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Time Dilation, Black Hole Mysteries & Cosmic Curiosities | Space Nuts: Astronomy Insights &... · Space News Today

• 0:00
  Hello again. Thanks for joining us. This
• 0:01
  is Space Nuts Q&A edition. My name is
• 0:04
  Andrew Dunley. This will be our last
• 0:06
  official show for 2025. We'll go into a
• 0:09
  short recess and be back with you early
• 0:12
  in the new year. Uh but we've got some
• 0:15
  questions to nail down before any of
• 0:17
  that happens. And we've got a whole
• 0:20
  bunch of topics that seem to have
• 0:22
  stirred the imaginations of uh our
• 0:25
  audience. Uh Andrew wants to know about
• 0:27
  time dilation of stars.
• 0:29
  Uh Adriano is talking black holes
• 0:32
  becoming stars. Uh Ishtto uh is wanting
• 0:36
  to ask about free space.
• 0:40
  H
• 0:41
  I always thought it was expensive
• 0:43
  officially all the space around where we
• 0:45
  live. Y and Ggo red shift and graars. We
• 0:49
  will tackle all of that in this edition
• 0:51
  of Space Nuts.
• 0:53
  >> 15 seconds. Guidance is internal. 10 9
• 0:58
  ignition sequence start.
• 0:59
  >> Space nuts.
• 1:00
  >> 5 4 3 2
• 1:03
  >> 1 2 3 4 5 5 4 3 2 1
• 1:05
  >> Space nuts.
• 1:06
  >> Astronauts report. It feels good.
• 1:09
  >> And here he is again. It's Professor
• 1:11
  Fred Watson, an astronomer at large.
• 1:13
  Hello, Fred.
• 1:15
  >> Hello, Andrew.
• 1:16
  >> Good to see you again.
• 1:18
  >> Fancy seeing you.
• 1:19
  >> Yeah. How odd. How strange.
• 1:21
  >> How strange. Hm. Uh getting ready for
• 1:24
  your Christmas break. I mean, you've
• 1:26
  just come back from a break, so you'd
• 1:27
  be, you know, probably
• 1:31
  feeling rather relaxed. Well, no. Uh
• 1:34
  because only the last six days weren't
• 1:36
  work.
• 1:38
  >> Ah.
• 1:38
  >> Yeah.
• 1:40
  So, um No, that's not quite true because
• 1:42
  we did have some time off with my family
• 1:44
  in Scotland. Um but we did have a proper
• 1:46
  holiday at the end of our trip. But yes,
• 1:48
  we did two months of pretty hard work.
• 1:50
  Ku had a tour in Japan and then uh the
• 1:52
  conference in Ireland and a few other
• 1:54
  things like that that um kept us busy.
• 1:57
  So uh
• 1:58
  >> if you if you want to call international
• 1:59
  travel a job that's you know that's
• 2:02
  fine.
• 2:04
  >> Um
• 2:05
  >> want to call it work.
• 2:07
  >> Um if you Yeah. But when you've got a
• 2:10
  tour group when you got 20 people who
• 2:11
  you were entertained for a month or it's
• 2:15
  actually three and a half weeks. Um it
• 2:18
  is work. Yeah. Yeah. Well, we've got a
• 2:21
  similar problem in the coming week or
• 2:23
  two with four grandchildren that we're
• 2:25
  taking to the co.
• 2:26
  >> Yeah. To be honest, I'd rather have 20
• 2:28
  tourists than four grandchildren.
• 2:30
  Although my grandchildren are now
• 2:32
  totally self-propelled, apart from the
• 2:33
  youngest one, Agie. She's on it. She's
• 2:36
  she's nine months like yesterday
• 2:37
  actually.
• 2:38
  >> Anyway,
• 2:38
  >> anyway, yes,
• 2:41
  >> it's a matter of But we Yeah. So, we The
• 2:44
  bottom line is we will have a relaxing
• 2:46
  end of year break, I hope.
• 2:48
  >> Very good.
• 2:49
  Um, you mentioned Edinburgh. Well, uh,
• 2:51
  our first question comes from Andrew in
• 2:54
  Edinburgh. Uh, he says, "I have a
• 2:56
  two-part question about, uh, the gravity
• 2:58
  and subsequent d time dilation that
• 3:00
  occurs in and around super giant stars.
• 3:03
  If the super giants can collapse into
• 3:05
  black holes, then they must have as much
• 3:08
  or even more mass than the resulting
• 3:10
  black hole just spread over a much
• 3:12
  larger area." Uh, I guess my question
• 3:15
  is, is there significant time dilation
• 3:18
  near these stars or are they simply not
• 3:21
  dense enough to have meaningful amounts
• 3:23
  of time dilation? If they do, it's weird
• 3:26
  that it never comes up. And a slight
• 3:29
  followup would be, what about time
• 3:32
  dilation within the star itself?
• 3:34
  Presumably near the core of these stars,
• 3:37
  the density ramps right up. Does a large
• 3:40
  difference in time dilation within a
• 3:42
  star have any impact on how it behaves?
• 3:45
  Hope that all makes sense. Thanks. Love
• 3:47
  the show. That's Andrew in Edinburgh.
• 3:50
  >> They're great questions. Um um
• 3:55
  I'm just not sure about
• 3:59
  the first sentence. If the super giants
• 4:02
  can collapse into black holes, then they
• 4:05
  must have as much or even more mass than
• 4:08
  the resulting black hole. Yeah. Okay.
