Hunting for Black Holes, with Janna Levin - StarTalk All-Stars

If light can’t escape from black holes, how can we observe them at all? Find out from astrophysicist Janna Levin, co-host Matt Kirshen, and Shep Doeleman, the MIT astrophysicist leading the Event Horizon Telescope project to study black hole Sgr A* at the center of our galaxy. NOTE: StarTalk All-Access subscribers can watch or listen to this entire episode commercial-free. Find out more at https://www.startalkradio.net/startalk-all-access/

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

• 0:00Speaker 00

  This is StarTalk.

• 0:08Janna Levin?

  Welcome to StarTalk All-Stars. I'm Janna Levin, and I'm your All-Star host today. I'm an astrophysicist and author, but nowhere near as interesting as my co-host, the incredibly talented Matt Kirshen. Matt, welcome to New York.

• 0:21Matt Kirshen?

  Hey, thank you for welcoming me both here and to the show, and for pointing out that I'm more interesting than an astrophysicist.

• 0:26Janna Levin?

  That's right, and we're going to hold you to that for the rest of the hour.

• 0:28Matt Kirshen?

  Much more interesting.

• 0:29Janna Levin?

  Also, in the studio, we have special guest Sheppard Dolman, who has a long list of accomplishments, including getting through graduate school at MIT, same year as me.

• 0:37Matt Kirshen?

  And getting here this morning.

• 0:39Janna Levin?

  Getting me through general relativity. Shep is an astrophysicist at the Harvard Smithsonian Center for Astrophysics and the director of the Event Horizon Telescope Project. Event Horizon Telescope is a fantastic project, not yet complete, still under development. It is a telescope essentially the size of the entire Earth that is going to try to take the first real picture of a black hole. Very exciting stuff. So this is what we're going to talk about today.

• 1:06Matt Kirshen?

  Good day's work if we can pull it off.

• 1:07Janna Levin?

  It's a good day's work. So we're going to be talking about black holes, how we observe them so far, why we think they're real, and what it would mean to take a real picture of them for the first time. So Shep, thanks so much for coming, making the trip from MIT to Harvard.

• 1:21Matt Kirshen?

  Thanks for having me. It's a pleasure.

• 1:23Janna Levin?

  Today, we're going to delve into one of the weirdest and sort of most exciting topics in astrophysics. Everyone loves to talk about black holes, and particularly how we observe them. But first, let's just start with, you know, what is a black hole? Shep?

• 1:41Matt Kirshen?

  So everybody, I think-

• 1:42Janna Levin?

  Matt?

• 1:42Matt Kirshen?

  You throw straight to Shep. I get it. I see how things are. Someone's already playing favorites. I didn't go to school with you.

• 1:49Janna Levin?

  You didn't graduate-

• 1:49Matt Kirshen?

  Go back 20 years. You just go to Shep to immediately ask about the black holes.

• 1:52Janna Levin?

  Yeah, you didn't graduate from MIT.

• 1:54Matt Kirshen?

  Well, I'll give you an opening.

• 1:55Janna Levin?

  We have rings that have a beaver on them.

• 1:59Matt Kirshen?

  Really?

• 1:59Janna Levin?

  Yeah, the beaver ring is the MIT class ring.

• 2:01Speaker 03

  The industrious engineers.

• 2:02Janna Levin?

  It's quite appalling. I know.

• 2:05Matt Kirshen?

  All right.

• 2:05Janna Levin?

  That face says it all.

• 2:06Matt Kirshen?

  Oh, because of building things, all right. That makes a lot more sense.

• 2:09Speaker 03

  We build telescopes, we image black holes. That's what we're all about.

• 2:12Janna Levin?

  So, black holes.

• 2:13Speaker 03

  So, black holes, what are they?

• 2:14Janna Levin?

  What are they?

• 2:16Speaker 03

  Well, everyone has some idea of what a black hole is. But essentially, it's when gravity's run amok. It's when mass collapses in on itself to the point where gravitational runaway is inevitable. And nothing can keep matter from in-falling to a singularity to a point. And the interesting and defining thing about a black hole, and this is what we all probably know about, is that there's this membrane called the event horizon around the black hole. And that's the point outside the singularity where gravity is so strong that even light can't escape.

• 2:46Matt Kirshen?

  And that's named after the movie.

• 2:48Speaker 03

  It's the other way around, actually, you know? But it's, uh...

• 2:51Matt Kirshen?

  Interesting.

• 2:52Speaker 03

  It's what most people think about when they think about the event horizon, the movie, and the spaceship that went into hell and then came back out haunted.

• 2:58Janna Levin?

  So, the event horizon means no events that happen on the other side of that line will ever be known to you. So, it separates causally, right, two parts of space.

• 3:09Matt Kirshen?

  Okay.

• 3:09Janna Levin?

  But...

• 3:10Speaker 03

  What happens in the event horizon stays in the event horizon.

• 3:13Janna Levin?

  So, is it an actual membrane?

• 3:15Speaker 03

  It's not an actual membrane, it's just a region of spacetime that demarks where gravity is so strong that the escape velocity from that mass is the speed of light. So, once you pass through it, you really can't get back out again.

• 3:27Janna Levin?

  If, you could actually stick a light pulse right at the event horizon and racing outwards at the speed of light, it wouldn't go anywhere. It would just sit there.

• 3:35Speaker 03

  It would be frozen.

• 3:36Janna Levin?

  It would be, yep, just hovering there. It's as though, almost as though spacetime's falling in like a waterfall.

• 3:40Matt Kirshen?

  So, what would you see if you were actually right at that event horizon?

• 3:43Janna Levin?

  You would pass the light pulse and think it's traveling at the speed of light. So, but this is a good question, Matt, because you say matter is a dense, you know, crushes under its own weight. A big enough star will crush under its own weight eventually. So, is there stuff there? Like, people think of a black hole as this incredibly dense object. So, when I cross the event horizon, like Matt asked, is there anything there?

• 4:04Speaker 03

  Usually, there's nothing there.

• 4:05Janna Levin?

  Nothing there. It's the weirdest.

• 4:07Speaker 03

  Especially for a supermassive black hole, like the ones that are in the center of our galaxy or in other galaxies. You just pass right through the event horizon like it's not there, but you can't get back out again. It's one of these strange things. That's why philosophers get very dreamy when you talk to them about black holes in a way that they don't when you talk to them about stars, because world lines can go through the event horizon and you don't know what happens.

• 4:26Janna Levin?

  What's a world line? What's a world line, Chad?

• 4:28Speaker 03

  A world line is where you are following space and time on your own trajectory and I go from this point to that point, from point A to point B. But if point B is inside the event horizon, you can't get back out again. You can't tell your friends where you were or how you got there.

• 4:43Janna Levin?

  Yeah, you know how Google Maps plots your spatial path? They should do a space-time diagram, right? So the world line's your path through space and through time.

• 4:51Matt Kirshen?

  But sometimes it gets it wrong and it picks like the wrong Massachusetts or whatever and then it says you need to take a boat.

• 4:57Janna Levin?

  And then you need to take a left turn.

• 4:59Matt Kirshen?

  Right.

• 5:00Janna Levin?

  And then a boat.

• 5:01Matt Kirshen?

  And then you'll never escape. All right, I get it, I get it.

• 5:03Janna Levin?

  But the thing about the GPS units is they do actually have to correct for relativity to get your location right on the map. So our clocks run a little bit slower here on Earth than they do, say, at the satellites. And so they have to correct for that time difference, the fact that our clocks are running slower, that we're aging slightly more slowly, in order to locate you properly on the Earth. So.

