Cosmic Queries – Stoner Edition with Janna Levin

Is anything real? Is time just a construct? On this episode, Neil deGrasse Tyson and comic co-host Matt Kirshen answer your far-out questions about black holes, dark matter, and the universe with astrophysicist Janna Levin.

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.

• 0:14Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson here, your personal astrophysicist. We're gonna do cosmic queries today. Everything, black holes, and spacetime. I got with me my co-host Matt Kirshen. Matt, welcome back, dude.

• 0:29Matt Kirshen?

  Thank you. Thank you. I'm joining you from my family's spare bedroom in London right now.

• 0:35Neil deGrasse Tyson?

  Oh, you mean your parents' basement where you live?

• 0:36Matt Kirshen?

  That's exactly it, yeah. I commute to LA every day from

• 0:42Matt Kirshen?

  from the basement where all my toys and games are.

• 0:45Neil deGrasse Tyson?

  I knew you were a full geek, but the full, the whole story is still in your parents' basement.

• 0:50Matt Kirshen?

  That's it.

• 0:50Neil deGrasse Tyson?

  You can confess that. You're in safe grounds here, dude, with that, too.

• 0:56Matt Kirshen?

  This is no judgment podcast?

• 0:58Neil deGrasse Tyson?

  No judgments at all. Good to have you back, and you're the host of Sometimes Science?

• 1:04Matt Kirshen?

  Probably Science, Neil.

• 1:06Neil deGrasse Tyson?

  Probably Science. Probably Science, on which I have been a guest.

• 1:10Matt Kirshen?

  You have indeed.

• 1:12Neil deGrasse Tyson?

  I have, and I enjoyed my time there. So Matt, while I know a little bit about black holes and a little more about spacetime, I don't count myself among the world's experts, but we have a friend of StarTalk who is, of course, that's Janna Levin. Jana, welcome back to StarTalk.

• 1:26Janna Levin?

  Thanks, I'm glad to be here.

• 1:27Neil deGrasse Tyson?

  Yeah, yeah. Jana, you're like a neighbor up the street from the American Museum of Natural History. You're a professor of physics and astronomy at Barnard College of Columbia, and it's just great to have you just a friend of what we do and a supporter of all of this.

• 1:42Janna Levin?

  Yeah, I loved being here.

• 1:43Neil deGrasse Tyson?

  And to lend your expertise, you're not lending it because we're not giving it back. You're giving us your expertise on black holes, cosmology, the spacetime continuum, and all that goes with it. So just before we start off, I just want to alert people that in your spare time, you actually are one of the founders of marvelously conceived project Pioneer Works over in Brooklyn across the river. You merge art and science in highly creative and imaginative ways. I just want to congratulate you on even going there. And you've been at it for like years now.

• 2:24Janna Levin?

  Yeah, I really appreciate that. Yeah, we have a live programming where we feature scientists in conversation. You've been over. We've had parties with you, Neil.

• 2:34Neil deGrasse Tyson?

  Yeah, but you haven't put me on the stage.

• 2:36Janna Levin?

  No, I'm waiting for the right time.

• 2:39Matt Kirshen?

  Oh, okay. I have also been there and not on the stage. They didn't want my expertise, but I went to...

• 2:47Neil deGrasse Tyson?

  Matt, you and I don't cut it. We're good enough for the audience, but not to actually do it.

• 2:52Matt Kirshen?

  I mean, I think I'll get there eventually, but I'm not so sure about you, Neil. I've got some deep expertise to share.

• 2:57Janna Levin?

  I'm happy to put you both to work. Be careful what you wish for. So the big project there has been lately broadcast Pioneer Works broadcast since the pandemic, which is our virtual manifestation. It's Pioneer Works Beyond the Walls, where we cover art, science, music, tech, kind of multimedia extravaganza.

• 3:18Neil deGrasse Tyson?

  Excellent. So I can reach a far greater audience than who shows up in Brooklyn. All right. So Matt, you collected questions from our Patreon members. They have exclusive access to our Cosmic Queries format, and everyone else gets to hear their questions. And so what do you have lined up for us?

• 3:35Matt Kirshen?

  I did. Well, I've got...

• 3:35Neil deGrasse Tyson?

  This is like a grab bag. It's a grab bag of black holes and stuff.

• 3:38Matt Kirshen?

  Yeah, there's a really nice assortment of questions. I'm going to start off with this one from Matthew Power, my kind of superhero namesake. But...

• 3:49Neil deGrasse Tyson?

  You're Matt Kirshen, and this is Matthew Power.

• 3:50Matt Kirshen?

  It's Matt Power. This is Matt from New Jersey, who is also currently reading Black Hole Blues, which is one of Jana's books. I've read that. It's an excellent book, and Matt is also enjoying it.

• 4:01Matt Kirshen?

  And Matt says, "My question is, if there were two black holes orbiting one another and generating powerful gravitational waves, is there a possibility that a small object, he says perhaps a ping pong ball, could actually be carried away by the waves, thus making gravity a repulsive force in this particular case?"

• 4:18Neil deGrasse Tyson?

  Wow, this is like a surfing ping pong ball. I love it.

• 4:22Janna Levin?

  That's...

• 4:23Neil deGrasse Tyson?

  I... I... I love it.

• 4:25Janna Levin?

  What do you think, Neil?

• 4:26Neil deGrasse Tyson?

  Oh, I love the idea. So, because probably he's thinking deeply, because if you're surfing on a wave in the ocean, the water isn't actually moving, it's just going up and down, and you're somehow exploiting this fact, isn't that right?

• 4:42Janna Levin?

  Moving with it. Yeah. I think it's a subtle question. I've wondered about this, but I haven't ever really worked it out. I'm sure somebody might off the cuff know the answer, but definitely what you're doing in spacetime, if you're near those two black holes, is you're falling freely. We literally call it free fall. So you're falling freely on the natural curves in the space. So if those curves are changing, that's certainly going to change your fall. For instance, the Earth is falling around the Sun on a curve, on a circle, and if the Sun were to disappear tomorrow, the gravitational waves would radiate out, taking the time it takes until it reaches us, and then we'd go in a straight line as

• 5:23Janna Levin?

  though the Sun was gone, right? So in some sense, we are definitely moving with those waves. But thinking of it as like surfing, it's cool. I don't know.

