Black Holes, Gravitational Waves, & Interstellar: Kip Thorne & Brian Greene in Conversation

[00:00:00]Kip: My collaboration with Christopher Nolan is just a   wonderful collaboration, a wonderful experience.  He is a highly creative man, very different   background from me, and he could ask questions  of me that I would never have asked myself.

[00:00:14]Brian: Hey,   everyone. Thanks for joining us. Today we are  going to be talking about gravitational physics,   black holes, wormholes, gravitational waves,  both from the science, of course, but also   from the artistic and filmic perspectives. And I'm so pleased that we're being joined   by someone who, for more than half a  century, has been a pioneer behind our   understanding of gravitational physics. He was  the leading force behind the LIGO experiment,   the Laser Interferometer Gravitational-Wave  Observatory, that first detected gravitational   waves back in 2015, for which he  shared the 2017 Nobel Prize in physics.  You've guessed who that is, no doubt,  by this point. Kip Thorne, thank you- Kip: Thank you, Brian.

[00:01:06]Brian:... so much for joining us.

[00:01:07]Kip: It's a pleasure to be here.

[00:01:08]Brian: Thank you.

[00:01:08]Kip: You exaggerate, but thank you.

[00:01:10]Brian: Not at all, not at all. So I thought we would   begin with black holes, a subject near and dear  to your heart. And if it's not asking too much,   can we go just, for a moment, all the way back to  John Michell and Laplace, the folks who even long   before the general theory of relativity intuited  the possibility of things like black holes?

[00:01:36]Kip: Yeah. And so back in that era,   the understanding of gravity was that of Newton.  And nobody knew anything about the speed of light   limit, but you could imagine an object that was  so strong that whatever the speed of light was,   that light couldn't escape it. And  that's what John Michell did. And   it was just very plausible that he  was right, but they didn't know enough   about the laws of physics to really be  able to determine whether he was right.

[00:02:16]Brian:  Was there a reaction in those  days to that possibility?

[00:02:20]Kip: I don't   know. I haven't looked into it deeply enough.  Certainly, the real embrace of these ideas didn't   come until awfully recently. And I presume  that there was a lot of skepticism then,   as there was in the 1920s and even into  the 1930s and '40s and '50s and '60s.

[00:02:47]Brian: For sure, for sure. So let's get into   the more modern version, which takes us really to  the trenches in World War I, Karl Schwarzschild.

[00:02:59]Kip: Amazing   man. Karl Schwarzschild was a great astronomer,  astrophysicist. He's sitting in the trenches in   World War I, and Einstein has just formulated his  general relativity laws. And Schwarzschild reads   about this, and he does a little calculation,  and he sends Einstein a letter and says,   "I found an exact solution of your equations." It  quickly became named the Schwarzschild Solution,   but it was a great mystery as  to what it really described.  It was perhaps the external gravitational field  of the Earth, but I suppose you take the Earth   away and you still have a solution, and suppose  you go down toward the center, what's going on?   And that's what it took decades to really sort  out. It did turn out to be the gravitational   field of a compact star, the gravitational  field of a black hole, the gravitational   field of a wormhole. It turned out to be all these  things depending on just how you manipulated it.

[00:04:06]Brian: And this   was the first exact solution to Einstein's- Kip: It was the first, exactly.

[00:04:12]Brian: Einstein himself   didn't have an exact solution  of his own equations, right?

[00:04:16]Kip: Precisely, precisely. So it was rather momentous.

[00:04:19]Brian: I mean,   when you look in the textbooks, it can  be very misleading because we clean up   the history and make it all very logical and  straightforward. But at least when you read   Schwarzschild's textbook solution, it doesn't  take that much. You makes some assumptions,   spherical symmetry, aesthetics. So why  didn't Einstein find that solution?

[00:04:45]Kip: I don't   know. I think his attention was mostly focused in  other directions is primarily the case. I mean,   he had so much going on intellectually in his  life. He wasn't just doing general relativity   at this time. He was doing other things in  statistical physics. He was doing early thinking   about quantum theory. It was amazing how many  different irons he had in the fire in that period.

[00:05:11]Brian: Now,   he was a champion of this solution.  It's not like you can imagine- Kip: Oh, yes. Absolutely.

[00:05:16]Brian:...the letter shows up and he's,   conveniently puts it into the waistband and does   his own version of it or something  like that. So he was very open and- Kip: He was very open to it,   but it did have this very puzzling property that  when you went down to a certain distance away from   the center, called the Schwarzschild radius, not  surprisingly, or the gravitational radius now,   the mathematics goes singular. So one thing blows  up, becomes infinite, another thing goes to zero,   and it looks like time and space reverse rolls.  It just looks crazy when you go to that location.   So that came to be called the Schwarzschild  singularity, and it was called that for decades.   It turned out not to really be a physical  singularity, but it was a singularity of   the mathematics in the actual form that  Schwarzschild wrote down the mathematics.

[00:06:13]Brian: And so that was   a puzzle for a long time. And it wasn't the only  reason, but it was part of the reason why people,   like Einstein, resisted taking this solution as  seriously as, for instance, we take it today.

[00:06:29]Kip: Yeah. So Einstein, trying to sort this out,   imagine taking a star and shrinking it down  to a very small size, and he couldn't shrink   it down all the way to that radius. And he began  to believe that maybe everything below there was   in some sense fictitious. He just couldn't  understand what was going on. It's not that   Einstein was dumb. It was a real, real hard thing  that did subsequently take decades to sort out.

[00:07:03]Brian: And so as I recall, I think in the late 30s,   Einstein even wrote a paper where he tried to  specifically model a bunch of masses that would be   in some spherical configuration. They were moving,  and he tried to model them collapsing inward.

[00:07:22]Kip: Well, he moved   them in slowly. He didn't have the wherewithal, he  hadn't even asked the question about a dynamical   collapse. He said, let me shrink it smaller  and smaller. And once it got down to something   a little bit larger than this Schwarzschild  radius, he couldn't shrink it any farther,   and that was one of the key reasons that he was  skeptical about what was going on below there.  And it then required Robert Oppenheimer and  his student Hartland Snyder to actually,   for the first time, do a dynamical collapse  of a ball of dust down through that radius   and down to the Schwarzschild radius and then  change coordinate systems, change the actual   way the mathematics was being done and carry  it all the way down inside there and discover,   in Oppenheimer's own words, "We see that the star  shuts itself off from the rest of the universe."

[00:08:32]Brian: Cuts itself off.

[00:08:34]Kip: Cuts off. It cuts   itself off from the rest of the  universe, which we, in the modern time,   we recognize it has gone through the horizon  of a black hole. It's left behind the horizon   of the black hole, but that aspect of  it wasn't understood until the 1960s.

[00:08:50]Brian: Sure. Now in the Oppenheimer and Snyder work,   if I remember correctly, part of the way they made  a breakthrough was much like Schwarzschild, making   simplifying assumptions that somehow still capture  enough of the physics to give you real insight.

[00:09:09]Kip: This is really one   of the... I learned over the years the greatest  minds of, the physicists with the greatest minds   that I have met, and this included Oppenheimer,  it included Yakov Borisovich Zeldovich in Moscow,   they could somehow understand what simplifications  capture the correct physics without losing the   essential physics. Because most simplifications,  you may throw away the essential physics,   or you may not even be capturing correct physics,  but Oppenheimer and Snyder succeeded in this.

[00:09:56]Brian: And I guess part of their- Kip: In retrospect.

[00:09:58]Brian: Right. And part   of their assumption, I guess, was they  assumed there wasn't undue pressure within- Kip: Yes. So for   simplicity, they just assumed this was dust,  so there's no pressure at all. And of course,   skeptics then immediately said,  well, that's not how things work   in the real world. You put pressure in  and it's not going to keep shrinking.

[00:10:21]Brian: Right. They could say   that the very reason it's shrinking is because you  neglected the very thing that could push outward.

[00:10:28]Kip: That's right. But in fact,   it turned out that that's not the case. That once  you put the pressure in, this still happens. But   Oppenheimer and Snyder did not have the technical  know-how to put the pressure in and keep going.

[00:10:44]Brian: So what   did it require for people to get to that point?

[00:10:48]Kip: Well, I think what required, the key   thing that happened, I think, was the insights of  Roger Penrose for which he actually got the Nobel   Prize a few years ago, a half a century after he  did the work, more than half a century, in which   he introduced, he brought into physics a branch  of mathematics called differential topology, which   had the capability to prove theorems that were so  powerful that the theorems were correct whether   you had dust or whether you had pressure. And he  was able to prove that indeed you really, even   with pressure, that there would be circumstances  in which you would still form this horizon.

[00:11:38]Brian: And did   that convince the community at  that point, or was it still- Kip: Well, it was really quite interesting that   it ultimately convinced the community, but his  techniques were sufficiently alien to physicists.   They were familiar to some mathematicians,  but sufficiently alien to physicists that   it took a few years for the community to come  around, particularly the community in Moscow.  I had very close relationships with the Russian  physicists early in my career and was commuting   back and forth. So I knew these people. I  discussed that this happened before I came   on the scene. So what Yevgeny Lifshitz, one of the  great physicists of that era, said to me is, "Kip,   you cannot understand how alien to the human mind  this business of what Oppenheimer and Snyder saw   was, nor how alien to our minds the mathematics  that Roger Penrose was introducing because it   was just so different from what we were doing,  what we had ever done." And he basically said,   "It took us a while to really come around and  understand." A while meant three, four years.

[00:12:58]Brian: Right. But it is   funny how what's alien to one generation  just becomes the vernacular of the next.

[00:13:07]Kip: It's just common sense.

[00:13:09]Brian:  But part of what was alien too, I presume,  was there are two different narratives,   two different stories that you need to tell  if you're watching something fall to a black   hole versus the story that will be told by the  individual, unfortunately, who is passing into   the black hole. Can you just take us through  that because that's also deeply unfamiliar?

[00:13:34]Kip: Yeah. So I'll be the one that goes through it.

[00:13:39]Brian: Thank you.

[00:13:40]Kip: But if I fall into the black   hole or I ride on the surface of a star that's  shrinking to form a black hole and you're outside,   time for me, as you see time, my time slowing to  a halt, so you see me going to slow motion then   freeze right at the horizon because my time is  halted compared to the rate of flow of your time.  On the other hand from my point of view, time  just flows willy-nilly forward, and I go through   the horizon, and I keep on going. But once I'm  inside the horizon, time flows in what you would   have thought was a spatial direction toward the  center, which is why one reason I can't go back,   and I can't send signals back because nothing can  move backward against the local forward flow of   time. Now time travel might be possible,  but only by going out in space and coming   back before you started. You can't go backward  against the local flow of time. You just can't.  And so I go in, and I like to say inside the  black hole, there's a down cascading time.   Time is flowing inward. The technical phrase  is that the light cone is pointing inward. But   this is all invisible to you because you've  seen me go down. And as far as you're concerned,   I'm plastered on the horizon and frozen there,  except that the last photon I emitted to tell   you what was going on has long since reached  you, and there are no more photons because   photons are discreet. No more photons left  to communicate to you what happened to me.

[00:15:36]Brian: So there's   two things worthy of emphasis there. One, your  motion, as you described, once you pass the edge,   the horizon toward the center of the black  hole, locally is motion through time,   so it is as inevitable that you're going to go  toward the center as tomorrow becomes today.

[00:15:55]Kip: Absolutely.

[00:15:56]Brian: I mean, that's hard   to grasp in its own right. But the second thing  is how long or how do people reconcile these two   radically different pictures? I mean, we used to  say from special relativity, your clock is going   slow. My clock, we can get our minds around.  This one just seems so radically bizarre.

[00:16:17]Kip: Well, I think we generally do it by   finding a third point of view where everything  fits together in a beautifully elegant way.

[00:16:27]Brian: Like Finkelstein.

[00:16:28]Kip: Yeah,   so called Eddington-Finkelstein coordinate system.  And so you basically, if you adopt this idea that   space and time are unified, and you think in terms  of four dimensional space-time and its properties,   instead of thinking in terms of space  and time individually, then everything,   if you think about it for a little while and go  read some decent textbooks, modern textbooks,   it just becomes natural. It's obvious.  It's beautiful. It's elegant, and it's   a marvel to behold and fits beautifully.  There's no paradoxes, no problem at all.

