The Rest Is Science - The Magic Math Trick That Fools Everyone

Episode Date: December 11, 2025

What makes a simple brain-teaser about two identical swords one of the most deceptively tricky logic puzzles of the last century? And why has this seemingly innocent riddle fascinated mathematicians, programmers and puzzle-solvers for decades? First shared in recreational maths circles before spreading across classrooms and online forums, the “swords of truth” puzzle asks a disarmingly straightforward question — yet its solution reveals deep ideas about reasoning, information, and the limits of what we can deduce from what we’re told. Is the puzzle just a clever bit of misdirection, or a gateway into the foundations of logic itself? And why does a question about two swords feel so strangely relevant in an age of misinformation? Welcome to The Rest Is Science: Field Notes. Every Thursday, Hannah and Michael rummage through their personal troves of scientific treasure and source discoveries that explain our understanding the universe, oddities that scramble our brains, objects that hint at forces we’ll never see...and a few things that are essentially just plain cool. Expect deep dives into the science behind each pick, the spark that grabbed their attentions, and the sheer delight they get from sharing it all with you. They’ll also be tackling your questions, so email The Rest Is Science at [e-mail]. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit ⁠⁠https://cancerresearchuk.org/restisscience⁠⁠ Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ. EXCLUSIVE NordVPN Deal ➼ https://nordvpn.com/restisscience Try it risk-free now with a 30-day money-back guarantee 🌍 ------------------- Find The Rest Is Science all over the internet by ⁠clicking here.⁠ ------------------- Video Producer: Adam Thornton Video & Social: Bex Tyrrell Assistant Producer: Imee Marriott Producer: Becki Hills Senior Producer: Lauren Armstrong-Carter Head Of Digital: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

This episode is brought to you by Cancer Research UK. Imagine this. Inside all of us, billions of cells follow millions of instructions written in microscopic code. And when a new cell grows, it copies those instructions, but the smallest error can lead cancer to develop. Right. And this is the reason why there isn't a single cure for cancer, because, you know, there are more than 200 different types. Each of them have got different distinct characteristics, you know, different challenges, different mysteries. And that means that trying to cure cancer isn't like following a single path. It's like trying to map out an entire

forest. That's right. And Cancer Research UK is the world's largest charitable funder of cancer research. I mean, their work spans more than 20 countries with over 4,000 scientists, doctors and nurses pushing knowledge forward to save and improve lives worldwide. You know, over the last 50 years, the work that this charity has done has helped to double cancer survival in the UK. And you have to think about that is more parents at the dinner table, right? That is more friends at their birthday parties. That is more people who are living longer, better lives. For more information about Cancer Research UK, their research, breakthroughs, and how you can support them, visit cancerresearch.uk.org forward slash rest to science.

AI was supposed to take over the parts of the job you hate. Turns out, it made your job even harder. Instead of doing the work, it gave you homework. ServiceNow's AI specialists get work done from start to finish. Cases get resolved, loops get closed. With ServiceNow, you can do the parts of your job you're best at and delegate the rest. To put AI to work for people, visit servicenow.com. This episode is brought to you by Defender. With a towing capacity of 3,500 kilograms and a waiting depth of 900 millimeters,

The Defender 110 pushes what's possible. Learn more at landrover.ca. The Devil Wears Prada 2 is the perfect sequel that has audiences talking. She knows how did you blab? It exceeds all expectations. I always knew that you would end up doing something great. See the movie that's fun, fierce, and well worth the way. This is what runway does best.

And now the devil is back in all her glory. My boss is badder than your boss. Don't miss the iconic movie event now playing Only and Theory. That's all. The Devil Wares Prada 2. Now playing everywhere. Welcome to The Rest of Science. This is field notes.

This is a kind of podcast expedition diary where Michael and I trade off on our exciting objects, our exciting discoveries, big questions that have been occupying our minds. Yeah, it's kind of like show and tell, but for nerds with a capital N. Absolutely. Every week, one of us is going to bring something strange, something quirky, something interesting, some objects or some story. and yeah, we're going to chat about it together. That's right. And please send us your own weird stories, thought experiments or questions because we will address them on this show. What do we got today?

All right. It's basically a number of wooden swords on a key chain. Yeah. On a key ring. And each one has six two-digit numbers on it. And some of the numbers are surrounded by a square and some by a circle. And how many swords are there? Eight swords. Eight swords.

And they're all what? Like how many centimeters long? Okay, so I would say that they're about 10 centimeters long. They have quite a sharp edge. Yeah, they do. That's one thing that's noticeable. They're sort of, they're engraved with these numbers along the side. Each of them has six numbers in total, two digit numbers.