• 5:33Neil deGrasse Tyson?

  Right, right. If we're not so heavy as the Earth, let's say, or something as responsive as a ping pong ball, wouldn't the waves, wouldn't the expanding gravitational wave from the disappeared Sun or from the collapsed black hole, will that have any effect on us at all to push us? How can a wave move out, but we can't now move with it?

• 5:55Janna Levin?

  Yeah, I mean, the gravitational energy in the wave can be quite powerful, right? We, that, the collision of the two black holes was the most powerful event human beings have detected since the detection of the Big Bang. Right? And all of it came out in the gravitational waves. But actually, um, I think their effect is really quite weak. In the sense, you would feel the squeezing and the stretching as you kind of bobbed around on the wave. But I don't think it would have enough power to actually carry you along. But we also do know, I think the question was also about repulsive gravitational forces. And actually, we do know that gravity can be repulsive.

• 6:35Janna Levin?

  So for instance, the dark energy in the universe creates a repulsive effect on the expansions. The universe is expanding. Things are getting farther apart because of the dark energy. And that's happening at an accelerated rate.

• 6:51Neil deGrasse Tyson?

  Yeah, but you're calling that gravity. And are we allowed to do that yet?

• 6:55Janna Levin?

  What do you, what do you mean? In what sense?

• 6:58Neil deGrasse Tyson?

  You say, well, this is dark energy and it's, it's actually the opposite of gravity. So are you legitimately calling it negative gravity?

• 7:05Janna Levin?

  No, I'm not calling it negative gravity. I'm saying that when we think about curved spacetime, that coming together is not the only possibility. Although that is with Newton's laws, in general relativity, when I think of a dark energy as a particular source for the way it deforms spacetime, we see a very clear example where its effect on spacetime is expansive. And uh,

• 7:30Neil deGrasse Tyson?

  Oh, wait, I got a good answer. I got another good answer. I got, can I, can I?

• 7:33Janna Levin?

  Okay.

• 7:34Neil deGrasse Tyson?

  Can I raise my hand? Jenna, I'm raising my hand in the front row.

• 7:38Janna Levin?

  You're the boss, you're the boss. Neil, Neil.

• 7:42Neil deGrasse Tyson?

  Yeah, thank you, thank you, Jenna. So it's just thinking about this more holistically. The very expansion of the universe is carrying galaxies in the fabric of

• 7:54Janna Levin?

  Exactly.

• 7:55Neil deGrasse Tyson?

  the expanding spacetime. So in a, in a way, we are moving in a sense, not through space, but with space. And space is carrying it.

• 8:06Janna Levin?

  Oh, yeah.

• 8:06Neil deGrasse Tyson?

  And though it's not a gravitational wave, but it's, I'll, I'll take it as something that's sort of surfing, even if it's not.

• 8:14Janna Levin?

  Yeah, that's excellent. The dark energy is just a particular example of that. Causing the expansion in an accelerated way. But lots of things cause the universe to expand. Like, the fact that it's full of light and energy in all directions causes the universe to expand. And I think you really hit it on the head, Neil. We are moving with the expansion of the space. We are not moving with respect to our local area, right? So that is like the surfer riding the wave.

• 8:43Neil deGrasse Tyson?

  Yeah, yeah. All right, Matt?

• 8:47Matt Kirshen?

  Well, I'm going to jump from a question that is very theoretical to one that I know you have a good answer to, because I know this is something you've both been asked before. Alexander Newhouse wants to know, what is the universe expanding into?

• 9:00Neil deGrasse Tyson?

  Yeah, Jana. Everybody wants to know that.

• 9:04Janna Levin?

  I know, you've done this a bunch of times.

• 9:06Neil deGrasse Tyson?

  No, no, I just make stuff up, what I think, what I've read. But you actually work on these problems. So let's hear it out of the horse's mouth.

• 9:13Janna Levin?

  Well, if, let's take it as though the universe was expanding into something. Just pretend. Then we would be saying, oh, there's some distance the universe has traveled into this other space. But what we mean by the universe is the space. So there's really no logic to thinking of it expanding into something else. The universe is the whole space. There are some relational possibilities that you can think of where the expansion of the universe is like a map of the universe, where we're only reading the legend between things as changing over time. But the map itself doesn't move into anything else.

• 9:58Janna Levin?

  That's one kind of very strange relational way of thinking about it. But no, we do not need to nest the universe into another universe to have it expand.

• 10:06Neil deGrasse Tyson?

  Okay, I get that. But, but, who, what, okay, so let's up this game a notch. What, what conditions would, what dimensionality, what location, what, what state of existence must one have to observe the entire expansion of our universe?

• 10:29Janna Levin?

  Well, you, okay, that's...

• 10:31Neil deGrasse Tyson?

  From the outside.

• 10:32Janna Levin?

  So there is, there is no way to stand outside the universe?

• 10:37Neil deGrasse Tyson?

  No, not really, but so, but so what?

• 10:41Janna Levin?

  You're trying to just prove the existence of God with me right now. What kind of trouble are you getting into?

• 10:48Neil deGrasse Tyson?

  I don't think I really know you, God, in that.

• 10:50Janna Levin?

  Nobody can see and know the entire universe at one time. There's no way of...

• 10:56Neil deGrasse Tyson?

  Yeah, who are you to say that you can't... There is not some platform, some vista outside of everything we know and see that can just simply observe what's going on?

• 11:06Janna Levin?

  Well, by observe, we mean collect particles and interact. And we do that through Paus in spacetime. So if you want to literally be in a position where you're gathering lights so that you can see the universe and deduce what's happening to it, you're really talking about interacting with something. And that requires that we be in the same universe. Now, I mean, you could fundamentally say...

• 11:33Neil deGrasse Tyson?

  You're no fun. You're no fun.

• 11:36Janna Levin?

  We could say things that I think are actually quite...

• 11:39Neil deGrasse Tyson?

  Matt, she could have said, "God is out there and he's watching us all," right? Or Santa Claus, he knows when you are bad and good.

• 11:46Matt Kirshen?

  And then roll credits.

• 11:50Janna Levin?

