The Supermassive Podcast - Why Is There Motion in the Universe?

Episode Date: June 12, 2026

What happens if two diamond core stars collide? Will the Moon drift away from Earth? Why is there motion in the universe? And why we need a space AND time machine. Izzie, Dr Becky and Robert dive into The Supermassive Mailbox to answer your questions. For ad-free listening and to view Izzie's trajectory to becoming a better astronomer, join The Supermassive Club. Every member helps keep the show running, so thank you! Send us your astronomy attempts, questions (and nonsense!) to [e-mail], on Instagram at @supermassivepod or post in The Supermassive Club. The Supermassive Podcast is a Boffin Media production. The producers are Izzie Clarke and Richard Hollingham. Hosted on Acast. See acast.com/privacy for more information.

Hello and welcome to another bonus episode of the Supermassive podcast from the Royal Astronomical Society. With me, science journalist, Izzy Clark, astrophysicist, Dr. Becky Smethurst, and the Society's deputy director, Dr. Robert Massey. What have you all been up to recently? Not much. You know, not like that at all at the moment for me. I know I'm still on my, I got married high. I presume when this episode comes out, I won't even be in the country because I'll be like, I'm on my honeymoon. Bye.

Yeah, rightly so, man. Deserved, you're going to have such a good time. Robert, what have you been up to recently? Oh, me? Well, I'm doing my thing, you know, doing lots of astronomy. I'm actually, because I've got to have some surgery later this year for Crohn's disease, I'm not going to be able to go to Spain to see the eclipse, which is annoying. So I know, I know.

So anyway, what can I say? Cancel the accommodation. But I am looking forward to see it in the UK. Yeah, yeah. It's great. It's a great view here. It's just not the same as totality as we always. say so but I'll still look forward to that there'll still be lots of people here enjoying the

view as well look mark that day what is it the 16th of august something like that thing yeah yeah well I have some exciting news oh yeah I've bought a C star 50 oh wow I'm doing it I've wanted it for over well everyone whoever's been a long-term listener I've just heard me talk every year I go maybe maybe I will and I went fully free law and I went fully freelance I'm full-time freelance now and I went, I'm just going to treat myself to a really nice telescope. To a nice present. Nice.

No, I just wanted a little treat. And, you know, I said at the beginning of the year, be a better astronomer. So this is my step into becoming a better, bad astronomer. Oh, I'm so glad you brought it. Can you put some pictures of you're using it in the forum? Oh, you bet. Absolutely.

And, you know, guys, be. That's the super massive club forum. if you're not there you're square. Please be kind and tell me what I'm doing wrong. Okay, thanks. I've got it. You know, I've been lent to dwarf two, right? And it's fairly old by the space artist Sally Russell.

She's got a better one now. She lent me this dwarf two after I give this door. I have just about taken a picture of the sun with it. I'm still definitely learning. The app looks to me like, I'm just looking at you thinking, people do these things. I need to learn all this. They're amazingly powerful.

They take pictures of galaxies four billion light years away. How does it do that, this tiny piece? Oh my gosh, I feel like they're... No pressure, no pressure. I don't know, but I feel like we're creating a new, you know, discussion channel for the forum that is just the bad astronomers club where people can post their questions of like, so, this has happened. How do I fit it?

I was going to say, and there'll be us asking the question. Yeah, I'll be like number one poster on there, yeah. Okay, so let's go on to some questions. Becky, listener Paul Newton has sent us an email. It says, hi, team, thanks for all you do. can you predict what might happen if two diamond core stars collided? Are we talking cosmic billions or would the extra energy inputs cause something to happen? Well, I think what you're talking about with diamond core stars is like white dwarf stars.

So the thing that's going to be left behind when the sun eventually runs out of fuel and novas and dies and leaves behind a mostly carbon core, which, yes, you could describe as a diamond. because it would be crystallized because of the heat. So I think that's what you're talking about. So if two white dwarf stars collided, it would be, I mean, if you had a direct head-on collision, which would be very, very rare, right? But technically possible,

then yes, maybe you would have a cosmic, like pool ball thing, cosmic billions like you've described. But the more likely collision of two white dwarf stars is going to be the fact that they were like a binary star pair. So two stars in orbit around each other, which both, you know, died and ended up as white dwarfs. So imagine, you know, the sun being on its own is not the normal.

