The Science of High-Wire Stunts with Philippe Petit

Put on your safety harness as Neil deGrasse Tyson investigates the world of death defying stunts with high-wire artist Philippe Petit, co-host Eugene Mirman, and guests Charles Liu, tight-rope instructor Sonja Harpstead, and Bill Nye the Science Guy.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk. Your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:21Neil deGrasse Tyson?

  From the American Museum of Natural History in New York City, and beaming out across all of space and time, this is StarTalk. Where science and pop culture collide.

• 0:36Neil deGrasse Tyson?

  Welcome to the Hall of the Universe of the American Museum of Natural History, right here in New York City. I'm your host Neil deGrasse Tyson, your personal astrophysicist for tonight on StarTalk. We are going to be talking about the physics of stunts, the physics of high-wire acts. And we're featuring my interview with the French high-wire artist Philippe Petit. Back in 1974, he walked a wire between the Twin Towers of the World Trade Center, and I had to ask him why. All of that and more tonight on StarTalk. Let's do this.

• 1:15Neil deGrasse Tyson?

  So I got with me Eugene Mirman. Welcome back Eugene.

• 1:18Eugene Mirman?

  Hello, great to be here.

• 1:19Neil deGrasse Tyson?

  My comedic co-host.

• 1:22Neil deGrasse Tyson?

  And Charles Liu. Give it up.

• 1:24Charles Liu?

  Thank you so much.

• 1:25Neil deGrasse Tyson?

  He's a professor of physics and astronomy at the City University of New York on Staten Island.

• 1:30Charles Liu?

  That's right.

• 1:30Neil deGrasse Tyson?

  And I bring him on the show anytime there's stuff I don't know quite enough about. But he knows everything about everything. So Charles, there's a lot of physics in high-wire acts.

• 1:40Charles Liu?

  Incredible amounts. Balance, gravity, rotational inertia.

• 1:46Neil deGrasse Tyson?

  Okay, so this is how you restore your balance.

• 1:48Charles Liu?

  That's right.

• 1:48Neil deGrasse Tyson?

  Right. And so Philippe Petit, it wasn't just the World Trade Towers. Now, I'm a resident of New York. I remember when he did this. It was all over the news. But apparently that's not the only stuff he's walked between. All right? If he sees any two things, he wants to walk. So apparently, he walked, you know, the Notre Dame Tower in Paris? That has two main towers? He walked between those, okay? He also walked the two uprights of the Sydney Harbour Bridge in Australia. And so, so let's just have a look at his historic walk across the towers. Check it out.

• 2:20Neil deGrasse Tyson?

  There he is.

• 2:21Charles Liu?

  Amazing.

• 2:22Eugene Mirman?

  Well, now that I know he had a pole, it doesn't seem so hard.

• 2:27Neil deGrasse Tyson?

  The pole weighs fifty-five pounds or so. Well, I've got the, I've got, I've got the data here. You do? So, here we go. So, what is it? So, it took six years in the planning. This was not just an afterthought, you know, on a Sunday afternoon. And the cable between the two buildings weighed four hundred and fifty pounds. Wow. So, you have, you have to, you have to secure that cable. Mm-hmm. Some way while nobody notices you're doing it. And of course, it's a hundred and ten stories above the ground. And he went out there and hung out for forty-five minutes. Amazing. Didn't come back. He just laid down, waved, you know, just walked, turned around, slept. No, he didn't sleep. But he looked very comfortable up there.

• 3:08Neil deGrasse Tyson?

  And so, I, I, I'm just curious, what is the, the, what motivates somebody to do this? And, and I brought him to my office and I just had to ask him, what, what, what's up? Basically. Him, honestly. Let's check it out. Are you crazy?

• 3:27Speaker 03

  Absolutely, certified. But the capital C is like a beautiful garamond type with serif. It's noble. It's beautiful craziness. It's not crazy craziness.

• 3:37Neil deGrasse Tyson?

  Oh, so you've thought about this? How to be crazy in an artistic way?

• 3:42Speaker 03

  Well, I never thought of wanting to become crazy. But I became a crazy man about details, a crazy man about perfection, a crazy man about doing the most beautiful performance to inspire people. So, in that sense, you know, there is a certain noble madness to those performers who inspire us.

• 4:02Neil deGrasse Tyson?

  I like the pair of words, noble madness.

• 4:05Speaker 03

  Yeah, it goes well together, yes.

• 4:07Neil deGrasse Tyson?

  Yes, that works, that works. Uh, reading up on your, on your background, you're a magician, right?

• 4:13Speaker 03

  Yes, yes.

• 4:14Neil deGrasse Tyson?

  So, when was this transition between the magic tricks that you might do at a party or on a street corner and raising?

• 4:23Neil deGrasse Tyson?

  The level of performance art to the high wire.

• 4:26Speaker 03

  This is a great question. Because actually, from the little kid doing magic tricks, six years old, I became the little kid at fourteen, learning juggling. Only because in the world of magic, they advocate to juggle because it, you know, open your sensibility, your coordination. So here I am, with no circus school, no videocassette, by myself, learning how to juggle. And then, six, fourteen, around fifteen or so, I put my nose in the, in the variety show, in the music hall, in the theatre, in the circus, to see more magicians and to see more jugglers.

• 4:59Neil deGrasse Tyson?

  People pay to do it.

• 5:00Speaker 03

  Yeah, absolutely. And I see those amazing men and women who walk in thin air, the high wire walkers. And here I am at sixteen, and I am a self-taught wire walker because I spent my entire childhood climbing with trees, playing with ropes, doing, performing. So I am a born wire walker. And that's in very short, the story of my short life.

• 5:24Charles Liu?

  Wow.

• 5:25Neil deGrasse Tyson?

  What a charmer, too, right?

• 5:26Charles Liu?

  Yeah.

• 5:27Neil deGrasse Tyson?

  Yeah, he got that, that French accent and it makes it all sound like very, like... So, so he's, what, what he's doing professionally is merging that which the laws of physics enable and that which the creativity of, creativity of art um, will display. So, I'm just curious, he, I've, I've met artists that don't think at all about science or precision or accuracy. They, they do it for the pure love of the art. In my interview with Philippe, there was a scientist deep down inside of him. He knew how he was using the laws of physics for his art. And I was just impressed by that.

• 6:04Charles Liu?

  I have always felt that when you combine arts with sciences, that's when true innovation comes about.

• 6:12Neil deGrasse Tyson?

  Artistic innovation or scientific innovation?

• 6:14Charles Liu?

  Both.

