case, it turns out to be two black holes going around each other like this, that-

Lex Fridman 40:17 So how's that different than basic oscillation back and forth? Is it-

Barry Barish 40:21 That, that-

Lex Fridman 40:21 ... just more common in nature to have-

Barry Barish 40:22 Oscillation is a dipole moment, sup-

Lex Fridman 40:24 So it has to be in three-dimensional space-

Barry Barish 40:25 Yeah.

Lex Fridman 40:25 ... some kind of oscillation.

Barry Barish 40:26 It's got to be. So you have to have something that's three-dimensional that'll give what's, what I, what I call the quadruple moment. That's just built into this.

Lex Fridman 40:33 And luckily, in nature, you have stuff h- uh...

Barry Barish 40:35 And luckily, things exist. And it is luckily because the effect is so small that you could say, "Look, I could take a barbell and, and spin it," right?

Lex Fridman 40:47 Yeah.

Barry Barish 40:47 And detect the gravitational waves. But unfortunately, no matter how much I spin it, how fast I spin it-

Lex Fridman 40:53 Oh, interesting.

Barry Barish 40:53 ... it's... So I know how to make gravitational waves, but they're so weak I can't detect them. So we have to take something that's stronger than I can make. Otherwise, we would do what Hertz did for electromagnetic waves, go in our lab, take a barbell, put it on something, spin it.

Lex Fridman 41:09 Can I ask a dumb question? So, a, a single object that's weirdly shaped, does that generate gravitational waves? So if it's-

Barry Barish 41:16 If it's-

Lex Fridman 41:17 ... and if it's rotating.

Barry Barish 41:18 I- uh, sure. It, it, it w-

Lex Fridman 41:20 But it's just much weaker signal.

Barry Barish 41:21 It, it's wea- it's weaker. Well, we didn't know what the strongest signal would be that we would see. Uh, we targeted seeing something called neutron stars actually, because black holes, we don't know very much about. It turned out we were a little bit lucky, there was a stronger source, which was the black holes.

Lex Fridman 41:38 Well, another ridiculous question. So y- you say waves. What does, what does a wave mean? Like, um, the most ridiculous version of that question is, w- what does it feel like to, uh, ride a wave as you get closer to the source?

Barry Barish 41:56 Uh-

Lex Fridman 41:56 Or experience it?

Barry Barish 41:57 Well, if you experience a wave, imagine tha- this is what happens to you. I- I don't know what you mean about getting close, it comes to you. So it's like, it's like a, this light wave or something that comes through you. So when the light hits you, it ma- makes your eyes detect it. I flashed it. What does this do? It's, uh, it's like going to the amusement park, and they have these mirrors. You look in this mirror and you look short and fat, and the one next to you, it makes you s- tall and thin.

Lex Fridman 42:26 Mm-hmm.

Barry Barish 42:27 Okay? Imagine that you went back and forth between those two mirrors once a second.

Lex Fridman 42:33 Mm-hmm.

Barry Barish 42:33 That would be a gravitational wave with a period of once a second. Uh, if you did it 60 times a second, go back and forth, and, a- and then that's all that happens, it makes you taller and shorter and fatter, back and forth, as it goes through you, uh, at the frequency of the gravitational wave.

Lex Fridman 42:50 Mm-hmm.

Barry Barish 42:50 So, the frequencies that we detect are higher than one a second, but that's the idea, so.

Lex Fridman 42:56 But, uh-

Barry Barish 42:57 And, and the si- amount is small.

Lex Fridman 42:59 Amount is small, but when, if, if you're closer to the, to the source of the wave is it the same amount?

Barry Barish 43:08 Yeah, it's, it doesn't dissipate. It-

Lex Fridman 43:11 It doesn't dissipate. (sighs) Okay, so it's not that fun of an amusement ride.

Barry Barish 43:16 Well, it, it, it, it does dissipate, but it doesn't, it doesn't, it's just, it's proportional to the distance.

Lex Fridman 43:22 Right. It's not s-

Barry Barish 43:23 It's not a big power.

Lex Fridman 43:24 Right. Gotcha. So, but so, (laughs) it would be a fun ride if you get a little bit closer, or a lot closer. I mean, like I, I wonder what the, okay this is a ridiculous question, but I have you here. (laughs) Like the getting fatter and taller, I mean that experience, for some reason that's mind-blowing to me.

Barry Barish 43:45 (laughs)

Lex Fridman 43:45 Because it, it brings the distortion of spacetime to you. I mean, spacetime is being morphed, right? Like this is a way-

Barry Barish 43:56 That's right.

Lex Fridman 43:57 ... that how, that's so weird.

Barry Barish 43:59 And we're in space, so we're affected by it.

Lex Fridman 44:01 Yeah, we're in space, and now it's moving.

Barry Barish 44:04 We're a part of space.

Lex Fridman 44:05 I don't know what to do with it. I mean, does it fr- Okay. Um,

Lex Fridman 44:08 how much do you think about the philosophical implications of general relativity? Like that we're in spacetime and it can be bent by gravity. Like, is that just what it is? Are we, are we supposed to be okay with this? 'Cause like Newton, even Newton's a little weird, right? But that at least like makes sense. That's our physical world, you know, when an apple falls, it makes sense. But like the fact that entirety of the spacetime we're in can bend.

Barry Barish 44:43 Well-

Lex Fridman 44:43 That's uh, that's a, I, I, that's really mind-blowing.

Barry Barish 44:47 Well may, may, let me make you another analogy.

Lex Fridman 44:49 This is a therapy session for me at this point.

Barry Barish 44:51 Yeah, right. Another analogy.

Lex Fridman 44:53 Thank you.

Barry Barish 44:53 So, so imagine you have a trampoline.

Lex Fridman 44:56 Yes.

Barry Barish 44:57 Okay. What happens if you put a marble on a trampoline? Doesn't do anything, right?

Lex Fridman 45:03 No.

Barry Barish 45:03 Just sits there.

Lex Fridman 45:04 Moves it a little bit, but not much.

Barry Barish 45:05 Yeah. I mean, just if I drop it, it's not going to go anywhere. Now imagine I put a bowling ball at the center of the trampoline. Now I come up to the trampoline and I put a marble on. What happens?

Lex Fridman 45:19 It'll roll towards the bowling ball.

Barry Barish 45:21 Okay. All right. So what's happened is the presence of this massive object distorted the space that the trampoline did. This is the same thing that happens to the presence of the earth, the earth and the apple. The presence of the earth affects the space around it just like the, uh, bowling ball on the trampoline.

