Cosmic Q&A: Red Giants, Accretion Disks, and Dark Energy
In this captivating Q&A episode of Space Nuts , hosts Andrew Dunkley and Professor Fred Watson tackle a variety of listener questions that span the cosmos. From the fate of our Sun as it becomes a red giant to the mysteries of dark energy, this episode is a treasure trove of astronomical insights and engaging discussions.
Episode Highlights:
- The Fate of Our Sun: Jeff from Arkansas asks about the implications of the Sun swelling into a red giant in approximately 5 billion years. Andrew and Fred explain the process and its potential effects on the outer planets, addressing concerns about rogue planets and gravitational influences.
- Understanding Accretion Disks: Blue from London inquires about the apparent high-speed motion of material in accretion disks around black holes despite gravitational time dilation. The hosts clarify the dynamics at play and the distances involved in these cosmic phenomena.
- Expanding Universe Mysteries: Julian from Canada poses questions about the expansion of the universe and its acceleration. Andrew and Fred dive into the complexities of dark energy and the Hubble constant, shedding light on current theories and ongoing research.
- Dark Energy and the Multiverse: Peter from Sandy Kaye explores the possibility of unseen matter in the universe affecting expansion and whether other universes could influence ours. The discussion delves into speculative theories and the nature of gravity.
For more Space Nuts, including our continuously updating newsfeed and to listen to all our episodes, visit our website. (https://www.spacenutspodcast.com/) Follow us on social media at SpaceNutsPod on Facebook, Instagram, and more. We love engaging with our community, so be sure to drop us a message or comment on your favorite platform.
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Stay curious, keep looking up, and join us next time for more stellar insights and cosmic wonders. Until then, clear skies and happy stargazing.
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Episode link: https://play.headliner.app/episode/32214243?utm_source=youtube
00:00:00 --> 00:00:02 Hi there. Thanks for joining us. This is
00:00:02 --> 00:00:04 a Q&A edition of Space Nuts, uh, where
00:00:04 --> 00:00:07 we talk astronomy and space science. And
00:00:07 --> 00:00:09 in the Q&A episode, we answer questions
00:00:09 --> 00:00:11 from our audience. We've got a whole
00:00:11 --> 00:00:14 bunch today. Uh, we're going to, uh,
00:00:14 --> 00:00:17 hear from Jeff, uh, who wants to discuss
00:00:17 --> 00:00:20 the effect when the sun goes red giant,
00:00:20 --> 00:00:21 which is going to happen in a couple of
00:00:21 --> 00:00:24 weeks. Uh, no, it's not. No, it's not.
00:00:24 --> 00:00:26 Uh, Blue is asking about accretion
00:00:26 --> 00:00:28 discs. Julian about the expansion of the
00:00:28 --> 00:00:30 universe and one of our old favorite
00:00:30 --> 00:00:33 topics from Peter, dark energy. That's
00:00:33 --> 00:00:35 all coming up in this episode of Space
00:00:35 --> 00:00:36 Nuts.
00:00:36 --> 00:00:41 >> 15 seconds. Guidance is internal. 10 9g
00:00:41 --> 00:00:42 Ignition sequence start.
00:00:42 --> 00:00:43 >> Space nuts.
00:00:43 --> 00:00:48 >> 5 4 3 2 1 2 3 4 5 5 4 3 2 1
00:00:48 --> 00:00:49 >> Space Nuts.
00:00:49 --> 00:00:53 >> Astronauts report. It feels good.
00:00:53 --> 00:00:55 And back again to furnish us with his
00:00:55 --> 00:00:56 wisdom or just to have a couple of lucky
00:00:56 --> 00:00:58 guesses is Professor Fred Watson,
00:00:58 --> 00:01:00 astronomer at large. Hello, Fred.
00:01:00 --> 00:01:02 >> How are you doing, Andrew? Good to see
00:01:02 --> 00:01:02 you.
00:01:02 --> 00:01:03 >> Good. And you?
00:01:03 --> 00:01:06 >> Yes. Uh, firing on all cylinders as far
00:01:06 --> 00:01:07 as I know.
00:01:07 --> 00:01:09 >> That's all right. Um, although back then
00:01:09 --> 00:01:13 they only made them with three Celad.
00:01:13 --> 00:01:15 >> Oh gosh, I'm in a wicked mood today.
00:01:15 --> 00:01:18 Sorry about that.
00:01:18 --> 00:01:20 >> Yep. Okay, we better get on with it now.
00:01:20 --> 00:01:23 Um, I will put out an appeal like I did
00:01:23 --> 00:01:25 at the end of the last episode for audio
00:01:25 --> 00:01:27 questions. Questions in general, but
00:01:28 --> 00:01:29 audio questions particularly. We are
00:01:29 --> 00:01:32 desperately short and we don't know why.
00:01:32 --> 00:01:34 It's just a weird quirk of fate, I
00:01:34 --> 00:01:36 suppose. But if you would like to send
00:01:36 --> 00:01:38 us some audio questions, you can do that
00:01:38 --> 00:01:41 on our website, spacenuts.io,
00:01:41 --> 00:01:44 and click on the AMA ask me anything tab
00:01:44 --> 00:01:47 at the top and send us the message. Uh,
00:01:47 --> 00:01:48 don't forget to tell us who you are and
00:01:48 --> 00:01:50 where you're from. Our first question,
00:01:50 --> 00:01:53 Fred, uh, comes from Jeff in Fatville,
00:01:53 --> 00:01:55 Arkansas in the United States. Hello,
00:01:55 --> 00:01:57 gentlemen. Well, he's wrong for a start.
00:01:57 --> 00:02:00 I mean, come on. Um, I happened upon
00:02:00 --> 00:02:03 your podcast several months ago and
00:02:03 --> 00:02:05 enjoy it very much. Last month, you
00:02:05 --> 00:02:07 discussed the thought experiment having
00:02:07 --> 00:02:09 to do with uh what would happen if the
00:02:09 --> 00:02:11 rest uh to the rest of the solar system
00:02:11 --> 00:02:13 if the sun suddenly disappeared. My
00:02:13 --> 00:02:15 question is a little bit more concrete.
