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

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Language: en

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Hi there. Thanks for joining us. This is


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a Q&A edition of Space Nuts, uh, where


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we talk astronomy and space science. And


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in the Q&A episode, we answer questions


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from our audience. We've got a whole


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bunch today. Uh, we're going to, uh,


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hear from Jeff, uh, who wants to discuss


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the effect when the sun goes red giant,


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which is going to happen in a couple of


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weeks. Uh, no, it's not. No, it's not.


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Uh, Blue is asking about accretion


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discs. Julian about the expansion of the


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universe and one of our old favorite


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topics from Peter, dark energy. That's


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all coming up in this episode of Space


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Nuts.


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>> 15 seconds. Guidance is internal. 10 9g


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Ignition sequence start.


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>> Space nuts.


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>> 5 4 3 2 1 2 3 4 5 5 4 3 2 1


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>> Space Nuts.


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>> Astronauts report. It feels good.


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And back again to furnish us with his


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wisdom or just to have a couple of lucky


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guesses is Professor Fred Watson,


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astronomer at large. Hello, Fred.


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>> How are you doing, Andrew? Good to see


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you.


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>> Good. And you?


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>> Yes. Uh, firing on all cylinders as far


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as I know.


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>> That's all right. Um, although back then


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they only made them with three Celad.


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>> Oh gosh, I'm in a wicked mood today.


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Sorry about that.


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>> Yep. Okay, we better get on with it now.


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Um, I will put out an appeal like I did


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at the end of the last episode for audio


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questions. Questions in general, but


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audio questions particularly. We are


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desperately short and we don't know why.


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It's just a weird quirk of fate, I


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suppose. But if you would like to send


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us some audio questions, you can do that


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on our website, spacenuts.io,


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and click on the AMA ask me anything tab


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at the top and send us the message. Uh,


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don't forget to tell us who you are and


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where you're from. Our first question,


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Fred, uh, comes from Jeff in Fatville,


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Arkansas in the United States. Hello,


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gentlemen. Well, he's wrong for a start.


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I mean, come on. Um, I happened upon


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your podcast several months ago and


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enjoy it very much. Last month, you


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discussed the thought experiment having


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to do with uh what would happen if the


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rest uh to the rest of the solar system


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if the sun suddenly disappeared. My


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question is a little bit more concrete.


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Uh, in 5 billion years or so, our sun is


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expected to swell into a red giant


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before perhaps collapsing into a white


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dwarf. What will this do to our sun's


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total mass? And what effect will it have


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on the outer planets that survive being


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engulfed? Earth not being one of them,


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as it turns out. I um a follow-up


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question. Uh, are other suns dying


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throughout our galaxy responsible for


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the rogue planets far out in space


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between stars that I've read about?


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Thank you for your time and the


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stimulating discussions you allow me to


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listen into. Thank you Jeff. That's uh


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lovely. Uh a few questions in there


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Fred. Uh so um yes our our sun which we


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have talked about going you know


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ballistic uh in about five billion or so


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years. Uh what happens to the outer


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planets?


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>> Uh that's yes it is a great question. Um


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and I I think the um the sort of


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implicit assumption is that is that the


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inner planets are not going to be around


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>> no which probably will include the earth


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and possibly even Mars. So the um yes


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the process uh towards the end of the


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sun's life and somewhere in the region


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of 3 to 5 billion years I think the


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process starts about three billion years


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hence. So it's a little bit earlier than


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Jeff says. So, um, I hope that's not a


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cause for alarm. Uh, 3 billion at his


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watch, so he's going to have to reset


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that. And that's always a pain.


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>> It is. That's right. Yeah. Um, I the


00:03:51.120 --> 00:03:53.910
other day set dutifully set the timer to


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time down on my uh my phone because I


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had to take things out of the oven and


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um um it got to the end of the time and


00:04:01.760 --> 00:04:03.429
didn't do anything. Just


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>> Oh, I hate it.


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>> It stopped.


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>> I did too.


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My phone suddenly decided to put all


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calls through to voicemail before I can


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even before I even know it's ringing.


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Picked it up the other day and thought,


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why is it vibrating? And then I realized


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my sister was ringing me, but it was


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making no sound. There was no


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indication. It just filtered and and


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when I I I pushed a couple of buttons,


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eventually found her and she said, "Oh


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yeah, I was just listening to your


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message."


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>> Well, there you go. Voicemail,


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>> which is not a problem we'll be really


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worried about in 3 minutes. No, not just


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time because but if anyone knows the


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answer to that, please let me know.


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>> Oh, well, I can tell you the answer. You


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have a smartwatch and that wings as


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well.


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>> Well, I yeah, I don't think I had it on


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at the time. So, ah


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>> anyway um so uh so yes, the inner


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planets get swallowed up um as the sun


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swells. It's it doesn't happen suddenly.


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It is a it's a fairly leisurely process.


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There is a collapse of the core down to


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a white dwarf star which is the end


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product is this white dwarf star which


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is the size of the earth but with quite


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a lot of the mass of the sun still


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tucked in there uh and an outer shell of


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expanding gas and we if we were looking


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at that from the outside we'd call it a


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planetary nebula. So that outer shell of


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gas uh is hot. Uh it's hot enough to


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basically vaporize the the inner


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planets. Uh so but Jeff's question is


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not about that. It's about how do things


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look from the outside. And so the outer


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planets uh interestingly their orbits


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will be perturbed


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um which means changed but maybe not as


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dramatically as you might think because


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um that swelling


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it what it's doing is if you look at the


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center of gravity of all that it's still


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at the center of the solar system uh


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even though the outer layers of the star


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and there's a significant amount of mass


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in that even though most of the mass


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going to be concentrated in the white


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dwarf star, but the outer layers are are


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expanding. You're outside that zone. So


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to you, the center of gravity, center of


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mass of the solar system remains where


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the sun is now. And so the effect on the


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orbits of the planets might not be as


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dramatic as propelling one of them out


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uh to become a rogue planet.