• 5:25Speaker 03

  And I think that's hugely interesting, right? Because Einstein developed this theory of general relativity in 1915, 101 years ago. And sometimes I imagine going back and talking to Einstein and saying, "Here, Professor Einstein, you know, 100 years from now..."

• 5:40Matt Kirshen?

  You don't have to put on the voice.

• 5:41Speaker 03

  I do have to put on the voice. If I don't put on the voice, it doesn't sound good, right? So you go back in time and you say to Einstein...

• 5:47Janna Levin?

  Do you talk to everyone in the accents that they have? Are you gonna start speaking British to Matt?

• 5:51Speaker 03

  Don't get me started. But you talk to Einstein, you would say, "100 years from now, corrections that you discovered will enable me with my phone to take down links from a constellation of satellites around the Earth and pinpoint my location to anywhere on the Earth." And of course, he'd be very excited and he would say, "What's a phone?"

• 6:10Janna Levin?

  Right.

• 6:11Speaker 03

  Because our technology has gone so far beyond what Einstein had that the first thing he'd be interested in is, "Well, what's a phone?"

• 6:19Janna Levin?

  I thought he wouldn't, he refused to memorize his phone number because he said, "Why would I memorize anything I could look up? Like, why clutter your mind?"

• 6:26Speaker 03

  And you're as bright as Einstein, you can get away with a lot of stuff.

• 6:28Janna Levin?

  Yeah, well, he also said, "When I was a student, I was no Einstein."

• 6:33Janna Levin?

  So, how do we know that these crazy-

• 6:35Matt Kirshen?

  I was also no Einstein as a student, so does that make us kind of on a par?

• 6:38Janna Levin?

  That's right. It works in both directions.

• 6:40Matt Kirshen?

  Also, I don't know Einstein's phone number, so we're kind of exactly the same person.

• 6:43Speaker 03

  Did he have a phone number?

• 6:44Janna Levin?

  Intellectually clearly very similar.

• 6:46Matt Kirshen?

  Yeah.

• 6:46Janna Levin?

  Wouldn't he have had a phone number?

• 6:48Speaker 03

  Maybe.

• 6:48Janna Levin?

  So maybe this is one of those apocryphal stories that I'm propagating without having properly looked into the history.

• 6:53Speaker 03

  I think he had an assistant that just took care of all that for him. That's what I think.

• 6:56Janna Levin?

  So, black holes, Einstein understood the mathematical solution, but he wasn't sure that they were real. In fact, he sort of thought nature would protect us from their formation. I mean, after all, I can't crush this desk very easily. It's very, very hard to do. I mean, it's hard to fold a piece of paper more than, what's the number, 11 times or something like that?

• 7:15Speaker 03

  The 11th.

• 7:15Janna Levin?

  It starts to really fight. So, he believed quite sensibly that nature would not allow something to collapse all the way to a black hole. And there were decades between that time, 1916, this guy in the trenches, infantry soldier on the Russian front, you know, is calculating ballistic trajectories and writing to Einstein, naturally. And he wrote down the first solution for a black hole. Do you know when it got its name, the black hole? Do you know who gave it its name?

• 7:43Speaker 03

  People's gave it-

• 7:44Janna Levin?

  It was Wheeler, I think.

• 7:45Speaker 03

  Wheeler.

• 7:45Janna Levin?

  Also Princeton guy. Yeah.

• 7:47Speaker 03

  I don't know what year that was.

• 7:48Janna Levin?

  Apparently, it was 67, and I'm not going to tell you why I know that year, but I haven't.

• 7:53Speaker 03

  The year I was born.

• 7:53Janna Levin?

  It's the year Shep was born. And, he was tired of saying end state of complete gravitational collapse, apparently, so someone from the audience shouted, "How about black hole?" And the name stuck. That's 50 years, right? 50 years it took for people to really start to believe that black holes were real. So why do we believe they're real now?

• 8:14Speaker 03

  Well, the way I think about it is that, for a long time, people didn't think that anything could be much denser than water, right? So, if you take our sun, the average density of the sun is not too much more than water, given its volume. Like, you could fill the whole volume of the sun with water, it would weigh about what the sun weighs. And it wasn't until people found white dwarves, which are very dense end states of stars, like cinders of stars, it'll be the end state of our sun, for example, and neutron stars, that people began to really-

• 8:46Speaker 03

  You know, think that matter could be compressed to extreme densities.

• 8:50Matt Kirshen?

  So just to be clear, this is scientists who didn't think things could be denser than water, not just like people in the pub.

• 8:54Speaker 03

  Yeah, well.

• 8:55Matt Kirshen?

  People have theories. Like, I remember my friend Jordan telling me, when we were like eight, that the way we could travel faster than light is, I don't know if you saw the end of Jaws, but like, the way the canister of, like, exploded in the shark's mouth was so powerful, and he's like, "That's as big an explosion as you can get, and that'll get us like faster than the speed of light." And it turns out Jordan was wrong. But...

• 9:16Janna Levin?

  Jordan's one of those people, apparently, who write me those, you know, their theories of everything.

• 9:21Matt Kirshen?

  Do you get those? I bet you do, both scientists get like...

• 9:23Janna Levin?

  I'm gonna look, I'm gonna search for the name Jordan in my crazy folder.

• 9:26Speaker 03

  You always get these letters that say Einstein got it wrong by a minus sign, and here's why.

• 9:29Matt Kirshen?

  Right.

• 9:30Janna Levin?

  Although he did have a minus sign error in some of his first papers. He, yeah, but not in relativity. I mean, he made mistakes. He wasn't really afraid of that. I mean, the stuff is, you know, it's not written on a tablet somewhere. It takes some trial and error. But, sorry, was there more to Jordan's theory?

• 9:43Matt Kirshen?

  No, that was mostly it, to me, like...

• 9:45Speaker 03

  I think we should just call it Jordan's theory.

• 9:47Matt Kirshen?

  Basically, anything that can explode a shark has got to be pretty powerful.

• 9:50Janna Levin?

  Well, actually, it's quite amazing. They really needed to understand the nuclear physics that goes into the bomb technology before they were sophisticated enough in their understanding of small-scale matter forces to realize that a black hole would form. So, so all these guys really did work on the bomb. But, on that happy note, we're switching to cosmic queries. Matt, what do you got for us?

• 10:12Matt Kirshen?

  Okay, so on that note, here's a question from Victor Furttenbach on Facebook, who says, oh, from Stockholm, Sweden as well, "Is it possible to kill or destroy a black hole?"

• 10:25Janna Levin?

  Is it alive?

• 10:25Speaker 03

  A black hole hunt. I really like that.

• 10:28Matt Kirshen?

  Like, Wood putting a compressed air canister in the black hole's mouth and then shooting it from a boat.

• 10:33Speaker 03

  I think a shark could easily...

• 10:34Matt Kirshen?

  Right. Like, how big would a shark have to be to eat a black hole?

• 10:37Janna Levin?

  I guess it depends on what you mean by destroy.

• 10:40Speaker 03

  Well, black holes will evaporate by themselves if just left to their own devices. And that's because of something called Hawking radiation. So the boundary of the black hole, this event horizon, is a turbulent place and you can get particle and pair production. And one particle will go into the black hole and one will go out of the black hole. And from a distance, it looks like the black hole is giving off particles, slowly evaporating. And over billions of years, a stellar mass black hole can just vanish. So that's one way to get rid of a black hole, just leave it alone.

• 11:09Matt Kirshen?

  Just wait for a very long time.

• 11:10Speaker 03

  Ignore it.

• 11:11Janna Levin?

