Latest / The Smart Cookies podcast / The MIND-BENDING science of BLACK HOLES, with Marcus Chown

Transcript

The MIND-BENDING science of BLACK HOLES, with Marcus Chown · The Smart Cookies podcast

• 0:05
  Marcus Chown is an award -winning writer, broadcaster,
• 0:08
  and former radio astronomer at the California
• 0:10
  Institute of Technology in Pasadena. He's the
• 0:13
  author of The Ascent of Gravity, Quantum Theory
• 0:16
  Cannot Hurt You, and Afterglow of Creation. His
• 0:20
  latest title, A Crack in Everything, How Black
• 0:22
  Holes Came in from the Cold and Took Cosmic Center
• 0:26
  Stage, will be the focus of our conversation
• 0:28
  today. Mr. Chown, welcome to the show. Thanks
• 0:33
  for inviting me. Absolute pleasure. Before we
• 0:37
  begin, let me just say this really quick. I don't
• 0:40
  know if you had a look at the previous guests
• 0:41
  of this podcast, but there's not a lot of space
• 0:43
  talk in the resume here. Now, that certainly
• 0:47
  doesn't mean that I'm not interested, but it
• 0:49
  does mean that I am scared a little bit. So I
• 0:51
  have to warn you that some... hand -holding will
• 0:54
  be required please don't be square scared because
• 0:56
  i actually write my books for my wife who's a
• 0:59
  nurse in england and she doesn't have any science
• 1:03
  background so i try and make it accessible to
• 1:06
  her all right perfect That sounds really good.
• 1:10
  But yeah, I did want to warn you a little bit
• 1:13
  because there's probably going to be a lot of
• 1:16
  those could you break this down in even simpler
• 1:18
  terms moments. Hope you won't mind. Just wanted
• 1:21
  to emphasize that since this isn't an episode
• 1:23
  about, I don't know, Adolf Hitler's daily drug
• 1:26
  consumption, which would be more normal for this
• 1:28
  podcast. I will be skating on some very thin
• 1:31
  ice indeed. But now that I've gotten this disclaimer
• 1:35
  out of the way, let's dive in because this stuff
• 1:37
  is... mind -bendingly fascinating and let's maybe
• 1:41
  first try to explain what a black hole actually
• 1:44
  is because my understanding mainly informed by
• 1:48
  a bunch of b -list sci -fi movies is that a black
• 1:51
  hole is some sort of a super scary void floating
• 1:55
  around in space You know, like a greedy wound
• 1:58
  that's sucking up everything around it, including
• 2:00
  energy and time into it. And most importantly,
• 2:03
  of course, that you would die a horrible death
• 2:05
  if you were somehow dropped into one. How close
• 2:08
  am I here? You're pretty close. I mean, black
• 2:12
  holes are regions of space where gravity is so
• 2:16
  strong that nothing, not even light, can escape,
• 2:18
  which is, of course, why they are black. They
• 2:22
  most commonly form when a massive star... gets
• 2:25
  to the end of its life, it's run out of fuel,
• 2:27
  it's no longer able to generate the heat to push
• 2:31
  outwards against gravity, gravity crushes it
• 2:33
  down to a point, and it leaves this bottomless
• 2:37
  pit in the fabric of space -time from which nothing
• 2:40
  can climb out, not even light. Now what you actually
• 2:44
  said, so they do suck in material, that's absolutely
• 2:46
  right, but it turns out that in the universe
• 2:50
  they come in a variety of sizes, and some of
• 2:52
  the most massive ones... Billions of times the
• 2:56
  mass of the sun have some of the most spectacular
• 2:59
  effects, but you could actually fall into them
• 3:02
  uninjured. So they don't actually all rip you
• 3:07
  apart as you fall in. Sorry. Okay, let's stop
• 3:11
  there real quick. What do you mean you would
• 3:13
  be uninjured? So the thing you're thinking about
• 3:16
  is called spaghettification. It's a really weird
• 3:19
  idea. But basically, if you were an astronaut
• 3:22
  and you were to fall... feet first towards the
• 3:25
  black hole, and the gravity on your feet would
• 3:28
  be so much stronger than the gravity on your
• 3:30
  head that you would literally be pulled apart.
• 3:33
  Actually, it's called a tidal effect. You would
• 3:36
  be ripped apart. But it turns out that this effect
• 3:38
  gets lessened the bigger the black hole. And
• 3:43
  we now know, bafflingly, that there's a supermassive
• 3:48
  black hole often... billions or even tens of
• 3:51
  billions of times the mass of the sun in the
• 3:53
  heart of every galaxy. So we live in a galaxy
• 3:55
  called the Milky Way, but in the heart of every
• 3:57
  galaxy. Now, no one knows what they're doing
• 3:59
  there. Nobody knows how they got there. But if
• 4:02
  you were to fall into one of these bigger black
• 4:05
  holes, this kind of tidal effect, this spaghettification
• 4:07
  would not be as severe. You could just fall in
• 4:11
  and you would just cross into the black hole.
• 4:14
  You'd never be able to get out again, but you
• 4:16
  wouldn't be ripped apart as it happened. And
• 4:18
  then what would happen to you inside? Well, I
• 4:21
  mean, this is why these objects are so important.
• 4:26
  Pretty much for 100 years, people thought they
• 4:28
  couldn't possibly exist because they are too
• 4:30
  ridiculous. You know, they're actually stranger
• 4:33
  than science fiction. Surely they can't exist.
• 4:36
  But we've actually discovered that they do exist.
• 4:38
  And they're not only objects which exist in the
• 4:42
  real universe, but they're objects that actually
• 4:44
  where our physics, our basic physics breaks down,
• 4:47
  where we don't have the explanation to the question
• 4:49
  you just asked. We don't know what happens inside
• 4:53
  a black hole. We are pretty certain. that space
• 4:56
  and time itself fragment into something more
• 4:59
  fundamental. But we've got no idea what that
• 5:02
  is, because we would need what's known as a quantum
• 5:05
  theory of gravity, which is a theory of gravity
• 5:07
  better than Einstein's theory of gravity, to
• 5:10
  tell us what actually happens. So you'll constantly
• 5:14
  hear speculation, many, many books, many films,
• 5:18
  telling you that if you fall into a black hole,
• 5:20
  you'll appear in a different part of the universe,
• 5:22
  you'll appear in a different time. You know,
• 5:26
  none of these things are known. All of these
• 5:29
  things are speculation. Again, we need a better
• 5:33
  theory of physics, a better theory of gravity
• 5:36
  to tell us. And this is why black holes not only
• 5:39
  surprisingly exist in the real world, I mean,
• 5:42
  they exist in the real universe, they're all
• 5:43
  over the place, but they challenge us to improve
• 5:47
  our theories of physics. Did you say that...
• 5:51
  A couple of giant ones are kind of swarming around
• 5:53
  at the edge of our galaxy? No, but we've discovered
• 5:57
  that there is a supermassive black hole in the
• 6:00
  center of every galaxy. This was actually discovered
• 6:03
  by the Hubble Space Telescope. So, I don't know
• 6:06
  if you remember, it was launched in 1990. It
• 6:08
  was the NASA's Hubble Space Telescope. I don't
• 6:11
  know if you remember, but it was launched with
• 6:12
  the telescopic equivalent of a squint. A big
• 6:15
  arrow was made in grinding its mirror. It cost
• 6:17
  $800 billion to fix it, which probably would
• 6:20
  have been $2 billion in today's money. The most
• 6:23
  complex mission ever mounted by astronauts fixed
• 6:27
  it. In effect, correcting spectacles were put
• 6:32
  in front of all of its instruments. But this
• 6:36
  gave it super sharp eyesight. You have to remember
• 6:38
  that when you look through a telescope from the
• 6:40
  ground, you're looking through the turbulence
• 6:42
  of the atmosphere. It's rather like lying on
• 6:45
  the bottom of a swimming pool looking at the...
• 6:47
  the lights on the ceiling. They flip backwards
• 6:49
  and forwards, blur out. That's what happens.
• 6:51
  But Hubble, once it had above the atmosphere,
• 6:54
  had super sharp eyesight. And in the center of
• 6:58
  scores of nearby galaxies, like our Milky Way,
• 7:00
  it saw that in the very center, the stars were
• 7:03
  whizzing around far, far too fast. By rights,
• 7:07
  they should have been flung off into intergalactic
• 7:09
  space, unless they were in the grip of the powerful
• 7:14
  gravity. of a really compact, massive object.
• 7:18
  So Hubble discovered that there's a supermassive
• 7:20
  black hole in the center of every galaxy. We
• 7:22
  actually have one in the center of our galaxy.
• 7:24
  It's called Sagittarius A -star. It was discovered
• 7:27
  exactly 51 years ago. And the great mystery about
• 7:31
  it is that it is very small compared to all the
• 7:34
  other supermassive black holes. So if you take
• 7:36
  the nearby galaxy, Andromeda, which is very,
• 7:40
  very similar to ours, a spiral galaxy, you can
• 7:42
  actually see it with the naked eye. It has a
• 7:45
  supermassive black hole 50 times bigger than
• 7:47
  ours. So it's a mystery why we have this tiny,
• 7:49
  tiny supermassive black hole. But it's actually
• 7:52
  connected to me and you having this conversation.
• 7:54
  But maybe that's got in too deep too early. We
• 7:57
  can discuss that a bit later. One question following
• 8:00
  up from that. Why isn't it sucking us in then?
• 8:03
  Why isn't it drawing us in? That is a really,
• 8:05
  really, really, really good question. And the
• 8:08
  reason for that is that everything in the universe
• 8:10
  is spinning. Okay, so the Earth is spinning.
• 8:13
  The sun is spinning. Everything is rotating.
• 8:16
  The planets are rotating around the sun. The
• 8:19
  galaxy is rotating. Everything is rotating. So
• 8:22
  there's a kind of centrifugal force, you know,
• 8:24
  which stops that happening. So, for instance,
• 8:26
  it's the same question, why does the Earth not
• 8:29
  fall into the sun? The Earth doesn't fall into
• 8:31
  the sun because it's moving, you know, in a circle
• 8:34
  around the sun. So there is a counteractive force.
• 8:38
  And that is, of course, that is why. Nothing
• 8:43
  falls into a black hole. If we were to kill its
• 8:45
  rotational speed matter that was outside a black
• 8:49
  hole, you're absolutely right, it would fall
• 8:51
  directly into a black hole. But actually, that
• 8:55
  doesn't happen, and material kind of swirls into
• 8:58
  black holes, like water down a plug hole. And
• 9:01
  in fact, as this happens, the material friction
• 9:05
  within this material heats it to millions of
• 9:07
  degrees. And this makes these objects, these
• 9:10
  black holes, the most luminous objects in the
• 9:12
  universe. So you thought that a black hole would
• 9:16
  suck in material, and that isn't quite true.
• 9:20
  That's what you might expect, but it isn't true
• 9:22
  because everything is rotating. And you probably
• 9:24
  thought that a black hole would be black. Yeah,
• 9:27
  it's a black hole. It's got this really cool,
• 9:30
  eerie name, so it has to be... Yes, so really
• 9:34
  the term black hole was coined in 1967 by an
• 9:37
  American physicist called John Wheeler. He had
• 9:40
  a famous student that you might have heard of.
• 9:43
  His name was Richard Feynman. And before this
• 9:48
  term was coined, there was hardly any research
• 9:50
  in black holes. Afterwards, the field exploded.
• 9:53
  And it just goes to show how important it is
• 9:56
  to pick a term. that paints a vivid picture in
• 9:59
  people's minds. You know, so vivid a picture
• 10:02
  does black hole paint that there's pretty much
• 10:04
  no one on the planet who doesn't know the term
• 10:06
  black hole. But it turns out that in many ways
• 10:11
  the term black hole is entirely the wrong, paints
• 10:13
  entirely the wrong image. Because first of all,
• 10:16
  it implies a hole down which everything falls,
• 10:19
  and I've just told you that doesn't happen. It
• 10:21
  swirls in like water down a plug hole, and it
• 10:24
  implies that they're black. And actually, the
• 10:26
  black holes we see in the universe are among
• 10:28
  some of the most luminous objects in the whole
• 10:30
  of the universe. This is because the material,
• 10:33
  as it swirls in, friction within the gas heats
• 10:37
  it to millions of degrees. And really, if I go
• 10:41
  back to the beginning, black holes were predicted
• 10:44
  by a man who was dying of a really bad skin disease
• 10:48
  in a World War I field hospital. His name was
• 10:51
  Karl Schwarzschild. And he'd attended a lecture
• 10:55
  by Einstein in Berlin in 1915 when he was on
• 10:58
  leave from the Western Front in the First World
• 11:01
  War. And he'd been captivated by Einstein's theory.