Binary stars are very, very common. So you can imagine two suns in orbit around each other, and they both ended up as two white dwarfs by the end. Those can slowly in spiral together and eventually collide. And if that happens, then they don't just collide. they do merge together. We've seen the likes of like two neutron stars collide before with LIGO, and we've perhaps seen the remnants of a white dwarf merger.

It's thought that maybe even some type 1A supernovas are actually white dwarf mergers as well. So it's not a rare thing necessarily. What happens afterwards is really depends on how big the two white dwarfs are that merge, and it's whether you're over what's known as the Chandra Seychard limit, which is like the limit for how big a white dwarf can be and how much how big it can be before that crystalline structure of that sort of diamond core thing that you're talking about is overwhelmed by the mass essentially.

And if that happens, then you're going to end up with a neutron star, which is neutrons in a very tight crystalline structure as tightly packed as they can go. So that's what would happen in terms of the collision and that would completely get rid of the diamond aspect of it as well. You're more likely to have this sort of like, Diamonds are not forever then, Becky. Boo.

No, indeed. No. Diamonds are not forever, especially if they merge together, and the white dwarf stars, because you just get runaway fusion taking it to like nickel, coal, and then probably iron. Just as glamorous, yeah. Colbolt doesn't really cast it.

You know, iron engagement rings. Maybe. Maybe. To each their own. Robert, Kane Lynch on Instagram says, Hi, I have a question about the moon, which maybe you guys will be able to help with. It also links with your episode on rogue space objects. Given that the moon is receding from Earth at a rate, which I've inconveniently forgotten,

is there a point at which the moon will no longer be tidily locked with the Earth? Love the podcast. Thank you, Cain, for the love. And I've realised I've inconveniently forgotten the second part of your question, but I've written an answer anyway. So it's indeed receding from the Earth. The moon is moving away about three point. 8 centimeters a year, slightly sprightly, but not really rushing. And we know this because we fire terrestrial lasers at the moon.

They're based around the world. You fire a powerful enough laser, and it hits one of these six reflectors that were left behind by Apollo's 11, 14 and 15, the Soviet Lunacod Rovers, both of those in the 60s and 70s, and the Indian Shandrian 3 mission. And if you fire it, knowing the speed of light, you time how long it takes to go to the moon. are back and from that you can work out the moon is indeed slowly moving away from the earth now it's moving away by gaining energy from the slowing down the rotation of the earth because our day increases by about 2.3 milliseconds a century so a tiny tiny change it's enough that you get a leap second every so often although we haven't had those for quite a long time and in theory the earth would definitely become tidily blocked to the moon in about 50 billion years time but the problem is that the

sun won't last that long so the sun slowly getting brighter 2 billion years time it won't be Earth won't be habitable because of that. But in about seven and a half billion years time, the Earth-moon system will be further from the Sun because the mass of the Sun, because the nuclear fusion will have gone down, the gravitational force will a weaken. However, the Sun will become a red giant, swell up enormously, and the Earth and Moon, by every expectation, will be within the Sun's atmosphere. So I think before the Moon could ever drift so far away that it was no longer in orbit, which I think is the point at which the tidal locking would probably no longer happen, both worlds will be consumed by the sun's atmosphere. So that's that. So sadly we don't get to see that, nor do we get the Earth to tidily lock with the moon. Because it just, there just isn't enough time. But if you want an example of where two worlds are tidily locked, and I don't, you know, they're never going to get consumed by the sun. Then look at Pluto and Sharon. Sharon is big compared with Pluto, about half the size. And they're even closer to being a double, double dwarf planet at least than we are with the Earth and Moon. So sadly,

that the sun wins in this case and the Earth and Moon aren't going to go to that state. I still hear that though, unlike the Moon and Earth are BFFs is basically. Yeah, they are. To the very end. To the very end as it happens. That's all I took from that. Thank you for that. Good to know.

