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Cosmic Questions: Dark Energy, Stellar Birth & the Nature of Black Holes | Space Nuts: Astronomy... · Space News Today

• 0:00
  Hi there. Thanks for joining us. My name
• 0:02
  is Andrew Dunley and this is Space Nuts
• 0:06
  Q&A edition. It also happens to be our
• 0:08
  sixth hundth episode, believe it or not.
• 0:11
  And what are we doing special today?
• 0:14
  Nothing. We're just going to answer a
• 0:17
  Well, it happens so often now. Uh we're
• 0:20
  just going to answer audience questions.
• 0:21
  And we've got a bunch of them. Um the
• 0:24
  question of dark matter and dark energy
• 0:26
  theory has come up again. Uh, in fact,
• 0:28
  one of our listeners has come up with a
• 0:30
  theory about dark matter and dark energy
• 0:32
  theory. So, we'll investigate that. We
• 0:35
  also have a question from somebody using
• 0:37
  a very interesting pseudonym. Uh,
• 0:40
  finding where our sun was born. I think
• 0:43
  we've been down that road before
• 0:45
  recently, so they're revisiting that.
• 0:48
  The temperature of black holes has been
• 0:50
  raised yet again. We talked about that
• 0:52
  recently. And Peter has asked us about
• 0:56
  the expansion of the universe. That's
• 0:58
  all coming up on this edition of Space
• 1:01
  Nuts.
• 1:01
  >> 15 seconds. Guidance is internal. 10 9g
• 1:06
  Ignition sequence start.
• 1:08
  >> Space nuts.
• 1:09
  >> 5 4 3 2 1 2 3 4 5 5 4 3 2 1
• 1:14
  >> Space Nuts.
• 1:15
  >> Astronauts report. It feels good. once
• 1:18
  again joining us from the oh it's not
• 1:21
  the 600th time because we've had time
• 1:23
  off so it's probably 592
• 1:26
  or something like that maybe I don't
• 1:28
  know maybe a few less but um his name is
• 1:31
  Fred Watson professor Fred Watson in
• 1:32
  fact astronomer at large hi Fred
• 1:35
  >> how you doing to see you again
• 1:37
  >> good to see you too
• 1:39
  >> can you believe it's 600 episodes my
• 1:41
  goodness
• 1:42
  >> so we because we now have two a week
• 1:44
  that you go through a hundred every year
• 1:46
  basically doesn't more or less.
• 1:48
  >> Yeah.
• 1:49
  >> Whereas it used to be every couple of
• 1:51
  years. So
• 1:52
  >> yes,
• 1:53
  >> we're just moving faster. It's it's the
• 1:55
  expansion of the universe because it's
• 1:56
  accelerating. That's what it is.
• 1:58
  >> It's a relative relativistic effect
• 2:01
  >> indeed. Uh let us uh get straight into
• 2:04
  our questions because we've got a whole
• 2:06
  bunch of them. Daryl has sent us in a
• 2:08
  question. Good day, Space Nuts. I've
• 2:10
  been giving dark energy and dark matter
• 2:12
  some thought. If I've got this right,
• 2:15
  dark matter matter pushes the universe
• 2:17
  apart or away while um dark energy
• 2:21
  attracts or brings stuff together. So
• 2:24
  could dark matter and dark energy be the
• 2:26
  same thing but have uh like a north and
• 2:29
  south pole? I.e. dark matter north would
• 2:32
  be the particle that clumps together and
• 2:34
  dark energy south would be the particle
• 2:36
  that pushes outwards creating negative
• 2:39
  pressure and expanding the universe.