• 11:04
  And he'd found that the theory basically says
• 11:08
  that gravity is curved space, curved space -time.
• 11:11
  You can't see it because it's four -dimensional.
• 11:15
  And that's why it took the genius of Einstein
• 11:16
  to realize it. But Schwarzschild found the shape
• 11:19
  of the space -time. around a compact spherical
• 11:23
  body that kind of looked like a valley. Then
• 11:26
  he realized that if the body were to become more
• 11:28
  and more compressed, the valley would become
• 11:31
  steeper and steeper until it became like a bottomless
• 11:34
  pit from which nothing could escape, a black
• 11:37
  hole. Now, Einstein never believed in that, in
• 11:39
  black holes. There's a particular reason for
• 11:42
  that. But everyone who thought about black holes
• 11:44
  over the succeeding decades made exactly the
• 11:47
  same mistake. They thought... black holes would
• 11:51
  be black and very small. So how would you see
• 11:55
  a black hole against the black of space? But
• 11:57
  what they didn't realise, or what they'd forgotten,
• 12:02
  is that the black hole was likely to be embedded
• 12:04
  in an environment. So if you think of stars,
• 12:08
  most stars are binary stars, so they come in
• 12:11
  pairs or triples. The Sun is quite unusual in
• 12:15
  being a solitary star, and having a companion
• 12:17
  makes all the difference. because that means
• 12:20
  that material can be ripped off the companion
• 12:22
  star, swirl down onto a black hole, and friction
• 12:26
  can heat it to millions of degrees and make these
• 12:28
  objects very luminous. So in the centre of these
• 12:30
  galaxies, we're not talking about stellar -mass
• 12:33
  black holes, we're talking about supermassive
• 12:35
  black holes. You can ask me where they come from.
• 12:38
  We have no idea. We have no idea how these supermassive
• 12:41
  black holes form and why there's one in the centre
• 12:43
  of every galaxy. But they basically suck in gas
• 12:46
  and ripped apart stars. and it's heated to millions
• 12:50
  of degrees as it falls in. And this makes these
• 12:53
  things phenomenally luminous. So typically, they
• 12:57
  can pump out 100 times the light of a typical
• 13:01
  galaxy from a volume, a tiny volume, equivalent
• 13:06
  maybe to the size of the solar system. So yeah,
• 13:08
  so now we've exploded all the myths. Black holes
• 13:11
  do not suck material directly in, and they're
• 13:14
  not black. Okay, I did see a photo. of a black
• 13:19
  hole i don't know when was released a couple
• 13:21
  of years ago or some and it did seem like there
• 13:23
  was light around it it was like a donut but in
• 13:26
  the middle it was pitch black it seemed like
• 13:29
  that's right it's a void it's an absolute void
• 13:31
  that's right so what you were seeing the first
• 13:33
  ever image of a of a black hole uh which is in
• 13:37
  a nearby galaxy called m87 was obtained by the
• 13:42
  very um sorry, the Event Horizon Telescope, which
• 13:45
  is an array of radio dishes, similar radio dishes,
• 13:48
  scattered all over the Earth. There's one in
• 13:50
  Antarctica, one in Hawaii, one's in Europe, one's
• 13:53
  in Mexico. And by all looking at the same objects
• 13:58
  at the same time, flying the hard drives with
• 14:02
  the signals together, processing them on a supercomputer,
• 14:05
  they were able to obtain an image they would
• 14:07
  have got had they had a telescope the size of
• 14:11
  the Earth. And the big telescope, allows you
• 14:13
  to see fine detail and they'd seen this supermassive
• 14:16
  black hole in this galaxy called m87 and you're
• 14:18
  absolutely right what they were seeing was the
• 14:21
  super hot material swirling into the black hole
• 14:24
  around the central void so it was exactly what
• 14:27
  we what we expected to see and three years later
• 14:30
  they obtained an image of sagittarius a star
• 14:33
  which is the supermassive black hole at the centre
• 14:36
  of our galaxy. And the two images look very,
• 14:39
  very similar, which is really amazing because
• 14:41
  it turns out the M87 supermassive black hole
• 14:44
  is 6 .5 billion times the mass of the Sun and
• 14:47
  more than a thousand times bigger than the one
• 14:50
  in our galaxy. But it turns out it's a thousand
• 14:53
  times further away. So they look to be an identical
• 14:56
  size. And I should just tell you, you mentioned
• 15:00
  the void, the black void at the centre and this
• 15:03
  glowing kind of orange glow. around it of infalling
• 15:06
  material. But when that material crosses into
• 15:08
  that void, it's like water going over a waterfall.
• 15:12
  And that material is never seen in our universe
• 15:16
  again, you know, because nothing can come out
• 15:19
  of the black hole. And inside the black hole,
• 15:22
  as I told you, we think space and time come to
• 15:24
  an end. So I think, you know, often we beat ourselves
• 15:26
  up as human beings for all the terrible things
• 15:28
  we've actually done, you know, global warming,
• 15:31
  pollution. Donald Trump. There's a lot, isn't
• 15:34
  there? Yeah. But sometimes I think we need to
• 15:36
  pat ourselves on the back because, you know,
• 15:38
  we came down from the trees onto an African plain
• 15:41
  a few million years ago. We've got a brain, which
• 15:43
  is one and a half kilograms of jelly and water.
• 15:46
  But we have seen to the edge of space and time.
• 15:49
  And I think that's an amazing achievement. Wait,
• 15:52
  you just, I'm sorry, this occurred to me just
• 15:54
  now. You said that there's a black hole. At the
• 15:57
  center of every galaxy. Another thing I had no
• 16:00
  idea about. Does that mean that they're important
• 16:02
  for the galaxies? That's a very, very interesting
• 16:06
  question. Because, first of all, black holes
• 16:09
  were so ridiculous, as I told you, as to be the
• 16:12
  preserve of science fiction. And I should tell
• 16:14
  you why. And that is because, as far as we know,
• 16:18
  if a star shrinks down to form a black hole,
• 16:20
  it shrinks to a point. That's what Einstein's
• 16:24
  theory tells us. It shrinks to what we call a
• 16:26
  singularity, where everything explodes to infinity,
• 16:29
  so the density becomes infinite, whatever. And
• 16:32
  that's basically telling you your physics has
• 16:34
  actually broken down. Could we stop just for
• 16:39
  a second? Can you break down singularity a little
• 16:42
  bit more? Basically, everything becomes infinite,
• 16:45
  okay? And infinity is something that is unreal.
• 16:50
  It doesn't happen in the real world. So it's
• 16:52
  telling you the theory has been stretched beyond
• 16:55
  the point at which it breaks down. And this is
• 16:58
  why Einstein did not like the idea of black holes,
• 17:01
  because within a few weeks of actually proposing
• 17:04
  it, he gets a letter from a man on the Western
• 17:06
  Front in the German army who has actually found
• 17:10
  the description of the curved spacetime around
• 17:14
  a point object. and it has a singularity, and
• 17:19
  that's telling him that his theory's already
• 17:20
  got a flaw in it. Now, he'd just spent 10 years
• 17:22
  of blood and sweat developing his theory. He
• 17:25
  didn't want to hear that there was a flaw in
• 17:26
  it. So the existence of singularities, by the
• 17:29
  way, we don't think they really exist. We think
• 17:31
  if you have a better theory of physics, we'll
• 17:33
  find there's something else at the centre of
• 17:34
  a black hole. But this is one of the reasons
• 17:36
  why people think they can't possibly exist. Then,
• 17:39
  again, in 1971, the first one was discovered
• 17:42
  in a constellation of Cygnus. It's called Cygnus
• 17:45
  X -1. At that point, it was thought, well, maybe,
• 17:48
  yeah, okay, they exist, but maybe they're just
• 17:50
  really anomalies. There aren't many of them around.
• 17:52
  They're not important. But eight years before
• 17:55
  that, in 1963, quasars had been discovered. And
• 18:00
  these turn out to be galaxies which are pumping
• 18:03
  out, as I say, 100 times the energy of a normal
• 18:05
  galaxy from an incredibly small volume, smaller
• 18:08
  than a solar system. And by 1964... One year
• 18:12
  later, theorists had realised there was only
• 18:14
  one conceivable source of that energy, and that
• 18:18
  was matter swirling down onto a black hole, heated
• 18:21
  to millions of degrees as it swirls down, but
• 18:25
  not a black hole of a few times the mass of the
• 18:28
  Sun, a supermassive black hole of billions or
• 18:31
  tens of billions of times the mass of the Sun.
• 18:33
  Now, at that point, again, to answer your question,
• 18:37
  it was still thought, well, maybe there's still
• 18:38
  anomalies, because it turned out that galaxies...
• 18:41
  that were like quasars, accounted for only 1
• 18:44
  % of galaxies. So it's possible to sweep it under
• 18:47
  the carpet and think, well, these supermassive
• 18:49
  black holes, they're only in very rare galaxies.
• 18:51
  We don't need to think about them. But then,
• 18:54
  as I said, Hubble Space Telescope in the 1990s
• 18:56
  discovers there's one in the centre of every
• 18:59
  galaxy. And even at that point, it's still possible
• 19:02
  to think they're not important because they are
• 19:04
  very, very tiny. So if you imagine a... I think
• 19:08
  you're in Tokyo. Are you in Tokyo? Yes. If you
• 19:11
  imagine a bacterium compared to Tokyo, that's
• 19:15
  the size of a supermassive black hole compared
• 19:18
  to its parent galaxy. A single bacterium. That's
• 19:20
  what we're talking about. Compared to Tokyo.
• 19:22
  That's the size of the supermassive black hole
• 19:24
  compared to its galaxy. Now, would you expect
• 19:29
  that a single bacterium would control the street
• 19:32
  plan of Tokyo? You wouldn't. But it turns out
• 19:36
  these supermassive black holes... do actually
• 19:38
  leave their imprint on their parent galaxies.
• 19:42
  So, for instance, in every galaxy we look at,
• 19:45
  we find that the supermassive black hole is one
• 19:48
  thousandth the mass of the central, what we call,
• 19:51
  bulge of stars. So that's showing you there's
• 19:53
  some kind of link. And it's almost impossible
• 19:58
  to believe, because their reach, their gravitational
• 20:01
  reach, is only a few tens of light years, yet
• 20:03
  the central galaxies are hundreds of thousands
• 20:06
  of light years across. but it turns out that
• 20:10
  size does not matter as far as supermassive black
• 20:13
  holes are concerned. Energy is the important
• 20:16
  thing. So if I were to walk past a house and
• 20:19
  a slate were to fall on my head, what's actually
• 20:23
  happened is gravitational potential energy, so
• 20:25
  that's the energy that the slate has, by virtue
• 20:28
  of being high up in a gravitational field, has,
• 20:31
  as it's fallen to a lower point, been converted
• 20:34
  into other forms. gravitational energy has been
• 20:37
  converted into the energy of motion of the slate,
• 20:39
  the energy of my headache. Okay, so we don't
• 20:43
  know how supermassive black holes form, but somehow
• 20:46
  a lot of matter has got to come together. And
• 20:48
  that's the equivalent of quadrillions of slates
• 20:51
  all falling together. And when you do the calculation,
• 20:54
  you find that enough energy is liberated, maybe
• 20:58
  a thousand times as much energy is needed to
• 21:01
  explode the entire galaxy. So you only need...
• 21:04
  a tiny proportion of that energy goes into disturbing
• 21:09
  the gas around the supermassive black hole. Remember,
• 21:13
  the gas is the raw material of new stars for
• 21:15
  this supermassive black hole to leave its imprint.
• 21:19
  And then I think I just told you we're having
• 21:21
  this conversation because of a supermassive black
• 21:24
  hole. So this all comes back, are they important?