00:02:16 --> 00:02:18 Uh, in 5 billion years or so, our sun is
00:02:18 --> 00:02:20 expected to swell into a red giant
00:02:20 --> 00:02:22 before perhaps collapsing into a white
00:02:22 --> 00:02:25 dwarf. What will this do to our sun's
00:02:25 --> 00:02:28 total mass? And what effect will it have
00:02:28 --> 00:02:30 on the outer planets that survive being
00:02:30 --> 00:02:32 engulfed? Earth not being one of them,
00:02:32 --> 00:02:35 as it turns out. I um a follow-up
00:02:35 --> 00:02:37 question. Uh, are other suns dying
00:02:37 --> 00:02:39 throughout our galaxy responsible for
00:02:39 --> 00:02:41 the rogue planets far out in space
00:02:42 --> 00:02:43 between stars that I've read about?
00:02:44 --> 00:02:45 Thank you for your time and the
00:02:45 --> 00:02:47 stimulating discussions you allow me to
00:02:47 --> 00:02:50 listen into. Thank you Jeff. That's uh
00:02:50 --> 00:02:52 lovely. Uh a few questions in there
00:02:52 --> 00:02:55 Fred. Uh so um yes our our sun which we
00:02:55 --> 00:02:58 have talked about going you know
00:02:58 --> 00:03:02 ballistic uh in about five billion or so
00:03:02 --> 00:03:05 years. Uh what happens to the outer
00:03:05 --> 00:03:07 planets?
00:03:07 --> 00:03:09 >> Uh that's yes it is a great question. Um
00:03:10 --> 00:03:13 and I I think the um the sort of
00:03:13 --> 00:03:15 implicit assumption is that is that the
00:03:15 --> 00:03:18 inner planets are not going to be around
00:03:18 --> 00:03:20 >> no which probably will include the earth
00:03:20 --> 00:03:25 and possibly even Mars. So the um yes
00:03:25 --> 00:03:28 the process uh towards the end of the
00:03:28 --> 00:03:30 sun's life and somewhere in the region
00:03:30 --> 00:03:32 of 3 to 5 billion years I think the
00:03:32 --> 00:03:35 process starts about three billion years
00:03:35 --> 00:03:37 hence. So it's a little bit earlier than
00:03:37 --> 00:03:40 Jeff says. So, um, I hope that's not a
00:03:40 --> 00:03:43 cause for alarm. Uh, 3 billion at his
00:03:43 --> 00:03:45 watch, so he's going to have to reset
00:03:45 --> 00:03:47 that. And that's always a pain.
00:03:47 --> 00:03:51 >> It is. That's right. Yeah. Um, I the
00:03:51 --> 00:03:53 other day set dutifully set the timer to
00:03:53 --> 00:03:56 time down on my uh my phone because I
00:03:56 --> 00:03:59 had to take things out of the oven and
00:03:59 --> 00:04:01 um um it got to the end of the time and
00:04:01 --> 00:04:03 didn't do anything. Just
00:04:03 --> 00:04:04 >> Oh, I hate it.
00:04:04 --> 00:04:05 >> It stopped.
00:04:05 --> 00:04:06 >> I did too.
00:04:06 --> 00:04:09 My phone suddenly decided to put all
00:04:09 --> 00:04:11 calls through to voicemail before I can
00:04:11 --> 00:04:13 even before I even know it's ringing.
00:04:13 --> 00:04:15 Picked it up the other day and thought,
00:04:15 --> 00:04:16 why is it vibrating? And then I realized
00:04:16 --> 00:04:18 my sister was ringing me, but it was
00:04:18 --> 00:04:19 making no sound. There was no
00:04:20 --> 00:04:22 indication. It just filtered and and
00:04:22 --> 00:04:24 when I I I pushed a couple of buttons,
00:04:24 --> 00:04:26 eventually found her and she said, "Oh
00:04:26 --> 00:04:28 yeah, I was just listening to your
00:04:28 --> 00:04:30 message."
00:04:30 --> 00:04:32 >> Well, there you go. Voicemail,
00:04:32 --> 00:04:33 >> which is not a problem we'll be really
00:04:34 --> 00:04:35 worried about in 3 minutes. No, not just
00:04:35 --> 00:04:37 time because but if anyone knows the
00:04:37 --> 00:04:39 answer to that, please let me know.
00:04:39 --> 00:04:41 >> Oh, well, I can tell you the answer. You
00:04:41 --> 00:04:43 have a smartwatch and that wings as
00:04:44 --> 00:04:44 well.
00:04:44 --> 00:04:47 >> Well, I yeah, I don't think I had it on
00:04:47 --> 00:04:50 at the time. So, ah
00:04:50 --> 00:04:53 >> anyway um so uh so yes, the inner
00:04:53 --> 00:04:56 planets get swallowed up um as the sun
00:04:56 --> 00:04:58 swells. It's it doesn't happen suddenly.
00:04:58 --> 00:05:01 It is a it's a fairly leisurely process.
00:05:01 --> 00:05:04 There is a collapse of the core down to
00:05:04 --> 00:05:07 a white dwarf star which is the end
00:05:07 --> 00:05:10 product is this white dwarf star which
00:05:10 --> 00:05:12 is the size of the earth but with quite
00:05:12 --> 00:05:14 a lot of the mass of the sun still
00:05:14 --> 00:05:17 tucked in there uh and an outer shell of
00:05:18 --> 00:05:20 expanding gas and we if we were looking
00:05:20 --> 00:05:21 at that from the outside we'd call it a
00:05:21 --> 00:05:25 planetary nebula. So that outer shell of
00:05:25 --> 00:05:28 gas uh is hot. Uh it's hot enough to
00:05:28 --> 00:05:31 basically vaporize the the inner
00:05:31 --> 00:05:34 planets. Uh so but Jeff's question is
00:05:34 --> 00:05:36 not about that. It's about how do things
00:05:36 --> 00:05:39 look from the outside. And so the outer
00:05:39 --> 00:05:43 planets uh interestingly their orbits
00:05:43 --> 00:05:45 will be perturbed
00:05:45 --> 00:05:48 um which means changed but maybe not as
00:05:48 --> 00:05:51 dramatically as you might think because
00:05:51 --> 00:05:53 um that swelling
00:05:53 --> 00:05:55 it what it's doing is if you look at the
00:05:55 --> 00:05:57 center of gravity of all that it's still
00:05:57 --> 00:06:00 at the center of the solar system uh
00:06:00 --> 00:06:02 even though the outer layers of the star
00:06:02 --> 00:06:04 and there's a significant amount of mass
00:06:04 --> 00:06:05 in that even though most of the mass
00:06:06 --> 00:06:07 going to be concentrated in the white
00:06:07 --> 00:06:10 dwarf star, but the outer layers are are
00:06:10 --> 00:06:14 expanding. You're outside that zone. So
00:06:14 --> 00:06:16 to you, the center of gravity, center of
00:06:16 --> 00:06:19 mass of the solar system remains where
00:06:19 --> 00:06:23 the sun is now. And so the effect on the
00:06:23 --> 00:06:25 orbits of the planets might not be as
00:06:25 --> 00:06:28 dramatic as propelling one of them out
00:06:28 --> 00:06:30 uh to become a rogue planet.