[00:17:19]Brian: Right, with the two stories.

[00:17:21]Kip: With the two stories.

[00:17:22]Brian: But there is still a problem   that remains about what actually happens right at  that center point, that end of the time journey.

[00:17:31]Kip: Down in   the center there is a singularity, again, in  the Schwarzschild solution, where we say the   curvature of space-time goes to infinity, that  the strength of gravity truly goes to infinity   in any kind of a measure that you might try to  introduce to measure the strength of gravity.   And this is also something that Roger Penrose  basically predicted. His theorem said something   goes wrong because anything that falls in there  can no longer exist. It basically proves using   his topological techniques. But again, it then  took quite a while after that to really sort   out what was going on. And it turns out that that  singularity in there is unstable, and that's not   really what you wind up with. That when stuff  falls into it, it changes its whole character.  So by contrast with the horizon of a  black hole, which is highly stable,   you perturb it and it vibrates a bit and then  settles back down. It's just so stable. You can't   blast it apart. By the contrast, what's going  on down beneath there is highly unstable. And   when stuff falls in, the gravity of the  stuff that falls in completely changes   what's going on down inside the black hole. So as best we understand it today, and this is   part of the backstory of the movie Interstellar,  I know you don't want to talk about that yet.

[00:19:17]Brian: But we will get there, for sure.

[00:19:18]Kip: But there are three singularities   in there, as far as we can best tell. Three  regions with three different characters   where Einstein's general relativity theory  completely fails and you've got to replace   it with a... And it completely fails in a way  that isn't intimately entwined with the laws of   quantum gravity, and the loss of quantum gravity  take over and govern whatever happens in there.   But so three regions with a weird breakdown  in the loss of physics as we know them. So   it was a much richer interior to a black  hole than we ever knew a few decades ago.

[00:20:03]Brian: And so   if you go back to Einstein's hesitation,  and this may not be historically accurate,   but if you imagine that part of the dominant  hesitation was the fact that the curvature   goes haywire at the true center of the  black hole, you can't fault him for- Kip: Oh no,   not at all. And this is also a very interesting  story between two of my Princeton colleagues,   Robert Oppenheimer and John Wheeler. John Wheeler  looks at the Oppenheimer-Snyder analysis and says,   "You've got a singularity at the center.  There's something wrong with your analysis.   And when there's a singularity, all bets  are off. I don't believe your analysis   because that singularity is a signal that  we've got to rethink the whole thing."

[00:20:56]Brian: Right.

[00:20:56]Kip: And Oppenheimer says,   and there's a big confrontation between  the two of them, at what's called a Solvay   Congress in '56 or '57, in which Oppenheimer  says, "Well, it's very simple. It just cuts us   off from... The collapsing star cuts itself  off from the rest of the universe and what   happens down inside there has no influence  on the external universe, so why worry?"  And so they have this radically different  viewpoint. And in fact, sorting out what   happens with the singularity turns out to  be absolutely crucial for modern physics.

[00:21:41]Brian: Sure.

[00:21:41]Kip: And John Wheeler is quite correct.   And Oppenheimer is also quite correct that it has  no influence on what's going on on the outside.

[00:21:51]Brian: Right. Now,   John Wheeler, if I, again please correct me,  but he posited the possibility that there would   be quantum processes at the center that would  generate outward streaming radiation carrying   away enough mass and energy to avoid the formation  of the black hole itself. Wasn't that his vision?

[00:22:14]Kip: Yeah, that   was his vision, and that was what he was  pushing when I was his graduate student.   That's what he was pushing when we were writing  a book together called Gravitation Theory and   Gravitational Collapse. And that's where  I told him, "We can't put this in there."

[00:22:28]Brian: Oh, really?

[00:22:29]Kip: "We can't   put this in our book. It can't be right." And- Brian: And what did he say?

[00:22:35]Kip: Well, he argued with me. And so I went and got all   the big guns that I could find among his former  students and postdocs and colleagues to lean   on him. And finally, he gave in, and it does not  appear in there. It appears in his other writings,   but in our little book that we did together, it's  not in there. And I forever regret this because- Brian: Radiation, yeah.

[00:23:02]Kip:...John Wheeler had tremendous physical insight,   and he didn't have the whole story correct, but  he was basically intuiting Hawking radiation,   which as we now understand it comes... And  one of the deepest way to understand Hawking   radiation was one that Steven Hawking and his  colleague, James Hartle, worked out in which   there actually is a connection to the singularity  inside that gives rise to the Hawking radiation.

[00:23:42]Brian: But that's interesting because   the Hawking radiation as I... And maybe you're  going to enlighten me in ways that... Usually   we describe it as pair production, the event  horizon of a black hole, one particle falls in,   the other strings away and so forth. And it's  the disconnection between that process and the   center that sets up the so-called information  problem. They were describing more of a link?

[00:24:07]Kip: If you want to really   prove that you're right on Hawking radiation,  you got a problem because the Hawking radiation   is basically triggered by, in Hawking's  original calculation, vacuum fluctuations,   just fluctuations of electron positron pairs  fluctuating in and out of existence of photons.   They flow onto the star, onto the black hole  when the black hole is being born, and they suck   energy out of the expanding space as the black  hole is born. And all that radiation is created   just above the horizon as the black hole is born,  and then it takes millions of years to leak out.  But there's a real problem that the  stuff that leaks out a million years   later. It has humongously high energy at the  beginning, far, far beyond where the laws of   quantum gravity have any right to. And so  it was Hartle and Hawking that went in,   and they did a very different calculation in which  they basically turned time into imaginary time.

[00:25:21]Brian: Sure.

[00:25:22]Kip: And then so they were   setting up a different way of thinking about it.  But in this different way of thinking about it,   a key role is played by the singularity at the  center. They're basically having virtual particles   that go in and out of the singularity at the  center. Virtual particle can go faster than the   speed of light. There's no information flow. But that analysis was the thing that finally   I think got people who were highly  skeptical to throw in the towel and say,   okay, you don't have to pause it, pretend to  think that this Hawking radiation forms with   humongously high energies and then waits a  million years trying to climb out with its   energy decaying lower and lower and lower until  it finally comes out, which feels like nonsense.  So there was this period that was in the '70s,  when this was all being sorted out, that when the   tools that were used to sort it out were closely  related to John Wheeler's in 1950s and '60s   viewpoint on Oppenheimer that I did everything  I could to prevent John from publicizing it.

[00:26:55]Brian: And so   did John ever say, "Hey, Kip. I  wish we would've included that?"

[00:27:05]Kip: No, no, no. No, but by contrast, because   of this idea, he was totally skeptical about black  holes. He was totally skeptical about Oppenheimer   and Snyder until work by a student of Charlie  Misner, by Beckedorff, who did a different way   of analyzing Oppenheimer and Snyder's work that  suddenly made it obvious that this made sense.  And this was 1962. Quasars are discovered in '63.  There's a big Texas symposium on relativistic   astrophysics in '63 where people are struggling  to understand quasars. And John Wheeler gives   a talk about gravitational collapse, and that  and the formation of a black hole as being what   really is ultimately behind powering quasars. And John views this as his public apology to   Oppenheimer because he's now saying Oppenheimer is  right, and you really do form a black hole. He's   not using the word black hole yet. But Oppenheimer  sits out in the hall at that meeting. He doesn't   deign to go into Wheeler's. There's been enough  bad blood over the years between the two of them.

[00:28:43]Brian: Oh, he skipped the talk.

[00:28:45]Kip: He skipped the talk.

[00:28:45]Brian: Really?

[00:28:46]Kip: And Wheeler comes in. I was there.   I was with Wheeler. Wheeler comes out and sees  that Oppenheimer's out in the hall and he wilts.

[00:28:55]Brian: Yeah, I can imagine.

[00:28:56]Kip: His   apology and Oppenheimer didn't... And so it was a  momentous moment in the history of science that,   of miscommunication between these two great men.

[00:29:13]Brian: And was   it an arrogance on Oppenheimer's or just a- Kip: No, no.

[00:29:19]Brian:...feeling bad?

[00:29:20]Kip: I don't think so.

[00:29:20]Brian: Or what do you think the emotion was?

[00:29:22]Kip: I think he   was just... I don't know. I didn't know. I  knew Wheeler better than I knew Oppenheimer.   Certainly Oppenheimer is capable of arrogance,  but I don't think so. It's more my impression   that it's just that he had had it with these  arguments with Wheeler, but I don't know.

[00:29:41]Brian: Right, right. Just fed up a little bit.

[00:29:42]Kip: Yeah.

[00:29:43]Brian: Now you said that,   excuse me, Wheeler wasn't yet using  the term black hole. Ultimately,   he does. He's actually credited in some  stories as having named them. Is that correct?

[00:29:54]Kip: Well,   the phrase black hole was used by others earlier  in this context, but Wheeler was unaware of it,   and it didn't catch on. And Wheeler introduced it  in 1968, as I recall, in an article that he wrote.   And he doesn't say, "Let's call it a black  hole." It's vintage Wheeler. He just writes   it as though we had always called it a black  hole, and suddenly people, everybody does.

[00:30:31]Brian: Now, I heard a   story that there was a conference on 112th Street  and Broadway at the Goddard Institute for Space- Kip: Well, I was there.

[00:30:39]Brian: Oh, you were there?

[00:30:40]Kip: I was there, yeah.

[00:30:41]Brian: And the story that   I heard was that somebody in the audience, as John   Wheeler's talking about these objects  says, "Oh, that's like a black hole."

[00:30:48]Kip: So I don't remember that. I was there.

[00:30:50]Brian: Ah.

[00:30:51]Kip: I've heard the story,   and that may be, but certainly  it didn't stick at that time. And   I don't think it probably had any  influence on Wheeler at that time.

[00:31:01]Brian: I see. I see.

[00:31:01]Kip: This is- Kip: The influence on Wheeler at that time.

[00:31:01]Brian: I see. I see.

[00:31:02]Kip: This was probably '67,   I think. I think it was a year before John started  using the phrase. John understood the power of   words. He spent a lot of time crafting phrases  and words to describe things. As he described   it to me, he liked to lie in a warm bathtub, and  just think about what is the right phrase to use.  Now, it could be that he was triggered  by that a year or so earlier,   and didn't remember it at all, but in the  back of his subconscious, remembered it.

[00:31:49]Brian: What was it like then   working with John Wheeler who cares so much about  language and words on a book that winds up being,   I don't know, 1,200 pages dense with  words, pictures, equations, and so forth.

[00:32:03]Kip: The second thickest books I ever wrote.

[00:32:06]Brian: Yes.

[00:32:07]Kip: No, that was a   real pleasure. That was an enormous pleasure. This  book, Gravitation, was a textbook on relativity.   We finished it in 1973, and published it in '73.  We began at about '68. It took about five years.  When we began it, general relativity was truly  and had been for the preceding several decades,   more a province of mathematicians than a  physicist. John felt, and I certainly agreed,   as did Charlie Misner, that there was an  issue that mathematicians is great and   the mathematics is crucial, but that you  really need physical intuition as a tool,   if you're going to make rapid progress.  Calculations can be slow, tedious,   and complicated. You've got to be able  to decide what's worth calculating.  You develop physical intuition as a tool  for making those decisions of what's worth   calculating. Then you intuit something, then you  go in and do a calculation, you see whether you're   right or not, and you get the details right.  The foundation for physical intuition, for John,   for me, and for Stephen Hawking, was pictures,  mental pictures or diagrams that you draw, as   well as words that go along with those pictures. The ratio of words and pictures to equations in   that book has absolutely never been seen before  in any relativity textbooks. It's a book that is   designed to try to teach physical intuition  to a new generation of physicists who are   just beginning to get interested in relativity  because quasars and pulsars have recently been   discovered in the cosmic microwave background.  Suddenly, it's relevant to the astronomical world.  We need to build a generation that  thinks physically. That's what the   purpose of the book was. Bill Press, who  was a student of mine at the time... Brian: He was my advisor   when I was an undergraduate at Harvard.

[00:34:53]Kip: Okay.

[00:34:53]Brian: Look at that.

[00:34:54]Kip: You're my grandson.

[00:35:00]Brian: Grandpa!