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>> So uh it could be a lot gentler than I


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mean a supernova is different. If it


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explodes, then you're talking about


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dramatic and cataclysmic events that


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would certainly disturb the orbits of


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planets, although some planets seem to


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be able to survive that. We can see


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supernova remnants with with planets


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chugging around. Anyway, this this um


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this scene, this scenario is that uh


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there may still be planets which will be


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outside


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uh the um you know the envelope of the


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of the white of the red giant. Now


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eventually that envelope is going to


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pass the uh pass the the outer planets


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uh and may evaporate them as well uh


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depending on what sort of temperature it


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is. But um the the the so the red giant


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phase the outer planets might be still


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okay and still say it's stable. But once


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it progresses beyond that and you get to


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the planetary nebula stage where the


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outer layer is light years in diameter


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rather than rather than just a few


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hundred million kilometers in diameter


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trillion kilometers in diameter um then


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you're you're probably in trouble if


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you're on the outer planets as well.


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>> Okay. How long does that process take to


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to reach that nebula state?


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>> It's it's it's relatively slow. You're


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talking about billions of years. Wow.


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>> Uh yeah. Uh so I mean there must be


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there must be a collapse phase for the


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nucleus. Uh I'm not an expert on these


00:08:05.919 --> 00:08:08.550
what we call highly evolved stars. Uh


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but as as it goes from red giant to a


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planetary nebula that's when you you you


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change into a white dwarf in the middle


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you've got the nucleus of the star


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collapsing. So these are the end


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products of normal stars. Actually a


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normal star will go through this phase.


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A massive star will become a supernova.


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It will explode.


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>> Wow. Okay. So, you pretty well answered


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everything in one hit. Um, the white


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dwarf will have the same mass as our sun


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at the moment, more or less. So, it


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won't really have an impact on the outer


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planets until after the halo effect over


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billions of years


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>> and probably not enough effect to cause


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rogue planets.


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>> I think that's right. Yes. I mean, I


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think evaporated planets is more likely.


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>> Yeah. Uh um so rogue planets uh are most


00:08:56.880 --> 00:09:00.070
likely formed either


00:09:00.080 --> 00:09:03.030
just formed in in gas clouds collapsing


00:09:03.040 --> 00:09:04.949
into stars. These are things that aren't


00:09:04.959 --> 00:09:06.630
big enough to collapse into stars though


00:09:06.640 --> 00:09:09.670
they become little planets on their own


00:09:09.680 --> 00:09:11.910
or by being ejected because of a


00:09:11.920 --> 00:09:13.750
gravitational influence. You know, if


00:09:13.760 --> 00:09:15.670
you get two planets that pass very close


00:09:15.680 --> 00:09:17.030
to each other or something like that,


00:09:17.040 --> 00:09:19.509
one of them might get booted out of the


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of their solar system.


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>> There you go, Jeff. Hopefully that


00:09:22.720 --> 00:09:24.710
answered all of your questions. Uh we


00:09:24.720 --> 00:09:27.190
like multifaceted questions. It um takes


00:09:27.200 --> 00:09:29.030
us up into all sorts of strange


00:09:29.040 --> 00:09:30.550
directions sometimes. Great to hear from


00:09:30.560 --> 00:09:33.350
you. Hope all is well in Arkansas. Uh


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Fred, our next question comes from Blue.


00:09:36.240 --> 00:09:38.150
He's from London. Uh I have a question


00:09:38.160 --> 00:09:40.230
about accretion discs. Given that


00:09:40.240 --> 00:09:42.630
gravitational time dilation causes time


00:09:42.640 --> 00:09:45.030
to pass much slower near a black hole


00:09:45.040 --> 00:09:47.430
relative to Earth, why does the disc


00:09:47.440 --> 00:09:50.870
appear to move at high speeds to us? Uh,


00:09:50.880 --> 00:09:52.710
I would have expected the material to


00:09:52.720 --> 00:09:55.110
look like it's moving at extreme slow


00:09:55.120 --> 00:09:58.230
motion or even stop moving the closer


00:09:58.240 --> 00:10:00.710
you get to the event horizon. Love the


00:10:00.720 --> 00:10:04.470
show, guys. Thanks, Blue. Um, okay. I


00:10:04.480 --> 00:10:05.590
know you're going to know the answer to


00:10:05.600 --> 00:10:07.190
this one because I think we've had a


00:10:07.200 --> 00:10:09.030
similar question before, but it seems to


00:10:09.040 --> 00:10:12.230
be a an an ongoing theme with black


00:10:12.240 --> 00:10:13.990
holes. Why do we see things that we


00:10:14.000 --> 00:10:16.230
don't think we should see?


00:10:16.240 --> 00:10:19.670
Um so yes, the the accretion disc um is


00:10:19.680 --> 00:10:21.590
actually quite a long way from the black


00:10:21.600 --> 00:10:25.030
hole. Uh and a lot of that swirling


00:10:25.040 --> 00:10:28.949
material is uh ejected from the black


00:10:28.959 --> 00:10:30.550
hole rather than getting sucked in by


00:10:30.560 --> 00:10:32.710
the magnetic fields that the black hole


00:10:32.720 --> 00:10:35.990
generates. It sort of projects um the


00:10:36.000 --> 00:10:37.910
accretion disc material at very high


00:10:37.920 --> 00:10:39.590
velocities to the sort of north and


00:10:39.600 --> 00:10:42.949
south of the of the accretion disc. So


00:10:42.959 --> 00:10:46.389
um there will be a time dilation effect.