• 6:14Neil deGrasse Tyson?

  Both?

• 6:15Charles Liu?

  Albert Einstein himself said that imagination was more important than knowledge in the big deal.

• 6:21Neil deGrasse Tyson?

  You can say that when you're Einstein. But when you try to get an A on an exam, that doesn't work.

• 6:27Charles Liu?

  What he said was very clear. Imagination encircles the world. Knowledge is limited. And imagination is literally an important ingredient in scientific discovery. You can't just toss it aside and pretend that all you're doing is solving problems that already existed.

• 6:44Neil deGrasse Tyson?

  Well, if you're solving problems, Philippe Petit approached the walk between the towers like a scientific experiment. He had attention to detail, much like any of us would perform an experiment in a lab.

• 6:57Eugene Mirman?

  Yeah, or if we were walking between two buildings thousands of feet in the air. You'd put a little work into it.

• 7:04Neil deGrasse Tyson?

  And there's even, it's not just the physics of it, there's also the engineering of how this came to pass. Let's check out my next clip where he goes there.

• 7:14Speaker 03

  I learned about the towers as they were being built from France. And at some point, I realized, oh, they are about to be finished. I have to run to America to do my work. So I arrived here and I stayed eight months in New York spying on the towers. And I looked at all the interviews and the movies and the construction and I was there, you know, these guys. And trying to understand the towers. And at some point, some architects, I heard those towers were designed to move three feet, three feet, six feet. So my wire, now I'm talking about an engineer, my wire there being tied at three ton will tend to prevent the towers to move, I would say to breathe is more human, you know, actually, I could hear them in some of my spy visit.

• 7:56Speaker 03

  I would hear in the staircase, a little bit like the bones of the human body, creaking, breathing. So if they want to breathe because of a sudden change of temperature, a cloud in front of the sun, or because of the wind, what is not my miserable little cable three ton tie that will prevent them from moving? My cable will be pushed from three ton to thirty thousand ton and it will explode and I will evaporate in thin air and I will kill people below. So it was a very serious engineering problem. How can I put my wire, tighten it, and yet let the tower breathe if they want to?

• 8:32Neil deGrasse Tyson?

  And...

• 8:33Speaker 03

  Ahahaha, well, and actually, the answer to that came from an old man from the circus. So he said, "Make sure you put some wood around the steel I-beam that you anchored to, so that if the towers want to breathe, what will happen is that the cable will eat the protective wood."

• 8:52Neil deGrasse Tyson?

  It'll squeeze the wood.

• 8:53Speaker 03

  You know, of course, you will lose tension, but that will be another problem, as they were working, but at least you will not evaporate and the cable will not break. Um, I did it. I did that, and it saved my life.

• 9:04Neil deGrasse Tyson?

  Doesn't want to evaporate in midair.

• 9:06Eugene Mirman?

  I like that he said it saved his life, like he will, I'm obviously gonna walk between the two buildings.

• 9:11Charles Liu?

  That's terrific.

• 9:12Eugene Mirman?

  There's no avoiding that.

• 9:15Charles Liu?

  And a wonderful example of using old knowledge, the old man coming to tell him, "Use it this way," and he used it. It's like elephants telling the previous or the future generations of elephants where the nearest watering holes are, even if they're a hundred miles away or a thousand miles away. We learn.

• 9:30Neil deGrasse Tyson?

  So, tell me about the breathing of the towers. What do you know about it?

• 9:34Charles Liu?

  Basically, when you have a structure that's big and tall, they sway. The differential in airflow speeds between what's on the ground and the top can sometimes be fifty, sixty, or even seventy miles an hour. So that's nearly hurricane-force winds. Furthermore, if you have the temperature, as Philippe described, and the temperature difference between, say, one part of the building and another, sometimes can be forty, fifty, sixty degrees. The combination results in literally swaying back and forth. Even though they're a thousand, thirteen-hundred feet tall, they could sway three, four feet back in just a matter of seconds. So that's what he's talking about. If he's got a cable that's stretched nicely, tightly through, and they decide to swing three feet this way and three feet that way, that's six more feet.

• 10:17Charles Liu?

  He goes, "Boing, pshoom," that's his evaporation.

• 10:22Neil deGrasse Tyson?

  With that sound effect, for sure. That sounds like a cartoon sound effect.

• 10:26Eugene Mirman?

  He'd probably yell, "Nah!"

• 10:28Charles Liu?

  Well, he would look down, hold in the air for a second, not realize he was gonna drop, then notice he's over in the air, and then he'd fall.

• 10:35Neil deGrasse Tyson?

  Right, like Wile E. Coyote.

• 10:36Charles Liu?

  Like Wile E. Coyote.

• 10:37Neil deGrasse Tyson?

  Yeah, yeah.

• 10:38Charles Liu?

  Falling from that height, by the way, takes just under nine seconds. By the time he hit the bottom, it would be a hundred and eighty miles per hour. On the other hand, if he hacked a loogie that far down, no problem. Because by just a sh- uh, by just a few feet... It would reach terminal velocity and gently float down like raindrops do. Oh.

• 10:58Neil deGrasse Tyson?

  He's talking about phlegm.

• 10:59Eugene Mirman?

  Yeah, yeah, no, that part I got. I'm just trying to figure out can he turn himself into spit and then be fine? I think the answer is no.

• 11:08Neil deGrasse Tyson?

  So, what's interesting to me is for any given tension in a wire, there are things that affect that, such as the weight of the wire.

• 11:17Charles Liu?

  Yes.

• 11:17Neil deGrasse Tyson?

  That, uh, the, how heavy the person is. And you combine these two, that should affect how he designs this walk.

• 11:26Charles Liu?

  Literally, everything had to be designed. The cable is steel, usually, and it's about 3/4 of an inch thick for most high-wire things. I think that was probably the diameter he used as well. And as you said earlier...

• 11:36Neil deGrasse Tyson?

  If it's too wide, then you're just walking on a...

• 11:38Charles Liu?

  That's right.

• 11:38Neil deGrasse Tyson?

  You're just walking on a road.

• 11:39Charles Liu?

  That's right.

• 11:40Eugene Mirman?

  It's called a, yeah, a bridge.

• 11:40Neil deGrasse Tyson?

  A bridge, yeah, yeah, yeah, yeah.

• 11:42Charles Liu?

  And as you said, it was, uh, more than 400 pounds. So that means the stretch distance is about 140 feet, which means that every foot was almost 3 pounds' worth of metal.

• 11:51Neil deGrasse Tyson?

