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Stellar Evolutions, Dark Energy Mysteries & Your Questions Answered | Space Nuts: Astronomy... · Space News Today

• 0:00
  Hi there. Thanks for joining us. This is
• 0:02
  a Q&A edition of Space Nuts, uh, where
• 0:04
  we talk astronomy and space science. And
• 0:07
  in the Q&A episode, we answer questions
• 0:09
  from our audience. We've got a whole
• 0:11
  bunch today. Uh, we're going to, uh,
• 0:14
  hear from Jeff, uh, who wants to discuss
• 0:17
  the effect when the sun goes red giant,
• 0:20
  which is going to happen in a couple of
• 0:21
  weeks. Uh, no, it's not. No, it's not.
• 0:24
  Uh, Blue is asking about accretion
• 0:26
  discs. Julian about the expansion of the
• 0:28
  universe and one of our old favorite
• 0:30
  topics from Peter, dark energy. That's
• 0:33
  all coming up in this episode of Space
• 0:35
  Nuts.
• 0:36
  >> 15 seconds. Guidance is internal. 10 9g
• 0:41
  Ignition sequence start.
• 0:42
  >> Space nuts.
• 0:43
  >> 5 4 3 2 1 2 3 4 5 5 4 3 2 1
• 0:48
  >> Space Nuts.
• 0:49
  >> Astronauts report. It feels good.
• 0:53
  And back again to furnish us with his
• 0:55
  wisdom or just to have a couple of lucky
• 0:56
  guesses is Professor Fred Watson,
• 0:58
  astronomer at large. Hello, Fred.
• 1:00
  >> How are you doing, Andrew? Good to see
• 1:02
  you.
• 1:02
  >> Good. And you?
• 1:03
  >> Yes. Uh, firing on all cylinders as far
• 1:06
  as I know.
• 1:07
  >> That's all right. Um, although back then
• 1:09
  they only made them with three Celad.
• 1:13
  >> Oh gosh, I'm in a wicked mood today.
• 1:15
  Sorry about that.
• 1:18
  >> Yep. Okay, we better get on with it now.
• 1:20
  Um, I will put out an appeal like I did
• 1:23
  at the end of the last episode for audio
• 1:25
  questions. Questions in general, but
• 1:28
  audio questions particularly. We are
• 1:29
  desperately short and we don't know why.
• 1:32
  It's just a weird quirk of fate, I
• 1:34
  suppose. But if you would like to send
• 1:36
  us some audio questions, you can do that
• 1:38
  on our website, spacenuts.io,
• 1:41
  and click on the AMA ask me anything tab
• 1:44
  at the top and send us the message. Uh,
• 1:47
  don't forget to tell us who you are and
• 1:48
  where you're from. Our first question,
• 1:50
  Fred, uh, comes from Jeff in Fatville,
• 1:53
  Arkansas in the United States. Hello,
• 1:55
  gentlemen. Well, he's wrong for a start.
• 1:57
  I mean, come on. Um, I happened upon
• 2:00
  your podcast several months ago and
• 2:03
  enjoy it very much. Last month, you
• 2:05
  discussed the thought experiment having
• 2:07
  to do with uh what would happen if the
• 2:09
  rest uh to the rest of the solar system
• 2:11
  if the sun suddenly disappeared. My
• 2:13
  question is a little bit more concrete.
• 2:16
  Uh, in 5 billion years or so, our sun is
• 2:18
  expected to swell into a red giant
• 2:20
  before perhaps collapsing into a white
• 2:22
  dwarf. What will this do to our sun's
• 2:25
  total mass? And what effect will it have
• 2:28
  on the outer planets that survive being
• 2:30
  engulfed? Earth not being one of them,
• 2:32
  as it turns out. I um a follow-up
• 2:35
  question. Uh, are other suns dying
• 2:37
  throughout our galaxy responsible for
• 2:39
  the rogue planets far out in space
• 2:42
  between stars that I've read about?
• 2:44
  Thank you for your time and the
• 2:45
  stimulating discussions you allow me to
• 2:47
  listen into. Thank you Jeff. That's uh
• 2:50
  lovely. Uh a few questions in there
• 2:52
  Fred. Uh so um yes our our sun which we
• 2:55
  have talked about going you know
• 2:58
  ballistic uh in about five billion or so
• 3:02
  years. Uh what happens to the outer
• 3:05
  planets?