  So the... It is interesting to push this idea and to say, "Look, these ideas about space being infinite or being finite or expanding, these are just ways of talking." We could also talk differently about the entire universe only as relations, only as interactions. And that's the only thing we understand, that interactions happen over a certain span of space and time. And there's no need to even think about geometry at all or to think about the universe as a space at all. It just appeals to our intuition.

• 12:26Neil deGrasse Tyson?

  Wow, okay.

• 12:28Janna Levin?

  You're looking at me like I've had this woman on this show many times.

• 12:34Neil deGrasse Tyson?

  Okay, Matt, she's crossed over.

• 12:36Janna Levin?

  I've crossed over.

• 12:36Neil deGrasse Tyson?

  And I don't know that they're bringing her back at this point, okay?

• 12:40Janna Levin?

  I mean, and we know that we're often fooled by these interactions. So right now, I have the illusion that you're a solid person, that Matt's a solid person, but really, you're mostly empty space. These are illusions that we cling on to to more easily comprehend the world, but we know that they're not true.

• 12:57Neil deGrasse Tyson?

  Matt is mostly empty space.

• 12:58Matt Kirshen?

  Yeah, a lot of people say that about me.

• 12:59Neil deGrasse Tyson?

  I'm solid.

• 13:00Matt Kirshen?

  Neil is solid. There's nothing going on in here.

• 13:06Neil deGrasse Tyson?

  So Janet, you're referring to the fact that atoms are mostly completely empty?

• 13:09Janna Levin?

  Right, and then even if you look at fundamentally what the fundamental particles are with atoms, we only understand them in terms of the way in which they interact with things. That's the meaning of an electron, is the way it interacts with things. So in some sense, we're just these sort of lists of interactions.

• 13:25Neil deGrasse Tyson?

  Yeah, she got all philosophical.

• 13:27Matt Kirshen?

  That's making me very much...

• 13:28Neil deGrasse Tyson?

  Quickly, go to the next question before this gets worse.

• 13:31Matt Kirshen?

  Because you got so philosophical, I'm gonna jump onto Scott Allen's question. Because Scott from Arlington, who by the way, gives the caveat that Scott is stoned right now.

• 13:42Neil deGrasse Tyson?

  Okay.

• 13:42Matt Kirshen?

  I'm putting that right in there, and if Scott is still stoned trying to listen to these answers, I think we're gonna put him in some real trouble.

• 13:47Janna Levin?

  We should do a stoner version of this show.

• 13:51Matt Kirshen?

  I'll host it and just get my mate. I mean, that's basically it, my podcast. That is probably why we're just winging it.

• 13:58Neil deGrasse Tyson?

  Star talk for stoners. Oh my gosh. We get all the topics best suited for when you're high. Oh my god. You know, Janet, we'll bring you back. That's gonna be a show. I promise our audience, that's gonna be a show.

• 14:11Janna Levin?

  I just fall asleep. It'll be a very boring show.

• 14:15Neil deGrasse Tyson?

  Yeah, while you're eating potato chips. Yeah, okay.

• 14:17Matt Kirshen?

  So Scott says, "Is everything just a form of energy? Is time just a human invention? Combining the two ideas is what we call life and everything we can observe and understand with our limited senses and minds, simply a flow energy constantly changing form. There is no beginning, there is no end, there is no past, there is no future. There is just the present in whatever form of energy we can sense and understand with our mind." That is Scott's question. I... Make of that what you will, professional scientist.

• 14:45Neil deGrasse Tyson?

  Yeah, okay. Wait, did you just give the answer and you said definitely? And now you go on to the next question?

• 14:51Matt Kirshen?

  I think the answer is yes, and everything's fine right now, and...

• 14:56Janna Levin?

  I just think he's definitely stoned. That is such a stoner question.

• 15:01Neil deGrasse Tyson?

  But let's think about this. Is, is, how do, how, what confidences do, I want to restate the question. What confidences do we have, Janet, can you and I offer as scientists? That there is a physical reality and just, we're not all just perceiving ourselves in the moment.

• 15:22Janna Levin?

  Yeah, I mean, I think you made it worse for me, man.

• 15:27Neil deGrasse Tyson?

  The universe has meaning and existence outside of our perceptions.

• 15:31Janna Levin?

  Yeah, I mean, we're all, I mean, which one of us is the one perceiving? Am I in your mind or solely, or are you solely in my mind?

• 15:43Neil deGrasse Tyson?

  Or we both in Matt's mind.

• 15:45Janna Levin?

  Which one of us is the genius that created?

• 15:48Matt Kirshen?

  Before Scott started combining his, his ideas, there are two questions at the beginning that I don't, that are more grounded in, I think, physical of theory. And that is everything just a form of energy? And also, is time just a human invention? And I think, I think those two are questions that are potentially

• 16:08Janna Levin?

  Yeah.

• 16:09Matt Kirshen?

  More answerable.

• 16:10Janna Levin?

  Well, to deal with the first one, yes, I think matter and everything is a form of energy that interacts in prescribed ways.

• 16:21Neil deGrasse Tyson?

  Wait, Janet, you just don't think that, you know that. Janet, be careful how you use the word think, okay? Like, you think it might rain tomorrow, but you know matter is, is she okay?

• 16:31Janna Levin?

  Right, it's true. We know that matter is definable, essentially. Yeah. And, and that is interesting. I mean, I think that's also related to this kind of tangent we went on, which is that, what does it mean to have atoms in your body? What does it mean to be made up of atoms? Is it means that you have a certain amount of energy and that those particles interact in very prescribed ways? That's what makes an electron different from the positron, is just the prescribed interactions, if not their energies. So, so, yeah, that's really all we are. It's beyond that to say what's real is, is again, part of this illusion we have to cope with our perceptions of the world.

• 17:12Neil deGrasse Tyson?

  We'll take a quick break, and when we come back, we'll pick up the second part of that question, whether time is just some kind of a human construct. With the help of Janna Levin giving us her insights into the universe on StarTalk Cosmic Queries.

• 17:35Speaker 03

  I'm Joel Cherico and I make pottery. You can see my pottery on my website, cosmicmugs.com. Cosmic Mugs, art that lets you taste the universe every day. And I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 17:57Neil deGrasse Tyson?

  We're back. StarTalk Cosmic Queries. I got Matt Kirshen as my co-host. Matt, how do we find you on social media?

• 18:05Matt Kirshen?