00:06:30 --> 00:06:34 >> So uh it could be a lot gentler than I
00:06:34 --> 00:06:36 mean a supernova is different. If it
00:06:36 --> 00:06:38 explodes, then you're talking about
00:06:38 --> 00:06:41 dramatic and cataclysmic events that
00:06:41 --> 00:06:43 would certainly disturb the orbits of
00:06:43 --> 00:06:44 planets, although some planets seem to
00:06:44 --> 00:06:46 be able to survive that. We can see
00:06:46 --> 00:06:49 supernova remnants with with planets
00:06:49 --> 00:06:52 chugging around. Anyway, this this um
00:06:52 --> 00:06:55 this scene, this scenario is that uh
00:06:55 --> 00:06:57 there may still be planets which will be
00:06:57 --> 00:06:59 outside
00:06:59 --> 00:07:02 uh the um you know the envelope of the
00:07:02 --> 00:07:06 of the white of the red giant. Now
00:07:06 --> 00:07:09 eventually that envelope is going to
00:07:09 --> 00:07:13 pass the uh pass the the outer planets
00:07:13 --> 00:07:16 uh and may evaporate them as well uh
00:07:16 --> 00:07:18 depending on what sort of temperature it
00:07:18 --> 00:07:23 is. But um the the the so the red giant
00:07:23 --> 00:07:25 phase the outer planets might be still
00:07:25 --> 00:07:27 okay and still say it's stable. But once
00:07:27 --> 00:07:29 it progresses beyond that and you get to
00:07:29 --> 00:07:31 the planetary nebula stage where the
00:07:31 --> 00:07:34 outer layer is light years in diameter
00:07:34 --> 00:07:36 rather than rather than just a few
00:07:36 --> 00:07:39 hundred million kilometers in diameter
00:07:39 --> 00:07:42 trillion kilometers in diameter um then
00:07:42 --> 00:07:44 you're you're probably in trouble if
00:07:44 --> 00:07:46 you're on the outer planets as well.
00:07:46 --> 00:07:49 >> Okay. How long does that process take to
00:07:49 --> 00:07:50 to reach that nebula state?
00:07:50 --> 00:07:52 >> It's it's it's relatively slow. You're
00:07:52 --> 00:07:54 talking about billions of years. Wow.
00:07:54 --> 00:07:59 >> Uh yeah. Uh so I mean there must be
00:08:00 --> 00:08:02 there must be a collapse phase for the
00:08:02 --> 00:08:05 nucleus. Uh I'm not an expert on these
00:08:05 --> 00:08:08 what we call highly evolved stars. Uh
00:08:08 --> 00:08:11 but as as it goes from red giant to a
00:08:11 --> 00:08:14 planetary nebula that's when you you you
00:08:14 --> 00:08:16 change into a white dwarf in the middle
00:08:16 --> 00:08:17 you've got the nucleus of the star
00:08:17 --> 00:08:19 collapsing. So these are the end
00:08:19 --> 00:08:21 products of normal stars. Actually a
00:08:21 --> 00:08:23 normal star will go through this phase.
00:08:23 --> 00:08:25 A massive star will become a supernova.
00:08:25 --> 00:08:27 It will explode.
00:08:27 --> 00:08:30 >> Wow. Okay. So, you pretty well answered
00:08:30 --> 00:08:32 everything in one hit. Um, the white
00:08:32 --> 00:08:35 dwarf will have the same mass as our sun
00:08:35 --> 00:08:38 at the moment, more or less. So, it
00:08:38 --> 00:08:39 won't really have an impact on the outer
00:08:39 --> 00:08:42 planets until after the halo effect over
00:08:42 --> 00:08:44 billions of years
00:08:44 --> 00:08:46 >> and probably not enough effect to cause
00:08:46 --> 00:08:48 rogue planets.
00:08:48 --> 00:08:49 >> I think that's right. Yes. I mean, I
00:08:49 --> 00:08:52 think evaporated planets is more likely.
00:08:52 --> 00:08:56 >> Yeah. Uh um so rogue planets uh are most
00:08:56 --> 00:09:00 likely formed either
00:09:00 --> 00:09:03 just formed in in gas clouds collapsing
00:09:03 --> 00:09:04 into stars. These are things that aren't
00:09:04 --> 00:09:06 big enough to collapse into stars though
00:09:06 --> 00:09:09 they become little planets on their own
00:09:09 --> 00:09:11 or by being ejected because of a
00:09:11 --> 00:09:13 gravitational influence. You know, if
00:09:13 --> 00:09:15 you get two planets that pass very close
00:09:15 --> 00:09:17 to each other or something like that,
00:09:17 --> 00:09:19 one of them might get booted out of the
00:09:19 --> 00:09:21 of their solar system.
00:09:21 --> 00:09:22 >> There you go, Jeff. Hopefully that
00:09:22 --> 00:09:24 answered all of your questions. Uh we
00:09:24 --> 00:09:27 like multifaceted questions. It um takes
00:09:27 --> 00:09:29 us up into all sorts of strange
00:09:29 --> 00:09:30 directions sometimes. Great to hear from
00:09:30 --> 00:09:33 you. Hope all is well in Arkansas. Uh
00:09:33 --> 00:09:36 Fred, our next question comes from Blue.