• 21:28
  It turns out that one of the most striking features
• 21:31
  of these supermassive black holes are these titanic
• 21:33
  jets. So again, you think of supermassive black
• 21:36
  holes as sucking in stuff, but in many of these
• 21:39
  objects, we see these titanic jets which come
• 21:42
  out along the north and south poles of these
• 21:45
  supermassive black holes. Come out. Come outwards,
• 21:48
  yeah. And they're actually created outside the
• 21:52
  black hole, so we're not talking about material
• 21:54
  coming inside. And these amazing jets, they stab
• 21:58
  outwards for millions of light years across space.
• 22:02
  And they're the most striking feature. So again,
• 22:04
  black holes are not black. Their most striking
• 22:06
  feature is of material coming out. So if we look
• 22:10
  at the biggest supermassive black holes, these
• 22:13
  jets are so powerful, they drive away all the
• 22:17
  gas out of these centers of galaxies. That gas
• 22:20
  is the raw material for new stars. So in these
• 22:23
  objects with the galaxies, the big supermassive
• 22:26
  black hole, star formation is snuffed out after
• 22:29
  one generation. But in our galaxy, with a tiddler,
• 22:32
  a really tiny supermassive black hole, star formation
• 22:36
  has never been snuffed out. So there have been
• 22:39
  multiple generations of stars. So the Sun is
• 22:41
  a third -generation star. Two generations of
• 22:44
  stars had to die beforehand. So a generation
• 22:47
  of stars explodes. That becomes the raw material
• 22:53
  of the next generation, and then the same process
• 22:55
  happens again. But the key thing is... In each
• 22:59
  generation, more heavy elements are forged inside
• 23:03
  the stars. So more carbon, more oxygen, more
• 23:07
  iron, more calcium. Precisely the elements needed
• 23:11
  to make a rocky planet like the Earth, precisely
• 23:14
  the ingredients needed to make you and me. So
• 23:18
  it turns out that we could only have arisen in
• 23:21
  a galaxy with a really tiny supermassive black
• 23:24
  hole because the actual elements we're made of,
• 23:28
  would not have actually formed in any other galaxy.
• 23:31
  So the supermassive black hole at the center
• 23:33
  of our galaxy is only 4 .2 million times the
• 23:35
  mass of the Sun. And Andrea Ghez, who's a Californian
• 23:39
  astronomer, and Reinhard Genzel in Germany, got
• 23:42
  the Nobel Prize in 2022 for determining that
• 23:47
  mass. Wow. Okay, I don't even know where to continue,
• 23:53
  where to begin here. But am I correct in understanding
• 23:56
  that... So black holes are not simply sucking
• 24:00
  stuff in. They're also pumping these jets out.
• 24:03
  These jets are necessary for the formation of
• 24:05
  what you were just explaining. Yes. So in every
• 24:08
  single way, the term black hole is painting the
• 24:11
  wrong picture. It's a fantastic image because
• 24:13
  it's such a good image that we all have it in
• 24:15
  our minds. And we use it in everyday language.
• 24:18
  We'll say, I've lost my passport down a black
• 24:20
  hole. I've lost my pencil. So it's really painted
• 24:24
  a wonderful, wonderful picture. But the reality
• 24:27
  is when we see these objects out in the universe,
• 24:29
  they are phenomenally luminous. The most striking
• 24:32
  features of stuff coming out in these tremendous
• 24:34
  oppositely directed jets. And it's hard to see
• 24:39
  material falling in. It's mostly we see stuff
• 24:41
  coming out. So they are intriguing objects that
• 24:46
  defy our common sense. Okay, there was one last
• 24:52
  sci -fi trope that I wanted to explore. You kind
• 24:55
  of... talked about it already before we go to
• 24:58
  the history of the idea of black holes. And that's,
• 25:00
  of course, time travel. The idea being that if
• 25:03
  you fling yourself into one of these black holes,
• 25:06
  when you'd come out at the other end, dinosaurs
• 25:08
  would still be roaming the earth or something.
• 25:10
  Is there any credence to this popular trope?
• 25:12
  Or is that just another iteration of we don't
• 25:15
  really know what happens inside of one? Well,
• 25:17
  it goes back to your first question. And within
• 25:20
  inside the black hole, we don't really know.
• 25:23
  Okay. And all these things are speculation. So,
• 25:26
  I mean, really, you could speculate anything
• 25:28
  you like and it'd be as good as anyone else's
• 25:30
  speculation because you don't know. So, basically,
• 25:34
  we have two major theories of the 20th century.
• 25:38
  One is Einstein's theory of gravity. And the
• 25:40
  other one is quantum theory. So Einstein's theory
• 25:42
  of gravity is a theory of really big things.
• 25:44
  So things like stars, galaxies, the whole universe,
• 25:47
  you know, big things. And quantum theories is
• 25:50
  essentially a theory of very small things, you
• 25:52
  know, the size of atoms or smaller. And quantum
• 25:55
  theory is fantastic, successful. It's given us
• 25:58
  lasers and computers and nuclear reactors and
• 26:00
  iPhones, you know. And we don't need to worry.
• 26:08
  about one of them in normal life, one of them's
• 26:11
  domain of application is the very small and the
• 26:14
  other one is the very big. But in black holes,
• 26:17
  we do have to worry because basically something
• 26:19
  that was big, a star, has shrunk down to something
• 26:23
  very small. So we can only understand this if
• 26:27
  we can combine the theory of the very big with
• 26:29
  the theory of the very small. And we think, we
• 26:32
  call it quantum gravity, we don't have that theory.
• 26:35
  You may have heard of the theory of everything.
• 26:37
  Similar idea. And so if we can do that, then
• 26:42
  we can find out what it's like inside a black
• 26:45
  hole. There are fundamental problems. So the
• 26:50
  problem with Einstein theory is a theory of certainty.
• 26:54
  So it's a theory of gravity. It tells us exactly
• 26:57
  what will happen. If we know where the moon is
• 26:59
  today, we can predict where it will be tomorrow
• 27:01
  with 100 % certainty. So it's a theory that predicts
• 27:05
  the future. with 100 % certainty. Quantum theory
• 27:08
  is a theory of uncertainty. It doesn't allow
• 27:12
  us to predict things. It only allows us, so for
• 27:14
  instance, if an atom's moving through space,
• 27:16
  it can take multiple paths between A and B. But
• 27:20
  all we can predict with quantum theory is the
• 27:22
  probability or the chance that it will go along
• 27:25
  one path, the chance it will go along another
• 27:27
  path. So you can see trying to unite two theories,
• 27:30
  one of which is fundamentally about certainty
• 27:33
  and one which is fundamentally about uncertainty,
• 27:35
  is a big ask. So that's why we're stuck. But
• 27:41
  if we can answer this and we can unite these
• 27:43
  two theories, then we can certainly predict what
• 27:45
  it's like inside a black hole. So the person
• 27:49
  who in 1963 predicted what it was like outside
• 27:53
  the black hole was a New Zealander called Roy
• 27:55
  Kerr. He was 29 years old. And the problem with
• 27:59
  Einstein's theory is that Newton had one formula
• 28:05
  to describe gravity, one formula. But Einstein
• 28:08
  replaced it by 10. So in order to find the curvature
• 28:11
  of space for any given mass, and the curvature
• 28:14
  of space is gravity, is phenomenally complicated.
• 28:18
  And Einstein thought it was impossible. That's
• 28:20
  why he was amazed when he got that letter from
• 28:22
  the Western Front, where... Karl Schwarzschild
• 28:25
  had found the shape of the spacetime around a
• 28:27
  static spherical mass. Now, as I told you, everything
• 28:31
  in the universe is spinning, so that wasn't realistic.
• 28:33
  So it was possible to think that black holes
• 28:36
  might not exist because if the object was spinning,
• 28:38
  there might not be any description of the spacetime
• 28:41
  around it, you know, from Einstein's theory.
• 28:44
  But in 1963, Roy Kerr defied everyone's expectations
• 28:49
  and found the shape of the spacetime, the exact
• 28:52
  shape, around a spinning... black hole. And even
• 28:57
  he tried to find out what the shape of the space
• 29:01
  -time inside the black hole was and gave up.
• 29:04
  He's still alive. He's 91 years old. He's still
• 29:07
  publishing scientific papers. And he's never
• 29:10
  managed to achieve for the inside of a black
• 29:13
  hole what he achieved for the outside of a black
• 29:15
  hole. So it's a hard problem. All right. Let's
• 29:20
  track down the very history. of this idea. So
• 29:23
  like you referenced already a couple of times,
• 29:25
  a hundred years ago, the idea of a black hole
• 29:28
  was a pretty preposterous notion, right? But
• 29:30
  before we go to those conceptual beginnings,
• 29:32
  can you tell us what was going on in the world
• 29:35
  of astronomy or astrophysics at the beginning
• 29:37
  of the 20th century? Where were we at the time
• 29:40
  and what did we manage to figure out? Well, I
• 29:43
  suppose that the major thing was the development
• 29:47
  of quantum theory. At the end of the 19th century,
• 29:51
  Lord Kelvin, William Thompson, who was a Scottish
• 29:54
  physicist, had famously said physics was over.
• 29:59
  All we had to do was dot the i's and cross the
• 30:02
  t's. All we needed to do was to fill out the
• 30:06
  details. This was in 1900. In 1900, Max Planck,
• 30:10
  the German physicist, was trying to explain the
• 30:13
  light that came out of a furnace. And he was
• 30:18
  unable to do it without making a radical assumption.
• 30:23
  And that radical assumption was that light or
• 30:26
  heat came in chunks, in tiny indivisible chunks
• 30:29
  called quanta. At the time, he thought this was
• 30:33
  just a mathematical sleight of hand, didn't have
• 30:38
  any significance whatsoever. But five years later,
• 30:41
  a patent clerk in Bern in Switzerland called
• 30:45
  Albert Einstein explained something called the
• 30:48
  photoelectric effect. So this is when you illuminate
• 30:52
  a piece of metal with light and you find electrons
• 30:55
  get kicked out. And the only way he could explain
• 30:59
  it was if the light was a stream of tiny little
• 31:03
  bullets, a stream of tiny little quanta. We now
• 31:06
  call them photons. And each individual photon
• 31:09
  ejected a single electron. And by the way, that
• 31:12
  was what Einstein got the Nobel Prize for. He
• 31:15
  did not get the Nobel Prize for relativity. He
• 31:18
  got the Nobel Prize for that. So then it took
• 31:22
  25 years, and we are actually talking now the
• 31:25
  centenary of the birth of quantum theory. So
• 31:28
  in the first 25 years of the century, people
• 31:33
  created a patchwork of ideas stitched together.
• 31:36
  we call the old quantum theory, and then it was
• 31:39
  developed from scratch by a number of people
• 31:43
  like Erwin Schrödinger, Werner Heisenberg, Paul
• 31:48
  Dirac, the British physicist, and that was quantum
• 31:51
  theory. So that was mainly what was going on.
• 31:54
  But at the height of the First World War, well,
• 31:58
  basically Einstein... Again, when he was a patent
• 32:01
  clerk in 1905, in his miraculous year, he published
• 32:04
  four papers which were all groundbreaking. And
• 32:08
  no one's ever done anything like that. Well,
• 32:10
  it was the first time anyone had done anything
• 32:12
  as significant as that since Isaac Newton in
• 32:15
  the 17th century. And Einstein did that. And
• 32:20
  he developed his theory of special relativity.
• 32:24
  And a cornerstone of that is that... basically
• 32:30
  nothing can travel faster than the speed of light.
• 32:32
  And he also discovered that mass equals mc2.
• 32:37
  Mass is a very compact form of energy and of
• 32:41
  course that energy was released in nuclear bombs,
• 32:45
  nuclear reactors, that kind of stuff. So at that
• 32:49
  point he realized that his theory was incompatible
• 32:53
  with Newton's law of gravity. So Newton assumed
• 32:55
  that Basically, gravity travelled at an infinite
• 32:59
  speed. So the Earth feels the gravity of the
• 33:03
  Sun instantaneously. Well, Einstein immediately
• 33:05
  realised this couldn't be true because he knew
• 33:07
  there was an upper limit to speed and light.
• 33:09
  The second thing he knew was, because of his
• 33:12
  E equals mc squared, that all forms of energy
• 33:16
  have an effective mass. So Newton had assumed
• 33:19
  it was only mass that was a source of gravity,
• 33:21
  but it turns out that all forms of energy have
• 33:23
  a mass. So the energy of your voice has gravity.