• 3:07
  >> Uh that's yes it is a great question. Um
• 3:10
  and I I think the um the sort of
• 3:13
  implicit assumption is that is that the
• 3:15
  inner planets are not going to be around
• 3:18
  >> no which probably will include the earth
• 3:20
  and possibly even Mars. So the um yes
• 3:25
  the process uh towards the end of the
• 3:28
  sun's life and somewhere in the region
• 3:30
  of 3 to 5 billion years I think the
• 3:32
  process starts about three billion years
• 3:35
  hence. So it's a little bit earlier than
• 3:37
  Jeff says. So, um, I hope that's not a
• 3:40
  cause for alarm. Uh, 3 billion at his
• 3:43
  watch, so he's going to have to reset
• 3:45
  that. And that's always a pain.
• 3:47
  >> It is. That's right. Yeah. Um, I the
• 3:51
  other day set dutifully set the timer to
• 3:53
  time down on my uh my phone because I
• 3:56
  had to take things out of the oven and
• 3:59
  um um it got to the end of the time and
• 4:01
  didn't do anything. Just
• 4:03
  >> Oh, I hate it.
• 4:04
  >> It stopped.
• 4:05
  >> I did too.
• 4:06
  My phone suddenly decided to put all
• 4:09
  calls through to voicemail before I can
• 4:11
  even before I even know it's ringing.
• 4:13
  Picked it up the other day and thought,
• 4:15
  why is it vibrating? And then I realized
• 4:16
  my sister was ringing me, but it was
• 4:18
  making no sound. There was no
• 4:20
  indication. It just filtered and and
• 4:22
  when I I I pushed a couple of buttons,
• 4:24
  eventually found her and she said, "Oh
• 4:26
  yeah, I was just listening to your
• 4:28
  message."
• 4:30
  >> Well, there you go. Voicemail,
• 4:32
  >> which is not a problem we'll be really
• 4:34
  worried about in 3 minutes. No, not just
• 4:35
  time because but if anyone knows the
• 4:37
  answer to that, please let me know.
• 4:39
  >> Oh, well, I can tell you the answer. You
• 4:41
  have a smartwatch and that wings as
• 4:44
  well.
• 4:44
  >> Well, I yeah, I don't think I had it on
• 4:47
  at the time. So, ah
• 4:50
  >> anyway um so uh so yes, the inner
• 4:53
  planets get swallowed up um as the sun
• 4:56
  swells. It's it doesn't happen suddenly.
• 4:58
  It is a it's a fairly leisurely process.
• 5:01
  There is a collapse of the core down to
• 5:04
  a white dwarf star which is the end
• 5:07
  product is this white dwarf star which
• 5:10
  is the size of the earth but with quite
• 5:12
  a lot of the mass of the sun still
• 5:14
  tucked in there uh and an outer shell of
• 5:18
  expanding gas and we if we were looking
• 5:20
  at that from the outside we'd call it a
• 5:21
  planetary nebula. So that outer shell of
• 5:25
  gas uh is hot. Uh it's hot enough to
• 5:28
  basically vaporize the the inner
• 5:31
  planets. Uh so but Jeff's question is
• 5:34
  not about that. It's about how do things
• 5:36
  look from the outside. And so the outer
• 5:39
  planets uh interestingly their orbits
• 5:43
  will be perturbed
• 5:45
  um which means changed but maybe not as
• 5:48
  dramatically as you might think because
• 5:51
  um that swelling
• 5:53
  it what it's doing is if you look at the
• 5:55
  center of gravity of all that it's still
• 5:57
  at the center of the solar system uh
• 6:00
  even though the outer layers of the star
• 6:02
  and there's a significant amount of mass
• 6:04
  in that even though most of the mass
• 6:06
  going to be concentrated in the white
• 6:07
  dwarf star, but the outer layers are are
• 6:10
  expanding. You're outside that zone. So
• 6:14
  to you, the center of gravity, center of
• 6:16
  mass of the solar system remains where
• 6:19
  the sun is now. And so the effect on the
• 6:23
  orbits of the planets might not be as
• 6:25
  dramatic as propelling one of them out
• 6:28
  uh to become a rogue planet.