He's just like, we're just on course. Might right or die. And Becky, can you help give Sam Isaacs a headache? Sure. Sam says, hi from British Columbia, Canada. Oh, beautiful, by the world. I know. I'm so jealous.

Tell us what it's like there, Sam. Tell us about the sky. Thank you for, yeah. Tells about the Aurora. They say, thank you so much for your wonderful podcast and accessibility to listener questions. It's very much appreciated. Here's a simple question to ask. I'm not sure if the answer will be simple.

Why is there motion in the universe? Of course, if there wasn't any motion, I wouldn't be here to ask this question. you wouldn't be here to answer it, but presumably at some initial point and before there was matter, there was no motion. So how did motion and associated velocity and acceleration come into existence? I presume there was some process converting pure energy into something, but why did that require there to be motion and is motion an inherent property of time? Thanks for your time and for my opportunity to have my head hurt a bit. It's a great question, Sam.

Honestly, it's fantastic. I think at the very, very root, if we were going to go to the very root of it, we'd get to quantum physics and we'd just be like, because there is. But I think perhaps an easier way to think about it would be to think of just thermal motion, as it's called. If you think about a gas that has a certain temperature that is inherent energy to that gas, so therefore the molecules are moving. And if something is an absolute zero temperature-wise, then yes, there would technically be no movement. So coming back to your idea of, you know, you said, you know, before there was matter, was there no motion?

Comes back to this thing, the fact that our physics breaks down at, what, 10 to the minus 36 seconds, you know, into the universe's lifetime before that we don't really know what was going on. It doesn't really make sense to ask was there before a big bang because the big bang created. space and time, so the concept of it before didn't exist, you know, so it's one of those strange things, but there was obviously a huge amount of energy involved in those first initial seconds of the universe. We know that through inflation that has to have happened to give us the universe around us, at least that's our best theory of it anyway. It has to be lots of energy. So there was energy, there's therefore thermal energy in any particles that were created, and they will have random thermal motion, just like.

little jumps from the fact that they have some temperature and some energy. If that's the case, then as soon as you have random jumps, there are random jumps that could take you closer to other particles, and then gravity is like, oh, well, I'll just come together. You know, they'll stick together. And then so on and so on in a snowball until you start to get bigger objects forming, but bigger objects that inherit all of the energy from the things that formed them. and from the fact that if there was gravity,

starting to pull in things from nearby, that will have also then added motion into those particles as well. And so everything that clumps together, every object that you end up with, is its motion is inherited from everything that went into making it, and anything that's collided with it and things like that. So for the fact that there is just inherent energy, which again, if you're going to go from a lower perspective,

it goes into the quantum things of like probabilistic nature of things, that is why there's motion. Motion in the ocean. Okay. Thank you, Becky. I'm so glad you tackled that because as soon as I saw the line, is motion an inherent property of time? I was like, I didn't even think about that either. Well, if we're thinking about motion as inherent property of time, and we think about time and we think about it in terms of entropy in the universe, right? The second law of thermodynamics is that entropy must decrease. Things must get. Increase.

No, entry was increased. What? Is that entropy, yeah, is that entropy must increase and that things must get more disorganized with time. That's the only sort of with time law we really have. But if you think about disorganization, it is probably motion, but more chaotic motion. Yeah. So there is no inherent like motion must come with time. But similarly, right, because if we have this law of entropy, then yes, that kind of is in the same way.

Yeah, love it. Really love it. I have a headache too, but I love it. Yeah, that killed my headache. I don't know what you don't. And Robert, here's a final question from Craig Hollingsworth. Hi, I love the pod and mentioned before my little connection to being in Chapel Hill where the Apollo astronauts trained in celestial navigation. My question today is based on listening to The Extinct Zoo, a podcast I like a lot. I hope it's a good one, but not as good as ours. Anyway, the narrator says, the dinosaurs lived so long ago that technically they lived on the other side of the galaxy. I found that fascinating. He noted that the Earth and solar system is always flying through space like a bullet. And since the time of the dinosaurs has travelled through different galactic neighborhoods within the Milky Way.