And around each of these numbers is a shape, which is either a square or a circle. That's right. And they were made by Creative Craft House, a just wonderful group of people that make wooden puzzles and toys. I gave this to Hannah all the way back during our photo shoot. So we have talked about it. We know what it is. But today we're going to tell you all about it. You know what, though?

I think people watching will be aware that our delight of nerdy things is absolutely authentic. That we do this in our own time, people. We did this in our own time. That's right. That's right. And we're just recreating the magic of that moment. So this one's a magic trick. So what I want you to do is look through the swords and pick one of the swords.

And I actually cannot see what you're doing because of your laptop. Yeah, yeah, yeah. No trickery. Okay. Okay. Now pick a number on that sword. Don't tell me what you've picked. I'm going to pick this one here.

Okay, you've got it. So now what I want you to do is to read the numbers. Well, not the numbers, but the shapes that surround them. And say the name of the shape, left to right. But when you reach the number you've picked, lie and say the opposite of what its shape is. So if it's a square, say circle. If it's a circle, say square. Okay, here we go.

So we're going to go circle, circle. square square square square square circle okay circle square square square circle exactly okay now what I need to do is I need you to think about your number I want you to think about it very deeply and then we're going to speed this up because it's going to take me a while to do this in my head because I'm out of practice but I will come up with it Hannah yes did you pick the number 36 I did pick the number 36 I could tell I could feel it Hang on, let me just check. Is there any other 36 on here?

There is not. You managed to get that exactly correct. How did you do that? Thank you for asking. I was able to deduce that you had chosen 36. Is it deduce the right word? You told me. I knew you chose 36 because you told me.

How did I tell you? In code. In binary. In binary codes. Yeah. So think of it this way. Imagine that the circles are actually zeros and the squares are actually zeros. And the squares are actually.

ones. You gave me the digit three and the digit six because 0-1-1 is three in binary. But who wants to describe the rules of binary? I think you could do it. Okay, so we use a denary system, a decimal system, where our place values go from ones to tens to a hundreds, right? A three-digit number is in the hundreds. And with binary, you're only going up by two each time. So you'll write down zero for zero, one for one, Two, nope, nope, we're not going to do a two. Two moves us to another place value.

We put a one and then a zero. So we have one, two, and no ones. One zero is two in binary. It's 10 in hours. I mean, using base 10 is for lame people who have to take their socks off when they want to count to 20, basically. I'm not interested in that. I want something much more efficient. I want something where you can cram more in.

And the way that you do that with binary, it sort of seems like when you start off, You know, your first value, it only goes up to one. It's zero or one, nothing else, right? It sort of feels like very inefficient. The second values are moving right to left is two. It can be if it's zero, it's zero. If it's one, it's actually a two. Right.

Right. So one, one in binary is two plus one, which is three. That's right. It feels like, hang on a second, you've got ages to go. Counting to base 10 is so much more efficient. You can kind of cram way more in. But very, very quickly, binary numbers get you up to like extremely high levels. So, for example, on your hand, if you use this as binary digits instead, right?

So in our ordinary way of counting, you go one, two, three, five, six, nine, ten. You can count ten on your fingers. On two hands. On two hands, right? I mean, lame. Yeah. Using binary, you can do way more. It's a way more efficient way of counting.

And if I was doing base ten on my hand, then I could have the tens, hundreds, thousands, ten thousands. 100,000s just on my hand. You could. You could. One thing very briefly, just to note, anytime someone flips you the double bird, right, in your mind, you can just think, 132. 132. Okay, so four is one of them. Yeah.

And then two of them is 132. 132. So going back to the swords then, so actually if you just take the last three shapes, square, square circle, is the same as saying like that. Which is six. It's one four and one two.

combined. And as you can see, you can get any integer you want using this system. So you told me circle, square square, square, square, circle. Those first three, circle square square square is three. It's a two and a one. And then square circle, one, one zero is six. So 36. The thing that I love about these, right, so I brought them home, I showed them to my children, and who are eight and six, by the way or sorry, they are. Eight.

Eight and six. And they absolutely love them. I've managed to, using this, Michael, I've managed to trick them into learning binary numbers. Can't get them to do,

you know, normal edition in their math same work, but binary numbers using the sorts of truth. It's fun and it shows them that maths is not a who done it where we all know the answers

already, but it is a practice. It's like a fun activity. It's a craft. Quite a lot of, magic tricks actually have these mathematical elements to them, right? I know a lot of like ones that use decks of cards. Yeah.

I mean, there's the old like 108-9 trick. I don't know how it works though. But if you take a three-digit number whose first and last digits are different and then you reverse it and you subtract the smaller from the larger. Take that number, you reverse it and you add both of those together. you will always get 1,089. Okay. Yeah.