• 4:09
  I've read that properly now. Uh just
• 4:11
  spread.
• 4:12
  >> Maybe I didn't read it properly.
• 4:13
  >> No, it's all right. No, it's it's fine.
• 4:15
  Um so, so yeah, Andrew's first question
• 4:18
  is there significant time dilation near
• 4:20
  these stars? And the answer is yes. Uh
• 4:23
  the there would be. Um um it's I mean
• 4:26
  the time dilation in a black hole is so
• 4:30
  great that uh to an outside observer,
• 4:33
  time stops on the event horizon. uh for
• 4:36
  a star because it's it's spread over a
• 4:40
  larger volume of space, the time
• 4:41
  dilation is nowhere near as great.
• 4:43
  >> Uh but time dilation will be something
• 4:46
  that you would have to take into account
• 4:48
  if you had um a spacecraft orbiting near
• 4:51
  a giant star. Um the bottom line is with
• 4:54
  and time dilation is is it's a little
• 4:58
  bit spooky in the sense that to to the
• 5:02
  star itself and to something uh you know
• 5:06
  say you've got something in orbit around
• 5:07
  this star their time ticking away at the
• 5:09
  normal rate the time dilation is only
• 5:11
  what you see from the outside.
• 5:13
  >> So this is this is basically the same as
• 5:15
  we were talking about in the last
• 5:17
  episode regarding Mars. Same problem.
• 5:19
  >> Yes that's right it is the same thing.
• 5:21
  Yeah. So, so time ticks away normally
• 5:25
  for the star, but to to watch it from
• 5:27
  the outside, you basically see time
• 5:30
  ticking away a little bit more slowly.
• 5:32
  Um, so so they they would have time
• 5:35
  dilation. Um, and Andrew is asking
• 5:37
  whether they're not simply not dense
• 5:39
  enough to have a meaningful amount of
• 5:41
  time dilation. And um, I don't think
• 5:44
  that's true. I think that this time
• 5:45
  dilation is significant, especially if
• 5:47
  you're looking at microsconds as we were
• 5:49
  in the last episode. Um yeah. Uh so they
• 5:53
  they do and look you're not talking
• 5:56
  about time dilation of the kind that was
• 5:58
  depicted in Interstellar where you know
• 6:01
  time kind of grinds to a halt almost. Uh
• 6:04
  it's a it's a more modest amount of time
• 6:06
  dilation but it would would actually
• 6:08
  happen. And uh Andrew's follow-up
• 6:11
  question. What about time dilation
• 6:13
  within the star itself? Presumably near
• 6:14
  the core this of these stars the density
• 6:17
  ramps right up. Does a large difference
• 6:19
  in time?
• 6:20
  >> I'm not going in there to find out.
• 6:23
  >> Does a large difference in time dilation
• 6:24
  within a star have any impact on how it
• 6:27
  behaves? Um, and there's a curious thing
• 6:30
  there because as you uh get near the the
• 6:33
  core of an object uh with spherical
• 6:36
  symmetry,
• 6:37
  um your gravitational field gets less
• 6:39
  and less. Uh and in fact, at the center,
• 6:42
  you wouldn't feel any gravity. And
• 6:43
  that's because everything's pulling you
• 6:45
  in the same direction all around. And I
• 6:48
  so I believe that time dilation will
• 6:50
  probably stop in the middle of a star.
• 6:51
  That might be right. So something I've
• 6:53
  never thought about before. Uh maybe
• 6:56
  that's not true because you you're still
• 6:58
  in a gravitational field. The fact that
• 7:00
  it cancels out everywhere. I'll check
• 7:02
  that one out actually and try and
• 7:04
  remember for our first show next year
• 7:06
  because that's a really interesting
• 7:07
  question. Time dilation in the center of
• 7:09
  a star. How does it behave?
• 7:12
  >> Yeah.
• 7:12
  >> Very interesting. But there wouldn't be
• 7:14
  a I I think the bottom line is there
• 7:15
  wouldn't be a a big difference in time
• 7:17
  dilation from one part of a star to
• 7:19
  another. That's that's what I'm trying
• 7:21
  to say.
• 7:21
  >> But he brings up another interesting
• 7:23
  point. You've got time dilation around a
• 7:25
  massive star. Yeah. Then it goes, you
• 7:28
  know, whatever black hole. Uh the time
• 7:32
  dilation changes.
• 7:33
  >> Yes, it does. Because um as it
• 7:35
  collapses, the the gravitational field
• 7:38
  increases. uh in increases in in um sort
• 7:43
  of angle in the sense that you know it's
• 7:44
  a steeper gravitational uh field as you
• 7:48
  get as the black hole collapses. And by
• 7:50
  that I'm thinking of the gravitational
• 7:51
  well you know this dip in in the in the
• 7:54
  trampoline sheet that's the
• 7:55
  gravitational well of an object which
• 7:57
  turns into something like a plug hole.
• 8:00
  Yeah. With water going around it as a
• 8:02
  vortex for a black hole. Uh so that's
• 8:05
  what I mean by the steepness of the
• 8:06
  gravitational field. Um and yes, it is
• 8:09
  so steep that the event horizon
• 8:11
  delineates where the time dilation
• 8:13
  becomes uh such that time appears to
• 8:16
  stop on the surface of the event
• 8:17
  horizon.
