Cosmic Queries – The Experience of Time with Charles Liu

Is our experience of time a result of our perpetual movement? Neil deGrasse Tyson and co-hosts Chuck Nice and Gary O’Reilly explore spacetime, metaphysics, the Brachistochrone problem and more with astrophysicist Charles Liu.

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

• 0:00Neil deGrasse Tyson?

  Today on StarTalk Special Edition, we brought in our geek in chief, the one and only Charles Lu. We talk about all kinds of things like our experience with time relative to a beam of light. We also talk about what our favorite objects were in Star Trek that came true. What else? We also wonder, what direction should you launch a rocket? Is it straight up or is it sideways? That and more, coming up on StarTalk Special Edition.

• 0:34Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:43Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:47Neil deGrasse Tyson?

  This is StarTalk Special Edition. Neil deGrasse Tyson here, your personal astrophysicist. And as always for these editions, we got Gary O'Reilly. Gary? Hey Neil, good to be here again. Former professional footballer and professional announcer. And thank you to the soccer universe for lending you to us. That's very kind of you. Yeah, and we got Chuck. Nice Chuck, always good to see you, man. Hey, that's right. And to the professional soccer universe, you're not getting them back. We got them. We got them now. You suckers, you lost. This is a grab bag cosmic queries. Anytime the grab bag goes everywhere,

• 1:31Neil deGrasse Tyson?

  guys, we gotta pull out the big guns. Ooh. All right, we, we open the shed and we pull out.

• 1:39Neil deGrasse Tyson?

  Our guest has wheels? Undisputed Charles Lu. Friend and colleague, he's a professor of astronomy and physics at the City University of New York, based in Staten Island, and with the Graduate Center there, and he's got a podcast called The Universe, which showcases up and coming science talent. We need some of that on this landscape, so good to see that happening. And so here's what happens. If you don't know Charles, he will bail us out of anything we don't otherwise know. And it works every time. He's the geek in chief. All hail. That's right, the geek in chief.

• 2:17Chuck Nice?

  Charles Cocktail Party Lou, because if there's anything you want to know, he's the guy at the cocktail party that knows everything.

• 2:24Neil deGrasse Tyson?

  And I count myself high among the ranks of in the geekiverse. But in the geekiverse, the scale is infinite. So however far I am, you can be geekier. And that's the man in the studio right now. Okay, so you, this is a cosmic queries or just queries. It's a special edition. So, so Gary, Chuck, what, who's first?

• 2:51Gary O'Reilly?

  I'll go first. All right.

• 2:52Neil deGrasse Tyson?

  Okay. Gary, go for it.

• 2:53Gary O'Reilly?

  These are from our Patreon audience and we love them and bless them for their curiosity. And this is Chris Hampton's question. Could it be that our perpetual experience of time is because of our perpetual movement through the fabric of spacetime?

• 3:08Neil deGrasse Tyson?

  Ooh, I like that. So Charles, let me add to that. If nothing moved in the universe, would we have any perception of time at all?

• 3:17Charles Liu?

  We would, but it's a strange, strange concept, right? Because as it turns out, many people will say, when one interpretation of the special theory of relativity, which talks about space, traveling through space and traveling through time, is that everything is always moving at the speed of light. But it's speed of light, not through regular three space, but through four dimensional spacetime. So you and I, we move through space and we have mass, we have spacetime and we're moving sort of at the equivalent of a speed of light. A photon, which is a piece of light, has no mass and it's moving always at the speed of light also. So in a sense, in this four dimensional way of thinking, instead of a three dimensional

• 4:01Charles Liu?

  way of thinking, we are all always moving at the speed of light. But light itself is moving through space faster than we are moving through space only.

• 4:11Charles Liu?

  So this perception of time is always a matter of what we perceive based on where we are and how we're moving through three dimensional space, but also four dimensional space time.

• 4:22Neil deGrasse Tyson?

  Why am I more confused than than what?

• 4:24Chuck Nice?

  I was gonna say, first of all, I hate to do this, but you gotta tell me, why are we always moving at the speed of light? Because I know that's what everybody is asking.

• 4:35Neil deGrasse Tyson?

  Right now, right this minute.

• 4:36Chuck Nice?

  What do you mean when you say, why are we always moving at the?

• 4:39Neil deGrasse Tyson?

  Translated from Chuck, what were you smoking before you began this interview?

• 4:42Charles Liu?

  Okay.

• 4:43Neil deGrasse Tyson?

  That's my Chuck translation right there.

• 4:45Charles Liu?

  A little bit of Albert Einstein 1905.

• 4:47Neil deGrasse Tyson?

  Okay.

• 4:48Charles Liu?

  Think about it this way, if you are traveling, say, in one dimension, you measure how many, say, miles per hour you're going along the road.

• 4:57Neil deGrasse Tyson?

  In a straight line, in a line.

• 4:58Charles Liu?

  In a straight line, right. But if you're moving in two dimensions, say you're moving diagonally, like an airplane, right, moving up diagonally during takeoff, it's moving both in the horizontal direction and the vertical direction.

• 5:13Neil deGrasse Tyson?

  At the same time.

• 5:15Charles Liu?

  Yeah, and so when you take the combination of those, then you wind up with a new velocity vector, and the amount of speed you're going doesn't look the same as either right along the ground or vertically upward.

• 5:28Neil deGrasse Tyson?

  Right.

• 5:29Charles Liu?

  So it's adding this vector thing. Now, imagine spacetime being that. Space is the horizontal axis. Time, the fourth dimension, shall we say, is a vertical axis.

• 5:41Neil deGrasse Tyson?

  So all three dimensions of space are this one axis right now?

• 5:44Charles Liu?

  Right.

• 5:45Chuck Nice?

  It's one axis.

• 5:46Charles Liu?

  Collapse them all together.

• 5:47Chuck Nice?

  Time being now the vertical axis.

• 5:49Neil deGrasse Tyson?

  Exactly, okay.

• 5:50Chuck Nice?

  Or the fourth dimension or?

• 5:51Neil deGrasse Tyson?

  Okay, let's keep going, so now go.

• 5:52Charles Liu?

  It's not that hard, so.

• 5:54Neil deGrasse Tyson?

  No, we ain't done yet. Don't be saying it ain't hard yet.

• 5:57Charles Liu?

  No, no.

• 5:58Chuck Nice?

  Yeah, go ahead.

• 5:59Charles Liu?

  Then you do the same kind of thing where you use kind of like a Pythagorean theorem, right, for what spacetime does in terms of measuring distances and velocities and so forth. And so you wind up with the velocity that is what the speed of light would be just through space. So we all, everything is moving at that same velocity. But depending on how we're moving through space, we also move through time a little bit differently. That vector, which toggles back and forth between the vertical and the horizontal, is always constant.

• 6:32Neil deGrasse Tyson?