00:09:36 --> 00:09:38 He's from London. Uh I have a question
00:09:38 --> 00:09:40 about accretion discs. Given that
00:09:40 --> 00:09:42 gravitational time dilation causes time
00:09:42 --> 00:09:45 to pass much slower near a black hole
00:09:45 --> 00:09:47 relative to Earth, why does the disc
00:09:47 --> 00:09:50 appear to move at high speeds to us? Uh,
00:09:50 --> 00:09:52 I would have expected the material to
00:09:52 --> 00:09:55 look like it's moving at extreme slow
00:09:55 --> 00:09:58 motion or even stop moving the closer
00:09:58 --> 00:10:00 you get to the event horizon. Love the
00:10:00 --> 00:10:04 show, guys. Thanks, Blue. Um, okay. I
00:10:04 --> 00:10:05 know you're going to know the answer to
00:10:05 --> 00:10:07 this one because I think we've had a
00:10:07 --> 00:10:09 similar question before, but it seems to
00:10:09 --> 00:10:12 be a an an ongoing theme with black
00:10:12 --> 00:10:13 holes. Why do we see things that we
00:10:14 --> 00:10:16 don't think we should see?
00:10:16 --> 00:10:19 Um so yes, the the accretion disc um is
00:10:19 --> 00:10:21 actually quite a long way from the black
00:10:21 --> 00:10:25 hole. Uh and a lot of that swirling
00:10:25 --> 00:10:28 material is uh ejected from the black
00:10:28 --> 00:10:30 hole rather than getting sucked in by
00:10:30 --> 00:10:32 the magnetic fields that the black hole
00:10:32 --> 00:10:35 generates. It sort of projects um the
00:10:36 --> 00:10:37 accretion disc material at very high
00:10:37 --> 00:10:39 velocities to the sort of north and
00:10:39 --> 00:10:42 south of the of the accretion disc. So
00:10:42 --> 00:10:46 um there will be a time dilation effect.
00:10:46 --> 00:10:51 Uh I I should check this uh as to how
00:10:51 --> 00:10:54 much it would be. But I think the
00:10:54 --> 00:10:57 overarching point is that you're far
00:10:57 --> 00:11:00 enough away from the event horizon that
00:11:00 --> 00:11:03 time dilation in the accretion disc is
00:11:03 --> 00:11:05 not great. It's not high enough. Uh I
00:11:06 --> 00:11:07 think it's all a matter of scale rather
00:11:07 --> 00:11:09 than being a matter of the phenomenon
00:11:09 --> 00:11:12 which I think Blue's right. I think is
00:11:12 --> 00:11:14 you know anything that gets close to the
00:11:14 --> 00:11:17 uh to the black holes event horizon is
00:11:17 --> 00:11:20 going to show up um a time dilation
00:11:20 --> 00:11:21 phenomenon.
00:11:21 --> 00:11:23 >> I suppose it would also depend on what
00:11:23 --> 00:11:25 kind of black hole it is. I mean some of
00:11:25 --> 00:11:27 them are massively massive.
00:11:27 --> 00:11:29 >> The massive Yes, that's right. Uh that's
00:11:29 --> 00:11:34 correct. Um so um a super massive black
00:11:34 --> 00:11:36 hole will produce a a bigger a bigger
00:11:36 --> 00:11:40 phenomenon. Um, I'm just going to try
00:11:40 --> 00:11:43 looking something up, uh, to see if I
00:11:43 --> 00:11:48 can put any detail on that. Uh,
00:11:48 --> 00:11:49 um,
00:11:49 --> 00:11:50 which I should have done.
00:11:50 --> 00:11:55 >> I'm helping you a lot here.
00:11:55 --> 00:11:57 >> Yeah. Okay. All right. Here you are.
00:11:57 --> 00:12:00 Here's a number for a 10 solar mass
00:12:00 --> 00:12:03 black hole. And that's a bit I mean
00:12:03 --> 00:12:08 that's the kind of limit um uh of what
00:12:08 --> 00:12:10 we call an intermediate mass black hole
00:12:10 --> 00:12:12 something measured in tens of thousands
00:12:12 --> 00:12:15 of solar masses. Uh for a 10 solar
00:12:15 --> 00:12:17 mass black hole the time dilation of the
00:12:17 --> 00:12:20 incre the accretion disc inner edge is
00:12:20 --> 00:12:23 only 22%. So it's what I've said it's
00:12:23 --> 00:12:25 the scale of the process that makes
00:12:25 --> 00:12:28 makes the difference.
00:12:28 --> 00:12:31 Fair enough. Okay. Simple answer really.
00:12:31 --> 00:12:34 it. Yep. Seems to be
00:12:34 --> 00:12:36 all right. Thank you, Blue. Hope you're
00:12:36 --> 00:12:38 going well. Love London. Uh only been
00:12:38 --> 00:12:42 there twice, I think. Twice. Yes. And uh
00:12:42 --> 00:12:43 yeah, really enjoyed my time. It's a
00:12:44 --> 00:12:46 It's a beautiful city. Really love that
00:12:46 --> 00:12:49 place. I'd go back tomorrow if I could.
00:12:49 --> 00:12:51 Um thank you, Blue. And um this is Space
00:12:51 --> 00:12:54 Nuts. You're listening to it with Andrew
00:12:54 --> 00:12:58 Dunley and Professor Fred Watson.
00:12:58 --> 00:13:00 We choose to go to the moon in this
00:13:00 --> 00:13:03 decade and do the other things not
00:13:03 --> 00:13:05 because they are easy but because they
00:13:05 --> 00:13:06 are hard.
00:13:06 --> 00:13:08 >> These nuts.
00:13:08 --> 00:13:12 >> Next question. Fred. Hey nutters.
00:13:12 --> 00:13:16 Uh Julian from Bmpton, Ontario, Canada.
00:13:16 --> 00:13:19 Here. Uh what is causing the expansion
00:13:19 --> 00:13:21 of the universe? Oh, that old chestnut.
00:13:21 --> 00:13:25 I mean, uh, are we a black hole eating
00:13:25 --> 00:13:29 outside matter or are other fundamental
00:13:29 --> 00:13:32 forces responsible or are the forces
00:13:32 --> 00:13:34 actually keeping us together? Part two,
00:13:34 --> 00:13:36 I think we're up to part four actually.
00:13:36 --> 00:13:38 Part two of this question would be, Fred
00:13:38 --> 00:13:40 mentioned the universe is expanding
00:13:40 --> 00:13:43 slower. Does that mean we know exactly
00:13:43 --> 00:13:45 how fast the universe is expanding and
00:13:45 --> 00:13:48 does that mean speeds faster than light?
00:13:48 --> 00:13:50 I hope you all got that. Love the show.