00:10:46.399 --> 00:10:51.590
Uh I I should check this uh as to how


00:10:51.600 --> 00:10:54.389
much it would be. But I think the


00:10:54.399 --> 00:10:57.750
overarching point is that you're far


00:10:57.760 --> 00:11:00.870
enough away from the event horizon that


00:11:00.880 --> 00:11:03.030
time dilation in the accretion disc is


00:11:03.040 --> 00:11:05.990
not great. It's not high enough. Uh I


00:11:06.000 --> 00:11:07.750
think it's all a matter of scale rather


00:11:07.760 --> 00:11:09.670
than being a matter of the phenomenon


00:11:09.680 --> 00:11:12.310
which I think Blue's right. I think is


00:11:12.320 --> 00:11:14.949
you know anything that gets close to the


00:11:14.959 --> 00:11:17.110
uh to the black holes event horizon is


00:11:17.120 --> 00:11:20.150
going to show up um a time dilation


00:11:20.160 --> 00:11:21.350
phenomenon.


00:11:21.360 --> 00:11:23.269
>> I suppose it would also depend on what


00:11:23.279 --> 00:11:25.430
kind of black hole it is. I mean some of


00:11:25.440 --> 00:11:27.509
them are massively massive.


00:11:27.519 --> 00:11:29.750
>> The massive Yes, that's right. Uh that's


00:11:29.760 --> 00:11:34.150
correct. Um so um a super massive black


00:11:34.160 --> 00:11:36.790
hole will produce a a bigger a bigger


00:11:36.800 --> 00:11:40.069
phenomenon. Um, I'm just going to try


00:11:40.079 --> 00:11:43.350
looking something up, uh, to see if I


00:11:43.360 --> 00:11:48.389
can put any detail on that. Uh,


00:11:48.399 --> 00:11:49.910
um,


00:11:49.920 --> 00:11:50.710
which I should have done.


00:11:50.720 --> 00:11:55.430
>> I'm helping you a lot here.


00:11:55.440 --> 00:11:57.670
>> Yeah. Okay. All right. Here you are.


00:11:57.680 --> 00:12:00.870
Here's a number for a 10,000 solar mass


00:12:00.880 --> 00:12:03.430
black hole. And that's a bit I mean


00:12:03.440 --> 00:12:08.790
that's the kind of limit um uh of what


00:12:08.800 --> 00:12:10.949
we call an intermediate mass black hole


00:12:10.959 --> 00:12:12.389
something measured in tens of thousands


00:12:12.399 --> 00:12:15.910
of solar masses. Uh for a 10,000 solar


00:12:15.920 --> 00:12:17.590
mass black hole the time dilation of the


00:12:17.600 --> 00:12:20.470
incre the accretion disc inner edge is


00:12:20.480 --> 00:12:23.190
only 22%. So it's what I've said it's


00:12:23.200 --> 00:12:25.829
the scale of the process that makes


00:12:25.839 --> 00:12:28.150
makes the difference.


00:12:28.160 --> 00:12:31.670
Fair enough. Okay. Simple answer really.


00:12:31.680 --> 00:12:34.389
it. Yep. Seems to be


00:12:34.399 --> 00:12:36.550
all right. Thank you, Blue. Hope you're


00:12:36.560 --> 00:12:38.949
going well. Love London. Uh only been


00:12:38.959 --> 00:12:42.470
there twice, I think. Twice. Yes. And uh


00:12:42.480 --> 00:12:43.990
yeah, really enjoyed my time. It's a


00:12:44.000 --> 00:12:46.629
It's a beautiful city. Really love that


00:12:46.639 --> 00:12:49.030
place. I'd go back tomorrow if I could.


00:12:49.040 --> 00:12:51.910
Um thank you, Blue. And um this is Space


00:12:51.920 --> 00:12:54.230
Nuts. You're listening to it with Andrew


00:12:54.240 --> 00:12:58.710
Dunley and Professor Fred Watson.


00:12:58.720 --> 00:13:00.949
We choose to go to the moon in this


00:13:00.959 --> 00:13:03.509
decade and do the other things not


00:13:03.519 --> 00:13:05.829
because they are easy but because they


00:13:05.839 --> 00:13:06.470
are hard.


00:13:06.480 --> 00:13:08.629
>> These nuts.


00:13:08.639 --> 00:13:12.949
>> Next question. Fred. Hey nutters.


00:13:12.959 --> 00:13:16.150
Uh Julian from Bmpton, Ontario, Canada.


00:13:16.160 --> 00:13:19.430
Here. Uh what is causing the expansion


00:13:19.440 --> 00:13:21.110
of the universe? Oh, that old chestnut.


00:13:21.120 --> 00:13:25.670
I mean, uh, are we a black hole eating


00:13:25.680 --> 00:13:29.030
outside matter or are other fundamental


00:13:29.040 --> 00:13:32.310
forces responsible or are the forces


00:13:32.320 --> 00:13:34.470
actually keeping us together? Part two,


00:13:34.480 --> 00:13:36.230
I think we're up to part four actually.


00:13:36.240 --> 00:13:38.389
Part two of this question would be, Fred


00:13:38.399 --> 00:13:40.230
mentioned the universe is expanding


00:13:40.240 --> 00:13:43.110
slower. Does that mean we know exactly


00:13:43.120 --> 00:13:45.750
how fast the universe is expanding and


00:13:45.760 --> 00:13:48.470
does that mean speeds faster than light?


00:13:48.480 --> 00:13:50.470
I hope you all got that. Love the show.


00:13:50.480 --> 00:13:53.269
Thanks, Julian. Oh, he's packed in a lot


00:13:53.279 --> 00:13:57.990
there in three or four sentences. Um,


00:13:58.000 --> 00:13:59.910
what's causing the expansion of the


00:13:59.920 --> 00:14:01.750
universe, Fred? And I know the answer to


00:14:01.760 --> 00:14:03.910
this one.