[00:35:01]Kip: Bill comes in. We've just   distributed to the people in my research  group a draft of a chapter from this book.   The chapter has a dialogue between [inaudible  00:35:16] and Segridas about what is a black   hole. It is very much a Wheelarian thing. Bill slaps that down on my desk and says,   "Why the hell did you let John Wheeler write  something like this in your book?" I said,   "With great pride, I wrote that. I'm  capable of writing in Wheelerian style."

[00:35:38]Brian: Fantastic.

[00:35:39]Kip: I agree   with John. That we need to be building up  physical intuition, and this is part of it.

[00:35:45]Brian: Absolutely.

[00:35:45]Kip: That   was one of the joys of working with John Wheeler.

[00:35:50]Brian: Now, one thing in   that book, which is interesting to me is  that when physicists typically learn the   mathematical methods of general relativity,  differential geometry to be concrete,   most physicists learn it in a so called  coordinate form, which is the more nuts and   bolts ingredients necessary to really carry out  certain kinds of calculations. You're at great   pains in that book to do both the coordinate  version, and the coordinate-free version,   which is perhaps maybe the way more mathematicians  think about things in a more global perspective.   It's powerful to have both. But was this  your bread and butter or did you and John,   did you need to study to learn that stuff or  was it already how you were thinking about this?

[00:36:39]Kip: That was the way Charlie Misner was thinking.   Charlie was very, very deep in the mathematics.  John was an enthusiast for mathematics.   He was capable of doing deep mathematics.  Let me just tell you a little side story.

[00:36:58]Brian: Please.

[00:36:59]Kip: One day,   John had a reputation in my era, and going back  a decade or two, for not doing much mathematics,   for a reputation for functioning on physical  intuition. One day, I was sitting at Caltech in   a party with Richard Feynman who had been John's  student several decades before me. We were both   a little inebriated. He was reminiscing. He said, "Yes, I remember when Professor   Wheeler," he always called him Professor  Wheeler. I called him Johnny. Feynman says,   "I remember one day Professor Wheeler and I were  doing a calculation together. Professor Wheeler   went from this step to that step. I didn't see  how he got there. He showed me. As he'd showed me,   he said, 'Little steps for little people.'" Now, John Wheeler was the most polite person   I ever knew. I never saw him do anything impolite  like that. Now, it's clear that Feynman was full   of himself as a graduate student. Wheeler felt  that he needed to be taken down a notch or two.

[00:38:16]Brian: Wow.

[00:38:17]Kip: Wheeler did. But   the fact that he could was an indication that he  really himself was quite deep in the mathematics.

[00:38:26]Brian: That is so interesting.

[00:38:28]Kip: He could outthink Feynman. Of course,   he had more a number of years behind him.  Feynman was just getting started. But still... Brian: But Feynman is... Kip: Feynman is phenomenal.

[00:38:39]Brian: If I can just give   one story that you may be familiar with too.  I was taking quantum field theory with Sidney   Coleman. Sidney Coleman, I think this was an act  that he did every year that he talked quantum   field through. I don't think it was spontaneous. But he put up some problem on the board. He said,   "Let me first show you how Feynman would solve  it." He turns dramatically to the board, puts his   hand on his head, and then writes down the answer. He said, "Feynman, he can just do all those   calculations in his head. We, little  people, have to do step by step."  For Wheeler to play the same on  Feynman is sort of astounding.

[00:39:17]Kip: It is   astounding. But it really showed. Feynman  still remembered this with chagrin.

[00:39:24]Brian: Wow.

[00:39:25]Kip: It showed what he   was capable of. Back when we were writing the book  together, he was embracing what for physicists was   new mathematics. But coordinate-free notations,  thinking about things without coordinate systems,   which is part and parcel of the unification  of space and time that was central to really   understanding what goes on inside black holes. Wheeler was enthusiastic about it. He was   embracing it. Charlie Misner was much deeper than  either of the two of us in the mathematics. I was   learning it from the two of them. I brought  to this an understanding of the astrophysics,   but not the kind of depth in  mathematics that the other two.

[00:40:13]Brian: Yeah, what a wonderful   experience though to be learning, contributing,  and creating something timeless as that book.  Now, one of the other things that I  deeply appreciated about that book   is you had track one and track two. Track  one was for maybe the beginner. Track two,   the person wants to go more deeply, which  is a great structure. From that point on,   when I read your book, for years when I  would give a technical lecture, I would do,   here are the track one slides, here are the track  two slides, and try to appeal to a broader group   of individuals who could follow the ideas. But  perhaps maybe not the mathematics, which I think   is a powerful way of going about it. But back to black holes then. By what   era would you say the community  had pretty much been convinced,   through all of the things that we've discussed  historically, that these things should be real?

[00:41:13]Kip: I think depends on which community.   There were people like Phil Morrison at MIT,  very highly respected, a superb astrophysicist   who never, ever embraced black holes. After  they died, the community was convinced.

[00:41:36]Brian:  Is that the famous adage that physics  progresses one funeral at a time kind of thing?

[00:41:41]Kip:  I hadn't heard that one, but yes. But certainly the younger generation,   the people who were learning stuff and  thinking stuff through, my generation   had all embraced this, and had, I think, a very  clear understanding by the early to mid 1970s.   It took some of the older generation another few  years beyond that. But certainly by the 1980s,   it was pretty universal except for a very small  number of people who hung off on till death.

[00:42:27]Brian: Psychologically, for those who were   convinced, were they waiting for observational  confirmation or it was just a foregone conclusion?

[00:42:35]Kip: The observations were coming in on things related   to black holes. There were a number of black  hole candidates in the sky. The gravitational   waves didn't come along until decades later. But  electromagnetic observations, we were learning   about the cosmic microwave background, and we  were learning about black holes through quasars,   pulsars, and jets sticking out of galactic  nuclei, and so forth. That the theories that were   being developed and the models that were being  developed were by 1980s were pretty much right on.

[00:43:21]Brian: For instance,   additional data that ultimately was awarded the  Nobel Prize, observations of stellar trajectories   in the center of our galaxy, was that viewed  as just adding to the mountain of evidence?

[00:43:40]Kip: I think there was   always a worry, I would say, a worry of hope  that there was something wrong. I saw over my   career some huge surprises where we were wrong.  For example, the acceleration of the universe,   which I didn't believe until there were several  very different pieces of data that insisted the   universe was accelerating its expansion. I saw things like that, that were sacred   to me. It was just obvious that there was  no acceleration of the universe. We really   did understand that the cosmology of the  early universe, and my nose was rubbed in   it. That has associated with it, huge potential  surprises that we still haven't sorted out. I'm   always hoping that something will similarly  be wrong with black holes. There's something   going on at the horizon. We've got it wrong. Going all the way up to the present time,   I'm certainly a strong advocate of going in  and really pushing the observation really   hard to be sure that we're right, and hope that  we're wrong because it'll lead to a revolution.

[00:45:08]Brian: The Event   Horizon Telescope, the images when  you first saw those, what was that?

[00:45:14]Kip: They were fabulous,   just to see it, just to see it. But for me, the  key thing there is to see movies. There has been   various skepticism and complicated plasma physics  arguments over how the jets are launched from the   vicinity of a black hole, as we see jets sticking  out of black holes. How are they launched?  There are very interesting and probably correct  theories and models related to it. I began with   the so called Blandford-Znajek effect. But there  are skeptics in the plasma physics community.   I can't be absolutely sure that  skeptics are wrong. I want to see   a movie of the launching of these jets. That's what I think we will ultimately   get from the Event Horizon Telescope. I'm just  waiting for them to come out with movies now,   not of the black hole in M87. Because  that's such a humongously big black hole.

[00:46:43]Brian: Timescales.

[00:46:43]Kip: Movie's just too long a timescale.   But the black hole in the center of our galaxy. That is technically very, very difficult. But   that's where the really exciting payoff  from the Event Horizon Telescope is going   to come. It could come most anytime. I  don't know precisely where they stand.

[00:47:03]Brian: Yeah. I've   had conversations on occasion with Shep  Doeleman. Movies has certainly been the   top next step. But timescale, I don't know.  But it's interesting that you're still open   to the possibility that our understanding may  need to be fine-tuned or changed in some way.

[00:47:23]Kip:  It may be much more than fine-tuned. As I say,  I've seen several huge surprises. I have come   to believe that there are situations where we're  not as smart as we think we are, and where we're   quite sure of things that will turn out to be  wrong. You take any given thing. I look at it, and   say the odds that were wrong there are pretty damn  small, but we're going to be wrong somewhere among   things that we hold near and dear to ourselves.  We should work very hard to search for a failure.

[00:48:06]Brian: By any chance, there is a   proposal in string theory. I don't know if you're  familiar with the Fuzzball proposal, Samir Mathur,   Ohio State University. This idea that maybe  black holes are not the thing that we've long   thought there. Maybe they're closer to an entity.  It could be a agglomeration of strings and other   membrane-like objects within string theory. He finds it can mimic the features of a black   hole, but if you really got in, and  looked at it with adequate resolution,   it wouldn't be what Schwarzschild wrote down  per se. Is that a thing that you can imagine?

[00:48:46]Kip: Now, I don't know much about that. I do know other   speculations about what goes on at the horizon.  Let me just make a remark about string theory.

[00:48:57]Brian: Uh-oh.

[00:48:59]Kip: No, I think that   string theory and the laws of quantum gravity  are the most important and the most interesting   area of physics. They have been for several  decades. They will be for a few more decades.  I haven't touched them with a 10-foot pole  because I need elbow room. I'm not happy if   I'm working in a community where there are huge  numbers of people working. They're all really   smart. My mind works slower than any of theirs  do. I need elbow room. I've stayed clear of that.  But I admire you and your colleagues  who do this. I follow what goes on   at sort of a semi-popular level,  and keep hoping for big surprises.

[00:49:49]Brian: Sure. Yeah. No,   we are hoping too. Yeah, it goes both ways. When  you do have a lot of people working so closely,   we find that things do go in fads. An idea catches  on. It spreads through the community through no   other reason than excitement and wanting to make  progress, which weirdly online you do have these   people having conspiracy theories about how  we're trying to shut out every... It's not.   It's excitement. It is a group of individuals  that do work closely. The elbows are touching,   as you're saying. That's sort of a good  thing and a bad thing about it all.  But with that, maybe we could turn to the next  arena in which you've had a tremendous impact,   which is gravitational wave physics.  We can't go as far back, I don't think,   as John Mitchell or Laplace or anybody here.  But we can go back to Einstein in 1916, 1918.  He writes a couple of papers that suggest this  possibility, but he himself, I don't know,   is a little confused. It goes back to  coordinates, and how to really determine   what's real in your mathematics. Maybe you can  just give us a sense of what that story is.

[00:51:03]Kip: Yeah. Yeah. Einstein, 1916,   he formulates his general relativity theory in  1915. He writes his first paper on gravitational   waves in 1916. He's pretty confused in that  paper. He recognizes it rather quickly. Basically,   in some sense retracts it, does it write aside  from maybe a factor to run formula in 1918.  But at that point, I think it's my  impression that he really believes   in these as physical gravitational waves.  But there is a lot of confusion over that.   He has moments later on when he has  misgivings, but I think they're only moments.

[00:51:50]Brian: Oh, really?

[00:51:51]Kip: That's certainly my impression.

[00:51:52]Brian: Yeah. I got the impression   that he was a little more skeptical, but  I haven't really delved into it in detail.

[00:51:57]Kip: Certainly, that's my   impression that there are moment, a month  or two, when he's having some cold feet.  The central thing was how do you describe  the gravitational waves in a way that is   absolutely clear physically, that it has a  physical reality. This ultimately comes from   something called the equation of geodesic  deviation that is formulated around 1956,   '57, '58, by Felix Pirani in London. He identifies something called the Riemann   curvature tensor as the thing that stretches  and squeezes. He says, "If you begin with   two particles, and they're running alongside  by side with a fixed distance between them,   then this Riemann curvature tensor,"  which has nothing to do with coordinates,   it is a true geometric object, and everybody  agrees on that, "That it actually squeezes and   stretches the space between the particles. They  move back and forth relative to each other."  But it's only then. I think he publishes  it in '58. He has it in '57 or '56. He   talks about it at a famous conference on general  relativity in Chapel Hill, North Carolina in '57,   and then publishes it the year later. But  it then becomes the foundation for Feynman,   Herman Bondi, and others to start thinking  about this in a totally physical sort of a way.

