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

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Hi there. Thanks for joining us. My name


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is Andrew Dunley and this is Space Nuts


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Q&A edition. It also happens to be our


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sixth hundth episode, believe it or not.


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And what are we doing special today?


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Nothing. We're just going to answer a


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Well, it happens so often now. Uh we're


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just going to answer audience questions.


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And we've got a bunch of them. Um the


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question of dark matter and dark energy


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theory has come up again. Uh, in fact,


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one of our listeners has come up with a


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theory about dark matter and dark energy


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theory. So, we'll investigate that. We


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also have a question from somebody using


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a very interesting pseudonym. Uh,


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finding where our sun was born. I think


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we've been down that road before


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recently, so they're revisiting that.


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The temperature of black holes has been


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raised yet again. We talked about that


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recently. And Peter has asked us about


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the expansion of the universe. That's


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all coming up on this edition 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. once


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again joining us from the oh it's not


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the 600th time because we've had time


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off so it's probably 592


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or something like that maybe I don't


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know maybe a few less but um his name is


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Fred Watson professor Fred Watson in


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fact astronomer at large hi Fred


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>> how you doing to see you again


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>> good to see you too


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>> can you believe it's 600 episodes my


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goodness


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>> so we because we now have two a week


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that you go through a hundred every year


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basically doesn't more or less.


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>> Yeah.


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>> Whereas it used to be every couple of


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years. So


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>> yes,


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>> we're just moving faster. It's it's the


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expansion of the universe because it's


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accelerating. That's what it is.


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>> It's a relative relativistic effect


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>> indeed. Uh let us uh get straight into


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our questions because we've got a whole


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bunch of them. Daryl has sent us in a


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question. Good day, Space Nuts. I've


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been giving dark energy and dark matter


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some thought. If I've got this right,


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dark matter matter pushes the universe


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apart or away while um dark energy


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attracts or brings stuff together. So


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could dark matter and dark energy be the


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same thing but have uh like a north and


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south pole? I.e. dark matter north would


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be the particle that clumps together and


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dark energy south would be the particle


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that pushes outwards creating negative


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pressure and expanding the universe.


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Thoughts. Now, that's his question. But


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he says, "By the way, Martin's joke


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about the Ganab Gibb being a lost BG


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brother made me laugh out loud for a


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couple of minutes." That's Daryl from


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South Australia. Yeah, I thought it was


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funny, too. And that's the first time


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Martin's ever been funny. But, um, no,


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we It was a good one. It was a very good


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one. Um, yes. So, um, this is an


00:03:04.800 --> 00:03:06.790
interesting theory. as a dark matter


00:03:06.800 --> 00:03:10.149
south pole dark energy north pole


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opposites attract type of scenario I


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don't know what do you think so the the


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issue yes uh it's a nice thought because


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the you know we naturally think along


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those lines when we recognize that one


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of these forces entities


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pull stuff together and the other pushes


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it apart


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um


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And


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in in many ways that's the crux of the


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matter because the the two of them are


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fundamentally different in their uh in


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their effect on the universe. So dark


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energy which comes as a man which is


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manifested to us in the accelerated


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expansion of the universe that's an


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energy of space itself and to the best


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of our ability uh to determine these


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things it is isotropic uh in other words


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it's the same in all directions. Now


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some people have questioned that


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>> uh s suggesting that maybe you know for


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all we are looking at a big chunk of the


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universe with a horizon of 13.8 8


00:04:18.239 --> 00:04:21.670
billion light years. Um it may be that


00:04:21.680 --> 00:04:23.350
that's just a small part of the universe


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and there are other bits where where you


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know the


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the acceleration is not sorry the


00:04:29.759 --> 00:04:32.469
expansion is not accelerating uh and the


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two sort of even out. Um that's that's


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a a a caveat that we can't really deal


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with because we've no idea what happens


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beyond the little bubble of the universe


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that we can observe. Yeah. And certainly


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it's true within that bubble the


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acceleration is basically this or the


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accelerated sorry the accelerated


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expansion is basically the same in all


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directions. So it's a property of space


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itself. It's a fundamental property. Um


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whereas dark matter yes that's got


00:05:03.520 --> 00:05:05.030
gravitation


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um and pulls stuff in. It's definitely


00:05:08.479 --> 00:05:13.029
clumpy. Uh it it it actually um well it


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follows the the the visible matter. That


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was the way it was thought to be when we


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first started thinking about dark


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matter. But now we think it's probably


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the other way around that the visible


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matter is visible because dark matter


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acted as a kind of scaffolding uh in the


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early universe for uh the gravitational


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pull of dark matter uh in order to bring


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the clouds of hydrogen together,


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compress them and make them turn into


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stars. So um that's why dark matter and


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normal matter stick together but they do


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stick together. Uh and when you you know


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when you observe the universe on the


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larger scales we can see um by for


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example gravitational lensing uh we can


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see that the uh the the um dark matter


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definitely follows the visible matter.


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So there will be places where uh there's


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hardly any visible matter and there's


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hardly any dark matter whereas with the


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dark energy it's everywhere


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>> and so there's there are fundamental


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differences between them and I suspect


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in the end you know if we were having


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this conversation in 20 or 30 years time


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we probably will be actually but anyway


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um when we look back on this we we might


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have realized that uh the dark uh energy


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is a bzon. It's a it's a force particle.


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Uh whereas dark matter is some sort of


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matter particle made of quarks and


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things of that sort. So there probably


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fundamental differences rather than just


00:06:43.039 --> 00:06:46.230
that sort of the idea that they might be


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the same thing but with a different


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polarity.


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>> Yeah.


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>> Um I I I don't think the evidence


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supports that. I suppose we could say


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Daryl's fallen for the naming error uh


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of of these two things because um we


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we've said all along that dark energy is


00:07:02.240 --> 00:07:06.390
poorly named. It's it's not really


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the right thing to call it. Well, well,


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neither of them are really, you know,


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they're invisible would have been far


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better, but dark. It was actually Fritz


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Vicki back in 1933 who labeled um this


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stuff dark matter. He didn't what it was


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and he said there must be something


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there which he was calling dark matter


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that um that's providing enough of a


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gravitational attraction to stop


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clusters of galaxies from dispersing


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altogether.