Lex Fridman 45:44 Yeah. This doesn't make me feel better. I'm referring from the perspective of an ant walking around on that trampoline. Then some guy just dropped a ball, and then not only dropped the ball, right? It's not just dropping a bowling ball. It's making the b- the ball go up and down or doing some kind of oscillation thing, where it's like waves. And that's so fundamentally different from the experience on being on flat land and walking around and just finding delicious sweet things as ant does, and just, it just feels like to me from a human experience perspective completely, it's humbling. It's truly humbling.

Barry Barish 46:22 It, it's humbling, but we see that kind of phenomenon all the time. Let, let me give you another example. Imagine that you walk up to a, a, a still pond.

Lex Fridman 46:33 Yes.

Barry Barish 46:33 Okay? Now I throw, like you, you throw a rock in it, what happens?

Lex Fridman 46:39 Ripples.

Barry Barish 46:39 The rock goes in, sinks to the bottom, fine. And these little ripples go out.

Lex Fridman 46:43 Yeah.

Barry Barish 46:44 And they travel out.

Lex Fridman 46:46 Yeah.

Barry Barish 46:46 That's exactly what happens. I mean there's a disturbance which is these say f- the bowling ball or our black holes, and then the ripples that go out in the water, they're not r- they don't have any m- they don't have the rock, any part, pieces of the rock.

Lex Fridman 47:02 But see the thing is, I guess what's not disturbing about that is it's a, I mean it's a, a guess a, a flat two-dimensional surface that's being disturbed. Like, for a three-dimensional surface, uh, three-dimensional space to be disturbed feels weird.

Barry Barish 47:20 It's even worse. It's four-dimensional.

Lex Fridman 47:21 Four-dimensional.

Barry Barish 47:21 Because it's space and time.

Lex Fridman 47:23 Time, yeah.

Barry Barish 47:24 (laughs) So that's why you need Einstein is to make it, uh, four-

Lex Fridman 47:28 Make it okay?

Barry Barish 47:28 ... four-dimensionally. No. To make a-

Lex Fridman 47:31 (laughs) To make it four-dimensional. Yeah. I mean it-

Barry Barish 47:33 To take the same phenomenon and, and look at it in all of space and time.

Lex Fridman 47:38 (laughs)

Barry Barish 47:38 Anyway, luckily, for you and I-

Lex Fridman 47:42 (laughs)

Barry Barish 47:42 ... and all of us, the amount of distortion is incredibly small. So it turns out that if you think of space itself, now this is going to blow your mind too, if you think of space as being like a material, like this table.

Lex Fridman 47:57 Mm-hmm.

Barry Barish 47:58 Uh, it's very stiff. You know, we have materials that are very pliable, materials that are very stiff. So space itself is very stiff, so when gravitational waves come through it, luckily for us it doesn't distort it so much that it affects our ordinary life very much.

Lex Fridman 48:14 Mm-hmm. No, I mean that's great. That's gr- Wait, I thought there was something bad coming. No, this is great.

Barry Barish 48:20 No, not bad.

Lex Fridman 48:20 That's great news. So I mean that, I mean perhaps we evolved as life on earth do we-

Barry Barish 48:27 So-

Lex Fridman 48:27 ... to be such that for us this particular set of uh, effects of gravitational waves uh, is not that significant maybe. May- maybe that's why there-

Barry Barish 48:37 It is. You, you probably used s- this effect today or yesterday.

Lex Fridman 48:42 To do what?

Barry Barish 48:43 So it's, it's pervasive. Well because-

Lex Fridman 48:46 You mean gravity or, or the way the or external, 'cause I only-

Barry Barish 48:50 Uh, curvature of space and time.

Lex Fridman 48:51 Curvature of space. How? I only care personally as a human, right, the gravity of earth. That's per-

Barry Barish 48:56 But you use it every day almost.

Lex Fridman 49:00 Oh, it's curving. Uh-huh.

Barry Barish 49:01 Because... No, no, no.

Lex Fridman 49:02 What?

Barry Barish 49:02 It's in this thing. Every time it tells you where you are-

Lex Fridman 49:07 Yeah.

Barry Barish 49:07 ... it, how does it tell you where you are? It tells you where you are because we have 24 satellites or some number that are going around in space, and it asks how long it takes the beam to go to the satellite and come back, the signal-

Lex Fridman 49:23 Yeah.

Barry Barish 49:23 ... to different ones, and then it triangulates-

Lex Fridman 49:26 Yeah.

Barry Barish 49:26 ... and tells you where you are. And then if you go down the road, it tells you where you are. Do you know that if you did that with the satellites and you didn't use Einstein's equations-

Lex Fridman 49:35 Oh, no. New- New- you wouldn't even knew that.

Barry Barish 49:36 ... you won't get the right answer. That's right. And in fact, if you take a road, let's say 10 meters wide, I've done these numbers, and you ask how long you'd stay on the road if you didn't make the correction for general relativity, this thing you're pooh-poohing is you're using every day.

Lex Fridman 49:54 Yeah.

Barry Barish 49:54 Uh, you'd go off the road by a minute.

Lex Fridman 49:56 You'd go off the road? Well, actually that might be my problem.

Barry Barish 49:57 So you use it. So don't pooh-pooh it.

Lex Fridman 50:00 Well, I think I'm using an Android so maybe... and the GPS doesn't work that well, so maybe I'm using Newton's physics.

Barry Barish 50:05 (laughs) .

Lex Fridman 50:05 Uh, so I need to upgrade to general relativity. Um, so (laughs) gravitational waves and Einstein had, uh... Wait, Feynman really does have a part in the story?

Barry Barish 50:17 Yeah.

Lex Fridman 50:17 Was that one of the first kind of experimental prop- pro- proposed to detect gravitational waves?

Barry Barish 50:22 Well, I, well, he did what, what we call a Gedanken experiment. That's a thought experiment.

Lex Fridman 50:25 Yes. Okay.

Barry Barish 50:26 Not a real experiment. But then after that, then people believed gravitational waves must exist. You can kind of calculate how big they are. They're tiny. And so people started searching. The first idea that was used was Feynman's idea. Uh, and then, or a variant of it.

Lex Fridman 50:43 Mm-hmm.

Barry Barish 50:44 And it was to take a great big, huge bar of aluminum and then put around... and it's a, it's made like a cylinder, and then put around it some very, very sensitive detectors so that if a gravitational wave happened to go through it, it would go (whispering noise) and you'd detect this extra strain that was there. And that was this method that was used until we came along. It wasn't a very good method to use.

Lex Fridman 51:12 And what was the...

Lex Fridman 51:14 So we're talking about a pretty weak signal here.

Barry Barish 51:17 Yeah, that's why that method didn't work.

Lex Fridman 51:19 So what... Can you tell the story of figuring out what kind of method would be able to detect this very weak signal of gravitational waves?