[00:53:50]Brian: Then people, at least one   person starts to think seriously in those older  times about detecting these, way before LIGO.

[00:54:01]Kip: This is Joseph Weber. Weber,   he has already just before this, he in some ways  is a disciple of John Wheeler. He is a professor   of electrical engineering at the University  of Maryland. But he's interested in gravity   and gravitational waves. He goes with Wheeler to  Leiden when Wheeler has a sabbatical in Leiden,   Netherlands. They're there, so is Charlie Misner,  and a few other people around Wheeler. They're   thinking about gravitational waves together. We have no evidence that he's thinking about any   detection methods in Leiden yet, though he might  have been. But there's no evidence of it. A few   months after Leiden, is this conference in Chapel  Hill where Wheeler and Weber together present the   analysis of gravitational waves, but not with of  an experiment, but a mathematical analysis that   emphasizes the physical reality of the waves. Then it's immediately after that, that he is   thinking about gravity wave detection. That  we have evidence he's thinking about it. '57,   '58, he's beginning. He even writes a little  textbook of his own on general relativity.

[00:55:30]Brian: Really?

[00:55:30]Kip: That is a nice little textbook,   unconventional approach, but one in which it's  clear that he's thinking about it from a point   of view of experiment, and building things that  will measure the stretch and squeeze of space.  He then actually starts to put together an  instrument in gravitational waves, and works   on this until '69. In spring of 1969, there's  a conference in Cincinnati, Ohio, at which he   announces evidence for having seeing gravitational  waves with his instrument, which is a large   cylinder. The equator of the cylinder is amounted  crystals called piezoelectric transducers,   which when they're squeezed ever so slightly,  they develop a voltage across them. Then he's   instrumented to see this voltage as this twistal  squeezed back and forth by a gravitational wave.

[00:56:38]Brian: It's very clever.

[00:56:38]Kip: It's a very   clever. It's clever to the point that other people  keep pushing on that particular technology until   we and LIGO have better sensitivity than  they do. But that's not until about 2006,   2007. This technology that he invents, that he  conceives, keeps getting pushed by some very good   experimental physicists from then in the '60s  all the way up to 2006. 40 years, basically.

[00:57:16]Brian: Wow. Just to give people a sense of the   challenge, what sort of squeezing and stretching  would they need to be able to detect that?

[00:57:23]Kip: They were   hoping that if they stretched and squeezed a bar  that's a meter long, that by an amount that is,   say, a sizeable fraction of the nucleus  of an atom, that that would be enough.  We know today, it was not enough. That you  need something that is quite a bit smaller   than that. But that was where he was headed.  It was astounding that he could do, as well,   as he actually did. But it wasn't nearly enough.  In retrospect, we know it wasn't nearly enough.

[00:58:08]Brian: Was he   ever convinced that he had not  detected gravitational waves?

[00:58:13]Kip: No, I think he wasn't in the end up until   his death. He believed, after Charlie's death,  "Nobody has precisely replicated my experiment.   I'm seeing something. I don't know for sure it's  gravitational waves, but I'm seeing something.   Nobody has precisely replicated what I've done.  We really need to sort out what it is I'm seeing."

[00:58:39]Brian:  You're convinced though that  he was not in no way... Kip: Yeah.

[00:58:44]Brian: Yeah. When was... Kip: It took a few years to get   to the point where I was convinced that he wasn't  seeing them. Negative experiments by a number of   different groups, I was hopeful that it was fairly  quick that I began to think he probably wasn't.

[00:59:10]Brian: Were you   rooting for him or did you want it not  to be so the field would still be... Kip: I was absolutely   rooting for him, absolutely rooting for him.

[00:59:18]Brian: Okay. Then   where did the idea of a new technology  that ultimately succeed it come from?

[00:59:23]Kip: The new technology was that you have mirrors   that hang from overhead supports. You have laser  beam bouncing back and forth between the mirrors.   You use a technique called laser interferometry  to monitor the motion of the mirrors.  That idea was first conceived by Mikhail  Gertzenstein and Vladislav Pustovoit in Moscow   just a few years before I started developing my  close collaboration with the physicists in Moscow.   I knew them well. They were theorists. They didn't  really understand the noise sources that this   instrument would face. They just had the idea.  They had the idea clearly before anyone else did.  The idea was fairly obvious once you  began to think about it. It was in the   air. But it was Ray Weiss at MIT who had the idea  completely independently in the mid to late '60s,   who then carried out, after doing  some experimental work to see   various things like whether he could get  a laser down to its so called shot noise   level and some things that would be required. He wrote a technical paper in 1972 in which he   described this radio detector. He analyzed, he  identified all the major sources of noise that   it would face. For each major source of noise,  he conceived a way to deal with it. He then   analyzed how far down he could push that noise  source by the method he conceived of doing it.  He concluded then that if he were to make this  instrument a few kilometers long, he might have   a shot at seeing gravitational waves. This paper,  interestingly, it's an absolutely classic paper.   It's the most prescient paper in this field  that was ever written as far as I can see in... Kip:... field that was ever written as   far as I can see, the most important paper really.  He didn't publish it in a journal. He published   it in an internal progress report series at MIT  'cause he thought you shouldn't publish it until   you've actually built the detector, maybe  seen gravitational waves. This is Ray.

[01:02:20]Brian: Right. Yeah, yeah, yeah.

[01:02:20]Kip: Who became   one of my dearest friends. But he sent  this out to colleagues. And so I got a   copy, he sent it to me. It was [inaudible  01:02:35] at the time that I was... I had   been thinking about gravitational waves and  their detection, and what you could do with   gravitational waves for astronomy for a few  years. And Bill Preston and I had just written,   or were just finishing our first paper on  a vision for gravitational wave astronomy.  And so this thing comes in from Ray Weiss,  and I look at it cursorily, quickly. And   I am at the same time, we are about to send to the  publisher the manuscript of our book, Gravitation,   with Charlie Misner and John Wheeler. I look at  it and it just seems to me crazy to think that   it could succeed. And so in this manuscript that's  about to go to press, I write a brief description   of this technique. And then it's an exercise for  the reader to explain why it's not very promising.  Our book goes off to press. And then on and off  over a period of about three or four years, I keep   thinking about this. I have long conversations  with Ray Weiss. I have long conversations with   Vladimir Braginsky in Moscow, and I gradually  become convinced that it has a shot at succeeding.

[01:03:58]Brian: But a shot at succeeding, it's still audacious.

[01:04:02]Kip: Well, it's going to   be very difficult. But by 1976, I guess it is,  by autumn of '76, I think November of '76, I'm   convinced it has a good enough possibility of  success that because the payoff would be so   enormous if it does succeed, that I decide  Caltech ought to get into this business.

[01:04:33]Brian: Now when you say the payoff, I guess   there's two ways to look at it. One is you're  confirming a prediction of general relativity- Kip: Big deal.

[01:04:42]Brian: Or you're opening a new...   That's what I'm wondering. Was that the driver  or was it opening a new window of astronomy?

[01:04:46]Kip: Totally opening a new window of astronomy.

[01:04:47]Brian: Okay.

[01:04:47]Kip: It was to just   confirm the existence of gravitational waves,  what was going to be several decades of work   and enormous effort. I was going to spend  most of my career and that of my students.

[01:05:07]Brian: But what   about Ray Weiss? Was it similar vision to yours?

[01:05:10]Kip: It was a similar vision. Similar vision.   The driving issue was to create gravitational  astronomy. The issue was that Galileo,   400 years earlier, had built a little optical  telescope, pointed it at Jupiter, seen Jupiter's   four largest moons, and initiated instrument-based  electromagnetic astronomy. Which blossomed and   revolutionized our understanding of the universe. There's only one other kind of wave that we knew   about at the time and that we know about today  that could be created in the distant universe   and bring us information about what's far away,  and that's gravitational wave. And so, the vision   was to do for gravitational waves what Galileo  did. And over periods of decades to centuries,   that will revolutionize our  understanding of the universe.

[01:06:05]Brian: That certainly is motivation, framing it that way.

[01:06:08]Kip: And so   that was truly the motivation, but it  was going to be very difficult. And so,   when I could see that we had a reasonable  shot at success, better than a 50/50 chance,   I then wrote a document proposing that Caltech get  into this game. Gave it to the chair of Physics,   Math and Astronomy at Caltech. At the time it  was Martin Schmidt, who was the discoverer of   Quasars. And Martin and I had discussed it before,  he said, "You write it up." I wrote it up. And he   appointed a committee of Caltech physicists,  and one radio astronomer who were deep in the   relevant physics of these instruments, to look at  this proposal in depth and make a recommendation.

[01:07:16]Brian: And there were some skeptics.

[01:07:18]Kip: Oh, yeah. There were skeptics on the committee.

[01:07:20]Brian: Was Dick Garwin part of that?

[01:07:22]Kip: This a later   thing. This is '68 at NSF. I mean, that was '76  at NSF. This is 60s... Just a minute. I confused   my decades. This is '76, and that is '86, Garwin. And so this is at Caltech. And this is at a time   when NSF is invested in Ray Weiss, I think  $56,000. That's the total amount of money   he's gotten from NSF, and total amount of money  he will get in the 1970s. And when MIT won't   give him the time of day. And so there's  just, everywhere there's skepticism. And   I couldn't fault the skeptics because I had been  skeptical for four years. But, I had come around.  And so this committee is appointed. We as  a committee, it includes Barry Barish who   becomes the key director [inaudible 01:08:47].  But, the committee then talks to everybody who's   working in this field, and a lot of other people  who have knowledge about the technology. And,   after a year decides we should go into the  field. Spends a year trying to identify   who we might bring to Caltech to help start it,  identifies Ronald Drever in Glasgow, Scotland. And   our recommendation gets enthusiastically  endorsed by the Physics, Math, and Astronomy   faculty and by the Caltech administration. I even do presentations of the board of trustees,   though they don't have to embrace  it. They don't make a decision.  And so, it's embraced at Caltech. And Murph  Goldberger, who's the new president of Caltech,   he phones up Bob Dickey back at Princeton and  says... That's where Murph comes from. He says,   "What do you think of this?" Well, Ray Weiss had  been Dickey's postdoc, and I had been a graduate   student in Dickey's group, although I did my  thesis with John Wheeler. Dickey is the great   experimental physicist in relativity of that  era. And he gives it his enthusiastic blessing.  He knows Ray, he knows me, and he knows  the field. As a result, Goldberger says,   "Okay, we will invest what we need to  get this started." And that turns out to   be that he forks over $2 million of Caltech  money, which inflates to $14 million today.

[01:10:26]Brian: $14 million in today's dollars. Wow.

[01:10:29]Kip: To get it   started. At a time when NSF has invested  56,000, and MIT has invested zero.

[01:10:37]Brian: So that's a bold, bold... Kip: It's a very bold move,   but Caltech's a unique institution. It's  small, it's intimate, and it's a place where   you can make things happen. The relationship  between the trustees and the faculty and the   administration is very strong, and the trustees  are the sources of startup money like this.

[01:11:03]Brian: Was there   any outcry? "How can you put  that much money into this?" No.

[01:11:08]Kip: No, this had been embraced by the PMA faculty.

[01:11:12]Brian: Yeah.

[01:11:13]Kip: And Murph   Goldberger is a physicist. He got  the blessing from Bob Dickey. No.

[01:11:21]Brian: And so, off you go.

[01:11:24]Kip: Off, we're- Brian: Running there.

[01:11:24]Kip: NSF sees   this and says, "Well, we'll do our own  study." And they do their own study,   quickly over a period of about four months.  And come up with the same conclusion. They   start investing money both in Caltech  and in MIT. And we're off and running.

[01:11:44]Brian: And so what's the first thing you do when you... Kip: Well,   so Caltech starts building with Ron Drever,  whom we have hired, brings Stan Whitcomb   from Chicago. Ron is commuting back and  forth between Caltech and MIT. Stan is   a superb experimental physicist who becomes  ultimately, effectively the chief scientist,   although he didn't carry that time, he was at  various times, deputy director, acting director   of LIGO. But he's just absolutely superb, and  he really makes things happen in the laboratory.