• 6:30
  >> So uh it could be a lot gentler than I
• 6:34
  mean a supernova is different. If it
• 6:36
  explodes, then you're talking about
• 6:38
  dramatic and cataclysmic events that
• 6:41
  would certainly disturb the orbits of
• 6:43
  planets, although some planets seem to
• 6:44
  be able to survive that. We can see
• 6:46
  supernova remnants with with planets
• 6:49
  chugging around. Anyway, this this um
• 6:52
  this scene, this scenario is that uh
• 6:55
  there may still be planets which will be
• 6:57
  outside
• 6:59
  uh the um you know the envelope of the
• 7:02
  of the white of the red giant. Now
• 7:06
  eventually that envelope is going to
• 7:09
  pass the uh pass the the outer planets
• 7:13
  uh and may evaporate them as well uh
• 7:16
  depending on what sort of temperature it
• 7:18
  is. But um the the the so the red giant
• 7:23
  phase the outer planets might be still
• 7:25
  okay and still say it's stable. But once
• 7:27
  it progresses beyond that and you get to
• 7:29
  the planetary nebula stage where the
• 7:31
  outer layer is light years in diameter
• 7:34
  rather than rather than just a few
• 7:36
  hundred million kilometers in diameter
• 7:39
  trillion kilometers in diameter um then
• 7:42
  you're you're probably in trouble if
• 7:44
  you're on the outer planets as well.
• 7:46
  >> Okay. How long does that process take to
• 7:49
  to reach that nebula state?
• 7:50
  >> It's it's it's relatively slow. You're
• 7:52
  talking about billions of years. Wow.
• 7:54
  >> Uh yeah. Uh so I mean there must be
• 8:00
  there must be a collapse phase for the
• 8:02
  nucleus. Uh I'm not an expert on these
• 8:05
  what we call highly evolved stars. Uh
• 8:08
  but as as it goes from red giant to a
• 8:11
  planetary nebula that's when you you you
• 8:14
  change into a white dwarf in the middle
• 8:16
  you've got the nucleus of the star
• 8:17
  collapsing. So these are the end
• 8:19
  products of normal stars. Actually a
• 8:21
  normal star will go through this phase.
• 8:23
  A massive star will become a supernova.
• 8:25
  It will explode.
• 8:27
  >> Wow. Okay. So, you pretty well answered
• 8:30
  everything in one hit. Um, the white
• 8:32
  dwarf will have the same mass as our sun
• 8:35
  at the moment, more or less. So, it
• 8:38
  won't really have an impact on the outer
• 8:39
  planets until after the halo effect over
• 8:42
  billions of years
• 8:44
  >> and probably not enough effect to cause
• 8:46
  rogue planets.
• 8:48
  >> I think that's right. Yes. I mean, I
• 8:49
  think evaporated planets is more likely.
• 8:52
  >> Yeah. Uh um so rogue planets uh are most
• 8:56
  likely formed either
• 9:00
  just formed in in gas clouds collapsing
• 9:03
  into stars. These are things that aren't
• 9:04
  big enough to collapse into stars though
• 9:06
  they become little planets on their own
• 9:09
  or by being ejected because of a
• 9:11
  gravitational influence. You know, if
• 9:13
  you get two planets that pass very close
• 9:15
  to each other or something like that,
• 9:17
  one of them might get booted out of the
• 9:19
  of their solar system.
• 9:21
  >> There you go, Jeff. Hopefully that
• 9:22
  answered all of your questions. Uh we
• 9:24
  like multifaceted questions. It um takes
• 9:27
  us up into all sorts of strange
• 9:29
  directions sometimes. Great to hear from
• 9:30
  you. Hope all is well in Arkansas. Uh
• 9:33
  Fred, our next question comes from Blue.
• 9:36
  He's from London. Uh I have a question
• 9:38
  about accretion discs. Given that
• 9:40
  gravitational time dilation causes time
• 9:42
  to pass much slower near a black hole
• 9:45
  relative to Earth, why does the disc
• 9:47
  appear to move at high speeds to us? Uh,
• 9:50
  I would have expected the material to
• 9:52
  look like it's moving at extreme slow
• 9:55
  motion or even stop moving the closer
• 9:58
  you get to the event horizon. Love the
• 10:00
  show, guys. Thanks, Blue. Um, okay. I
• 10:04
  know you're going to know the answer to
• 10:05
  this one because I think we've had a
• 10:07
  similar question before, but it seems to
• 10:09
  be a an an ongoing theme with black
• 10:12
  holes. Why do we see things that we
• 10:14
  don't think we should see?