  It's a very long time. Because right now, the light left over from the Big Bang is hotter than all the astrophysical black holes we think we know of, so that the black holes right now are absorbing the light from the Big Bang. They're not emitting it yet. In a long time, everything will fall into black holes and then all those black holes will evaporate.

• 11:27Matt Kirshen?

  This is like a long, like if this black hole is currently terrorizing a seaside town, like this is not the approach that you want.

• 11:33Janna Levin?

  Yeah, that would not be a good, yeah, protective measure. Yeah, that wouldn't work.

• 11:38Speaker 03

  Yeah, but also a shark-sized black hole would be, a shark-mast black hole would be really tiny.

• 11:44Matt Kirshen?

  Can you make that? Can you have a black hole that's that size?

• 11:47Speaker 03

  Oh, sure. So if you had a black hole that was the mass of an asteroid, for example, let's say 100 trillion kilograms, it's a good-sized asteroid, it would be smaller than an atom. So it wouldn't terrorize the town. It would just drop right to the center of the Earth, because there'd be no support for it.

• 12:03Janna Levin?

  Well, you know, we don't actually know how to force an asteroid to become a black hole, but there was...

• 12:08Speaker 03

  By direct pressure.

• 12:09Janna Levin?

  You're right, more, more, more. But in the Large Hadron Collider, people were afraid that by smashing particles together, one of the byproducts was going to be subatomic-sized black holes. And so people did try to take an injunction against turning on the Large Hadron Collider.

• 12:27Matt Kirshen?

  Now, I remember that being a thing. Did any mini, like, micro-black holes actually get created? And if so, what happens?

• 12:33Janna Levin?

  Awesome, no.

• 12:35Matt Kirshen?

  Like if one were to happen.

• 12:36Speaker 03

  Clearly.

• 12:37Janna Levin?

  Thank god.

• 12:37Speaker 03

  Clearly we're safe.

• 12:38Matt Kirshen?

  Okay. So if one were to happen, it would actually do bad things? Like even if it is the.

• 12:43Janna Levin?

  It wouldn't, actually. So physicists just are never willing to say never. They're only willing to say it's very, very improbable.

• 12:48Matt Kirshen?

  Right.

• 12:49Janna Levin?

  So the argument was, uh, black holes could be made, um, depending on whether there were extra spatial dimensions and what gravity is really like at higher energies. But if they were made, they actually evaporate through the process Shep's describing much faster, um, than big black holes. The smaller the black hole, the faster they evaporate. So the idea was they would just be gone in a flash. It would be like an explosion.

• 13:12Speaker 03

  They're tiny and they burn brightly.

• 13:13Janna Levin?

  Yeah. At least that's the theory.

• 13:15Speaker 03

  The other thing, so the other thing that, that people should feel safe about is that nature has already done this experiment for us. So people worry about CERN and the Large Hadron Collider slamming particles together to make a little black hole. But cosmic rays hit the earth all the time and they're hugely high energy. They're higher energy than you can make in the LHC. So they're slamming into the earth all the time and they haven't made a black hole yet that devoured the earth. Maybe they made a black hole, but remember, black holes have these tiny little mouths, right? They're like huge animals with a tiny little mouth, right? And so it's very difficult for them to eat.

• 13:49Matt Kirshen?

  I like you keeping everything in shock, Tim, to me, and I really appreciate that.

• 13:53Speaker 03

  They're like the hummingbird of the exotic object world.

• 13:56Janna Levin?

  So do we have some more cosmic queries?

• 13:57Matt Kirshen?

  Yeah. So again, and I think this question might turn out to be slightly off in terms of the way it's phrased, but Hunts105 on Instagram, I don't know how you ask a question on Instagram. Uh, I don't know if this is just done by posing for a picture that conveys this question.

• 14:10Janna Levin?

  What about holding up a cardboard sign?

• 14:13Matt Kirshen?

  Yeah, right. Oh, maybe. But Hunter from the United States says, how close would a black hole have to be in order to see it with the unaided eye?

• 14:20Speaker 03

  The unaided eye.

• 14:23Janna Levin?

  Hmm, you'd have to see the shadow cast because that's all there is to see.

• 14:26Speaker 03

  Yeah, so one of the mysteries of black holes, maybe we'll get to this later, but this is the perfect time, is that by definition, you can't see them. By definition, all the action happens within the event horizon. Once things fall through, even light, you can't see it. So. Why are black holes actually some of the brightest things we see in the sky? That's because all the gas and dust that's being attracted to the black hole is trying to fit into this impossibly small volume. And just as when you rub your hands together, they get hot, the friction of all that gas and dust madly trying to get into this teeny little volume heats everything up to hundreds of billions of degrees.

• 15:00Matt Kirshen?

  See, what you're seeing is everything clamoring to get into the black hole rather than the actual black hole itself.

• 15:05Janna Levin?

  Yes.

• 15:06Speaker 03

  It's like, you know...

• 15:07Matt Kirshen?

  You're seeing like the line outside the nightclub, rather than... Something's happening inside there and it's pretty special, but all you can see is like this big, exciting line outside.

• 15:14Speaker 03

  And the bouncer is kind of like the heat, keeping people, everybody out.

• 15:17Matt Kirshen?

  Right.

• 15:17Janna Levin?

  Right, but then you think, you know, right, maybe it's all hype. So what Shep wants to do is take an actual picture of the shadow, so that's something amazing. But to see the shadow means there has to be something bright behind it. So if the black hole is just against a dark sky, there is no hope of seeing it, even unaided. But if it was, had the Milky Way galaxy shining behind it, you would see a sort of lensed image of the Milky Way, and that's how, and you would see the shadow. So it's an interesting question, how close would it have to be? So a black hole the size of the sun is about six kilometers across. So how close would six kilometers have to be, Shep, do you think, to be able to see it? In the case of my eyes, like, right here.

• 15:59Speaker 03

  It would be like within the solar system. So if you're out, if you're out in the orbit of Pluto, for example, and you look back to the sun, you can't even see that, right? So you'd have to be well within the orbit of Mercury, I would imagine, to even see this kind of thing.

• 16:14Matt Kirshen?

  Also, Sebastian Dubus on Facebook says, "Where is the closest black hole? And could we send something to orbit around it?"

• 16:19Speaker 03

  Well, that's a great question. We often joke that the best way to study a black hole is to send an undergraduate with a laser pointer to the nearest black hole and throw them in, right? And then as they go in, the laser, of course, would be Doppler-shifted and you'd see the dynamics.

• 16:33Matt Kirshen?

  They'd get extra credit for that, though, right?

• 16:34Speaker 03

  They'd totally pass the course.

• 16:35Matt Kirshen?

  Okay. That's gonna look really good on the recipe.

• 16:37Speaker 03

  Well, the nearest one is, it's just like a few tens of light years away, I think. Like, Cygnus X1, that's one.

• 16:43Janna Levin?

  I thought it was 6,000 light years away. Oh, fact-checkers.

• 16:47Matt Kirshen?

  Well, is there a black hole at the center of the Milky Way?

• 16:49Speaker 03

  There's absolutely a black hole.

• 16:51Janna Levin?

  And that's further away than the nearest black hole.

• 16:53Speaker 03

  Yeah, that's about 25,000 light years away.

• 16:55Matt Kirshen?

  Okay, so the nearest black hole, is that also part of the Milky Way? Or how does it...

• 16:59Janna Levin?

  Yes.

• 17:00Matt Kirshen?

  Okay.

• 17:01Janna Levin?