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>> Yeah. Interesting. Um they'll figure it


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out one day, but um for now it it


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remains a mystery. But that there's got


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to be something in that connection


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between real matter and dark matter


00:07:48.319 --> 00:07:51.430
plumping. Like if you go somewhere there


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isn't much matter, there isn't much dark


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matter. So there's got to be some


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connection there that


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>> there is. That's right.


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>> That will that will give us the answer


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one day if we can figure out what the


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connection is.


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>> Yeah. Well, the connection is gravity


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and um it's the only um


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>> Well, we haven't figured that out


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either.


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>> No, that's right. We basically we we


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know how it behaves. We know very


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accurately how it behaves, but we don't


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know what it is.


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>> Yeah,


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>> it is indeed a mystery, Darl. Uh but


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coming up with an idea always is um a


00:08:23.280 --> 00:08:25.110
good way to get people thinking and


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maybe maybe somewhere in the dark


00:08:28.160 --> 00:08:29.670
reaches of the internet someone will


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hear this and go, "Hang on, Daryl's on


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to something." And then he'll go to his


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Wikipedia or his uh encyclopedia


00:08:36.560 --> 00:08:39.190
Bratannica or his Funkin Wagnoff, flick


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a few pages and go,


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I've got it figured out thanks to


00:08:43.519 --> 00:08:45.829
Daryl's question on space nuts. So, you


00:08:45.839 --> 00:08:48.070
know, there are no dumb questions in


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astronomy, are there, Fred?


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>> No, that's absolutely right. There's


00:08:52.320 --> 00:08:55.750
just dumb answers from the likes of me.


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>> Thanks, Daryl. Great to hear from you.


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Our next question comes from the fjords


00:09:00.320 --> 00:09:05.430
of Norway. Uh and um this uh question


00:09:05.440 --> 00:09:07.030
goes by the name of someone will


00:09:07.040 --> 00:09:09.990
recognize this Slatty Bfast. Uh


00:09:10.000 --> 00:09:11.829
listening from the fields of Norway last


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week. Someone asked the question about


00:09:13.600 --> 00:09:15.910
viewing the birth of the sun and Fred


00:09:15.920 --> 00:09:19.190
answered with the hypothetical mirror in


00:09:19.200 --> 00:09:22.870
space. My question is if we calculated


00:09:22.880 --> 00:09:25.670
the exact location in space for the sun


00:09:25.680 --> 00:09:28.230
4.6 six billion years ago and pointed a


00:09:28.240 --> 00:09:30.550
telescope at those coordinate uh


00:09:30.560 --> 00:09:36.310
coordinates, would we see anything?


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>> Cuz slatty Bfast won an award, didn't


00:09:38.880 --> 00:09:41.910
he, for the fields of Norway? So that


00:09:41.920 --> 00:09:44.389
>> Oh, that's right. That's right. Yes,


00:09:44.399 --> 00:09:46.710
that wasn't because he he designed them


00:09:46.720 --> 00:09:47.430
or


00:09:47.440 --> 00:09:49.430
>> designed them. Yes, he made he made


00:09:49.440 --> 00:09:50.470
fjords.


00:09:50.480 --> 00:09:52.790
>> That's right. That was what Zan Bartfast


00:09:52.800 --> 00:09:55.030
was famous for. One of my favorite


00:09:55.040 --> 00:09:56.470
Douglas Adams characters.


00:09:56.480 --> 00:09:58.949
>> Oh, yeah. Brilliant. I think the moment


00:09:58.959 --> 00:10:01.350
where he's forced to say his name is one


00:10:01.360 --> 00:10:04.310
of the the the funniest moments I've


00:10:04.320 --> 00:10:06.230
ever experienced


00:10:06.240 --> 00:10:08.790
cuz first time I ever listened to it. I


00:10:08.800 --> 00:10:12.470
listened to the audio version. That just


00:10:12.480 --> 00:10:14.470
caught me so beautifully. I just


00:10:14.480 --> 00:10:17.190
couldn't stop cackling.


00:10:17.200 --> 00:10:20.630
>> Very No, it's it's epic. Epic stuff. One


00:10:20.640 --> 00:10:22.550
of the all-time greats in science


00:10:22.560 --> 00:10:24.470
fiction. Absolutely. Yes.


00:10:24.480 --> 00:10:27.350
>> Yeah. Um anyway, the answer to Slatty


00:10:27.360 --> 00:10:31.670
Bfast's question is no. So, um do you


00:10:31.680 --> 00:10:33.269
want to keep going?


00:10:33.279 --> 00:10:35.750
>> Well, I mean, he he's basically saying


00:10:35.760 --> 00:10:37.670
we So, you're saying we would not see


00:10:37.680 --> 00:10:39.670
anything if we could figure out where


00:10:39.680 --> 00:10:41.750
the sun was 4.6 billion years ago and


00:10:41.760 --> 00:10:43.670
then pointed a telescope at it.


00:10:43.680 --> 00:10:46.470
>> Yeah. Because um first of all, the sun


00:10:46.480 --> 00:10:47.750
isn't there anymore.


00:10:47.760 --> 00:10:49.750
>> No, I know where it is.


00:10:49.760 --> 00:10:52.630
>> Yes. The odds are there.


00:10:52.640 --> 00:10:56.470
>> That that point uh you Let me see which


00:10:56.480 --> 00:10:57.350
way you're pointing.


00:10:57.360 --> 00:10:58.710
>> I'm pointing that way.


00:10:58.720 --> 00:11:00.150
>> That way. That's good. That's probably


00:11:00.160 --> 00:11:02.470
correct, too. In fact, it's behind me,


00:11:02.480 --> 00:11:07.670
too. It's to my It's to my right rear.


00:11:07.680 --> 00:11:07.990
>> That way.


00:11:08.000 --> 00:11:09.990
>> All right. Okay. At the moment. That's a


00:11:10.000 --> 00:11:11.430
bit intimate, isn't it? Anyway, never


00:11:11.440 --> 00:11:15.350
mind. Um the uh the sun is certainly not


00:11:15.360 --> 00:11:17.750
shining out of that particular part of


00:11:17.760 --> 00:11:20.150
me at the moment, but it's it's in that


00:11:20.160 --> 00:11:23.670
kind of direction.


00:11:23.680 --> 00:11:25.110
>> It's what all your fans think though,


00:11:25.120 --> 00:11:25.990
isn't it?


00:11:26.000 --> 00:11:29.190
>> They don't. Uh I don't even have any I


00:11:29.200 --> 00:11:32.310
don't get fan mail. I get abuse.