  I'm Matt Kirshen on Twitter. I think Matt underscore Kirshen on the Instagram I very rarely use. Twitter's the main place I am.

• 18:13Neil deGrasse Tyson?

  Okay.

• 18:14Matt Kirshen?

  And if you don't know the spelling, just kind of get vaguely close and Google will find me.

• 18:19Neil deGrasse Tyson?

  Yeah, okay. And we'll find you on Twitter then without the underscore because that's where you mostly.

• 18:23Matt Kirshen?

  That is, that's me.

• 18:24Neil deGrasse Tyson?

  And Jana, tell me about your social media footprint.

• 18:26Janna Levin?

  Yeah, I'm more on Twitter, at Janna Levin, two N's, like Anna. And I'm on the Insta, same handle. I sort of treat them a little differently. On Instagram, I kind of post my personal stuffs, my personal business. And on Twitter.

• 18:45Neil deGrasse Tyson?

  We want to get all up in your situation and we go there, okay?

• 18:48Janna Levin?

  You know, yeah, exactly. You know, not exactly what I had for lunch, but yeah. So but Twitter, I have pretty serious conversations with people if they want to ask questions. I'm there. I love answering questions when I'm in the mood at least, you know?

• 19:00Neil deGrasse Tyson?

  Okay. Very good. Very good. All right. So we left off, what's the name of that last questioner?

• 19:07Matt Kirshen?

  So Scott, we left off, his part of the question was, is time just a human invention?

• 19:14Neil deGrasse Tyson?

  Yeah. So Jana, the only thing I can say about time is a quote I remember from Einstein or from his student, John Archibald Wheeler, was it, "Time is invented to make motion look simple."

• 19:28Neil deGrasse Tyson?

  Have you heard that?

• 19:28Janna Levin?

  I have heard it. I feel like it was Wheeler, because he said lots of witty things. I also think it was Wheeler who said, "Time is what keeps everything from happening at once."

• 19:42Janna Levin?

  Which is a good one.

• 19:43Neil deGrasse Tyson?

  Yeah, okay.

• 19:45Janna Levin?

  Um, so...

• 19:46Neil deGrasse Tyson?

  And just, just, I gotta throw it, throw it in here. Um, I first noticed the woman who would become my wife in a class taught by John Archibald.

• 19:55Janna Levin?

  Oh, wow. No way. I didn't know that.

• 19:58Neil deGrasse Tyson?

  Yeah, we, we took the class together, yeah. I was sitting in the back row, she was in the front row. So I, I, I don't, she probably didn't notice me, but I noticed her.

• 20:06Janna Levin?

  That's adorable.

• 20:07Neil deGrasse Tyson?

  Yeah. I can say, I noticed her in the space-time continuum on the chalkboard.

• 20:11Janna Levin?

  Right.

• 20:12Neil deGrasse Tyson?

  Okay, so what do you have to say about his comment?

• 20:15Janna Levin?

  Well, I think, I definitely don't think it's a human construct. Um, whether time exists in this kind of block-time model of the universe where the past exists, the future exists, every bit as much as left and right exist, but we're confined on a particular path through this four-dimensional space where time is the fourth dimension. Um, that wouldn't be just human beings, though. That would be, everything would be confined to that space. I presume my cat's death comes before its, you know, after its birth, rather. And, you know, I just presume flowers die after they bloom. And that those are, um, things that are happening to everything in the universe.

• 20:58Janna Levin?

  There are other models that time is sort of, not an invention of, uh, the mind, but it's like, it emerges from very subtle processes and that in some sense it's not fundamental. Um, but I think that, again, it's a very good thing to talk about. So if we wanna meet, we don't just specify a point in space. We have to say a moment in time. And it's very convenient that we all are able to find that moment in time and collect and get together at that moment in time. So that suggests it's not just a figment of our imagination or a human construct.

• 21:36Neil deGrasse Tyson?

  So maybe I should save this for the stoner edition, but...

• 21:40Neil deGrasse Tyson?

  If, if you, if you could find a region of the universe where nothing changes, then time cannot possibly have meaning.

• 21:50Janna Levin?

  Absolutely. And in fact, that's, that's kind of a, you know, a death of the universe model, that the universe will, everything that can fall into black holes will possibly, if the expansion doesn't dominate, and those black holes will evaporate into random particles. And then the expansion will just make it so that there's only one particle in the entire observable horizon, that, you know, and that's disconnected from all the other particles. And so there will be no meaning to time passing. I mean, even for me to experience time passing, there has to be change, which is my thoughts

• 22:29Janna Levin?

  changed, my breath accumulated. Uh, there's, there's actual measurable change that I experience as the passage of time. So that is true, that we do have internal clocks. Um, but they are very well aligned with our external clocks, making it seem as though there is something external and universal.

• 22:52Matt Kirshen?

  Well, while we're talking about external and internal clocks, Geoff Johnson wants to know, why does gravity or high speed cause an entity to move faster through time?

• 23:00Janna Levin?

  Oh, uh, I see the question. Time dilation is the question. Yeah. Why does time, so, um.

• 23:08Neil deGrasse Tyson?

  But first, first he got it backwards. So gravity slows down time, not speeds it up.

• 23:12Janna Levin?

  Yeah. So it doesn't actually slow my experience of time. So my experience of time, if I'm standing near a black hole, is exactly like very ordinary. My nicely made watch that I had once synced with my friend back at a safe space station is working perfectly well. It's still matching the number of breaths I take. Time seems to be passing completely normally.

• 23:35Neil deGrasse Tyson?

  Your heart rate, everything?

• 23:36Janna Levin?

  My heart rate, everything is absolutely normal. I don't get any benefit out of this dilation. The dilation is only relative to somebody far away. And to somebody far away, I look like I'm moving slowly, like I'm breathing slowly, like I'm aging slowly, like my watch is ticking slowly. So it's only, uh, relative to them that it looks odd. But in my experience, it's quite normal. I think the deeper question is, why does this happen? And we can think of both gravity and moving quickly as creating rotations between the spacetimes of two observers. So if one observer thinks that this is left and another observer is facing them,

• 24:19Janna Levin?

  they understand that they're going to disagree about which way is left. They're not surprised. But they know they can just rotate their systems and then they'll agree. Right? So in some senses, you go closer and closer to the black hole, it's as though you're rotating in spacetime. So some of what you were calling space is folding into some of what your friend was calling time. And that leads to time, almost as though you're rotating left into right, almost as though you've rotated time away entirely, relative to your other observer. And...