[01:12:18]Brian: And is MIT   and Caltech sort of in partnership now in this?

[01:12:22]Kip: Well, not yet. But R&D is now underway vigorously   at MIT with a 1.5 meter prototype, at Caltech  with a 40 meter prototype. In Glasgow, Scotland,   a 10 meter prototype. That's Ron Drever's group,  and he's commuting back and forth. And in the Max   Planck Institutes originally in Munich and then in  Garking, they moved to Garking, they built a three   meter prototype, then a 30 meter prototype. And these four groups interacting with each   other are pushing hard to... And what we  know is we have to... I know approximately   how strong the waves are. And it's clear  to me already by 1978, and I was trying- Brian: Well, what were you assuming the source   at that... Did it matter, or you're  just saying [inaudible 01:13:17].

[01:13:17]Kip: No. Well, by '78,   it was black holes and neutron stars.

[01:13:23]Brian: You've already   concluded that that's [inaudible 01:13:26].

[01:13:25]Kip: That's right. And I had zeroed in. I knew, my best   guess was right on, 10 to the minus 21 strain.  With an uncertainty that was pretty clear by 1992,   about a factor of 100, between 10 to minus 20,  10 to minus 22, which becomes important later.

[01:13:48]Brian: Sure.

[01:13:50]Kip: And so,   we know where we're going. And we know where we're  beginning. And we have to improve our displacement   noise on the mirrors by a factor of a million. And the team by 1986, after about 10 years of   effort, has gotten a factor of a thousand. So in  logarithmic scale, they're about halfway there.   So the prototype work is going  pretty well. Our colleagues have- Brian: Is logarithmic   the way to think about it psychologically?

[01:14:34]Kip: Yeah, yeah.

[01:14:34]Brian: You think so?

[01:14:35]Kip: Yeah. Yeah. It was in that era, in that era.

[01:14:40]Brian: Because   obviously you hear a thousand to a million, it's  like, "Ooh, you got a ways to go." But, yeah.

[01:14:45]Kip: And no wonder I was skeptical.

[01:14:48]Brian: Right.

[01:14:48]Kip: I mean,   that's why I was skeptical, a factor  of a million. You're going to do that?

[01:14:54]Brian: Yeah.

[01:14:55]Kip: But as I say, I came around.  And so the folks at NSF, the key people, Marcel  Bardon, who's head of physics. And Richard   Isaacson, who's head of gravitational physics,  reports to Marcel. They understand two things.   One, that there's no way that Caltech and  MIT separately can build up enough manpower,   enough technical strength to pull this  off. They've got to collaborate. And two,   there's no way Congress is going  to give money to a field of- Brian: To multiple groups competing.

[01:15:36]Kip:... where there are   two different groups competing.

[01:15:37]Brian: Right, right, right.

[01:15:38]Kip: And so they tell us,   "You've got to build a collaboration." And  Ed Stone, who's now the head of Physics,   Math and Astronomy, says, "Absolutely yes,  we've got to collaborate." John Deutsch,   who's the Dean of Science and becoming the provost  at MIT says, "No way. We have no interest in this.   This project's going to fail. We have no interest  in supporting this." So MIT administration has no   interest. Caltech is enthusiastic. There's a  troika of leadership, Ray Wiess, Ron Drever,   and me. Ray and I say, "Of course we collaborate."  Ron Drever says, "No, I can't collaborate."  Ron is a very interesting guy. He's highly  creative. He invents a set of things that   are in the final interferometers that are  really crucial for ultimate success, that   are improvements on what Ray began with. So he's  made some substantial improvements. But he cannot   psychologically somehow, function efficiently and  enthusiastically unless he's in complete control   over everything that that he's involved in. But he's also the most disorganized physicist   I ever met. There's no way he can be  the head of this project. Just no way.   And so, this is a whole recipe for dysfunction.  Somehow, however, we do build a collaboration.   We define it. I head a steering committee of the  three of us, a troika we were called. And we get a   lot done over that period then from '84 to '86. In 1986, we've got this factor thousand   improvement in sensitivity, not just us, but  the four research groups that are doing this.   And it's 1986 that we're beginning to talk with  NSF about going big, going up to kilometer scale.  Richard Garwin, the most politically  influential physicist of that era.

[01:18:07]Brian: Who was at IBM?

[01:18:09]Kip: He was at IBM.

[01:18:09]Brian: I used to be a summer student,   so I knew him from my days as a summer kid at IBM.

[01:18:12]Kip: Yeah. No,   he'd played a huge role in the  hydrogen bomb development project,   but he had also built one of the detectors to  check Weber, a bar detector in that era. So he   had credibility from that point of view. And had  very quickly built a very good, but very rapidly   built experiment, and not seen gravity waves. He writes a letter to NSF, to Marcel Bardon. And   he says basically that, "If you're really thinking  about spending 40 or $100 million on this,   I advise against it. And if you're going to do  that, you should appoint a summer study committee   to look at this in depth of people who are from  outside the field and give advice." And so, Bardon   does the best he can. He can't get it together  for a summer study. He does it in the autumn,   and appoints a committee that Garwin is on. He puts Garwin on, because Garwin goes in as   a total skeptic. And the other committee members  are highly respected experts in the technology,   plus one person from the gravitational  community, which is Saltakolski who at the... Brian: At Cornell, yeah.

[01:19:37]Kip: Is at Cornell at the time, a theorist.

[01:19:39]Brian: Yes.

[01:19:40]Kip: A superb physicist, just a theorist,   but who could provide understanding for the  committee about the thinking of the gravi-wave   community in the committee's deliberations. But,  the real heart of the committee is this whole set   of something like eight other experimenters. And so, the committee does a one week long   study. Brings in all the people from around  the world who are working on this, grills them,   looks in depth at the technology. And comes  out with a report that says, "This is likely   to succeed. It is likely to revolutionize our  understanding of gravity and of astrophysics. You   should move forward now. You should build two  instruments, separated by at least a thousand   kilometers." Even though the Europeans are  thinking of building several instruments because   a network of the European instruments and the US  instruments is going to be crucial for getting all   the science out that can be gotten out. And as I said, "You move forward now."

[01:21:00]Brian: Were you   surprised by their report? Relieved by it?

[01:21:04]Kip: Well, certainly   relieved. I was surprised that it was so strong  and so specific, and particularly with regard   to build two, even though the Europeans  are aiming to build. But it was in fact   a blueprint for what actually happened over the  subsequent decades. It just foresaw this. And... Brian: So sometimes, committees work.

[01:21:28]Kip: Well, these   committees worked. And this was the secret to  our success with funding in subsequent years, was   these kinds of committees that were experts in the  technology. And so I'm told that Richard Garwin,   when LIGO actually discovered gravitational waves,  that he... Well, I know he was very enthusiastic.   Barry Barish saw him shortly thereafter, and  he was euphoric, Garwin. But I'm told he also   took great pride in having triggered this  1986 study that enabled it to go forward.  And so, over the subsequent few years, as we  submitted a proposal and the proposal got funded,   it was crucial time and again that we have this  kind of review committee. Because, we had eminent   astronomers who were fighting us tooth and nail in  Congress, totally skeptical. And I couldn't fault   them because I was so skeptical initially, but  totally skeptical about this and thinking that   this money should go for conventionalist  astronomical telescopes, not for LIGO.

[01:22:47]Brian: And so you   get the go ahead there, and you settle  on two locations in the United States,   Washington and Louisiana. You go forward, but  there's still enormous challenges to overcome.

[01:23:04]Kip: Oh, yeah.

[01:23:05]Brian:  So you're building the plane kind of while  you're flying it, does that make sense?

[01:23:10]Kip: Yeah, that's right. And so, we also have   a sequence of several directors who come... This  committee had also said as part of their report,   "Get rid of this troika, this semi-dysfunctional  troika leadership, and get a single director."  So they bring in Robbie Vogt, who had been  the Caltech provost. He'd been the first chief   scientist at the jet propulsion laboratory  and defined the job of chief scientist.   He was tough. Tough, charismatic. And he forced  the Caltech and MIT to start collaborating.   And he was central to getting Congress  to provide the funds, central to winning   the battle against the astronomers who were  trying to prevent us from getting the funding.  But, due to some misunderstanding between him  and NSF, he wound up with a budget that was   not adequate to have a robust management. And so  he was running a lien management, because there   had been some misunderstanding and he was stuck  with... I think lien management was also probably   his preference, but I know that he recognized that  it would be safer to have a robust management.

[01:24:36]Brian: Right.

[01:24:36]Kip: The difference between   lien management and robust management in  this case was several tens of millions of   dollars in costs, just to have  a robust management structure.

[01:24:46]Brian: And robust, just more people.

[01:24:47]Kip: More people.

[01:24:49]Brian: More layers.

[01:24:50]Kip: More layers, more documentation,   more continuing response to queries that come  from NSF and elsewhere. So, NSF gets cold feet   once we're ready to start construction. And when  they get cold feet, then Congress gets cold feet.   And they come back and they say, "You've got  to have a robust management." Robbie says,   "I don't have the money for robust management." They won't give him more money. Because they   don't really trust him to do a robust management,  although he's done a superb job up to this point.

[01:25:37]Brian: Right.

[01:25:38]Kip: And so the   president of Caltech, who has the authority to  change the director, he fires Robbie basically,   and brings in Barry Barish to take over the  leadership. And Barry asks for an additional,   something like $30 million for the robust  management, which NSF will give to him.  But then the really interesting thing,  Robbie Vogt, who has never functioned   very effectively under somebody else, he and  Barry make an agreement that he will take over,   at Barry's request, to be in charge of the  design of the first gravity wave detectors   and leading into their construction.  Working under Barry Barish as director.  And there's a huge respect between these  two people, and Robbie does that for two   years of transition. You have this team that is  very loyal to Robbie, and he's just been fired,   but he stays on in this capacity. And then  with Barry, he smooths everything out.

[01:26:51]Brian: So, strategically, this is a great move.

[01:26:53]Kip: It's a great move,   and it's something that I would not have believed  that Robbie was capable of, but he did for two   years. And then when things were really solidly in  place, Robbie left the project and moved off and   started doing other things. And Barry was solidly  in place, and Barry carried it forward through the   absolutely crucial period of... We knew that...  So Barry identifies... Robbie had not thought much   about advanced detectors. We knew that the initial  detectors, as we were planning to design them,   would probably not see gravitational waves, and  we would have to go beyond that. And we knew that   with Robbie, and that was part of our... When we  submitted a construction proposal, we said that.

[01:27:48]Brian: And people bought into   this idea of building a machine that you think  is likely not to succeed as a stepping stone.

[01:27:57]Kip: They bought in. That's right.

[01:27:57]Brian: Okay.

[01:27:58]Kip: But, this was also part of   the problem with NSF and the robust management  business was that they didn't see adequate   planning for the advanced detectors, while  the initial detectors were still under design,   much less under construction. But Robbie didn't  have sufficient budget to be doing much on the   advanced detectors. So, when Barry comes on board,  he analyzes the whole thing and he says, "Look,   there's no way that if the advanced detectors see  nothing and the first detectors see nothing, we're   dead in the water." And so the advanced detectors  have to have a very high probability of success.

[01:28:42]Brian: Because you can't fail twice, I guess.

[01:28:44]Kip: No. And so, the initial interferometers   become a precursor, a test bed, someplace where  you can find out what the problems are going to be   in order to design the advanced interferometers to  deal with that. And so you don't expect the first   interferometer to see anything, but the advanced  interferometers, they've got to see something.

[01:29:06]Brian: And did you clue Congress in enough,   I mean to say, "We're going to come back to  you and say this is going to fail first time."

[01:29:13]Kip: Yes, yes, yes,   absolutely. And so, when Barry then formally  came on and took over the project, and he had   gone through and redone the budget and seen how  much more he needed, he needed to get buy-in from   NSF and then from Congress to restart the project. And he did so in the context of this   two interferometer strategy. So, Barry and I met  with the National Science Board that oversees NSF   and then they would make a report that Congress  would see. And when we met with the National   Science Board, folks at NSF were really quite  nervous. And I was supposed to be sort of the guru   on where the gravity waves were, how strong they  were going to be. And I was very blunt and said,   "The odds are the first interferometers  will not see anything, but the advanced   interferometers will have a high probability of  success, and we have to be prepared for that."  And we had a detailed discussion with the  National Science Board over this. And in the   end, the National Science Board bought into  it and then Congress bought into it. And part   of that then was that Barry went in and started  asking for funds for the R&D and the construction   for components of the advanced interferometers,  several years before the initial interferometers   reached their design sensitivity. And so,  you're not even doing [inaudible 01:30:59].