  Yeah, so there's 100 billion stars in the Milky Way, and about a million of them... What'd I say, 100 billion? About a billion of them, actually, will one day become black holes. It doesn't mean that they all are now. So there's a lot of black holes just speckled around the galaxy, a lot.

• 17:14Speaker 03

  We may talk about this later, but the black hole at the center of our galaxy is one of the only ones that we can hope to resolve with any kind of astronomical instrument. So the kind of telescope that Jana was referring to before, the Event Horizon Telescope, can just make out the 4 million solar mass black hole in the center of our galaxy.

• 17:33Janna Levin?

  This is a perfect place to break, because we're going to come back to talk about the Event Horizon Telescope and how it's going to resolve that shadow and the excitement of that project. So we're going to take a short break, but stick around so we can talk more with Shep and Matt about Event Horizon Telescope on StarTalk All-Stars. Welcome back to StarTalk All-Stars as we continue to talk about black holes and Event Horizon Telescope. I'm your host, Janna Levin, and I'm very excited to have my wonderful comedic co-host, Matt Kirshen.

• 18:03Speaker 03

  Hey, Jana.

• 18:04Janna Levin?

  Hey, Matt. A long time no see.

• 18:06Speaker 03

  Been a while.

• 18:06Janna Levin?

  In a few seconds. And our science guest, Shep Dolman. Shep is the leader of the Event Horizon Telescope project. So tell me a little bit more about Event Horizon Telescope.

• 18:16Speaker 03

  So the Event Horizon Telescope is a project dedicated to the notion that we can see something that we've always been taught is unseeable, right? Everybody knows that a black hole is something that absorbs light, matter, nothing come out from the Event Horizon once it's gone into the Event Horizon. But because all the gas and dust is heated up and you get this effective three-dimensional flashlight all around the black hole illuminating it from all angles, you can see its shadow or the silhouette that it casts against all that hot gas.

• 18:45Janna Levin?

  So what about interstellar? Do you know how in interstellar, they show the disk around the black hole, but you can kind of see it above and below? Do you think that was a pretty accurate portrayal?

• 18:53Speaker 03

  I think that's very accurate.

• 18:54Janna Levin?

  It was very accurate.

• 18:54Speaker 03

  Because it turns out that, just like water going down the bathtub drain, everything kind of falls into this pancake shape that's swirling around the black hole.

• 19:02Janna Levin?

  It makes like a disk.

• 19:03Speaker 03

  Does that mean that black holes spin the other way around in Australia? That is not true, actually. Although toilets do not also spin the other way in Australia.

• 19:13Janna Levin?

  They do not? I was just in Australia, I should have checked.

• 19:16Speaker 03

  It's one of the great experiments of our time, looking at toilet bowls. Astronomers spend a lot of time looking at toilet bowls.

• 19:21Janna Levin?

  Astronomers spend all kinds of time looking at things.

• 19:23Speaker 03

  But the point that Janet is talking about is quite true. There is no behind of a black hole, right? So that came out wrong, didn't it? Anything that's behind the black hole, by definition, gets bent up and around. So the light rays from on the other side of the black hole get bent up and around. So you have this pancake object, and you're seeing the rear side of it flipped up.

• 19:42Janna Levin?

  Yeah, I always stole this line from you, Shep. You once said, "You can't hide behind a black hole." And it's actually a great description. You're crouching down behind the black hole, and they can see you.

• 19:53Speaker 03

  Exactly.

• 19:53Matt Kirshen?

  And then if you step one step too close, you're in the black hole. Like, "Ah, that was a bad game."

• 19:57Speaker 03

  You're godfucked.

• 19:58Matt Kirshen?

  "Ah, I shouldn't have done that."

• 19:59Janna Levin?

  I should have paid attention in astrophysics class.

• 20:01Matt Kirshen?

  Rosie Reed on Instagram is asking, "What is the telescope made of?"

• 20:07Speaker 03

  Oh, what a great question. So first of all, black holes are extremely small. They're the smallest objects theorized by Einstein's gravitational theory. And so to see them, you need a large telescope. Because the larger the telescope, the smaller the object you can see on the sky. So to do this, we take radio dishes all around the globe, and we synchronize them with atomic clocks. We point them all at the same time. It's kind of incredible when you think about it, but they swivel at the same moment, look at the black hole, take radio wave data from the outside of the event horizon of this black hole, and they record it on hard disk drives. We essentially freeze the light everywhere around the globe.

• 20:48Speaker 03

  And we bring them all back to a specialized supercomputer that compares them all. It operates exactly the same way that an optical mirror does for an optical telescope. So for an optical telescope, the light rays hit this perfect paraboloidal shape. And they focus it all to a point where your camera sits. All the light is focused to a point. In the Event Horizon Telescope, we replay all of these recordings that we've made all around the Earth, and we adjust the timing of them to make it seem as though there is this huge dish the size of the Earth. And then we synthesize this focal point, and that's where we make the image.

• 21:24Janna Levin?

  So the whole Earth is a telescope?

• 21:26Speaker 03

  Well, telescopes around the Earth form it.

• 21:28Janna Levin?

  Right, so it makes, right, it makes this like giant machine. So how big, I mean, I remember this comparison. If you resolve the shadow of the black hole from the supermassive black hole at the center of our galaxy, which is, how, how big is it again?

• 21:40Speaker 03

  It weighs about four million times what our sun does.

• 21:43Janna Levin?

  And about how big across is it?

• 21:45Speaker 03

  Well, on, on the sky, it measures about 10 microarc seconds, and the shadow would be about 50 microarc seconds. This is the same as trying to observe your favorite citrus fruit on the moon. So a tangelo, grapefruit, you know, a pomelo.

• 22:02Matt Kirshen?

  This is gonna sound weird, but I don't actually have a favorite citrus fruit.

• 22:05Janna Levin?

  It does sound weird, and I'm disappointed.

• 22:07Matt Kirshen?

  I know, and I've been mocked for it in the past, because it comes up a lot. And people are always like, you know, what is your favorite? I'm like, oh, like, I just like them all the same.

• 22:15Janna Levin?

  You have to choose, Matt, you have to choose.

• 22:18Matt Kirshen?

  I sound like one of those parents who like, you can't love all of your children the same, like, I just don't have a favorite amongst.

• 22:24Janna Levin?

  When you next go to the moon, I want you to put one that you chose on the surface of the moon, and we will try to resolve it with Event Horizon Telescope for gags.

• 22:32Speaker 03

  I can't believe I'm on the show with someone that doesn't have a favorite citrus fruit. It's kind of awkward.

• 22:38Janna Levin?

  I heard it's, it's like resolving a quarter on the moon. Is that the same?

• 22:41Speaker 03

  Almost. So it'd be a citrus fruit on the moon.

• 22:44Janna Levin?

  Citrus fruit is bigger than a quarter.

• 22:45Speaker 03

  Or, if you were in New York, as we are now, and your friend was in Los Angeles holding a quarter, it would be equivalent to reading the date on that quarter.

• 22:55Janna Levin?

  And that's what you guys are trying to do?

• 22:56Speaker 03

  That's what we are trying to do.

• 22:57Matt Kirshen?

  How much of being a professional scientist is coming up with different size analogies? Because that does seem like a lot of the job of like, it'd be like if Pluto were a baseball and like your hand was Alpha Centauri and your dad was throwing Pluto from... It just seems like there's a lot of that. Like, that's what we are, is we're idiots.

• 23:20Janna Levin?

  I feel that I'm not living up to it.

• 23:22Speaker 03

  He has a real future in this business.

• 23:23Matt Kirshen?

  Put this in terms of swing pulls and whales and fruit. That's how I need to understand science.

• 23:29Speaker 03

  Like hamsters, have a trails.