00:14:03.920 --> 00:14:07.750
>> Um, I think, well, you know, the way we


00:14:07.760 --> 00:14:11.430
usually interpret the big bang is,


00:14:11.440 --> 00:14:13.430
um,


00:14:13.440 --> 00:14:15.110
in the beginning there was nothing and


00:14:15.120 --> 00:14:16.389
then it exploded.


00:14:16.399 --> 00:14:17.670
>> Yeah.


00:14:17.680 --> 00:14:21.269
And that's kind of more or less what it


00:14:21.279 --> 00:14:24.470
was. Uh and so it's we're still seeing


00:14:24.480 --> 00:14:26.389
the aftermath or the effect of that


00:14:26.399 --> 00:14:29.030
explosion in the expansion. So it's


00:14:29.040 --> 00:14:34.310
driven by uh by a you know a some


00:14:34.320 --> 00:14:37.189
fundamental injection of energy at the


00:14:37.199 --> 00:14:38.949
start of the universe. We can kind of


00:14:38.959 --> 00:14:40.790
quantify how much it was. It's a very


00:14:40.800 --> 00:14:43.590
large number. uh that set the expansion


00:14:43.600 --> 00:14:47.670
in motion and it's still going on now.


00:14:47.680 --> 00:14:50.069
Um


00:14:50.079 --> 00:14:53.110
the second bit of the question is the is


00:14:53.120 --> 00:14:55.430
the interesting bit part two.


00:14:55.440 --> 00:14:57.910
>> Uh so so


00:14:57.920 --> 00:15:00.230
let me just yes there are a number of


00:15:00.240 --> 00:15:02.949
parts here. Are we a black hole eating


00:15:02.959 --> 00:15:06.470
outside material? U some scientists have


00:15:06.480 --> 00:15:08.230
suggested that we are within the event


00:15:08.240 --> 00:15:10.790
horizon of a black pole and that's


00:15:10.800 --> 00:15:11.590
what's I've heard


00:15:11.600 --> 00:15:13.030
>> what's causing the expansion of the


00:15:13.040 --> 00:15:15.670
universe. It's a very uh speculative


00:15:15.680 --> 00:15:18.710
idea. Um it's not one I'm very fond of


00:15:18.720 --> 00:15:20.470
because I


00:15:20.480 --> 00:15:21.910
you know I think I think we need a bit


00:15:21.920 --> 00:15:23.990
more hard evidence as to whether that


00:15:24.000 --> 00:15:27.110
black hole is there. Um are we a black


00:15:27.120 --> 00:15:29.910
hole eating outside material? Probably


00:15:29.920 --> 00:15:32.150
not. Or are there other fundamental


00:15:32.160 --> 00:15:34.949
forces responsible? Uh well yes maybe


00:15:34.959 --> 00:15:37.670
and that comes to the second bit of the


00:15:37.680 --> 00:15:40.870
question. Uh it says Fred mentioned the


00:15:40.880 --> 00:15:43.030
universe is expanding slower. That's


00:15:43.040 --> 00:15:46.389
actually not the case. Uh it's expanding


00:15:46.399 --> 00:15:48.710
faster all the time but that


00:15:48.720 --> 00:15:51.189
acceleration is reducing reducing.


00:15:51.199 --> 00:15:51.910
>> Yes.


00:15:51.920 --> 00:15:54.310
>> So the conundrum isn't it?


00:15:54.320 --> 00:15:56.389
>> It is thought expanding at a faster


00:15:56.399 --> 00:16:00.389
rate. Now it's expanding faster slower.


00:16:00.399 --> 00:16:02.870
>> Faster slower. That's right. Um I mean


00:16:02.880 --> 00:16:04.550
before we used to think it was expanding


00:16:04.560 --> 00:16:06.069
at a slower rate. We used to think in


00:16:06.079 --> 00:16:08.949
the in the 70s and 80s that it was


00:16:08.959 --> 00:16:10.470
slowing down. The expansion was slowing


00:16:10.480 --> 00:16:12.310
down and one day they'd be perhaps a


00:16:12.320 --> 00:16:14.389
reversal of the expansion and a big


00:16:14.399 --> 00:16:17.269
crunch. Then in 1998 along came Branch


00:16:17.279 --> 00:16:19.430
Schmidt and Saul Pearlmuta and between


00:16:19.440 --> 00:16:21.749
them they figured out and Adam Ree of


00:16:21.759 --> 00:16:23.829
course the three Nobel Prize winners in


00:16:23.839 --> 00:16:26.710
2011 uh they figured out that actually


00:16:26.720 --> 00:16:29.189
uh the expansion is accelerating.


00:16:29.199 --> 00:16:31.990
>> Um and that's still the case today. That


00:16:32.000 --> 00:16:33.990
is the situation we have. The expansion


00:16:34.000 --> 00:16:37.350
is still is accelerating but there is


00:16:37.360 --> 00:16:41.030
now new evidence uh that suggests that


00:16:41.040 --> 00:16:45.590
the ex the acceleration is reducing. So


00:16:45.600 --> 00:16:47.749
it's not that the expansion of the


00:16:47.759 --> 00:16:49.749
universe is slowing down, it's that the


00:16:49.759 --> 00:16:51.430
acceleration of the expansion of the


00:16:51.440 --> 00:16:53.430
universe is slowing down. Yeah. And


00:16:53.440 --> 00:16:56.069
that's a different matter. So it's still


00:16:56.079 --> 00:16:58.230
>> Yeah. It's still accelerating in its


00:16:58.240 --> 00:17:02.069
expansion. And we attribute that to dark


00:17:02.079 --> 00:17:07.990
energy. Um that is something that


00:17:08.000 --> 00:17:10.390
the new results that suggest that the


00:17:10.400 --> 00:17:13.510
acceleration is slowing down uh actually


00:17:13.520 --> 00:17:15.029
throw a spanner in the works because we


00:17:15.039 --> 00:17:18.069
thought we understood dark energy as uh


00:17:18.079 --> 00:17:20.150
what's called a cos a co cosmological


00:17:20.160 --> 00:17:22.549
constant. A force that basically is


00:17:22.559 --> 00:17:24.949
proportional to the size of space. The


00:17:24.959 --> 00:17:26.549
more space you have, the more e


00:17:26.559 --> 00:17:28.309
expansion force there is a kind of


00:17:28.319 --> 00:17:31.270
pressure if you like of space itself. Uh


00:17:31.280 --> 00:17:33.029
springiness of space.