[01:30:58]Brian: You're not doing stage   one and stage two, you're doing  stage two while stage one is... Kip: That's right.

[01:31:03]Brian: Yeah.

[01:31:03]Kip: So it was a very   bold move, but it was essential because  it would have driven the cost way up,   because of the stretch out time if  you were not ready with the advanced   interferometers just as soon as you had done  a search with the initial interferometers.

[01:31:21]Brian: And was Barry... Of course,   particle physics, he had already managed big...  Was this part of his own experience in the past?

[01:31:30]Kip: Well, this was quite different in some   respects, but Barry was a superb strategist, and  the designer and manager of big projects. Look,   I'm not an expert in this, but it's certainly  my impression that he was the best we've ever   seen. And he was dealing with a situation  where you were doing technology development   hand in hand with then designing and building  instruments in two generations. You don't do   that in particle physics. It's just not  done. So, it was a unique situation.

[01:32:09]Brian: Yeah.

[01:32:10]Kip: Similarly, it was very interesting.   With the first interferometers, he was building  the facilities to house the interferometers, big   vacuum systems and so forth. And then he was going  to start installing the interferometers in them as   soon as they were ready. And the preparation for  the installation of the first interferometers was   all going on. And so, he ran two organizational  structures in parallel. And if you were working   on facilities, you were in one organizational  structure, which was very pyramidal. There was a   boss, like you do on a big construction project.  But if you were working on the interferometers   in preparation for beginning installation  of components, you were in a very flat- Kip: Installation of components, you're in a very flat   organizational structure. And he successfully  ran the two simultaneously for a couple of years.

[01:33:13]Brian: It's amazing.

[01:33:15]Kip: It was quite amazing. That's the first thing   I saw. That was in the 1990s and on into the early  2000s. And then this business of initial inventor   ferometers and advanced interferometers running  along with only a time lag between them. But the   advanced was very far developed before the initial  interferometers even reached design sensitivity.

[01:33:43]Brian: Now when   we left the numerical sensitivity a little  while ago in our conversation, we were at a   thousand versus a million, effective a thousand  to go. How is that gap closing through all this?

[01:33:56]Kip: That gap is closing through   continuing R&D in the four kilometer long arms.  And so, the initial interferometers are installed   and they are being driven down over  a period of about four or five years,   being driven down to their design sensitivity. And  that's picking up this next factor of a thousand.

[01:34:23]Brian: So you see the gap closing?

[01:34:26]Kip: You see the gap   closing. And that was the plan. That's basically  what we said in 1986 is how you would do it.

[01:34:35]Brian: So when does the first LIGO actually turn on?

[01:34:38]Kip: So the first interferometers,   they begin installation around 2000, 2001.  They get close enough to design sensitivity   to start doing very serious gravitational wave  searches around 2005, 2006. We have a delay,   because of a no new start policy in the George  W. Bush administration. So we have a several year   delay. And so, by 2006, 2007, we're at design  sensitivity. And the advanced interferometers   can't be installed with a new start until 2010.  So what do you do? Well, there's this graduate   student of Ray Weiss named Rana Adhikari  who proposes a detailed plan to get another   factor two of sensitivity beyond the original  design sensitivity and then do another run.  And that plan is accepted and they do get this  other factor two at frequencies above about   150 hertz, something like that, or 200 hertz, a  little less improvement at the lower frequencies.   But I mean, it's quite remarkable. That means  you're saying twice as far into the universe,   eight times as big a volume, eight times  bigger event rates for things in the   higher frequency band than the original  interferometry even designed to have.

[01:36:38]Brian: Right.

[01:36:38]Kip: And we picked that up during this delay period.

[01:36:41]Brian: This period. But   you mentioned graduate students, and I'm  just wondering, so in this whole period,   there are graduate students involved. Their  careers in some sense are hanging on this idea.   What sort of pressure to say you or does Ray  feel that you've brought these young researchers   into a field? And obviously it's their choice to  take this chance, but it's a big chance, right?

[01:37:13]Kip: Yeah. Well, so when gravitational   waves are finally discovered in 2015, this shows  up in our reactions, our emotional reactions. And   Ray and I have long since become very close  buddies. I called him my transcontinental   soulmate. And when it's finally clear, we've  seen gravitational waves. My reaction is profound   satisfaction that we had made wise choices in a  number of places along the way. Ray's reaction   is profound relief, because of just this, that he  had convinced hundreds of students and postdocs,   not just at Caltech and MIT, but around the  world, because Barry had expanded LIGO in order   to have this succeed, to what in the end became  15 countries, 80 institutions, a thousand people   in order to succeed. And by the way, and Barry had  actually left the leadership of LIGO at about 2006   when the first detectors were reaching design  sensitivity, because the high energy physicists   needed him back to lead the biggest international  collaboration that they had ever conceived.  And he was told, "This won't go forward  unless you come lead it." The so, called   design of the international linear collider.  And so he leaves LIGO, but he leaves it in the   superb hands of Jay Marks who we bring down  from Berkeley to do that. And then Dave Reitze,   who comes in from Florida to take over after  that. So we have a series of superb subsequent   directors with Barry down to 20% time on  the project while he does hydrogen physics.   But anyway, so there's all this goes on, but by  the time we finally see the gravitational waves,   as I say, Ray's reaction is profound relief.  And the younger generation, it's just euphoria.

[01:39:40]Brian: And so,   take us through the period of September 2015  to February 2016. So you get a signal, I forget   the exact date, September 14th or something of  2015 at like 5:21 in the morning, or you know   the details better than I do. Yeah, you're not  convinced immediately that this is a real signal.

[01:40:04]Kip: I have an email from Christian Ott, a young   colleague of mine, who says, "Go to such and such  an internal website. We may have a detection."  And the signal has come in. It's been  entirely processed by an automated system,   untouched by human hands. And this automated  system has laid out what the data are and is   basically announced to everybody that this is  a likely detection. It seemed too good to be   true. And during the initial, and this has come  in three or four days before we're going to do   our first serious gravity wave search with  the advanced interferometers. The advanced   interferometers have been installed. They  have been brought down to a good sensitivity,   good enough to do a search. They have a  sensitivity, but that by then is, I've forgotten,   something like five times better than the initial  interferometers ever were. So a substantial   improvement beyond the initial interferometers and  they're just being tuned and the signal comes in.  So Dave Reitze announces, "Our first search  has just started, freeze the interferometers   and the signal." But for the international  interferometers, the team had done blind   injections in which they went in and they applied  electrostatic or magnetic forces to wiggle the   mirrors back and forth in both sites, in Louisiana  and in Washington state, in a pattern that   corresponds to a particular source, say a binary  black hole merger, particular location on the sky.

[01:42:06]Brian: Just mocking it up.

[01:42:07]Kip: Mocking it up.

[01:42:08]Brian: Yeah.

[01:42:09]Kip: And then   you see whether or not the team can find the  signal and analyze the data, and then you- Brian: Keep everybody on their toes sharpened.

[01:42:21]Kip: That's right. So I said,   I responded to Christian, I sent him an email back  and I said, "This is obviously a blind injection."  And Christian responds, "No, I'm on  the team that does blind injections   and we didn't do it." And so, then I  began to wonder if this is really true,   but there is then a big issue of being  absolutely sure that this is the real thing.

[01:42:49]Brian: Were you afraid of like hackers or anything?

[01:42:51]Kip: Yes. And so, that was the big worry   is hackers. When it was pretty clear that this  was a very, appeared to be a quite a clean signal,   but the instrument had been designed so  that every component in the instrument,   you could probe that component, ask what was it  doing at that time. So there are 100,000 data   channels you could get out if you wanted, because  there were 100,000 critical components inside,   but also in the environment. Much fewer than that,  say a thousand or so that are really interesting.   But I mean, when I was told there are 100,000  data channels, I said, "How's that possible?"  The answer is every component was built with  a data channel coming out of it. But that   was crucial, because you could then go in and  query everything. And the very best experts,   hands-on experts of this younger  generation, among the experimenters,   I'm not involved in this at this  point, but they cannot conceive how to   hack the system without leaving fingerprints  in a number of different data channels. They   just don't see any way you could do that,  and there are no fingerprints anywhere.   And if they can't do it, then if there's a  hacker that did it, this hacker is super- Brian: Be smarter than everybody.   Right. Yeah, right, right.

[01:44:34]Kip: And so,   that's the point at which we're really convinced.  And the committee that investigates this   spends about six weeks doing all this probing,  pushing and probing, but then a bit after that,   another signal comes in the day after  Christmas. It's not a big, strong signal,   but it's another signal. And that for anybody  who had any questions, that was the clincher,   but we don't announce, the team does not  announce that signal until sometime later   that year. It's just an internal thing that gives  confidence. So then we go into mode of preparing   for a press conference, an announcement,  which ultimately then happens in February.

[01:45:28]Brian: And the world takes notice.

[01:45:31]Kip: And the world takes notice, yeah.

[01:45:33]Brian: Now,   one final thing that I want to  talk about in this story is,   there's a whole computational side to this story,  where you've got to reverse engineer signals to   figure out what source created this particular  wiggle in Washington state and Louisiana. My   understanding of that is that was also a bit of  flying the plane while building it too, right?

[01:45:58]Kip: Yes. Well,   let me tell you again from a personal perspective.

[01:46:02]Brian: Yeah, please.

[01:46:03]Kip: So about 1992, I am really thinking   very hard. I've been thinking through this whole  thing. I sit on the sidelines as a theorist who,   however, is very close to the experiment. I've  done some design of some pieces of the apparatus.   For example, baffles of controlled scattered  light and beam tubes together with Ana Flanagan.   So I'm pretty knowledgeable about the experiment,  but not a real experimenter, but I have enough   understanding of the astrophysics, of the theory  of gravitational waves, and of the experiment   that I can think about the whole picture. And I've  become concerned about two things. The first thing   I'm concerned about is that I am already by then  can think it's likely the first thing we'll see   is two black holes merge. This is not a popular  viewpoint, because we didn't have a nearly as   good a handle on the event rate for binary black  hole mergers as we did for neutron star mergers,   because the neutron stars show up, many  of them as pulsars and the black holes   don't show up as anything you can observe. And so, you have to get a handle on this   through more indirect means. But I have this  view that the black holes binaries are going   to be roughly 10 times heavier than the neutron  star binaries, which means you will see them 10   times farther away, which means you'll see them  over a volume of the universe that is 10 cubed,   so a million times bigger volume of the universe.  And it seemed to me just very likely that that   factor of a million It would outweigh the greater  rarity of black hole mergers than neutron star   mergers. And so, it seemed to me very likely  that the first thing we would see binary black   holes. It also seemed pretty clear to me that if  we were going to really understand the waves when   we see waves from a binary black hole, we would  have to have computer simulations of the black   hole mergers, because the details of the waves  from the merger phase could only be understood   with numerical relativity simulations,  all Einstein's equation on a computer.  So I start pushing very, very hard in 92, as  does Richard Isaacson who has a similar view   at NSF on the computer simulations. Then there's a  second thing at about the same time that concerns   me. That is, I have based on all we know about the  sources, I have this range from 10 to the minus 20   to 10 to the minus 22, this sensitivity for the  first detections with 10 to minus 21, which is   where it actually was in the end, is best guess.  But in the vicinity of 10 to the minus 22, if it's   two 10 of the minus 22, maybe even three 10 of  the minus 22, quantum noise in these gravity wave   detectors is going to kill us. Each mirror,  these detectors are designed to monitor the   center of mass motion of mirrors. And we spent a  hundred million dollars or more to guarantee that   you see only the motion of the center of mass.  So each mirror is like a 40 kilogram particle.

[01:49:54]Brian: You've got the uncertainty principle.