• 2:41
  Thoughts. Now, that's his question. But
• 2:43
  he says, "By the way, Martin's joke
• 2:45
  about the Ganab Gibb being a lost BG
• 2:48
  brother made me laugh out loud for a
• 2:50
  couple of minutes." That's Daryl from
• 2:52
  South Australia. Yeah, I thought it was
• 2:54
  funny, too. And that's the first time
• 2:56
  Martin's ever been funny. But, um, no,
• 2:58
  we It was a good one. It was a very good
• 3:00
  one. Um, yes. So, um, this is an
• 3:04
  interesting theory. as a dark matter
• 3:06
  south pole dark energy north pole
• 3:10
  opposites attract type of scenario I
• 3:12
  don't know what do you think so the the
• 3:16
  issue yes uh it's a nice thought because
• 3:19
  the you know we naturally think along
• 3:21
  those lines when we recognize that one
• 3:24
  of these forces entities
• 3:28
  pull stuff together and the other pushes
• 3:30
  it apart
• 3:32
  um
• 3:33
  And
• 3:36
  in in many ways that's the crux of the
• 3:38
  matter because the the two of them are
• 3:41
  fundamentally different in their uh in
• 3:44
  their effect on the universe. So dark
• 3:46
  energy which comes as a man which is
• 3:50
  manifested to us in the accelerated
• 3:53
  expansion of the universe that's an
• 3:55
  energy of space itself and to the best
• 3:58
  of our ability uh to determine these
• 4:01
  things it is isotropic uh in other words
• 4:04
  it's the same in all directions. Now
• 4:07
  some people have questioned that
• 4:10
  >> uh s suggesting that maybe you know for
• 4:13
  all we are looking at a big chunk of the
• 4:16
  universe with a horizon of 13.8 8
• 4:18
  billion light years. Um it may be that
• 4:21
  that's just a small part of the universe
• 4:23
  and there are other bits where where you
• 4:25
  know the
• 4:27
  the acceleration is not sorry the
• 4:29
  expansion is not accelerating uh and the
• 4:32
  two sort of even out. Um that's that's
• 4:37
  a a a caveat that we can't really deal
• 4:39
  with because we've no idea what happens
• 4:41
  beyond the little bubble of the universe
• 4:43
  that we can observe. Yeah. And certainly
• 4:45
  it's true within that bubble the
• 4:48
  acceleration is basically this or the
• 4:50
  accelerated sorry the accelerated
• 4:53
  expansion is basically the same in all
• 4:56
  directions. So it's a property of space
• 4:58
  itself. It's a fundamental property. Um
• 5:01
  whereas dark matter yes that's got
• 5:03
  gravitation
• 5:05
  um and pulls stuff in. It's definitely
• 5:08
  clumpy. Uh it it it actually um well it
• 5:13
  follows the the the visible matter. That
• 5:15
  was the way it was thought to be when we
• 5:17
  first started thinking about dark
• 5:19
  matter. But now we think it's probably
• 5:20
  the other way around that the visible
• 5:21
  matter is visible because dark matter
• 5:24
  acted as a kind of scaffolding uh in the
• 5:27
  early universe for uh the gravitational
• 5:30
  pull of dark matter uh in order to bring
• 5:33
  the clouds of hydrogen together,
• 5:34
  compress them and make them turn into
• 5:36
  stars. So um that's why dark matter and
• 5:40
  normal matter stick together but they do
• 5:42
  stick together. Uh and when you you know
• 5:45
  when you observe the universe on the
• 5:47
  larger scales we can see um by for
• 5:50
  example gravitational lensing uh we can
• 5:53
  see that the uh the the um dark matter
• 5:58
  definitely follows the visible matter.
• 6:00
  So there will be places where uh there's
• 6:03
  hardly any visible matter and there's
• 6:05
  hardly any dark matter whereas with the
• 6:08
  dark energy it's everywhere
• 6:10
  >> and so there's there are fundamental
• 6:12
  differences between them and I suspect
• 6:14
  in the end you know if we were having
• 6:16
  this conversation in 20 or 30 years time
• 6:21
  we probably will be actually but anyway
• 6:24
  um when we look back on this we we might
• 6:26
  have realized that uh the dark uh energy
• 6:30
  is a bzon. It's a it's a force particle.
• 6:33
  Uh whereas dark matter is some sort of
• 6:36
  matter particle made of quarks and
• 6:38
  things of that sort. So there probably
• 6:40
  fundamental differences rather than just
• 6:43
  that sort of the idea that they might be
• 6:46
  the same thing but with a different
• 6:47
  polarity.
• 6:48
  >> Yeah.
• 6:48
  >> Um I I I don't think the evidence
• 6:51
  supports that. I suppose we could say
• 6:53
  Daryl's fallen for the naming error uh
• 6:57
  of of these two things because um we
• 7:00
  we've said all along that dark energy is
• 7:02
  poorly named. It's it's not really
• 7:06
  the right thing to call it. Well, well,
• 7:09
  neither of them are really, you know,
• 7:11
  they're invisible would have been far
• 7:14
  better, but dark. It was actually Fritz
• 7:17
  Vicki back in 1933 who labeled um this
• 7:21
  stuff dark matter. He didn't what it was
• 7:23
  and he said there must be something
• 7:24
  there which he was calling dark matter
• 7:26
  that um that's providing enough of a
• 7:30
  gravitational attraction to stop
• 7:31
  clusters of galaxies from dispersing
• 7:33
  altogether.
• 7:34
  >> Yeah. Interesting. Um they'll figure it
• 7:37
  out one day, but um for now it it
• 7:40
  remains a mystery. But that there's got
• 7:42
  to be something in that connection
• 7:44
  between real matter and dark matter
• 7:48
  plumping. Like if you go somewhere there
• 7:51
  isn't much matter, there isn't much dark
• 7:53
  matter. So there's got to be some
• 7:56
  connection there that
• 7:57
  >> there is. That's right.