00:11:32.320 --> 00:11:33.829
>> Well,


00:11:33.839 --> 00:11:36.310
uh anyway, um notwithstanding all that,


00:11:36.320 --> 00:11:38.069
what was the question again? Yes. If you


00:11:38.079 --> 00:11:40.550
could work out where the sun was 4.6 six


00:11:40.560 --> 00:11:43.350
billion years ago and point a telescope


00:11:43.360 --> 00:11:46.710
at it, you wouldn't see anything because


00:11:46.720 --> 00:11:50.470
the the point where the sun was formed.


00:11:50.480 --> 00:11:53.990
Um, and it it it will be only a few at


00:11:54.000 --> 00:11:58.389
most 100 million light years away. Uh,


00:11:58.399 --> 00:12:00.470
so yeah, you've got to look back time,


00:12:00.480 --> 00:12:02.069
but you've got to look back time. It's


00:12:02.079 --> 00:12:04.630
probably less than 100 million years.


00:12:04.640 --> 00:12:07.590
Uh, and the sun 100 million years ago


00:12:07.600 --> 00:12:09.190
was a lot like what it is now. It's


00:12:09.200 --> 00:12:11.509
slightly hotter uh and a few other


00:12:11.519 --> 00:12:13.350
things that were going on at the time,


00:12:13.360 --> 00:12:15.750
but not much different. But the fact is


00:12:15.760 --> 00:12:20.389
it's not there, it's here. Um so even


00:12:20.399 --> 00:12:23.110
as I think I said uh in that thought


00:12:23.120 --> 00:12:25.670
experiment, you'd have to have a mirror


00:12:25.680 --> 00:12:29.750
uh something like 2.3 billion light


00:12:29.760 --> 00:12:31.590
years away


00:12:31.600 --> 00:12:33.430
uh which is going to take you quite a


00:12:33.440 --> 00:12:36.629
lot of time to put in place anyway. But


00:12:36.639 --> 00:12:39.269
if that mirror was looking back to


00:12:39.279 --> 00:12:40.949
wherever the sun was formed, and we


00:12:40.959 --> 00:12:43.670
don't know where that was. Uh we know


00:12:43.680 --> 00:12:45.590
it's within the present vicinity of the


00:12:45.600 --> 00:12:47.910
sun because stars don't move that fast.


00:12:47.920 --> 00:12:50.949
Uh anyway, um you you have this mirror


00:12:50.959 --> 00:12:54.470
and you capture a reflection of the sun


00:12:54.480 --> 00:12:57.269
being born. Uh that thought experiment I


00:12:57.279 --> 00:13:00.790
think would work, but just um looking at


00:13:00.800 --> 00:13:04.550
where the sun was when it was born isn't


00:13:04.560 --> 00:13:06.629
going to tell you very much. There's got


00:13:06.639 --> 00:13:08.470
to be something there though, right?


00:13:08.480 --> 00:13:10.389
>> Well, there be Yeah. Probably other


00:13:10.399 --> 00:13:12.150
stars and things like that, you know.


00:13:12.160 --> 00:13:13.910
It's just part of the the solar


00:13:13.920 --> 00:13:15.910
neighborhood. Yeah.


00:13:15.920 --> 00:13:18.870
>> Yeah. Our our son, I suspect, came from,


00:13:18.880 --> 00:13:21.190
you know, a pretty rough neighborhood


00:13:21.200 --> 00:13:23.990
and that's why it left. It uh inherited


00:13:24.000 --> 00:13:26.710
money and managed to managed to get


00:13:26.720 --> 00:13:27.990
away.


00:13:28.000 --> 00:13:29.590
>> Yeah. But then it discovered drugs,


00:13:29.600 --> 00:13:30.230
didn't it? That's


00:13:30.240 --> 00:13:32.550
>> Yeah. Well, that's that's what happened.


00:13:32.560 --> 00:13:35.269
Yes. And and then we turned up and um


00:13:35.279 --> 00:13:36.870
Yeah.


00:13:36.880 --> 00:13:39.509
>> Well, hell broke loose. Yes. Uh but


00:13:39.519 --> 00:13:41.190
there'd be nothing to see there. Nothing


00:13:41.200 --> 00:13:43.190
to see there. No.


00:13:43.200 --> 00:13:44.710
>> Nothing that's really of any interest.


00:13:44.720 --> 00:13:45.910
Just other stars.


00:13:45.920 --> 00:13:46.470
>> Yeah.


00:13:46.480 --> 00:13:48.470
>> Yeah. Although we're still looking for


00:13:48.480 --> 00:13:50.790
Earth's siblings. Uh sorry, the sun's


00:13:50.800 --> 00:13:51.990
siblings. That's


00:13:52.000 --> 00:13:52.629
>> That's right.


00:13:52.639 --> 00:13:54.230
>> Because there there would be some, but


00:13:54.240 --> 00:13:55.670
they wouldn't be there either, would


00:13:55.680 --> 00:13:59.590
they? Well, that you know that the stars


00:13:59.600 --> 00:14:01.829
and that I'm sorry, the stars that were


00:14:01.839 --> 00:14:04.150
born alongside the sun in the same cloud


00:14:04.160 --> 00:14:06.550
of gas and dust uh are probably not that


00:14:06.560 --> 00:14:13.030
far away. Uh but um they


00:14:13.040 --> 00:14:14.949
yeah


00:14:14.959 --> 00:14:17.910
100 Yeah, 100 100 million light years I


00:14:17.920 --> 00:14:19.509
mentioned before. It's probably much


00:14:19.519 --> 00:14:21.350
much less than that. I don't know quite


00:14:21.360 --> 00:14:25.189
why I thought of that, but anyway,


00:14:25.199 --> 00:14:26.949
because the center of our galaxy is only


00:14:26.959 --> 00:14:30.389
25,000 light years away. Uh, so um I


00:14:30.399 --> 00:14:33.509
probably meant 100,000 light years as


00:14:33.519 --> 00:14:36.870
when I said 100 million. Um,


00:14:36.880 --> 00:14:38.069
something's going wrong with this


00:14:38.079 --> 00:14:39.750
program today. I'm not quite sure. Well,


00:14:39.760 --> 00:14:39.990
we


00:14:40.000 --> 00:14:42.150
>> It's 100 It's a 600.


00:14:42.160 --> 00:14:44.310
>> That's what it is. That's what it is.