00:13:50 --> 00:13:53 Thanks, Julian. Oh, he's packed in a lot
00:13:53 --> 00:13:57 there in three or four sentences. Um,
00:13:58 --> 00:13:59 what's causing the expansion of the
00:13:59 --> 00:14:01 universe, Fred? And I know the answer to
00:14:01 --> 00:14:03 this one.
00:14:03 --> 00:14:07 >> Um, I think, well, you know, the way we
00:14:07 --> 00:14:11 usually interpret the big bang is,
00:14:11 --> 00:14:13 um,
00:14:13 --> 00:14:15 in the beginning there was nothing and
00:14:15 --> 00:14:16 then it exploded.
00:14:16 --> 00:14:17 >> Yeah.
00:14:17 --> 00:14:21 And that's kind of more or less what it
00:14:21 --> 00:14:24 was. Uh and so it's we're still seeing
00:14:24 --> 00:14:26 the aftermath or the effect of that
00:14:26 --> 00:14:29 explosion in the expansion. So it's
00:14:29 --> 00:14:34 driven by uh by a you know a some
00:14:34 --> 00:14:37 fundamental injection of energy at the
00:14:37 --> 00:14:38 start of the universe. We can kind of
00:14:38 --> 00:14:40 quantify how much it was. It's a very
00:14:40 --> 00:14:43 large number. uh that set the expansion
00:14:43 --> 00:14:47 in motion and it's still going on now.
00:14:47 --> 00:14:50 Um
00:14:50 --> 00:14:53 the second bit of the question is the is
00:14:53 --> 00:14:55 the interesting bit part two.
00:14:55 --> 00:14:57 >> Uh so so
00:14:57 --> 00:15:00 let me just yes there are a number of
00:15:00 --> 00:15:02 parts here. Are we a black hole eating
00:15:02 --> 00:15:06 outside material? U some scientists have
00:15:06 --> 00:15:08 suggested that we are within the event
00:15:08 --> 00:15:10 horizon of a black pole and that's
00:15:10 --> 00:15:11 what's I've heard
00:15:11 --> 00:15:13 >> what's causing the expansion of the
00:15:13 --> 00:15:15 universe. It's a very uh speculative
00:15:15 --> 00:15:18 idea. Um it's not one I'm very fond of
00:15:18 --> 00:15:20 because I
00:15:20 --> 00:15:21 you know I think I think we need a bit
00:15:21 --> 00:15:23 more hard evidence as to whether that
00:15:24 --> 00:15:27 black hole is there. Um are we a black
00:15:27 --> 00:15:29 hole eating outside material? Probably
00:15:29 --> 00:15:32 not. Or are there other fundamental
00:15:32 --> 00:15:34 forces responsible? Uh well yes maybe
00:15:34 --> 00:15:37 and that comes to the second bit of the
00:15:37 --> 00:15:40 question. Uh it says Fred mentioned the
00:15:40 --> 00:15:43 universe is expanding slower. That's
00:15:43 --> 00:15:46 actually not the case. Uh it's expanding
00:15:46 --> 00:15:48 faster all the time but that
00:15:48 --> 00:15:51 acceleration is reducing reducing.
00:15:51 --> 00:15:51 >> Yes.
00:15:51 --> 00:15:54 >> So the conundrum isn't it?
00:15:54 --> 00:15:56 >> It is thought expanding at a faster
00:15:56 --> 00:16:00 rate. Now it's expanding faster slower.
00:16:00 --> 00:16:02 >> Faster slower. That's right. Um I mean
00:16:02 --> 00:16:04 before we used to think it was expanding
00:16:04 --> 00:16:06 at a slower rate. We used to think in
00:16:06 --> 00:16:08 the in the 70s and 80s that it was
00:16:08 --> 00:16:10 slowing down. The expansion was slowing
00:16:10 --> 00:16:12 down and one day they'd be perhaps a
00:16:12 --> 00:16:14 reversal of the expansion and a big
00:16:14 --> 00:16:17 crunch. Then in 1998 along came Branch
00:16:17 --> 00:16:19 Schmidt and Saul Pearlmuta and between
00:16:19 --> 00:16:21 them they figured out and Adam Ree of
00:16:21 --> 00:16:23 course the three Nobel Prize winners in
00:16:23 --> 00:16:26 2011 uh they figured out that actually
00:16:26 --> 00:16:29 uh the expansion is accelerating.
00:16:29 --> 00:16:31 >> Um and that's still the case today. That
00:16:32 --> 00:16:33 is the situation we have. The expansion
00:16:34 --> 00:16:37 is still is accelerating but there is
00:16:37 --> 00:16:41 now new evidence uh that suggests that
00:16:41 --> 00:16:45 the ex the acceleration is reducing. So
00:16:45 --> 00:16:47 it's not that the expansion of the
00:16:47 --> 00:16:49 universe is slowing down, it's that the
00:16:49 --> 00:16:51 acceleration of the expansion of the
00:16:51 --> 00:16:53 universe is slowing down. Yeah. And
00:16:53 --> 00:16:56 that's a different matter. So it's still
00:16:56 --> 00:16:58 >> Yeah. It's still accelerating in its
00:16:58 --> 00:17:02 expansion. And we attribute that to dark
00:17:02 --> 00:17:07 energy. Um that is something that
00:17:08 --> 00:17:10 the new results that suggest that the
00:17:10 --> 00:17:13 acceleration is slowing down uh actually
00:17:13 --> 00:17:15 throw a spanner in the works because we
00:17:15 --> 00:17:18 thought we understood dark energy as uh
00:17:18 --> 00:17:20 what's called a cos a co cosmological
00:17:20 --> 00:17:22 constant. A force that basically is
00:17:22 --> 00:17:24 proportional to the size of space. The
00:17:24 --> 00:17:26 more space you have, the more e
00:17:26 --> 00:17:28 expansion force there is a kind of
00:17:28 --> 00:17:31 pressure if you like of space itself. Uh
00:17:31 --> 00:17:33 springiness of space.
00:17:33 --> 00:17:35 >> Um the fact that as time goes on that
00:17:35 --> 00:17:38 expansion seems to be uh the
00:17:38 --> 00:17:40 acceleration of the expansion seems to
00:17:40 --> 00:17:44 be reducing is uh sus it's actually
00:17:44 --> 00:17:46 suggestive of new physics which might
00:17:46 --> 00:17:48 mean higher dimensions and all the other
00:17:48 --> 00:17:50 good stuff that we love talking about on
00:17:50 --> 00:17:50 space nuts.