• 7:58
  >> That will that will give us the answer
• 7:59
  one day if we can figure out what the
• 8:01
  connection is.
• 8:03
  >> Yeah. Well, the connection is gravity
• 8:05
  and um it's the only um
• 8:07
  >> Well, we haven't figured that out
• 8:09
  either.
• 8:09
  >> No, that's right. We basically we we
• 8:11
  know how it behaves. We know very
• 8:13
  accurately how it behaves, but we don't
• 8:14
  know what it is.
• 8:17
  >> Yeah,
• 8:17
  >> it is indeed a mystery, Darl. Uh but
• 8:19
  coming up with an idea always is um a
• 8:23
  good way to get people thinking and
• 8:25
  maybe maybe somewhere in the dark
• 8:28
  reaches of the internet someone will
• 8:29
  hear this and go, "Hang on, Daryl's on
• 8:31
  to something." And then he'll go to his
• 8:33
  Wikipedia or his uh encyclopedia
• 8:36
  Bratannica or his Funkin Wagnoff, flick
• 8:39
  a few pages and go,
• 8:41
  I've got it figured out thanks to
• 8:43
  Daryl's question on space nuts. So, you
• 8:45
  know, there are no dumb questions in
• 8:48
  astronomy, are there, Fred?
• 8:49
  >> No, that's absolutely right. There's
• 8:52
  just dumb answers from the likes of me.
• 8:55
  >> Thanks, Daryl. Great to hear from you.
• 8:57
  Our next question comes from the fjords
• 9:00
  of Norway. Uh and um this uh question
• 9:05
  goes by the name of someone will
• 9:07
  recognize this Slatty Bfast. Uh
• 9:10
  listening from the fields of Norway last
• 9:11
  week. Someone asked the question about
• 9:13
  viewing the birth of the sun and Fred
• 9:15
  answered with the hypothetical mirror in
• 9:19
  space. My question is if we calculated
• 9:22
  the exact location in space for the sun
• 9:25
  4.6 six billion years ago and pointed a
• 9:28
  telescope at those coordinate uh
• 9:30
  coordinates, would we see anything?
• 9:36
  >> Cuz slatty Bfast won an award, didn't
• 9:38
  he, for the fields of Norway? So that
• 9:41
  >> Oh, that's right. That's right. Yes,
• 9:44
  that wasn't because he he designed them
• 9:46
  or
• 9:47
  >> designed them. Yes, he made he made
• 9:49
  fjords.
• 9:50
  >> That's right. That was what Zan Bartfast
• 9:52
  was famous for. One of my favorite
• 9:55
  Douglas Adams characters.
• 9:56
  >> Oh, yeah. Brilliant. I think the moment
• 9:58
  where he's forced to say his name is one
• 10:01
  of the the the funniest moments I've
• 10:04
  ever experienced
• 10:06
  cuz first time I ever listened to it. I
• 10:08
  listened to the audio version. That just
• 10:12
  caught me so beautifully. I just
• 10:14
  couldn't stop cackling.
• 10:17
  >> Very No, it's it's epic. Epic stuff. One
• 10:20
  of the all-time greats in science
• 10:22
  fiction. Absolutely. Yes.
• 10:24
  >> Yeah. Um anyway, the answer to Slatty
• 10:27
  Bfast's question is no. So, um do you
• 10:31
  want to keep going?
• 10:33
  >> Well, I mean, he he's basically saying
• 10:35
  we So, you're saying we would not see
• 10:37
  anything if we could figure out where
• 10:39
  the sun was 4.6 billion years ago and
• 10:41
  then pointed a telescope at it.
• 10:43
  >> Yeah. Because um first of all, the sun
• 10:46
  isn't there anymore.
• 10:47
  >> No, I know where it is.
• 10:49
  >> Yes. The odds are there.
• 10:52
  >> That that point uh you Let me see which
• 10:56
  way you're pointing.
• 10:57
  >> I'm pointing that way.
• 10:58
  >> That way. That's good. That's probably
• 11:00
  correct, too. In fact, it's behind me,
• 11:02
  too. It's to my It's to my right rear.
• 11:07
  >> That way.
• 11:08
  >> All right. Okay. At the moment. That's a
• 11:10
  bit intimate, isn't it? Anyway, never
• 11:11
  mind. Um the uh the sun is certainly not
• 11:15
  shining out of that particular part of
• 11:17
  me at the moment, but it's it's in that
• 11:20
  kind of direction.
• 11:23
  >> It's what all your fans think though,
• 11:25
  isn't it?
• 11:26
  >> They don't. Uh I don't even have any I
• 11:29
  don't get fan mail. I get abuse.