• 10:16
  Um so yes, the the accretion disc um is
• 10:19
  actually quite a long way from the black
• 10:21
  hole. Uh and a lot of that swirling
• 10:25
  material is uh ejected from the black
• 10:28
  hole rather than getting sucked in by
• 10:30
  the magnetic fields that the black hole
• 10:32
  generates. It sort of projects um the
• 10:36
  accretion disc material at very high
• 10:37
  velocities to the sort of north and
• 10:39
  south of the of the accretion disc. So
• 10:42
  um there will be a time dilation effect.
• 10:46
  Uh I I should check this uh as to how
• 10:51
  much it would be. But I think the
• 10:54
  overarching point is that you're far
• 10:57
  enough away from the event horizon that
• 11:00
  time dilation in the accretion disc is
• 11:03
  not great. It's not high enough. Uh I
• 11:06
  think it's all a matter of scale rather
• 11:07
  than being a matter of the phenomenon
• 11:09
  which I think Blue's right. I think is
• 11:12
  you know anything that gets close to the
• 11:14
  uh to the black holes event horizon is
• 11:17
  going to show up um a time dilation
• 11:20
  phenomenon.
• 11:21
  >> I suppose it would also depend on what
• 11:23
  kind of black hole it is. I mean some of
• 11:25
  them are massively massive.
• 11:27
  >> The massive Yes, that's right. Uh that's
• 11:29
  correct. Um so um a super massive black
• 11:34
  hole will produce a a bigger a bigger
• 11:36
  phenomenon. Um, I'm just going to try
• 11:40
  looking something up, uh, to see if I
• 11:43
  can put any detail on that. Uh,
• 11:48
  um,
• 11:49
  which I should have done.
• 11:50
  >> I'm helping you a lot here.
• 11:55
  >> Yeah. Okay. All right. Here you are.
• 11:57
  Here's a number for a 10,000 solar mass
• 12:00
  black hole. And that's a bit I mean
• 12:03
  that's the kind of limit um uh of what
• 12:08
  we call an intermediate mass black hole
• 12:10
  something measured in tens of thousands
• 12:12
  of solar masses. Uh for a 10,000 solar
• 12:15
  mass black hole the time dilation of the
• 12:17
  incre the accretion disc inner edge is
• 12:20
  only 22%. So it's what I've said it's
• 12:23
  the scale of the process that makes
• 12:25
  makes the difference.
• 12:28
  Fair enough. Okay. Simple answer really.
• 12:31
  it. Yep. Seems to be
• 12:34
  all right. Thank you, Blue. Hope you're
• 12:36
  going well. Love London. Uh only been
• 12:38
  there twice, I think. Twice. Yes. And uh
• 12:42
  yeah, really enjoyed my time. It's a
• 12:44
  It's a beautiful city. Really love that
• 12:46
  place. I'd go back tomorrow if I could.
• 12:49
  Um thank you, Blue. And um this is Space
• 12:51
  Nuts. You're listening to it with Andrew
• 12:54
  Dunley and Professor Fred Watson.
• 12:58
  We choose to go to the moon in this
• 13:00
  decade and do the other things not
• 13:03
  because they are easy but because they
• 13:05
  are hard.
• 13:06
  >> These nuts.
• 13:08
  >> Next question. Fred. Hey nutters.
• 13:12
  Uh Julian from Bmpton, Ontario, Canada.
• 13:16
  Here. Uh what is causing the expansion
• 13:19
  of the universe? Oh, that old chestnut.
• 13:21
  I mean, uh, are we a black hole eating
• 13:25
  outside matter or are other fundamental
• 13:29
  forces responsible or are the forces
• 13:32
  actually keeping us together? Part two,
• 13:34
  I think we're up to part four actually.
• 13:36
  Part two of this question would be, Fred
• 13:38
  mentioned the universe is expanding
• 13:40
  slower. Does that mean we know exactly
• 13:43
  how fast the universe is expanding and
• 13:45
  does that mean speeds faster than light?
• 13:48
  I hope you all got that. Love the show.
• 13:50
  Thanks, Julian. Oh, he's packed in a lot
• 13:53
  there in three or four sentences. Um,
• 13:58
  what's causing the expansion of the
• 13:59
  universe, Fred? And I know the answer to
• 14:01
  this one.
• 14:03
  >> Um, I think, well, you know, the way we
• 14:07
  usually interpret the big bang is,
• 14:11
  um,
• 14:13
  in the beginning there was nothing and
• 14:15
  then it exploded.
• 14:16
  >> Yeah.