• 8:18
  >> Yeah, I've I've seen that demonstration
• 8:20
  done with like a a big rubber sheet and
• 8:23
  they say that right that's that's the
• 8:25
  time space-time continuum. Then they put
• 8:27
  a bowling ball in it and they said
• 8:28
  that's gravity.
• 8:30
  >> Yeah, that's right. Yep. Um I know.
• 8:34
  Yeah,
• 8:36
  >> it's a simple way of explaining it, but
• 8:38
  that's that's what it is. Um I suppose.
• 8:41
  >> Um great questions, Andrew, and I hope
• 8:43
  all is well in Edinburgh. Um Fred's uh
• 8:46
  Fred's home stomping ground. Um
• 8:48
  >> yep.
• 8:49
  >> Yeah, I'll give you his address and he
• 8:50
  can go and rock his roof. This is Bas
• 8:53
  Arts with Andrew Dunley and Professor
• 8:55
  Fred Watson. Uh we have got an audio
• 8:57
  question, Fred. This is from Adriano.
• 9:01
  Hi guys, Adrianiano from Florence in
• 9:03
  Italy. I have my first question about
• 9:05
  black holes. So if I understood
• 9:07
  correctly, a star continue to burn his
• 9:09
  fuel like hydrogen and helium and there
• 9:12
  are nuclear fusions and there is enough
• 9:14
  energy for the star to fight against its
• 9:17
  own gravitational pool. But at some
• 9:20
  point there is not enough fuel and the
• 9:22
  star collapse into a black hole. After
• 9:25
  this the black hole will start to absorb
• 9:28
  material like hydrogen and then it
• 9:30
  should have enough energy enough fuel to
• 9:34
  have nuclear fusions and to fight
• 9:37
  against the gravitational pool but uh so
• 9:40
  why a black hole cannot turn back into a
• 9:43
  star? I'm sure this is not possible but
• 9:45
  I cannot understand why. And also guys
• 9:48
  we had a lot of beautiful updates from
• 9:50
  the princess. Can we also have some
• 9:52
  updates from Fred? Thank you guys.
• 9:54
  Bye-bye,
• 9:55
  >> Adrianiano. Thank you very much. Um Fred
• 9:57
  gave us his update when he got back.
• 10:01
  >> But uh yeah, your point is well made. Um
• 10:04
  Florence, what a beautiful beautiful
• 10:06
  city.
• 10:06
  >> Yeah. Isn't it just
• 10:08
  >> uh we we visited Florence a few years
• 10:09
  ago and uh it was it was
• 10:13
  amazing, but it was also terrible timing
• 10:15
  because it was All Saints weekend, which
• 10:17
  is a 4-day long weekend, and there were
• 10:19
  like tens of thousands of people there.
• 10:22
  You couldn't move. You absolutely
• 10:24
  couldn't move. So, um uh we went to what
• 10:28
  was it called? The Ponttovecia. Um and
• 10:31
  we couldn't get near it. You just
• 10:32
  couldn't. It was um it was insane. Yeah.
• 10:36
  We didn't know until we got there.
• 10:37
  That's what was happening. But yeah, we
• 10:40
  still got to see it. It was a beautiful
• 10:41
  place. And all those amazing statues and
• 10:44
  Galileo got got up close with Galileo.
• 10:47
  >> Very good. Yeah.
• 10:49
  >> Yeah. Yeah. Did you see his um I think
• 10:51
  it's his it's one of his fingers or his
• 10:53
  thumb. I can't remember which is on
• 10:54
  display in the science museum there.
• 10:56
  >> Oh, no. No. Couldn't get near that. Um
• 10:59
  honestly, it was just mayhem. But um
• 11:01
  yeah, understandable though. Um all
• 11:04
  right, so the bottom line with Adriano's
• 11:06
  question is um why can't a black hole
• 11:10
  turned back into a star? Um yeah, I
• 11:13
  would I would think there'd be all sorts
• 11:14
  of reasons why not.
• 11:16
  >> Well, that's right. I think once you've
• 11:18
  turned into a singularity uh as the um
• 11:22
  >> you can't double down. Boom. Boom.
• 11:26
  >> Sorry.
• 11:27
  >> That you took the words out of my mouth.
• 11:30
  >> No, you didn't. Um I mean all bets are
• 11:33
  off basically once you once you've gone
• 11:35
  into a singularity. Uh and so um I think
• 11:39
  you know it's it's a great thought that
• 11:42
  um Adriano's had. I and that it's never
• 11:44
  occurred to me before, but but you know,
• 11:47
  you're talking about hydrogen uh which
• 11:49
  certainly would get sucked into a black
• 11:51
  hole because a lot of the gas clouds
• 11:54
  that um that a black hole um accretion
• 11:57
  disc would would draw in and and suck
• 12:00
  into the center. Uh that um uh that
• 12:04
  that's that's hydrogen. Uh and hydrogen
• 12:07
  is the raw material of stars. Why can't
• 12:09
  nuclear fusion kick in again and drive
• 12:12
  the star back into being a star rather
• 12:14
  than a black hole? And I think the
• 12:16
  answer is in structure. Um so stars have
• 12:20
  quite a complex structure uh to make
• 12:23
  them work uh with the the core with all
• 12:26
  the nuclear burning taking place. Then
• 12:28
  there's a convection zone and then
• 12:30
  there's an sort of outer layer before
• 12:32
  you get to the photosphere. the layer
• 12:33
  that you can see um when you've put
• 12:36
  something into a singularity all
• 12:39
  structure disappears and um it almost
• 12:44
  relates to um an issue that occupied the
• 12:48
  mind of Steven Hawking for a while which
• 12:50
  is that does information get lost when
• 12:53
  when it goes into a black hole
• 12:55
  >> and I think there was some argument with
• 12:58
  another well-known physicist in fact I
• 13:00
  think they had a bet uh which Hawin lost
• 13:03
  Um because the um the the b the I think
• 13:06
  the bottom line was hawking bet that
• 13:08
  information couldn't come out of a black
• 13:10
  hole but somebody proved a theory that
• 13:12
  information could come out of a black
• 13:14
  hole. I think I've got the the right way
• 13:15
  round.