• 11:32
  >> Well,
• 11:33
  uh anyway, um notwithstanding all that,
• 11:36
  what was the question again? Yes. If you
• 11:38
  could work out where the sun was 4.6 six
• 11:40
  billion years ago and point a telescope
• 11:43
  at it, you wouldn't see anything because
• 11:46
  the the point where the sun was formed.
• 11:50
  Um, and it it it will be only a few at
• 11:54
  most 100 million light years away. Uh,
• 11:58
  so yeah, you've got to look back time,
• 12:00
  but you've got to look back time. It's
• 12:02
  probably less than 100 million years.
• 12:04
  Uh, and the sun 100 million years ago
• 12:07
  was a lot like what it is now. It's
• 12:09
  slightly hotter uh and a few other
• 12:11
  things that were going on at the time,
• 12:13
  but not much different. But the fact is
• 12:15
  it's not there, it's here. Um so even
• 12:20
  as I think I said uh in that thought
• 12:23
  experiment, you'd have to have a mirror
• 12:25
  uh something like 2.3 billion light
• 12:29
  years away
• 12:31
  uh which is going to take you quite a
• 12:33
  lot of time to put in place anyway. But
• 12:36
  if that mirror was looking back to
• 12:39
  wherever the sun was formed, and we
• 12:40
  don't know where that was. Uh we know
• 12:43
  it's within the present vicinity of the
• 12:45
  sun because stars don't move that fast.
• 12:47
  Uh anyway, um you you have this mirror
• 12:50
  and you capture a reflection of the sun
• 12:54
  being born. Uh that thought experiment I
• 12:57
  think would work, but just um looking at
• 13:00
  where the sun was when it was born isn't
• 13:04
  going to tell you very much. There's got
• 13:06
  to be something there though, right?
• 13:08
  >> Well, there be Yeah. Probably other
• 13:10
  stars and things like that, you know.
• 13:12
  It's just part of the the solar
• 13:13
  neighborhood. Yeah.
• 13:15
  >> Yeah. Our our son, I suspect, came from,
• 13:18
  you know, a pretty rough neighborhood
• 13:21
  and that's why it left. It uh inherited
• 13:24
  money and managed to managed to get
• 13:26
  away.
• 13:28
  >> Yeah. But then it discovered drugs,
• 13:29
  didn't it? That's
• 13:30
  >> Yeah. Well, that's that's what happened.
• 13:32
  Yes. And and then we turned up and um
• 13:35
  Yeah.
• 13:36
  >> Well, hell broke loose. Yes. Uh but
• 13:39
  there'd be nothing to see there. Nothing
• 13:41
  to see there. No.
• 13:43
  >> Nothing that's really of any interest.
• 13:44
  Just other stars.
• 13:45
  >> Yeah.
• 13:46
  >> Yeah. Although we're still looking for
• 13:48
  Earth's siblings. Uh sorry, the sun's
• 13:50
  siblings. That's
• 13:52
  >> That's right.
• 13:52
  >> Because there there would be some, but
• 13:54
  they wouldn't be there either, would
• 13:55
  they? Well, that you know that the stars
• 13:59
  and that I'm sorry, the stars that were
• 14:01
  born alongside the sun in the same cloud
• 14:04
  of gas and dust uh are probably not that
• 14:06
  far away. Uh but um they
• 14:13
  yeah
• 14:14
  100 Yeah, 100 100 million light years I
• 14:17
  mentioned before. It's probably much
• 14:19
  much less than that. I don't know quite
• 14:21
  why I thought of that, but anyway,
• 14:25
  because the center of our galaxy is only
• 14:26
  25,000 light years away. Uh, so um I
• 14:30
  probably meant 100,000 light years as
• 14:33
  when I said 100 million. Um,
• 14:36
  something's going wrong with this
• 14:38
  program today. I'm not quite sure. Well,
• 14:39
  we
• 14:40
  >> It's 100 It's a 600.
• 14:42
  >> That's what it is. That's what it is.
• 14:44
  There's a there's a a gap in spaceime
• 14:46
  has opened up uh which I'm floundering
• 14:49
  in at the moment. Yeah. So, you know,
• 14:51
  you might it's it's not gone very far.
• 14:54
  Uh that's what I'm saying. The siblings
• 14:56
  from from the sun in the born in the
• 14:59
  same gas cloud from the sun are probably
• 15:01
  within they might even be within the
• 15:03
  nearest 100 million sorry 100 light
• 15:06
  years not million light years. Um so uh
• 15:11
  and that's why we can use very high
• 15:16
  resolution instruments, ones that uh
• 15:19
  really analyze the spectrum of a star in
• 15:21
  great detail but need the star to be
• 15:23
  relatively bright. That's why we can use
• 15:25
  that technology with a real hope of
• 15:27
  finding the solar siblings because it's
• 15:29
  by analyzing the the spectrum the
• 15:32
  chemical composition of a star uh in
• 15:34
  very great detail. That's how we would
• 15:37
  identify that a star had exactly the
• 15:40
  same chemical composition as the sun and
• 15:42
  could be regarded as likely to be a
• 15:44
  solar sibling.