00:14:44.320 --> 00:14:46.870
There's a there's a a gap in spaceime


00:14:46.880 --> 00:14:49.350
has opened up uh which I'm floundering


00:14:49.360 --> 00:14:51.670
in at the moment. Yeah. So, you know,


00:14:51.680 --> 00:14:54.949
you might it's it's not gone very far.


00:14:54.959 --> 00:14:56.710
Uh that's what I'm saying. The siblings


00:14:56.720 --> 00:14:59.430
from from the sun in the born in the


00:14:59.440 --> 00:15:01.350
same gas cloud from the sun are probably


00:15:01.360 --> 00:15:03.189
within they might even be within the


00:15:03.199 --> 00:15:06.150
nearest 100 million sorry 100 light


00:15:06.160 --> 00:15:11.030
years not million light years. Um so uh


00:15:11.040 --> 00:15:16.310
and that's why we can use very high


00:15:16.320 --> 00:15:19.030
resolution instruments, ones that uh


00:15:19.040 --> 00:15:21.430
really analyze the spectrum of a star in


00:15:21.440 --> 00:15:23.590
great detail but need the star to be


00:15:23.600 --> 00:15:25.590
relatively bright. That's why we can use


00:15:25.600 --> 00:15:27.829
that technology with a real hope of


00:15:27.839 --> 00:15:29.750
finding the solar siblings because it's


00:15:29.760 --> 00:15:32.069
by analyzing the the spectrum the


00:15:32.079 --> 00:15:34.870
chemical composition of a star uh in


00:15:34.880 --> 00:15:37.350
very great detail. That's how we would


00:15:37.360 --> 00:15:39.990
identify that a star had exactly the


00:15:40.000 --> 00:15:42.710
same chemical composition as the sun and


00:15:42.720 --> 00:15:44.310
could be regarded as likely to be a


00:15:44.320 --> 00:15:46.230
solar sibling.


00:15:46.240 --> 00:15:50.230
>> Okay. We may one day find one of them,


00:15:50.240 --> 00:15:52.790
but who knows? Yeah,


00:15:52.800 --> 00:15:55.030
>> we'll see. Uh, and thank you Slatty


00:15:55.040 --> 00:15:57.509
Bartfast. Um, whatever your real name


00:15:57.519 --> 00:15:59.430
is. That maybe that's it. Um,


00:15:59.440 --> 00:16:00.389
>> could be. Could be.


00:16:00.399 --> 00:16:02.069
>> Thanks. Thanks for the question and and


00:16:02.079 --> 00:16:03.749
thank you for sending me the Babel fish


00:16:03.759 --> 00:16:06.470
so I could read the question. That was


00:16:06.480 --> 00:16:08.629
that was a good idea. Very very good


00:16:08.639 --> 00:16:11.189
idea. This is Space Nuts. Andrew Dunley


00:16:11.199 --> 00:16:14.629
here with Professor Fred Watson.


00:16:14.639 --> 00:16:16.150
Let's take a break from the show to tell


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00:17:54.559 --> 00:17:56.230
>> Okay, we've had a problem here.


00:17:56.240 --> 00:17:58.310
>> This is Houston. Say again, please.


00:17:58.320 --> 00:17:59.669
>> Houston, we had a problem. We had a


00:17:59.679 --> 00:18:00.870
main.


00:18:00.880 --> 00:18:03.510
>> Roger. Main. Okay, stand by 13. We're


00:18:03.520 --> 00:18:04.070
looking at it.


00:18:04.080 --> 00:18:06.950
>> Space nuts. You know, that moment where


00:18:06.960 --> 00:18:09.590
they realized they had a problem on um


00:18:09.600 --> 00:18:12.230
Apollo 13 sounded much better in the


00:18:12.240 --> 00:18:14.789
movie.


00:18:14.799 --> 00:18:17.990
>> It just um Yeah,


00:18:18.000 --> 00:18:21.029
>> you bro you broke up exactly as you were


00:18:21.039 --> 00:18:21.669
saying.


00:18:21.679 --> 00:18:23.190
>> I noticed that and I was going to keep


00:18:23.200 --> 00:18:25.510
talking until you came back, but um


00:18:25.520 --> 00:18:26.710
>> tell me what you said.


00:18:26.720 --> 00:18:29.909
>> I said that that moment where Apollo 13


00:18:29.919 --> 00:18:32.630
realized they had that problem sounded


00:18:32.640 --> 00:18:35.270
much better in the movie.


00:18:35.280 --> 00:18:35.750
Yeah.


00:18:35.760 --> 00:18:37.990
>> Wasn't nearly as dramatic in real life,


00:18:38.000 --> 00:18:39.029
was it?


00:18:39.039 --> 00:18:39.830
>> Well, that's


00:18:39.840 --> 00:18:41.430
>> Well, it was dramatic, but the way they


00:18:41.440 --> 00:18:41.990
announced it.


00:18:42.000 --> 00:18:42.789
>> Absolutely.


00:18:42.799 --> 00:18:44.470
>> Yeah. They they basically just said,


00:18:44.480 --> 00:18:47.510
"Yeah, this button didn't work."


00:18:47.520 --> 00:18:48.230
>> More or less.


00:18:48.240 --> 00:18:49.510
>> Um,


00:18:49.520 --> 00:18:51.909
>> yeah. Epic stuff. I mean, it still gives


00:18:51.919 --> 00:18:54.710
me tingles. Does Apollo 13.


00:18:54.720 --> 00:18:57.830
>> Absolutely. Yeah. Now, Fred, let's move


00:18:57.840 --> 00:19:00.470
on to our third question. This one comes


00:19:00.480 --> 00:19:02.950
from Bejorn.


00:19:02.960 --> 00:19:06.870
>> Good evening, Fred. And Andrew, I have


00:19:06.880 --> 00:19:10.070
to thank you for a fantastic podcast. My


00:19:10.080 --> 00:19:13.909
first choice every evening


00:19:13.919 --> 00:19:17.110
among lots of interesting stuff. It's


00:19:17.120 --> 00:19:20.230
the first one I choose.


00:19:20.240 --> 00:19:22.310
Uh it's regarding the question you had


00:19:22.320 --> 00:19:25.350
about temperature of black holes.


00:19:25.360 --> 00:19:30.710
I must ask you to clarify.


00:19:30.720 --> 00:19:33.430
If material accretes


00:19:33.440 --> 00:19:35.990
close to the end horizon, it's millions


00:19:36.000 --> 00:19:38.310
of degrees hot.