  Wait, so just hold on. So if we're just sitting here having this conversation, we are moving in time.

• 6:39Gary O'Reilly?

  Yeah, time.

• 6:40Neil deGrasse Tyson?

  And so we're moving vertically right now in time, because we're not really going anywhere.

• 6:45Charles Liu?

  Yes.

• 6:46Gary O'Reilly?

  You know where we're at right now.

• 6:47Neil deGrasse Tyson?

  So now, light is moving not only in time, but also in space.

• 6:52Charles Liu?

  Yes.

• 6:52Neil deGrasse Tyson?

  So now, it's got, let's call it a 45-degree angle up there.

• 6:56Charles Liu?

  There's the difference. See, light has no mass. So it's always going horizontally only. So light particles don't actually age. We age as we sit here.

• 7:08Gary O'Reilly?

  So they're constantly in the present?

• 7:10Neil deGrasse Tyson?

  In their own present. Exactly. They're constantly in their own present.

• 7:13Charles Liu?

  In their own present, that's right. One of the hypotheses that was trying to decipher whether or not the cosmological redshift was actually expansion of the universe or not, was something proposed many decades ago by people like Fred Hoyle, who suggested that maybe the reason we see cosmological redshift, that things moving, things appearing redder than they actually are.

• 7:37Neil deGrasse Tyson?

  Yeah.

• 7:37Charles Liu?

  Right.

• 7:38Gary O'Reilly?

  Oh, yes.

• 7:38Charles Liu?

  Not expansion, but just that light, as it travels, it gets tighter. It loses energy as it moves, almost as if it had mass.

• 7:46Neil deGrasse Tyson?

  That was called the tired light hypothesis.

• 7:48Charles Liu?

  Right.

• 7:48Gary O'Reilly?

  But does it still travel at the speed of light? If it now sort of denuded its way through... Really, what Gary just said is, what is redshift?

• 7:58Gary O'Reilly?

  That's really what he just said.

• 7:59Charles Liu?

  That's for another time. But basically, it's the way the cosmos moves. It expands throughout, right? What used to be tiny is now huge. But... As far as relativity goes and how our motion through spacetime goes, right? We are this way and light is that way.

• 8:19Neil deGrasse Tyson?

  Horizontal.

• 8:20Charles Liu?

  Horizontal, horizontal. And we wind up with this kind of.

• 8:23Neil deGrasse Tyson?

  Who's going, who's going at an angle between us?

• 8:25Charles Liu?

  We do when we move.

• 8:27Neil deGrasse Tyson?

  When we move?

• 8:27Charles Liu?

  Right.

• 8:28Neil deGrasse Tyson?

  Got it.

• 8:29Charles Liu?

  If we're on a spaceship or on an airplane or something like that, we are going that.

• 8:32Neil deGrasse Tyson?

  Then there's an angle because we're not only moving in space, but also in time.

• 8:36Chuck Nice?

  Yeah.

• 8:36Charles Liu?

  Yes.

• 8:37Chuck Nice?

  Cause we're going up and horizontal at the same time.

• 8:41Charles Liu?

  Right, that's why, that's why one of my, uh, college professors who really understood this super well, explained to all of us that you can do special relativity using hyperbolic trigonometry. And he always thought, wow, that was much easier.

• 8:54Chuck Nice?

  Oh, well, who does, who knows that?

• 8:55Charles Liu?

  Who does that, right?

• 8:56Chuck Nice?

  I mean, come on.

• 8:57Charles Liu?

  Why wouldn't you?

• 8:58Chuck Nice?

  Who doesn't do that?

• 9:00Charles Liu?

  Which, which was cool, uh, but I never quite understood it so well, so.

• 9:05Neil deGrasse Tyson?

  Yeah, alright.

• 9:05Chuck Nice?

  Wow.

• 9:06Charles Liu?

  You're making me feel good, Charles, cause if you don't quite understand it, I think I'm in a better place. This is a tough thing, guys. Yeah, man, it is.

• 9:14Neil deGrasse Tyson?

  Wait, just to, just to put the nail in this coffin. Our, so Charles, isn't it just being provocative to say we are moving at the speed of light? What you're saying is we're moving at our natural speed through time, whatever we wanna call that. Light is moving at its natural speed through space. But to say we are moving at the speed of light, that's a little needlessly provocative, it seems to me.

• 9:38Charles Liu?

  It might be. That kind of phrasing probably is an attention grabbing device more than anything else. But it also implies with it a need for you to understand what it means to move through spacetime.

• 9:49Neil deGrasse Tyson?

  Correct. It forced me into that.

• 9:51Charles Liu?

  To move through spacetime.

• 9:52Neil deGrasse Tyson?

  It forced me to think about that differently.

• 9:54Charles Liu?

  Right.

• 9:54Neil deGrasse Tyson?

  Cause I'm naturally just moving forward in time at one second per second. And the light is naturally going through space, not aging at all. We're just doing our thing.

• 10:05Charles Liu?

  That's right.

• 10:05Chuck Nice?

  However, what it did do for me was it allowed me to visualize the axes. That you were talking about. That's really what it did. So, alright, cool.

• 10:16Neil deGrasse Tyson?

  Next one.

• 10:16Chuck Nice?

  Alright, this is Kevin, this Kevin the Samoyed. And Kevin the Samoyed says, glad the luniverse is here.

• 10:23Neil deGrasse Tyson?

  Nice, nice. The luniverse has landed. The luniverse has landed.

• 10:27Chuck Nice?

  The luniverse has landed. If we are able to achieve warp capability one day, will we experience time dilation in accordance to Einstein's general relativity? Tebby, if Star Trek is correct, they age at the same rate as Starfleet in San Francisco. P.S. Neil, get your hands on some Hartford Old Vine Zinfandel from Russian River.

• 10:51Neil deGrasse Tyson?

  Oh, nice, nice.

• 10:51Charles Liu?

  Russian River?

• 10:52Neil deGrasse Tyson?

  Excellent. Love Russian River.

• 10:53Charles Liu?

  Napa's not cool enough anymore?

• 10:55Neil deGrasse Tyson?

  The Russian River does it right, and Old Vines can't argue with that.

• 11:02Charles Liu?

  Yep, yep, yep.

• 11:02Neil deGrasse Tyson?

  Thank you. Love Old Vine.

• 11:03Charles Liu?

  All right. Yeah, well, Kevin, the bottom line is that Star Trek does it wrong, right? In order for... Yeah, I know.

• 11:11Chuck Nice?

  Excuse me.

• 11:12Charles Liu?

  I know, I know. I know what I just said.

• 11:14Chuck Nice?

  How dare you!

• 11:15Charles Liu?

  I know what I just said.

• 11:16Neil deGrasse Tyson?

  Take that back right now!

• 11:17Chuck Nice?