• 13:16
  >> Okay.
• 13:16
  >> But basically it's all completely
• 13:18
  mangled in in terms of you know we don't
• 13:21
  understand the physics of what would
• 13:23
  happen inside a singularity. We just
• 13:25
  have no idea what the physical processes
• 13:27
  would be and they almost certainly would
• 13:29
  rule out hydrogen atoms getting together
• 13:34
  uh and with enough temperature to to to
• 13:36
  produce the nuclear fusion that we see
• 13:38
  in a normal star.
• 13:41
  A a black hole is a very abnormal
• 13:43
  object. Nothing relates to normal in a
• 13:46
  black hole. And so I think that is the
• 13:49
  answer to Adriana's question. uh physics
• 13:52
  physics doesn't work the way it works on
• 13:54
  the outside of a black hole and I think
• 13:55
  that's why we don't see black holes
• 13:57
  turning into stars.
• 13:58
  >> Yeah. Well, there's also the fuel issue
• 14:01
  like um you know the the star has
• 14:03
  collapsed because of fuel depletion has
• 14:06
  it not?
• 14:07
  >> Yes, that's right. But what we're saying
• 14:08
  and what Adriano is saying is that um
• 14:10
  among the stuff that is accreted by the
• 14:13
  black hole when it's sitting there
• 14:15
  gobbling stuff up, a lot of that is
• 14:17
  hydrogen which is the fuel. So, they're
• 14:20
  getting more fuel, but they don't any
• 14:22
  longer have the process to make it turn
• 14:24
  into something that will deliver energy.
• 14:27
  >> I think that's the bottom line.
• 14:28
  >> I get it. I get it. Okay. Um, great
• 14:32
  question though because uh
• 14:35
  we we've
• 14:37
  been talking black holes for I don't
• 14:39
  know how long. Probably since the very
• 14:41
  beginning of the time that this podcast
• 14:44
  began. And I don't think we've ever been
• 14:46
  asked that question before.
• 14:47
  >> No, I think that's right. Yeah.
• 14:50
  >> Says a lot for our for our listeners,
• 14:53
  doesn't it? That they can produce
• 14:55
  questions that we've never had before
• 14:57
  after however many episodes. Is it? It's
• 14:59
  getting on for 500 now.
• 15:01
  >> This is 582.
• 15:02
  >> Oh, 582. Okay.
• 15:04
  >> 582. Yeah.
• 15:05
  >> Right. There you go. Getting on for 600.
• 15:07
  >> I know. It's nuts. I mean, it's
• 15:10
  happening faster because of time
• 15:11
  dilation and the fact that we
• 15:14
  decided to do two episodes a week
• 15:16
  instead of one, but
• 15:19
  I think it's nuts by definition, isn't
• 15:20
  it? Um, I've got a feeling
• 15:23
  >> probably.
• 15:24
  >> Yeah.
• 15:25
  >> Uh, anyway, thank you, Adriano, and hope
• 15:27
  all is well in the beautiful Florence.
• 15:30
  This is Space Nuts with Andrew Dunley
• 15:32
  and Professor Fred Watson.
• 15:36
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  or you can tap on the link in the show
• 17:10
  notes.
• 17:12
  >> 3 2 1
• 17:15
  >> Space nuts.
• 17:17
  >> Our next question doesn't come from
• 17:18
  Italy. It comes from Slovenia. Um Russia
• 17:21
  next door.
• 17:22
  >> Yeah. Uh I am listening to your podcast
• 17:24
  while driving to and from work. Great
• 17:27
  show. I hope you managed to keep control
• 17:29
  because you know this gets a bit crazy
• 17:31
  sometimes. Uh I'm curious about wait for
• 17:33
  it Fred black holes. Uh we know that an
• 17:36
  atom is actually a lot of free space
• 17:38
  where electrons fly around. Uh
• 17:41
  eliminating that we probably probably
• 17:44
  get a neutron star uh with high density.
• 17:47
  But what about a black hole? How does
• 17:49
  this work? Where is the free space uh
• 17:52
  that can be squeezed even further to get
• 17:54
  a black hole uh get black hole material
• 17:56
  and density and to calculate the density
• 17:58
  of the black hole? Would it be a correct
• 18:00
  assumption to take the event horizon as
• 18:03
  the boundary and um based on that
• 18:07
  calculate the volume or is it something
• 18:09
  else? Um thank you. Best regards Isht.