Barry Barish 51:30 So remembering the, remembering what happens in, when you go to the amusement park-

Lex Fridman 51:36 Yeah.

Barry Barish 51:37 ... that it's going to do something like stretch this way and squash that way, squash this way, and stretch this way. We do have an instrument that can detect that kind of thing. It's called an interferometer. And what it does is it just basically takes usually light, and the two directions that we're talking about, you send light down one direction and the perpendicular direction. And if nothing changes, it takes the same... and the arms are the same length, it just goes down, bounces back. And if you invert one compared to the other, they cancel. So there's nothing happens. But if it's like the amusement park and one of the arms got, you know, it got shorter and fatter, so it got... took longer to go horizontally than it did to go vertically. Then when they come back, when the, when the light comes back, it comes back somewhat out of time. And that basically is the scheme. The only problem is that that's not a very... done very accurately in general. And we had to do it extremely accurately.

Lex Fridman 52:46 So what, uh, what- what's the, what's the difficulty of, uh, doing so accurately?

Barry Barish 52:52 Okay. So the measurement that we have to do is a distortion in time. How big is it? One, it's a distortion that's one part in 10 to the 21. That's 21 zeros and a one. Okay?

Lex Fridman 53:08 Wow. And this, so this is like a delay in the thing coming back.

Barry Barish 53:13 Uh, it's a, one of them coming back after the other one, but the difference is just one part in 10 to the 21.

Lex Fridman 53:19 Wow.

Barry Barish 53:20 So for that reason, we make it big. Let it, let the arms be long. Okay? So one part in 10 to the 21. In our case, it's kilometers long. So we have an instrument that's kilometers in one direction, kilometers in the other. So four, four-

Lex Fridman 53:35 How many kilometers are we talking about? Four kilometers?

Barry Barish 53:37 Four kilometers in each direction. Um, if you take then one part in 10 to the 21, we're talking about measuring something to 10 to the minus 18 meters.

Lex Fridman 53:53 (laughs) . Okay. This is good.

Barry Barish 53:55 Now to tell you how small that is-

Lex Fridman 53:57 Yeah.

Barry Barish 53:58 ... the proton-

Lex Fridman 53:59 Yeah.

Barry Barish 54:00 ... thing we're made of this you can't go and grab so easily is 10 to the minus 15 meters.

Lex Fridman 54:05 Okay.

Barry Barish 54:05 So this is 1/1000 the size of a proton. That's the effect, size of the effect. Einstein himself didn't think this could be measured and ever seen. Actually, he said that. Uh, but that's because he didn't, you know, anticipate modern lasers and, and techniques that we developed.

Lex Fridman 54:27 Okay.

Lex Fridman 54:28 So maybe can you tell me a little bit what you're referring to as LIGO, the Laser Interferometer Gravitational Wave Observatory? What is LIGO? Can you just elaborate kind of the big picture view here before I ask you specific questions about it?

Barry Barish 54:44 (laughs) Yeah. So in the same idea that I just said, we have two long vacuum pipes, 10 to the, uh, 4 kilometers long. Okay. Uh, we start with a laser beam and we divide the beam-... going down the two arms, y- and we have a mirror at the other end, reflects it back. It's more subtle, but we s- bring it back. If there's no distortion in spacetime and the lengths are exactly the same, which we calibrate them to be, then when it comes back, if we just invert one signal compared to the other, they'll just cancel.

Lex Fridman 55:22 Mm-hmm.

Barry Barish 55:22 So we see nothing. Okay? But if one arm got a little bit longer than the other, then they don't come back at exactly the same time, they don't exactly cancel, that's what we measure. So to give a number to it, we have to do that to, we have w- the change of length to be able to do this 10 to the -18 meters, to one part in 10 to the 12th, and that was the big experimental challenge that, uh, uh, required a lot of innovation to be able to do.

Lex Fridman 55:57 So w- what... y- you gave a lot of credit to, I think, Caltech and MIT for some of the technical developments like within this project. Is there some interesting things you can speak to, like at the low level of some cool stuff that had to be solved? Like what are, what are we talking-

Barry Barish 56:13 Yeah. Yeah. Yeah. So-

Lex Fridman 56:14 I'm a software engineer, so-

Barry Barish 56:15 Okay.

Lex Fridman 56:16 ... all of this-

Barry Barish 56:16 Well, well-

Lex Fridman 56:16 I have so much more respect for everything done here than anything I've ever done.

Barry Barish 56:20 Okay.

Lex Fridman 56:20 So it's just code when I use it.

Barry Barish 56:22 So, so, so I'll give you an example of doing, uh, uh, mechanical engineering-

Lex Fridman 56:30 Mm-hmm.

Barry Barish 56:31 ... at a better l- at a, at a... basically, mechanical engineering and geology-

Lex Fridman 56:36 Yeah.

Barry Barish 56:36 ... at maybe at a level.

Lex Fridman 56:38 Geology. Okay. (laughs)

Barry Barish 56:38 Uh, so what are we... what's the problem? The problem is the following, that I've given you this picture of an instrument that I, by some magic, I can make good enough to f- measure this very short distance.

Lex Fridman 56:49 Yeah.

Barry Barish 56:49 But then, I put it down here, it won't work. And the reason it doesn't work is that the Earth itself is moving all over the place all the time. You don't realize-

Lex Fridman 57:00 Oh, no.

Barry Barish 57:00 ... it. It seems pretty good to you.

Lex Fridman 57:01 Yeah. No, I get it.

Barry Barish 57:02 But it's moving all the time. So somehow, it's moving so much that you... we can't deal with it. We happen to be trying to do the experiment here on Earth, but we can't deal with it. So, we have to make the instrument isolated from the Earth.

Lex Fridman 57:17 Oh, no.

Barry Barish 57:18 At the frequencies we're at, we've got to float it. That's a mechanical, that's an engineering problem, not a physics problem.

Lex Fridman 57:24 So when you actually... like, uh, we're doing... we're having a conversation on our podcast right now, there's, uh... and people who record music work with this, you know, how to create an isolated room. (laughs) And they usually build a room within a room, but that's still not isolated. In fact, they say it's impossible to truly isolate from sound, uh, from noise and stuff like that. But that, that, th- that's like one step of millions that you took, is building a room inside a room, bec-... you basically have to isolate all-

Barry Barish 57:57 No, this is actually an easier problem. It's just you have to do it really well. So the... making a clean room is really a tough problem, because you have to put a room inside a room-

Lex Fridman 58:05 Yeah.

Barry Barish 58:05 ... and you have to...