  Take it back!

• 11:19Charles Liu?

  Star Trek is completely correct in the Star Trek universe. Star Trek, when it comes to warp speed and time dilation, is not correct when it comes to our understanding of the theory of relativity.

• 11:31Neil deGrasse Tyson?

  So you're saying they shouldn't age while they're doing their high warp maneuvers?

• 11:37Charles Liu?

  Right. What should be happening... The problem is, you see, the high warp maneuvers are faster than the speed of light.

• 11:44Neil deGrasse Tyson?

  Yes.

• 11:44Charles Liu?

  And if an object moves through our current space at faster than the speed of light, then it can violate causality. And so that whole aspect of relativity and so forth is necessary to make sure that the arrow of time and the way that we know, understand history and the changing of the universe stays okay.

• 12:06Neil deGrasse Tyson?

  The causes occur before events.

• 12:08Charles Liu?

  Yes. When you have a circumstance like...

• 12:10Neil deGrasse Tyson?

  Rather than after them.

• 12:11Charles Liu?

  When you have a circumstance like warp speed, right? That goes out the window. This object, because it's in a subspace bubble, right? By the Alcubierre drive or whatever, it goes through so fast that it can actually outrace a radio signal to a distant star. And so you can tell something that happened before the radio signal was even arriving, which means that you violate causality. The way that they get around that problem is to say that communications also goes faster than speed of light.

• 12:43Chuck Nice?

  Also go through subspace.

• 12:44Charles Liu?

  So you know those subspace communications and so forth, right? And what that means is that I can still radio ahead... Not with a radio, though, but with something that's going faster than my spaceship is going, which is faster than the speed of light at that moment. And therefore causality is not violated because all information that they get before and after in that subspace is retained.

• 13:05Neil deGrasse Tyson?

  Got it, okay.

• 13:06Charles Liu?

  So, bottom line is, as soon as you throw in these fanciful ideas of how to go faster than light, then you have to assume that your communications also go faster than light and that that light is no longer a speed limit for objects in the universe, therefore causality can be preserved because you have everything able to go faster than light.

• 13:29Chuck Nice?

  So am I correct that that's why the wormhole works as, without that violation? Because you're not actually going faster than the speed of light, moving through the medium of spacetime.

• 13:41Neil deGrasse Tyson?

  Right, right, right. It seems to me a wormhole should be just a clean step through.

• 13:44Chuck Nice?

  It should just be clean, a clean step through.

• 13:46Charles Liu?

  Yes, except that wormholes at the moment have not been determined to exist.

• 13:49Neil deGrasse Tyson?

  No, no, but wait, Rick has wormholes.

• 13:51Chuck Nice?

  Well, they are in Star Trek.

• 13:54Neil deGrasse Tyson?

  Rick has wormholes, Doctor Strange has wormholes, don't tell me we don't have wormholes.

• 13:58Charles Liu?

  Oh, we have wormholes. Does the universe have wormholes? I love all those wormholes. But, yes, do we have one right now? That's from, it's faster than light travels.

• 14:08Neil deGrasse Tyson?

  Rick and Morty, it's good enough for Rick and Morty, it's good enough for me.

• 14:10Chuck Nice?

  That's right, Morty, that's right.

• 14:14Neil deGrasse Tyson?

  Thank you. Chuck, do we really need the drunken burp? Was that really necessary?

• 14:21Chuck Nice?

  You can't do Rick without it.

• 14:36Neil deGrasse Tyson?

  So who's next? Who's got the next burp?

• 14:38Gary O'Reilly?

  All right, uh, next up is Manny Byers from New York City. All my life, I've always thought there is some connection from these three subjects: time, universe, and dreams.

• 14:51Gary O'Reilly?

  Like as in one is dependent on the other in order to unlock the center of this pyramid for answers. It may be that the answer can be a combination of science and philosophy, but do you think this pyramid of subjects has anything to do with answering questions such as the value of life or why we exist in this universe?

• 15:11Charles Liu?

  What a wonderful question. And linking, you know, linking the universe with some sort of metaphysics is something that has been done since the very beginning. In fact, Neil will tell you that in the history of science, until such time as there was a true separation between empirical science and metaphysics, it was called natural philosophy. And we were always trying to philosophize until people like Galileo said, you know what, I don't think we should really mix like how beautiful is a tree or how righteous is a star. Let's just talk about the tree and the star and then worry about the philosophy separately.

• 15:49Neil deGrasse Tyson?

  Yeah, in fact, Newton's most famous book, which we call Principia, the full title of that is Mathematical Principles of Natural Philosophy. And so the natural philosophy is part of that framing.

• 16:04Charles Liu?

  Great point, right. So your ideas are great, Manny. They're right on target. And I would say is the following, as far as we know right now, human dreams are limited in our existence, our perception. There is no evidence yet that our dreams are actually connected with the rest of the universe. That's the key here in terms of tying them together. For us and for our existence, dreams and time and the universe are late.

• 16:36Gary O'Reilly?

  Charles, let me throw this at you. Premonitions. You can't get the future before...

• 16:43Gary O'Reilly?

  You're out of the present. But I've had, I've had premonitions that have come true.

• 16:48Charles Liu?

  Right.

• 16:49Gary O'Reilly?

  So that's the future before. And in the present. So how, how does that connect?

• 16:54Chuck Nice?

  Or is it, or is it, wait a minute. Or is it a convergence of the past and all of your past? That be, that converges on one moment because the surroundings uh, inform you in such a way that you say, oh, this is going to happen. And so it appears to you that it has already happened. But really, it's just your vast past experience coming together in one point. Pray another event.

• 17:28Charles Liu?

  Well said.

• 17:29Gary O'Reilly?

  Can I explain one thing? Uh, I'm nineteen years of age. I have not played in my football club's first eleven, right? So I'm, I'm way off of that. And about ten days before it actually happens. I have a dream. I'm running towards my own goal. I'm in the center of the field and I get punched in my left cheek.

• 17:51Gary O'Reilly?

  So wow, random. So I'm playing in my full debut. About ten days later, I'm running towards my own goal in the center of the field. I get punched in my left cheek. I'm like, you are kidding me.

• 18:05Charles Liu?

  Yellow card?

• 18:06Gary O'Reilly?

  No, carried on. It was allowed.

• 18:08Charles Liu?

  Carried on.

• 18:09Gary O'Reilly?

  We played a different game back then. It was more rollerball.

• 18:12Charles Liu?

  Oh, man.

• 18:13Gary O'Reilly?

  For that, yeah. For that to be part and parcel.

• 18:17Charles Liu?

  Okay.

• 18:17Gary O'Reilly?

  Of that dream way ahead of time was just so random, so.

• 18:21Charles Liu?