• 14:17
  And that's kind of more or less what it
• 14:21
  was. Uh and so it's we're still seeing
• 14:24
  the aftermath or the effect of that
• 14:26
  explosion in the expansion. So it's
• 14:29
  driven by uh by a you know a some
• 14:34
  fundamental injection of energy at the
• 14:37
  start of the universe. We can kind of
• 14:38
  quantify how much it was. It's a very
• 14:40
  large number. uh that set the expansion
• 14:43
  in motion and it's still going on now.
• 14:47
  Um
• 14:50
  the second bit of the question is the is
• 14:53
  the interesting bit part two.
• 14:55
  >> Uh so so
• 14:57
  let me just yes there are a number of
• 15:00
  parts here. Are we a black hole eating
• 15:02
  outside material? U some scientists have
• 15:06
  suggested that we are within the event
• 15:08
  horizon of a black pole and that's
• 15:10
  what's I've heard
• 15:11
  >> what's causing the expansion of the
• 15:13
  universe. It's a very uh speculative
• 15:15
  idea. Um it's not one I'm very fond of
• 15:18
  because I
• 15:20
  you know I think I think we need a bit
• 15:21
  more hard evidence as to whether that
• 15:24
  black hole is there. Um are we a black
• 15:27
  hole eating outside material? Probably
• 15:29
  not. Or are there other fundamental
• 15:32
  forces responsible? Uh well yes maybe
• 15:34
  and that comes to the second bit of the
• 15:37
  question. Uh it says Fred mentioned the
• 15:40
  universe is expanding slower. That's
• 15:43
  actually not the case. Uh it's expanding
• 15:46
  faster all the time but that
• 15:48
  acceleration is reducing reducing.
• 15:51
  >> Yes.
• 15:51
  >> So the conundrum isn't it?
• 15:54
  >> It is thought expanding at a faster
• 15:56
  rate. Now it's expanding faster slower.
• 16:00
  >> Faster slower. That's right. Um I mean
• 16:02
  before we used to think it was expanding
• 16:04
  at a slower rate. We used to think in
• 16:06
  the in the 70s and 80s that it was
• 16:08
  slowing down. The expansion was slowing
• 16:10
  down and one day they'd be perhaps a
• 16:12
  reversal of the expansion and a big
• 16:14
  crunch. Then in 1998 along came Branch
• 16:17
  Schmidt and Saul Pearlmuta and between
• 16:19
  them they figured out and Adam Ree of
• 16:21
  course the three Nobel Prize winners in
• 16:23
  2011 uh they figured out that actually
• 16:26
  uh the expansion is accelerating.
• 16:29
  >> Um and that's still the case today. That
• 16:32
  is the situation we have. The expansion
• 16:34
  is still is accelerating but there is
• 16:37
  now new evidence uh that suggests that
• 16:41
  the ex the acceleration is reducing. So
• 16:45
  it's not that the expansion of the
• 16:47
  universe is slowing down, it's that the
• 16:49
  acceleration of the expansion of the
• 16:51
  universe is slowing down. Yeah. And
• 16:53
  that's a different matter. So it's still
• 16:56
  >> Yeah. It's still accelerating in its
• 16:58
  expansion. And we attribute that to dark
• 17:02
  energy. Um that is something that
• 17:08
  the new results that suggest that the
• 17:10
  acceleration is slowing down uh actually
• 17:13
  throw a spanner in the works because we
• 17:15
  thought we understood dark energy as uh
• 17:18
  what's called a cos a co cosmological
• 17:20
  constant. A force that basically is
• 17:22
  proportional to the size of space. The
• 17:24
  more space you have, the more e
• 17:26
  expansion force there is a kind of
• 17:28
  pressure if you like of space itself. Uh
• 17:31
  springiness of space.
• 17:33
  >> Um the fact that as time goes on that
• 17:35
  expansion seems to be uh the
• 17:38
  acceleration of the expansion seems to
• 17:40
  be reducing is uh sus it's actually
• 17:44
  suggestive of new physics which might
• 17:46
  mean higher dimensions and all the other
• 17:48
  good stuff that we love talking about on
• 17:50
  space nuts.
• 17:50
  >> Yes. Um indeed. Uh so so um his last bit
• 17:55
  of the question uh does that mean speeds
• 17:57
  faster than light? Uh there will be a
• 18:01
  limit beyond which we can't see the
• 18:03
  universe because it's expanding from us
• 18:07
  faster than light can get to us and
• 18:09
  that's already the case. Uh but we don't
• 18:12
  see that because we see the cosmic
• 18:14
  microwave background radiation first.