• 24:50Neil deGrasse Tyson?

  So Matt, we should just rename this show Stone... Stone Talkers.

• 24:56Janna Levin?

  I don't think it's fair that we're not stones.

• 24:59Neil deGrasse Tyson?

  It is happening in front of our eyes, Matt.

• 25:05Matt Kirshen?

  There is a beautifully related question as well on this note from...

• 25:08Neil deGrasse Tyson?

  Wait, wait, wait, wait, Matt. I just gotta wrap my head around what Jenna just said. So Jenna, so what you're saying is, you use the left-right as an interesting analog to this. What you're saying is, when you are moving faster in the vicinity of a black hole, your time coordinate is... Let's use their term, rotates in such a way that it's giving of itself to a space coordinate.

• 25:38Janna Levin?

  That's right.

• 25:39Neil deGrasse Tyson?

  So one is losing time relative to the other.

• 25:42Janna Levin?

  Exactly. And just like you can rotate left all the way into right, at the edge of a black hole in particular, you've basically rotated your time away entirely. And in fact, when you cross the event horizon, what your friend far away thought was a region in space, a center of the black hole, is for you a direction in time. So you've rotated it completely by the time you cross the event horizon, to the point where you think... That the dire singularity at the center isn't a point in space at all. It's in your future. And it is as inevitable that you will crush into that singularity as the passage of time is inevitable.

• 26:27Neil deGrasse Tyson?

  Wow.

• 26:27Janna Levin?

  So you can't dodge the singularity in the center of a black hole.

• 26:30Neil deGrasse Tyson?

  That was Roger Penrose, wasn't it?

• 26:32Janna Levin?

  Yeah. Yeah, actually, I wrote this little article after he won the Nobel Prize for that beautiful work in 1965 for Pioneer Works Broadcast, actually, because we do this series called Picture This, where you draw. We scientists write about technical articles, like technical drawings. And Roger Penrose has the most wonderful drawing that he drew in this 1965 paper where he shows basically time starting to move in a spatial direction. He shows that rotation. And he proves that at the event horizon, what's happened is basically time is starting to point inward towards the black hole. It's quite beautiful.

• 27:15Neil deGrasse Tyson?

  So I love the left-right starter analogy there. You know what that reminds me? So Matt, have you ever heard this joke? It's funny. It says, so someone says, well, two wrongs don't make a right, right? But then you can say, but three rights make a left. You ever try that? Just try it. Make three left turns, you've just turned right. If you do the geometry on that, it works out. All right, cool. Janet, thanks for that answer. I think we should rebrand this for stoners, AKA for stoners. The stoner edition of Cosmic Queries. Matt, keep them coming.

• 27:52Matt Kirshen?

  Well, so Frederick Johansson asks, and this is related because you just talked about the difference of effects of both speed and gravity. Frederick wants to know, if I stand on the equator, my head would age less compared to my feet due to the speed difference, but wouldn't we have the opposite effect due to gravity? Would my feet or head age more in the end? So I believe he's asking that if he's standing on the globe, his head is moving faster than his feet because it's further out. But also, his head is further away from the gravitational center of the Earth than his feet. So do these two things both have an effect on the time perception of your head and your feet?

• 28:36Matt Kirshen?

  And if so, do they cancel each other?

• 28:39Janna Levin?

  I would have to actually do the calculation because both are pretty tiny, right? But I can tell you that with the GPS units, we see the effect of the time dilation when we send signals to satellites and back again. And they have two effects. One is you're deeper in the gravitational potential. So let's say we take the twins, like one astronaut that was in the ISS and the other twin astronaut who stayed on Earth, the Kelly Twins. Which one actually was younger? The one who stayed on Earth, deeper in the gravitational potential well, or the one who was traveling very quickly in the ISS? And it's actually a known answer, and I forget which one it was.

• 29:22Janna Levin?

  I think the speed of the ISS dominates over being on the Earth in that case. I'm pretty sure.

• 29:34Neil deGrasse Tyson?

  Okay, however, with GPS satellites, the fact that they are much farther away from Earth than the International Space Station, that they experience much, much less strength of gravity, which speeds up their time relative to us. And so their time that they send us is pre-corrected

• 29:54Janna Levin?

  Right.

• 29:55Neil deGrasse Tyson?

  to accommodate the fact that their clocks tick faster. So, right, Janet, you have to do the math, right? Because they're two competing effects and to know for sure. But I agree with you. Everything I know about the orbiting astronauts, which are in low Earth orbit rather than middle Earth orbit. Matt, it's not middle Earth, like, you know.

• 30:13Janna Levin?

  Right.

• 30:14Neil deGrasse Tyson?

  Okay, just to be clear.

• 30:15Janna Levin?

  Orbit.

• 30:17Matt Kirshen?

  It's not a basement, Neil. I'm not in a basement.

• 30:19Neil deGrasse Tyson?

  It's Leo, Mio, and Gio, right? Low Earth orbit, middle Earth orbit, and geosynchronous orbit. So when you do the math there, the lower gravitational field wins out over what effect their speed has on their timekeeping.

• 30:37Janna Levin?

  Oh, interesting.

• 30:38Neil deGrasse Tyson?

  Yeah.

• 30:39Janna Levin?

  Interesting. So, thinking about the GPS, we could also think about how if we didn't correct for the time dilation, we would never be able to catch our Uber, because it wouldn't it wouldn't be in the right location. And I learned this from Neil recently, that it's actually the rotation of the Earth, that's the issue, that that if the satellite, let's suppose we lost a second, if the correction was never made and the error accumulated up to, let's say, a second, then if you consider how quickly the Earth is rotating, and that the grid would be changing, you would find that we could be off by several blocks. So

• 31:21Janna Levin?

  you'd be trying to catch your Uber, you know, in Chinatown, and it would be in Little Italy.

• 31:27Neil deGrasse Tyson?

  Which is five, six blocks away.

• 31:30Janna Levin?

  My Uber's never where I need it to be.

• 31:33Neil deGrasse Tyson?

  These are adjacent communities in Lower Manhattan, Little Italy.