• 15:46
  >> Okay. We may one day find one of them,
• 15:50
  but who knows? Yeah,
• 15:52
  >> we'll see. Uh, and thank you Slatty
• 15:55
  Bartfast. Um, whatever your real name
• 15:57
  is. That maybe that's it. Um,
• 15:59
  >> could be. Could be.
• 16:00
  >> Thanks. Thanks for the question and and
• 16:02
  thank you for sending me the Babel fish
• 16:03
  so I could read the question. That was
• 16:06
  that was a good idea. Very very good
• 16:08
  idea. This is Space Nuts. Andrew Dunley
• 16:11
  here with Professor Fred Watson.
• 16:14
  Let's take a break from the show to tell
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• 17:54
  >> Okay, we've had a problem here.
• 17:56
  >> This is Houston. Say again, please.
• 17:58
  >> Houston, we had a problem. We had a
• 17:59
  main.
• 18:00
  >> Roger. Main. Okay, stand by 13. We're
• 18:03
  looking at it.
• 18:04
  >> Space nuts. You know, that moment where
• 18:06
  they realized they had a problem on um
• 18:09
  Apollo 13 sounded much better in the
• 18:12
  movie.
• 18:14
  >> It just um Yeah,
• 18:18
  >> you bro you broke up exactly as you were
• 18:21
  saying.
• 18:21
  >> I noticed that and I was going to keep
• 18:23
  talking until you came back, but um
• 18:25
  >> tell me what you said.
• 18:26
  >> I said that that moment where Apollo 13
• 18:29
  realized they had that problem sounded
• 18:32
  much better in the movie.
• 18:35
  Yeah.
• 18:35
  >> Wasn't nearly as dramatic in real life,
• 18:38
  was it?
• 18:39
  >> Well, that's
• 18:39
  >> Well, it was dramatic, but the way they
• 18:41
  announced it.
• 18:42
  >> Absolutely.
• 18:42
  >> Yeah. They they basically just said,
• 18:44
  "Yeah, this button didn't work."
• 18:47
  >> More or less.
• 18:48
  >> Um,
• 18:49
  >> yeah. Epic stuff. I mean, it still gives
• 18:51
  me tingles. Does Apollo 13.
• 18:54
  >> Absolutely. Yeah. Now, Fred, let's move
• 18:57
  on to our third question. This one comes
• 19:00
  from Bejorn.
• 19:02
  >> Good evening, Fred. And Andrew, I have
• 19:06
  to thank you for a fantastic podcast. My
• 19:10
  first choice every evening
• 19:13
  among lots of interesting stuff. It's
• 19:17
  the first one I choose.
• 19:20
  Uh it's regarding the question you had
• 19:22
  about temperature of black holes.
• 19:25
  I must ask you to clarify.
• 19:30
  If material accretes
• 19:33
  close to the end horizon, it's millions
• 19:36
  of degrees hot.
• 19:38
  If I follow the material spiraling
• 19:41
  inwards, it does not suddenly become
• 19:44
  cold when it enters the event horizon.
• 19:46
  Right?
• 19:48
  It's still extremely hot, maybe even
• 19:51
  hotter, even if it's supposedly hard to
• 19:53
  measure.
• 19:54
  because it's hard to get a thermometer
• 19:57
  in there and have a reference.
• 20:00
  But it extremely hot.
• 20:02
  That seems cold to an outside observer
• 20:05
  because it does not radiate anything.
• 20:09
  But maybe it could be clarified somehow.
• 20:13
  It's not magic that it suddenly gets
• 20:15
  cold. It just
• 20:18
  stops emitting. Right.
• 20:22
  Take care. It's Bjon from Goththingberg.
• 20:24
  I love your show.
• 20:26
  >> Thank you, Bjorn. That Babel Fish is
• 20:28
  working well because his English was
• 20:29
  excellent.
• 20:31
  >> He lives in a nice place as well.
• 20:33
  Goththingberg's got a very nice city
• 20:35
  center with a lovely opera house.
• 20:37
  >> Yeah, I haven't been there. In fact, I
• 20:39
  haven't been to Sweden yet, but um yeah,
• 20:42
  it's it's on the wish list. So, we'll
• 20:44
  we'll see how we go.
• 20:45
  >> It's great. Now, he's referring to a
• 20:47
  question that came from Casey in
• 20:49
  Colorado when she was asking about the
• 20:51
  temperature of a of a black hole. Uh, so
• 20:54
  he's basically kind of saying, "Look,
• 20:58
  I understand what you were saying when
• 20:59
  you answered Casey, but now everyone
• 21:01
  thinks they're cold when they're
• 21:04
  probably not cold. They're just not
• 21:05
  emitting anything."