00:17:33.039 --> 00:17:35.830
>> Um the fact that as time goes on that


00:17:35.840 --> 00:17:38.390
expansion seems to be uh the


00:17:38.400 --> 00:17:40.150
acceleration of the expansion seems to


00:17:40.160 --> 00:17:44.390
be reducing is uh sus it's actually


00:17:44.400 --> 00:17:46.710
suggestive of new physics which might


00:17:46.720 --> 00:17:48.470
mean higher dimensions and all the other


00:17:48.480 --> 00:17:50.070
good stuff that we love talking about on


00:17:50.080 --> 00:17:50.950
space nuts.


00:17:50.960 --> 00:17:55.430
>> Yes. Um indeed. Uh so so um his last bit


00:17:55.440 --> 00:17:57.830
of the question uh does that mean speeds


00:17:57.840 --> 00:18:01.110
faster than light? Uh there will be a


00:18:01.120 --> 00:18:03.830
limit beyond which we can't see the


00:18:03.840 --> 00:18:07.110
universe because it's expanding from us


00:18:07.120 --> 00:18:09.750
faster than light can get to us and


00:18:09.760 --> 00:18:12.470
that's already the case. Uh but we don't


00:18:12.480 --> 00:18:13.990
see that because we see the cosmic


00:18:14.000 --> 00:18:16.310
microwave background radiation first.


00:18:16.320 --> 00:18:19.590
That's the nearer phenomenon. So um yes.


00:18:19.600 --> 00:18:22.789
So uh it's a interesting set of


00:18:22.799 --> 00:18:26.710
questions uh which I I guess


00:18:26.720 --> 00:18:28.230
highlighting some of the mysteries that


00:18:28.240 --> 00:18:31.430
we face with uh uh with our current


00:18:31.440 --> 00:18:33.350
understanding of cosmology.


00:18:33.360 --> 00:18:35.750
>> In truth in truth though we do not know


00:18:35.760 --> 00:18:37.909
how fast the expansion rate currently


00:18:37.919 --> 00:18:39.669
is. We can't put a number on that can


00:18:39.679 --> 00:18:40.470
we?


00:18:40.480 --> 00:18:41.750
>> Yes we can.


00:18:41.760 --> 00:18:45.430
>> Uh that's the Hubble constant. uh um


00:18:45.440 --> 00:18:45.909
which is


00:18:45.919 --> 00:18:47.669
>> yeah we have talked about that before


00:18:47.679 --> 00:18:49.669
and I remember because there's this


00:18:49.679 --> 00:18:52.150
tension that between the Hubble constant


00:18:52.160 --> 00:18:54.710
as we measure it now uh and the Hubble


00:18:54.720 --> 00:18:57.909
constant as we determine it from the


00:18:57.919 --> 00:18:59.830
cosmic microwave background radiation


00:18:59.840 --> 00:19:02.310
called the Hubble tension which may be


00:19:02.320 --> 00:19:04.470
something that really is just to do with


00:19:04.480 --> 00:19:05.909
our measurements. So the Hubble


00:19:05.919 --> 00:19:08.789
constants in odd units in it's in


00:19:08.799 --> 00:19:12.789
kilometers/s per mega par sec. Uh which


00:19:12.799 --> 00:19:15.830
is basically a fancy way of saying we do


00:19:15.840 --> 00:19:17.029
know how fast


00:19:17.039 --> 00:19:20.390
>> it is. Yeah. The the answer is 70 to 74


00:19:20.400 --> 00:19:23.590
kilometers per second per megap.


00:19:23.600 --> 00:19:24.630
>> Yep.


00:19:24.640 --> 00:19:26.549
>> Give or take.


00:19:26.559 --> 00:19:29.430
>> Well that's right. You know, when when


00:19:29.440 --> 00:19:31.350
when I was a young astronomer, I keep


00:19:31.360 --> 00:19:34.630
saying this, back in the 70s, um there


00:19:34.640 --> 00:19:37.990
were two the estimates of that number


00:19:38.000 --> 00:19:40.230
were out by a factor of two. There was


00:19:40.240 --> 00:19:42.390
one group said it's 50 km per second per


00:19:42.400 --> 00:19:43.990
mega par sec. Another group said it's


00:19:44.000 --> 00:19:46.710
100 kilometers/s mega par sec. And look


00:19:46.720 --> 00:19:48.310
what we've got with the Hubble telescope


00:19:48.320 --> 00:19:49.669
and other instruments. We've got


00:19:49.679 --> 00:19:52.150
basically the average of those two. Uh


00:19:52.160 --> 00:19:54.150
which is quite neat really.


00:19:54.160 --> 00:19:55.990
>> But we still got some uncertainty. There


00:19:56.000 --> 00:19:58.630
was also this um conflict, wasn't there,


00:19:58.640 --> 00:20:01.190
that they were they couldn't figure out


00:20:01.200 --> 00:20:03.270
the answer for, but we did a story about


00:20:03.280 --> 00:20:05.750
them figuring out that the conflict was


00:20:05.760 --> 00:20:08.549
actually normal and we, you know, that's


00:20:08.559 --> 00:20:11.270
within acceptable parameters. I think


00:20:11.280 --> 00:20:14.630
>> we did. Yeah. Okay. Uh did we answer all


00:20:14.640 --> 00:20:17.750
his question? I think we did. Yeah. Um


00:20:17.760 --> 00:20:19.430
Oh, I did look up something else. How


00:20:19.440 --> 00:20:21.830
how powerful was the big bang? uh


00:20:21.840 --> 00:20:25.669
greater than 10^ the 68 jewels.