• 33:27
  Electrical energy has gravity. Sound energy has
• 33:30
  gravity. So he knew these two things needed to
• 33:33
  be incorporated. He needed a new theory of gravity.
• 33:37
  And he developed that over 10 years. And in November
• 33:42
  1950, he presented it in a series of four lectures
• 33:47
  in Berlin. This was at the height of the First
• 33:50
  World War. And one of those lectures... was,
• 33:54
  well, Carl Schwarzschild was on leave from the
• 33:57
  Western Front, and he attended one of those lectures.
• 34:01
  And he went back to a place called Mollhaus,
• 34:04
  which was on the Alsace Front between northern
• 34:07
  France and Germany, the only place on the Western
• 34:09
  Front that was mountainous. And in spare moments,
• 34:12
  he did something that Einstein had considered
• 34:15
  impossible. He found the shape of the spacetime
• 34:18
  for a realistic object, an object like a star.
• 34:20
  So that's the beginning of... Modern black holes.
• 34:25
  So the idea of black holes began with this quite
• 34:30
  unfortunate man living in pre -First World War
• 34:33
  Berlin, I believe. One might contradict that
• 34:36
  because it turns out that a British clergyman
• 34:40
  in the 1700s had actually realized that if an
• 34:46
  object were massive enough, its gravity would
• 34:50
  be strong enough. to trap light. But his picture
• 34:56
  of a black hole was very unrealistic because
• 34:59
  he assumed this thing would be enormous and would
• 35:03
  be of uniform density. But of course, what would
• 35:07
  actually happen is an object would collapse under
• 35:09
  its own gravity. So the first realistic picture
• 35:12
  of a black hole was actually Schwarzschild. And
• 35:16
  oddly enough, Schwarzschild's name in German
• 35:19
  means black shield. So it's quite ironic that
• 35:22
  he finds the solution, he finds what we call
• 35:25
  the black hole solution of Einstein's equations,
• 35:27
  and his name is Black Shield. Okay, we're going
• 35:31
  to disregard those 17th century monks because
• 35:33
  they were too early to send a letter to Einstein.
• 35:37
  Can you tell us more about who was he and how
• 35:40
  did he manage to get this pretty radical, crazy
• 35:44
  idea? Well, he was actually the director of the
• 35:48
  Berlin Observatory. at the outbreak of the first
• 35:51
  world war. So he wasn't just some random guy,
• 35:53
  an amateur physicist or something? No, he wasn't.
• 35:57
  No, he was a very prominent physicist. In fact,
• 36:00
  he'd actually been to America within a few years
• 36:03
  before, and he traveled all across America with
• 36:05
  American astronomers. He was very well known
• 36:08
  internationally. He'd actually thought about
• 36:11
  curved space, actually. The decades before, he'd
• 36:16
  written papers, you know, could the universe,
• 36:18
  could the space of the universe be curved in
• 36:21
  a dimension that we couldn't see? So he was very
• 36:24
  well primed for Einstein's idea that gravity
• 36:27
  is just curved space. And at the outbreak of
• 36:31
  the First World War, he immediately joined the
• 36:34
  German army. There was absolutely no need for
• 36:37
  him to do so. He was 40 years old. Why did he
• 36:38
  then? He was 40 years old, but anti -Semitism
• 36:43
  was on the rise in Germany and he was Jewish.
• 36:45
  He was not a practicing Jew. And even his children
• 36:49
  did not know he was Jewish. And in fact, he left
• 36:51
  a letter with his wife to say that if he died,
• 36:53
  that they were to be told that he was Jewish
• 36:55
  when they were 16 or whatever. So they didn't
• 36:58
  even know. So because anti -Semitism was on the
• 37:01
  rise, he wanted to show that he was a patriotic
• 37:04
  German like anyone else. So that's why he ended
• 37:07
  up... running a weather station in Belgium, calculating
• 37:12
  shell trajectories in France, and they ended
• 37:14
  up at this place called Mole House on the Alsace
• 37:17
  Front. I should tell you, you might think predicting
• 37:20
  the weather was an innocuous thing, but actually
• 37:24
  they needed to predict the weather for their
• 37:26
  gas attacks because they needed to know. So there
• 37:30
  was a horrible reason for it. And very often
• 37:34
  they got the weather forecast wrong. And there
• 37:37
  were many instances in which the gas blew back
• 37:40
  over the actual army that initiated the attack.
• 37:46
  So it turns out that poor old Schwarzschild had,
• 37:52
  in December 1915, at all the time he was playing
• 37:57
  with Einstein's theory, he developed these blisters
• 37:59
  in his mouth. They spread all over his body.
• 38:02
  They were weeping and bleeding. He ended up in
• 38:05
  a field hospital. And it was many weeks before
• 38:07
  he was diagnosed with a condition called pemphigus
• 38:10
  vulgaris, which is a condition in which the immune
• 38:13
  system attacks the skin. Now, our skin is our
• 38:17
  barrier against microorganisms, against diseases.
• 38:21
  So he knew he was going to die. Even today, there
• 38:24
  is no cure for this disease, although it can
• 38:26
  be controlled with steroids. So he went back
• 38:30
  to Berlin and he died, unfortunately, in May.
• 38:36
  And one of the speculations in my book is that
• 38:40
  it was accidental exposure to gas that triggered
• 38:43
  this condition. I did actually phone a dermatologist
• 38:48
  at a hospital in London, but he couldn't tell
• 38:52
  me definitively. He said it's possible, but they
• 38:55
  don't really know. So it could just have... This
• 39:01
  condition is a genetic condition. that is more
• 39:06
  prevalent in Ashkenazi Jews. So these are Jews
• 39:08
  from Eastern Europe. So, you know, he had a pre,
• 39:12
  you know, he had a likelihood of getting this
• 39:15
  disease and we don't know why it was treated
• 39:16
  when he was 40. However, despite his theoretical
• 39:22
  breakthrough, it didn't establish black holes
• 39:25
  as a fact straight away, right? Because there
• 39:27
  was some pretty stubborn, if not impossible obstacles
• 39:30
  standing in the way of this theory. Yes. So everyone
• 39:34
  thought, for instance, that, well, first of all,
• 39:37
  these objects were monstrous because they exploded.
• 39:41
  They had these singularities which were not realistic.
• 39:44
  So no one really believed in them. And they were
• 39:47
  convinced that something must stop the collapse
• 39:50
  of a star to form a black hole. There must be
• 39:52
  some force that nobody had considered. And in
• 39:57
  the 1920s, we just talked about quantum theory,
• 39:59
  such a force became apparent. It turns out that
• 40:04
  the building blocks of us, the atoms and their
• 40:09
  constituents, have this really strange dual nature.
• 40:14
  They can behave like waves, like ripples on a
• 40:16
  pond, as well as little tiny billiard balls.
• 40:20
  Now, if you know anything about a ripple on a
• 40:22
  pond, it's got some extent. You can't make the
• 40:25
  wave smaller. And this is the same of matter.
• 40:29
  When you try and squeeze it, because it's actually
• 40:31
  got this wave -like character. You can't squeeze
• 40:34
  it as small as you'd like. So that means there's
• 40:36
  kind of an opposing force. So this force is known
• 40:40
  as degeneracy pressure. And in 1930, a 19 -year
• 40:45
  -old Indian was on a ship from Bombay, which
• 40:49
  is now Mumbai in India, to England. He was going
• 40:52
  to go to Cambridge University. And sitting on
• 40:55
  the deck of this ship as it went through the
• 40:57
  Suez Canal, he was thinking about the death of
• 41:00
  stars. And he realized that although people thought
• 41:05
  this quantum effect opposing gravity would stop
• 41:10
  the formation of a black hole, he realized that
• 41:13
  everyone had forgotten one thing, and that was
• 41:17
  they'd forgotten Einstein's theory of relativity.
• 41:20
  So these, inside a star, the electrons would
• 41:23
  be moving around, he realized, at almost the
• 41:26
  speed of light. Now, it's the drumming of those
• 41:29
  electrons. If you imagine like drumming of water
• 41:31
  drops on a rooftop, it's that kind of drumming
• 41:35
  that's pushing backwards and stopping gravity
• 41:36
  crush a star. But if there's a limit to how fast
• 41:41
  they can move, and the limit was the speed of
• 41:42
  light, then they're kind of sapped of the ability
• 41:45
  to oppose it. And he realized that if the star
• 41:49
  was above a certain mass when it died, we now
• 41:52
  know that's one and a half times the mass of...
• 41:55
  the Sun. He was called, by the way, Subramanian
• 41:57
  Chandrasekhar, and this is known as the Chandrasekhar
• 42:01
  limit. If a star, when it dies, is bigger than
• 42:03
  one and a half times the mass of the Sun, no
• 42:06
  force can stop its collapse down to a black hole.
• 42:10
  Later it was realized that, so basically a star
• 42:14
  that's smaller than that becomes what we call
• 42:16
  a white dwarf. And even though it's got no heat
• 42:20
  generating, a force to push out against gravity.
• 42:23
  It has this kind of quantum jittering, pushing
• 42:27
  outwards. Later, it was realized that the electrons
• 42:31
  in atoms could be squeezed into the nuclear at
• 42:35
  the center to make what we call a neutron star.
• 42:38
  And a neutron star is something like the size
• 42:40
  of Mount Everest, but super dense. A neutron
• 42:44
  star, a sugar cube of its volume would weigh
• 42:47
  as much as the whole human race. So very dense.
• 42:51
  But actually, it turns out that the neutrons
• 42:54
  in this star, so the electrons and protons get
• 42:57
  squeezed together to make neutrons. The neutrons
• 42:59
  themselves are affected by quantum theory, and
• 43:02
  they also have this jittery outward force. That
• 43:05
  changes the mass, maximum mass, that a star can
• 43:08
  be stable to about two and a half times the mass
• 43:10
  of the sun. But if it's bigger than that, gravity
• 43:14
  wins. And so it turns out that black holes are
• 43:18
  inevitable. And they were discovered in 1971
• 43:20
  by Paul Merdin and Louise Webster, an Australian
• 43:24
  woman who has been entirely written out of the
• 43:27
  history of science. But she was the co -discoverer
• 43:29
  of black holes. By the way, did Einstein kind
• 43:33
  of concede before he died that the existence
• 43:36
  of black holes is indeed possible or likely?
• 43:40
  No, he didn't. He didn't. One of the extraordinary
• 43:43
  things about Einstein is that he was wrong more
• 43:47
  than any other physicist. And that tells you
• 43:50
  something about his genius, because he was never
• 43:54
  afraid to be wrong. And most physicists, they're
• 43:58
  wrong one or two times, and then they think to
• 44:00
  themselves, I can't be wrong anymore, because
• 44:02
  what will my peers think of me? Will I be promoted?
• 44:06
  Will I get tenure at the university? So they
• 44:08
  live in fear. But Einstein was able to basically
• 44:12
  fire lots and lots of shots, knowing that some
• 44:15
  would be on target, and he was never fearful.
• 44:19
  Major predictions of his theory of gravity he
• 44:21
  never believed in. So initially he believed in
• 44:25
  a static universe. This is what Newton believed
• 44:27
  in, where nothing changed. You know, the past
• 44:29
  was the same as the future. And then, of course,
• 44:33
  in 1929, Edwin Hubble discovered that the universe
• 44:36
  was expanding its constituent galaxies, which,
• 44:40
  of course, Einstein didn't know about in 1915.
• 44:42
  We didn't know that the building blocks of the
• 44:44
  universe were galaxies like the Milky Way. There
• 44:46
  are two trillion of them, by the way. Our Milky
• 44:48
  Way is one of them. But they're all flying apart
• 44:50
  like bits of cosmic shrapnel in the aftermath
• 44:52
  of the Big Bang. And if we run that expansion
• 44:54
  backwards in our minds, like a movie in reverse,
• 44:57
  we come to a point where everything is compressed
• 45:01
  into one point. 13 .8, two billion years ago,
• 45:04
  the Big Bang. So the universe is actually evolving.
• 45:07
  And this is not what Einstein believed. But his
• 45:10
  theory actually predicts that the universe cannot
• 45:12
  be static. His theory also predicts that black
• 45:15
  holes should exist. He didn't believe in that
• 45:17
  either. His theory also makes it quite easy to
• 45:22
  see how to build a time machine, which he never
• 45:27
  believed in. And most physicists don't believe
• 45:29
  in, even though the theory permits it. It permits
• 45:32
  it because it turns out that the rate at which
• 45:38
  time flows depends on how strong gravity is.