00:17:50 --> 00:17:55 >> Yes. Um indeed. Uh so so um his last bit
00:17:55 --> 00:17:57 of the question uh does that mean speeds
00:17:57 --> 00:18:01 faster than light? Uh there will be a
00:18:01 --> 00:18:03 limit beyond which we can't see the
00:18:03 --> 00:18:07 universe because it's expanding from us
00:18:07 --> 00:18:09 faster than light can get to us and
00:18:09 --> 00:18:12 that's already the case. Uh but we don't
00:18:12 --> 00:18:13 see that because we see the cosmic
00:18:14 --> 00:18:16 microwave background radiation first.
00:18:16 --> 00:18:19 That's the nearer phenomenon. So um yes.
00:18:19 --> 00:18:22 So uh it's a interesting set of
00:18:22 --> 00:18:26 questions uh which I I guess
00:18:26 --> 00:18:28 highlighting some of the mysteries that
00:18:28 --> 00:18:31 we face with uh uh with our current
00:18:31 --> 00:18:33 understanding of cosmology.
00:18:33 --> 00:18:35 >> In truth in truth though we do not know
00:18:35 --> 00:18:37 how fast the expansion rate currently
00:18:37 --> 00:18:39 is. We can't put a number on that can
00:18:39 --> 00:18:40 we?
00:18:40 --> 00:18:41 >> Yes we can.
00:18:41 --> 00:18:45 >> Uh that's the Hubble constant. uh um
00:18:45 --> 00:18:45 which is
00:18:45 --> 00:18:47 >> yeah we have talked about that before
00:18:47 --> 00:18:49 and I remember because there's this
00:18:49 --> 00:18:52 tension that between the Hubble constant
00:18:52 --> 00:18:54 as we measure it now uh and the Hubble
00:18:54 --> 00:18:57 constant as we determine it from the
00:18:57 --> 00:18:59 cosmic microwave background radiation
00:18:59 --> 00:19:02 called the Hubble tension which may be
00:19:02 --> 00:19:04 something that really is just to do with
00:19:04 --> 00:19:05 our measurements. So the Hubble
00:19:05 --> 00:19:08 constants in odd units in it's in
00:19:08 --> 00:19:12 kilometers/s per mega par sec. Uh which
00:19:12 --> 00:19:15 is basically a fancy way of saying we do
00:19:15 --> 00:19:17 know how fast
00:19:17 --> 00:19:20 >> it is. Yeah. The the answer is 70 to 74
00:19:20 --> 00:19:23 kilometers per second per megap.
00:19:23 --> 00:19:24 >> Yep.
00:19:24 --> 00:19:26 >> Give or take.
00:19:26 --> 00:19:29 >> Well that's right. You know, when when
00:19:29 --> 00:19:31 when I was a young astronomer, I keep
00:19:31 --> 00:19:34 saying this, back in the 70s, um there
00:19:34 --> 00:19:37 were two the estimates of that number
00:19:38 --> 00:19:40 were out by a factor of two. There was
00:19:40 --> 00:19:42 one group said it's 50 km per second per
00:19:42 --> 00:19:43 mega par sec. Another group said it's
00:19:44 --> 00:19:46 100 kilometers/s mega par sec. And look
00:19:46 --> 00:19:48 what we've got with the Hubble telescope
00:19:48 --> 00:19:49 and other instruments. We've got
00:19:49 --> 00:19:52 basically the average of those two. Uh
00:19:52 --> 00:19:54 which is quite neat really.
00:19:54 --> 00:19:55 >> But we still got some uncertainty. There
00:19:56 --> 00:19:58 was also this um conflict, wasn't there,
00:19:58 --> 00:20:01 that they were they couldn't figure out
00:20:01 --> 00:20:03 the answer for, but we did a story about
00:20:03 --> 00:20:05 them figuring out that the conflict was
00:20:05 --> 00:20:08 actually normal and we, you know, that's
00:20:08 --> 00:20:11 within acceptable parameters. I think
00:20:11 --> 00:20:14 >> we did. Yeah. Okay. Uh did we answer all
00:20:14 --> 00:20:17 his question? I think we did. Yeah. Um
00:20:17 --> 00:20:19 Oh, I did look up something else. How
00:20:19 --> 00:20:21 how powerful was the big bang? uh
00:20:21 --> 00:20:25 greater than 10^ the 68 jewels.
00:20:25 --> 00:20:27 >> Okay,
00:20:27 --> 00:20:29 >> that's what you call a bag.
00:20:29 --> 00:20:32 >> That's a big big big big big bang. But
00:20:32 --> 00:20:34 we just shortened it to big bang.
00:20:34 --> 00:20:35 >> Write that down. This is a good number.
00:20:35 --> 00:20:37 10^ the 68 jewels.
00:20:37 --> 00:20:40 >> Yes. Yeah. Put that on your calculator
00:20:40 --> 00:20:44 and see what happens. Um thank Julian.
00:20:44 --> 00:20:47 Uh hope you're well. Uh let's uh answer
00:20:47 --> 00:20:48 one more question before we finish up
00:20:48 --> 00:20:50 today. And this is a question with 47
00:20:50 --> 00:20:53 parts. Hi, Professor Fred and Andrew
00:20:53 --> 00:20:56 Peter here from San Diego, California. I
00:20:56 --> 00:20:59 have a dual question about dark energy.
00:20:59 --> 00:21:01 My understanding is that dark energy is
00:21:01 --> 00:21:05 causing our universe to expand. Also, we
00:21:05 --> 00:21:07 have an observable part of the universe
00:21:07 --> 00:21:09 where light is able to reach us and an
00:21:09 --> 00:21:11 unobservable part of the universe. Funny
00:21:11 --> 00:21:13 how we already talked about this, but
00:21:13 --> 00:21:15 the these all these questions kind of
00:21:15 --> 00:21:18 dovetailed. Question one, is it feasible
00:21:18 --> 00:21:20 that the unobservable part of the
00:21:20 --> 00:21:22 universe contains enough matter to act
00:21:22 --> 00:21:24 gravitationally on the observable
00:21:24 --> 00:21:27 universe, thus causing the expansion?
00:21:27 --> 00:21:28 And question two, which we'll get back
00:21:28 --> 00:21:31 to, uh, same question within the context
00:21:31 --> 00:21:33 of the multisphere. Could universes
00:21:33 --> 00:21:35 other than our own be gravitationally
00:21:35 --> 00:21:38 impacting the expansion of our universe?