  So, all of this has to be calculated. And if you know you're gonna, if, if you're a particular length and you're gonna stretch 3 feet, plus another 3 feet, it's gotta be able to accommodate that slack.

• 12:01Charles Liu?

  That's right. And that's why that wood around the I-beam that he attached was so important. Because as he said, if the cables stretched, or they came loose, it stretched this way, then it would actually dig into the wood. But it wouldn't be able to dig into steel, but digging into wood makes it okay.

• 12:17Eugene Mirman?

  Why does it make it okay to dig into the wood?

• 12:19Charles Liu?

  Uh, then the, the steel doesn't snap the cable. So you have a little bit of give, and as he described in the clip, uh, indeed, he has to adjust for the change in tension and all the things that happen, but those are not fatal failures. Those are things that...

• 12:33Neil deGrasse Tyson?

  Yeah, that's, that's a good point. If, if you don't have something that can, that can respond to the, to the change in length, then something breaks. And that would be ugly if it happened that way.

• 12:44Charles Liu?

  That's right.

• 12:45Neil deGrasse Tyson?

  Yeah. Yeah, and also, uh, something many people see but might not think about, every single bridge has breaks in the roadway to enable expansion and contraction...

• 12:54Charles Liu?

  That's right.

• 12:55Neil deGrasse Tyson?

  Of the, of the, of the roadway.

• 12:57Charles Liu?

  That's why every time you drive over the George Washington Bridge up here, it goes... The dong, the dong, the dong, the dong, the dong.

• 13:02Neil deGrasse Tyson?

  He lives in New Jersey, so that's why.

• 13:04Eugene Mirman?

  Yeah, it's like, why would we ever have that experience?

• 13:10Neil deGrasse Tyson?

  Also, I was, where was I? I was in San Francisco. And there was a park that has a telescope with a caliper inside, I mean, like a measuring lines inside of the view of the telescope. And you're looking at the Golden Gate Bridge. And you get to measure, like, was it the curvature or the uprights? There's something you're looking at. And you see how much it has bent, and it tells you what temperature it is outside. Wow. Yes, it was very cool. Yeah, yeah, you're watching the physics of the bridge respond to the temperature. And if it can't respond to the temperature, something breaks. It's the world's most expensive thermometer. Yes.

• 13:50Eugene Mirman?

  Yeah, what a weird way to tell temperature in San Francisco.

• 13:55Neil deGrasse Tyson?

  Yeah, just pull out your iPhone, right? So, more on the physics of high-wire feats and how the high-wire worker Philippe Petit pulled this off when StarTalk returns.

• 14:19Neil deGrasse Tyson?

  Welcome back, StarTalk. We're talking about the physics of that high-wire walk between the train towers in 1974 by Philippe Petit. And let's check out my interview with the man who sells.

• 14:33Neil deGrasse Tyson?

  Everyone's first question would be, how do you get a wire from one building to another? If the wire is strong enough to hold your weight, not that you're heavy, but if it's strong enough to hold your weight, you can't, you're not, you can't just feed it.

• 14:48Speaker 03

  Okay, well, in the case of the World Trade Center, how do you pass the cable across? Silently and quickly, because it was illegal.

• 14:55Neil deGrasse Tyson?

  That's how you do it.

• 14:56Speaker 03

  But you know what? I'm gonna answer with a visual thing, because I did something I never do. I brought the historic bow and arrow.

• 15:03Neil deGrasse Tyson?

  This is the?

• 15:03Speaker 03

  That's the bow, that's the bow, which is actually a cheap, you know, plastic thing in two parts.

• 15:08Neil deGrasse Tyson?

  Right.

• 15:09Speaker 03

  Which was hidden in a blueprint tube, because my friends were disguised as architects. And that's the arrow, and I know the scientist in you is... Not going to ask me, what did you pad at the end? It's obvious, right?

• 15:24Neil deGrasse Tyson?

  Cause you're shooting to someone else on the other side.

• 15:26Speaker 03

  My accomplice on the north tower shot the bow and arrow, to which was attached a fishing line. So imagine that in the middle of the night crawling on the south tower in complete darkness. You're looking for a fishing line that in itself is a movie scene, which is actually in the movie. And this is, you know, this was for my trunk and you're the first one that let you touch it for a few, a few seconds, thank you.

• 15:51Speaker 03

  So anyway, um.

• 15:52Neil deGrasse Tyson?

  Okay, so, so now that's the fishing line and presumably at this point, the cable is just dangling straight down.

• 15:59Speaker 03

  No, the cable is still in a south tower ready to be paid off. And what I need when I got a fishing line, I need to pay off a cordina, a little rope. And then they got the little rope and they attach a big rope. They send it to me and to the big rope, I can attach the very, very heavy steel cable. So it was like all night of rigging.

• 16:17Neil deGrasse Tyson?

  Because the fishing line is not strong enough to hold the weight of the cable. But it gets, but it connects you.

• 16:22Speaker 03

  Exactly, yeah, yeah.

• 16:23Neil deGrasse Tyson?

  It, it creates, it's the, it's the engagement ring. Before the marriage.

• 16:30Speaker 03

  I love that you say that because very often the poet in me cannot resist describing what happened by saying. I saw the twin towers being born, I had the idea before they were born. I saw them grow up and when they, they were adult, I married them with the smile of my cat in a curve. So marriage, ring, we, we're all in the same story.

• 16:48Neil deGrasse Tyson?

  Yes, yes, that it's, it's romantic, indeed.

• 16:51Speaker 03

  Well, French are very romantic.

• 16:54Charles Liu?

  Wonderful. He used that magic word, catenary.

• 16:57Neil deGrasse Tyson?

  Catenary.

• 16:57Charles Liu?

  Catenary.

• 16:58Neil deGrasse Tyson?

  Catenary. So Charles, let's talk catenary.

• 17:00Charles Liu?

  Okay, you've got a rope there.

• 17:03Neil deGrasse Tyson?

  I've got a rope.

• 17:04Charles Liu?

  You suspend it.

• 17:05Neil deGrasse Tyson?

  I can suspend it from two ends.

• 17:06Charles Liu?

  And the shape it makes is called a catenary.

• 17:08Neil deGrasse Tyson?

  Very nice.

• 17:09Charles Liu?

  Not a parabola, but a catenary and it's actually a hyperbolic cosine shape.

• 17:15Neil deGrasse Tyson?

  I knew that.

• 17:15Charles Liu?