And since the time of the dinosaurs has traveled through different galactic neighborhoods within the Milky Way. It's very interesting and I wondered what you thought. Is that true? Love you. Mean it. Craig. Thank you, Craig for the love. We love you back. But, okay, so to turn to your question, they are, yeah, the solar system and sun are indeed moving through space actually much faster than a bullet really, very, very quickly when you got tens a glumpt a second. But to turn to your question, so the solar system completes an orbit around the Milky Way galaxy. We're thinking about between 225 and 250 million years. So quite a long time, but that does mean there's been enough time for it. to go around many times since the solar system was formed. But if you look at when the dinosaurs were around, if you take that as, say, the start of the Triassic geological era, which is 250 million years ago, then when dinosaurs first emerged, our sun was in more or less the same place, but then the middle Jurassic, the dinosaurs were around for a very long time, 165 million years ago. It'd be a long way around its orbit. And by the middle of the Cretaceous, so 100 million years before the present day,

then the sun was definitely on the opposite side of the galaxy. Now, one complicated, when you think about this is that all the stars around us are moving at slightly different rates. So even if you looked at the sky and say 100,000 years' time, yet alone a million years' time, it would look completely unlike the way it does today. You'd still have, I guess you'd still have a Milky Way, you'd still have the same kind of distribution of stars. I think there'd be bright ones and faint ones, probably in similar numbers. But the constellations would be completely unrecognizable. So we have to think about your question.

We also have no idea what sky the dinosaurs saw, that, you know, it would have been something not recognizable, similar types of stars in the sky, but none of the constellations were familiar with but would be there. It would just be very, very different to the sky we see above our heads today. That's really cool.

That also question reminded me of, I was listening to The Rest is Science podcast with Hannah Frye and Michael from Vsauce, which I'm loving, by the way, if anyone else is. They were talking about, like, how you prove, it was like in the episode about how you prove that you are a time traveler if you find yourself accidentally traveling through time either to the past or the future. It was very interesting. Love that. So good. But it was also

talking about how if you did travel back to the time of the dinosaurs millions of years ago on Earth, you actually wouldn't be able to survive because there'd be nothing you could eat. Not only would you be on the other side of the galaxy, you'd also be like, I can't really eat any of the plants because they're all carcinogenic, and the dinosaurs eat all of the plants. And the other dinosaurs eat the plants. So everything in the food shake. It's toxic. It's poisonous and toxic to me. And you'd be on the other side of the galaxy. So, you know.

So. Oh my gosh. It's one of those questions when you pull on the thread and you're like, oh my goodness. Everything's unraveling. And also like with this as well, if you think about it, when, you know, the earth would be over the other side of the galaxy. If you were going to time travel, you would have to space and time travel. Exactly. Because wherever you were going, right.

Otherwise you end up in the middle of space. It's true. Well, yeah. Exactly. So don't just invent a time machine, invent a space and time machine. Please, someone. I'll work on it. Don't worry.

Yeah, Izzy, you've got your C-Star now. Now I want to go over there. I didn't know it had that built-in feature. Wow, God, they've done so much. It's the next recording, you know, live broadcast from. Oh, gosh. Well, I think that's all the questions and nonsense that we have time for today. So do keep your questions coming.

We love them. They're just so fun. You can email podcast at r.res. Atac.org. Find us in Instagram at supermassive pod or join the supermassive club. It's a lovely little space. Space like we did the. Oh, there we go.

And there are no adverts there as well, lovely times. But also you can post on the forum and we chit chat about how I will become a better astronomer at some point. Hey, everything, you know, with time. You know, we learn on the job all the time. Every day's a school day. We'll be back, though, in a few weeks' time with an episode all about neutrinos, which I'm very excited about. I presume we're talking about the picture that was taken through the earth at some point is, because that's one of my favorite neutrino pictures.

Yes. It was taken at night of the sun. How did they do it? Until next time, though, everybody, happy stargazing.