00:21:38 --> 00:21:40 Love your show. Keep up the great work.
00:21:40 --> 00:21:43 Uh, thank you, Peter. Um question one is
00:21:44 --> 00:21:46 it feasible that the unobservable part
00:21:46 --> 00:21:48 of our universe contains enough matter
00:21:48 --> 00:21:51 to act gravitationally on the observable
00:21:51 --> 00:21:53 observable universe thus causing the
00:21:53 --> 00:21:54 expansion.
00:21:54 --> 00:21:58 Um yes once again we've got to unpick uh
00:21:58 --> 00:22:02 what we mean by the expansion. So um
00:22:02 --> 00:22:04 Peter says my understanding is that dark
00:22:04 --> 00:22:07 energy is causing our universe to expand
00:22:07 --> 00:22:08 and that's not the case as we've just
00:22:08 --> 00:22:10 described. It's the big bang that caused
00:22:10 --> 00:22:12 the universe to expand. But dark energy
00:22:12 --> 00:22:14 is what's causing the expansion to
00:22:14 --> 00:22:15 accelerate
00:22:15 --> 00:22:17 >> uh to to get faster.
00:22:17 --> 00:22:18 >> It's easy to get confused though, isn't
00:22:18 --> 00:22:19 it? Because
00:22:19 --> 00:22:21 >> it is absolutely
00:22:21 --> 00:22:22 >> this is an event with a lot of moving
00:22:22 --> 00:22:23 parts.
00:22:23 --> 00:22:25 >> It is. Yes. As you'd expect, it's a
00:22:25 --> 00:22:27 universe after all.
00:22:27 --> 00:22:27 >> Yeah.
00:22:27 --> 00:22:31 >> Um but what Peter says is is correct. Um
00:22:31 --> 00:22:34 because we, as we've just said, there
00:22:34 --> 00:22:35 are, you know, there are parts of the
00:22:35 --> 00:22:38 universe well beyond 13.8 8 billion
00:22:38 --> 00:22:41 light years. Um, which we can't see
00:22:41 --> 00:22:42 because what we run into is the cosmic
00:22:42 --> 00:22:44 microwave background radiation, the
00:22:44 --> 00:22:46 flash of the big bang. So, we know
00:22:46 --> 00:22:47 there's universe beyond that, but we
00:22:47 --> 00:22:49 can't see it.
00:22:49 --> 00:22:52 >> Um, and Peter's suggestion is it
00:22:52 --> 00:22:54 feasible that the unobservable part of
00:22:54 --> 00:22:56 the universe contains enough matter to
00:22:56 --> 00:22:57 act gravitationally on the observable
00:22:57 --> 00:23:01 universe. Uh, and as and thus causing
00:23:01 --> 00:23:02 the expansion. It's actually thus
00:23:02 --> 00:23:04 causing the acceleration of the
00:23:04 --> 00:23:06 expansion. Uh that is one of the
00:23:06 --> 00:23:07 theories that people have looked at
00:23:07 --> 00:23:10 exactly that that are we in a kind of
00:23:10 --> 00:23:13 local bubble where the density is low
00:23:13 --> 00:23:16 compared with what we what we what is
00:23:16 --> 00:23:19 outside the boundary that we can see
00:23:19 --> 00:23:21 where the density might be higher and
00:23:21 --> 00:23:23 hence having a gravitational effect on
00:23:23 --> 00:23:26 our local bubble. Um it's a it's
00:23:26 --> 00:23:28 certainly a you know a conjecture that
00:23:28 --> 00:23:32 is raised by uh by astrophysicists and
00:23:32 --> 00:23:34 cosmologists. So Peter's on the right
00:23:34 --> 00:23:36 track there. And then question two, the
00:23:36 --> 00:23:38 same question within the context of the
00:23:38 --> 00:23:40 multiverse. Could universes other than
00:23:40 --> 00:23:42 our own gravitationally be
00:23:42 --> 00:23:44 gravitationally impacting the expansion
00:23:44 --> 00:23:47 of our universe? And I think um that is
00:23:47 --> 00:23:50 also something that's considered. Um,
00:23:50 --> 00:23:53 one of the reasons why people think
00:23:53 --> 00:23:55 there might be multiverses,
00:23:55 --> 00:23:59 uh, it is that gravity itself
00:23:59 --> 00:24:03 is compared with the other three
00:24:03 --> 00:24:06 fundamental forces in nature, it is
00:24:06 --> 00:24:09 incredibly weak. So the fundamental
00:24:09 --> 00:24:11 forces are the strong and weak nuclear
00:24:11 --> 00:24:13 forces, things that hold atoms together.
00:24:13 --> 00:24:15 The electromagnetic force causes
00:24:15 --> 00:24:18 chemical reactions and and photons so
00:24:18 --> 00:24:20 that we can talk to each other. Those
00:24:20 --> 00:24:22 are the three uh which are best known.
00:24:22 --> 00:24:25 Gravity is the fourth fundamental force.
00:24:25 --> 00:24:28 But it is gazillions of times weaker
00:24:28 --> 00:24:30 than the other three and some people
00:24:30 --> 00:24:33 suggest that maybe that is because it is
00:24:33 --> 00:24:36 leaking into other universes. Hence the
00:24:36 --> 00:24:39 idea of a multiverse scenario. But that
00:24:39 --> 00:24:41 is very speculative. We don't have any
00:24:41 --> 00:24:43 hard evidence that points towards a
00:24:43 --> 00:24:47 multiverse. But yes, once again, maybe
00:24:47 --> 00:24:48 there are gravitational influences
00:24:48 --> 00:24:50 coming from the outside of our universe,
00:24:50 --> 00:24:51 whatever that means, because the
00:24:51 --> 00:24:53 universe by definition means everything
00:24:53 --> 00:24:56 you can observe or or understand. Um, so
00:24:56 --> 00:24:59 it is possible. So, um, I think Peter's,
00:24:59 --> 00:25:01 you know, his questions are are well
00:25:01 --> 00:25:04 well directed. He's on the right track.
00:25:04 --> 00:25:07 >> Yeah. Uh I think as you said there's no
00:25:08 --> 00:25:09 direct evidence whatsoever of
00:25:09 --> 00:25:12 multiverses but we've said it before
00:25:12 --> 00:25:14 mathematically
00:25:14 --> 00:25:15 it's plausible. It
00:25:15 --> 00:25:18 >> it's possible. That's right. Yeah.