  It's uncanny, right? Well, here, here is the point, right? We have not yet been able to scientifically confirm whether these things are random or whether they are actually connected. Think about this way. The human brain is essentially designed to make predictions of the future. Right? We are spending our entire existences. From the early days, right, we predict that if that lion over there will come after me in this direction, therefore I will run in that direction. We predict later on, right, that the stock market will go up, therefore we will invest, right? These predictions do not always come true, in fact, they rarely come true, but there are thousands of them. The brain is a prediction generator.

• 19:02Charles Liu?

  So could it have been that your brain, in its generation of predictions, which dreams to some extent are, right, go on and had so many predictions in your lifetime that just that one random one came true just by chance? And you remember the hits and you forget the misses?

• 19:22Gary O'Reilly?

  I knew which stadium I was in and it was just as dreamt.

• 19:29Charles Liu?

  So it's really remarkable that way, too. And then there's a second factor, which I only recently learned by psychologist friends. Apparently, we humans will adjust our memories To match. Backwards. Yes. We humans actually have a, it's hard to know whether it's a defect or whether it's a reality truth thing. We re, every time we remember things, our brain is recreating the memory, it's drawing it out. It's not like the typical, say, computer where it comes out and brings out a perfect copy. It goes through a lot of It's not a movie camera. It goes through a lot of filters and it resets things.

• 20:09Charles Liu?

  And people wind up misremembering, not on purpose, not to be lying, but their brains have actually shifted what they thought was real from the past. So could it be that when you got hit in the face

• 20:22Gary O'Reilly?

  Yep.

• 20:23Charles Liu?

  And maybe, you know, it was similar to feeling being hit in the face in the dream, your brain set it up so that thinking back to the dream It wound up matching the two pieces and getting them confused. It is possible. And again, like I said, so many of you things are speculation and it's hard for us to establish what is actually scientifically causal or the case, but that does happen.

• 20:46Neil deGrasse Tyson?

  And the part of the problem, Gary, is that you didn't write that down when you had the dream. That's part of the challenge here of verifying it scientifically. So that leaves whatever your dream was susceptible to exactly what Charles is saying about when you recover the dream, so wow, this was bang on to exactly what happened.

• 21:05Gary O'Reilly?

  Well, the dream, the dream was about 10 days before the actual event happened.

• 21:08Neil deGrasse Tyson?

  So it's. Yeah, you should just write down your dreams every single day.

• 21:11Gary O'Reilly?

  Okay.

• 21:11Neil deGrasse Tyson?

  And 999 times, it won't come true. And one time it comes true, you can't then claim special.

• 21:17Gary O'Reilly?

  I gotta get me a dream diary.

• 21:19Neil deGrasse Tyson?

  Exactly.

• 21:20Charles Liu?

  To, I guess to wrap up Manny's question, you know, the idea is basically to say dreams definitely affect human experience.

• 21:27Gary O'Reilly?

  Yeah.

• 21:28Charles Liu?

  And how humans interact with the universe. Does the rest of the universe, however, sense those dreams or react as a result of them? That is something we don't know. Probably not.

• 21:39Neil deGrasse Tyson?

  Yeah, it's a, it's a, it's a very probably not, but you know, people still claim it.

• 21:47Chuck Nice?

  Yeah, yeah. And, and, and listen, it informs a lot of people on what they do. So there is a significance there, no matter what, because there are a lot of people who are reacting to their lives based upon, you know, that, what they think is that information.

• 22:01Neil deGrasse Tyson?

  And by the way, there's another thing, Charles, I think, a, a dream, as you know, is a neurosynaptic firings of your brain. And should that be fundamentally different from deep thoughts you might be having while you're not asleep? So, so what I find intriguing is almost every movie that shows somebody who by some bolt of lightning or through drugs becomes insanely brilliant.

• 22:28Gary O'Reilly?

  Yeah.

• 22:29Neil deGrasse Tyson?

  Okay. Like the movie Lucy or the one phenomenon, I think it was.

• 22:33Gary O'Reilly?

  Yeah.

• 22:34Chuck Nice?

  Oh, tho- oh, those kind of.

• 22:35Neil deGrasse Tyson?

  Okay, no, no, no. In those movies, in every one of them, the person can control things with their brain. And I'm intrigued by that because.

• 22:46Neil deGrasse Tyson?

  If they're just really smarter, they should just simply solve problems faster or better.

• 22:51Chuck Nice?

  Right.

• 22:51Neil deGrasse Tyson?

  And they, they somehow the urge in the storytelling is to have the power of the brain jump out of itself. To manipulate.

• 23:00Chuck Nice?

  Metaphysical.

• 23:00Neil deGrasse Tyson?

  Manipulate physical objects in your environment. In almost every case, that's the power they give them. But from the smartest person on earth to the dumbest person on earth, neither of them can move stuff in front of them without touching them. So to say, let's make the smart person even smarter, now they can spin tops and, and, and float objects? I, I don't, I don't get it.

• 23:23Chuck Nice?

  However, the truly smart people know how to get other people to move stuff. So.

• 23:32Neil deGrasse Tyson?

  Okay.

• 23:33Chuck Nice?

  Pick that up. Pick that up.

• 23:36Charles Liu?

  Please pick that up.

• 23:37Neil deGrasse Tyson?

  Please, please pick that up.

• 23:38Chuck Nice?

  Thank you. Oh yeah, that's right.

• 23:39Neil deGrasse Tyson?

  Give me another question. Chuck, what do you have?

• 23:41Chuck Nice?

  All right, here we go. This is Camilla Caffetall, who says, hello, Dr. Lou and Dr. Tyson. Camilla here from Baltimore, Maryland. How is the cosmic microwave background temperature so constant everywhere in the universe? When there are hot stars like our sun?

• 24:01Neil deGrasse Tyson?

  Oh.

• 24:02Chuck Nice?

  Oh.

• 24:02Charles Liu?

  Beautiful question.

• 24:04Chuck Nice?

  Conspiracy!

• 24:06Neil deGrasse Tyson?

  Oh, Charles.

• 24:07Charles Liu?

  Temperature, temperature.

• 24:08Neil deGrasse Tyson?

  Take that one, Charles.

• 24:10Charles Liu?

  Camilla, you've asked a great question, which sometimes astronomers don't do a good job of explaining outward. The cosmic microwave background does get contaminated by foreground objects. So if we were just measuring, like say, for example, the WMAP satellite or the Koki satellite did, the cosmic microwave energy that's reaching us from the cosmos, right? What will happen is that we will pick up the stars in the front, the galaxy that is we're in, and the cosmic microwave background in the back. The trick that astronomers do, and it's not a trick, it's really hard work, is actually getting rid of that foreground signal. So your insight is exactly right, Camilla.

• 24:53Charles Liu?

  The cosmic microwave background is contaminated.

• 24:57Neil deGrasse Tyson?