• 18:12
  Um another black hole question. Not
• 18:14
  surprising we get a lot of them.
• 18:17
  >> We do. Yeah. So um the it's a it's a
• 18:21
  great question and I you that's
• 18:23
  absolutely right. An atom is a lot of
• 18:25
  free space empty space
• 18:27
  >> uh with cloud of electrons doing their
• 18:29
  quantum thing. Um if you collapse the
• 18:33
  space down so that only the electrons
• 18:35
  are pushing uh the atoms apart, you've
• 18:37
  got a white dwarf star uh which is
• 18:39
  called electron degenerate. Uh and if
• 18:42
  you get rid of the electrons, then you
• 18:43
  get a neutron star. Exactly as Ishtuk
• 18:45
  says uh with um very high density uh
• 18:49
  where only the neutrons keep the thing
• 18:52
  from collapsing into a black hole. But
• 18:54
  with a black hole um well the free space
• 18:58
  is is is basically disappeared down the
• 19:00
  black hole. Um it's uh it's and in terms
• 19:05
  of its density, you have a definition of
• 19:09
  a black hole. Uh, one of the definitions
• 19:12
  is a point in space with infinite
• 19:14
  density. So, the volume the volume is
• 19:16
  zero. See, Jordi Jordi thinks that as
• 19:18
  well. He does. Gosh, I don't know what's
• 19:21
  happening out there, but
• 19:22
  >> yeah,
• 19:23
  >> I love it.
• 19:25
  >> Oh, we had to hear we had to hear him
• 19:27
  from the last show of the year, didn't
• 19:29
  he?
• 19:29
  >> Last show of the year. That's right.
• 19:32
  >> In full flight.
• 19:34
  >> Um, so yes, so it's a point of infinite
• 19:36
  density. So um it's a comment about
• 19:39
  calculating the density of the black
• 19:41
  hole. Would it be a correct assumption
• 19:42
  to take the event horizon as the
• 19:44
  boundary? Uh no it wouldn't. The event
• 19:47
  horizon is just that imaginary point
• 19:49
  where of no return. Uh and the volume is
• 19:52
  zero. Uh the volume of the black hole is
• 19:54
  zero which is how the the density gets
• 19:57
  infinite because um mass over density
• 20:01
  sorry mass over volume is density. The
• 20:03
  mass is a is a parameter. Um, but the
• 20:06
  volume is zero. I have no idea what's
• 20:08
  happening out there. I drew it with
• 20:10
  Jordy, but he obviously likes this
• 20:11
  conversation.
• 20:12
  >> Yes. Yes, he does. He wants in.
• 20:16
  >> Yeah.
• 20:17
  >> Oh dear. Um, yeah. Look, I still don't
• 20:21
  get
• 20:23
  >> receding into the distance.
• 20:26
  >> Yeah. Probably chasing a snake. Um,
• 20:29
  yeah. Uh,
• 20:30
  >> go ahead, Andrew. No, it's it's hard to
• 20:34
  get your head around something like a
• 20:36
  black hole
• 20:38
  having
• 20:41
  no density.
• 20:45
  >> No volume.
• 20:47
  >> It's got no size. It's got zero
• 20:49
  dimensions.
• 20:50
  >> I mean, we we we give them names based
• 20:53
  on size and yet it has no size. Has no
• 20:56
  volume.
• 20:56
  >> Super massive. Yeah. Well, but it's the
• 20:58
  mass. That's the thing. So the mass is
• 21:00
  defined for a black hole. It's one of
• 21:02
  the properties that they have. The
• 21:03
  there's this thing called the the no
• 21:06
  hair theorem uh which I like very much.
• 21:09
  >> Yeah.
• 21:10
  >> And it's about you know
• 21:11
  >> would that wouldn't
• 21:12
  >> Yeah, that's right. Which there's it's
• 21:15
  about the very few parameters that you
• 21:18
  can get from a black hole. I think it's
• 21:20
  mass, charge and spin. I think that's
• 21:22
  all you know about a black hole. Um
• 21:25
  because the volume's zero and that's why
• 21:27
  the density is zero. Density is mass
• 21:29
  over volume. Volume zero. So the density
• 21:31
  goes to infinite infinity but you can
• 21:34
  vary the mass and that's why we talk
• 21:36
  about super massive black holes and
• 21:37
  intermediate mass black holes and things
• 21:39
  of that sort.
• 21:40
  >> Okay. So what was the answer to the
• 21:43
  question?
• 21:44
  >> Uh no. Right. Right. What was the
• 21:48
  question again? Hang on. Uh yeah. Would
• 21:51
  it be yes would it be correct assumption
• 21:53
  to take the event horizon as a boundary
• 21:55
  and and use that to calculate the
• 21:56
  volume? No. The event horizon is an
• 21:58
  imaginary sphere that um is where the
• 22:02
  thing turns black basically because no
• 22:04
  light can escape
• 22:05
  >> precisely.
• 22:07
  Um hope that helped is uh it's a great
• 22:10
  question.
• 22:11
  >> It is terrific question. Uh just a very
• 22:13
  difficult subject cuz we we just don't
• 22:16
  know a hell of a lot about black holes.
• 22:19
  They're just such a mysterious and
• 22:23
  weird object. And um we we're we're
• 22:26
  still trying to gather information about
• 22:28
  them and they just keep throwing up
• 22:30
  these curve balls at us and not letting
• 22:32
  us in. Not that you want to go in, but
• 22:34
  you know what I mean.