• 23:31Janna Levin?

  Okay, but this black hole, which is four million times the mass of the sun, probably fits in about three sun widths. Is that, does that sound like about right?

• 23:38Speaker 03

  Well, no, no, it's about, probably about the, the event horizon would be about a third the orbit of Mercury.

• 23:43Janna Levin?

  Oh, so that's bigger.

• 23:44Speaker 03

  It's actually, because it's four million times.

• 23:46Janna Levin?

  Oh, yeah.

• 23:47Speaker 03

  That six kilometer figure that you gave before, so it's quite large.

• 23:51Janna Levin?

  Yeah, so it's quite large, but it's 25, 26,000 light years away.

• 23:54Speaker 03

  Exactly. So as I said, black holes, they toss, you know, stars around like planets, you know, these supermassive ones, they're hugely dynamically important, but the, the largest one that we know of that's close to us is 25,000 light years away, so it's not gonna hurt us, we're not in any danger.

• 24:12Janna Levin?

  We are falling into it, just really slowly.

• 24:14Speaker 03

  Very, very slowly.

• 24:15Janna Levin?

  Like, much worse things are gonna happen to us in the next 10 years.

• 24:18Speaker 03

  Well, and I can think of several.

• 24:20Janna Levin?

  But not to get off topic. So this is the biggest black hole in our galaxy, it's at the center of our galaxy, and we think that there are black holes this big in all the galaxies, more or less. Do we have any aspiration for observing the shadow, of taking a picture of the shadow of another black hole, a supermassive black hole in another galaxy?

• 24:38Speaker 03

  Yeah, so, so it turns out there's one other wonderful candidate for doing this. So the number one target for us is the supermassive black hole in the center of the Milky Way Galaxy.

• 24:48Janna Levin?

  Sag A star.

• 24:49Speaker 03

  Which is called Sagittarius A star, in the constellation Sagittarius. And the other one is in the Virgo A galaxy, and that weighs six billion times what our sun does.

• 24:59Janna Levin?

  So it's big.

• 24:59Speaker 03

  So it's a real monster. It's a huge monster.

• 25:01Janna Levin?

  So it's a thousand times, more than a thousand times bigger.

• 25:04Speaker 03

  Yeah, it's about one and a half, 1,500 times.

• 25:06Matt Kirshen?

  So it's still part of the Milky Way?

• 25:08Speaker 03

  No, no, no, it's a different galaxy, a whole different galaxy.

• 25:11Janna Levin?

  And so that, so it, the only reason why we have any hope of resolving that is because it's so much bigger, even though it's much further away. How much further away is it?

• 25:20Speaker 03

  It's proportional, so it's about 1,500 times more massive. It's also about 1,500...

• 25:26Speaker 03

  Times farther away.

• 25:27Janna Levin?

  So it works out.

• 25:28Speaker 03

  It looks about the same on the sky. So a telescope with the same magnifying power would see them both about the same size.

• 25:33Janna Levin?

  So you're basically building a telescope the size of the Earth to take the picture of two things.

• 25:39Speaker 03

  Yeah, but what two things they are. Like, you know, I like to say it this way. If I were to be trapped on a desert island with two targets, these would be the two targets, right? So we have one that is kind of a Rosetta Stone, if you will, or it's an exemplar of most of the supermassive black holes in the universe. They're nondescript in smaller galaxies. We wouldn't see them if they were very far away.

• 26:03Janna Levin?

  Why can't we see our black hole?

• 26:05Speaker 03

  It's just not bright.

• 26:06Janna Levin?

  It's just, it's not bright because it's just not taking anything down right now?

• 26:10Speaker 03

  Yeah, well, it's on a starvation diet. It's kind of eating with, you know, a teaspoon. And so it's not, it's not, the gas around it is hot, but it's not enough to really be seen from very, very far away. Whereas the Virgo A, the supermassive black hole, is much, much brighter. And that's driving a jet of relativistic particles from its north and south pole that's literally piercing the entire galaxy.

• 26:34Janna Levin?

  Now, is that because we're seeing it in the past? When it was more active?

• 26:38Speaker 03

  Well, it, well.

• 26:39Janna Levin?

  Is it not that far away?

• 26:40Speaker 03

  We're, it's about, let's see, it's about eighteen, seventeen megaparsecs away, seventeen million light-years away.

• 26:46Janna Levin?

  So it's not really old enough.

• 26:47Speaker 03

  So it's not too old. We're probably seeing it as it's eating, as it's driving these jets from its north and south pole through the galaxy.

• 26:53Janna Levin?

  So in the past, was our black hole, the center of our galaxy, bright?

• 26:57Speaker 03

  Oh, almost definitely.

• 26:59Janna Levin?

  So there's probably some alien civilization on the other side of the universe where the light's taking billions of years to get there that thinks that our black hole's like a quasar.

• 27:07Speaker 03

  How do you think the show is going?

• 27:12Speaker 03

  It couldn't be going better.

• 27:13Janna Levin?

  It could not be going better. This is the best universe in which this show is going the best.

• 27:18Speaker 03

  Well, so I'll.

• 27:19Janna Levin?

  I feel like Trump, it's the best.

• 27:21Speaker 03

  It's huge.

• 27:22Janna Levin?

  It's huge and it's the best.

• 27:23Speaker 03

  The, well, what I'll say very briefly on this is that about 300 light years from the center of the galaxy, they see these wisps of X-ray light. And they think that what causes that is that 300 years ago, there was a burst of activity in the center of our galaxy and the shock wave has reached the clouds that bound that area and it's fluorescing.

• 27:45Janna Levin?

  So, speaking of which, we're seeing the black hole 25,000 years ago, as it was then. So, wasn't there this excitement for a while that a cloud was about to be torn apart by the black hole? G2, gas cloud 2. And we watched, people watched it for how long? Were they watching this gas cloud?

• 28:03Speaker 03

  Yeah, so there was a gas, a cloud of gas that they thought was about three times the mass of Earth and it was falling into the black hole. And they knew it was falling in because it began to be tidally stretched. So, the front part of the cloud was feeling more gravity than the rear part of the cloud is being stretched.

• 28:18Janna Levin?

  It was like streaming out.

• 28:19Matt Kirshen?

  Right.

• 28:20Speaker 03

  Right?

• 28:20Matt Kirshen?

  So, it's like the exciting bit when you're watching the water drain out of the bath, like when it just suddenly starts going.

• 28:25Janna Levin?

  It's the only fun part of that, that watch.

• 28:27Speaker 03

  Before you hit the towel. But in any event, people thought there was going to be fireworks. There were going to be fireworks and we haven't seen anything. It's been the biggest dud.

• 28:37Janna Levin?

  Right. So, what do you think happened?

• 28:39Speaker 03

  Well.

• 28:40Janna Levin?

  Did it just not fall in?

• 28:41Speaker 03

  A lot of it depends on how you engage the black hole. So, if the black hole is spinning this way and you're coming in counter to that rotation, you could get a lot of fireworks. But if it's spinning in the same direction as you, you'd just be sucked along with it.

• 28:55Janna Levin?

  Yeah.

• 28:55Speaker 03

  And it might take a long time for the gas that you're contributing to the black hole to find its way all the way to the event horizon where it would light up.

• 29:01Janna Levin?

  Yeah, let's be clear. If I were to fall across the supermassive black hole in the center of the galaxy, I would not be torn to shreds. I would just drift across, right? Just drift across happily because I am wee compared to the size of the event horizon. Matt, what do we got?

• 29:14Matt Kirshen?

  So, Carl West on Instagram is saying, "Will this telescope be studying the effects of Hawking radiation?"