  In fact, there was a result that reported some new discovery in the cosmic background. And it was later found that they did not properly remove the effects of our galaxy.

• 25:09Charles Liu?

  Correct. That happens a lot.

• 25:11Neil deGrasse Tyson?

  Yeah.

• 25:12Charles Liu?

  Foreground.

• 25:12Chuck Nice?

  It's like the erase, it's like the erase feature on your phone.

• 25:16Charles Liu?

  Foreground contamination is actually one of the things in astronomy that we have to worry about much more than say typical laboratory physicists. They can try to remove as much of the foreground as possible, but we're stuck looking through the gas and the dust and the stars and the galaxies.

• 25:33Neil deGrasse Tyson?

  We can't change our angle of view. Yeah.

• 25:35Charles Liu?

  Yeah, we can't change it, but we like it.

• 25:36Neil deGrasse Tyson?

  Very cool. Very cool.

• 25:37Charles Liu?

  Fun stuff.

• 25:38Neil deGrasse Tyson?

  Thank you. Yeah, Gary, what do you got?

• 25:40Gary O'Reilly?

  Okay, Kyle M., if a black hole is infinitely dense, why are some bigger than others?

• 25:47Neil deGrasse Tyson?

  Hmm. Hmm.

• 25:49Gary O'Reilly?

  Answer please.

• 25:51Chuck Nice?

  First of all, Kyle, you know, it's not always about size. Okay, that's number one.

• 25:57Charles Liu?

  Oh, well, that sounds like somebody might need some size. I don't know. Chuck, I'll leave you to ponder that one.

• 26:07Neil deGrasse Tyson?

  Yeah.

• 26:07Charles Liu?

  Here's the story.

• 26:09Gary O'Reilly?

  All right.

• 26:10Charles Liu?

  A black hole is not infinitely dense. The only part of a black hole that's infinitely dense is its singularity. See, a black hole, the event horizon that surrounds it, the edge, shall we say, of the black hole, contains a certain amount of mass. Within that container, the average mass is always less than anything. It is just in the spot where we think exists, the singularity, where the density is in. I hope that helps.

• 26:43Neil deGrasse Tyson?

  Wait, just to be clear, just to be clear. So when we describe the size of a black hole, it's the size of the event horizon just for practical purposes to describe how big things are. But the matter is deep within, normally we think of the size of the earth as the edge of the matter of the earth, but the black hole, we just go to the event horizon and we're happy with that.

• 27:05Charles Liu?

  Right. We do not know what's in size.

• 27:07Neil deGrasse Tyson?

  We don't, we don't know.

• 27:08Charles Liu?

  How it's distributed.

• 27:09Neil deGrasse Tyson?

  Correct.

• 27:09Chuck Nice?

  So if that's the case, right, it means that if it were a star at one point, I'm not talking about a supermassive at the center of a galaxy. I'm talking about just a star that collapses in on itself. We know that that star had a certain mass before it collapsed in upon itself. So if it had a certain mass before it collapsed in upon itself, how can the density of that mass become infinite at one single point? If it started off with a finite mass?

• 27:35Charles Liu?

  The mass itself doesn't become infinite, but the density becomes it, right? So for example, mass, let's say something is the weight of my head or something. If I squish my head very small, as a black hole would do if I fall into it, right? It would become more dense, but not more massive. It would still take the same amount of energy or force to lift my head, but you would need a smaller container. Why are you using your head as an example?

• 28:04Chuck Nice?

  Wait, this is more good, Chuck. Now, I was gonna say, that was a painful example.

• 28:10Charles Liu?

  It just popped into my head, what can I say? Use a watermelon or something, you know? I don't have a head for those kinds of jokes, so.

• 28:16Chuck Nice?

  So Chuck Low, Chuck Low, here's the deal. So if that's the case, how can something become infinitely smaller and smaller and smaller and smaller? At some point, doesn't it have to just be so tightly compact that it can't get any smaller?

• 28:33Charles Liu?

  Great question, Chuck. And in fact, it is the people who study matter, mostly quantum physicists, who say that, yes, there must be a limit. But when Albert Einstein established the general theory of relativity, he did not see it. He did not, he was not happy with the fact that the mathematical equations of spacetime allowed for the existence of these singularities. That's why they called singularities, right? Because they, they don't follow the mathematical rules that you would expect for the space. It's where God is dividing by zero.

• 29:09Chuck Nice?

  Oh, who said that?

• 29:11Charles Liu?

  You've never heard that one? No, that's an interesting point. But it's kind of, it's kind of, Neil is right. That's exactly what it is. You're dividing by zero, you're creating something that should not exist. If you've never done that before, do it on your calculator.

• 29:25Gary O'Reilly?

  Can you then make this thing that's reducing inside disappear altogether? Or does it reappear somewhere else?

• 29:33Charles Liu?

  Don't know. The current hypothesis suggests that black holes are not, say, tears in spacetime, in which case the matter or the mass would flow from one point to another, but rather a kind of like a hernia in spacetime. A water balloon where the mass goes in and kind of collects in a space or a time or something that's not part of the spacetime we have access to. And then over many, many trillions and trillions of years, slowly gets expanded outward again through the process called Hawking radiation.

• 30:09Chuck Nice?

  So check it out because Neil said do it. I just divided by zero on my... So the first time I did it, I did zero divided by zero and it said, invalid format, please do not do. And then the second, and then the second time I put one divided by zero and it said, can't divide by zero. And then the third time I did it and it went, no.

• 30:32Charles Liu?

  The fourth time you did it said, I already told you no.

• 30:34Chuck Nice?

  I told you.

• 30:39Charles Liu?

  But it's the examination of these singularities and unusual points in the equations of spacetime that have led to these amazing discoveries and thought processes like black holes, like the Big Bang, like those kinds of things that we're wondering about today that fire our imagination.

• 31:06Neil deGrasse Tyson?

  Let's go to the next question. This special edition with Cosmic Queries.

• 31:09Gary O'Reilly?

  Okay, all these questions, yeah, thank you, Neil. All these questions from our Patreon audience. So thank you very much for your curiosity. Craig Cordwell from the UK. Please can you briefly explain how it is more efficient and easier to launch a rocket going directly up rather than taking off similar to an airplane does? So answers please.

• 31:30Gary O'Reilly?

  Well.

• 31:31Chuck Nice?

  Uh, now Gary, could you please do that again, but do it in Craig Caldwell's accent?

• 31:36Neil deGrasse Tyson?

  Cause you're both Brits.

• 31:37Gary O'Reilly?