• 21:07
  Is that right?
• 21:08
  >> Yeah, that's that's right. They're cold
• 21:12
  because they're not emitting anything.
• 21:14
  But uh but uh Bjorn's right that you
• 21:18
  know the temperature of the accretion
• 21:21
  disc and and probably the way to look at
• 21:23
  it is the temperature of the event
• 21:24
  horizon is millions of degrees because
• 21:27
  that's where all this stuff is is
• 21:30
  circulating at high speed uh and with
• 21:33
  huge amounts of energy and emitting
• 21:35
  X-rays. um it disappears over the event
• 21:38
  horizon uh at very high temperature and
• 21:42
  presumably within the event horizon it's
• 21:45
  still got that high temperature but then
• 21:48
  it hits the black hole it's sucked in uh
• 21:52
  and if you could measure the temperature
• 21:54
  of the black hole itself you'd find it
• 21:57
  was virtually absolute zero very very
• 22:00
  small temperature
• 22:01
  >> okay
• 22:02
  >> um because it's not emitting anything's
• 22:04
  going in um and it is it is hard to
• 22:09
  imagine and Bjorn mentioned magic and
• 22:11
  that's almost what it is um you know
• 22:14
  stuff that's going in at very high
• 22:15
  temperature but if you could measure the
• 22:17
  black hole itself supposing it stopped
• 22:19
  accreating material and you could then
• 22:21
  measure its temperature it would be
• 22:23
  virtually zero
• 22:25
  >> well well they are so complicated though
• 22:29
  aren't they? I mean, we we we we're
• 22:31
  still learning a lot about um black
• 22:35
  holes and and we we're starting to image
• 22:38
  a few of them. We've got a couple of
• 22:39
  good pickies now, but uh we we
• 22:43
  they are still mesmerizing and
• 22:46
  mystifying because until dark matter
• 22:48
  came along, um we got more questions
• 22:50
  about black holes than anything else.
• 22:52
  they they are the thing that people want
• 22:54
  us to unravel in terms of understanding.
• 22:57
  But um we're I think we're a long way
• 22:59
  away from that at the moment, aren't we?
• 23:01
  >> Um I actually I think you know that we
• 23:05
  know a lot about black holes. Um
• 23:09
  considering that 60 years ago nobody
• 23:12
  believed they existed.
• 23:13
  >> Yeah. Well, the point um and um we've
• 23:17
  observed them. We've actually observed
• 23:19
  the uh radiation coming from the the the
• 23:23
  accretion disc, the region around the
• 23:25
  event horizon. We've we've observed the
• 23:27
  effectively the shadow of the event
• 23:29
  horizon of several black holes now. Uh
• 23:32
  and even detected the polarization of
• 23:34
  the material that's being sucked into
• 23:36
  it. And this is extraordinary stuff.
• 23:38
  These are measurements that really only
• 23:40
  a few years ago would have been thought
• 23:41
  to be impossible, but we're I think
• 23:44
  doing it rather well. So, we're still
• 23:47
  learning about black holes. They are and
• 23:49
  that that's the reason why they're so
• 23:51
  fascinating is that they are completely
• 23:52
  counterintuitive.
• 23:54
  How do you have something that's
• 23:55
  simultaneously at zero and a million
• 23:57
  degrees and that's what you've got? Uh
• 24:01
  so, yeah. So, it's um it it yeah, there
• 24:06
  still very very interesting object.
• 24:08
  >> But, um back to Bjorn's question, the
• 24:12
  temperature is
• 24:15
  zero absolute zero or thereabouts
• 24:18
  because of the fact that it doesn't
• 24:21
  >> it doesn't radiate anything. Yeah.
• 24:23
  Exactly. So, so the the way to imagine
• 24:25
  it I think and this probably puts it
• 24:27
  more succinctly. Yes. While while it's
• 24:30
  accreting, you can't you can't see the
• 24:32
  black hole because it's surrounded by
• 24:33
  this hot material at very high
• 24:36
  temperature that's being swallowed into
• 24:38
  it. But if there was if that supply of
• 24:40
  gas ran out and the black hole stopped
• 24:42
  accreting then you would and you could
• 24:44
  measure its temperature then um it would
• 24:47
  be zero effectively be absolute zero a
• 24:49
  little bit above but not very much.
• 24:51
  >> Okay there you go Bjorn and I'm looking
• 24:54
  at uh photographs of Gottenberg. It's it
• 24:57
  is an absolute beauty of a city isn't
• 25:00
  it? What a lovely part of the world. So
• 25:03
  uh yeah, very lucky. Nice tra
• 25:08
  um thanks buen. Great to hear from you
• 25:10
  uh in Sweden.
