The Supermassive Podcast - Can Time Travel be sped up? What is the Bootes Void? And G'day to Australians

Episode Date: July 10, 2026

What is the Bootes Void? Why do we only see one side of the Moon? Can time travel be sped up? And what's the smallest amount of visible space debris? The Supermassive Podcast team answer your questions... And work on their Australian accents!?For the first time ever, you can now watch this episode on YouTube.For ad-free listening, 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. Hayley Wilson is the video editor. Hosted on Acast. See acast.com/privacy for more information.

Oh, I've just found a rock in my pocket. Oh, cute. Yeah, I went to the beach last night. I'm in Devon, obviously. We can obviously tell. It looks like Jupiter. Look at those little stripes. That's why I chose it.

And it's so perfectly smooth. Anyway. It's even the right shape. It's even the right shape for Jupiter, is he? I know. It's in a blate. Sveroids, babe. Oh, okay.

Right. Let's go on with this show then, shall we? Oh, yeah. 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 deputy... I've literally forgot what your title was there, Robert.

I'm sorry. And the Society's deputy director, Dr. Robert Massey. I'll be doing this for six years is. Come on. I overthought it. I was like, I know this. I was like, do it. I know it. And the fun thing is you can watch all of those hijinks and shenanigans on video now.

Hello to everyone who's now watching this on YouTube. I finally convinced everyone that we should film the podcast. We all regretted it this morning when we realized we weren't just doing audio anymore and our faces had to be presentable. But we are hoping to do a bit more video content throughout the year. So if there's something in particular, you'd like us to cover and you'd like to see our faces while we do it. And then let us know. Now, before we dive into the supermassive mailbox, there's something in our running order that says producer Richard has some listener feedback.

I'm scared. Why has this been hidden from us? What's going on? You may remember in the last main episode, we had an email from Chris in Australia talking about miniature telescopes. And you attempted Australian accents. Oh, God.

Hi, team. We're going to get marked. He writes, I just listened to the space telescopes pod during a flight from Sydney to Melbourne and cracked up like a maniac when I heard Izzy and Becky attempt a good day mate. And then there's multiple laughing emojis. Well done, team. Love it.

And thank you to Robert for the fantastic answer. Well, I had an email exchange then with Chris. And I said, well, look, send us some voice notes. about how you say it. So we're going to do a little bit of Chris followed by some repeating. So here we go. He's recorded a couple of good days for us. Good a mate.

Good a mate. Do you want to hear that again? Yeah, here again, but Robert didn't have a girl last time. So I feel like Robert has to have a go. Good aim, mate. Good day, mate. No. No.

That's really good. That's really good. That's absolutely the best. Okay, I'll go next. Oh, I'm laughing too much. This is like duolingo. Yes. If they weren't offended before, they aren't.

Good-day, mate. Not bad. I feel like I need to hear it again. I need to hear it again. Okay, here we go. Good-day, mate. Giday, mate. I don't think that was that bad.

I've got one more. If you want to have another go. Yeah, go. I've got to have this one as well. Goody-A-mate. How you going? Good-day, mate. How are you going? Good-oy, mate. How are you going? Robert's good at this.

I can do it. It's duolingo practice, although duolingo often argues with me about my pronunciations. Is it an Australian duolingo? No. I don't know. That's a good question. Can you imagine? Hello? Okay, all right, my turn. Oh, God, I'm laughing too much.

Do you want it again? We'll go on them, yeah. Good a day mate. How are you going? Good eye mate. How are you going? I sort of go cockney. You do a little bit. You do a little bit. You're right, mate. Yeah. And if anyone's wondering why this is necessary for an astronomy podcast,

there are many radio astronomy telescopes in the deserts of Australia. Thank you, Becky, for making you slightly more credible, potentially. Sure. But thank you, Chris, and thank you to all our listeners in Australia, Please keep listening to the show. Thank you. Don't send us. Don't send us too much hate mail, please.

Yeah. No. Right. I'm going to try and steer this back on course. Let's get into some questions. Becky, we've had this email from listener Joe Coots, who says, I have a question about time travel. Great.