  Okay, I don't know what part of, I don't know what part of the UK, Craig. How about if he's from Cornwall? I, I love the Cornwall. Cornwall? Ker- Kerneal? Yeah. Or is it, uh, Craig from Kerneal here? Please can you briefly explain who it is more of, oh, it's how embarrassing. Sorry, Craig. Because he might be, he may be from Glasgow, in which case it would be very, very different. Or he could be a, you know, he could be a Scouse, or he could be all sorts of things. So I'll just have to go with. Liverpudlian. Oh my God, no. Um. Liverpudlian. Could be a Liverpudlian. Um, can't, can't dial up a Scouse accent on demand. Um. Sorry, not to worry. Asking too much. Yeah, um, obviously.

• 32:18Charles Liu?

  So the, the answer to the question actually is that we do try to launch our rockets horizontally. When you see on the launch pad, a rocket going upward vertically. The only reason it tries to go up first is because it's trying to build up speed because it will then start curling sideways. It starts moving horizontally because the best way to get into orbit or out of the gravitational well of a planet is to travel at a tangent, not straight up vertical. It's only up vertically to get off of the ground, away from the launch pad, over mountains and so forth.

• 33:00Charles Liu?

  And then the trajectory starts to curl, right? That's why, for example, we launch from Florida. Because it goes up for a short while and then goes horizontally over the Atlantic Ocean. So our sense that we launch vertically is actually just those first few seconds of our perception. Later on, if you want to go further and further upward while you're in orbit, you move tangentially. You move horizontally and that actually has been shown mathematically and, and engineering wise to be the most efficient way to gain altitude up in space.

• 33:35Neil deGrasse Tyson?

  Once you're outside of the slowing down effects of the atmosphere of the earth. Yeah. So Charles, here's something fucking amazing. You ready?

• 33:42Charles Liu?

  Yeah, go ahead.

• 33:43Neil deGrasse Tyson?

  The exact trajectory of a rocket, you know what it is? It's it's an exact trajectory. Do you know? I'll tell you what it is.

• 33:50Charles Liu?

  Uh.

• 33:51Neil deGrasse Tyson?

  It is, it is the, it is the inverted, the physically inverted solution to the Baruchishtakron problem.

• 34:00Charles Liu?

  No kidding?

• 34:01Neil deGrasse Tyson?

  Yes.

• 34:02Charles Liu?

  Wow.

• 34:02Neil deGrasse Tyson?

  Yes.

• 34:03Charles Liu?

  I was gonna guess catenary, but.

• 34:05Neil deGrasse Tyson?

  No, no.

• 34:05Charles Liu?

  Makes much more sense.

• 34:06Neil deGrasse Tyson?

  It's way, think about it.

• 34:08Charles Liu?

  Makes much more sense. Yeah, yeah, yeah.

• 34:10Chuck Nice?

  Yeah, I'm not telling you.

• 34:14Chuck Nice?

  Yeah, of course, the ice cream cone problem. Everybody knows that. Yeah.

• 34:19Neil deGrasse Tyson?

  So here, there was a, there was a, was it Bernoulli? Someone posed a, some famous mathematician of, of, from the 19th century. Posed the question, might have been the 18th century. Posed the question, if I have a ball up here and I want it to get down over, down, but over to the right a little. What path should I take? Should I put a plank connecting the two of them and roll it down? Will that get there faster than if it drops first and then curls around at the bottom? Okay, is there a shape? Is there an arc that I could drop this ball? We'll get to that point at a lower elevation the fastest?

• 35:05Neil deGrasse Tyson?

  This turned out to be a very hard problem and it is not the straight line. There is a curve where it builds up speed falling. And then that speed gets forward, moves it forward very quickly. And the minimization of that is that we learn this in advanced mechanics, right? And I think that's what I did, Charles, we. Uh, what, what class did you learn there? I think I was, I might have learned.

• 35:30Charles Liu?

  I think, I think we, we got it as a bonus from my calculus.

• 35:34Neil deGrasse Tyson?

  Yeah, yeah, yeah.

• 35:35Charles Liu?

  My calculus teacher in high school, brilliant man. In fact, went on to write some really great books, review books about calculus. And he would throw in just these little things. Uh, just like, oh, by the way, you know, that's what kind of made math class cooler because math can be just like learning grammar or learning punctuation or learning vocabulary.

• 35:53Neil deGrasse Tyson?

  Learn extra little tricks and tricks and fun things.

• 35:56Charles Liu?

  But when you put them into like, hey, was this useful in some way? Was this a thing that you actually find out? You know, those are the opportunities where you make connections and go, aha, this math stuff is cool.

• 36:08Chuck Nice?

  You bring it to life, Charles. Alright, guys, guys, guys, we have digressed from the ice cream cone principle.

• 36:16Neil deGrasse Tyson?

  On purpose.

• 36:17Chuck Nice?

  We need to know what.

• 36:19Charles Liu?

  We haven't diverged. We've, we've embraced it, Chuck. As Gary just said, it brings it to life. Now I bet there are thousands of people out in the podcast first that are wondering, what's the ice cream cone problem? And now they're gonna look it up and now they're gonna learn math, which is based on ice cream because they like it. It livens up the subject. It makes people say, oh, it's not just.

• 36:41Neil deGrasse Tyson?

  What is the ice cream cone problem?

• 36:43Chuck Nice?

  No sprinkles. You said that the in, the exact inverse of a trajectory of a rocket is the exact inverse of the ice cream cone.

• 36:52Neil deGrasse Tyson?

  Oh, yeah, yeah, sorry, I was not.

• 36:53Chuck Nice?

  Principle or whatever.

• 36:54Neil deGrasse Tyson?

  The brachristicron problem.

• 36:57Chuck Nice?

  Oh, bro, oh, oh, excuse me, the brachristicron, which is, which is very much like, um, uh, cookies and cream.

• 37:05Neil deGrasse Tyson?

  It's a new flavor, the brachristicron.

• 37:08Chuck Nice?

  It's a new Ben and Jerry's brachrist. Let me tell you something, Neil, if they ever give you a Ben and Jerry's ice cream, you better name it brachristicron.

• 37:18Neil deGrasse Tyson?

  But my only point is, this, this math exercise is designed to find the fastest minimum energy path between these two points.

• 37:29Charles Liu?

  That's awesome.

• 37:29Neil deGrasse Tyson?

  And so the, so the minimum, no, just down and, and to the point. You take that, flip it up. It is the minimum energy expenditure into orbit. Cause if you go up too high first, you wasted too much energy gaining altitude. If you go downwind first, you're wasting too much energy trying to go horizontal.

• 37:51Chuck Nice?

  Trying to go.

• 37:52Neil deGrasse Tyson?

  So it's the, it's the perfect inversion of that problem.

• 37:55Gary O'Reilly?

  Is there a way to launch by spinning?

• 38:00Gary O'Reilly?

  And then launching that.

• 38:02Chuck Nice?

  Oh, yeah.

• 38:03Charles Liu?

  This is actually a startup company. I heard about this um just recently. A startup company.

• 38:10Neil deGrasse Tyson?