• 31:37Janna Levin?

  Yes, they're adjacent neighborhoods.

• 31:38Neil deGrasse Tyson?

  Right.

• 31:39Janna Levin?

  In China.

• 31:39Neil deGrasse Tyson?

  Yes, yes, they are. For those who are not native to the city. Let's take a quick break, and when we come back, more Cosmic Queries, stoner edition with Janna Levin. We're talking about black holes, cosmology, and the spacetime continuum. And I got Matt Christian to help me. We'll be right back. We're back. Third and final segment of Cosmic Queries, Black Holes and Spacetime Continuum Edition, which we are dubbing Cosmic Queries Stoner Edition, based on the answers we've been getting,

• 32:21Neil deGrasse Tyson?

  and what kind of state of mind we have to be in to even follow them, much less understand them. So, Jana, again, it's always good to have you here. Your last two books, so one of them was The Black Hole Blues, published by, was that Knopf?

• 32:36Janna Levin?

  Yeah, by Knopf.

• 32:38Neil deGrasse Tyson?

  Is that right?

• 32:39Janna Levin?

  Yeah.

• 32:39Neil deGrasse Tyson?

  Yeah, yeah, Black Hole Blues. I didn't know black holes had emotional states.

• 32:46Janna Levin?

  Well, the people who were searching for black holes had emotional states.

• 32:51Neil deGrasse Tyson?

  Oh.

• 32:52Janna Levin?

  They had the black hole blues. They had the black hole blues.

• 32:55Neil deGrasse Tyson?

  I got you. So this is a story of black holes in our field of astrophysics and the relationship we have to them. Got it, got it. And more recently, you have a book called The Black Hole Survival Guide, which is like a pocketbook, fits right in your coat pocket. And how useful did you, how soon do you think such a book will be useful, where everyone has to have one?

• 33:18Janna Levin?

  Yeah, they have to have a survival guide. Well, I hope not very soon at all, but we are in orbit.

• 33:26Neil deGrasse Tyson?

  For the sake of the sales of your book.

• 33:31Janna Levin?

  Well.

• 33:33Matt Kirshen?

  Let's stoke some worry in the public.

• 33:35Janna Levin?

  I have a spoiler alert. It doesn't end well.

• 33:42Neil deGrasse Tyson?

  Oh, yeah, yeah, yeah.

• 33:44Janna Levin?

  The survival guide doesn't go well.

• 33:47Neil deGrasse Tyson?

  All right.

• 33:48Janna Levin?

  It's pretty much many ways to die.

• 33:51Neil deGrasse Tyson?

  We'll keep a copy of this in our go, in our go bag, right? When you're in disaster strikes.

• 33:57Janna Levin?

  Don't you have a book titled Death by Black Hole? I've always wanted to steal that title from you.

• 34:02Neil deGrasse Tyson?

  Oh, Death by Black Hole. Yeah, yeah, I do. It's one, so that's, that title is the title of one chapter in a book that goes a lot of different places.

• 34:09Janna Levin?

  It was this collection of essays, as I remember.

• 34:11Neil deGrasse Tyson?

  Yeah, that's right. That's right. On all manner of things in the universe.

• 34:15Janna Levin?

  Yeah, so the survival guide could also be called like Death by Black Hole.

• 34:21Neil deGrasse Tyson?

  Okay, all right. It's how to not, so it's the non-survival guide?

• 34:26Janna Levin?

  Yeah.

• 34:26Neil deGrasse Tyson?

  Death by Black Hole.

• 34:30Neil deGrasse Tyson?

  All right, Matt, what more do you have for us?

• 34:31Matt Kirshen?

  Well, I've got, I'm gonna turn this to some black hole survival questions because we've got a few and, and they're great. So from the Czech Republic, Patreon patron Jindric Prokupec, I hope I've got that close to correct, asks you, I read that black holes are almost zero Kelvin inside. Why are they so cold and not very hot due to a high pressure caused by enormous gravity forces and lack of heat escape? And is there a temperature gradient between a black hole center and its event horizon?

• 35:00Neil deGrasse Tyson?

  And what's zero K anyway, Jenna?

• 35:03Janna Levin?

  Oh, literally, it just means particles are so cold, they have so little energy that they're just not moving. It's as though, you know, what we experience, temperature, what we're really experiencing is the collection of atoms moving at a certain rate and a certain speed on average, and that creates the temperature. And the faster that they're moving, the hotter it feels, and the slower they're moving, the colder they are. And it is true, there's an expression, PV equals NKT, that, you know, in highly pressured situations, the temperature can go up. And

• 35:37Matt Kirshen?

  Right, that's the, that's the thing, I, the, the level of physics that I understand, like, a bicycle pump gets hotter if you, and if you, if you spray one of those compressed air canisters, they get cold because you're a

• 35:49Janna Levin?

  Yeah, exactly.

• 35:50Neil deGrasse Tyson?

  Jenna, I can't believe you wrote it on the chalkboard.

• 35:53Matt Kirshen?

  I, I love that Jenna's in front of her. The people who are audio only are not aware that Jenna is, you look like you're posing for a professor photograph right now.

• 36:03Janna Levin?

  What were we talking about? Oh.

• 36:04Matt Kirshen?

  We were talking about the compression.

• 36:06Neil deGrasse Tyson?

  Matt was sharing his life experience that in a bicycle pump, you, because he's living in his parents' basement, he doesn't own a car, just has a bicycle. So, in his bicycle pump, the valve gets hot.

• 36:16Matt Kirshen?

  Well, I've got his compressed dad to keep me happy.

• 36:19Neil deGrasse Tyson?

  Right, and a spray can, as the, as the air releases, the nozzle feels cold. So, so the pressure can heat up or, or cool it, depending which way it's going. So, so what's happening inside a black hole? Is, is, is the person right about it being zero?

• 36:35Janna Levin?