Lex Fridman 58:07 So this is not as-

Barry Barish 58:07 This is just, this is really simple engineering or physics.

Lex Fridman 58:11 Uh-huh.

Barry Barish 58:12 Okay. So what do you have to do? How do you isolate yourself from the, from the Earth?

Lex Fridman 58:15 Yes.

Barry Barish 58:16 First, we work at, uh... we're not looking at all frequencies for gravitational waves, we're looking at particular frequencies that you can deal with here on Earth. So what frequencies would those be? You were just talking about frequencies.

Lex Fridman 58:33 I, I mean, I don't know. Yeah.

Barry Barish 58:34 We know by evolution, our bodies know, it's the audio band. Okay? The reason our ears work where they work is that's where the Earth isn't going... making too much noise.

Lex Fridman 58:45 Okay. So w- the reason our ears work the way they work is 'cause this is where it's quiet. (laughs)

Barry Barish 58:49 That's right. So if you go to-

Lex Fridman 58:51 (laughs)

Barry Barish 58:52 ... if you go to one hertz instead of 10 hertz, it's... the Earth is (mimics earth shaking) it's really moving around. So, so somehow, we live in a, what we call the audio band.

Lex Fridman 59:04 Yeah.

Barry Barish 59:04 It's tens of hertz to thousands of hertz, that's where we live. That's where we live, okay? If we're gonna do an experiment on the Earth-

Lex Fridman 59:13 Might as well do it in the same-

Barry Barish 59:13 ... it's the same frequency. That's where the Earth is the quietest. So we have to work in that frequency. So we're not looking at all frequencies. Okay? So the solution for the, for the shaking of the Earth, to get rid of it, is pretty mundane, if we do the same thing that you do, uh, to make your car drive smoothly down the road. So what happens when your car goes over a bump? Early cars did that, they bounced.

Lex Fridman 59:40 Right.

Barry Barish 59:41 Okay? But you don't feel that in your car. So what happened to that energy? You can't just disappear energy.

Lex Fridman 59:48 Right. Absolutely.

Barry Barish 59:48 So we have these things called shock absorbers in the car. What they do is they absorb... they take the, the thing that went like that, and they basically can't get rid of the energy, but they move it to very, very low frequency. So what you feel isn't... (mimics earth shaking)

Lex Fridman 1:00:04 Yeah.

Barry Barish 1:00:04 You feel like, oh, shh... smoothly. Okay?

Lex Fridman 1:00:07 Mm-hmm.

Barry Barish 1:00:08 All right. So, uh, we also work at this frequency. So if we... so we basically... why... wha- why don't we have to do anything other than shock absorbers? So we made the world's fanciest shock absorbers. Okay? Uh, not just like in your car where there's one layer of them, they're just the right squishiness and so forth. They're better than what's in the cars. And we have four layers of it. So whatever shakes and gets through the first layer, we treat in a second, third or fourth layer.

Lex Fridman 1:00:38 So it's almost... so some mechanical engineering problem

Barry Barish 1:00:41 Yeah, that's what I said. So it's a real-

Lex Fridman 1:00:43 So it's not... there's no weird tricks to it like a, like a chemistry type thing or-

Barry Barish 1:00:47 No, no. Just, well, the right squishiness, the right... need the right material inside-

Lex Fridman 1:00:52 Yeah. So materials-

Barry Barish 1:00:52 And ours look like little springs, but they're... so-

Lex Fridman 1:00:55 Springs? They're springs?

Barry Barish 1:00:57 They look like-

Lex Fridman 1:00:57 So like legitimately like shock absorbers?

Barry Barish 1:01:00 Yeah.... there, then-

Lex Fridman 1:01:01 What? Okay.

Barry Barish 1:01:03 ... and, okay. And this is now experimental physics at the, at its limit. Okay. So, you do this, and we make the world's fanciest shock absorbers, just mechanical engineering.

Lex Fridman 1:01:13 Just mechanic... but you know, this is hilarious.

Barry Barish 1:01:15 But we didn't test-

Lex Fridman 1:01:16 Yeah.

Barry Barish 1:01:16 We weren't good enough to discover gravitational waves.

Lex Fridman 1:01:20 Mm-hmm.

Barry Barish 1:01:22 So, uh, so we did another, we added another feature, and it's something else that you're, uh, aware of, probably have one, and that is to get rid of noise. You've probably... noise, which is, you don't like, and that's the same principle that's in these little Bose, uh, uh, earphones.

Lex Fridman 1:01:43 Mm-hmm. Noise-canceling?

Barry Barish 1:01:44 Noise-canceling. So, uh, th- so how do they work? They basically... you go on an airplane, and they, uh, sense the ambient noise from the engines and cancel it 'cause it's just the same over and over again.

Lex Fridman 1:01:57 Mm-hmm.

Barry Barish 1:01:57 They cancel it. And when the stewardess comes and asks you whether you want coffee or a tea or a drink or something, you hear her fine 'cause she's not ambient. She's a signal. So...

Lex Fridman 1:02:08 Are we talking about active canceling, like where they-

Barry Barish 1:02:10 Active canceling. So-

Lex Fridman 1:02:12 This is... you... okay.

Barry Barish 1:02:13 So, another-

Lex Fridman 1:02:14 Don't tell me you have a- active-canceling, uh, on this-

Barry Barish 1:02:18 Yeah.

Lex Fridman 1:02:18 ... besides the shock absorbers.

Barry Barish 1:02:19 Yeah. So, we add the sh- so inside this array of shock absorbers-

Lex Fridman 1:02:23 Yeah.

Barry Barish 1:02:23 ... we... you asked for some interesting-

Lex Fridman 1:02:26 This is awesome.

Barry Barish 1:02:27 (laughs)

Lex Fridman 1:02:28 (laughs)

Barry Barish 1:02:28 So, inside this, it's harder than the, the earphone problem, but it's just engineering. We have to see, measure not just that the, uh, engine still made noise, m- but the Earth is shaking. It's moving in some direction, so we have to actually tell not only that there's noise and cancel it, but what direction it's from. So, we put this array of seismometers inside this array of shock absorbers and measure the residual motion and its direction, and we put little actuators that push back against it and cancel it. And so-

Lex Fridman 1:03:08 That is awesome. So, you have the actuators, and y- you have the thing that is sensing the, the vibrations, and then, and then you have the actua- actuators that adjust for that-

Barry Barish 1:03:16 Yeah.

Lex Fridman 1:03:16 ... and do so in perfect synchrony.

Barry Barish 1:03:18 Yeah.

Lex Fridman 1:03:19 What-

Barry Barish 1:03:19 If it all works right.

Lex Fridman 1:03:21 (laughs)

Barry Barish 1:03:21 And so, how much do we reduce the shaking of the Earth?