00:19:38.320 --> 00:19:41.270
If I follow the material spiraling


00:19:41.280 --> 00:19:44.789
inwards, it does not suddenly become


00:19:44.799 --> 00:19:46.950
cold when it enters the event horizon.


00:19:46.960 --> 00:19:48.630
Right?


00:19:48.640 --> 00:19:51.110
It's still extremely hot, maybe even


00:19:51.120 --> 00:19:53.669
hotter, even if it's supposedly hard to


00:19:53.679 --> 00:19:54.789
measure.


00:19:54.799 --> 00:19:57.669
because it's hard to get a thermometer


00:19:57.679 --> 00:20:00.310
in there and have a reference.


00:20:00.320 --> 00:20:02.950
But it extremely hot.


00:20:02.960 --> 00:20:05.909
That seems cold to an outside observer


00:20:05.919 --> 00:20:09.430
because it does not radiate anything.


00:20:09.440 --> 00:20:13.110
But maybe it could be clarified somehow.


00:20:13.120 --> 00:20:15.830
It's not magic that it suddenly gets


00:20:15.840 --> 00:20:18.710
cold. It just


00:20:18.720 --> 00:20:21.990
stops emitting. Right.


00:20:22.000 --> 00:20:24.150
Take care. It's Bjon from Goththingberg.


00:20:24.160 --> 00:20:26.070
I love your show.


00:20:26.080 --> 00:20:28.070
>> Thank you, Bjorn. That Babel Fish is


00:20:28.080 --> 00:20:29.750
working well because his English was


00:20:29.760 --> 00:20:31.669
excellent.


00:20:31.679 --> 00:20:33.110
>> He lives in a nice place as well.


00:20:33.120 --> 00:20:35.510
Goththingberg's got a very nice city


00:20:35.520 --> 00:20:37.510
center with a lovely opera house.


00:20:37.520 --> 00:20:39.430
>> Yeah, I haven't been there. In fact, I


00:20:39.440 --> 00:20:42.710
haven't been to Sweden yet, but um yeah,


00:20:42.720 --> 00:20:44.549
it's it's on the wish list. So, we'll


00:20:44.559 --> 00:20:45.669
we'll see how we go.


00:20:45.679 --> 00:20:47.270
>> It's great. Now, he's referring to a


00:20:47.280 --> 00:20:49.110
question that came from Casey in


00:20:49.120 --> 00:20:51.110
Colorado when she was asking about the


00:20:51.120 --> 00:20:54.390
temperature of a of a black hole. Uh, so


00:20:54.400 --> 00:20:58.149
he's basically kind of saying, "Look,


00:20:58.159 --> 00:20:59.590
I understand what you were saying when


00:20:59.600 --> 00:21:01.909
you answered Casey, but now everyone


00:21:01.919 --> 00:21:04.230
thinks they're cold when they're


00:21:04.240 --> 00:21:05.510
probably not cold. They're just not


00:21:05.520 --> 00:21:07.909
emitting anything."


00:21:07.919 --> 00:21:08.630
Is that right?


00:21:08.640 --> 00:21:12.390
>> Yeah, that's that's right. They're cold


00:21:12.400 --> 00:21:14.630
because they're not emitting anything.


00:21:14.640 --> 00:21:18.630
But uh but uh Bjorn's right that you


00:21:18.640 --> 00:21:21.029
know the temperature of the accretion


00:21:21.039 --> 00:21:23.430
disc and and probably the way to look at


00:21:23.440 --> 00:21:24.870
it is the temperature of the event


00:21:24.880 --> 00:21:27.510
horizon is millions of degrees because


00:21:27.520 --> 00:21:29.990
that's where all this stuff is is


00:21:30.000 --> 00:21:33.590
circulating at high speed uh and with


00:21:33.600 --> 00:21:35.270
huge amounts of energy and emitting


00:21:35.280 --> 00:21:38.710
X-rays. um it disappears over the event


00:21:38.720 --> 00:21:42.630
horizon uh at very high temperature and


00:21:42.640 --> 00:21:45.510
presumably within the event horizon it's


00:21:45.520 --> 00:21:48.549
still got that high temperature but then


00:21:48.559 --> 00:21:52.070
it hits the black hole it's sucked in uh


00:21:52.080 --> 00:21:54.630
and if you could measure the temperature


00:21:54.640 --> 00:21:57.510
of the black hole itself you'd find it


00:21:57.520 --> 00:21:59.990
was virtually absolute zero very very


00:22:00.000 --> 00:22:01.350
small temperature


00:22:01.360 --> 00:22:02.070
>> okay


00:22:02.080 --> 00:22:04.789
>> um because it's not emitting anything's


00:22:04.799 --> 00:22:09.270
going in um and it is it is hard to


00:22:09.280 --> 00:22:11.750
imagine and Bjorn mentioned magic and


00:22:11.760 --> 00:22:14.390
that's almost what it is um you know


00:22:14.400 --> 00:22:15.909
stuff that's going in at very high


00:22:15.919 --> 00:22:17.909
temperature but if you could measure the


00:22:17.919 --> 00:22:19.669
black hole itself supposing it stopped


00:22:19.679 --> 00:22:21.830
accreating material and you could then


00:22:21.840 --> 00:22:23.669
measure its temperature it would be


00:22:23.679 --> 00:22:25.750
virtually zero


00:22:25.760 --> 00:22:29.029
>> well well they are so complicated though


00:22:29.039 --> 00:22:31.830
aren't they? I mean, we we we we're


00:22:31.840 --> 00:22:35.190
still learning a lot about um black


00:22:35.200 --> 00:22:37.990
holes and and we we're starting to image


00:22:38.000 --> 00:22:39.430
a few of them. We've got a couple of


00:22:39.440 --> 00:22:43.750
good pickies now, but uh we we


00:22:43.760 --> 00:22:46.070
they are still mesmerizing and


00:22:46.080 --> 00:22:48.470
mystifying because until dark matter


00:22:48.480 --> 00:22:50.710
came along, um we got more questions


00:22:50.720 --> 00:22:52.710
about black holes than anything else.


00:22:52.720 --> 00:22:54.710
they they are the thing that people want


00:22:54.720 --> 00:22:57.430
us to unravel in terms of understanding.


00:22:57.440 --> 00:22:59.190
But um we're I think we're a long way


00:22:59.200 --> 00:23:01.830
away from that at the moment, aren't we?