• 29:22Speaker 03

  Probably not. So-

• 29:24Matt Kirshen?

  Suck it, Kyle.

• 29:26Speaker 03

  No, Kyle. It's a great question, Kyle. Don't suck, Kyle. I'm gonna protect Kyle from Matt here. It's a great question. We know that Hawking radiation exists, but the Event Horizon Telescope is gonna see this outline, and Hawking radiation is not likely to affect that outline. There are some cases in which it might. There are some quantum effects that might affect the shadow size, and that's an active area of debate right now. But Hawking radiation itself is something that happens over very long periods of time, and so we probably wouldn't see that dynamically affect the shadow.

• 29:54Janna Levin?

  You know, I should point out that we are getting cosmic queries from our audience through social media, so next time, tune in and send your questions ahead of time, and we may or may not actually get to them.

• 30:07Matt Kirshen?

  Yeah, so Blair Jackson on Facebook asks, "Could the Big Bang be the birth of a black hole, and are we all living within a black hole?"

• 30:16Janna Levin?

  Hmm, I almost think it would be the other way around. People have speculated that the black hole could harbor a Big Bang inside. So the black hole's much bigger on the inside than it is on the outside. It could be as big as the universe on the inside. It's like Doctor Who's TARDIS. You know, you go into the small, little red box, but inside is an enormous lab. So you fall into the black hole, and you think you've got a microsecond before you hit the singularity, but your quantum bits get blown out into a Big Bang.

• 30:43Matt Kirshen?

  So the second part of that question, where Blair says, "Are we all living within a black hole?" We could be, like, this could be the-

• 30:49Janna Levin?

  When we look back at the Big Bang, we might be looking back at the singularity inside a black hole. In that sense, it's not really inside, but in that sense, yeah. Although, most people don't really take that speculation very seriously. It's intriguing to contemplate. I always find myself kinda going back to that suggestion. No matter how many times people tell me why it's faulty, or what the problems are, there's something appealing about that.

• 31:14Speaker 03

  Well, there's something interesting about the singularity being in every direction, right? So the Big Bang is everywhere you look, right? So in that sense, it is not unlike a black hole.

• 31:23Janna Levin?

  Yeah, the singularity of the Big Bang and the singularity of a black hole are so similar that people have just kind of tried to artificially sew them together like a quilt, and see if it matches.

• 31:32Matt Kirshen?

  On that same note, Dale Cheslet Rose on Facebook says, "If sound needs air to pass through, did the Big Bang actually make a noise?"

• 31:41Janna Levin?

  Well, we're gonna talk about this in a gravitational wave episode. In a sense, the Big Bang probably did make a bang in the sense that it rang the drum of spacetime. Where, you know, we imagine the three-dimensional drum of spacetime is ringing in response to this kind of chaotic event. So in that sense, it might have, yeah, made, in a sense, a noise that if we could record the shape of the ringing drum, we would interpret a sound.

• 32:06Matt Kirshen?

  Okay.

• 32:07Janna Levin?

  Even in the absence of air.

• 32:08Speaker 03

  Whatever black hole eats, it changes its shape slightly, and that changes the gravitational waves that it's emitting.

• 32:14Janna Levin?

  And also, around the black hole, the accretion disk can support sound waves, can't it? So this disk that you were describing of all this material falling in around the black hole and flattening it out, it can have a sound wave through that material.

• 32:27Speaker 03

  As long as you think of sound waves not as being something we can hear with our eardrum, but as being waves mediated by some kind of medium, like gas or dust.

• 32:36Janna Levin?

  Or spacetime.

• 32:37Matt Kirshen?

  You sound like a Brooklyn DJ.

• 32:38Janna Levin?

  That's shut.

• 32:40Speaker 03

  Take that as a compliment.

• 32:41Matt Kirshen?

  It's just not...

• 32:42Janna Levin?

  What's your handle?

• 32:43Matt Kirshen?

  It's not just something you can appreciate through your ears, but it's also just about just the feel of the spacetime, you know? Anyway, here's my disk. Important question, also coming from Nick Spinell on Facebook, and I don't know which of you two is gonna be the best to answer this. Can we send Hillary and Trump to a black hole?

• 33:03Speaker 03

  They might annihilate each other before they got there. Well, here's the interesting thing about black holes. No matter how you feed them, they all look the same. So you can take a black hole and you can fill it full of Hello Kitty dolls. You can put old rusty refrigerators in it. You could throw Donald Trump into it. You could throw Hillary Clinton into it. And after it's done settling down, you would have no idea what went into it.

• 33:27Janna Levin?

  This is kind of deep. There is no way to tell the difference between a black hole made by crushing Donald Trump to a point, and that made by crushing Hillary Clinton to a point.

• 33:36Matt Kirshen?

  Except their mass. Politicians are the same, man.

• 33:38Janna Levin?

  Because all politicians are the same.

• 33:41Speaker 03

  Massachusetts would vote for one and not the other. That's the only way you can tell.

• 33:46Janna Levin?

  So do we have a last cosmic query in our final few seconds?

• 33:49Matt Kirshen?

  Uh...

• 33:50Janna Levin?

  Our last minute? At least here on Earth.

• 33:53Matt Kirshen?

  Uh, let me see.

• 33:55Janna Levin?

  Take one from the International Space Station, it'll last longer.

• 33:58Matt Kirshen?

  Uh, this is, um, "Is there a correlation between the law of conservation of energy and the fact that time stops at the speed of light? Does this have to do with light having no mass because it is pure energy?" Says Jacob Seymour on Facebook. I have to read that again.

• 34:12Janna Levin?

  Yeah, okay, so I'm going to try this. Anything that has no mass will travel at the speed of light, anything. So we think that there might be subatomic particles that, like neutrinos, some neutrinos, which might also have no mass, and they would have to travel also at the speed of light. And their energy can be converted to mc squared, equals mc squared energy. But it is a pure energy of kinetic energy. One way to think of E equals mc squared, which I've struck upon lately, which I really like, is to think of it as your kinetic energy through time. The amount of energy you transport by your motion through time. So if we were to draw those spacetime diagrams, when you're running in your Google Maps, you know you have some energy as you move through New York City, but you haven't plotted your energy as you move through time.

• 34:57Janna Levin?

  And that's E equals mc squared energy. And on that note, unfortunately, we have to take a quick break, but we'll be right back with StarTalk All-Stars so we can answer some more of your cosmic queries with Shep Doeleman and Matt Kirshen. Stick around. Welcome back to StarTalk All-Stars, where the topic of the day is black holes, how they work, and how we hope to take a picture of our first black hole. I can't think of two better people to talk to on this topic than Shep Doeleman, an astrophysicist and leader of the Event Horizon Telescope Project, and the very funny Matt Kirshen, who also hosts Probably Science, probably not science?

• 35:36Matt Kirshen?

  It's Probably Science, that's what it is.

• 35:38Janna Levin?

  Is it Probably Science?

• 35:39Matt Kirshen?

  We didn't need the word "not" in there. We're not simply by the "probably."

• 35:44Janna Levin?

  I'm Janna Levin, your All-Star host for today, and I want to pick up with Shep on the Event Horizon Telescope, because this is still a project under development. You're talking about we will observe, we hope to observe, and there are these two objects. So first of all, when do you expect to start making these first pictures of the black hole at the center of our galaxy? And why are you going to do this?