Lex Fridman 1:03:25 I mean, and b- uh-

Barry Barish 1:03:26 Uh, one part in 10 to the 12th.

Lex Fridman 1:03:29 One part in 10-

Barry Barish 1:03:31 So, what gets through us is one part in 10 to the 12th. That's, that's pretty r- big reduction. You don't need that in your car, but that's what we do. And so, that's how isolated we are from the Earth. And that was the biggest, uh, I, I'd say technical problem outside of the physics instrument, the interferometer.

Lex Fridman 1:03:50 Can I ask you a, a, a, a weird question here? You, you make it very poetically and humorously. You're just saying it's just a mechanical engineering problem. But is this one of the biggest precision mechanical engineering efforts ever? I mean, this seems exceptionally difficult.

Barry Barish 1:04:09 It is. And so, it took a long time, and, uh, I think nobody seems to challenge the statement that this is the most precision, precise instrument that's ever been built, LIGO.

Lex Fridman 1:04:22 I just... I wonder what, like, listening to Led Zeppelin sounds on this thing 'cause it's-

Barry Barish 1:04:26 (laughs)

Lex Fridman 1:04:26 ... so isolated. I mean, this is like, uh, I don't know.

Barry Barish 1:04:30 No background noise.

Lex Fridman 1:04:31 No, p- no back-... it's... wow. Wow. Wow. Now, uh, so, when you were first (laughs) concei- conceiving this, um, I would probably, uh, if I was knowledgeable enough, kind of, uh, laugh off the possibility this is even possible. I'm sure... like, how many people believe that this is possible? Did you believe this was possible?

Barry Barish 1:04:54 Oh, oh, uh, I did. Um, I didn't know that we need- for sure that we needed active. When we started, we did just passive. But we were doing the tests to develop the active to add as a second stage, which we ended up needing. Uh, but there was a lot of, you know, now, now there was a lot of skepticism. A lot of us, especially astronomers, w- felt that money was being wasted 'cause we were also expensive. Doing what I told you is not cheap.

Lex Fridman 1:05:24 Yeah.

Barry Barish 1:05:24 So, it was kind of controversial. It was funded by the National Science Foundation.

Lex Fridman 1:05:30 Uh, c- can you just linger on this just for a little longer? The actuator thing, the active canceling, it, um... d- do you remember m- like, little experiments that were done along the way to prove to the team, to themselves that this is even possible? So, from a r- uh, because I work with quite a bit of robots, and to me, the idea that you could do it this precisely is, uh, humbling and embarrassing, frankly. (laughs)

Barry Barish 1:05:59 (laughs)

Lex Fridman 1:05:59 Because, like, this is another level of precision that I can't even, um... 'cause robots are a mess, and this is basically one of the most precise robots ever, right? So, like-

Barry Barish 1:06:15 Yeah.

Lex Fridman 1:06:15 ... uh, can you... is there, um-

Barry Barish 1:06:16 Yeah, we have-

Lex Fridman 1:06:16 ... do you have any, like, small-scale experiments that were done that's just being-

Barry Barish 1:06:19 We've-

Lex Fridman 1:06:19 ... like, this is possible?

Barry Barish 1:06:21 ... we... yeah, and, and larger scale. We made, we made, uh, test, uh, cha- that also has to be in vacuum, too. But we made test chambers that had this system in it, our first mock of this system that w- so we could test it, um, and, uh, optimize it and make it work. But it's just a mechanical engineering problem.

Lex Fridman 1:06:42 Okay. (laughs)

Barry Barish 1:06:43 (laughs)

Lex Fridman 1:06:44 Uh, humans are just ape descendants. I gotcha. (laughs) I, I gotcha. Uh, is there any video of this? Like, um, v- some kind of educational purpose visualizations of this active canceling and-

Barry Barish 1:06:58 Uh, I don't think so.

Lex Fridman 1:07:00 And, uh-

Barry Barish 1:07:01 There's some.

Lex Fridman 1:07:01 ... has th- I mean, is this, does this live on?

Barry Barish 1:07:05 Well, we-

Lex Fridman 1:07:05 And so, uh-

Barry Barish 1:07:05 ... we worked for parts of it, for the active canceling, we worked with, uh, for the instruments, for the sen- sensor and instruments, we worked with, uh, um, a small company in, uh, near where you are, 'cause it was our MIT people that got them, that were, you know, interested in the problem because they thought they might be able to commercialize it for-

Lex Fridman 1:07:26 Right.

Barry Barish 1:07:26 ... making stable tables to make microelectronics, for example, which are limited by the, how stable the table is. I mean, at this point, it's a little expensive. (laughs) So-

Lex Fridman 1:07:37 You never know, you never know where this leads.

Barry Barish 1:07:39 Yeah.

Lex Fridman 1:07:39 Okay. So maybe on the... Let me ask you, just s- sticking it a little longer, this, uh, silly old mechanical engineering problem. Uh, what was, um, to you, kind of the darkest moment of what was the hardest stumbling block to get over on the engineer side? Like, was there any time where there was a doubt, where it was like, "I'm not sure we'll be able to do this," a kind of a engineering challenge that was hit? Do you remember anything like that?

Barry Barish 1:08:10 Well, I think the, I think the one that, that, uh, my colleague at, uh, MIT, Rai Weiss, worked on so hard, and, uh, was much more of a worry than this, this is only a question if you're not doing well enough, you have to keep making it better somehow.

Lex Fridman 1:08:27 Right.

Barry Barish 1:08:28 But this whole huge instrument has to be in vacuum.

Lex Fridman 1:08:32 Right.

Barry Barish 1:08:33 And, uh, the vacuum tanks are, you know, this big around. And, uh, so it's the world's biggest high-vacuum system.

Lex Fridman 1:08:41 Oof.

Barry Barish 1:08:41 And the cons- so how do you make it, first of all? Uh, how do you make this four-meter-long sealed vacuum system? It has to be made out of-

Lex Fridman 1:08:51 Four kilometers long.

Barry Barish 1:08:52 Four kilometers long. What'd I say? Something else.

Lex Fridman 1:08:54 Meters.

Barry Barish 1:08:54 Four, four kilometers long.

Lex Fridman 1:08:56 Big difference.

Barry Barish 1:08:57 Yeah.

Lex Fridman 1:08:57 (laughs)

Barry Barish 1:08:57 And, uh, so, but to make it, yeah, we started with, uh, um, a roll of stainless steel, and then we spi- roll it out like a spiral so that there's a spiral weld on it.

Lex Fridman 1:09:11 Yeah.