00:23:01.840 --> 00:23:05.350
>> Um I actually I think you know that we


00:23:05.360 --> 00:23:09.350
know a lot about black holes. Um


00:23:09.360 --> 00:23:12.470
considering that 60 years ago nobody


00:23:12.480 --> 00:23:13.830
believed they existed.


00:23:13.840 --> 00:23:17.190
>> Yeah. Well, the point um and um we've


00:23:17.200 --> 00:23:19.110
observed them. We've actually observed


00:23:19.120 --> 00:23:23.590
the uh radiation coming from the the the


00:23:23.600 --> 00:23:25.510
accretion disc, the region around the


00:23:25.520 --> 00:23:27.750
event horizon. We've we've observed the


00:23:27.760 --> 00:23:29.350
effectively the shadow of the event


00:23:29.360 --> 00:23:32.070
horizon of several black holes now. Uh


00:23:32.080 --> 00:23:34.630
and even detected the polarization of


00:23:34.640 --> 00:23:36.149
the material that's being sucked into


00:23:36.159 --> 00:23:38.070
it. And this is extraordinary stuff.


00:23:38.080 --> 00:23:40.470
These are measurements that really only


00:23:40.480 --> 00:23:41.830
a few years ago would have been thought


00:23:41.840 --> 00:23:43.990
to be impossible, but we're I think


00:23:44.000 --> 00:23:47.110
doing it rather well. So, we're still


00:23:47.120 --> 00:23:49.190
learning about black holes. They are and


00:23:49.200 --> 00:23:51.190
that that's the reason why they're so


00:23:51.200 --> 00:23:52.870
fascinating is that they are completely


00:23:52.880 --> 00:23:54.390
counterintuitive.


00:23:54.400 --> 00:23:55.430
How do you have something that's


00:23:55.440 --> 00:23:57.830
simultaneously at zero and a million


00:23:57.840 --> 00:24:01.029
degrees and that's what you've got? Uh


00:24:01.039 --> 00:24:06.149
so, yeah. So, it's um it it yeah, there


00:24:06.159 --> 00:24:08.950
still very very interesting object.


00:24:08.960 --> 00:24:12.870
>> But, um back to Bjorn's question, the


00:24:12.880 --> 00:24:15.830
temperature is


00:24:15.840 --> 00:24:18.149
zero absolute zero or thereabouts


00:24:18.159 --> 00:24:21.590
because of the fact that it doesn't


00:24:21.600 --> 00:24:23.190
>> it doesn't radiate anything. Yeah.


00:24:23.200 --> 00:24:25.430
Exactly. So, so the the way to imagine


00:24:25.440 --> 00:24:27.830
it I think and this probably puts it


00:24:27.840 --> 00:24:30.470
more succinctly. Yes. While while it's


00:24:30.480 --> 00:24:32.230
accreting, you can't you can't see the


00:24:32.240 --> 00:24:33.750
black hole because it's surrounded by


00:24:33.760 --> 00:24:36.230
this hot material at very high


00:24:36.240 --> 00:24:38.070
temperature that's being swallowed into


00:24:38.080 --> 00:24:40.149
it. But if there was if that supply of


00:24:40.159 --> 00:24:42.549
gas ran out and the black hole stopped


00:24:42.559 --> 00:24:44.310
accreting then you would and you could


00:24:44.320 --> 00:24:47.029
measure its temperature then um it would


00:24:47.039 --> 00:24:49.830
be zero effectively be absolute zero a


00:24:49.840 --> 00:24:51.830
little bit above but not very much.


00:24:51.840 --> 00:24:54.470
>> Okay there you go Bjorn and I'm looking


00:24:54.480 --> 00:24:57.750
at uh photographs of Gottenberg. It's it


00:24:57.760 --> 00:25:00.310
is an absolute beauty of a city isn't


00:25:00.320 --> 00:25:03.510
it? What a lovely part of the world. So


00:25:03.520 --> 00:25:08.390
uh yeah, very lucky. Nice tra


00:25:08.400 --> 00:25:10.710
um thanks buen. Great to hear from you


00:25:10.720 --> 00:25:14.149
uh in Sweden.


00:25:14.159 --> 00:25:16.470
>> Okay, we checked all four systems and


00:25:16.480 --> 00:25:17.110
with the go


00:25:17.120 --> 00:25:18.230
>> space nets


00:25:18.240 --> 00:25:21.269
>> and believe it or not, our next question


00:25:21.279 --> 00:25:24.789
comes from Sweden. Uh does the expansion


00:25:24.799 --> 00:25:27.590
of space mean that the universe gains


00:25:27.600 --> 00:25:30.230
more meters or are the meters becoming


00:25:30.240 --> 00:25:33.750
longer? related to this. Is it space


00:25:33.760 --> 00:25:36.710
only that is expanding or is it space


00:25:36.720 --> 00:25:40.789
time? If so, what's happening uh to the


00:25:40.799 --> 00:25:43.750
time part of it? Is time expanding too?


00:25:43.760 --> 00:25:45.990
What would that mean? Uh thanks for a


00:25:46.000 --> 00:25:49.510
most interesting podcast, Peter from


00:25:49.520 --> 00:25:50.710
uh I'm going to pronounce this


00:25:50.720 --> 00:25:55.269
incorrectly. Falloon in Sweden.


00:25:55.279 --> 00:25:57.430
>> So yeah, hopefully I got that right.


00:25:57.440 --> 00:25:59.430
think my babel my babel fish can't


00:25:59.440 --> 00:26:02.630
translate back into Swed Swedish.


00:26:02.640 --> 00:26:04.149
>> Well, if you put it the other way


00:26:04.159 --> 00:26:04.470
around,


00:26:04.480 --> 00:26:06.070
>> got to put in the other ear.


00:26:06.080 --> 00:26:08.070
>> Yeah, that's right.


00:26:08.080 --> 00:26:09.190
>> That'll do it.