Great. Thanks, too. No, I actually love this question. I think it's great. So I was wondering what would happen if, for example, another civilization was able to view us from a couple of light years away, but we're also moving towards us. Would that mean they would be seeing the earth but sped up? If so, does that mean they would be able to watch one person's life go by faster? This has been frying my brain for a long time and I was hoping that you'd be able to help me out here. Ha ha. Yes. Thank you much. Keep up the fantastic work. This is good, Joe. This is not actually.

time travel. This is like time delation. So I like it. And it's really, I think, to wrap your head around it, think about it in terms of a doppler shift. So we think about doppel shifts all the time when we hear, you know, sirens go past. Or if you stand on like a motorway bridge and you hear the cars going underneath you, right? You hear the sound of the engines of the cars get higher pitch as they come towards you and lower pitches they go away from you. And that's because like the sound wave is getting squashed as it comes towards you and then stretched out as it moves as they move away from you. And so we know the same thing happens to light. We see this with galaxy light. It gets redshifted because the space between us is expanding so it appears that they're moving away.

And so in your scenario where there's like an alien civilization that's like accelerating towards Earth or just moving towards us, then yes, technically, if you think about sort of light waves being sort of put out by Earth, they're going to get squished in the frame of reference of this alien civilization that's on its way to Earth, right? And so because the light waves are getting squished, it's almost like, think about it as like playing a video, which is like frames per second, right? Like 30 frames a second. There's a frame going out. They're sort of, they're speeding up how often the frames arrive at the spacecraft. So yes, they would see so time passing faster. Like they're putting like fast forward on Earth. In terms of watching like

a whole person's life go by faster, they would need to be traveling at very, close to the speed of light, right? So the faster they travel, the, the faster those frames arrive from their frame of reference, right? So they would have to be drawing very fast to watch like an entire person's lifespan, say like a hundred years passed by like in say one. That would have to be very close to the speed of light for that to happen. And also they'd have to have to have the distance to be able to go that fast and not just arrive at Earth as well, right? But the fun thing is we'd also be seeing stuff in reverse as well. Like they'd be coming towards us fast as well.

So it would appear like their journey didn't take as long from our perspective. So there's loads of weird effects that go on in terms of like relativity and time dilation in this scenario. Yeah. Okay. I love that. Great question from Joe. Thank you. And Robert, we've had an email from listener Debbie who says,

why is the moon locked to where we only have one side facing us at all times? what's going on. So yeah, Debbie, this is a good question. It's the famous-ish tidal locking. And I say famous-ish because we all, I think, pretty much are aware that you only see one side of the moon, more or less. And that's because the moon rotates, so turns on its axis in the same time that it revolves, completes an orbit around the earth. By the way, a way to convince yourself that it is turning, which if you're working in an office is a nice experiment to do, is to take an office chair, a rotating one, put it in the middle of your office and have someone walk around you. And then if you turn the chair to keep facing them, you know, they, they will, you will see each other's faces,

but you'll also both be seeing different walls of the room. So you must, by definition, be rotating. And that's what's happening with the moon. But it happens because the moon, it's our natural satellite, it's fairly close to us, 384,000 kilometres away. And it's quite massive. The fact that we can put that in kilometres. I know. Exactly. It's not light years. It's not vast distances. And it's quite massive. It's got an 81st of the mass of the Earth. So it's quite big. And those two things mean that the Earth exerts quite a pull on the moon and vice versa. And when the moon formed, and we think that's another episode altogether really, but we think in the aftermath of a huge collision between the proto-earth, slightly bigger Earth

than we have today, and something the size of Mars, then it would have been much closer. There would have been the moon came out of the debris of that. And would have been more molten as well. And it would have flexed as it rotated and the Earth pulled on it. So you imagine that tidal force you get on the oceans. It would have been happening more with the rocks as well. well. And the young moon would have been less solid, so there would have been this rising and falling of this bulge. And over time, that would go down. And that the Earth's gravity was essentially pulling it into line, locking the rotation. And that actually happens with many moons elsewhere in the solar system as well. So Pluto and Sharon is a good example, where they actually face each other.