  Would you like to find?

• 38:11Chuck Nice?

  I heard about that, Charles.

• 38:12Charles Liu?

  Rank up.

• 38:13Neil deGrasse Tyson?

  No, no, Charles, I know. Go, go.

• 38:15Charles Liu?

  Yeah, yeah.

• 38:16Neil deGrasse Tyson?

  It's a, it's a, it's a, they wanna spin something to high, to launch speeds.

• 38:22Charles Liu?

  There you go. And then they launch it.

• 38:24Neil deGrasse Tyson?

  They're not even using a rocket. It's just.

• 38:25Charles Liu?

  Right.

• 38:26Chuck Nice?

  No, it's like, what's, what's, what would be the equivalent of when you put the astronaut in the center?

• 38:32Gary O'Reilly?

  Like an old fashioned, yeah. Be like a medieval catapult.

• 38:35Charles Liu?

  No, you could not, you could not throw an astronaut. It's, it's, it's a, it's a trebuchet, but.

• 38:41Chuck Nice?

  It's like a medieval catapult. It spins around and then releases at a certain point.

• 38:46Charles Liu?

  Right. You can't send an astronaut in there though. The, the insides will turn to jelly. I mean, they're gonna leave the catapult.

• 38:52Chuck Nice?

  For real.

• 38:52Charles Liu?

  At like a thousand miles an hour, you know, just like sudden whoosh, you know, that kind of thing. You, you will, you will be squished.

• 39:00Neil deGrasse Tyson?

  Will kill you.

• 39:00Charles Liu?

  It would be too much. Yeah. So, so you're sending like payloads that can handle that sort of thing. But this is still in development.

• 39:07Chuck Nice?

  It's about payload. Yeah.

• 39:09Gary O'Reilly?

  But that would, I mean, okay, so if you've got no innards to explode or turn to jelly.

• 39:15Neil deGrasse Tyson?

  Then it's everything's fine.

• 39:16Gary O'Reilly?

  Does this have a commercial?

• 39:17Chuck Nice?

  Then everything's fine.

• 39:19Gary O'Reilly?

  Prospect in terms of, as you say, payload.

• 39:21Chuck Nice?

  Yeah, you don't, you don't use a rocket to put stuff in the space.

• 39:23Charles Liu?

  Well, the, the, it has, it has been thought for a long time that the easiest way or the least energy way to get payloads up into space is just create a tether, basically an elevator going from ground

• 39:37Gary O'Reilly?

  Stairway to heaven, Charles.

• 39:38Charles Liu?

  Thousands of miles in the air and just go up, up, up, up, up, up. And that'd be great.

• 39:42Gary O'Reilly?

  Stairway to heaven.

• 39:44Charles Liu?

  Uh, yeah. Well, there are two ways. I mean, you can go back, but in the long run, I mean, it's still time to change the road you're on.

• 39:50Chuck Nice?

  Is jet fuel cheaper than rocket?

• 39:52Charles Liu?

  At the moment, yes, by a lot.

• 39:54Chuck Nice?

  Okay, so then why is it that we were transporting the shuttle when it's here on Earth? By piggybacking it on the back of a big jet? But we wouldn't put it into space by piggybacking it up to the highest altitude possible, detaching it and then letting it just fire rockets to go into space? Um, because the atmosphere is a lot thinner and you got a lot, lot less space to go.

• 40:21Charles Liu?

  That kind of strategy is actually what was done in the early rocket planes, the early spacecraft. In fact, some spacecraft now, for example, I think one of the commercial spacecraft done by some billionaire or another, right, reaches space by doing precisely that. You carry some sort of a rocket on some sort of a plane. And then you let the rocket go and then the rocket takes it the rest of the way. The rocket engine is way more expensive to build than the jet engine. So even if you save on fuel, right, even if it's just hydrogen and oxygen versus some hydrocarbon or something. It's in construction. Making the rocket work and not blow up and not move and not change.

• 41:04Charles Liu?

  That's a lot harder than getting a jet engine on an airplane.

• 41:07Neil deGrasse Tyson?

  What's it is not the majority cost of what's going on. So you gotta watch where you.

• 41:12Chuck Nice?

  It's, it's, you gotta watch where you spend your money. I got you. And, and the real deal is this, the moment you say, uh, if we can get it up there without it blowing up, that's where you're lost. I'll see you when you get back. I will see you if you get back.

• 41:24Charles Liu?

  Sadly, it's true.

• 41:25Neil deGrasse Tyson?

  We'll try to get a couple more questions in here.

• 41:27Gary O'Reilly?

  All right, I'll jump in with this one because, uh, this is an interesting one. Uh, back to Star Trek, just as a spoiler. Connor Holm, um, in Star Trek, what is your favorite example of a scientific prediction slash concept that actually became true? But wasn't proven at the time?

• 41:45Charles Liu?

  Ooh, I know my answer, but I want to hear everybody else's answer.

• 41:48Neil deGrasse Tyson?

  I have an answer, but I don't know if it would, I don't know if it, it fits.

• 41:52Charles Liu?

  Really? Okay, so here's, here's my answer. My favorite thing that has come true is the communicator.

• 42:00Charles Liu?

  Indeed, all we have to do today is to pick up a something a little rectangular and say Scotty.

• 42:06Neil deGrasse Tyson?

  Mm-hmm.

• 42:07Charles Liu?

  Right, and Scotty can hear you. Yes, Captain. Oh, sorry, that's check off. Uh, same, same, same idea.

• 42:12Neil deGrasse Tyson?

  Get your accent straight, dude. Okay.

• 42:13Gary O'Reilly?

  You're worse than me.

• 42:14Neil deGrasse Tyson?

  Yeah, exactly.

• 42:15Charles Liu?

  Aye.

• 42:16Neil deGrasse Tyson?

  In fact, our communicators are way more advanced than anything they, they use in Star Trek. Than anything Star Trek ever had. Correct, correct.

• 42:22Gary O'Reilly?

  How about that when he just touches the badge? How he just touches his Starfleet badge and all of a sudden he opens up comms? That sort of touch, that touch activity on smartphones that we, that didn't exist at the time that now does?

• 42:33Charles Liu?

  That's right. It's amazing.

• 42:34Chuck Nice?

  Yeah. Mine would be talking to your computer and the computer talks back, which is their, their form of, uh, artificial intelligence. Computer, please tell me. And then the computer would give you information. So, and we have that today. Like, that's not science fiction anymore.

• 42:51Neil deGrasse Tyson?

  Right, great, good point. Right. Okay, and they don't use keyboards, right? That's not a thing. Yeah, yeah, yeah.

• 42:57Chuck Nice?

  Yeah, no.

• 42:58Neil deGrasse Tyson?

  Is it my turn here?

• 42:59Chuck Nice?

  Yes.