• 45:41
  Okay, so it turns out, for instance, if you're
• 45:44
  on the top floor of a building, you're further
• 45:48
  away from the mass of the Earth. So gravity is
• 45:50
  marginally weaker. So on the top floor of a building,
• 45:53
  time flows more quickly. Now this is an effect
• 45:58
  that can be measured with atomic clocks. In fact,
• 46:01
  if you were to stand on one step of a staircase,
• 46:04
  and someone were to stand on the step above you,
• 46:09
  you could show that your time will be flowing
• 46:11
  more slowly than theirs, even though they're
• 46:13
  just one step above you. Right, that's the whole
• 46:16
  premise of the film Interstellar. They go into
• 46:18
  space and then his daughter is already old. Yeah,
• 46:21
  so on Earth, you may think all these theories
• 46:23
  we're talking about are of no consequence to
• 46:26
  everyday life. But if you've got a smartphone
• 46:28
  or if you've got a sat -nav, that calculates
• 46:31
  your location relative to global positioning
• 46:34
  satellites. They're in highly elliptical orbits.
• 46:38
  And they contain on -board clocks. And when they
• 46:41
  come in close to the Earth, they're in stronger
• 46:43
  gravity, so the clock slows down. And when they're
• 46:45
  a long way from the Earth, the clock speeds up.
• 46:48
  And if your software in your phone did not compensate
• 46:52
  for that effect, you would get your location
• 46:55
  wrong by an extra 50 meters every day. So actually,
• 46:58
  these effects are used in everyday life. But
• 47:02
  to get back to the point, if gravity flows at
• 47:05
  different rates and different gravity, if you
• 47:06
  imagine the Earth and maybe the space around
• 47:10
  a black hole where gravity is much stronger,
• 47:13
  time will flow more slowly near the black hole.
• 47:16
  So if we start clocks on a Monday, by the time
• 47:20
  it's Friday on Earth, it's still only Wednesday
• 47:23
  by the black hole because time flows more slowly.
• 47:25
  If you could go instantaneously from the Earth
• 47:28
  to the black hole, you could go from Friday to
• 47:30
  Wednesday. And there is such a solution, what
• 47:33
  we call a Weinshine's equation, it's called a
• 47:35
  wormhole. So a black hole has a one -way membrane
• 47:39
  around it. We call it the event horizon. It's
• 47:42
  the point of no return for infalling matter.
• 47:45
  You cross the event horizon, you can't come out
• 47:47
  again. But a wormhole has a two -way membrane,
• 47:52
  so you can go in and come out. So if you were
• 47:55
  to connect the Earth to the region of a black
• 47:57
  hole by a wormhole, you could create a time machine.
• 48:00
  Wormholes, unfortunately, are highly unstable,
• 48:03
  and they require what we call matter with repulsive
• 48:07
  gravity to keep them open. You might think, well,
• 48:10
  that's ridiculous. But in 1998, we discovered
• 48:13
  that two -thirds of the universe has repulsive
• 48:17
  gravity. It's called dark energy. It's invisible,
• 48:21
  it fills empty space, and it has repulsive gravity,
• 48:23
  and its repulsive gravity is speeding up the
• 48:26
  expansion of the universe. contrary to all expectations.
• 48:30
  And the heads of the two teams that discovered
• 48:33
  that got the Nobel Prize. We don't know what
• 48:35
  dark energy is, but it shows you that there is
• 48:38
  stuff with repulsive gravity. So if you go to
• 48:39
  school today, if you go to high school, they
• 48:42
  probably tell you that gravity attracts, that
• 48:45
  it sucks. But actually, what they don't tell
• 48:48
  you is we've discovered that most gravity actually
• 48:51
  repels. Science in schools has not really caught
• 48:57
  up. But anyway, you would need material with
• 49:00
  repulsive gravity to keep open a wormhole. And
• 49:03
  it turns out the energy requirements to keep
• 49:07
  open a wormhole big enough, maybe a metre across,
• 49:10
  that you could crawl through would be significant.
• 49:14
  Way, way beyond the capabilities of any... of
• 49:19
  human beings and probably beyond the capabilities
• 49:22
  of extraterrestrial civilizations. But as far
• 49:28
  as physicists are concerned, that is extremely
• 49:31
  worrying that Einstein's theory permits the existence
• 49:34
  of time machines. Very, very worrying. Because
• 49:38
  obviously, we all know probably the grandfather
• 49:42
  paradox, you could go back in time. shoot your
• 49:45
  grandfather before your mother was born, and
• 49:47
  then you have to say, well, how could you go
• 49:48
  back in time because you weren't born? So Stephen
• 49:52
  Hawking, a British physicist, proposed the chronology
• 49:57
  protection conjecture, which is a very complicated
• 50:02
  phrase for basically time travel is impossible.
• 50:06
  So he basically said there has to be some law
• 50:08
  of physics that we have not discovered yet that
• 50:11
  stops time travel. Just to clarify, wormholes
• 50:15
  are different than black holes then, right? Yeah,
• 50:18
  so black holes have a one -way membrane. You
• 50:21
  cross it. You can never come out of it. The distinguishing
• 50:26
  feature of wormhole is that the horizon is two
• 50:29
  -way. You can go through it both ways. Right.
• 50:32
  Speaking of time, we mentioned the speeding up
• 50:36
  and stuff. I was watching a conversation with
• 50:40
  you and you... mentioned something fascinating
• 50:43
  that if you were hovering above a black hole
• 50:47
  while it was forming, you would somehow see,
• 50:50
  I don't know, back into past or into the future
• 50:53
  or something like this. I'm butchering it right
• 50:55
  now, but I think you see what I mean. As it was
• 50:59
  forming? Yeah, yeah, yeah. Or even when it's
• 51:03
  formed. So basically, we were talking about this
• 51:06
  effect that time flows at different rates and
• 51:08
  different gravity, and that effect is minuscule
• 51:11
  on the Earth because the gravity of the Earth
• 51:13
  is very tiny compared to a black hole. Nevertheless,
• 51:17
  we were saying that it's still... has an effect
• 51:20
  which has to be compensated for by our technology
• 51:22
  you know because we can measure it with atomic
• 51:24
  clocks and our phones wouldn't work unless we
• 51:27
  we took account of it but this effect becomes
• 51:30
  very very marked near black holes you know so
• 51:33
  they are the the most powerful sources of gravity
• 51:36
  in the universe so near them time flows very,
• 51:39
  very slowly compared to the rest of the universe.
• 51:42
  So if you were to hover just outside the horizon
• 51:45
  of a black hole, time would be flowing so slowly
• 51:48
  for you that as you looked out, you would see
• 51:51
  everything speeding up in the universe. So you
• 51:53
  could watch the entire future history of the
• 51:55
  universe flash past your eyes like a movie in
• 51:58
  Fast Forward. And you were talking about the
• 52:00
  formation of a black hole, that this effect happens
• 52:04
  as the black hole... as the star shrinks, because
• 52:07
  as the star shrinks, gravity becomes stronger
• 52:09
  and stronger, the mass becomes more concentrated,
• 52:12
  so time becomes more slow. And this means, really,
• 52:18
  from the point of view of an outsider, the black
• 52:22
  hole never actually falls. So the things become
• 52:27
  slower. If you were to watch an astronaut falling
• 52:29
  into a black hole, they would start moving more
• 52:33
  and more slowly. Until they actually became frozen.
• 52:37
  Because they would be moving so slowly. So actually
• 52:39
  the event horizon. Takes an infinite time to
• 52:42
  form. From outside. Now if you were falling in
• 52:44
  the black hole. You would cross the event horizon.
• 52:47
  And into the black hole. From outside it would
• 52:49
  take. Someone watching you. It would take an
• 52:51
  infinite time. So there's that huge huge disparity.
• 52:56
  Between the flow of time. Outside. Inside a black
• 53:02
  hole. So now we come to. why the term black hole
• 53:07
  was so important. So the Russians knew about
• 53:10
  theoretical black holes and they called them
• 53:12
  frozen stars, simply because they realised that
• 53:15
  as it collapsed down, time would flow more slowly
• 53:18
  and so the star would appear to freeze before
• 53:21
  it formed a black hole. So they called them frozen
• 53:24
  stars. But that didn't paint the really vivid
• 53:28
  picture in people's minds that black hole did.
• 53:31
  So that's why black hole has taken hold. It's
• 53:34
  amazing, really, because there are many terms
• 53:36
  like this. Big bang. So before Fred Hoyle was
• 53:40
  a British cosmologist, he coined the term big
• 53:43
  bang in a radio show in 1949 on the BBC in England.
• 53:48
  Before that time, no one had a word for it. And
• 53:52
  unfortunately, like black hole, it paints entirely
• 53:55
  the wrong picture. If you think of a Big Bang,
• 53:59
  it feels like a big explosion, right? Yeah. Okay,
• 54:02
  but the Big Bang was in no way like a big explosion.
• 54:05
  It wasn't like a stick of dynamite exploding,
• 54:07
  because that would explode into pre -existing
• 54:10
  space, pre -existing air. Okay, but the black
• 54:13
  hole, there was nothing pre -existing, because
• 54:15
  space and time itself was created in the black
• 54:18
  hole. So in that way, it wasn't anything like
• 54:20
  an explosion. And the other way it wasn't like
• 54:22
  an explosion is it didn't happen at a single
• 54:24
  point. It happened everywhere. So all of the
• 54:27
  universe suddenly pops into existence, and it
• 54:29
  could be infinite in extent, we don't know. And
• 54:32
  everything started rushing away from everything
• 54:34
  else, but there was no single point from which
• 54:37
  it all exploded, like a stick of dynamite. So
• 54:40
  once again, here's a term that has been fantastic
• 54:43
  in painting vivid pictures in people's minds,
• 54:46
  but actually, like black hole, paints entirely
• 54:48
  the wrong image. Wow. Okay. Yeah, I totally thought
• 54:53
  it was like a stick of dynamite. and then you
• 54:55
  know the universe since we said that it expanding
• 54:58
  it didn't make sense that it's starting out small
• 55:00
  and then it just but if you think that you start
• 55:02
  asking questions like what's it what is it expanding
• 55:05
  into which is of course yeah but of course the
• 55:07
  universe by definition is all there is so when
• 55:11
  you ask that question um you know you're not
• 55:14
  being very careful with your question but we
• 55:16
  don't know for instance i mean all but einstein
• 55:18
  theory tells us is that space and time So we
• 55:22
  have what we call Big Bang solutions. They describe
• 55:25
  the spacetime of the Big Bang in time, just like
• 55:28
  the Schwarzschilds describes a black hole in
• 55:31
  space. And all they tell us is that every point
• 55:38
  moves away from every other point. That's all
• 55:40
  they tell us. They don't tell us that there's
• 55:42
  a point, one single point that everything comes
• 55:46
  away from. So the theory doesn't tell us. Whether
• 55:52
  the universe is infinite in extent, many people
• 55:54
  think it's infinite in extent. So it doesn't
• 55:57
  actually have an age because it goes on forever.
• 55:59
  Or it could curve back on itself. So we know
• 56:03
  that the two -dimensional surface of a football
• 56:06
  curves back on itself. So if you were an ant
• 56:09
  and you lived on the surface of a football, you
• 56:12
  could come back to your starting point. But it
• 56:15
  could be that the... universe curves back on
• 56:18
  itself in a higher dimension. And there is a
• 56:21
  project at the moment to try and determine the
• 56:24
  shape of the universe. So if we think of something
• 56:28
  like a musical instrument, the sound waves that
• 56:32
  it makes depend on its shape. So in theory, if
• 56:36
  I told you what the loudness of the sounds made
• 56:40
  at different frequencies, if you're a physicist,
• 56:43
  you would probably be able to determine the shape
• 56:46
  of the instrument. So what we're doing is we're
• 56:48
  actually trying to determine the shape of the
• 56:52
  universe from sound waves in the universe. So
• 56:55
  it turns out that the Big Bang was a very turbulent
• 56:58
  fireball. And there were sound waves that moved
• 57:02
  through this fireball. And they caused the temperature
• 57:06
  to change slightly. And we can actually measure
• 57:10
  these temperature variations across the sky.