• 22:36
  >> Yes, that's right.
• 22:38
  >> Yeah, quite s.
• 22:39
  >> All right, thanks.
• 22:42
  >> Time to take a break from the show to
• 22:44
  tell you about our sponsor, NordVPN. If
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• 24:08
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  Nuts at the checkout.
• 24:11
  >> Space Nuts.
• 24:12
  >> We have one more question to finish
• 24:15
  things off for 2025 and it it's a real
• 24:19
  European flavor for this episode. This
• 24:21
  is Ggo.
• 24:22
  >> Greetings gentlemen. GGO from Slovakia
• 24:25
  here. I have a question about red
• 24:27
  shifting. Does it have a limit? Is there
• 24:30
  a point beyond which light cannot be
• 24:32
  stretched any further? If so, what
• 24:34
  happens if the light continues to travel
• 24:36
  through expanding space? And the second
• 24:39
  question, could you talk a bit about
• 24:41
  gra? Do you think they might be real?
• 24:44
  Uh, thank you for your time and for the
• 24:46
  great show. Bye.
• 24:48
  >> Thanks, Ggo. Uh, yeah, it's we an
• 24:52
  eclectic mix of nationalities this week.
• 24:55
  Yeah, it's terrific.
• 24:56
  >> Yeah, it's great.
• 24:57
  >> Uh, so two questions he's um he's thrown
• 25:00
  into the mix. Um, yeah. Is there a limit
• 25:03
  on red shift? Um,
• 25:06
  yeah, good one. So,
• 25:09
  uh, yeah, it is a good question. I mean,
• 25:12
  so, so red shift as a term we define as
• 25:19
  being due to the expansion of the
• 25:20
  universe. Um, and it's slightly
• 25:23
  different from the Doppler shift. Uh,
• 25:26
  Doppler shift is something we understand
• 25:28
  well. It's the way the light changes
• 25:30
  wavelength from a moving object. But
• 25:32
  with red shift, we're talking about
• 25:34
  space itself rather than rather than
• 25:36
  objects moving through space. We're
• 25:38
  talking about the way space behaves. Uh
• 25:40
  and so it's a a much more fundamental
• 25:43
  thing than the Doppler shift. So in a
• 25:46
  sense, um there's already a limit to red
• 25:49
  shift. Uh but it's one that is exactly
• 25:55
  related to the age of the universe. Um,
• 25:58
  so and for so what I'm thinking of here
• 26:02
  is the the uh cosmic microwave
• 26:06
  background radiation. That's the wall of
• 26:08
  radiation which corresponds to the
• 26:11
  brightness of the big bang fireball
• 26:15
  which we're still seeing because as we
• 26:17
  look further into space, we look back in
• 26:19
  time. So everywhere in space we see this
• 26:22
  wall of radiation which is now in the
• 26:24
  microwave region of the spectrum which
• 26:26
  is why we call it the cosmic microwave
• 26:28
  background radiation.
• 26:29
  >> Yeah.
• 26:29
  >> And so um it's if I remember rightly
• 26:34
  that is basically the visible flash of
• 26:38
  the big bang because it was it was
• 26:42
  basically a a visible light flash. It's
• 26:46
  the visible flash redshifted by I think
• 26:50
  about 1300 times. So everything in the
• 26:54
  universe must have a that we can observe
• 26:57
  must have a red shift less than that. Uh
• 27:00
  I think 1300 is the the number that
• 27:03
  comes into my mind. I've looked at this
• 27:05
  for a long time. Um but it's visible
• 27:07
  light um whose uh which whose waves have
• 27:11
  been stretched by that amount to give us
• 27:14
  microwaves. So stretched about 1300
• 27:17
  times thereabouts.
• 27:19
  Now um
• 27:21
  as the universe expands and time goes on
• 27:24
  that number will increase not by much
• 27:27
  might become 131 or 135 but as time goes
• 27:31
  on that number is increasing. So
• 27:34
  >> in a sense that's a limit to red shift.
• 27:37
  Uh physically though I don't think there
• 27:39
  is a limit. You could, you know, if if
• 27:41
  you expand the universe, if you're
• 27:43
  talking about 40 billion years into the
• 27:44
  future and the universe is expanding
• 27:46
  more, yes, the cosmic microwave
• 27:48
  background is going to be the cosmic
• 27:50
  long wavelength radio background. Uh,
• 27:53
  and so it's uh it's the the wavelength
• 27:57
  will have stretched more. Uh, so there
• 27:59
  isn't a physical limit, but there is a a
• 28:03
  limit in the real universe. uh simply
• 28:06
  because of the age of the universe. The
• 28:07
  universe hasn't hasn't expanded for long
• 28:10
  enough for the red shift to be more than
• 28:12
  about 1300.
• 28:14
  >> Right. Okay. Yeah. Got it.
• 28:17
  >> Good. What was the other thing? Oh,
• 28:19
  gravity stars.
• 28:20
  >> Oh, grav stars. Yeah, we've had we've
• 28:21
  had questions about gravis stars before
• 28:24
  more than once. Um it it seems to be
• 28:26
  something that sort of captured the
• 28:28
  imagination of uh of people that are so
• 28:31
  interested in astronomy and space
• 28:33
  science. So, I suppose we should start
• 28:36
  by reminding people what a graar is
• 28:39
  supposed to be because I don't think
• 28:40
  we've ever found one.