00:26:09.200 --> 00:26:13.110
>> Um, so, uh, yes, uh, that's a great


00:26:13.120 --> 00:26:16.470
question. And so um my view you know the


00:26:16.480 --> 00:26:21.350
intuitive view uh which is based on


00:26:21.360 --> 00:26:23.669
a few years of thinking about this kind


00:26:23.679 --> 00:26:26.950
of thing. Um the me the meters are


00:26:26.960 --> 00:26:31.430
becoming longer. Um and that's sort of


00:26:31.440 --> 00:26:32.789
illustrated by the fact that the


00:26:32.799 --> 00:26:34.470
wavelength of radiation is getting


00:26:34.480 --> 00:26:37.909
longer. Uh you know that radiation had a


00:26:37.919 --> 00:26:39.269
particular wavelength when it was


00:26:39.279 --> 00:26:42.950
emitted. Uh um and as the universe has


00:26:42.960 --> 00:26:44.310
expanded, whatever it's coming from,


00:26:44.320 --> 00:26:46.230
whether it's a distant galaxy or a


00:26:46.240 --> 00:26:48.470
quazar or whatever, uh as the universe


00:26:48.480 --> 00:26:50.470
has expanded, that radiation has been


00:26:50.480 --> 00:26:52.549
stretched, which means that the meat has


00:26:52.559 --> 00:26:54.630
been stretched because the frequency


00:26:54.640 --> 00:26:59.990
remains the same. Uh


00:27:00.000 --> 00:27:02.870
except when you observe it


00:27:02.880 --> 00:27:05.990
>> uh from our vantage point in the depths


00:27:06.000 --> 00:27:07.669
of the universe.


00:27:07.679 --> 00:27:10.390
>> Yeah. Forget about the frequency.


00:27:10.400 --> 00:27:12.630
That's a that's a fury. But the


00:27:12.640 --> 00:27:14.470
wavelength the wavelength stretches. So


00:27:14.480 --> 00:27:17.990
the time the um the length scale is


00:27:18.000 --> 00:27:20.230
increasing. Um in fact there's there's a


00:27:20.240 --> 00:27:21.909
thing called the scale factor of the


00:27:21.919 --> 00:27:26.230
universe. Uh and it's very easy to


00:27:26.240 --> 00:27:28.149
prove. It's one of the most simple


00:27:28.159 --> 00:27:30.870
geometrical equations in cosmology. Uh


00:27:30.880 --> 00:27:34.149
the scale factor of the universe. uh now


00:27:34.159 --> 00:27:35.990
compared with when the light was emitted


00:27:36.000 --> 00:27:37.830
the ratio of the two is equal to 1 over


00:27:37.840 --> 00:27:40.470
1 plus zed uh where zed is the red shift


00:27:40.480 --> 00:27:42.149
of the light that you're measuring and


00:27:42.159 --> 00:27:44.789
so there's this direct link between the


00:27:44.799 --> 00:27:46.710
sort of scale size of the universe which


00:27:46.720 --> 00:27:49.269
is the length of a meter effectively um


00:27:49.279 --> 00:27:51.350
and the red shift that we measure when


00:27:51.360 --> 00:27:55.750
we look in deep into the universe um you


00:27:55.760 --> 00:27:57.269
look as though you got a question now


00:27:57.279 --> 00:27:59.909
I'm confused so what you're basically


00:27:59.919 --> 00:28:02.549
saying in regard to his question was


00:28:02.559 --> 00:28:06.230
that um the meter is expanding. So a


00:28:06.240 --> 00:28:08.470
meter is not a meter.


00:28:08.480 --> 00:28:11.830
>> Well, it's it's still a meter, but it's


00:28:11.840 --> 00:28:14.870
a different meter.


00:28:14.880 --> 00:28:18.950
Okay. Um because the scale factor of the


00:28:18.960 --> 00:28:22.230
universe was less when the light was


00:28:22.240 --> 00:28:23.510
emitted. This is the thing, you know,


00:28:23.520 --> 00:28:25.110
you've got two different reference


00:28:25.120 --> 00:28:28.789
frames here. That's why this stuff gets


00:28:28.799 --> 00:28:30.950
a little bit complicated because in our


00:28:30.960 --> 00:28:33.830
reference frame the meter is longer. But


00:28:33.840 --> 00:28:35.669
if you were traveling along with your


00:28:35.679 --> 00:28:39.590
meter stick uh as it as it sped through


00:28:39.600 --> 00:28:41.990
the universe uh it would be changing in


00:28:42.000 --> 00:28:44.230
length. It would it would sorry appear


00:28:44.240 --> 00:28:46.710
to be the same length.


00:28:46.720 --> 00:28:49.110
Right?


00:28:49.120 --> 00:28:51.830
I'm sorry. This is just


00:28:51.840 --> 00:28:55.269
it's mindbending,


00:28:55.279 --> 00:28:56.789
>> isn't it?


00:28:56.799 --> 00:29:00.149
>> It it bends mine as well. Um, and so


00:29:00.159 --> 00:29:02.310
something similar happens to time, but


00:29:02.320 --> 00:29:05.110
once again, so so we are we're we're


00:29:05.120 --> 00:29:08.789
still inside the universe, but we're


00:29:08.799 --> 00:29:12.549
we're observers from a in a different


00:29:12.559 --> 00:29:15.269
reference frame from when the light was


00:29:15.279 --> 00:29:16.870
emitted. Because that's what we're


00:29:16.880 --> 00:29:18.149
talking about. We're talking about being


00:29:18.159 --> 00:29:19.590
able to measure the expansion of the


00:29:19.600 --> 00:29:21.110
universe through the through the light


00:29:21.120 --> 00:29:23.669
waves.


00:29:23.679 --> 00:29:27.590
So, so and we know that time dilation


00:29:27.600 --> 00:29:29.510
took place. We can we can measure that


00:29:29.520 --> 00:29:32.549
by looking at this rise and fall rates


00:29:32.559 --> 00:29:34.630
of supernovi in the distant universe and


00:29:34.640 --> 00:29:36.149
they actually appear to rise and fall


00:29:36.159 --> 00:29:40.470
slower. So, it is the time uh element of


00:29:40.480 --> 00:29:41.909
that changes as well.


00:29:41.919 --> 00:29:44.950
>> Okay. I think he chose a meter because


00:29:44.960 --> 00:29:48.470
um the meter was defined by uh the


00:29:48.480 --> 00:29:51.029
international system of units as a as


00:29:51.039 --> 00:29:53.750
the length of the path light travels in


00:29:53.760 --> 00:29:56.149
a vacuum during a time inter interval of


00:29:56.159 --> 00:30:02.950
1 299,792,458


00:30:02.960 --> 00:30:05.510
of the second.


00:30:05.520 --> 00:30:07.269
>> Yeah, that's how it's that that's how


00:30:07.279 --> 00:30:09.990
it's defined today. It was originally


00:30:10.000 --> 00:30:11.350
defined as being what was it?