• 42:59Neil deGrasse Tyson?

  Yes, it is. Go ahead. Gary, did you give your answer?

• 43:02Gary O'Reilly?

  I did. That, you touch the Starfleet badge and all of a sudden your comms just touch, just a touch.

• 43:07Neil deGrasse Tyson?

  Badge touching. So I have two answers. One, which I never thought would ever happen, happened, where you could just walk up to a door and it will open.

• 43:18Charles Liu?

  But wait, even then you could go to a supermarket and do that?

• 43:21Neil deGrasse Tyson?

  No, no, no, no. The supermarkets of the day had a touch pad. And you step on the pad, it would complete a circuit and that would open the door.

• 43:29Charles Liu?

  Okay.

• 43:30Neil deGrasse Tyson?

  But there were no pads. They would just walk up and the door just somehow knew that they were there. And I said that's-

• 43:36Chuck Nice?

  That's because there were two guys on either side of the door.

• 43:38Neil deGrasse Tyson?

  Go ahead.

• 43:43Charles Liu?

  Post-production must have had a blast with that shit.

• 43:46Neil deGrasse Tyson?

  So, I, I was, I said, I believe the photon torpedoes, the aliens, the warp drive, but door opening, just by walking up to it, never. Okay? That's my first one. Another one, I don't think it was developed yet, even if the science was there, and maybe they wouldn't have known about it, but they have this machine that instantly heats food. Which is basically be a modern-

• 44:08Charles Liu?

  The replicator.

• 44:09Chuck Nice?

  The replicator.

• 44:11Neil deGrasse Tyson?

  I don't know if it's the replicator or it's just something that makes the hot food. I mean, the replicator doesn't necessarily heat it, right? So there's this, this cavity where I want some chicken soup. They push a button and hot chicken soup comes out.

• 44:24Charles Liu?

  That's okay.

• 44:24Neil deGrasse Tyson?

  I count that like as a microwave oven.

• 44:27Chuck Nice?

  That's the original starch.

• 44:28Gary O'Reilly?

  Is that not a precursor to 3D printing?

• 44:30Charles Liu?

  Oh.

• 44:31Chuck Nice?

  Well, the replicator is a.

• 44:32Neil deGrasse Tyson?

  Yeah, the replicator, I would say.

• 44:34Chuck Nice?

  The replicator would be the 3D printer.

• 44:36Gary O'Reilly?

  That's, that's, that's another one that got us considered as well.

• 44:39Charles Liu?

  Wow.

• 44:39Neil deGrasse Tyson?

  And you know, there was a big prize, was it an X Prize even? That was announced.

• 44:43Charles Liu?

  The tricorder?

• 44:44Neil deGrasse Tyson?

  The tricorder, yes, yes. Tell everybody about that.

• 44:46Charles Liu?

  Oh, well, tricorder was the thing that phones waved over somebody and figured out exactly what was wrong with them medically.

• 44:53Chuck Nice?

  Yeah.

• 44:54Charles Liu?

  And so.

• 44:54Chuck Nice?

  I'm a doctor, not a computer technician.

• 44:57Charles Liu?

  I'm a doctor, not a fill in the blank, right? So the whole point was that if we somehow could do the same through uh, remote sensing, just wave something over somebody and get all kinds of things, vital signs, things like that. We're getting close already, actually. For example, now we can take people's temperatures without touching them.

• 45:15Neil deGrasse Tyson?

  Right.

• 45:16Charles Liu?

  That little thing, and then you get the radio, you know, the infrared off of the surface.

• 45:19Neil deGrasse Tyson?

  There was a NASA, NASA thing, by the way.

• 45:22Charles Liu?

  That's right. Oh, absolutely.

• 45:23Gary O'Reilly?

  For a tricorder to work, would you need to have certain implants in the body? That would allow.

• 45:28Charles Liu?

  It would help, but it would not be necessary.

• 45:30Gary O'Reilly?

  He's like, he's just scanning your code then, aren't you?

• 45:32Charles Liu?

  That's right. That would be very useful, but it would not be necessary.

• 45:36Gary O'Reilly?

  Okay.

• 45:36Charles Liu?

  The whole point of the tricorder is that you can just diagnose what's wrong just by remote sensing. And some things you can.

• 45:43Chuck Nice?

  But you know, we're really close already because we're using light. So that, that, you know, a lot of these instrumentations uses light to actually get the reading from the body.

• 45:52Charles Liu?

  That's right.

• 45:53Chuck Nice?

  So.

• 45:53Gary O'Reilly?

  So that's photonic.

• 45:54Chuck Nice?

  What, what?

• 45:55Neil deGrasse Tyson?

  So, so Charles, so there are two kinds of, of, of tools then. One of them is receiving whatever your body is giving it. So if your body's like radiating a little warmer, you see that extra high temperature infrared.

• 46:08Charles Liu?

  Passive.

• 46:09Neil deGrasse Tyson?

  Passive, but another one, maybe you'd have to like have the person walk in front of X-rays and then the, it reads something that you've actually put through the body.

• 46:17Charles Liu?

  Right. The Dop, the Doppler radar. For weather forecasting, for example, you do that. You send a radar pulse down to the ground. It comes back up. And depending on what it's like when it comes back up, what the time delay is, how strong it is and things like that. You know, whether there were clouds, whether it's raining, whether it's clear.

• 46:33Neil deGrasse Tyson?

  Or how much rain there was even.

• 46:34Charles Liu?

  Right. By the same token, maybe it can send some sort of pulse, a harmless piece of information, radiation down through the body or onto the skin. When it bounces back, it can read the results and see, ah, yes, this person has a skin infection of this kind on their, you know, that part of their skin. And therefore we need to run.

• 46:55Neil deGrasse Tyson?

  Or Captain.

• 46:56Chuck Nice?

  You need to cut off their arm. Oh, no, no. Which is my answer to everything medically.

• 47:02Neil deGrasse Tyson?

  What?

• 47:02Chuck Nice?

  Look at that, we're living in the future, people.

• 47:08Neil deGrasse Tyson?

  Anyhow, guys, we're out of time.

• 47:11Neil deGrasse Tyson?

  It was a good question to end on. That was fun.

• 47:13Charles Liu?

  Yeah.

• 47:13Neil deGrasse Tyson?

  Uh, we each had our own little bit of thing there. So, very good. StarTalk Special Edition with the one and only Charles Lu. Charles, thanks for coming in for this.

• 47:23Charles Liu?

  Always a pleasure. Thank you so much. Great to have me.

• 47:27Neil deGrasse Tyson?

  Undisputed, Ekin Shae, Charles Lu.

• 47:29Charles Liu?

  You guys are too kind. Thank you so much.

• 47:31Neil deGrasse Tyson?

  All right, StarTalk Special Edition signing out. Neil deGrasse Tyson, keep looking up.