[01:49:56]Kip: And you've got the uncertainty   principle, not the uncertainty principle for an  atom or electron, but for a 40 kilogram particle.   And that uncertainty principle says that there  will be fluctuations at the level of 10 to the   minus 18 meters, a few 10 to the minus 19  meters that will hide the gravity waves. And   to get down to this level of few 10 to the minus  22 sensitivity, you can't. It's going to hide the   signal. And so, we have to invent and build and  make robust technology to circumvent Eisenberg's   uncertainty principle. Quantum technology, quantum  measurement technology. It's now called quantum   precision measurement technology. It was Vladimir  Burginski in Moscow, whom I mentioned before,   who first pointed out this was going to be a  problem. He points it out in 1968, before Weber   sees his first gravity wave. He says, "Whatever  kind of instrument you build, you're going to   have to face this." And by this, fortunately, the  fundamental idea for how to do this technology   that you needed has been conceived in 1981,  about 11 years earlier by a student of mine.

[01:51:29]Brian: This is the quantum non-demolition- Kip: This is the quantum non-demolition   technique. It's a technique called squeezing or  frequency dependence squeezing. Carlton Caves   has conceived this of what's required. And Jeff  Kimball is a perfect experimenter down the hall   from Carl has invented the necessary technology  by something called degenerate parametric down   conversion in a non-linear crystal, if  you want to be fancy. He's invented it.   '92, the ideas are basically there and the issue  is to bring it into the LIGO frequency band, and   make it robust and implement it. And you've got to  do that before it's needed. And so, that's when I   started pushing very hard in LIGO that we need a  parallel effort and in this quantum non-demolition   to get there, because if nature is unkind, we will  have to have this to see the first waves. And at   the same time, I push very hard that we need the  computer simulations, as is Richard Isaacson.

[01:52:45]Brian: See, these are two ways that you could fail.

[01:52:47]Kip: Two ways   that you could fail. Well, we would  still see the gravitational waves- Brian: You just wouldn't know what to do with it, right?

[01:52:53]Kip: Yeah. You wouldn't know what to say.

[01:52:55]Brian: In fact, I'm wondering about that. If you   didn't have the numerical simulations, let's say  everything else work, quantum and non-demolition,   and you see the signal, would you be convinced  that it was a gravitational wave signal?

[01:53:08]Kip: I think we would have   been convinced, and I think we would have been  convinced it was black holes merging. We would   not have had a good handle at all on the masses of  the black holes or the spins of the black holes,   but we knew enough about  signals that I think we would- Brian: Have had confidence.

[01:53:33]Kip:... have confidence   of what it was as a type of  source that is binary black holes.

[01:53:40]Brian: And so where   are we today then? So this very clean  signal that comes in September 2015.

[01:53:47]Kip: So the community that's   working computer simulations, those simulations,  the foundations for them start being laid in John   Wheeler's group in the 1950s, before I'm even on  the scene. And they've been carried up through   and they're not going well in the '90s. And so,  I leave the day to day involvement with LIGO   in the early 2000s. I'm no longer needed.  I've trained several generations of young   theorists who can work close to experiment  and play the roles I was playing. And so,   I turned my attention to the simulations. I'm  not an expert on simulations, but I know what's   needed and I know what science we need to get  out. And so, we build a collaboration between   Caltech and Cornell, Saul Teukolsky's group  at Cornell, and I mentioned Teukolsky before.

[01:54:54]Brian: Yeah,   my first job was at Cornell,  so I knew Saul very well.

[01:54:58]Kip: So we build what's called the SXS collaborations,   simulate extreme space times with Lee Lindbloom  at Caltech, who's on the research faculty playing   key role in getting it started at Caltech.  And so, we build this collaboration and we,   Saul and I together and also in consultation with  others, becomes clear to us that in order to be   confident that we're going to have the simulations  in hand before the gravitational waves come in, we   need an intermediate scale effort, an effort of a  roughly 15 computational physicists at Cornell and   roughly 15 at Caltech. There was only one group  of that kind of a scale that had been built, a   group of 15, roughly at one institution that's in  Ed Seidel's group at the Albert Einstein Institute   in Germany. That's the only one. There's no way  NSF politically can provide the funds for this.  And so again, I go to Caltech and Caltech provides  the seed funds to get started, and then helps me   find permanent funding of about a million dollars  a year from the Sherman Fairchild Foundation,   which then we can combine with funding we have  from NSF and NASA and other sources to pull this   off. And that's still what we have. The Fairchild  Foundation has been crucial for us to pull it off   the private funds. And so, the SXS team is put  together and the goal is to have the... The first   successful simulations are by a postdoc in my  group at Caltech, who however is really working   on his own. And he's a prize postdoc. He adds the  freedom to do whatever he wants with prize money.  And he conceives of a combination of techniques,  where everybody else had failed and wasn't able   to get mergers to go. He makes the first merger  breakthrough, Frans Pretorius, Frans make enough   deal that he wound up as a professor at Princeton  very quickly. And Frans was just wonderful,   but to get something that was robust where you  could do hundreds of simulations over a period   of a few months with different parameters for  the masses and the spins of the black holes,   this really required this team of 30 people  under Saul Teukolsky's leadership. And that   team had that in hand, had what we needed  by about 2013. The signal came in 2015.

[01:58:04]Brian: So just under the wire, so to speak.

[01:58:07]Kip: Under the wire. And then   the quantum precision measurement, the quantum  non-demolition, this turned out wasn't needed.

[01:58:15]Brian: In the initial.

[01:58:16]Kip: In the initial. It's needed today. It was needed   as of about four years ago or so. The first piece  of it was needed quite early in advanced LIGO,   squeezing, but not so called frequency-dependent  squeezing. But the LIGO team had worked hard to   bring the technology to the point where it could  do the job and had it in place when needed. It   just worked beautifully, thanks largely to  the group of Nergis Mavalvala at MIT and   Roman Schnabel in Germany and David McClellan  in Australia, so three group collaboration.

[01:59:09]Brian: And so, where do you think we stand   now on the original vision that pushed you forward  of really having gravitational wave astronomy?

[01:59:17]Kip: Well, we are there. It's the beginning. I believed   from the beginning that the real payoffs, the huge  payoffs will come over the following decades and   centuries, and I still believe that. Now we have  this quantum precision measurement in place. It's   responsible for the fact that LIGO is able to  see several black hole collisions every week,   whereas when we first turned on, we were seeing  about one every six weeks. And with this,   that means we have much lower noise. That means  we're seeing details of the waves that we couldn't   see before. And that has led us to the domain,  where the team is really testing the laws of black   hole mechanics that were devised by, discovered  by Steven Hawking and colleagues in the 1970s,   detailed tests. Tests, for example, at the five  sigma level, which is the standard of physicists   to say it's absolutely true, for proof that the  surface area of the final black hole is bigger   than the sum of the surface areas of the initial  black hole. Those tests have been published   within the last few weeks. So it's really an  exciting period, but it's just the beginning.

[02:00:57]Brian: Do you see one of the big prizes,   presumably, to finally hear gravitational waves  from the beginning, from the Big Bang? Is that- Kip: That's to me,   that's the biggest prize, the biggest prize  of all, because the primordial graph... Well,   then I'm going to ask you a question. I have the  view that there was a plank era in which space and   time came into existence, and the conventional  wisdom is that when they came into existence,   that the only thing that was present in terms  of fluctuations were vacuum fluctuations,   the smallest, weakest fluctuation that could  possibly exist of everything, of electrons,   protons, photons, gravitational waves. And that  those fluctuations sucked energy out of the early   inflationary phase of expansion of the universe  and created all the matter and radiation we see in   the universe today, and created them with just the  fluctuations of density and temperature that were   required to make galaxies. So it's a beautiful,  beautiful picture. Do you believe that picture?

[02:02:29]Brian: Well, I believe it has an effective   picture in the language that we commonly use. I  think it's a good model for what happened after   some kind of primordial stage, but I wouldn't take  it as the guide to that primordial stage. I think   it is based upon conventional ideas of space and  time, for instance, and I think like many of us   have become fairly convinced that space and time  are emerging quantities. And that there is some   more fundamental description. String theory is  hinting at it from various directions today,   but I don't think we have it yet. So from a  certain point on, I think that is a really   good model, but I don't take it as the truth of  what's really going on. I mean, how about you?

[02:03:21]Kip: All I have is hopes.

[02:03:23]Brian: Yes.

[02:03:24]Kip: As I think I mentioned to you,   I've forgotten whether I mentioned this. I think  this area of understanding quantum gravity,   understanding the details of the birth of  the universe, this is the most interesting   and important area of all of physics and has  been for several decades, and will be for a few   more decades. And I've avoided like the plague,  because I want elbow room. And so, I then ask   you and your colleagues for what really goes  on, what you think goes on. My hope is that... Kip:... goes on, what you think goes   on. My hope is that something along these lines is  correct, but that what came off of that early era,   because we don't understand it properly yet, is  somewhat different from just vacuum fluctuations.

[02:04:16]Brian: Well, that would be astounding.

[02:04:18]Kip: And that if that turns out to   be the case, we will have by roughly the middle of  this century, gravitational wave data about this   in two widely separated frequency bands from the  polarization of the cosmic microwave background,   a polarization, a component of polarization  produced by the primordial gravitational waves.

[02:04:49]Brian: And Lisa, I guess? No.

[02:04:51]Kip: We will be seeing the indirectly   gravitational waves with periods of hundreds of  millions of years, and then a follow on mission   to Lisa. Lisa's not going to do it itself, but  a follow on mission to Lisa. There's a study for   one by Sterl Phinney and the team a few years ago  called the Big Bang Observer, which is a plausible   follow on direct observation of gravitational  waves with the periods of seconds to minutes.  You've got these hundreds of millions of  years, seconds to minutes. You've got data   in those two frequency bands. If there's  some huge incompatibility between those   data or between those data and people's best  theories, I just have this dream that it all   blows up in our faces, that there's a huge  mystery to be solved and that somehow these   gravity of observations together with the  struggles of brilliant theorists like you,   that this will lead to a true deep understanding  of quantum gravity and the birth of the universe.

[02:06:09]Brian: Yeah. No, I share that dream. It's a   tall order, but if we actually had some real data  and if that data pointed toward things that were   not quite the vanilla model that we sort of all  focus on, that would be astounding. I want to turn   in just a final few minutes to a related era. You  described the importance of simulations to being   able to interpret data from LIGO, for instance.  You have used simulations in another domain,   a sort of new chapter of your career where you've  collaborated with people like Christopher Nolan   and making Interstellar. And just tell us a bit  about that, because my understanding there is   you actually did real simulations that pushed  the boundaries of visualization there, right?

[02:07:00]Kip: Well,   sort of. So my collaboration with Christopher  Nolan is just a wonderful collaboration,   wonderful experience. He is a highly creative man,  very deep, very different background from me, has   enormous intuition about physics in the universe,  built up almost entirely by browsing the web.

[02:07:27]Brian: Really?

[02:07:28]Kip: Yeah.

[02:07:28]Brian: It can be good or bad.

[02:07:30]Kip: Well, in his case,   it's good because he understands the limitations,  but his creativity, you combine him with me with   my knowledge, but with coming in from almost  orthogonal direction in terms of knowledge,   it just turned into a fabulous collaboration. But  you asked about one aspect of it, and that is that   we agreed that we would base everything involving  the visualization of black holes and wormholes   on computer simulations based on  Einstein general relativity theory   in a universe where wormholes can exist. So there's aspects of the laws of physics   that we don't understand very well. And so we  pick a particular choice for those aspects of   the laws of physics in which a very advanced  civilization can build a wormhole and provide   it to the humans. And similarly, well,  then you have the physics of black holes.  So the question then is to do computer simulations  to visualize what goes on around a black hole. And   so he puts me in touch with the team at what  was at the time called the Double Negative   Visual Effects Company based in London where  Paul Franklin, who is the co-founder of that   company, is the Head of Visual Effects for the  movie Interstellar. His young collaborator,   Oliver James, is the Chief Scientist, and he  has a Master's degree in optics, in physics.

[02:09:28]Brian: I see.