00:30:11.360 --> 00:30:13.669
1/400,000th of the circumference of the


00:30:13.679 --> 00:30:14.470
I can't remember.


00:30:14.480 --> 00:30:15.029
>> Yeah, I can't


00:30:15.039 --> 00:30:16.070
>> something like that.


00:30:16.080 --> 00:30:16.870
>> Yeah.


00:30:16.880 --> 00:30:18.310
>> All right.


00:30:18.320 --> 00:30:19.029
>> Okay. So,


00:30:19.039 --> 00:30:22.149
>> well, no, it would be 140. Uh, yeah.


00:30:22.159 --> 00:30:24.630
Anyway, it was like it was a it was


00:30:24.640 --> 00:30:26.070
related to the circumference of the


00:30:26.080 --> 00:30:27.029
earth.


00:30:27.039 --> 00:30:28.630
>> Can't do the sums anymore. My brain's


00:30:28.640 --> 00:30:30.230
fried today. I don't know why. I mean,


00:30:30.240 --> 00:30:32.070
you're right. I think it's episode 300


00:30:32.080 --> 00:30:34.950
600 is a a relativistic phenomenon


00:30:34.960 --> 00:30:35.830
taking place here.


00:30:35.840 --> 00:30:37.830
>> It it it's just messing us up. I mean,


00:30:37.840 --> 00:30:41.669
if we need a holiday of some kind. Um,


00:30:41.679 --> 00:30:43.590
but anyway, uh, hopefully that helped,


00:30:43.600 --> 00:30:46.630
Peter. I don't know. Uh,


00:30:46.640 --> 00:30:48.470
but, um, I think somewhere in there we


00:30:48.480 --> 00:30:50.149
did answer a question. Thanks for


00:30:50.159 --> 00:30:52.389
sending it in. And and and good to have


00:30:52.399 --> 00:30:56.310
a, um, a very Scandinavian sort of, uh,


00:30:56.320 --> 00:30:58.950
600th episode. So, um, yeah, I mean, we


00:30:58.960 --> 00:31:02.149
we've got Slatty Bfast, we've got Sweden


00:31:02.159 --> 00:31:04.870
a couple of times over, Norway, and then


00:31:04.880 --> 00:31:07.350
South Australia. Uh, okay. Well, no.


00:31:07.360 --> 00:31:09.669
Anyway, close enough. Close enough.


00:31:09.679 --> 00:31:11.190
>> South Australia is not known for its


00:31:11.200 --> 00:31:12.789
fjords, but it is a nice place.


00:31:12.799 --> 00:31:14.549
>> It is a lovely place, except it was


00:31:14.559 --> 00:31:16.549
pouring rain and gale force winds when


00:31:16.559 --> 00:31:17.990
we visited. But anyway, that's the way


00:31:18.000 --> 00:31:20.149
it goes. Uh, thank you, Peter Bjorn,


00:31:20.159 --> 00:31:22.549
Slatty Badfast, and Daryl for sending in


00:31:22.559 --> 00:31:23.909
questions. If you've got questions for


00:31:23.919 --> 00:31:26.549
us, please send them in to us via our


00:31:26.559 --> 00:31:28.950
website, spacenutspodcast.com,


00:31:28.960 --> 00:31:30.870
spacenuts.io.


00:31:30.880 --> 00:31:32.950
uh click on the AMA button which stands


00:31:32.960 --> 00:31:35.269
for ask me anything and send us your


00:31:35.279 --> 00:31:37.430
text or audio questions. Don't forget to


00:31:37.440 --> 00:31:38.470
tell us who you are and where you're


00:31:38.480 --> 00:31:40.470
from. We'd love to hear from you,


00:31:40.480 --> 00:31:42.070
especially if you haven't sent in


00:31:42.080 --> 00:31:45.269
questions before. Uh also, if you'd like


00:31:45.279 --> 00:31:47.590
to help us out, um please, wherever you


00:31:47.600 --> 00:31:50.149
listen to us, uh leave reviews because


00:31:50.159 --> 00:31:53.190
the more reviews the the better. uh the


00:31:53.200 --> 00:31:56.149
the more we move up the the


00:31:56.159 --> 00:31:59.750
relativistic food chain that is podcast


00:31:59.760 --> 00:32:02.630
world and uh we we get more listeners


00:32:02.640 --> 00:32:04.710
perhaps that's that's the aim of the


00:32:04.720 --> 00:32:06.710
game anyway uh if you could do that for


00:32:06.720 --> 00:32:08.870
us that would be great and Fred thank


00:32:08.880 --> 00:32:10.549
you very much nice to chat we'll catch


00:32:10.559 --> 00:32:12.149
you on the next episode


00:32:12.159 --> 00:32:14.950
>> sounds great Andrew uh hope we get our


00:32:14.960 --> 00:32:16.389
breath back before then


00:32:16.399 --> 00:32:18.630
>> yes yes it's been a bit tiring hasn't it


00:32:18.640 --> 00:32:20.710
but uh we got there in the end professor


00:32:20.720 --> 00:32:23.029
Fred Watson astronomer at and he'll be


00:32:23.039 --> 00:32:24.950
back with us next week. Uh Hugh in the


00:32:24.960 --> 00:32:26.630
studio. We thank him too for all the


00:32:26.640 --> 00:32:29.909
work he's done over these last um well


00:32:29.919 --> 00:32:31.909
actually he doesn't turn up for most. So


00:32:31.919 --> 00:32:33.509
the last four episodes that he's been


00:32:33.519 --> 00:32:35.830
with us. Um in fact he couldn't be with


00:32:35.840 --> 00:32:37.909
us today because we told him he could


00:32:37.919 --> 00:32:40.950
have every 600th episode off. And from


00:32:40.960 --> 00:32:42.389
me Andrew Dunley, thanks for your


00:32:42.399 --> 00:32:44.389
company. We'll see you on the next


00:32:44.399 --> 00:32:46.389
episode of Space Nuts. Bye-bye.


00:32:46.399 --> 00:32:47.430
>> Space Nuts.


00:32:47.440 --> 00:32:49.509
>> You've been listening to the Space Nuts


00:32:49.519 --> 00:32:51.750
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00:32:51.760 --> 00:32:54.710
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00:32:54.720 --> 00:32:57.430
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00:32:57.440 --> 00:32:59.830
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