• 57:13
  So the afterglow of the Big Bang is still all
• 57:15
  around us. It's coming from every direction in
• 57:19
  the sky and we can observe it. In fact, 99 .9
• 57:23
  % of all the photons, so all the particles of
• 57:25
  light in the universe, are tied up in this afterglow
• 57:28
  of the Big Bang. And only 0 .1%, that's one thousandth
• 57:32
  of the light in the universe, comes from the
• 57:34
  stars and galaxies. 99 .9 % is this afterglow
• 57:38
  of the Big Bang. It was only discovered in 1965.
• 57:42
  scientists won the Nobel Prize. And you might
• 57:44
  think, well, why did we not discover it since,
• 57:46
  you know, until 1965, if it's the most striking
• 57:48
  feature of the universe? And the answer to that
• 57:50
  is it's absorbed by water vapor in the atmosphere.
• 57:53
  So it was quite difficult to spot. But if you're
• 57:55
  in space and you had eyes that didn't look at,
• 57:58
  you know, couldn't detect visible light, but
• 58:00
  detect microwaves. So the light of the fireball
• 58:04
  was initially was... blindingly bright, but as
• 58:09
  the universe is expanded and cooled, this radiation
• 58:12
  is cooled now and it appears as low -energy light,
• 58:14
  microwaves. If you had microwave eyes, you would
• 58:17
  see the entire universe glowing white. It'd be
• 58:20
  like being inside a light bulb. So this afterglow
• 58:24
  is the most striking feature of the universe.
• 58:26
  And we can see these little temperature variables,
• 58:28
  little ripples. They're called ripples in the
• 58:30
  temperature. And these ripples were produced
• 58:34
  by sound waves. By examining those sound waves,
• 58:37
  we can hopefully determine the shape of the universe.
• 58:43
  That was a long answer. This is fascinating,
• 58:47
  fascinating stuff. But if we go back to the history
• 58:51
  of the discovery of black holes, I think you
• 58:54
  mentioned the year 1971, right? Yes. When the
• 58:57
  existence of a black hole was actually confirmed.
• 59:00
  Can you tell us more about that? Yes. So this
• 59:03
  happened at the Royal Greenwich Observatory,
• 59:05
  which was in England. At the time, the observatory,
• 59:11
  which had been a naval institute, basically had
• 59:16
  been set up to map the constellations for ships
• 59:20
  hundreds of years before. It was actually in
• 59:24
  a 15th century castle surrounded by a moat in
• 59:28
  England. And in 1970, a man called Paul Murden,
• 59:32
  he was about 29, he was English, he came back
• 59:34
  from New York, he'd done a PhD, and he only had
• 59:38
  a temporary post at the Royal Greenwich Observatory.
• 59:41
  His problem was he had a wife and two young boys.
• 59:44
  He badly needed a job. He badly needed to make
• 59:47
  his name. A permanent job. Now, the problem in
• 59:50
  astronomy is that there are more stars in the
• 59:53
  universe than there are sand grains. on all the
• 59:57
  beaches around all the continents on Earth. So
• 1:00:00
  how do you find an interesting star? That's kind
• 1:00:03
  of like, how do you find an interesting sand
• 1:00:04
  grain? Was that the only way that you can make
• 1:00:09
  a name for yourself? As an archaeologist, you
• 1:00:11
  find a really fascinating fossil. He had to find
• 1:00:14
  a really interesting star. Yes, you've got to
• 1:00:16
  find something interesting. So when he was back
• 1:00:17
  in New York, him and the other graduate students
• 1:00:19
  would sit around drinking coffee, and they would
• 1:00:22
  think, how are we going to make a name for ourselves?
• 1:00:24
  How do we find an interesting star? and they
• 1:00:27
  determined that if it emitted X -rays, it was
• 1:00:29
  bound to be interested. So X -rays are emitted
• 1:00:32
  by light at a matter of millions of degrees.
• 1:00:35
  So anything that's at millions of degrees, that's
• 1:00:36
  going to be pretty unusual, isn't it? So in the
• 1:00:39
  early 1960s, the first X -ray telescopes were
• 1:00:42
  launched on sounding rockets. So these are rockets
• 1:00:44
  that went up above the atmosphere and dropped
• 1:00:46
  back down again. So they were only above the
• 1:00:48
  atmosphere for about a minute. The atmosphere,
• 1:00:51
  fortunately for us, absorbed the X -rays. So
• 1:00:54
  above the atmosphere, they could look at the
• 1:00:56
  X -ray sky, and they found tens of mysterious
• 1:00:59
  X -ray sources. Now, you only make progress in
• 1:01:04
  astronomy if you can kind of identify that with
• 1:01:09
  a known object and find out what it was. But
• 1:01:11
  the X -ray telescopes were incredibly crude,
• 1:01:14
  and we could only tell where the X -ray sources
• 1:01:17
  were within their constellation. So there was
• 1:01:20
  one X -ray source called Cygnus X -1. It was
• 1:01:23
  in the constellation of Cygnus the Swan. And
• 1:01:25
  we didn't know what it was associated with. But
• 1:01:28
  in 1970, as Merding was coming back from America,
• 1:01:32
  NASA launched Uhuru, which is the first X -ray
• 1:01:35
  satellite. And above the atmosphere, it was able
• 1:01:38
  to find hundreds of X -ray sources. And Merding
• 1:01:43
  got hold of the catalogue and he found that the
• 1:01:46
  box showing the location of Cygnus X -1 had shrunk.
• 1:01:50
  And when he looked at star charts, there was
• 1:01:53
  one interesting object in the box. It was a blue
• 1:01:56
  supergiant star. So this is an enormous star,
• 1:01:59
  a star weighed maybe 40 or 50 times the mass
• 1:02:02
  of the Sun, pumping out hundreds of thousands
• 1:02:04
  of times more light than the Sun. So this is
• 1:02:07
  clearly an interesting object. There was something
• 1:02:10
  unusual, but it couldn't be the source of the
• 1:02:13
  X -rays because even a blue supergiant has a
• 1:02:16
  surface temperature of only about 50 ,000 degrees,
• 1:02:18
  not a million degrees. So the question was, did
• 1:02:20
  it have a companion? Because if it had a companion,
• 1:02:24
  if it was a binary star, then it could be, Merdin
• 1:02:27
  thought, that matter could be sucked off the
• 1:02:30
  companion, swirled down onto the object, heat
• 1:02:34
  to millions of degrees and produce the X -rays.
• 1:02:36
  As luck would have it, Merdin was sharing an
• 1:02:40
  office. It was in an octagonal turret room. It
• 1:02:42
  looked out across the moat. and you could see
• 1:02:45
  the geese grazing. It was a pretty idyllic place.
• 1:02:48
  He was sharing the office with a 29 -year -old,
• 1:02:52
  same age, Australian woman called Louise Webster.
• 1:02:55
  She'd also worked in America, and she was working
• 1:02:58
  on a project with the director of the observatory
• 1:03:00
  to measure the speeds of stars. Now, if this
• 1:03:05
  supergiant had a companion, then, which it was
• 1:03:10
  orbiting, periodically, the blue supergiant star
• 1:03:13
  will be coming towards us and then going away
• 1:03:15
  from us. Now, we're all aware that a police siren,
• 1:03:20
  when it comes towards us, is a higher pitch,
• 1:03:23
  a higher frequency. When it goes away from us,
• 1:03:25
  lower pitch, lower frequency. And there's an
• 1:03:27
  analogous effect with light. And it means that
• 1:03:30
  when an object is coming towards us... It's got
• 1:03:33
  a higher frequency. It's what we call a blue
• 1:03:35
  shift. It's shifted to the blue end of the spectrum.
• 1:03:38
  When it's going away, it's red -shifted. So the
• 1:03:40
  question was, was this blue supergiant star being
• 1:03:43
  periodically blue and red -shifted? And it turns
• 1:03:46
  out that Louise Webster was using the Isaac Newton
• 1:03:50
  telescope at Hearst Monceau, this place in England.
• 1:03:54
  at the Royal Greenwich Observatory. It was a
• 1:03:56
  2 .5 -metre collecting mirror, one of the biggest
• 1:03:59
  telescopes in the world. It had been built in
• 1:04:01
  just about the worst possible place you could
• 1:04:04
  ever build a telescope because it was always
• 1:04:06
  cloudy and rainy. Eventually, it would be dismantled,
• 1:04:10
  taken to the Canary Islands off of Africa, the
• 1:04:13
  Spanish Canary Islands, reassembled at a greater
• 1:04:15
  cost than it cost to build it. But anyway, she
• 1:04:18
  looked at this star. And she found that it was
• 1:04:21
  actually orbiting something every 5 .6 days.
• 1:04:24
  So this enormous star was being whirled around
• 1:04:28
  every 5 .6 days by the gravity of another massive
• 1:04:32
  object. And Webster and Merdin sat down in her
• 1:04:36
  office. They did the calculations. They found
• 1:04:38
  out what would be the mass of the object whose
• 1:04:41
  gravity could be that great. And they determined
• 1:04:43
  it had to be at least four times the mass of
• 1:04:46
  the star. maybe six times the mass of the sun
• 1:04:48
  today we know it's 15 times the mass of the sun
• 1:04:50
  and they looked at each other because what could
• 1:04:53
  be invisible and that massive and there was only
• 1:04:56
  one object that could be invisible and that massive
• 1:04:58
  and it was a black hole and they discovered the
• 1:05:01
  first uh ever black hole and uh murdin got his
• 1:05:06
  permanent job um and he celebrated with his children
• 1:05:10
  and his wife in a cafe in hastings this is a
• 1:05:14
  a seaside place in England. It was the middle
• 1:05:16
  of winter, and they celebrated with knickerbocker
• 1:05:18
  glories. These are ice cream sundaes with fruit
• 1:05:21
  and syrup. And I only mention that because what
• 1:05:25
  a contrast. You know, the man who co -discovers
• 1:05:28
  black holes celebrates with his children with
• 1:05:30
  ice cream, but the man who predicted them, he
• 1:05:33
  dies of a horrible skin disease in the First
• 1:05:35
  World War. So there's quite a contrast there.
• 1:05:38
  And poor old Louise Webster. She went back to
• 1:05:41
  Australia. She had liver disease and she had
• 1:05:44
  one of the first successful liver transplants
• 1:05:46
  in Australia. But unfortunately, she died of
• 1:05:50
  cancer at the age of 49 in 1990. And she's been
• 1:05:53
  entirely written out of the history of science.
• 1:05:55
  So if there's anything you remember from this
• 1:05:57
  podcast today, please remember the name of the
• 1:06:00
  co -discoverer of black holes, Louise Webster.
• 1:06:03
  Why was she written out? She was just not mentioned
• 1:06:07
  anywhere or what? Was that intentional or was
• 1:06:09
  that... A number of reasons. I mean, she was
• 1:06:12
  working in optical astronomy. Progress in this
• 1:06:16
  field would be made in other types of astronomy,
• 1:06:19
  X -ray astronomy, radio astronomy. But the main
• 1:06:23
  reason, you have to say, is that she was a woman.
• 1:06:26
  There were so many examples of women who should
• 1:06:30
  have got the Nobel Prize who didn't. So, for
• 1:06:32
  instance, Lisa Meitner, who discovered nuclear
• 1:06:35
  fission, the... you know, the process that liberates
• 1:06:41
  energy in a nuclear bomb, in a nuclear reactor.
• 1:06:43
  She was nominated for the Nobel Prize 49 times.
• 1:06:47
  She was even nominated by Einstein and she was
• 1:06:51
  overlooked for the prize. Her co -worker, Otto
• 1:06:56
  Hahn, he got the prize. Jocelyn Bell, you know,
• 1:06:59
  she discovered pulsars. These are pulsating,
• 1:07:02
  spinning. hyper -compact, what we call neutron
• 1:07:05
  stars. There have been three Nobel Prizes. A
• 1:07:08
  supervisor got the Nobel Prize. There have been
• 1:07:10
  three Nobel Prizes for Pulsar. None have gone
• 1:07:12
  to her. And there's just so many examples of
• 1:07:15
  this across. So you have to think that it was
• 1:07:19
  sexism, really. And, of course, dying young.
• 1:07:23
  And she was also always very modest. She was
• 1:07:25
  a team player. She never pushed herself forward.