00:25:18 --> 00:25:19 >> A lot of things are mathematically
00:25:19 --> 00:25:22 possible that you don't see in reality.
00:25:22 --> 00:25:24 >> And how much of the universe can we not
00:25:24 --> 00:25:28 see? Is it like 75% or something?
00:25:28 --> 00:25:29 >> We have no idea.
00:25:29 --> 00:25:30 >> We don't know. We don't know how big it
00:25:30 --> 00:25:30 is.
00:25:30 --> 00:25:33 >> Could be infinite. We don't know.
00:25:33 --> 00:25:33 >> Yeah. Gosh,
00:25:33 --> 00:25:36 >> all we know is what we can see.
00:25:36 --> 00:25:38 >> It's It's crazy town, isn't it? When you
00:25:38 --> 00:25:41 >> It is. Yeah, it is. Um That's right.
00:25:41 --> 00:25:41 It's
00:25:41 --> 00:25:46 >> keeps you in a job.
00:25:46 --> 00:25:49 >> Yes, it does. Keeps me in a job. That's
00:25:49 --> 00:25:50 right.
00:25:50 --> 00:25:52 >> Yeah. Yeah. But that's, you know, that's
00:25:52 --> 00:25:53 when the critics come out. We got all
00:25:53 --> 00:25:56 you BS trying to figure out and ladies,
00:25:56 --> 00:25:58 what's going on? You've been working on
00:25:58 --> 00:25:59 it for hundreds of years and you still
00:25:59 --> 00:26:00 don't know the answer.
00:26:00 --> 00:26:02 >> Still, we still don't know. Um, the good
00:26:02 --> 00:26:04 the good news is that node is paying me
00:26:04 --> 00:26:06 now. So that's all right.
00:26:06 --> 00:26:09 >> So you don't have to worry about that.
00:26:09 --> 00:26:11 >> It's a costfree analysis now.
00:26:11 --> 00:26:12 >> There you go. You get it for free.
00:26:12 --> 00:26:14 That's right, ladies and gentlemen. This
00:26:14 --> 00:26:15 all comes to you free.
00:26:15 --> 00:26:18 >> Yes, it does. Um, all right. So I think
00:26:18 --> 00:26:21 we covered everything there. Um, thank
00:26:21 --> 00:26:23 you Peter. Great set of questions all
00:26:23 --> 00:26:25 up. Some um real intrigue in some of
00:26:25 --> 00:26:28 those as well which uh is really good.
00:26:28 --> 00:26:31 Uh, but as I've said many times, uh, we
00:26:31 --> 00:26:32 need some more questions. So, if you can
00:26:32 --> 00:26:34 get online to our website and click on
00:26:34 --> 00:26:36 the ask me anything tab at the top of
00:26:36 --> 00:26:40 our, uh, page, uh, send us text or audio
00:26:40 --> 00:26:42 questions. We certainly could use some
00:26:42 --> 00:26:44 more audio questions. We get a lot from
00:26:44 --> 00:26:46 people who might ask 10 at a time.
00:26:46 --> 00:26:49 Obviously, we can't run them all
00:26:49 --> 00:26:50 consecutively, otherwise no one else
00:26:50 --> 00:26:52 gets a bite. But, uh, if you've thought
00:26:52 --> 00:26:54 about asking a question and you haven't
00:26:54 --> 00:26:56 got around to it yet, don't be scared.
00:26:56 --> 00:26:58 We don't bite. Well, we do bite, but
00:26:58 --> 00:27:00 don't worry about that. It's harmless.
00:27:00 --> 00:27:03 We're not venomous. Uh, but you can send
00:27:03 --> 00:27:05 it in through spaceodcast.com
00:27:05 --> 00:27:08 or spacenuts.io
00:27:08 --> 00:27:10 and click on that tab and uh send us
00:27:10 --> 00:27:12 your question or just a comment. I mean,
00:27:12 --> 00:27:14 if you want to add a comment, we can
00:27:14 --> 00:27:16 throw that into the show. It's nice to
00:27:16 --> 00:27:18 have all these different voices on the
00:27:18 --> 00:27:21 air. Uh, so yeah, send them into us.
00:27:21 --> 00:27:22 Don't forget to tell us who you are and
00:27:22 --> 00:27:23 where you're from. I think I've already
00:27:23 --> 00:27:25 said that. Uh, we are done, Fred. Thank
00:27:25 --> 00:27:27 you so very very much.
00:27:28 --> 00:27:30 >> It's a great pleasure, Andrew. And um I
00:27:30 --> 00:27:31 hope we'll do it again sometime.
00:27:31 --> 00:27:33 >> I hope so too. Maybe in a week, maybe
00:27:33 --> 00:27:35 more, maybe less. You just, you know,
00:27:35 --> 00:27:38 it's all all to do withuling
00:27:38 --> 00:27:42 and availability and what our wives are
00:27:42 --> 00:27:43 doing at any particular time. That's the
00:27:43 --> 00:27:45 most significant factor.
00:27:45 --> 00:27:47 >> Thanks, Fred. We'll see you soon.
00:27:47 --> 00:27:49 >> Cheers for now. Bye-bye.
00:27:49 --> 00:27:51 >> Uh Professor Fred Watson, astronomer at
00:27:51 --> 00:27:53 large. Thanks to Hugh in the studio who
00:27:53 --> 00:27:55 couldn't be with us today because he's
00:27:55 --> 00:27:57 unobservable.
00:27:57 --> 00:27:59 And from me, Andrew Dunley, thanks for
00:27:59 --> 00:28:01 your company. See you on the next
00:28:01 --> 00:28:03 episode of Space Nuts. Bye-bye.
00:28:03 --> 00:28:04 >> Space Nuts.
00:28:04 --> 00:28:06 >> You've been listening to the Space Nuts
00:28:06 --> 00:28:08 podcast.
00:28:08 --> 00:28:11 >> Available at Apple Podcasts, Spotify,
00:28:11 --> 00:28:14 iHeart Radio, or your favorite podcast
00:28:14 --> 00:28:16 player. You can also stream on demand at
00:28:16 --> 00:28:19 byes.com. This has been another quality
00:28:19 --> 00:28:23 podcast production from diets.com.