They're locked to each other. But also, I think the moons of Jupiter and Saturn as well, the bigger moons all do it too. And one of the other effects is that if you're on the moon, so on Earth we just see one side of the moon. But if you're on the moon, you would see the earth rotates. You'd see the whole earth over time, but it would always sit in the same place in the sky. So astronauts on the moon, standing on the moon's surface, looking back towards the earth, it's always in the same place. Even as the sun rises and sets the moon, the earth or other is always in exactly the same place in the sky. Becky, Katow duck asked, can you explain the booties void? Yeah, I call it bootied. It might be boaties. No one comes for us on pronunciation.

I mean, if the start of this episode, as everything goes by, like, oh my gosh. We could just claim that that's how they pronounce it in Australia, the booties void. So go with that. So yeah, the booties void is like really cool. It's one of my favorite things. So you know how the universe has this structure where you have all of these like filaments

and it sort of forms like a web in terms of where the positions of galaxies are? We call it the cosmic web. And we've done an episode. on that as well. Go back to that. We've been around for a while. Yeah. We're old hats now. So this cosmic web, it has kind of like a sponge-like structure in 3D. So if you think about a sponge, right, you know, you have areas of the sponge, but you also have big holes in the sponge as well. And so what the Boutis void is is essentially a big hole in the cosmic web in terms of where there's just not very many galaxies. So it's about 700 million light years away and

there's about 330 million light years across. It's not completely empty. There's around about 60 or so galaxies in it. But given how big it is, like statistically we'd expect more like 2,000 galaxies in a region that big. So it's not like a like a true like vacuum of space. It's just like really, really underdense compared to what we'd expect, right? Like I think I've seen people say before, like if the Milky Way had been at the center of the booties void, like, galaxies nearby to us would have been so faint that we wouldn't have had the technology to detect them until like the 60s. Right. Okay. In terms of telescopes, right. I mean, the only reason that like we knew in the 20s was because like, you know, variable star in Andromeda that all of a

sudden Hubble realizes, oh, andromeda is not like a cloud of gas in our own galaxy, the Milky Way. It's a separate island of stars in its own. Right. So we couldn't have done that until the 60s, which is kind of crazy when you think about it. And like the night sky would be like so much darker than ours, right? You would see like stars in our own galaxy, but like, you know, everything else would be incredibly dark in terms of like, you know, extra galactic objects and stuff like that. And we think the reason we have it is the reason we have any structure in the universe, right?

It was just in the very other universe, there was lots of tiny quantum fluctuations, somewhere there was more matter, somewhere there was less matter. And so the booties void has just grown out of the fact. that there was less matter so that there wasn't as much to clump together when those quantum fluctuations got like inflated over a much larger distance. So it's a very cool thing.

And if you Google it, there's an image that comes up that is not the booties void, which always really annoys me. I'm going to check that it comes up now because it annoys me that it pops up. Yeah. And like people like, you know,

are using it as clickbait as like, this is the booties void and whatever. It's not the booties void. Is it that image where it looks like there's loads of, the stars and suddenly there's this empty blob in the middle and a galaxy banging. Yeah. And it's like it's it's not fake.

It's a real image. It's what's called a bock globule, which is also one of my most favorite things to say in astronomy, which is because of the amount of just like consonants and glockl stops in there. It's like boc globule. It's amazing. Which is basically just like a big clump of like really dense dust in our own Milky Way, hence why I like the stars in the background are blocked.

But people think it's the booties. because if you Google Bootie's Void, that's what comes up. Okay. The problem is there isn't really a picture of the Rootie's void because it's part of this massive structure of the universe. So it spans a huge amount on the sky. And if you take an image, there's loads of stars in the foreground. And if you like, you know, take out all those things, like, you know, sort of like actually process the image to take out the stars to get what you want. It's still, you would barely see anything because the galaxies would be so small, like, because it's covering such a large area. So there isn't an image, you know, of the,

booties. We can make a map and we can be like, there's all the positions of the galaxies and there's where it appears. And so I think that's where it's come from, but it's one of those like massive pet peeves I have because like you see so many like videos and articles on it and it's always using this image and I'm like, stop it. That is correct. I'm correct. I'm glad you cleared that up though because it is what comes up and I was like, is this what it is. I'm going to wait for Becky to explain this one. This doesn't seem right. But okay, cool. Thank you.