• 36:09Speaker 03

  Good, good questions. So, we started off on the Event Horizon Telescope project by linking three radio telescopes around the world together, in Hawaii, in Arizona, and California. And the first thing we realized was that the supermassive black hole in the center of our galaxy, Sagittarius A star, had a size that was predicted by this shadow feature. So, 100 years ago Einstein came up with this idea that a black hole would cast a shadow, and we saw exactly that size. And that really got us excited, right? Because with only three telescopes, all we can do is tell the size of the black hole. Now we want to build instrumentation and put it at all the other telescopes that we can around

• 36:50Speaker 03

  the world to fill in this Earth-sized telescope, and then we can make an image. Because the whole reason for doing this is to look at the size and shape of that shadow, predicted again by Einstein, to test whether Einstein's theories break down at the edge of a black hole, and also to study the dynamics of matter around the black hole.

• 37:08Janna Levin?

  Now, will you really be looking all the way at the event horizon? I mean, after all, light can orbit a black hole, but, you know, to actually get all the way to the shadow, are you really seeing the event horizon, or are you seeing a little bit further out?

• 37:21Speaker 03

  You see, you wind up seeing a little bit further out. There's something called the last photon orbit. And light, as fast as it goes, also is constrained to orbit around the black hole. That's how deformed the spacetime is. It's a crazy, crazy place.

• 37:34Janna Levin?

  You could stand there with a flashlight and look at the back of your head.

• 37:37Speaker 03

  Or you could illuminate the back of your head.

• 37:39Janna Levin?

  Right. And then it would bounce off your head, and you'd see it in front of you.

• 37:42Speaker 03

  If you were having a bad hair day, you would know it immediately, basically.

• 37:45Janna Levin?

  Because that's what you're worried about when you're, you know, right outside a black hole.

• 37:48Matt Kirshen?

  Yeah, wouldn't your hair automatically become bad just because it's kind of been sucked towards it? How much of it would...

• 37:54Speaker 03

  You would see how bad it was.

• 37:56Janna Levin?

  You think your hair feels gravity more strongly than the rest of you?

• 38:00Speaker 03

  That's the spaghettification of your hair.

• 38:02Janna Levin?

  Your hair might sort of be left behind.

• 38:04Matt Kirshen?

  Would it kind of be more frizzy, or would it be more like high volume? Like, what kind of shampoo would you need to use?

• 38:09Janna Levin?

  There might be special black hole products. I think we've just started. Somebody right now is scratching out a memo at their pharmaceutical company.

• 38:16Matt Kirshen?

  Just something else for women to be upset and worried about.

• 38:18Janna Levin?

  Right. More ways to oppress women.

• 38:20Matt Kirshen?

  Like, what would happen to your limbs? Would you, like, would satellite be changed near a black hole? How we...

• 38:28Janna Levin?

  Matt, you're fired.

• 38:28Speaker 03

  Okay, I was going to endorse the hair care products, but I'm not going to touch that one.

• 38:33Janna Levin?

  So, you are making your first observations, when?

• 38:36Speaker 03

  Right, so, from these three telescopes and these humble beginnings, a global international consortium has formed, and we are now instrumenting telescopes around the world, so in Chile, even the South Pole, in France, and Spain, and so forth, in addition to the ones we already have. And the new observations are occurring in the spring of 2017, under a year from now. That's when we light up most of the array. That'll be our first shot at taking the first image of a black hole.

• 39:05Janna Levin?

  Do you think that's going to be a successful shot?

• 39:07Speaker 03

  Of course I do. I'll be getting up every morning.

• 39:10Janna Levin?

  Well, a lot of times, you know, these experiments take decades, and the first shot's not expected to be successful, and you're thinking, 10 years down the line, we'll refine enough to really nail it. But you think, as early as spring, you're going to have an actual picture.

• 39:23Speaker 03

  Well, we are eternal optimists, and even, even experiments that are long shots are always assumed to perhaps give a good result, if not light the way to future innovations that make inevitable success, you know, a reality. So, we are really focused on success in the spring of 2017. At the same time, nature is nature. We have no idea what we're going to see.

• 39:47Janna Levin?

  Nature doesn't always comply.

• 39:49Speaker 03

  It does not always comply, and we may fall flat on our face, but the idea is that we get up and we...

• 39:54Janna Levin?

  So, is this a done deal? The consortium, the international collaboration is on board, and this is definitely going to happen?

• 40:01Speaker 03

  Absolutely. So, we have time on some of the biggest apertures, some of the biggest telescopes around the world, and we have these systems that are going to freeze the light at all of these telescopes at unprecedented rates.

• 40:13Janna Levin?

  I'm rooting for you, Shep. I'm rooting for you.

• 40:15Matt Kirshen?

  Is there ever a risk that, like, when you're setting up these huge telescopes, you'll see something you didn't plan to see, like...

• 40:21Janna Levin?

  Like Matt waving?

• 40:22Matt Kirshen?

  Yeah. Or like a neighbor doing a murder, or something like that, just like, "I wasn't expecting this, but like, I guess I'm going to have to report this now."

• 40:30Janna Levin?

  A quarter on the moon is like a freckle on the neighbor's...

• 40:34Matt Kirshen?

  Yeah.

• 40:35Janna Levin?

  Yeah.

• 40:36Speaker 03

  Oh, yeah. So, the, um, yeah, we could, this could be like a Milky Way CSI episode or something like that, like murder at the Galactic Center. Well, so, let me just say that we think we know what we're going to see, but... Nobody would be happier than most of the people in the consortium if we saw something unexpected. That would be hugely interesting. And the way I like to put it is that we will perhaps be able to test Einstein's theory, but it's never wise to bet against Einstein. But if we see something crazy, if the size of the shadow is not what Einstein would have predicted, given the mass of that black hole, we will be really scratching our heads, thinking about alternative forms of gravity, or thinking about objects even more exotic than a black hole.

• 41:19Janna Levin?

  So would that mean that the whole theory of general relativity is wrong and needs to be supplanted?

• 41:23Speaker 03

  Well, we know, Jana, that GR cannot be complete, right? Because at the center of the black hole, where everything is crushed to a point of singularity, GR has to come into accord with quantum mechanics. And nobody, not even Einstein, ever found a way to do that. So we know GR is complete. The just question is, how close do we have to get to the singularity before it becomes evident?

• 41:45Janna Levin?

  Right.

• 41:46Speaker 03

  It could be at the event horizon. There could be manifestations of this deep mystery at the event horizon that the Event Horizon Telescope could, you know, image.

• 41:55Janna Levin?

  So there, you know, you mentioned quantum phenomenon, the Hawking radiation, which happens at the event horizon. So a quantum fluctuation in empty space gets stolen by the black hole and the other particle radiates and to an observer far away, it looks like the black hole is actually emitting radiation. Is that something you think you could probe with this telescope?

• 42:14Speaker 03

  Well, we can't see the Hawking radiation itself, because that's going to be higher energy particles. We know that something strange is happening at the event horizon, right? There's this thing called the information paradox, right? So if you throw an encyclopedia into the black hole, what happens to the information in that encyclopedia?

• 42:34Matt Kirshen?

  It's a, I know this one, it's planted by Wikipedia that everyone now uses. And you free up a bookshelf that can be used for photos and that kind of thing.

• 42:43Speaker 03

  It's a real time saver.

• 42:44Matt Kirshen?

  Yeah.

• 42:44Speaker 03

  These black holes. But so it turns out that that information has to go somewhere. Either the Hawking radiation has to encode it as it evaporates or it gets frozen onto the surface. A lot of different theories. And in some of those, the quantum states inside the black hole may be in communication with the exterior of the black hole. And in that case, you could wind up with different orbits of photons around the black hole and the shadow would look different. Now, I don't know exactly how different it might look, but there are ways to think about it from that framework.