Barry Barish 1:09:11 Okay. So, uh, m- the engineering was fine. We did that. We worked through, uh, very good companies and so forth to build it. But, uh, the big worry, uh, i- it was what if you develop a leak? This is a high-vacuum, not just vacuum system. Typically, in your, in a laboratory, if there's a leak, you put helium around the, the thing you have, and then you detect where the helium is coming in. But if you have something as big as this, you can't surround it with helium.

Lex Fridman 1:09:44 So you might not actually even know that there's a leak, and then what would be affecting the data?

Barry Barish 1:09:47 Well, we, uh, we have, we can measure the vac, how good the vacuum is-

Lex Fridman 1:09:53 Right.

Barry Barish 1:09:53 ... so we can know that. But there, a leak can develop, and n- and then we don't, how do we fix it or how do we find it?

Lex Fridman 1:10:00 Got you, got you.

Barry Barish 1:10:00 And, uh, so that was-

Lex Fridman 1:10:02 Got you.

Barry Barish 1:10:02 ... you asked about a worry, that was always a really big worry, uh, my-

Lex Fridman 1:10:06 What's the difference between a high vacuum and a, and a vacuum? What, what, what is high vacuum? That's, like, some, a delta of, close to vacuum? Is it some threshold that you need?

Barry Barish 1:10:16 Well, there's a unit w- w- uh, high vacuum is, uh, when the vacuum and the units that are used, which are torrs, so it's 10 to the minus nine.

Lex Fridman 1:10:25 Gotcha.

Barry Barish 1:10:26 Uh, s- and there's high vacuum is usually used in small places. The biggest vacuum system, period, is at CERN, in this big particle accelerator. But the high vacuum, where they need really good vacuums so particles don't scatter in it, is smaller than ours. So ours is a really large, uh, uh, high-vacuum system.

Lex Fridman 1:10:49 I don't know. This is so cool. I mean, this is basically, by far, the greatest listening device ever built by humans. The fact that, like, descendants of apes could do this, that evolution started with single-cell organisms, I mean, is, is there any more... I'm a huge, uh, theory is like, yeah, yeah. But, like, bridges, when I look at bridges, uh, from a civil engineering perspective, it's one of the most beautiful creations by human beings. It's physics. You're using physics to construct objects that, uh, can support huge amount of mass. And it's, like, structural, but it's also beautiful in that humans can collaborate to create that throughout history. And then you take this on another level. This is, this is, like, this is, like, s- exciting to me beyond measure that humans can create something so precise. A-

Barry Barish 1:11:39 But, uh, but another concept lost in this, you just said.

Lex Fridman 1:11:42 Yeah.

Barry Barish 1:11:43 You started talking about single cell.

Lex Fridman 1:11:44 Yeah.

Barry Barish 1:11:45 Okay. You have to realize, this discovery that we made, that everybody's bought off on, happened 1.3 billion years ago, somewhere.

Lex Fridman 1:11:55 Right.

Barry Barish 1:11:55 And then the signal came to us. 1.3 billion years ago, we were just converting on the Earth from single-cell to multi-cell life.

Lex Fridman 1:12:03 That's cool.

Barry Barish 1:12:03 So when this actually happened, this collision of two black holes-

Lex Fridman 1:12:07 Yeah.

Barry Barish 1:12:08 ... we weren't here. We weren't even close to being here.

Lex Fridman 1:12:10 We were both developing slowly.

Barry Barish 1:12:11 There were single c- yeah, we were had- we were going from single-cell to multi-cell life at that point.

Lex Fridman 1:12:16 All to meet up at this, at this point.

Barry Barish 1:12:18 Yeah.

Lex Fridman 1:12:20 Wow, that's like a, that's almost romantic, uh, the- (laughs)

Barry Barish 1:12:25 It is.

Lex Fridman 1:12:25 ... ro- (laughs)

Barry Barish 1:12:26 (laughs)

Lex Fridman 1:12:27 Uh, okay. So on the human side of things, it's kind of fascinating, 'cause, uh, you're talking about a th- over a thousand people team for LIGO.

Barry Barish 1:12:38 Yeah.

Lex Fridman 1:12:38 Uh, that started out with, uh, you know, around 100. W- and you've, um, for parts of the time at least, led this team. Wh- what does it take to lead a team like this, of incredibly brilliant theoreticians and engineers, and just a lot of different parties involved, a lot of egos, a lot of ideas? You, you had this fun- funny example, I forget where-... where in publishing a paper, you have to all agree on like, uh, you know, the phrasing of a certain sentence or the title of the paper and so on. That's a very interesting simple example. I'd love you to speak to that, but just in general, how, what does it take to lead this kind of team?

Barry Barish 1:13:23 Okay. Uh, I, I think the, the general idea is one we all know. You wanna, you wanna, you wanna get, uh, where the, the sum of something is more than the individual parts is what we say, right?

Lex Fridman 1:13:39 Yeah.

Barry Barish 1:13:40 So, that's what you're trying to achieve.

Lex Fridman 1:13:42 Yes.

Barry Barish 1:13:42 Okay. How do you do that actually? Mostly, if we take multiple objects or people, and when you put them together, the sum is less.

Lex Fridman 1:13:51 Yes.

Barry Barish 1:13:52 Why? Because it, they overlap, so you don't have individual things that, you know, this person does that, this person does that, then, then you get exactly the sum. But what you want is to develop where you get more than what the individual contributions are. We know that's very common. People use that expression everywhere, and it's the expression that has to be kind of built into how people feel it's working. Because if you're part of a team and you realize that somehow the team is able to do more than the individuals could do themselves, then they buy on kind of in terms of the process. So, that's the, that's the goal that you have to have is to, to achieve that, and that means that you have to, uh, realize parts of what you're trying to do that require not that one person couldn't do it. It requires the combined talents to be able to do something that neither of them could do themselves, and we have a lot of that kind of thing. And I think, um, I mean, built into the, some of the examples that I gave you, and so, uh, how do you then... So, so the key almost in anything you do is the people themselves, right? So, in our case, the first and most important was to attract, to spend years of their life on this, the best possible people in the world to do it. So, the only way to convince them is that somehow it's better and more interesting for them than what they could do themselves.

Lex Fridman 1:15:36 Mm-hmm.

Barry Barish 1:15:37 And so, that's part of this, uh, idea.

Lex Fridman 1:15:40 I got you. Yeah, that's powerful. But nevertheless, there's best people in the world. There's egos. Is there something to be said about managing egos or is it-

Barry Barish 1:15:49 Oh, that's, uh, the human problem is always the hardest, and so there's, that's an art, not, uh, a science, I think. Uh, I think the fact here that combined there's a, was a romantic goal that we had to, you know, do something that people hadn't done before, which was, um, important scientifically and, and a huge challenge. Uh, enabled us to say, take and get, uh, I mean, what we did just to take an example, we used the light to go in this thing. It comes from lasers. We need a certain kind of laser. So, uh, the kind of laser that we used, there were three different institutions in the world that had the experts that do this, maybe in competition with each other.