  Yes, you did. Plus, it turns out that a catenary is really nice for hanging things and constructing things because there is no extra, what's called moment of curvature. It's being pulled in no extra direction, more than just its natural hanging. So, suspension bridges, for example, they have one huge catenary cable between the two piers. And then, from that cable, is suspended smaller cables which hold up the roadway. It's a light, yet strong way of supporting a tremendous amount of weight, without doing a whole lot other than just hanging a chain.

• 17:55Neil deGrasse Tyson?

  So, basically, gravity pointing downward against a flexible cable creates the shape.

• 18:01Charles Liu?

  That's right.

• 18:02Neil deGrasse Tyson?

  And so, I'd forgotten that, of course, the suspension, the large suspension cables between the two uprights of a suspension bridge, they're holding a catenary shape.

• 18:10Charles Liu?

  That's right.

• 18:11Neil deGrasse Tyson?

  I'd forgotten that, so thanks for reminding me.

• 18:12Charles Liu?

  Oh, no problem.

• 18:13Neil deGrasse Tyson?

  So, basically, this is too limp for him to walk across.

• 18:16Charles Liu?

  Yes.

• 18:17Neil deGrasse Tyson?

  So, he's gotta do it tighter, but it's still catenary.

• 18:18Charles Liu?

  That's still a catenary.

• 18:19Neil deGrasse Tyson?

  Still catenary. And even if I pulled it really tight...

• 18:22Charles Liu?

  That is a true catenary, also known as a line.

• 18:24Neil deGrasse Tyson?

  No, but there are other examples that we know of. For example, if I remember my athletic data, the center of a tennis net is six inches lower than the edges of the tennis net.

• 18:38Charles Liu?

  That's right.

• 18:39Neil deGrasse Tyson?

  Which is why you always wanna serve through the middle, then you get a really low serve.

• 18:42Charles Liu?

  Yes, exactly.

• 18:43Neil deGrasse Tyson?

  But it's accommodating the reality of the catenary drop.

• 18:45Charles Liu?

  Yes.

• 18:46Neil deGrasse Tyson?

  Of the cable that's holding up the net.

• 18:47Charles Liu?

  That's right.

• 18:48Neil deGrasse Tyson?

  And, so, and, here's, Charles, I bet, maybe you didn't know this. So, in the town of Sevres, France, there's the International Bureau of Weights and Measures. That's where they keep the kilogram, the meter, the stuff after, out of which everything else is measured. Now, here's what freaked me out, okay? Now, the meter is not defined by an artifact. But when it was, they're showing me the shape. And here's this meter. And you're supposed to support the meter on two points, okay? And then you measure it with a microscope, and then you, you scale anything else to that, to make your other meters, okay? He said, "You gotta put the support points here." I said, "Why?" Because that is the distance where they have calculated

• 19:31Neil deGrasse Tyson?

  the effect of the sagging of the weight of the meter under its own weight between these two points. Wow. I said, "It's only this big." "Of course, if you measured it to microscopic scales, you will see the sagging of this rigid bar, platinum iridium bar. And so even that is a catenary." Amazing.

• 19:50Eugene Mirman?

  All right, that's what I was gonna say.

• 19:51Neil deGrasse Tyson?

  Exactly. Now, I'm glad we cleared that up.

• 19:54Eugene Mirman?

  Yeah, yeah, yeah.

• 19:55Neil deGrasse Tyson?

  Okay. So, more on the physics of high-wire walking when StarTalk continues.

• 20:12Neil deGrasse Tyson?

  Welcome back to the American Museum of Natural History. You're watching StarTalk. And we're featuring my interview with high-wire artist Philippe Petit. For his famous walk across the Twin Towers in 1974, he used a 26-foot-long, 55-pound pole to balance himself over that wire. I asked him how that works. Let's check it out.

• 20:38Speaker 03

  May I actually tell you what a balancing pole is from my point of view? It is not a trick little toy to stand you on the wire. It's an extension of your arms. Because the human being on a high wire, when the winds are, you know, devouring the void, when the building or the landscape move and all that, you are being assailed by destroying equilibrium parameters.

• 21:01Neil deGrasse Tyson?

  All around you.

• 21:02Speaker 03

  Absolutely, and even inside you. So, the arms are nothing less than too short and not heavy enough. So, the extension of the arms throughout 4,000 years of history of wire walking became what is known as the balancing pole.

• 21:17Neil deGrasse Tyson?

  Wow.

• 21:17Speaker 03

  So, it's a little help. And if I show you how to walk on the wire, which I did for the young actor who played in a movie, you won't be able to negotiate that pole. That pole will move you left or right. It's easier to go without pole. But the minute you know how to negotiate the pole, it becomes... It's like driving a car. You don't really know what you're doing. You're talking to your friends, you're looking at the landscape, but your hands are constantly balancing left, right, left, right, in a very small way. And that's what the balancing pole does.

• 21:45Neil deGrasse Tyson?

  That's right, because as the car drifts ever so slightly, experienced drivers are not even conscious of the fact that you're bringing the car back and you're turning the wheel just the tiniest amount.

• 21:54Speaker 03

  Exactly, so the same for the wire walker. If you would focus very, you know, with a magnifying camera on the wire walker, you will see that he or she is constantly moving, because balance is a dance.

• 22:08Neil deGrasse Tyson?

  All right Chuck, let's unpack this.

• 22:09Charles Liu?

  Oh, yeah.

• 22:10Neil deGrasse Tyson?

  So I've got the famous cork with a nail in it. This is a Brad. And this was a very nice French wine, by the way, for the occasion. So I've got my French cork. Got it? I've got two forks. And I just dig one in like that. And put it in like that. This, we do this in physics class, right?

• 22:31Charles Liu?

  All the time, yes.

• 22:32Neil deGrasse Tyson?

  Like Physics 101.

• 22:33Charles Liu?

  Classic demonstration.

• 22:34Neil deGrasse Tyson?

  Classic demonstration. And there you have it.

• 22:37Charles Liu?

  And it balances, that's right.

• 22:38Neil deGrasse Tyson?

  So what's the physics of this, Charles?

• 22:39Charles Liu?

  Well, the way that all balances or levers work is that what's called L1M1 on one side has to equal L2M2, which is on the other side. Yeah. And all that really means is that if...

• 22:54Neil deGrasse Tyson?

  We're waiting for what it really means, yeah, yeah.

• 22:56Charles Liu?

  All it really means is if you have a longer thing on one side and the other side, small changes in your balance will be more easily balanced out than if they're shorter. So when Philippe was talking about his arms being too short, that's exactly right. As soon as he tips a little bit, he's going to swing all the way down and he can't bring enough lever arm on this side to balance him over. But once he has that 26-foot, 55-pound pole there, he's presenting himself with plenty of options in order to get himself back in balance by having that long lever arm on both sides.