[02:09:29]Kip: He's very deep and he's a superb physicist   in all aspects of optics, ever so much more than  I know. And so I provide the equation that we   need to do a propagation of light, say from the  accretion disc hot gas going around a black hole,   propagation of light around a black hole and  down to an IMAX camera. And it doesn't work   because he analyzes it, and he figures out the  problem is that if you have two adjacent pixels   on the camera and these light rays go out from  those adjacent pixels almost precisely parallel,   and they go over the black hole and down to  the disc, the tidal forces of gravity, the   difference in the strength of gravity along this  ray and along that ray is so great because you're   near the horizon of a black hole that these light  rays get pried apart. So they land very far apart.

[02:10:47]Brian: So one misses the camera.

[02:10:48]Kip: Well, you begin on the camera.

[02:10:50]Brian: Oh, he's   going backwards. Yeah, sure. Sure, yeah, yeah.

[02:10:53]Kip: He says, "We've got   to have another method. We've got to invent  a new method." And he says, "I have an idea.   We want to propagate not light rays, but light  beams, and they're going to begin as circular."

[02:11:08]Brian: They have some size to them.

[02:11:10]Kip: They have size to them. They begin overlapping.

[02:11:13]Brian: Got it.

[02:11:13]Kip: And then they go over the camera and they get   spread, but they still overlap and they collect  their data from the other side overlapping.

[02:11:22]Brian: Wow. Okay.

[02:11:23]Kip: And he says,   "But I need the equations for this." And so I  work out the equations in general relativity. It's   much more complicated than just propagating light  rays. And I test the equations out on Mathematica.   That's my level of computing, but Mathematica  is capable of doing that, to get stills,   not movies. And I get it debugged, give it to him.  He does this in C++, and it works. It works. And   so he makes the visuals for Interstellar this way. But then we say to each other, "Well, let's just   see what we can learn about gravitational  lensing." And so we take our black hole now,   our mathematical model for the black old  gargantua, and we surround it by a star field,   and the light comes in from the stars and it  goes in and it is lensed by the black hole.   We see all these wonderful things that  I've been told about caustics in the   past light cone structure of a pixel on the camera  and how the caustics lead to multiple images.  And we watch multiple images be created  in pairs out of nothing on the screen.   We watch these pair go out and this  one annihilates against some other   image and that one goes out and annihilates  against some other image. We see these rather   remarkable things that I've heard about, but  for the first time we have the resolution   to really be able to observe some remarkable  things about optics that we've not had before.

[02:13:36]Brian: And beautiful images.

[02:13:38]Kip: Beautiful images.  And so we publish a paper together also with other  colleagues from the team at Double Negative, Paul   Franklin and Von Tunzelmann. We publish a paper  in Classical and Quantum Gravity describing the   details of our method and then applications both  to the movie and to just star fields. That paper,   by a huge margin, is the most downloaded  paper in the history of this journal.

[02:14:20]Brian: So Kip,   in Interstellar and also in various  other science fiction stories,   wormholes play a key role. Where do you  stand? I mean, do you think they're real?   Are they a bonafide solution of Einstein's  equations? Where do you think about them?

[02:14:36]Kip: Well, I think the first thing that   I have to say is if they're going to be real, then  they have to be compatible both with Einstein's   classical general relativity equations and the  laws of quantum physics. And wormholes certainly   are compatible with Einstein's equations. They  arise naturally from Einstein's equations, but   there are reasons to suspect that quantum physics  then combined with general relativity prevent them   from existing or at least existing naturally in  our universe. So my best guess is that there are   wormholes in a quantum foam at the Planck scale,  at very small scales, that there are fluctuations   in the topology of space at very small scales,  John Wheeler postulated this as quantum foam, but   that you cannot have macroscopic wormholes that  live long enough for people to travel through.

[02:15:53]Brian: Even with some kind of exotic matter?

[02:15:55]Kip: Well, that's my best guess.  However, I can't prove it. And we know  a lot more about this question than we   did when I first started thinking about it,  triggered by Carl Sagan back in the mid-1980s.  And we do know that in order to hold a wormhole  open, you have to have something that repels   gravitationally, basically push the walls of the  wormhole apart. And I call it that exotic matter.   We know that with pretty high confidence that  you can make exotic matter by rearranging vacuum   fluctuations, and we have a very simple  example that I think is very compelling   that if you take two electrical plates, I'm  sorry, two conducting plates, let's make   them superconductors for simplicity, and I put  handles on them, and so I'm holding them apart,   that as they get closer and closer together,  the electric field parallel to the plates   basically gets annihilated because current flows  in the plates to annihilate it. And so you have   reduced fluctuations of the component of the  electric field that's parallel to the plates.  And the closer the plates get together, the  more reduction of fluctuations there is. And   there's a resulting attractive force between  the plates. And this attractive force has been   measured. It's called the Casimir force. And  this is the Casimir vacuum between the plates.   And you could feel this with your hands, and the  plates are being pulled together and they're doing   work on your hands. Your hands are extracting  energy from the vacuum between the plates.

[02:18:11]Brian: It's a purely quantum effect.

[02:18:11]Kip: It's a purely quantum effect,   but you're actually getting work out, and  you're getting it out of the vacuum. And   so if the vacuum began with zero energy, energy  in the sense of what produces gravity, then it   has negative energy and that you have exotic  matter in there that repels gravitationally.  I think it's pretty convincing,  I don't know that it's 100% sure,   but pretty convincing that thereby you  get exotic matter between the plates.  The question is, can you make enough exotic  matter and put it inside a wormhole to hold   the wormhole open because without it the  wormhole will implode so fast that nothing   can travel through. And that's where people  have done a number of calculations trying to   answer that question without a definitive answer. My impression is that the odds are against holding   wormhole open, but that's just the odds. And as I  like to say, I've been proved wrong often enough   in areas where I think I know the answer that  you shouldn't take my pronouncement seriously.

[02:19:36]Brian: Well, one final gut check though.   Imagine that you were able to keep the walls of a  wormhole open using Casimir energy or some kind of   like-minded exotic matter, do you think we'd ever  be able to use these for time travel and by towing   the opening to a black hole and having a time  warp set in between it and the other opening?

[02:19:58]Kip: I don't know.   But this intimately ties into a related issue and  that is whether or not time travel is possible at   all on either macroscopic or microscopic scales.  And so there is very interesting calculations   done by two different groups. One is Jim Hartle  and Murray Gell-Mann have developed a variant of   Feynman's so called path integral approach to  quantum mechanics, that is capable of dealing   with regimes that normal quantum mechanics  cannot deal with. And in normal regimes,   this path integral approach is absolutely  equivalent to the standard approach of quantum   mechanics. But if you have time travel, then  ordinary quantum mechanics can't deal with it.   Feynman approach, Gell-Mann/Hartle approach can. And so Jim Hartle did an analysis and a similar   analysis with a different but still Feynman-based  approach done by John Friedman and colleagues   at the University of Wisconsin at Milwaukee. In  both these calculations, they imagined that you   have some region, and if I run time up in space  horizontally, you have some region where there's   backward time travel. There's no backward time  travel allowed down here. There's none up there,   but there's a compact region in space-time  where it's allowed. Using the Feynman approach,   they could evolve quantum fields from initial  state down here to a final state up there. They   compute probabilities. Probabilities are  preserved. There's no problem whatsoever,   but information is lost. Or more precisely, the  evolution from here to there is non-unitarian.

[02:22:23]Brian: Non-unitarian. So you can't go back.

[02:22:24]Kip: So you can't go back.

[02:22:25]Brian: Yeah.

[02:22:26]Kip: And this is irrelevant   because there is the mystery, the paradox,  the question of whether information is lost.   If a black hole is created through implosion of  some matter, and then the black hole evaporates,   is information lost? And Stephen Hawking insisted  at one time that information gets lost. And we   even had a bet where he and I bet that it does get  lost. And John Preskill, our colleague at Caltech,   bet it doesn't get lost. And Stephen threw in  the towel. I have not thrown in the towel. I've   not thrown in the towel. I still think that it's  an open question because I think there's a real   possibility that backward time travel is allowed,  is required on microscopic scales, at least,   that when you do a path integral approach to  the quantum gravity of some of our histories,   that you have to have finite probability  amplitudes for backward time travel on microscopic   scales. And that's what eats the information.  That's what prevents the unitarian evolution.  And this is just saying that the true approach  and the real universe to quantum gravity is a   path integral approach and that the standard  approach is just not broad-minded enough to   deal with these bizarre kinds of situations. And I  think that's a very, very important open question.

[02:24:26]Brian: So you   think Hawking bought Preskill the  Encyclopedia of Baseball too soon?

[02:24:31]Kip: I do think that.

[02:24:33]Brian: Interesting.

[02:24:34]Kip: But on the macroscopic scale,   I think it is also an interesting question,  can the laws of physics accommodate themselves   to backward time travel? That is a kind of  question that I spent some fair amount of   effort trying to understand. And it appears to me  the answer is probably yes, they can accommodate.

[02:24:57]Brian: Some sort of self-consistent.

[02:24:59]Kip: You can build self-consistent solutions always,   though there'll be some circumstances where  these self-consistent solutions cannot have   a quasi classical approximation. Some situations  where you give initial data and the probability   gets all spread out all over the place because  you can't have classical health consistency.

[02:25:30]Brian: So it gets   sort of hidden in the quantum diffusion, but  you can't go back and kill your grandparents.

[02:25:35]Kip: Yes. Yeah.

[02:25:35]Brian: Right. Excellent.

[02:25:37]Kip: So anyway,   that's my view. But what happened was  I was really digging deep, as deep as   I could on these kinds of issues in the 1980s  and the early 1990s, and then LIGO got funded.

[02:25:55]Brian: So off and running.

[02:25:56]Kip: I shut   down all that research in my own research  group, and we had some non-trivial amount   of research on that, to focus on  LIGO, and I've never turned back.

[02:26:09]Brian: Right. Well, maybe that's the fourth act.

[02:26:12]Kip: Maybe.

[02:26:13]Brian: Unfortunately,   we're running a bit out of time. I could keep on  going for another few hours, but I just want to   close with one question. So you are now focused  more on trying to create experiences for people.   You're involved in live events on Zimmer and  visuals and stars and music and so forth,   Interstellar, and other projects of that sort.  What do you hope to bring? What do you hope the   experience of the public would be and why is it  important to you that they have that experience?

[02:26:48]Kip: Well, let me say my motivations are several   fold. One is I was a conventional professor for  almost 50 years, been there, done that. I want to   do other things that are really interesting, and  they're fun. So one of my motivations is have fun.

[02:27:07]Brian: Yeah.

[02:27:08]Kip: That was also my motivation   as a conventional professor too, and I had fun.  But I also see this as a means to communicate   and inspire people about science through these  collaborations between scientists and artists.   And I think I was particularly inspired by  my collaboration with Christopher Nolan.   So we had in depth discussion of his movie Tenet  before he ever started any filming when he was   just beginning to conceive it. What happens if you  have a person whose direction of flow of time is   opposite the rest of the universe? Entropy inside  me increases in the wrong direction relatively.

[02:28:03]Brian: From my perspective.

[02:28:04]Kip: Yeah. What happens at the interface between   those? As a physicist, if I try to do statistical  physics in that kind of a universe, that's just an   intellectually fascinating question, but it also  led me to give him some advice for that movie. But   I would never have asked that question,  but he did. And it was just so stimulating.   So I get enormous amount of joy out of  collaborating with people like that,   with Lia Halloran, the painter,  that I have done this book.

[02:28:43]Brian: That book, beautiful book.

[02:28:43]Kip: The Warped Side of Our Universe, her painting is   my verse and conceiving this new genre of tightly  integrated paintings and verse is a mechanism to   try to convey the essence of some pieces of  science, in this case, the Warped Side of Our   Universe, to a different kind of an audience than  I've ever tried to reach before. Really enjoyable,   and I know that we have some success in inspiring  people about science at the same time. And so I'm   just in a phase in life where I'm getting a  lot of joy out of that kind of collaboration.

[02:29:29]Brian: Well, look, it is a very   rich realization when people can see science, not  just as something that scientists and laboratories   or universities do, but it's something that seeks  truth in a pathway that's resonant with a pathway   that artists and poets and writers can follow. So  it's a wonderful way of really bringing science   into the cultural center, which is vital. So Kip  Thorne, thank you so much for this conversation.

[02:29:59]Kip: Thank you. Its' been wonderful, Brian. Thank you.