Lex Fridman 1:16:39 Mm-hmm.

Barry Barish 1:16:40 So, we got all three to join together and work with us, uh, to work on this, uh, as an example. So that you had, uh, and they had the thing that they were working together on a kind of object that they wouldn't have otherwise, and, uh, were part of a bigger team where they could discover something that isn't even engineers. These are engineers that do lasers, so, and they're part of, uh, our laser physicists and...

Lex Fridman 1:17:07 So, could you describe the moment or the period of time when finally this incredible creation of human beings led to a detection of gravitational waves?

Barry Barish 1:17:21 It's a long story. Unfortunately, this is a part that, uh, we started-

Lex Fridman 1:17:25 Lots of failures along the way kind of thing or what?

Barry Barish 1:17:28 All failures. That's all, it's built into it. Yeah.

Lex Fridman 1:17:31 Okay.

Barry Barish 1:17:31 If you're not a g- uh, if you're not-

Lex Fridman 1:17:33 It's just mechanical engineering. (laughs)

Barry Barish 1:17:36 You build on your failures. That's expected.

Lex Fridman 1:17:38 Sure.

Barry Barish 1:17:38 So, we're trying things that no one's done before. So, it's technically not just gravitational waves, and so it's built on failures. But anyway, we, we did before Meave and the, the people did, uh, R&D on the concepts, but starting in 1994, we got money from the National Science Foundation to build this thing. Um, it took about five years to build it. So, by 1999, we had built the basic, uh, unit. It did not have active seismic isolation at that stage. Didn't have some other things that we have now. What we did at that, at, at the beginning was, um, stick to technologies that we had at least enough knowledge that we could make work or had tested in our own laboratories. And so then we put together the instrument. We made it work. Uh, it didn't work very well, but it worked, and, uh, we didn't see any gravitational waves. Then we figured out what limited us and we went through this every year for almost 10 years, never seeing gravitational waves. We would, uh, run it, looking for gravitational waves for months, learn what limited us, fix it for months, then run it again. Eventually, we...... knew we had to take another big step, and that's when we made several changes, including going, adding these active seismic isolation, which turned out to be a key. Um, and we fortunately got the National Science Foundation to give us another couple $100 million, or $100 million more, and, um, we rebuilt it or fixed or improved it. And, uh, then in 19, uh, in 2015, uh, we turned it on and, uh, we, um, almost instantly saw, uh, this first collision of two black holes.

Lex Fridman 1:19:52 Wow.

Barry Barish 1:19:54 Um, and, um, then, then we went through a process of, "Do we believe what we've seen?"

Lex Fridman 1:20:00 Yeah. I think, I think you're one of the people that went through that process. It sounds like some people immediately believed it.

Barry Barish 1:20:05 Yeah.

Lex Fridman 1:20:05 And then, (laughs) and then you were like, "Uh, it's too skeptical."

Barry Barish 1:20:07 So, so as human beings, we all have different reactions to almost anything. And so, quite a few of my colleagues had a eureka moment-

Lex Fridman 1:20:14 Yeah.

Barry Barish 1:20:14 ... immediately. I mean, it's ... the, the-

Lex Fridman 1:20:17 That's amazing.

Barry Barish 1:20:18 The, the, the figure that we, that we put in our paper, first is just data. We didn't have to go through, you know, fancy computer programs to do anything. And, and we showed next to it, uh, the calculations of Einstein's equations and it looks just like the, what we detected.

Lex Fridman 1:20:38 Wow.

Barry Barish 1:20:39 And we did it in two different detectors halfway across the US. So, it was pretty convincing. But, uh, but you don't wanna, you don't wanna fool yourself. So, we had to ... Being a scientist, we had to, uh, for me, uh, we had to go through and try to understand that the instrument itself, which was new, I said we would rebuild it, couldn't somehow generate things that look like this. That took some tests. And then, uh, the second, you'll appreciate more, uh, we had to somehow convince ourselves we weren't hacked in some clever way.

Lex Fridman 1:21:14 A cybersecurity question.

Barry Barish 1:21:16 Yeah. Even though we're not on the internet, the, the ... but-

Lex Fridman 1:21:19 Yeah. No, it could be physical access too. Yeah. That's, that's (laughs) fascinating.

Barry Barish 1:21:24 (laughs)

Lex Fridman 1:21:24 It's fascinating that you would think about that.

Barry Barish 1:21:26 (laughs)

Lex Fridman 1:21:26 I mean, not (laughs) , not enough ... It ... (laughs) I mean, 'cause it's, it's, uh, it, it matches prediction, so the chances of it actually being manipulated is very, very low. But nevertheless ...

Barry Barish 1:21:40 We still could have disgruntled old graduate students who had worked with us earlier that-

Lex Fridman 1:21:45 W- want you to ... I don't know how that's supposed to embarrass you. I suppose, yeah, I, I suppose. I see. But, but about, uh, what I think you said within a month, you kind of convinced yourselves officially.

Barry Barish 1:21:57 Within a month, we convinced ourselves. Uh, we kept a thousand collaborators quiet during that time. Then we spent another-

Lex Fridman 1:22:04 That's funny.

Barry Barish 1:22:05 ... month or so, uh, trying to understand what we'd seen, uh, so that we could do the science with it instead of just putting it out to the world and let somebody else understand that it was two black holes and what it was.

Lex Fridman 1:22:19 The fact that a thousand collaborators were quiet is a really strong indication that this is a really close-knit team.

Barry Barish 1:22:25 Yeah. Or, and they're around the world.

Lex Fridman 1:22:28 Yes.

Barry Barish 1:22:29 Or either strong, uh, either strong-knit or tight-knit, or had a strong dictatorship or something.

Lex Fridman 1:22:36 Yeah. Either fear or love.

Barry Barish 1:22:37 (laughs)

Lex Fridman 1:22:37 You can rule by fear or love.

Barry Barish 1:22:38 Yeah. Right.

Lex Fridman 1:22:39 Like you can go back to Machiavelli.

Barry Barish 1:22:40 Yeah.

Lex Fridman 1:22:41 All right. Well, this ... I mean (sighs) , w- (laughs) , this is r- is really exciting, that that was, that, that's a success story, 'cause it didn't have to be a success story, right.? Uh, I mean, eventually perhaps you could say it'll be an inve- but it could have taken it over a century to get there.