• 23:29Neil deGrasse Tyson?

  So now, this is actually a different case from what you described, because this part of the fork is sitting below the wire.

• 23:36Charles Liu?

  That's true.

• 23:37Neil deGrasse Tyson?

  So if this wants to tip, he has to lift the center of mass higher than what it was before, and the center of mass doesn't want to do that. The center of mass of any system wants to stay as low as possible. Now, I asked him about this in a part of the clips we did not use. And what he said was, "Well, this is just a physics toy. You can buy this in a store." And a physics toy, is he just a physics toy up there who can't fall? Is he, is he a physics toy? And he said, no, he's not a physics toy. Because he's using his balancing talent. And the bar as an extension of his arms. Mm-hmm. To maintain balance, not as a physics toy. Such that it can't fall over at all. That's right.

• 24:20Neil deGrasse Tyson?

  And I said, well, I'm a little skeptical until I saw the pictures of his, his bar. And when you look at the pictures, they do not sit below him. They do not go below the wire. That's right. The way these do. So this is a physics toy. Mm-hmm. He's not. Yeah.

• 24:33Eugene Mirman?

  Wait, could you have a wire that, or a bar that was so long and weighted in such a way that you would almost definitely not fall?

• 24:40Neil deGrasse Tyson?

  Yeah, so for example, if you had, if he had a really long bar. That sunk well below the wire that he's walking on. Mm-hmm. As he begins to tip. The center of mass has to raise up for him to tip. And it won't let him do that. It'll just write him back. Again, he might misstep and it'll fall because he misstepped. But if he falls, it's not because he lost his balance. If he had one of these configurations. And so, so this is very stable. And I can just balance that right here. But this is slippery. Nope, it's slippery. Give me something to put this on. There we go.

• 25:16Neil deGrasse Tyson?

  Yeah, so.

• 25:17Eugene Mirman?

  I am no longer, I am no longer impressed by that guy.

• 25:23Neil deGrasse Tyson?

  Yeah, so, so, I mean, he, he knew this. And we chatted about why this is not him. And notice this is below the level of the bar. Below the level of the wire. And if he falls, he's lifting this weight to a higher point than it was before. And that's just not gonna happen.

• 25:45Neil deGrasse Tyson?

  We break it off.

• 25:46Eugene Mirman?

  Yep. I think if his arm fell off.

• 25:51Neil deGrasse Tyson?

  This is the physics of it, but Philippe Petit, he not only knows the physics, and he's got that. He takes it a step deeper. A step deeper. In his mind, body and soul. Let's check it out.

• 26:05Speaker 03

  I will never agree that this mystery of balance can be explained and put out in a question on a blackboard. I would say there is something that will never be put in a question. The human passion, the human intuition, the human, um, um, tenacity. Uh, and therefore, balance is a mysterious chemistry that even you, and I don't mean to insult you, I mean to respect very much science, because I love science, but

• 26:30Neil deGrasse Tyson?

  Insults welcome at all times.

• 26:31Speaker 03

  It could be explained in a scientific way. I mean, yes, we can look at the, the muscle and the nerve and the blood flowing, but what about the soul? What about the poetry in your head? What about things like, "I refuse to understand that something is impossible." Can you put that on the equation on the blackboard?

• 26:47Neil deGrasse Tyson?

  No, you can't.

• 26:48Speaker 03

  Good. At the same time, I am a lover of science. And I was a kid, I realized, I was told, that what is science? Well, science is not a vague notion floating above your head. Science is experiment. Do this experiment 20 times, write down, 19 out of 20 times, the, the knot broke, therefore this knot, and, and then slowly you create a parameter and then a rule that can be verified, and then you grow with civilization and you have all kind of more sophisticated experiment with more precise measurement, and it's basically experiment, it's trial and error. So I love science because it's human, it's us at work in trying to change the question mark around the "us" into exclamation point.

• 27:32Speaker 03

  I, I love when you are speechless.

• 27:36Neil deGrasse Tyson?

  He first said it wasn't science, and then he said it was science.

• 27:43Charles Liu?

  Yeah. It's just complicated science. When we're dealing with psychology, all the 100 billion neurons in your brain and being able to map those out in simple equations, that is still impossible, it's true. If you tried to break it all down, you were able to, then that would still be science. But what he said about science being something turning question marks into exclamation points, I don't know if I've heard a more poetic and beautiful way of explaining what science is all about.

• 28:10Neil deGrasse Tyson?

  Ooh. Well, up next, the psychology of attempting and surviving such death-defying stunts as he performed on StarTalk.

• 28:26Neil deGrasse Tyson?

  We're back in the Rose Center for Earth and Space, talking about the physics of high-wire acts, the physics in the mind, body, and soul of Philippe Petit. And I always wondered, I got the physics, but what kind of mind does it take to do what he's doing? To step out on that wire? Let's check it out.

• 28:49Speaker 03

  I have to be certain on the first step, I have to have a physical and a mental certitude that I will successfully perform the last step. If not, what am I doing? Well, I am full of doubts and fear, and I am risking my life. Well, I value life much more than that. I will never risk my life, or that of the building, or that of others below. So when I get on the wire, I have created, of course, thousands of, you know, hours of practice, dozens of years of experience. I have created a focus and a concentration that has no equal, and that only, I have no recipe for others. It's my own little chemistry. It is a very strange mood

• 29:32Speaker 03

  that really is physical. When I grab the pole, I am not wobbling, I am solid. And yet, I'm doing the most fragile action on earth. I am a miserable little human being who extracts itself from gravity, right? And who is now balancing and wants to become a half-man, half-bird. How presumptuous, you know? But that only can happen if there is this, I go back to poetry, but this sense of theatre, this sense of performing, this sense of measuring yourself with the elements, you know, a little dash of humbleness, which is not my speciality, but anyway, so that you know that you're not invincible. The minute you think you're invincible, you're gonna die. You know, that's what you deserve. But if you have a little dash of humbleness,

• 30:17Speaker 03

  and if you feel that you are controlling your life and the world, you see, it's a very strange, fragile chemistry, then you will give the image of solidité and majesty and panache and arrogance, why not, you know? But beauty, and beauty, the real beauty, inspires people.

• 30:36Neil deGrasse Tyson?

  Yeah, so, no, here, there's an interesting dimension to this. Why do we watch High Wire act at all? Unless we are thinking they might fall and that'd be something interesting to look at. Isn't that a weird thing?