00:20:25.679 --> 00:20:27.909
>> Okay,


00:20:27.919 --> 00:20:29.669
>> that's what you call a bag.


00:20:29.679 --> 00:20:32.070
>> That's a big big big big big bang. But


00:20:32.080 --> 00:20:34.470
we just shortened it to big bang.


00:20:34.480 --> 00:20:35.750
>> Write that down. This is a good number.


00:20:35.760 --> 00:20:37.669
10^ the 68 jewels.


00:20:37.679 --> 00:20:40.870
>> Yes. Yeah. Put that on your calculator


00:20:40.880 --> 00:20:44.470
and see what happens. Um thank Julian.


00:20:44.480 --> 00:20:47.110
Uh hope you're well. Uh let's uh answer


00:20:47.120 --> 00:20:48.950
one more question before we finish up


00:20:48.960 --> 00:20:50.870
today. And this is a question with 47


00:20:50.880 --> 00:20:53.830
parts. Hi, Professor Fred and Andrew


00:20:53.840 --> 00:20:56.789
Peter here from San Diego, California. I


00:20:56.799 --> 00:20:59.669
have a dual question about dark energy.


00:20:59.679 --> 00:21:01.909
My understanding is that dark energy is


00:21:01.919 --> 00:21:05.350
causing our universe to expand. Also, we


00:21:05.360 --> 00:21:07.190
have an observable part of the universe


00:21:07.200 --> 00:21:09.510
where light is able to reach us and an


00:21:09.520 --> 00:21:11.909
unobservable part of the universe. Funny


00:21:11.919 --> 00:21:13.830
how we already talked about this, but


00:21:13.840 --> 00:21:15.669
the these all these questions kind of


00:21:15.679 --> 00:21:18.470
dovetailed. Question one, is it feasible


00:21:18.480 --> 00:21:20.390
that the unobservable part of the


00:21:20.400 --> 00:21:22.549
universe contains enough matter to act


00:21:22.559 --> 00:21:24.710
gravitationally on the observable


00:21:24.720 --> 00:21:27.350
universe, thus causing the expansion?


00:21:27.360 --> 00:21:28.870
And question two, which we'll get back


00:21:28.880 --> 00:21:31.270
to, uh, same question within the context


00:21:31.280 --> 00:21:33.590
of the multisphere. Could universes


00:21:33.600 --> 00:21:35.750
other than our own be gravitationally


00:21:35.760 --> 00:21:38.549
impacting the expansion of our universe?


00:21:38.559 --> 00:21:40.870
Love your show. Keep up the great work.


00:21:40.880 --> 00:21:43.990
Uh, thank you, Peter. Um question one is


00:21:44.000 --> 00:21:46.070
it feasible that the unobservable part


00:21:46.080 --> 00:21:48.390
of our universe contains enough matter


00:21:48.400 --> 00:21:51.190
to act gravitationally on the observable


00:21:51.200 --> 00:21:53.190
observable universe thus causing the


00:21:53.200 --> 00:21:54.870
expansion.


00:21:54.880 --> 00:21:58.870
Um yes once again we've got to unpick uh


00:21:58.880 --> 00:22:02.630
what we mean by the expansion. So um


00:22:02.640 --> 00:22:04.710
Peter says my understanding is that dark


00:22:04.720 --> 00:22:07.110
energy is causing our universe to expand


00:22:07.120 --> 00:22:08.789
and that's not the case as we've just


00:22:08.799 --> 00:22:10.630
described. It's the big bang that caused


00:22:10.640 --> 00:22:12.390
the universe to expand. But dark energy


00:22:12.400 --> 00:22:14.070
is what's causing the expansion to


00:22:14.080 --> 00:22:15.430
accelerate


00:22:15.440 --> 00:22:17.110
>> uh to to get faster.


00:22:17.120 --> 00:22:18.789
>> It's easy to get confused though, isn't


00:22:18.799 --> 00:22:19.270
it? Because


00:22:19.280 --> 00:22:21.110
>> it is absolutely


00:22:21.120 --> 00:22:22.710
>> this is an event with a lot of moving


00:22:22.720 --> 00:22:23.430
parts.


00:22:23.440 --> 00:22:25.830
>> It is. Yes. As you'd expect, it's a


00:22:25.840 --> 00:22:27.029
universe after all.


00:22:27.039 --> 00:22:27.430
>> Yeah.


00:22:27.440 --> 00:22:31.750
>> Um but what Peter says is is correct. Um


00:22:31.760 --> 00:22:34.149
because we, as we've just said, there


00:22:34.159 --> 00:22:35.750
are, you know, there are parts of the


00:22:35.760 --> 00:22:38.710
universe well beyond 13.8 8 billion


00:22:38.720 --> 00:22:41.190
light years. Um, which we can't see


00:22:41.200 --> 00:22:42.950
because what we run into is the cosmic


00:22:42.960 --> 00:22:44.390
microwave background radiation, the


00:22:44.400 --> 00:22:46.149
flash of the big bang. So, we know


00:22:46.159 --> 00:22:47.909
there's universe beyond that, but we


00:22:47.919 --> 00:22:49.110
can't see it.