• 28:42
  >> No, that's correct. Um, I'm I'm going to
• 28:45
  read from uh that font of all knowledge,
• 28:47
  Wikipedia, who I do subscribe to uh
• 28:51
  despite the fact that they keep asking
• 28:52
  me for another subscription. Anyway,
• 28:54
  that's probably because I've got more
• 28:55
  than one username. Never mind. Let me
• 28:58
  read from Wikipedia. In astrophysics,
• 29:01
  the graar which is a blend word of
• 29:04
  gravitational vacuum star is an object
• 29:07
  hypothesized in a 2001 paper by Pavl O
• 29:11
  Mazour and Emil Moah as an alternative
• 29:16
  to the black hole theory. It has the
• 29:19
  usual black hole metric outside of the
• 29:21
  horizon and a metric is just a way of
• 29:23
  describing space but ditter metric
• 29:27
  inside and that's a different one. Don't
• 29:30
  worry about that. A typical grav star is
• 29:32
  as big as London but weighs 10 solar
• 29:36
  masses.
• 29:37
  >> Why?
• 29:38
  >> Yeah. So a neutron star would be about
• 29:40
  the size of London but weigh one solar
• 29:42
  mass basically.
• 29:44
  >> Didn't they find one in a sewer? Um,
• 29:46
  they called it a fatburgg or something.
• 29:48
  >> Fatburgg. That's right. Yeah. Which was
• 29:50
  just about to turn into a graver star.
• 29:52
  Yes. Um, on the horizon there is an
• 29:56
  ultra thin, incredibly tight shell of
• 29:59
  entirely new unique exotic matter named
• 30:03
  Galactic Flubber.
• 30:05
  >> I was close.
• 30:07
  >> You weren't far off. That's right. Which
• 30:09
  is the next thing to a fatburg. Yeah.
• 30:11
  Anyway, continuing to read. This
• 30:13
  solution to the Einstein equations is
• 30:15
  stable and there's no singularities
• 30:18
  which we've just been talking about
• 30:20
  singularities points of zero volume.
• 30:23
  Instead, a grav star is filled with
• 30:25
  either dark energy or with vacuum energy
• 30:28
  but also vacuum
• 30:30
  only the inside one 10 to the 44 times
• 30:33
  denser than the outside. I'm not sure
• 30:36
  how you can have a vacuum that's 10 to
• 30:38
  the 44 times denser than another one,
• 30:40
  but I'll just let that pass. Yes.
• 30:43
  >> Uh, as a bonus, further theoretical
• 30:46
  considerations of grav stars include the
• 30:48
  notion of a nest star, a second graar
• 30:51
  nested within the first one. So, that's
• 30:54
  the technical definition. I bet you're
• 30:56
  no wiser than I am. Um, but the bottom
• 30:59
  line is that um um and I'll read again.
• 31:03
  Mazour and Matahus suggest that the
• 31:06
  violent creation of a grab star might be
• 31:09
  an explanation for the origin of our
• 31:11
  universe and many other universes
• 31:14
  because all the matter from a collapsing
• 31:16
  star would implode through the central
• 31:18
  hole and explode into a new dimension
• 31:20
  and expand forever which would be
• 31:22
  consistent with the con current theories
• 31:25
  regarding the big bang.
• 31:27
  >> Okay. So now that we know what it is.
• 31:31
  >> Yeah. Do you think they exist? And will
• 31:34
  we ever find one?
• 31:35
  >> Uh, no and no, basically. Uh, it's um
• 31:39
  it's a it's a an alternative theory for
• 31:42
  the Big Bang.
• 31:43
  >> Uh, and it's certainly interesting and
• 31:46
  uh I you know I I think um uh GGO's
• 31:50
  asked us to talk about it and now we
• 31:52
  have so so um that's perhaps doing the
• 31:56
  best we can. Um interesting. There's
• 31:59
  there's just one other sentence I might
• 32:01
  like to read. Uh
• 32:04
  uh if I can find it. I've lost it now.
• 32:09
  Oh yeah. The the new dimension that will
• 32:12
  be created in this implosion. The new
• 32:15
  dimension exerts an outward pressure on
• 32:18
  the Bose Einstein condensate layer and
• 32:21
  present prevents it from collapsing
• 32:23
  further. So the Bose Einstein
• 32:26
  condensate, it sounds as though that's
• 32:28
  this thinned crust that it's got rather
• 32:30
  than an event horizon. And a Bose
• 32:33
  Einstein condensate is really
• 32:35
  interesting. I think we've just
• 32:37
  celebrated,
• 32:39
  is it the 30th anniversary of the first
• 32:43
  example of a Bose Einstein condenser
• 32:46
  being produced? I think that's right. I
• 32:48
  think it's 30 years. I think it's 1995.
• 32:51
  Uh what is it? It's a a it's a
• 32:54
  condensation of atoms at very low
• 32:56
  temperature that behave like one quantum
• 32:59
  object. Uh that's the crucial thing. So
• 33:02
  they it's almost like entanglement,
• 33:04
  Andrew, where you've got quantum
• 33:05
  particles being entangled. This is a
• 33:07
  whole bunch of stuff that is so
• 33:09
  entangled it just looks like one quantum
• 33:11
  object and we've we can now create them.