• 25:14
  >> Okay, we checked all four systems and
• 25:16
  with the go
• 25:17
  >> space nets
• 25:18
  >> and believe it or not, our next question
• 25:21
  comes from Sweden. Uh does the expansion
• 25:24
  of space mean that the universe gains
• 25:27
  more meters or are the meters becoming
• 25:30
  longer? related to this. Is it space
• 25:33
  only that is expanding or is it space
• 25:36
  time? If so, what's happening uh to the
• 25:40
  time part of it? Is time expanding too?
• 25:43
  What would that mean? Uh thanks for a
• 25:46
  most interesting podcast, Peter from
• 25:49
  uh I'm going to pronounce this
• 25:50
  incorrectly. Falloon in Sweden.
• 25:55
  >> So yeah, hopefully I got that right.
• 25:57
  think my babel my babel fish can't
• 25:59
  translate back into Swed Swedish.
• 26:02
  >> Well, if you put it the other way
• 26:04
  around,
• 26:04
  >> got to put in the other ear.
• 26:06
  >> Yeah, that's right.
• 26:08
  >> That'll do it.
• 26:09
  >> Um, so, uh, yes, uh, that's a great
• 26:13
  question. And so um my view you know the
• 26:16
  intuitive view uh which is based on
• 26:21
  a few years of thinking about this kind
• 26:23
  of thing. Um the me the meters are
• 26:26
  becoming longer. Um and that's sort of
• 26:31
  illustrated by the fact that the
• 26:32
  wavelength of radiation is getting
• 26:34
  longer. Uh you know that radiation had a
• 26:37
  particular wavelength when it was
• 26:39
  emitted. Uh um and as the universe has
• 26:42
  expanded, whatever it's coming from,
• 26:44
  whether it's a distant galaxy or a
• 26:46
  quazar or whatever, uh as the universe
• 26:48
  has expanded, that radiation has been
• 26:50
  stretched, which means that the meat has
• 26:52
  been stretched because the frequency
• 26:54
  remains the same. Uh
• 27:00
  except when you observe it
• 27:02
  >> uh from our vantage point in the depths
• 27:06
  of the universe.
• 27:07
  >> Yeah. Forget about the frequency.
• 27:10
  That's a that's a fury. But the
• 27:12
  wavelength the wavelength stretches. So
• 27:14
  the time the um the length scale is
• 27:18
  increasing. Um in fact there's there's a
• 27:20
  thing called the scale factor of the
• 27:21
  universe. Uh and it's very easy to
• 27:26
  prove. It's one of the most simple
• 27:28
  geometrical equations in cosmology. Uh
• 27:30
  the scale factor of the universe. uh now
• 27:34
  compared with when the light was emitted
• 27:36
  the ratio of the two is equal to 1 over
• 27:37
  1 plus zed uh where zed is the red shift
• 27:40
  of the light that you're measuring and
• 27:42
  so there's this direct link between the
• 27:44
  sort of scale size of the universe which
• 27:46
  is the length of a meter effectively um
• 27:49
  and the red shift that we measure when
• 27:51
  we look in deep into the universe um you
• 27:55
  look as though you got a question now
• 27:57
  I'm confused so what you're basically
• 27:59
  saying in regard to his question was
• 28:02
  that um the meter is expanding. So a
• 28:06
  meter is not a meter.
• 28:08
  >> Well, it's it's still a meter, but it's
• 28:11
  a different meter.
• 28:14
  Okay. Um because the scale factor of the
• 28:18
  universe was less when the light was
• 28:22
  emitted. This is the thing, you know,
• 28:23
  you've got two different reference
• 28:25
  frames here. That's why this stuff gets
• 28:28
  a little bit complicated because in our
• 28:30
  reference frame the meter is longer. But
• 28:33
  if you were traveling along with your
• 28:35
  meter stick uh as it as it sped through
• 28:39
  the universe uh it would be changing in
• 28:42
  length. It would it would sorry appear
• 28:44
  to be the same length.
• 28:46
  Right?
• 28:49
  I'm sorry. This is just
• 28:51
  it's mindbending,
• 28:55
  >> isn't it?
• 28:56
  >> It it bends mine as well. Um, and so
• 29:00
  something similar happens to time, but
• 29:02
  once again, so so we are we're we're
• 29:05
  still inside the universe, but we're
• 29:08
  we're observers from a in a different
• 29:12
  reference frame from when the light was
• 29:15
  emitted. Because that's what we're
• 29:16
  talking about. We're talking about being
• 29:18
  able to measure the expansion of the
• 29:19
  universe through the through the light
• 29:21
  waves.