00:22:49.120 --> 00:22:52.470
>> Um, and Peter's suggestion is it


00:22:52.480 --> 00:22:54.310
feasible that the unobservable part of


00:22:54.320 --> 00:22:56.070
the universe contains enough matter to


00:22:56.080 --> 00:22:57.830
act gravitationally on the observable


00:22:57.840 --> 00:23:01.590
universe. Uh, and as and thus causing


00:23:01.600 --> 00:23:02.950
the expansion. It's actually thus


00:23:02.960 --> 00:23:04.230
causing the acceleration of the


00:23:04.240 --> 00:23:06.310
expansion. Uh that is one of the


00:23:06.320 --> 00:23:07.909
theories that people have looked at


00:23:07.919 --> 00:23:10.549
exactly that that are we in a kind of


00:23:10.559 --> 00:23:13.590
local bubble where the density is low


00:23:13.600 --> 00:23:16.950
compared with what we what we what is


00:23:16.960 --> 00:23:19.350
outside the boundary that we can see


00:23:19.360 --> 00:23:21.350
where the density might be higher and


00:23:21.360 --> 00:23:23.110
hence having a gravitational effect on


00:23:23.120 --> 00:23:26.070
our local bubble. Um it's a it's


00:23:26.080 --> 00:23:28.549
certainly a you know a conjecture that


00:23:28.559 --> 00:23:32.149
is raised by uh by astrophysicists and


00:23:32.159 --> 00:23:34.070
cosmologists. So Peter's on the right


00:23:34.080 --> 00:23:36.390
track there. And then question two, the


00:23:36.400 --> 00:23:38.070
same question within the context of the


00:23:38.080 --> 00:23:40.549
multiverse. Could universes other than


00:23:40.559 --> 00:23:42.310
our own gravitationally be


00:23:42.320 --> 00:23:44.070
gravitationally impacting the expansion


00:23:44.080 --> 00:23:47.430
of our universe? And I think um that is


00:23:47.440 --> 00:23:50.630
also something that's considered. Um,


00:23:50.640 --> 00:23:53.110
one of the reasons why people think


00:23:53.120 --> 00:23:55.510
there might be multiverses,


00:23:55.520 --> 00:23:59.270
uh, it is that gravity itself


00:23:59.280 --> 00:24:03.270
is compared with the other three


00:24:03.280 --> 00:24:06.710
fundamental forces in nature, it is


00:24:06.720 --> 00:24:09.510
incredibly weak. So the fundamental


00:24:09.520 --> 00:24:11.750
forces are the strong and weak nuclear


00:24:11.760 --> 00:24:13.750
forces, things that hold atoms together.


00:24:13.760 --> 00:24:15.669
The electromagnetic force causes


00:24:15.679 --> 00:24:18.230
chemical reactions and and photons so


00:24:18.240 --> 00:24:20.230
that we can talk to each other. Those


00:24:20.240 --> 00:24:22.870
are the three uh which are best known.


00:24:22.880 --> 00:24:25.510
Gravity is the fourth fundamental force.


00:24:25.520 --> 00:24:28.630
But it is gazillions of times weaker


00:24:28.640 --> 00:24:30.789
than the other three and some people


00:24:30.799 --> 00:24:33.430
suggest that maybe that is because it is


00:24:33.440 --> 00:24:36.390
leaking into other universes. Hence the


00:24:36.400 --> 00:24:39.350
idea of a multiverse scenario. But that


00:24:39.360 --> 00:24:41.669
is very speculative. We don't have any


00:24:41.679 --> 00:24:43.510
hard evidence that points towards a


00:24:43.520 --> 00:24:47.190
multiverse. But yes, once again, maybe


00:24:47.200 --> 00:24:48.789
there are gravitational influences


00:24:48.799 --> 00:24:50.549
coming from the outside of our universe,


00:24:50.559 --> 00:24:51.669
whatever that means, because the


00:24:51.679 --> 00:24:53.269
universe by definition means everything


00:24:53.279 --> 00:24:56.390
you can observe or or understand. Um, so


00:24:56.400 --> 00:24:59.430
it is possible. So, um, I think Peter's,


00:24:59.440 --> 00:25:01.750
you know, his questions are are well


00:25:01.760 --> 00:25:04.070
well directed. He's on the right track.


00:25:04.080 --> 00:25:07.990
>> Yeah. Uh I think as you said there's no


00:25:08.000 --> 00:25:09.510
direct evidence whatsoever of


00:25:09.520 --> 00:25:12.710
multiverses but we've said it before


00:25:12.720 --> 00:25:14.310
mathematically


00:25:14.320 --> 00:25:15.510
it's plausible. It


00:25:15.520 --> 00:25:18.149
>> it's possible. That's right. Yeah.


00:25:18.159 --> 00:25:19.510
>> A lot of things are mathematically


00:25:19.520 --> 00:25:22.549
possible that you don't see in reality.


00:25:22.559 --> 00:25:24.549
>> And how much of the universe can we not


00:25:24.559 --> 00:25:28.149
see? Is it like 75% or something?


00:25:28.159 --> 00:25:29.029
>> We have no idea.


00:25:29.039 --> 00:25:30.310
>> We don't know. We don't know how big it


00:25:30.320 --> 00:25:30.870
is.


00:25:30.880 --> 00:25:33.029
>> Could be infinite. We don't know.


00:25:33.039 --> 00:25:33.909
>> Yeah. Gosh,


00:25:33.919 --> 00:25:36.710
>> all we know is what we can see.


00:25:36.720 --> 00:25:38.870
>> It's It's crazy town, isn't it? When you


00:25:38.880 --> 00:25:41.510
>> It is. Yeah, it is. Um That's right.


00:25:41.520 --> 00:25:41.909
It's


00:25:41.919 --> 00:25:46.870
>> keeps you in a job.


00:25:46.880 --> 00:25:49.909
>> Yes, it does. Keeps me in a job. That's


00:25:49.919 --> 00:25:50.149
right.