• 18:16
  That's the nearer phenomenon. So um yes.
• 18:19
  So uh it's a interesting set of
• 18:22
  questions uh which I I guess
• 18:26
  highlighting some of the mysteries that
• 18:28
  we face with uh uh with our current
• 18:31
  understanding of cosmology.
• 18:33
  >> In truth in truth though we do not know
• 18:35
  how fast the expansion rate currently
• 18:37
  is. We can't put a number on that can
• 18:39
  we?
• 18:40
  >> Yes we can.
• 18:41
  >> Uh that's the Hubble constant. uh um
• 18:45
  which is
• 18:45
  >> yeah we have talked about that before
• 18:47
  and I remember because there's this
• 18:49
  tension that between the Hubble constant
• 18:52
  as we measure it now uh and the Hubble
• 18:54
  constant as we determine it from the
• 18:57
  cosmic microwave background radiation
• 18:59
  called the Hubble tension which may be
• 19:02
  something that really is just to do with
• 19:04
  our measurements. So the Hubble
• 19:05
  constants in odd units in it's in
• 19:08
  kilometers/s per mega par sec. Uh which
• 19:12
  is basically a fancy way of saying we do
• 19:15
  know how fast
• 19:17
  >> it is. Yeah. The the answer is 70 to 74
• 19:20
  kilometers per second per megap.
• 19:23
  >> Yep.
• 19:24
  >> Give or take.
• 19:26
  >> Well that's right. You know, when when
• 19:29
  when I was a young astronomer, I keep
• 19:31
  saying this, back in the 70s, um there
• 19:34
  were two the estimates of that number
• 19:38
  were out by a factor of two. There was
• 19:40
  one group said it's 50 km per second per
• 19:42
  mega par sec. Another group said it's
• 19:44
  100 kilometers/s mega par sec. And look
• 19:46
  what we've got with the Hubble telescope
• 19:48
  and other instruments. We've got
• 19:49
  basically the average of those two. Uh
• 19:52
  which is quite neat really.
• 19:54
  >> But we still got some uncertainty. There
• 19:56
  was also this um conflict, wasn't there,
• 19:58
  that they were they couldn't figure out
• 20:01
  the answer for, but we did a story about
• 20:03
  them figuring out that the conflict was
• 20:05
  actually normal and we, you know, that's
• 20:08
  within acceptable parameters. I think
• 20:11
  >> we did. Yeah. Okay. Uh did we answer all
• 20:14
  his question? I think we did. Yeah. Um
• 20:17
  Oh, I did look up something else. How
• 20:19
  how powerful was the big bang? uh
• 20:21
  greater than 10^ the 68 jewels.
• 20:25
  >> Okay,
• 20:27
  >> that's what you call a bag.
• 20:29
  >> That's a big big big big big bang. But
• 20:32
  we just shortened it to big bang.
• 20:34
  >> Write that down. This is a good number.
• 20:35
  10^ the 68 jewels.
• 20:37
  >> Yes. Yeah. Put that on your calculator
• 20:40
  and see what happens. Um thank Julian.
• 20:44
  Uh hope you're well. Uh let's uh answer
• 20:47
  one more question before we finish up
• 20:48
  today. And this is a question with 47
• 20:50
  parts. Hi, Professor Fred and Andrew
• 20:53
  Peter here from San Diego, California. I
• 20:56
  have a dual question about dark energy.
• 20:59
  My understanding is that dark energy is
• 21:01
  causing our universe to expand. Also, we
• 21:05
  have an observable part of the universe
• 21:07
  where light is able to reach us and an
• 21:09
  unobservable part of the universe. Funny
• 21:11
  how we already talked about this, but
• 21:13
  the these all these questions kind of
• 21:15
  dovetailed. Question one, is it feasible
• 21:18
  that the unobservable part of the
• 21:20
  universe contains enough matter to act
• 21:22
  gravitationally on the observable
• 21:24
  universe, thus causing the expansion?
• 21:27
  And question two, which we'll get back
• 21:28
  to, uh, same question within the context
• 21:31
  of the multisphere. Could universes
• 21:33
  other than our own be gravitationally
• 21:35
  impacting the expansion of our universe?
• 21:38
  Love your show. Keep up the great work.