• 30:52Charles Liu?

  Well, it is true.

• 30:53Neil deGrasse Tyson?

  We could talk about his psychology, but what about the psychology of the people that are attracted to watch the thing in the first place?

• 30:59Eugene Mirman?

  Well, I think I might catch them.

• 31:00Neil deGrasse Tyson?

  Really? Yeah, no.

• 31:02Charles Liu?

  The humility that he describes is so correct and true. He has to be, on the one hand, confident and, on the other hand, understanding that he is one thing amongst others. There have been a number of tragedies in the history of High Wire. That probably the most famous name in High Wire, the Wallendas, the Flying Wallendas, Carl Wallenda himself, he died during an ad, performance.

• 31:25Neil deGrasse Tyson?

  Well, so, Philippe Petit asserts that it takes a special focus, maybe even a supernatural kind, that's the way he's speaking, he's pulling his focus from someplace none of us have ever seen or dreamt of. And it just so happens, we have, on our video call, I think we've brought them in, we have someone who's a tightrope instructor, Sonia Harpstead. She teaches at the Circus Warehouse here in New York. Sonia, do we have you on the line?

• 31:53Speaker 04

  Yeah, I'm here.

• 31:54Neil deGrasse Tyson?

  Oh, Sonia, hello. Thanks for being on StarTalk.

• 31:57Speaker 04

  Hi, it's great to be here.

• 31:58Neil deGrasse Tyson?

  Yeah, so, we know intellectually that people such as yourself exist, but to really see you, you teach people High Wire stunts. So, what kind of mindset does it take to, who comes to you to do this? That's really what I should be asking here.

• 32:18Speaker 04

  Well, you know, the funny thing is that a whole range of people come to us, and it's really interesting to see who's interested in the challenge. We teach the wire's not that high, so it's not a fear thing. It's really more about finding a way to get your body to do something that's really challenging.

• 32:41Neil deGrasse Tyson?

  So, are you saying you can actually teach this skill? It's not just some psychological state of the person who finds you?

• 32:53Speaker 04

  Well, and a little bit you also teach the psychological state. But you can absolutely teach tight-wire walking. Anyone can walk a tight wire.

• 33:01Neil deGrasse Tyson?

  And when did this begin in your life?

• 33:04Speaker 04

  When I was in high school, I went on vacation and they had a flying trapeze there. And when I jumped off, I just knew I was going to do this for the rest of my life. So I found some classes and I worked on it through college. And at the end of undergrad, it was med school or the circus. And I chose the circus.

• 33:24Neil deGrasse Tyson?

  So you're telling me by probably by age seventeen, you were in a position to tell your parents you want to run away and join the circus? That's what you're telling me here?

• 33:33Speaker 04

  Yeah.

• 33:36Neil deGrasse Tyson?

  Very cool. Well, Sonya, thanks for sharing some time with us on StarTalk.

• 33:39Speaker 04

  Thanks for having me.

• 33:40Neil deGrasse Tyson?

  And I'll come watch you one day.

• 33:42Speaker 04

  Please do.

• 33:42Neil deGrasse Tyson?

  And we'll take physics notes and we'll compare notes.

• 33:45Speaker 04

  Absolutely.

• 33:45Neil deGrasse Tyson?

  And we'll tell you what law of physics kept you alive and what would have killed you had you messed up, okay? All right, thanks, Sonya.

• 33:51Speaker 04

  Thank you.

• 33:52Neil deGrasse Tyson?

  All right.

• 33:55Neil deGrasse Tyson?

  More of my interview with legendary high-wire artist Philippe Petit when StarTalk continues.

• 34:11Neil deGrasse Tyson?

  We're back. StarTalk at the American Museum of Natural History, right here in New York City. We're featuring my interview with high-wire performer Philippe Petit. He's French. And he walked between the World Trade Towers in 1974. And I had to ask him, is there a difference between walking on a wire 1,350 feet above the ground? Or walking on a wire 10 feet above the ground? Check it out.

• 34:38Speaker 03

  There is a continent of difference between walking 10 feet high, 10 stories high, and walking between the highest towers of the world at the time. And yet, for a scientist who analyzed balance, it's the same thing on the floor.

• 34:52Neil deGrasse Tyson?

  Yes, scientifically, it's the same thing.

• 34:54Speaker 03

  But no, it's not because to walk on the wire, you have to not be devoid by the by the space, by the void. And when we say... Void in any language, you know, le vide, it's a nice word, you know. People think it's empty, there is nothing. While you scientists know the void is full of of surprises, full of myriads of molecules floating. The void is a continent that needs to be explored. So here I am in the void and the void is voracious. Because human beings are made by gravity.

• 35:24Neil deGrasse Tyson?

  You cross voracious voids.

• 35:26Speaker 03

  Well, what I tell you is because human beings are made to, I wouldn't say crawl on earth, but I mean, live on the surface of the earth. You know, very few people are going in the belly of the seas, in the in the mouth of fire, of a living volcano on Mars, in the moon, on a high wire between the twin towers. So when you venture in these inhuman, unhuman boundaries, then you find out the whole world is against you in some ways. So you have to have a certain tenacity and courage and and and sense of poetry to majestically walk in those in those voids.

• 36:01Neil deGrasse Tyson?

  So are you guys afraid of heights?

• 36:04Eugene Mirman?

  I'm gonna say ye- ye- yeah, and certainly that high.

• 36:08Neil deGrasse Tyson?

  You'd be afraid of that height.

• 36:10Eugene Mirman?

  Uh, ten feet up, yeah, I've done a zip lining by and uh accidentally did it where you were like, I don't know, like three quarters of a mile in the air or something, uh between mountains was very terrifying. I.

• 36:20Neil deGrasse Tyson?

  So zip line where you you.

• 36:21Eugene Mirman?

  You hold the thing and they're like, don't worry, you won't die. And then when you're doing it, you're like, are you sure?

• 36:26Neil deGrasse Tyson?

  And you're and you're sliding along a cable.

• 36:28Eugene Mirman?

  Yeah, yeah, but then you get stuck sometimes. It's great.

• 36:30Neil deGrasse Tyson?

  Oh, this is one of the way, this is one of the ways they had people escaping the the launch vehicles in Kennedy Space Center.

• 36:37Eugene Mirman?

  Yeah, if you have to do it, definitely do it.

• 36:39Neil deGrasse Tyson?

  But it was not just a zip line to get you away from the the spacecraft. It's a zip line that takes you basically to a bunker because your spacecraft is about to explode and you gotta be protected for that.