• 29:23
  So, so and we know that time dilation
• 29:27
  took place. We can we can measure that
• 29:29
  by looking at this rise and fall rates
• 29:32
  of supernovi in the distant universe and
• 29:34
  they actually appear to rise and fall
• 29:36
  slower. So, it is the time uh element of
• 29:40
  that changes as well.
• 29:41
  >> Okay. I think he chose a meter because
• 29:44
  um the meter was defined by uh the
• 29:48
  international system of units as a as
• 29:51
  the length of the path light travels in
• 29:53
  a vacuum during a time inter interval of
• 29:56
  1 299,792,458
• 30:02
  of the second.
• 30:05
  >> Yeah, that's how it's that that's how
• 30:07
  it's defined today. It was originally
• 30:10
  defined as being what was it?
• 30:11
  1/400,000th of the circumference of the
• 30:13
  I can't remember.
• 30:14
  >> Yeah, I can't
• 30:15
  >> something like that.
• 30:16
  >> Yeah.
• 30:16
  >> All right.
• 30:18
  >> Okay. So,
• 30:19
  >> well, no, it would be 140. Uh, yeah.
• 30:22
  Anyway, it was like it was a it was
• 30:24
  related to the circumference of the
• 30:26
  earth.
• 30:27
  >> Can't do the sums anymore. My brain's
• 30:28
  fried today. I don't know why. I mean,
• 30:30
  you're right. I think it's episode 300
• 30:32
  600 is a a relativistic phenomenon
• 30:34
  taking place here.
• 30:35
  >> It it it's just messing us up. I mean,
• 30:37
  if we need a holiday of some kind. Um,
• 30:41
  but anyway, uh, hopefully that helped,
• 30:43
  Peter. I don't know. Uh,
• 30:46
  but, um, I think somewhere in there we
• 30:48
  did answer a question. Thanks for
• 30:50
  sending it in. And and and good to have
• 30:52
  a, um, a very Scandinavian sort of, uh,
• 30:56
  600th episode. So, um, yeah, I mean, we
• 30:58
  we've got Slatty Bfast, we've got Sweden
• 31:02
  a couple of times over, Norway, and then
• 31:04
  South Australia. Uh, okay. Well, no.
• 31:07
  Anyway, close enough. Close enough.
• 31:09
  >> South Australia is not known for its
• 31:11
  fjords, but it is a nice place.
• 31:12
  >> It is a lovely place, except it was
• 31:14
  pouring rain and gale force winds when
• 31:16
  we visited. But anyway, that's the way
• 31:18
  it goes. Uh, thank you, Peter Bjorn,
• 31:20
  Slatty Badfast, and Daryl for sending in
• 31:22
  questions. If you've got questions for
• 31:23
  us, please send them in to us via our
• 31:26
  website, spacenutspodcast.com,
• 31:28
  spacenuts.io.
• 31:30
  uh click on the AMA button which stands
• 31:32
  for ask me anything and send us your
• 31:35
  text or audio questions. Don't forget to
• 31:37
  tell us who you are and where you're
• 31:38
  from. We'd love to hear from you,
• 31:40
  especially if you haven't sent in
• 31:42
  questions before. Uh also, if you'd like
• 31:45
  to help us out, um please, wherever you
• 31:47
  listen to us, uh leave reviews because
• 31:50
  the more reviews the the better. uh the
• 31:53
  the more we move up the the
• 31:56
  relativistic food chain that is podcast
• 31:59
  world and uh we we get more listeners
• 32:02
  perhaps that's that's the aim of the
• 32:04
  game anyway uh if you could do that for
• 32:06
  us that would be great and Fred thank
• 32:08
  you very much nice to chat we'll catch
• 32:10
  you on the next episode
• 32:12
  >> sounds great Andrew uh hope we get our
• 32:14
  breath back before then
• 32:16
  >> yes yes it's been a bit tiring hasn't it
• 32:18
  but uh we got there in the end professor
• 32:20
  Fred Watson astronomer at and he'll be
• 32:23
  back with us next week. Uh Hugh in the
• 32:24
  studio. We thank him too for all the
• 32:26
  work he's done over these last um well
• 32:29
  actually he doesn't turn up for most. So
• 32:31
  the last four episodes that he's been
• 32:33
  with us. Um in fact he couldn't be with
• 32:35
  us today because we told him he could
• 32:37
  have every 600th episode off. And from
• 32:40
  me Andrew Dunley, thanks for your
• 32:42
  company. We'll see you on the next
• 32:44
  episode of Space Nuts. Bye-bye.
• 32:46
  >> Space Nuts.
• 32:47
  >> You've been listening to the Space Nuts
• 32:49
  podcast.
• 32:51
  Available at Apple Podcasts, Spotify,
• 32:54
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• 32:57
  player. You can also stream on demand at
• 32:59
  byes.com. This has been another quality
• 33:02
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