• 33:14
  >> Um so that's what they're saying that
• 33:16
  maybe this thing is made of a Bose
• 33:18
  Einstein condenser. I think this is a
• 33:20
  really good way to end uh the year's uh
• 33:23
  space nuts episode because it is
• 33:25
  completely off the wall and talking
• 33:28
  about stuff that is right at the cutting
• 33:30
  edge of physics which I love
• 33:32
  >> indeed. Uh thank you for your questions
• 33:34
  Ggo and uh hope you're well. Uh good to
• 33:37
  hear from you. You sent in questions
• 33:39
  before so it's nice to catch up. Uh in
• 33:41
  fact I think um I think Isht uh has sent
• 33:45
  questions in before as well. But uh
• 33:47
  yeah, thank you for your questions
• 33:48
  everybody for uh contributing to this
• 33:50
  the final episode of 2025. Keep the
• 33:52
  questions coming in because we're coming
• 33:54
  back
• 33:55
  >> next year and we'll we'll need some
• 33:57
  fresh stuff cuz we're we're down to the
• 33:59
  last one or two um which I didn't use
• 34:02
  because they all came from the same
• 34:03
  source and I like to spread the love a
• 34:05
  bit. So um we'll get into those next
• 34:07
  year. Uh if you go to our website if
• 34:09
  you'd like to send a question in, click
• 34:11
  on the AMA link at the top and you can
• 34:14
  send text and audio questions there. As
• 34:16
  always, please remember to tell us who
• 34:18
  you are and where you're from. While
• 34:20
  you're at on the website, um check out
• 34:22
  how you might be able to support us uh
• 34:24
  through various channels. Um whatever
• 34:27
  you choose or don't choose to, we're not
• 34:29
  going to make you do it. Uh you can
• 34:31
  check out the shop as well. That's
• 34:32
  another way of supporting us. And so on
• 34:35
  and so forth. Um, while I
• 34:37
  >> I think Andrew, while you were talking
• 34:39
  about the questions, I think we've got a
• 34:40
  pending one still from Rusty, which we
• 34:43
  should
• 34:44
  >> I'm sure we'll take it next year.
• 34:46
  >> Yes. Yes, I I recall that. But, um, we I
• 34:50
  thought we'd sit on it till the new year
• 34:51
  because reading the question will
• 34:53
  actually take the pulp of the episode.
• 34:59
  >> Thank you, Andrew. Sorry to interrupt
• 35:00
  you there. That's okay. No, it's okay.
• 35:02
  Um, I just want to say thank you to you,
• 35:04
  Fred. Um,
• 35:06
  And and I should also um thank Jonty
• 35:10
  because he he did a fair chunk of the
• 35:12
  show and we also had our guest presenter
• 35:16
  Heidi while I was away. So thank you to
• 35:18
  Heidi for uh her amazing contribution
• 35:21
  because uh it really saved my uh my back
• 35:24
  because um there was probably no way in
• 35:27
  the world I could have recorded from a
• 35:28
  cruise ship and got away with it. But um
• 35:30
  yeah, fantastic. Uh we've got a great
• 35:32
  team. Um and and you know bring on the
• 35:37
  next uh the next year of Space Nuts. And
• 35:39
  I look I give him a hard time every
• 35:41
  week. I do. But I've got to say thanks
• 35:42
  to Hugh in the studio for his um amazing
• 35:46
  work. It's not just our podcast that he
• 35:48
  looks after. He's got a whole stable of
• 35:50
  them. And uh it's it's basically a
• 35:53
  full-time job trying to run all this. uh
• 35:55
  and you know there's not much money in
• 35:57
  it but uh uh there's certainly joy in
• 36:00
  putting our skills into something uh in
• 36:03
  our semi-retirement um from from radio.
• 36:06
  So um yeah but uh also without the
• 36:09
  audience we would be nothing. So we send
• 36:12
  out our um uh our thanks. We are so
• 36:16
  grateful to have you behind us. And I do
• 36:19
  keep an eye on the audience through the
• 36:21
  Space Nuts podcast group on Facebook
• 36:24
  because they uh they spend a lot of time
• 36:26
  there talking to each other, sharing
• 36:27
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• 36:31
  questions which occasionally we will
• 36:32
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• 36:35
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• 36:37
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• 36:38
  some time now and and you know obviously
• 36:41
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• 36:42
  willing to stick with us. So very much
• 36:45
  appreciated. Uh thank you Fred. Um thank
• 36:49
  you uh Jordy and um we'll talk to you in
• 36:53
  the new year.
• 36:55
  >> Sounds great. Look forward to it Andrew
• 36:56
  and all the very best for the festive
• 36:58
  season to you
• 36:58
  >> and to you and um thank you very much.
• 37:02
  Professor Fred Watson, astronomer at
• 37:03
  large. And from me, Andrew Dunley, have
• 37:05
  a great Christmas, a happy new year.
• 37:07
  We'll see you in 2026. Until then,
• 37:10
  bye-bye.
• 37:11
  >> Space. your Venus to the Space Nuts
• 37:14
  podcast
• 37:16
  >> available at Apple Podcasts, Spotify,
• 37:19
  iHeart Radio, or your favorite podcast
• 37:22
  player. You can also stream on demand at
• 37:24
  byes.com.
• 37:26
  This has been another quality podcast
• 37:28
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