00:25:50.159 --> 00:25:52.470
>> Yeah. Yeah. But that's, you know, that's


00:25:52.480 --> 00:25:53.909
when the critics come out. We got all


00:25:53.919 --> 00:25:56.149
you BS trying to figure out and ladies,


00:25:56.159 --> 00:25:58.070
what's going on? You've been working on


00:25:58.080 --> 00:25:59.669
it for hundreds of years and you still


00:25:59.679 --> 00:26:00.549
don't know the answer.


00:26:00.559 --> 00:26:02.390
>> Still, we still don't know. Um, the good


00:26:02.400 --> 00:26:04.630
the good news is that node is paying me


00:26:04.640 --> 00:26:06.390
now. So that's all right.


00:26:06.400 --> 00:26:09.350
>> So you don't have to worry about that.


00:26:09.360 --> 00:26:11.350
>> It's a costfree analysis now.


00:26:11.360 --> 00:26:12.789
>> There you go. You get it for free.


00:26:12.799 --> 00:26:14.149
That's right, ladies and gentlemen. This


00:26:14.159 --> 00:26:15.590
all comes to you free.


00:26:15.600 --> 00:26:18.710
>> Yes, it does. Um, all right. So I think


00:26:18.720 --> 00:26:21.190
we covered everything there. Um, thank


00:26:21.200 --> 00:26:23.430
you Peter. Great set of questions all


00:26:23.440 --> 00:26:25.750
up. Some um real intrigue in some of


00:26:25.760 --> 00:26:28.630
those as well which uh is really good.


00:26:28.640 --> 00:26:31.110
Uh, but as I've said many times, uh, we


00:26:31.120 --> 00:26:32.950
need some more questions. So, if you can


00:26:32.960 --> 00:26:34.950
get online to our website and click on


00:26:34.960 --> 00:26:36.789
the ask me anything tab at the top of


00:26:36.799 --> 00:26:40.549
our, uh, page, uh, send us text or audio


00:26:40.559 --> 00:26:42.070
questions. We certainly could use some


00:26:42.080 --> 00:26:44.870
more audio questions. We get a lot from


00:26:44.880 --> 00:26:46.710
people who might ask 10 at a time.


00:26:46.720 --> 00:26:49.110
Obviously, we can't run them all


00:26:49.120 --> 00:26:50.710
consecutively, otherwise no one else


00:26:50.720 --> 00:26:52.470
gets a bite. But, uh, if you've thought


00:26:52.480 --> 00:26:54.390
about asking a question and you haven't


00:26:54.400 --> 00:26:56.630
got around to it yet, don't be scared.


00:26:56.640 --> 00:26:58.470
We don't bite. Well, we do bite, but


00:26:58.480 --> 00:27:00.470
don't worry about that. It's harmless.


00:27:00.480 --> 00:27:03.029
We're not venomous. Uh, but you can send


00:27:03.039 --> 00:27:05.590
it in through spaceodcast.com


00:27:05.600 --> 00:27:08.310
or spacenuts.io


00:27:08.320 --> 00:27:10.630
and click on that tab and uh send us


00:27:10.640 --> 00:27:12.710
your question or just a comment. I mean,


00:27:12.720 --> 00:27:14.789
if you want to add a comment, we can


00:27:14.799 --> 00:27:16.230
throw that into the show. It's nice to


00:27:16.240 --> 00:27:18.630
have all these different voices on the


00:27:18.640 --> 00:27:21.510
air. Uh, so yeah, send them into us.


00:27:21.520 --> 00:27:22.710
Don't forget to tell us who you are and


00:27:22.720 --> 00:27:23.669
where you're from. I think I've already


00:27:23.679 --> 00:27:25.750
said that. Uh, we are done, Fred. Thank


00:27:25.760 --> 00:27:27.990
you so very very much.


00:27:28.000 --> 00:27:30.149
>> It's a great pleasure, Andrew. And um I


00:27:30.159 --> 00:27:31.510
hope we'll do it again sometime.


00:27:31.520 --> 00:27:33.669
>> I hope so too. Maybe in a week, maybe


00:27:33.679 --> 00:27:35.750
more, maybe less. You just, you know,


00:27:35.760 --> 00:27:38.950
it's all all to do withuling


00:27:38.960 --> 00:27:42.070
and availability and what our wives are


00:27:42.080 --> 00:27:43.750
doing at any particular time. That's the


00:27:43.760 --> 00:27:45.510
most significant factor.


00:27:45.520 --> 00:27:47.350
>> Thanks, Fred. We'll see you soon.


00:27:47.360 --> 00:27:49.269
>> Cheers for now. Bye-bye.


00:27:49.279 --> 00:27:51.029
>> Uh Professor Fred Watson, astronomer at


00:27:51.039 --> 00:27:53.269
large. Thanks to Hugh in the studio who


00:27:53.279 --> 00:27:55.909
couldn't be with us today because he's


00:27:55.919 --> 00:27:57.430
unobservable.


00:27:57.440 --> 00:27:59.269
And from me, Andrew Dunley, thanks for


00:27:59.279 --> 00:28:01.029
your company. See you on the next


00:28:01.039 --> 00:28:03.110
episode of Space Nuts. Bye-bye.


00:28:03.120 --> 00:28:04.070
>> Space Nuts.


00:28:04.080 --> 00:28:06.149
>> You've been listening to the Space Nuts


00:28:06.159 --> 00:28:08.470
podcast.


00:28:08.480 --> 00:28:11.430
>> Available at Apple Podcasts, Spotify,


00:28:11.440 --> 00:28:14.070
iHeart Radio, or your favorite podcast


00:28:14.080 --> 00:28:16.470
player. You can also stream on demand at


00:28:16.480 --> 00:28:19.350
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00:28:19.360 --> 00:28:23.960
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