  No. It's, but they're not right for a very interesting reason. So, we know that as the core of a remnant star, what's left after it goes through some very violent throws at the end of its life, continues to collapse and is in fact extremely dense, and probably absolutely an unusual, extraordinary, exceptional state of matter. We know that because we see neutron stars, which are in even black holes, they're a step on the way to black holes, they don't quite make it there. And we know that they're incredibly unusual in terms of their composition. But, once it makes it to be the black hole, so, it has created a curve

• 37:17Janna Levin?

  in spacetime that is so sharp that we know not even light can escape. That's what we mean by the event horizon. And you might think, therefore, the event horizon of a black hole is full of dense stuff, but it's not actually, because the star can no more sit there than it can expand outward at the speed of light. You can almost think of spacetime as like a waterfall raining into the black hole, and it would have to swim against the waterfall just to stay at the event horizon. And it can't do this, so it just continues to get dragged in with the waterfall of spacetime. And, you know, this is the great mystery. What happens to the star? We don't know. But it's gone. The star is gone.

• 38:00Janna Levin?

  So, black holes are cold because they're empty. So, if I go up to the event horizon of a black hole, nothing's there. There's no dense object, there's nothing solid, it's empty space. So, I like to say, you know, and I've said this, I'm sure, on your show before, black holes are more like a place than they are a thing. They're like a place in the universe, but there's really no matter left.

• 38:23Neil deGrasse Tyson?

  But you can measure the gravity that it has, right? So, something's gotta be there.

• 38:28Janna Levin?

  Yeah, that's right. It has gravitational energy in the curvature of the spacetime. There is energy in the curvature of the spacetime. That is gravitational energy. So, you know, it's often really hard to define gravitational energies, but in the case of a black hole, I can actually have a well-defined mathematical prescription for measuring its gravitational energy, and it happens to equal, not surprisingly, the mass of whatever fell into it. So, it's as though the matter, like, throws its heft into the gravitational imprint, but you don't, but the stuff is gone. Now, there's another question you could ask about temperature, which is about the Hawking radiation.

• 39:09Janna Levin?

  So, at the event horizon, we do think that through this very subtle quantum process, black holes do have a temperature, actually, and they are radiating, actually. But the bigger the black hole, the colder they are, and the smaller they are, the hotter they are. So, they have, they're very cold, they live their lives absorbing things, not emitting. But at the end, you know, in very, very far, far, far future of the universe, those black holes will eventually evaporate away, and the final stages will be explosive.

• 39:40Neil deGrasse Tyson?

  Yeah, in fact, if I remember correctly, the original paper... That described this phenomenon by Hawking, uh, explained these as that they would be bursts of high-energy gamma radiation because they, right at that last moment, would be at its hottest and very hot things emit gamma rays.

• 40:00Janna Levin?

  Exactly.

• 40:00Neil deGrasse Tyson?

  And so it's interesting.

• 40:02Janna Levin?

  Yeah, so you know, if you, if you are foolish enough to try to make a black hole in the laboratory, it will explode on you because the smaller they are, the more unstable they are. And you can kind of figure out like, how big would it be if it was like, kind of a stick of dynamite versus what you're describing gamma rays or nuclear weapon grade? And, um, and, uh, you, so you're kind of ill-advised to make a small black hole.

• 40:29Matt Kirshen?

  But if you do, you should start with a bigger one, just to, just for safety?

• 40:32Janna Levin?

  Well, then you're gonna fall in. You gotta, you know, it's a real, sorry, trying to.

• 40:36Neil deGrasse Tyson?

  Well, what a trade-off that is. And, and Earth, it could suck in the Earth. So, yeah, that would ruin your day.

• 40:41Janna Levin?

  That would ruin a lot of days, people's days.

• 40:45Neil deGrasse Tyson?

  So we can't, so Jenna, we can't call a black hole an area of nothing if it contains the severe curvature of the spacetime continuum, because that is something.

• 40:56Janna Levin?

  Yeah, um, I guess, right, that's fair. We can say, um, what do we really mean by nothing?

• 41:02Neil deGrasse Tyson?

  Man, notice how she didn't say it was right. She just said it was fair.

• 41:07Janna Levin?

  You're, you're, you're absolutely right. Spacetime is something and spacetime has energy.

• 41:12Neil deGrasse Tyson?

  It's a thing.

• 41:12Janna Levin?

  Spacetime moves and it's a thing. And in that sense, it's a thing, but it's also by definition, space, which is a place. I'll, I'll take that they very much act like things. Black holes move around, they, they orbit, they can fall together, they can collide, you know? But when we talk about the size of a black hole, we're talking about a shadow. That's all we're talking about. We're talking about a shadow, like the shadow of a tree. And there's nothing there, no matter.

• 41:39Matt Kirshen?

  While, while we're talking about matter, so, uh, listener Gonzalo Castilla, uh, from Mexico, asked, and Gonzales mentions black matter. I'd imagine this is, uh, what we would also call dark matter, unless there are two different things.

• 41:55Janna Levin?

  Yeah, I think it's probably dark.

• 41:56Matt Kirshen?

  So I, I'll say dark matter for this. I'd imagine that's a, that's a language thing. But if dark matter can interact gravitationally with normal matter. It is attracted and eaten by a black hole, just like normal matter, right? What happens with the dark matter as the black hole evaporates? Could there be a dark matter version of Hawking radiation? Or it only radiates normal matter and a black hole has some sort of mechanism that transforms this dark matter into normal matter?

• 42:25Neil deGrasse Tyson?

  So, Jana, that's a really interesting question. Oh, my gosh. But as we're running short on time, can you like, soundbite that answer? Is that possible?

• 42:33Janna Levin?

  Yeah, absolutely. The black hole will figure out how to radiate all of the information that went into it, if this works. So that includes dark matter information. So that the fact that it was dark would come out, in principle. Everything comes out.

• 42:50Neil deGrasse Tyson?

  Okay, so Hawking radiation, that calculation does not discriminate between ordinary matter or dark matter or any other kind of matter?

• 42:58Janna Levin?

  Nope. It can be electrons and positrons. It can be light coming out in the Hawking radiation. It can be dark matter pairs, pairs of dark matter.

• 43:06Neil deGrasse Tyson?

  And that assumes, so everything you said assumes that dark matter is actually comprised of matter and not some other mystical substance?

• 43:13Janna Levin?

  Right.

• 43:13Neil deGrasse Tyson?

  Okay.

• 43:14Janna Levin?

  Right. And there are people who think that black holes themselves might be enough to explain the missing mass in the dark matter.

• 43:21Neil deGrasse Tyson?

  Yeah, I'm not among them.

• 43:22Janna Levin?