• 1:07:29
  But it is a shame. I mean, when the Nobel Prize
• 1:07:31
  was given in 2022 to two physicists who'd worked
• 1:07:36
  out the mass of our supermassive black hole,
• 1:07:38
  there was no mention of Louise Webster or even
• 1:07:41
  Paul Merdin, actually. So it is terrible. You
• 1:07:46
  know, I mean, only three women have won the Nobel
• 1:07:48
  Prize for physics. Marie Curie, the only woman
• 1:07:52
  to have won the Nobel Prize twice, and no man.
• 1:07:55
  won it twice for about 50 years after that. So
• 1:07:57
  she was a phenomenon. Maria Gobert Meyer, she
• 1:08:01
  won the Nobel Prize and another woman in Canada
• 1:08:04
  more recently. But so many have made major discoveries
• 1:08:08
  and been overlooked, and she was certainly one
• 1:08:11
  of them. Okay, and then when was a black hole
• 1:08:17
  actually first seen? It's not the photograph
• 1:08:19
  that we mentioned at the beginning, right? It
• 1:08:22
  was the photograph we mentioned. Oh, it was?
• 1:08:23
  Yeah, yeah. So you have to remember that all
• 1:08:26
  Paul Murdin, let's go back. So Murdin and Webster,
• 1:08:30
  they found indirect evidence of a black hole,
• 1:08:33
  right? So all they could see was something really
• 1:08:35
  massive was swirling around this star. Okay,
• 1:08:39
  and they inferred it had to be a black hole.
• 1:08:40
  But of course, businesses could always say, well,
• 1:08:43
  maybe there's something else. Maybe there's a
• 1:08:44
  compact object that we don't know of that isn't
• 1:08:46
  a black hole. The definitive evidence came on
• 1:08:49
  the 14th of September 2015, when we picked up
• 1:08:53
  a giant detectors in America, four kilometers
• 1:08:58
  long, in Washington State and Louisiana, detected
• 1:09:02
  gravitational waves. So these are ripples in
• 1:09:05
  the fabric of space -time. They were also predicted
• 1:09:07
  by Einstein in 1960. And they came, these gravitational
• 1:09:12
  waves, think of them as the voice of space. You
• 1:09:15
  know, we can see the universe with our eyes.
• 1:09:18
  Gravitational waves are the sound of the universe,
• 1:09:21
  you know, another sense. And they came from the
• 1:09:24
  merger of two black holes. And the signal was
• 1:09:26
  the definitive evidence because it was exactly
• 1:09:29
  what Einstein predicted the gravitational waves
• 1:09:32
  from a merger of black holes would be. From that
• 1:09:35
  point on, we knew they actually existed. As far
• 1:09:38
  as supermassive black holes are concerned, Andrea
• 1:09:42
  Ghez and Reinhard Genzel, who got the Nobel Prize
• 1:09:45
  for measuring the mass of the black hole Sagittarius
• 1:09:49
  A star at the centre of our galaxy in 2022, they
• 1:09:53
  also had indirect evidence. So they observed
• 1:09:56
  the star cluster, called the S cluster, of the
• 1:09:59
  Sagittarius compact cluster around the central...
• 1:10:04
  black hole at the center of our galaxy and they
• 1:10:05
  observed the speed of the stars and from that
• 1:10:08
  they were able to infer the black hole so the
• 1:10:10
  mass of the black hole so again they hadn't seen
• 1:10:12
  it but the definitive evidence came as you say
• 1:10:15
  in 2019 with the event horizon telescope that
• 1:10:19
  created the first image of a black hole and as
• 1:10:22
  you say it's a black void surrounded by this
• 1:10:25
  glowing material in falling material and and
• 1:10:28
  in many ways people were underwhelmed because
• 1:10:31
  they so knew what a black hole was going to be
• 1:10:34
  like, because the films like Interstellar that
• 1:10:39
  had actually featured black holes had used physicists
• 1:10:43
  to actually tell them to work out what the black
• 1:10:46
  hole would look like. So when they actually got
• 1:10:49
  an image, it looked exactly like what we thought
• 1:10:51
  it would look like. So people were often underwhelmed.
• 1:10:53
  But to my mind, that image is one of the great
• 1:10:56
  images in the history of science. You know, you
• 1:10:58
  think of the... Earth rising above the moon,
• 1:11:01
  photographed by Apollo 8. That's one of the great
• 1:11:05
  images in science. Maybe the double spiral staircase
• 1:11:09
  of DNA. But I actually do think that this photograph
• 1:11:13
  or that image of the first black hole is one
• 1:11:15
  of the great images in the history of science.
• 1:11:18
  But you do need to know what you're looking at
• 1:11:20
  to understand why it's so amazing. And this podcast
• 1:11:25
  will help you do. Just that. We began this story
• 1:11:29
  over 100 years ago with one dying man's far -fetched
• 1:11:31
  idea. What's the state of research in this field
• 1:11:34
  these days? I suppose black holes still hold
• 1:11:37
  many mysteries that we have yet to unlock. I
• 1:11:40
  mean, this is a fantastically interesting field
• 1:11:43
  because lots of things are moving and there's
• 1:11:48
  loads of unanswered questions. So, number one,
• 1:11:51
  we don't know why there's a supermassive black
• 1:11:54
  hole in the center of every galaxy. We don't
• 1:11:57
  know how they form. We don't know whether they
• 1:11:59
  came first. Were they the seeds around which
• 1:12:03
  galaxies of stars later form? Or did galaxies
• 1:12:08
  of stars form and then maybe a cluster at the
• 1:12:10
  centre collapsed to form a black hole? We don't
• 1:12:12
  actually know. We're getting some hints from
• 1:12:14
  the James Webb Space Telescope, NASA's James
• 1:12:17
  Webb Space Telescope. So it's found these surprising
• 1:12:19
  things called little red dots. They announced
• 1:12:22
  their discovery a year ago. and they are incredibly
• 1:12:25
  compact, tiny galaxies, maybe about 1 % or 0
• 1:12:30
  .1 % the size of a normal galaxy, and they're
• 1:12:32
  incredibly red. And we think that they are newborn
• 1:12:37
  supermassive black holes, and they're shrouded
• 1:12:40
  in dust. So they are pumping out X -rays, and
• 1:12:45
  they are incredibly hot, but that radiation is
• 1:12:48
  absorbed by the dust and re -radiated as infrared.
• 1:12:51
  So we're seeing them shrouded. And what's interesting
• 1:12:54
  about them is that the mass of the supermassive
• 1:12:58
  black hole that we can determine is sometimes
• 1:13:01
  up to 10 % of the mass of their galaxies. Well,
• 1:13:04
  remember today, in all galaxies, it's 0 .1%.
• 1:13:06
  So that's indicating, it's a strong hint, that
• 1:13:10
  the supermassive black holes came first, and
• 1:13:13
  only later did stars form. So as the universe
• 1:13:16
  gets older, more and more stars form, and the
• 1:13:18
  supermassive black hole becomes a smaller and
• 1:13:20
  smaller fraction of the total mass. So that's
• 1:13:23
  an indication that that's the case. So this Event
• 1:13:26
  Horizon Telescope is going to get to see greater
• 1:13:29
  detail. It's going to be able to create movies
• 1:13:32
  of material falling into these supermassive black
• 1:13:35
  holes. But the most important thing is gravitational
• 1:13:38
  waves. So I told you they were initially detected
• 1:13:41
  in 2015 by two gravitational wave detectors in
• 1:13:46
  America. Since then, ones have been added in
• 1:13:50
  Japan and India. and in Europe. And so far, we've
• 1:13:55
  seen something like 100 black hole mergers. And
• 1:13:59
  one thing I didn't tell you is that the first
• 1:14:02
  merger, the power emitted in the gravitational
• 1:14:06
  waves was 50 times the power emitted by all the
• 1:14:09
  stars in the universe combined. So that merger
• 1:14:12
  that was observed, had it been given out visible
• 1:14:15
  light rather than gravitational waves, it would
• 1:14:18
  have shone. 50 times brighter than the entire
• 1:14:21
  universe. So that was the most violent, powerful
• 1:14:24
  event ever witnessed by human beings. And since
• 1:14:27
  then, we've observed the merger where the power
• 1:14:31
  was 150 times greater than that emitted by all
• 1:14:34
  the stars in the universe. And we are constantly
• 1:14:37
  surprised. So these black holes that we're seeing,
• 1:14:41
  stellar mass black holes that we're seeing combined,
• 1:14:43
  are far bigger than anything we expected. We
• 1:14:46
  thought we might see... black holes of maybe
• 1:14:49
  10 times the mass of the Sun maximum. Some of
• 1:14:52
  these black holes are 50, 60 times the mass of
• 1:14:56
  the Sun. So there is actually a theoretical reason
• 1:15:01
  why they shouldn't actually even exist. There's
• 1:15:04
  a gap. It turns out that when a star comes to
• 1:15:06
  the end of its life, a massive star, if it's
• 1:15:09
  massive enough, it blows itself completely apart.
• 1:15:12
  So there's nothing to collapse to form a supermassive
• 1:15:14
  black hole. So there should be a mass range where
• 1:15:17
  we shouldn't see any black holes, but we do see
• 1:15:21
  them. And the only explanation we can think of
• 1:15:24
  is that the black holes we are seeing merging
• 1:15:26
  individually are the result of earlier mergers.
• 1:15:31
  So we think that these mergers are much more
• 1:15:34
  common than we thought. So, you know, to cut
• 1:15:36
  a long story short, The field of gravitational
• 1:15:39
  wave astronomy has given us a new sense. It's
• 1:15:42
  allowing us to observe these black holes across
• 1:15:46
  the universe. They are already giving us baffling
• 1:15:49
  results. And the future looks bright. Apparently,
• 1:15:52
  I don't know if you heard this, there's been
• 1:15:54
  growing support recently for a pretty bonkers
• 1:15:57
  theory that our universe might in fact be inside
• 1:16:01
  a giant black hole. What do you think of that?
• 1:16:04
  It's a possibility. So remember... that the black
• 1:16:10
  hole has a horizon around it. It's called an
• 1:16:12
  event horizon. And the universe has an event
• 1:16:17
  horizon as well. So what's beyond? We can't say
• 1:16:22
  what's beyond. That question doesn't make sense,
• 1:16:24
  right? Well, it does make sense. It does make
• 1:16:26
  sense. So you have to remember that there are
• 1:16:28
  two universes, right? So there's the observable
• 1:16:31
  universe. There's the universe and there's the
• 1:16:33
  observable universe. Okay, so the observable
• 1:16:36
  universe is what we can see. Okay, so the observable
• 1:16:39
  universe has a finite size because the universe
• 1:16:43
  was born. Okay, so the universe was born 13 .82
• 1:16:47
  billion years ago. That means we can only see
• 1:16:50
  the objects whose light has taken less than 13
• 1:16:53
  .82 billion years to get to us. Okay, so objects
• 1:16:57
  whose light would take 14 billion years to get
• 1:16:59
  to us, its light's still on its way. It hasn't
• 1:17:02
  arrived yet. So this means there's a horizon
• 1:17:05
  around the universe, right? So within this horizon,
• 1:17:07
  imagine it's like a giant soap bubble, and we're
• 1:17:10
  in this giant soap bubble, okay? So within this
• 1:17:14
  bubble are all the objects whose light has had
• 1:17:16
  time to get to us, okay? That's two trillion
• 1:17:18
  galaxies. Beyond the bubble are objects whose
• 1:17:22
  light has not got here yet, okay? And this horizon,
• 1:17:28
  as the universe gets older, the horizon should
• 1:17:31
  expand outwards. Because we see objects, okay,
• 1:17:34
  there's a reason why it doesn't. But that's a
• 1:17:38
  complication. But so as far as we know, the universe
• 1:17:43
  could be infinite in extent beyond the horizon,
• 1:17:46
  right? So the horizon is exactly like the horizon
• 1:17:49
  at sea, right? So we know there's more of the
• 1:17:52
  sea over the horizon. We know there's more of
• 1:17:55
  the universe over the horizon. It's just that
• 1:17:57
  that's... So this horizon has some of the properties
• 1:18:01
  of the event horizon of a black hole. So, yeah,
• 1:18:04
  it is possibly, it's a possibility. I don't think
• 1:18:08
  it's a likely possibility that we're inside a
• 1:18:11
  black hole. But when I talked about the horizon,
• 1:18:15
  yes, every single year, the observable universe
• 1:18:18
  gets bigger by one light year. And more and more
• 1:18:22
  stuff comes over the horizon, like more and more
• 1:18:24
  ships coming over the horizon at sea. That's
• 1:18:27
  what you'd expect. But in 1998, we discovered
• 1:18:30
  that the expansion is speeding up because of
• 1:18:33
  this stuff called dark energy that we don't understand
• 1:18:35
  at all. And that means that the horizon is actually
• 1:18:38
  shrinking. And it means that if we go forward,
• 1:18:42
  if we fast forward to AD 100 billion, so when
• 1:18:46
  the universe is 10 times bigger, everything would
• 1:18:49
  have been pushed beyond the horizon of the universe
• 1:18:52
  and there will be only one galaxy in the universe,
• 1:18:54
  our Milky Way. So now they're 2 trillion, but
• 1:18:58
  in 100 billion years time, we will be at the
• 1:19:00
  center of a universe that contains only one galaxy.