• 21:40
  Uh, thank you, Peter. Um question one is
• 21:44
  it feasible that the unobservable part
• 21:46
  of our universe contains enough matter
• 21:48
  to act gravitationally on the observable
• 21:51
  observable universe thus causing the
• 21:53
  expansion.
• 21:54
  Um yes once again we've got to unpick uh
• 21:58
  what we mean by the expansion. So um
• 22:02
  Peter says my understanding is that dark
• 22:04
  energy is causing our universe to expand
• 22:07
  and that's not the case as we've just
• 22:08
  described. It's the big bang that caused
• 22:10
  the universe to expand. But dark energy
• 22:12
  is what's causing the expansion to
• 22:14
  accelerate
• 22:15
  >> uh to to get faster.
• 22:17
  >> It's easy to get confused though, isn't
• 22:18
  it? Because
• 22:19
  >> it is absolutely
• 22:21
  >> this is an event with a lot of moving
• 22:22
  parts.
• 22:23
  >> It is. Yes. As you'd expect, it's a
• 22:25
  universe after all.
• 22:27
  >> Yeah.
• 22:27
  >> Um but what Peter says is is correct. Um
• 22:31
  because we, as we've just said, there
• 22:34
  are, you know, there are parts of the
• 22:35
  universe well beyond 13.8 8 billion
• 22:38
  light years. Um, which we can't see
• 22:41
  because what we run into is the cosmic
• 22:42
  microwave background radiation, the
• 22:44
  flash of the big bang. So, we know
• 22:46
  there's universe beyond that, but we
• 22:47
  can't see it.
• 22:49
  >> Um, and Peter's suggestion is it
• 22:52
  feasible that the unobservable part of
• 22:54
  the universe contains enough matter to
• 22:56
  act gravitationally on the observable
• 22:57
  universe. Uh, and as and thus causing
• 23:01
  the expansion. It's actually thus
• 23:02
  causing the acceleration of the
• 23:04
  expansion. Uh that is one of the
• 23:06
  theories that people have looked at
• 23:07
  exactly that that are we in a kind of
• 23:10
  local bubble where the density is low
• 23:13
  compared with what we what we what is
• 23:16
  outside the boundary that we can see
• 23:19
  where the density might be higher and
• 23:21
  hence having a gravitational effect on
• 23:23
  our local bubble. Um it's a it's
• 23:26
  certainly a you know a conjecture that
• 23:28
  is raised by uh by astrophysicists and
• 23:32
  cosmologists. So Peter's on the right
• 23:34
  track there. And then question two, the
• 23:36
  same question within the context of the
• 23:38
  multiverse. Could universes other than
• 23:40
  our own gravitationally be
• 23:42
  gravitationally impacting the expansion
• 23:44
  of our universe? And I think um that is
• 23:47
  also something that's considered. Um,
• 23:50
  one of the reasons why people think
• 23:53
  there might be multiverses,
• 23:55
  uh, it is that gravity itself
• 23:59
  is compared with the other three
• 24:03
  fundamental forces in nature, it is
• 24:06
  incredibly weak. So the fundamental
• 24:09
  forces are the strong and weak nuclear
• 24:11
  forces, things that hold atoms together.
• 24:13
  The electromagnetic force causes
• 24:15
  chemical reactions and and photons so
• 24:18
  that we can talk to each other. Those
• 24:20
  are the three uh which are best known.
• 24:22
  Gravity is the fourth fundamental force.
• 24:25
  But it is gazillions of times weaker
• 24:28
  than the other three and some people
• 24:30
  suggest that maybe that is because it is
• 24:33
  leaking into other universes. Hence the
• 24:36
  idea of a multiverse scenario. But that
• 24:39
  is very speculative. We don't have any
• 24:41
  hard evidence that points towards a
• 24:43
  multiverse. But yes, once again, maybe
• 24:47
  there are gravitational influences
• 24:48
  coming from the outside of our universe,
• 24:50
  whatever that means, because the
• 24:51
  universe by definition means everything
• 24:53
  you can observe or or understand. Um, so
• 24:56
  it is possible. So, um, I think Peter's,
• 24:59
  you know, his questions are are well
• 25:01
  well directed. He's on the right track.
• 25:04
  >> Yeah. Uh I think as you said there's no
• 25:08
  direct evidence whatsoever of
• 25:09
  multiverses but we've said it before
• 25:12
  mathematically
• 25:14
  it's plausible. It
• 25:15
  >> it's possible. That's right. Yeah.