I mean, that is a very cool image that pops up, but it's not at the booties void. Make an article or a video about the boch globul. Well, it actually is a picture of. We'll put it on the episode list. The long list of more episodes on the moch globules because they're really, really, really cool. And Robert, we've actually had a follow-up question from our space debris episode. So Adam Harrison from Washington asks, with ground-based monitoring, what's the smallest size of space debris that we can see? And at what point does it become a threat to satellites or missions?

Yeah, this is a really good question, Adam. And I did some really good around this, as you might expect. And the typical lower limit on the size sounds quite small. It's about a centimeter for what can be detected in using ground-based radars for objects in low-earth orbit. So that's less than 2,000 kilometers above the Earth. I think it would be really hard to see things that's more visually. I mean, there are telescopes that can look for bigger things, but I think it'd be really tough to find something that small.

Now, that's not actually ideal because space debris is moving around the Earth at seven or eight kilometers a second. And that means that you could get a collision speed if you think about a head-on collision that's twice that, so maybe 15 kilometers a second, or 10 times as fast as a bullet with 100 times the kinetic energy. And that really could do some serious damage. So that's why, in short, that's why astronauts and space agencies take this stuff really seriously and why we have to find a way to clean up space.

It sounds as though these things are tiny and they are. But unfortunately, if you take something the size of a centimeter moving along those kind of speeds, it's going to do a lot of damage. For the very small things, for things like, say, flex of paint, you can look at measures like erosion on the space station. So if you see what is effectively weathering or sometimes in extreme cases, I think there was a famous image of the space shuttle windscreen where a paint ship had hit it and excavated a tiny crater. That's how you get an assessment of the very small stuff, but there's absolutely no way you can detect it. It's just far too small. So still a problem, unfortunately. And this is why I think after some decades of not worrying about it, we're really taking it seriously right now.

Okay. Thank you. And, I mean, that in itself is a topic. that we went into a lot of detail on it a few episodes ago, but like I was then looking at the satellite tracker websites and things like, oh my gosh, we're surrounded. I don't know if you have, well, you know, you both think, but when I look at the sky now, if I go out and I just pick up a pair of not

could just look at the sky, the odds of a satellite going through it are very, very high. Oh, so I was about to say that. Like, it's crazy. Like the other night, like I got up to use the bathroom like at night, right? at like three o'clock when it was dark. And I looked out of the window as a cursory glance, right? And even with sort of like the faint light that was in the room, my eyes obviously hadn't fully adjusted to the dark night sky.

The first thing I saw was a satellite. A really faint satellite as well, but it was there. And I was just like, how is that, you know, the first thing you see when you look up these days? And I did a long exposure just on my phone of the night sky a couple weeks ago. and, you know, it gives you like a stock image or it gives you your image and then it turned it turned it into a little video as well

and in a one second video it had caught three and okay, yes, that's an exposure sped up so fine, but still the exposure itself really wasn't that long at all a minute or so. And imagine if we have 100 times as many satellites which is possible or 200 times as many what the sky would be like.

I think I'm not sure people quite appreciate just want to change it with me. Yep. Well, we'll keep talking about it. And my side will keep arguing about it. I think he can fight. Thank you, Robert, for all the efforts with actual like, you know, governments and committees that can hopefully regulate this kind of stuff. And I think that's all we've got time for in terms of questions.

But do you keep sending them in. You can email podcast at r. RAS.ac.com. Find us on Instagram at supermassive pod. leave a comment on this first ever video, please. Look at you. He's such a YouTube. I'm such an audio nerd and I'm like, now. I'm on YouTube. Thank you. Okay, bye.

Or you can join the Supermassive Club for AdFrey listening. We've got a forum on there. We talk about books. You can send in your questions. Any pictures? Send us pictures of the night, sky. Yes, please do. There's some great ones on there. And I keep meaning to post them and I will do that. We'll be back in a few.

few weeks time, maybe with an episode on Boclobules. Who knows? Who knows? But until next time, everybody, happy stargazing.