• 36:48Eugene Mirman?

  How often did they do?

• 36:49Neil deGrasse Tyson?

  They've never you, they've never needed it.

• 36:51Eugene Mirman?

  Oh, I mean, good.

• 36:52Neil deGrasse Tyson?

  Yeah, yeah, that's right.

• 36:53Charles Liu?

  No, I I love zip lines, being harnessed, being tied to something like that. No fear at all. I could be a mile up. What freaks me out is when I'm looking over the edge of something and the only thing between me and a thousand feet down is a rail. And I look over and I know intellectually I'm gonna be just fine, but the butterflies, they just go. There's a natural, oh, craaah.

• 37:20Neil deGrasse Tyson?

  That's what the butterflies are saying. Okay.

• 37:29Neil deGrasse Tyson?

  Eugene, where were we?

• 37:33Charles Liu?

  It freaks me out when I look over the edge. It's simple as that.

• 37:35Neil deGrasse Tyson?

  I'd be afraid to tight-rope that.

• 37:38Eugene Mirman?

  Yeah, fair enough.

• 37:40Neil deGrasse Tyson?

  Other things, I don't really, I'm cool with heights. I mean, I grew up, I grew up in the city and tall buildings are just life. And, and I, I lugged my telescope to the roof of my 22-story building and I looked over and there's little people down there walking in it. I'd love going to the tallest buildings that I could.

• 37:56Eugene Mirman?

  But do you, but I like, looking over a railing, I agree mildly terrifying. What about like flying through the air or being in a precarious? Like so far, you're like, I don't mind being at the top of a building. I also am comfortable with that.

• 38:08Neil deGrasse Tyson?

  Okay, yes. So, no, no, but you can split it. There's the risk of thinking you're going to die.

• 38:13Eugene Mirman?

  Yeah.

• 38:13Neil deGrasse Tyson?

  Because the railing is frail and just being at a high height.

• 38:18Charles Liu?

  Right.

• 38:18Neil deGrasse Tyson?

  Right? These are two different things.

• 38:19Charles Liu?

  There have been-

• 38:20Neil deGrasse Tyson?

  It's probably, evolutionarily, you wanna fear heights.

• 38:24Charles Liu?

  That's right.

• 38:25Neil deGrasse Tyson?

  Because you don't wanna die.

• 38:27Charles Liu?

  Psychological experiments have indeed shown that when you have toddlers or young children going to the edge of something that's high, they naturally have a fear response.

• 38:37Neil deGrasse Tyson?

  Well, so, what's interesting, we, we researched some other creatures in the world.

• 38:43Charles Liu?

  Yeah.

• 38:43Neil deGrasse Tyson?

  And here we are, like, impressed with high-wire walkers, yet in the animal kingdom, are any of us impressed by a squirrel? Just runs along a power line?

• 38:53Charles Liu?

  They're small.

• 38:54Neil deGrasse Tyson?

  They're just running along, they're going back and forth, chasing each other on a power line.

• 38:58Eugene Mirman?

  If you saw a horse doing that, you'd be like, wow.

• 39:02Neil deGrasse Tyson?

  Okay, all right, all right. Not impressed with the squirrel. How about the mountain goats? That are just positioned on this much rock, exposed rock on a rake thing, and they're just chewing their cud, or whatever they chew, looking around like it's not even a thing.

• 39:17Eugene Mirman?

  That is very impressive.

• 39:19Charles Liu?

  A lot of them fall, you know?

• 39:20Neil deGrasse Tyson?

  A lot of what?

• 39:21Charles Liu?

  A lot of mountain goats and stuff fall.

• 39:23Neil deGrasse Tyson?

  Now, how do you know this? I've never seen one fall.

• 39:24Charles Liu?

  You just don't see that on National Geographic.

• 39:26Eugene Mirman?

  Is that true?

• 39:27Neil deGrasse Tyson?

  Wait a minute, this is the National Geographic channel.

• 39:29Charles Liu?

  Oops. You don't see that on Nova.

• 39:32Eugene Mirman?

  Is that a little true that a lot of the goats fall? Cause I've seen them, they seem very balanced.

• 39:36Charles Liu?

  It is, it is a little true that mountain goats, bighorn sheep, et cetera, fall often. But what they're really good at-

• 39:44Neil deGrasse Tyson?

  I have to say, if we ever saw that, that would just be hilarious.

• 39:46Charles Liu?

  Yes.

• 39:47Neil deGrasse Tyson?

  I mean, we laugh at kittens that fall off, they jump and then they fall.

• 39:50Charles Liu?

  Yes.

• 39:51Neil deGrasse Tyson?

  We make sport out of that on YouTube, right? So, so, so a mountain goat falling, no, I don't know anyone who has footage of a mountain goat losing its footage.

• 40:00Charles Liu?

  That's right. What mountain goats are great at...

• 40:03Neil deGrasse Tyson?

  Did that sentence make any...

• 40:04Eugene Mirman?

  Yeah. I mean, also, I'm gonna...

• 40:07Neil deGrasse Tyson?

  Footing, footing. No footage of a mountain goat losing its footing. Right.

• 40:13Charles Liu?

  Right. No, mountain goats, bighorn sheep, they fall, often. Well, we don't see them, of course, on nature specials.

• 40:19Neil deGrasse Tyson?

  Therefore, how do you know they fall?

• 40:21Charles Liu?

  Statistics, people actually do this research, do show that they do fall. But what they're really good at is recovering. They'll fall a ways, it looks like they will go down to their doom, but they're able to recover and catch themselves on the next ledge down.

• 40:34Neil deGrasse Tyson?

  They don't have thumbs. How, how, they have hooves. How do they catch themselves?

• 40:40Charles Liu?

  You know those horns?

• 40:41Neil deGrasse Tyson?

  No, no, am I...

• 40:42Charles Liu?

  Okay, think, think. Bighorn sheep...

• 40:44Neil deGrasse Tyson?

  They've just got four hooves.

• 40:45Eugene Mirman?

  Bighorn sheep catch their head on a ledge...

• 40:48Neil deGrasse Tyson?

  And they're not, and they're not apes that have like rotating, rotator cup shoulders.

• 40:53Charles Liu?

  Bighorn sheep with the horns, squirrels with their tails, they're almost like built-in bars. They're extra lever arms to the left and the right that allow them to have better balance than we otherwise would.

• 41:08Eugene Mirman?

  Wow. So, so those, those bighorn sheep are the, are the French of the...

• 41:15Charles Liu?

  We miss you.

• 41:18Neil deGrasse Tyson?