Barry Barish 1:23:00 Oh, yeah. Yeah. It's, uh, and, um, and it's only downhill now, kind of. It's ... (laughs)

Lex Fridman 1:23:08 (laughs) What, what do you mean, it's only ... Uh, h- you mean with gravitational waves?

Barry Barish 1:23:12 Well, we're, d- yeah. We've-

Lex Fridman 1:23:14 It's-

Barry Barish 1:23:14 We've now s- we now, uh, well, now we're off because of the pandemic, but when we turned off, we were seeing some sort of gravitational wave event each week.

Lex Fridman 1:23:26 Yeah.

Barry Barish 1:23:26 And now we're fixing, we're fixing, we're adding features where it'll probably be, when we turn back on next year, it'll probably be every, one every couple days. And they're not all the same. So it's, it's learning about what's out there in gravity instead of just optics and ... So it's all, uh, great. We're only limited by ... The fantastic thing, other than that this is, uh, a great field and, you know, it's all new and so forth, is that experimentally the, the great thing is that, uh, we're limited by technology and technical limitations, not by science. So, uh, the, the, the, uh, another ... A really important discovery that was made before ours was what's called the Higgs boson, made on the big accelerator at CERN. You know, this huge accelerator, they discovered R- a really important thing. It's ... You know how we have Einstein's equation, E equals MC squared. So energy makes mass or mass can make energy and that's the bomb. But the mechanism by which that happens, not fission, but, but how do you create mass from energy, uh, was never understood until there was a, a, uh, theory of it about 70 years ago now. And, uh, so they discovered it. It's named after a man named Higgs. It's called the Higgs boson. And so it was discovered, but since that time, and I, I worked on those ex- experiments, since that time, they haven't been able to progress very much further.... a little bit, but not a lot further. And the difference is that we're really lucky. We're in a, uh, in what we're doing, in that there, uh, you're, you see this Higgs boson, but there's tremendous amount of other physics that goes on, and you have to pick out the needle in the haystack kind of-

Lex Fridman 1:25:27 Mm-hmm.

Barry Barish 1:25:27 ... of physics. You can't make the physics go away. It's there. In our case, we have a very weak signal, but once we get it good enough to see it, the, it's weak compared to where we've reduced the background, but the background is not physics. It's just technology, you know? It's getting ourselves better isolated from the Earth or getting a more powerful laser. And so each time, each, since 2015 when we saw the first one, we continually can make improvements that are enabling us to turn this into a, a real science to do astronomy, a new kind of astronomy. It's a little like, uh, astronomy. I mean, uh, um, Galileo started the field. I mean, he basically took lenses that were made for glasses, uh, and he didn't invent the first telescope, but made a telescope, looked at, um, uh, Neptune and saw that it had four moons.

Lex Fridman 1:26:27 Mm-hmm.

Barry Barish 1:26:27 That was the birth of not just using your eyes to understand what's out there. And since that time, we've made better and better telescopes obviously, and astronomy thrives. And in a similar way, we're starting to be able to f- you know, crawl, but we're starting to be able to do that with, uh, gravitational waves. It's, and it's gonna be more and more that we can do as we can make better and better instruments because as I say, it's not limited by, um-

Lex Fridman 1:26:59 Physics.

Barry Barish 1:26:59 ... picking it out of others... Yeah, it's not limited by the physics. It's the limit you mentioned.

Lex Fridman 1:27:03 So you have an optimism about engineering, that even- you know, as we, as human progress marches on, engineering will always, uh, find a way to, uh, to build a large enough device, accurate enough device, to detect this thing.

Barry Barish 1:27:19 As long as it's not limited by physics, yeah, they'll do it.

Lex Fridman 1:27:25 So you, two other folks, and the entire team won the Nobel Prize for this-

Barry Barish 1:27:34 Yeah.

Lex Fridman 1:27:34 ... big effort. There's a million questions I can ask for, but looking back, where does the Nobel Prize fit into all of this? You know, if you think hundreds of years from now, I venture to say that people will not remember the winners of a prize, but they'll remember creations like these. Maybe I'm romanticizing engineering, but I guess I want to ask, how important is the Nobel Prize in all of this?

Barry Barish 1:28:12 Um, well that's a, that's a complicated question. It, it, uh ... As a physicist, it's something you, if you're, if you're (laughs) trying to win a Nobel Prize, forget it, because they give, you know, one a year. So there's, uh, there's been 200 physicists who have won the Nobel Prize since 1900. And-

Lex Fridman 1:28:33 Yeah.

Barry Barish 1:28:34 ... and so that's, you know, it's the aim. So things just have to fall right. So your goal cannot be to win a Nobel Prize. It wasn't my dream. Uh, it's, uh, it's, uh, tremendous for science. I mean, why the Nobel Prize for a guy that made dynamite and stuff is, you know, what it is-

Lex Fridman 1:28:55 Yeah.

Barry Barish 1:28:55 ... is a long story, but it's the one day a year where actually the science that people have done is all over the world and so forth. Forget about the people again, you know? The, it, it is really good for, for science.

Lex Fridman 1:29:08 Celebrating science.

Barry Barish 1:29:10 It celebrates science f- for, you know, several days, different fields. Uh, you know, chemistry, uh, medicine, and so forth. And, uh, everybody doesn't understand everything about these. They're generally fairly abstract. But then it's, you know, it's on the front page of newspapers around the world. So it's really good for science. It's not easy to get science on the front page of the New York Times. It's not there. Uh, should be, but it's not. And, uh, um, so the Nobel Prize is important in that way. Uh, it's, otherwise, you know, I have a certain celebrity that I didn't have before and, um ...

Lex Fridman 1:29:50 (laughs) And now you get to be a celebrity that advertises science. It's a mechanism to, uh, to remind us how incredible-

Barry Barish 1:29:59 Well, it-

Lex Fridman 1:30:00 ... like (laughs) how much credit science deserves in everything we have.

Barry Barish 1:30:02 Well, it, it, it has a little bit more. One thing I didn't expect, which is good, is that, you know, we have a, a government ... I, I'm not picking on ours necessarily, but it's true of all governments, are not run by scientists. In our case it's-

Lex Fridman 1:30:20 Yeah.

Barry Barish 1:30:20 ... run by, uh, lawyers and businessmen.

Lex Fridman 1:30:23 Lawyers. Yep.

Barry Barish 1:30:23 Okay? Uh, and at best they may have a, an aide or something that knows a little science. So, um, so our country is, and all countries are, hardly, um, t- hardly take into account science in making decisions.

Lex Fridman 1:30:42 Yes.

Barry Barish 1:30:43 Okay? And, um, having a Nobel Prize, the, uh, people in those positions actually listen, so you