  So that's not a particle answer at all.

• 43:24Neil deGrasse Tyson?

  Yeah.

• 43:24Janna Levin?

  Yeah.

• 43:25Neil deGrasse Tyson?

  Okay, Matt, keep coming.

• 43:26Matt Kirshen?

  All right, so Dylan, there's a couple of faster-than-light questions. So Dylan asks, "I've heard a lot about wormholes on this show and have a question. How would we open up a wormhole? I know as of right now they're impossible, but hypothetically speaking, what steps are taken? How much energy would it take? And could we just use a black hole? How do we cut spacetime?"

• 43:43Neil deGrasse Tyson?

  Yeah, Jana, we're waiting for this, and why aren't you giving us the wormhole? We're so disappointed.

• 43:49Janna Levin?

  I know. I'm busy. I'm gonna do it in the future and then come back.

• 43:55Neil deGrasse Tyson?

  Oh!

• 43:55Janna Levin?

  I'm gonna do it later.

• 43:58Neil deGrasse Tyson?

  Good answer! Good answer. Matt, that reminds me, during the science march, which is sad that in the United States we needed a march to defend science back several years ago. One of the placards said, "What do we want? Time machine. When do we want it? It doesn't matter."

• 44:19Janna Levin?

  That's perfect.

• 44:20Neil deGrasse Tyson?

  Yeah.

• 44:21Janna Levin?

  Um, I think MIT once scheduled a, a time traveler conference

• 44:28Janna Levin?

  for the previous year.

• 44:31Janna Levin?

  They were like, let's meet in 2019 and have a time traveler conference. Nobody showed up.

• 44:38Neil deGrasse Tyson?

  Nope, yeah. Time travelers didn't show up, yes.

• 44:41Janna Levin?

  I can tell you this about the wormhole. We absolutely on paper know how to make a wormhole. So basically what you do is you, you, you write down the shape of the space time you want, namely a wormhole shape, and then you force matter and energy to create it. And you ask then, well, what is the distribution of matter and energy have to be to create this shape? So you can go backwards and, and, and deduce what kind of matter and energy would be required. The problem is, is it requires negative energies and that's not something we see in our ordinary experience. Everything has positive energies. Negative energies are, are super weird. We, some people think that they're forbidden in nature. The one circumstance in which you can get negative energies is in some strange quantum situations. I've actually wondered about this.

• 45:26Janna Levin?

  Could we create where you have, um, like finite spaces made out of metals and the quantum oscillations or the quantum vibrations create a certain negative energy between like these strange geometric configurations?

• 45:44Neil deGrasse Tyson?

  So you need the energy, the negative energy to pry open a hole that would otherwise on its own want to collapse and just make a black hole, I guess.

• 45:52Janna Levin?

  Yeah, it just wants to keep pinching closed.

• 45:54Neil deGrasse Tyson?

  So that, that sounds really dangerous to enter one of these because suppose you're in one and then it collapses on you, that's a bad day.

• 46:01Janna Levin?

  That would be...

• 46:01Neil deGrasse Tyson?

  Right there.

• 46:05Neil deGrasse Tyson?

  Okay, so we're nowhere near this now, even though you can make it happen on paper.

• 46:09Janna Levin?

  Yeah, I mean, you know, people at Kip Thorm, they were writing down wormhole solutions decades ago, and they just looked around and said, "Well, we don't see any matter like that in the universe." So we've got to go back to the drawing board and think of a new way.

• 46:22Neil deGrasse Tyson?

  Okay, so just because something is mathematically possible doesn't mean the universe is going to cooperate. That's really what it comes down to.

• 46:29Janna Levin?

  There's other time machines that we know we can make. We can take two cosmic strings, which are literally strings of energy, tension, and energy density, and cross them in a very funny way that creates a kind of cut in spacetime that allows you to do a little time travel jig. But the problem is, is they have to be infinitely long and take an infinite amount of energy. So there's never anything that seems compatible with the universe that we live in. And even Kurt Gödel first, who was friends with Einstein, used to walk to the Institute for Advanced Study with him in the mornings to talk. And he was inspired by Einstein's work. And he wrote down a description of a hypothetical universe that was rotating, not our universe. And he showed that you could travel in time

• 47:14Janna Levin?

  in this peculiar space he invented. And Einstein didn't dispute it. It was correct mathematically. But we just don't live in those kinds of...

• 47:22Neil deGrasse Tyson?

  Okay, just admit it, Jenna. All we really need is 1.21 gigawatts. Okay? That's really all we need. Just admit it.

• 47:33Matt Kirshen?

  I believe it's pronounced jigawatts.

• 47:40Neil deGrasse Tyson?

  So Jenna, I think we've got to call it quits there. We ran out of time.

• 47:44Janna Levin?

  Aw, shame. It's always so fun.

• 47:46Neil deGrasse Tyson?

  Okay. So Matt, with your permission, I don't want to call it the Stoner Edition unless we have total buy-in from the three of us.

• 47:57Janna Levin?

  I'm fine calling it the Stoner Edition. But anybody who knows me knows if I'm stoned, I'm asleep. It's synonymous. Stoning equals sleeping.

• 48:08Matt Kirshen?

  And anyone who knows me knows I have a green card. And...

• 48:14Neil deGrasse Tyson?

  That's right, northern Europeans have green cards too.

• 48:19Matt Kirshen?

  I have a green card, which means I can't get the other kind of green card.

• 48:25Neil deGrasse Tyson?

  So we're good here. So Janet, thanks for coming back to StarTalk. It's always good to have you. And so, and continued good luck with, and it's not luck, it's your talent that helps make Pioneer Works what it has been and what it will continue to grow to become. So keep that going there. And Matt and I are still waiting for our invitation to be something other than in your audience.

• 48:51Janna Levin?

  Now I can't wait. Oh, you're gonna get an invitation.

• 48:54Neil deGrasse Tyson?

  You got it. Matt, always good to have you, dude.

• 48:56Matt Kirshen?

  Lovely to be here. Thank you for having me.

• 48:58Neil deGrasse Tyson?

  This has been StarTalk Cosmic Queries, Black Holes, Spacetime Continuum, which we dubbed the Stoner Edition. I'm Neil deGrasse Tyson, your personal astrophysicist. Keep looking up.