  But we can go even bigger, we get to elephants.

• 41:20Charles Liu?

  Yes.

• 41:21Neil deGrasse Tyson?

  Do you have elephants balancing on balls and stuff like that in the circus? Not in the...

• 41:25Eugene Mirman?

  In the wild.

• 41:26Neil deGrasse Tyson?

  Not in, not, what's in the wild.

• 41:28Charles Liu?

  Well, that's just practice, right?

• 41:31Neil deGrasse Tyson?

  Yeah, I haven't seen it in the wild, yeah. But now you don't see many elephants in circuses anymore, but when we did, they'd be balancing on balls.

• 41:37Charles Liu?

  Yeah.

• 41:38Neil deGrasse Tyson?

  So, why should we be impressed if we do it?

• 41:40Eugene Mirman?

  Well, if it's high enough, I think it's impressive.

• 41:43Charles Liu?

  Well, yes, if an elephant were on a cable balancing on a ball, we should be impressed.

• 41:49Neil deGrasse Tyson?

  An elephant on a cable balancing on a ball on the side of a cliff, okay.

• 41:53Eugene Mirman?

  But if an elephant walked a tightrope, holding even a small pole...

• 41:57Charles Liu?

  In his little trunk, yeah.

• 41:59Eugene Mirman?

  Yeah, in his little trunk. I'd be like, alright, elephant, now, now this is something.

• 42:03Neil deGrasse Tyson?

  Now you're talking.

• 42:06Eugene Mirman?

  Yeah.

• 42:08Neil deGrasse Tyson?

  Well, coming up on StarTalk, our StarTalk episode is not complete without a dispatch from Bill Nye the Science Guy when StarTalk continues.

• 42:28Neil deGrasse Tyson?

  Welcome back to StarTalk. We are featuring my interview with high-wire artist Philippe Petit, who walked between the Twin Towers of the World Trade Center. I always wanted to know what's next for him. Let's check it out.

• 42:43Speaker 03

  So, after that, people, some people said, "Well, what now? The highest towers in the world. Are you gonna kill yourself? You're gonna retire?" But, no. I was not collecting the gigantic. I was not interested in this absurd competition that the Book of Records, you know, offers. I hate that. No, it's curiosity. But noble curiosity. It is the feeling that we all have when we are born, that we want to maybe extract ourselves from our human condition. That's why people go on space and visit other planets. That's why people try to fly. That's why Warwalker exists. So, the competition, on those technical terms, is absurd. What is beautiful is the intellectual risk, you know? The breaking boundaries, surprising yourself.

• 43:27Speaker 03

  You know, we take ourselves so seriously. We never make a fool of ourselves. We never go in directions that are not

• 43:32Neil deGrasse Tyson?

  Not often enough.

• 43:33Speaker 03

  the ones we feel we are. If you like classical music, are you listening for a few hours to heavy metal? Probably not. Well, I do. I sometimes play with the extremes. I explore. And again, you see, I always use the word exploration, curiosity, intuition, because that's what I think we should do in our very, very short stay on this planet.

• 43:53Neil deGrasse Tyson?

  Charles, he's really a scientist.

• 43:55Charles Liu?

  He really is. He's talking right now about the innovation, creativity, imagination.

• 44:00Neil deGrasse Tyson?

  What's interesting to me is, he's not doing this to set records. He's doing this as art. And he's asking himself, "How can he extend the boundaries of his art?" And that's a noble cause. That's what any artist should be doing.

• 44:17Charles Liu?

  And that's what every scientist does, too. Looks at what's there and says, "What's next?"

• 44:22Neil deGrasse Tyson?

  So, before we wrap, we gotta catch up with my friend, Bill Nye the Science Guy, with his latest dispatch from the city. And he's gonna be reflecting just on what all this means. Check it out.

• 44:37Bill Nye?

  We're on the grounds of the World Trade Center. This is where a national tragedy occurred. But the building that stands here now is inspirational. When you're in here, you feel like you could soar like a bird over the city of New York. This is also where the Twin Towers once stood and where Philippe Petit managed to rig a wire 1,368 feet above the street. And he walked that tightrope for almost an hour one morning. People on the ground were riveted. They were amazed by this man who seemed to be flying over the city. When you come here now, I hope you get some of that same feeling. I hope you're inspired. So, thank you, or merci Monsieur Petit.

• 45:20Bill Nye?

  And, uh, thank you, Mr. Big Building Train Hub. You inspire us. When we come here, we feel like our imaginations can soar.

• 45:32Neil deGrasse Tyson?

  This is what architecture does.

• 45:37Neil deGrasse Tyson?

  A great architecture soars, and it forces your imagination to soar along with it. And what's interesting is that in this particular case, what did he do? He walked the World Trade Towers. And one of the nation's greatest tragedies occurred on that site. And we all know this. And when I try to remember the towers, because I lived near them, it happened in my backyard, the September 11th attacks. You know what I do? I look at the towers and I say, "Okay, these aren't just buildings to me. I have the lens of an astrophysicist." So, they mean something else. They mean something more to me.

• 46:17Neil deGrasse Tyson?

  First, there were a veritable indoor universe unto itself. Multiple levels below ground of shops, hundreds of shops. 110 stories up.

• 46:31Neil deGrasse Tyson?

  You'd reach the roof. At the top level, there was a little computer where you could type messages that would be sent out to aliens from the radio transmitter that was at the top of the North Tower. So, in a sense, the tower was trying to sort of help us reach for the stars. And that meant a lot to me, even though I knew nobody was probably listening or anyone would care. It was the gesture that mattered to me. And then I'm there at sunset. And at sunset, the towers are so tall that you can actually watch the sun set floor by floor up the building. The building is so high that from the top,

• 47:15Neil deGrasse Tyson?

  the sun sets nearly two minutes later for someone at the top floor than it does for someone at the bottom floor. That's how much beyond the horizon your view was granted from that height. And so, in fact, if you could run up the stairs, one floor per second, you could stop the sunset in its tracks because you'd be ascending at the same rate that the sun would be setting. And you'd run out of breath or run out of floors. Eventually, that would have to stop. And then the sun would set on the World Trade Center.

• 47:54Neil deGrasse Tyson?

  So, yes, the sun has forever set on the World Trade Center. But the sun has risen and set a trillion times before. And though it has set on the World Trade Center, it'll continue to rise and set for the rest of the time we have on Earth. And he married them. The science, the physics, the astrophysics, the poetry. What more could we ask for a pair of buildings that are no longer there? That's our show. As always, I bid you to keep looking up.