• 1:19:04
  So we are fortunate to have been arisen when
• 1:19:07
  we were around to actually see the universe.
• 1:19:09
  If we were unfortunate, remember that many stars
• 1:19:12
  live longer than the sun, like red dwarfs live
• 1:19:15
  much, much longer than the sun. If we were to
• 1:19:16
  have arisen in 100 billion years time, we couldn't
• 1:19:19
  have even developed astronomy. We couldn't have
• 1:19:21
  even... understood the things that we understand
• 1:19:24
  because we would have thought there's only one
• 1:19:25
  galaxy in the universe. I mean, wow. You know
• 1:19:33
  what? I understood much more than I thought I
• 1:19:35
  would, which is a testament to you, Mr. Chown.
• 1:19:39
  At the end, I have to risk a more existential
• 1:19:44
  question since I have you here as well. Does
• 1:19:47
  any of this kind of help us come to grips? with
• 1:19:51
  what we are doing here. I recently had a complexity
• 1:19:55
  scientist on the podcast, James Gladfelder, and
• 1:19:59
  he said that the fine -tuning argument makes
• 1:20:02
  him feel so uneasy. He thinks that our existing
• 1:20:06
  paradigms of science are kind of failing us at
• 1:20:09
  this point. What do you think? I think we're
• 1:20:11
  in an incredibly important point in history.
• 1:20:14
  You know, we're really, really lucky to be alive
• 1:20:16
  today. I mean, previous generations, you know,
• 1:20:19
  their theories of the universe and everything,
• 1:20:21
  they were just... speculation you know they were
• 1:20:24
  fantasies but now we we we do know for instance
• 1:20:27
  the universe was born in a hot dense phase because
• 1:20:29
  we can see the afterglow all around us so you
• 1:20:32
  know we do have a picture but we we we the things
• 1:20:36
  that we know about the universe previous generations
• 1:20:37
  would have killed to know you know we know we
• 1:20:40
  know the extent of the universe we can see to
• 1:20:43
  the edge of the observable universe we can count
• 1:20:45
  up the constituents of the universe two trillion
• 1:20:47
  galaxies we have a pretty good idea that it all
• 1:20:50
  burst into being 13 .82 billion years ago in
• 1:20:54
  a titanic explosion and the galaxies like Milky
• 1:20:58
  Way congealed out of the cooling debris. Now
• 1:21:02
  that doesn't mean, we still don't know basic
• 1:21:05
  questions like what is the universe? What was
• 1:21:09
  the Big Bang? What drove the Big Bang? What happened
• 1:21:13
  before the Big Bang? Are these even realistic
• 1:21:15
  questions? But we can actually pose these questions
• 1:21:17
  and have a realistic chance of answering them.
• 1:21:21
  answering them in the next maybe 10, 20 years.
• 1:21:23
  That's a fantastic place to be in history. And
• 1:21:27
  of course, we don't know. We don't know all the
• 1:21:29
  answers. But I mean, look how far we've come.
• 1:21:31
  I mean, we can never, we're on this tiny little
• 1:21:34
  planet. We can't leave it. The only information
• 1:21:36
  we get is from light that streams down that we
• 1:21:39
  collect. Essentially, that's it. Now gravitational
• 1:21:41
  waves. And yet we've pieced together this amazing
• 1:21:45
  picture of the universe where we're in it. how
• 1:21:49
  it formed. But again, the major questions we
• 1:21:53
  don't know the answer to. And to get back to
• 1:21:55
  black holes, you know, initially they were considered
• 1:21:59
  to be too ridiculous to even consider. But gradually,
• 1:22:04
  this is the story of my book, this is why I say
• 1:22:06
  black holes came in from the cold. Gradually
• 1:22:10
  they've moved more and more into the centre of
• 1:22:12
  science. Not only do they challenge us to come
• 1:22:16
  up with a better theory of... theory of everything,
• 1:22:20
  but they appear to be key to the universe that
• 1:22:25
  we see around us. So they're the key to actually
• 1:22:28
  creating the universe that we see around us,
• 1:22:31
  to creating galaxies. And they also, as I said,
• 1:22:34
  are probably the key to us having this conversation.
• 1:22:38
  So again, we don't actually, if this... process
• 1:22:43
  of coming into the center of science continues
• 1:22:45
  then in the future we realize that black holes
• 1:22:47
  were even more key to the universe being the
• 1:22:51
  way it is and us being here but again we don't
• 1:22:53
  know the answers to these these questions you
• 1:22:55
  know um that's why it's incredibly exciting time
• 1:22:58
  to be around in science i mean only last week
• 1:23:01
  the vera rubin observatory was opened in chile
• 1:23:06
  So remember Vera Rubin, we were talking about
• 1:23:08
  women are overlooked. You know, she confirmed
• 1:23:10
  the existence of dark matter, one of the biggest
• 1:23:13
  unsolved problems in science. And she was overlooked
• 1:23:15
  for the Nobel Prize as well. But they finally
• 1:23:17
  named a telescope after her. And it's a massive
• 1:23:24
  camera, a huge... one of the biggest cameras
• 1:23:28
  in the world, and it will be able to snap the
• 1:23:30
  entire sky every three days. So for the first
• 1:23:33
  time, we'll be able to see how the universe is
• 1:23:36
  changing on periods of a few days. So we're going
• 1:23:39
  to discover all kinds of asteroids, objects that
• 1:23:42
  we hadn't ever suspected that change on very
• 1:23:45
  short timescales. We're going to discover them
• 1:23:46
  in a matter of weeks. You know, this is incredible.
• 1:23:49
  But the main justification for this telescope
• 1:23:52
  was... and this is rather paradoxical, is to
• 1:23:56
  look for the invisible. So to look for dark matter.
• 1:23:59
  So here's an optical telescope looking for stuff
• 1:24:01
  that doesn't give out light. So we infer the
• 1:24:04
  existence of dark matter by the motion of the
• 1:24:07
  visible stuff. So we see that the visible stars
• 1:24:09
  and galaxies are moving in ways that they shouldn't
• 1:24:12
  do unless they're under the influence of the
• 1:24:14
  gravity of this invisible stuff, this dark matter.
• 1:24:16
  And we don't know what it is. So, you know...
• 1:24:20
  So to just finish, I mean, I'm not really helping
• 1:24:22
  you, really. I'm just telling you all the puzzles
• 1:24:24
  there are. We're now at the point where we have
• 1:24:30
  discovered that 95 % of the universe is invisible.
• 1:24:35
  So two -thirds of the universe is this dark energy,
• 1:24:39
  which is speeding up expansion of the universe.
• 1:24:40
  We don't know what it is. The visible stars and
• 1:24:43
  galaxies are outweighed by a factor of six by
• 1:24:46
  invisible stuff. We've got no idea what it is.
• 1:24:48
  And of the visible stars and galaxies, we've
• 1:24:51
  only seen half. So we've only seen 2 .5 % of
• 1:24:54
  the universe. We believe that the other 2 .5
• 1:24:56
  % of normal stuff is gas between the galaxies
• 1:24:59
  that is difficult to see. But basically, we've
• 1:25:03
  only seen 5 % of the universe. And we've constructed
• 1:25:05
  this incredible... theory of the universe, of
• 1:25:08
  its origin, from the 5%. So imagine if back in
• 1:25:11
  the 19th century, Charles Darwin only knew about
• 1:25:15
  frogs, and he only knew about trees, and he had
• 1:25:18
  to develop a theory of evolution, not knowing
• 1:25:20
  about most of life. Well, we've developed this
• 1:25:23
  incredible theory of the universe, not knowing
• 1:25:26
  what most of the universe is made of. I mean,
• 1:25:28
  hopefully it's not incorrect, but it just shows
• 1:25:31
  you there's a lot out there for us to learn.
• 1:25:35
  What a delightful conversation. Thank you so
• 1:25:37
  much. Where can people find your book? Find bookstores?
• 1:25:40
  I actually know it's find bookstores everywhere
• 1:25:42
  because this is how I found you. Because I was
• 1:25:45
  back home vacationing in my home country of Slovenia
• 1:25:48
  and I went to one of the best bookshops we have
• 1:25:51
  in Ljubljana in the capital. And I saw your book
• 1:25:53
  there prominently displayed. I was like, yes,
• 1:25:57
  this is it. I need to read this and I need to
• 1:25:59
  contact this one. I've got a copy of it. That's
• 1:26:01
  the paperback, which you're probably seeing back
• 1:26:03
  to front, of course. The paperback came out only
• 1:26:08
  last month, actually. So it's been out for a
• 1:26:11
  year. So, yeah, yeah. And by the way, it's principally
• 1:26:15
  about people. So don't be scared by my book because
• 1:26:18
  I really write about the people who made the
• 1:26:21
  discoveries. And anyone who was alive, I'm a
• 1:26:23
  journalist. I phoned them up and talked to them
• 1:26:26
  and get their stories, including 91 -year -old
• 1:26:29
  Roy Kerr, who discovered the shape of space around
• 1:26:33
  spinning black holes. All spinning black holes
• 1:26:35
  are called Kerr black holes after him. Unfortunately,
• 1:26:39
  obviously, Carl Schwarzschild was dead. I couldn't
• 1:26:40
  talk to him. So I had to use oral histories,
• 1:26:42
  that kind of stuff. But generally, I've tried
• 1:26:45
  to tell a story in terms of the people and interweave
• 1:26:48
  the science in as painless a way as possible.
• 1:26:53
  It's an amazing story. Thank you again. By the
• 1:26:57
  way, you do have some social media, I saw. You're
• 1:26:59
  pretty active on X, so people can follow your
• 1:27:01
  work. Yeah, yeah. I've moved a bit to Blue Sky,
• 1:27:04
  but that doesn't have as many people. Yeah, I
• 1:27:07
  was active on X, but obviously I'm not happy
• 1:27:10
  with... you know, mask and everything, you know.
• 1:27:13
  How could you be? It's a shame, you know, to
• 1:27:16
  build up a large following over the years, you
• 1:27:19
  know, and then abandon it. So at the moment,
• 1:27:21
  I'm posting on both, but I'm trying to move to
• 1:27:24
  Blue Sky, but I don't know if Blue Sky is going
• 1:27:26
  to take off. Nobody knows. All right. Mr. Tong,
• 1:27:30
  thanks again. Thank you very much. I really enjoyed
• 1:27:31
  it. Thank you so much for listening. Please subscribe
• 1:27:34
  to the podcast on YouTube. Follow and rate on
• 1:27:36
  Spotify and Apple Podcasts marketing tutorials.
• 1:27:40
  Insist, it's really important that I hassle you
• 1:27:42
  about that, so I'm doing it. Also, if you'd like
• 1:27:45
  to, please support me on Patreon. This is a one
• 1:27:47
  -person podcast. I know I say this every time,
• 1:27:49
  but I do everything by my little old self. There's
• 1:27:52
  no team behind me. It's very, very sad, I know.
• 1:27:55
  But you can help by hopping on Patreon and finding
• 1:27:58
  the smart... cookies podcast on there and then
• 1:28:01
  last but certainly not least i have to thank
• 1:28:03
  my existing patrons without you there would be
• 1:28:06
  no smart cookies which makes you the real actual
• 1:28:10
  producers of this show so eternal thanks to thank
• 1:28:13
  you so much your support means the world to me