• 25:18
  >> A lot of things are mathematically
• 25:19
  possible that you don't see in reality.
• 25:22
  >> And how much of the universe can we not
• 25:24
  see? Is it like 75% or something?
• 25:28
  >> We have no idea.
• 25:29
  >> We don't know. We don't know how big it
• 25:30
  is.
• 25:30
  >> Could be infinite. We don't know.
• 25:33
  >> Yeah. Gosh,
• 25:33
  >> all we know is what we can see.
• 25:36
  >> It's It's crazy town, isn't it? When you
• 25:38
  >> It is. Yeah, it is. Um That's right.
• 25:41
  It's
• 25:41
  >> keeps you in a job.
• 25:46
  >> Yes, it does. Keeps me in a job. That's
• 25:49
  right.
• 25:50
  >> Yeah. Yeah. But that's, you know, that's
• 25:52
  when the critics come out. We got all
• 25:53
  you BS trying to figure out and ladies,
• 25:56
  what's going on? You've been working on
• 25:58
  it for hundreds of years and you still
• 25:59
  don't know the answer.
• 26:00
  >> Still, we still don't know. Um, the good
• 26:02
  the good news is that node is paying me
• 26:04
  now. So that's all right.
• 26:06
  >> So you don't have to worry about that.
• 26:09
  >> It's a costfree analysis now.
• 26:11
  >> There you go. You get it for free.
• 26:12
  That's right, ladies and gentlemen. This
• 26:14
  all comes to you free.
• 26:15
  >> Yes, it does. Um, all right. So I think
• 26:18
  we covered everything there. Um, thank
• 26:21
  you Peter. Great set of questions all
• 26:23
  up. Some um real intrigue in some of
• 26:25
  those as well which uh is really good.
• 26:28
  Uh, but as I've said many times, uh, we
• 26:31
  need some more questions. So, if you can
• 26:32
  get online to our website and click on
• 26:34
  the ask me anything tab at the top of
• 26:36
  our, uh, page, uh, send us text or audio
• 26:40
  questions. We certainly could use some
• 26:42
  more audio questions. We get a lot from
• 26:44
  people who might ask 10 at a time.
• 26:46
  Obviously, we can't run them all
• 26:49
  consecutively, otherwise no one else
• 26:50
  gets a bite. But, uh, if you've thought
• 26:52
  about asking a question and you haven't
• 26:54
  got around to it yet, don't be scared.
• 26:56
  We don't bite. Well, we do bite, but
• 26:58
  don't worry about that. It's harmless.
• 27:00
  We're not venomous. Uh, but you can send
• 27:03
  it in through spaceodcast.com
• 27:05
  or spacenuts.io
• 27:08
  and click on that tab and uh send us
• 27:10
  your question or just a comment. I mean,
• 27:12
  if you want to add a comment, we can
• 27:14
  throw that into the show. It's nice to
• 27:16
  have all these different voices on the
• 27:18
  air. Uh, so yeah, send them into us.
• 27:21
  Don't forget to tell us who you are and
• 27:22
  where you're from. I think I've already
• 27:23
  said that. Uh, we are done, Fred. Thank
• 27:25
  you so very very much.
• 27:28
  >> It's a great pleasure, Andrew. And um I
• 27:30
  hope we'll do it again sometime.
• 27:31
  >> I hope so too. Maybe in a week, maybe
• 27:33
  more, maybe less. You just, you know,
• 27:35
  it's all all to do withuling
• 27:38
  and availability and what our wives are
• 27:42
  doing at any particular time. That's the
• 27:43
  most significant factor.
• 27:45
  >> Thanks, Fred. We'll see you soon.
• 27:47
  >> Cheers for now. Bye-bye.
• 27:49
  >> Uh Professor Fred Watson, astronomer at
• 27:51
  large. Thanks to Hugh in the studio who
• 27:53
  couldn't be with us today because he's
• 27:55
  unobservable.
• 27:57
  And from me, Andrew Dunley, thanks for
• 27:59
  your company. See you on the next
• 28:01
  episode of Space Nuts. Bye-bye.
• 28:03
  >> Space Nuts.
• 28:04
  >> You've been listening to the Space Nuts
• 28:06
  podcast.
• 28:08
  >> Available at Apple Podcasts, Spotify,
• 28:11
  iHeart Radio, or your favorite podcast
• 28:14
  player. You can also stream on demand at
• 28:16
  byes.com. This has been another quality
• 28:19
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