• 43:15Janna Levin?

  No, it's also possible that we just couldn't see any effect, but there's still something going on. It's just too difficult to imprint it in such a macroscopic object.

• 43:24Speaker 03

  Yeah, I make it sound easy. It's really difficult what we're doing.

• 43:29Janna Levin?

  You make it look easy, Shep.

• 43:31Speaker 03

  That's...

• 43:32Janna Levin?

  Well done. I'm proud of you. Okay.

• 43:34Matt Kirshen?

  So if people like at home want to build their own one of your telescopes, well, how should they go about it?

• 43:38Speaker 03

  They should not, because we don't want any competition.

• 43:41Janna Levin?

  Don't do this at home, folks.

• 43:43Speaker 03

  It's quite difficult. And I would say that the only way that we're able to think about doing it is because we have a global team of exceptionally talented collaborators that all make it happen.

• 43:52Janna Levin?

  So sometimes you have to kind of sublimate your own ego, right? To be part of this bigger team. It's not the lone pioneer.

• 43:59Speaker 03

  It's really a global effort. It really is. And it's a real privilege to work with all these people.

• 44:03Janna Levin?

  Yeah, we're excited for spring. Spring 2017?

• 44:08Speaker 03

  Spring 2017.

• 44:09Janna Levin?

  Okay, stay tuned, people. We hope this show airs before then.

• 44:11Speaker 03

  We'll have t-shirts by then.

• 44:12Janna Levin?

  Ah, I think it's time for the Cosmic Queries Lightning Round. I think I'm supposed to ding this bell.

• 44:17Matt Kirshen?

  Ding away, Jenna.

• 44:18Janna Levin?

  I'm not very good at taking instructions. I think that's what I'm supposed to do. What do we got, Matt?

• 44:22Matt Kirshen?

  All right, from Sean Resmussen, who's a Patreon patron. And I think you've sort of touched on this already. "Hi, Dr. Levin. Why is it that general relativity, the theory of the large, and quantum mechanics, the theory of the small, cannot be reconciled as one theory of everything? If I'm not mistaken, Dr. Tyson described general relativity as being a mathematical shortcut on a larger scale, but could these two be unified with the new discovery of gravitational waves or, say, a graviton?" Thanks for the show! That's in like caps and like a couple of exclamation marks. So like, really wants to know.

• 44:51Janna Levin?

  Let's hope you got the accent right.

• 44:52Matt Kirshen?

  Yeah.

• 44:53Janna Levin?

  Well, this is a really important question. I mean, this is what all theoretical physicists pine for, is a resolution of the theory of gravity with the theory of quantum mechanics. So the large theory of the universe on a large scale and the theory of the universe on the small scale. They're very hard to put together, even if I went through kind of a standard program, oh, this is what I always do when I try to quantize a model of the universe. It doesn't really work with gravity because gravity is so nonlinear, right? This is not, you know, the effects feed back onto themselves in these very complex mathematical ways that we don't know how to control. So, literally, we just don't know how to write it down.

• 45:34Janna Levin?

  It doesn't mean it doesn't exist in reality, but we just don't know how to mathematically write it down. Our tools fail us. And so many people have tried just to find better tools. But it might be the case that they're actually not reconcilable in nature, that gravity, in some sense, isn't a fundamental force. So, you know, when I say the temperature in this room is, you know, it's warm in this room, temperature isn't an actual quantity that belongs to anything. It's the collective behavior of group motions of small things. Gravity might be like that. It might be the collective behavior of quantum entanglement and phenomena like that. And that when we look small enough, we realize gravity's not really a thing at all.

• 46:17Janna Levin?

  It's something, an illusion, that only emerges on large scales. I mean, this stuff's really interesting. We love not knowing the answers, right? That's why we have jobs. That's why we have something to do.

• 46:27Matt Kirshen?

  That's why we build telescopes.

• 46:28Janna Levin?

  Yeah.

• 46:29Matt Kirshen?

  All right. Travis Severt on Facebook.

• 46:32Janna Levin?

  Oh.

• 46:33Matt Kirshen?

  Travis Severt on Facebook says, "How do black holes affect time? Presumably, there are sharp gravitational gradients in and around a black hole. If so, how do these affect the resulting temporal distribution of matter? Thank you."

• 46:47Speaker 03

  Oh, that's very interesting. So, well, you mentioned interstellar before. So, interstellar, in interstellar, they had this moment when people went close to the black hole, and, you know, every hour they spent down there was 20 years outside. That's a real thing, right? So, time really does slow down close to the black hole, and they spent time down there, and they came back, and everybody was 20 years older. So, there is a dark time gradient near a black hole, and they do affect the dynamics. And when we think about matter and light orbiting the black hole, we have to take those into account.

• 47:17Janna Levin?

  I'm dinging on chat.

• 47:18Speaker 03

  Wish I had one of those.

• 47:19Janna Levin?

  It was supposed to go more rapidly. We're learning, we're learning.

• 47:22Matt Kirshen?

  Pete Nellie on Facebook says, "Perhaps these questions are a little elementary, but how much of our understanding of black holes relies on our understanding of quantum physics? Are there minute values that influence the structure of black holes that we have identified?"

• 47:33Janna Levin?

  I mean, in some sense, astrophysically, not at all.

• 47:37Speaker 03

  Yeah, but black holes are typically classical kind of objects when you look at them from the outside. So unless we saw Hawking radiation, we wouldn't really be able to see those quantum fluctuations.

• 47:46Janna Levin?

  But there's a whole community of mathematicians that are at their desks with pen and paper who are studying only the quantum aspects.

• 47:52Speaker 03

  Yeah, only what happened.

• 47:53Janna Levin?

  You'll find them in different buildings on a university campus.

• 47:55Matt Kirshen?

  All right. Viantus Azierlis, great name, on Facebook says, "How useful would space-based radio telescopes be for taking black hole pictures?"

• 48:05Speaker 03

  Oh, they'd be fantastic. So it turns out that one of the big problems we have is the Earth's atmosphere. It's the water vapor in the atmosphere that's similar to what makes stars twinkle for optical telescopes, that limits the event horizon telescopes. If we could take a telescope, put it in orbit.

• 48:20Janna Levin?

  They're big, though.

• 48:21Speaker 03

  We'd have a telescope as big as the orbital size of that.

• 48:24Janna Levin?

  How big is a radio telescope? How big across?

• 48:27Speaker 03

  Well, the largest one, the largest single one we use is about 50 meters across, 150 feet across. And then we have one in Chile that is...

• 48:35Janna Levin?

  That'd be hard to get up in space.

• 48:36Matt Kirshen?

  All right. Mike Schneider's on Facebook says, "If two black holes, one being a bit stronger than the other, were to meet, would they, in theory, cancel each other out?"

• 48:43Janna Levin?

  Ah, they would just get bigger.

• 48:45Speaker 03

  That just happened. LIGO made that first detection and it's a wonderful and amazing result.

• 48:51Janna Levin?

  The first time in history we've seen two black holes collide and what happens is they make a bigger black hole.

• 48:55Speaker 03

  And some of the mass, though, is released as gravitational wave energy.

• 48:58Janna Levin?

  Thank you for the great questions in the lightning round, but sadly, we're at the end of our time today. It's been a great day here at StarTalk All-Stars. Once again, thanks to Shep. If you want to hear more about Event Horizon Telescope, go to eventhorizontelescope.org and follow Matt on Twitter, @MattKirschen, who is co-host of probably Science Podcast, which is especially funny when I'm on it. And I'm Jen Levin. Thanks for listening. See you around the multiverse.