So sometimes people use this to say they get a book that's got more than 100 pages. And they say, okay, you've got a four-digit number. Go to the, what's your number? 1-089. Go to the 108th page. Go to the 9th word long. Is it this thing here? Yeah.

Yeah. You can create, you can embellish it to make the trick really mind-blowing. Yeah. And those are my favorite kind of tricks because they work all the time. There's no sleight of hand. And I don't feel bad telling people how it worked because then I'm teaching math. Yeah. Hey, any opportunity to teach math as far as I'm concerned is absolutely fine by me.

The Swords of Truth, the original design of that trick was created by an inventor named Alex Elmsley. And he came up with a way to organize all these numbers and put squares or circles around them such that reversing any one of their shapes. revealed that number's identity, which is brilliant. Yeah, it's a really cute trick. It's a really cute trick. When it comes to these sorts of truth, though, I sort of had imagined that it was an error-correcting code. What's that?

If you've come across these things, they are a very clever little math trick that's not used in magic, but instead is used across the board to make, basically, the modern world function. So if you imagine that you've got a Sudoku, and I sort of pass your Sudoku but like a bit of the corner is rubbed out you don't need to see the original Sudoku to know what those numbers were

it's possible for you to work it out so now when you have a barcode for instance on an item and the item gets like bashed around the supermarket it gets to the checkout you don't need to have a perfect reading of the entire barcode in order to be able to fill out and work out what all the numbers are because what it has is things called parity checks in it so that it just needs a certain number of the numbers and then there'll be extra rules in there

like all of these numbers must add up to 100 or every alternate digit will be even so that you can still work out what it is even if you don't have the entire barcode itself. Okay, so you thought maybe there's a rule like, oh, there's always a pattern to the circles and squares and how it deviates tells you what the number is. Yeah, that you're lying.

That's actually what I thought first, too. Yeah, absolutely. You know that thing about error correcting codes, by the way? So QR codes are an example of error correcting codes. You actually can cover up a third of a QR code, and it still work absolutely fine. Which I think, for starters, gets sort of gamed by companies who put their logo in the middle of the QR. You see this? Right.

And they do this, not because you don't need that bit of the QR code. They're just using up the fact that you can cover up 30% of it. They've lost some of the error correcting ability. They've lost some of the error correcting ability. You cannot cover up a third of one which has a company logo in the middle. Right, right. It would have to be a third when you combined with the logo. Exactly.

But I think quite a lot of people often get caught out by this. So the classic one is where people post photos of their boarding passes when they're like going on a trip. Because even when you cover it up with your thumb or whatever, because you can recover a QR. code, even when you don't have the complete QR code itself. So there have been instances of people posting their boarding cards being like, oh, look, I'm flying to this place tomorrow. And then other people on the internet managing to go through, logging on to the airline, changing the seat for the individual, maybe getting them to sit next to the toilet.

You know, maybe canceling their flight, changing their, changing their flight days. Put them in a middle seat. Put them in the middle seat. Exactly. There was one particularly viral case. where someone changed a stranger's seat to have them sitting next to the toilet and post it online saying, you showed enough pixels to resurrect Jesus, let alone a QR code.

Well, look, after the break, we're going to resurrect Jesus. Or will we? Probably not, but who knows what we're going to do? We'll see after the break. This episode is brought to you by NordVPN. VPNs are an incredible invention, short for virtual private network. A VPN, it works to share. shield your IP address it. It virtually connects you to any network in the world and protects your

information from prying eyes. Yeah, no more worrying that that public network you joined that like didn't even require a password will end in disaster. No, just fire up NordVPN and its encryption software will keep your data safe. And NordVPN's unique threat protection pro, it blocks malicious links, it scans downloads for viruses for up to 10 devices for your whole house when attached to your router. NordVPN even protect. your wallet. How? Great question. You see, some online retailers will charge you a different price depending on where you are. That's a great way to ruin Christmas.

Fortunately, using NordVPN means you will never be subjected to algorithmic pricing again. To get the best discount off your NordVPN plan, go to NordVPN.com forward slash rest is science. And our link will also give you four extra months on their two-year plan. There is no risk either with Nord's 30-day money-back guarantee. The link is in the podcast episode description box. This episode is brought to you by Cancer Research UK. We often think of beating cancer as treatment, but imagine stopping it before it begins. After years of work, Cancer Research UK scientists are launching a clinical trial of lung

vacs, the first vaccine designed to prevent lung cancer. It builds on TracerX, the world's largest cancer evolution study, which tracked lung cancer cells over many years to uncover the disease's earliest warning signs. Lung Vax is designed to train the immune system to spot these signs early on, destroying 40 cells before cancer develops. So it's not treatment, but preventative with the potential to stop lung cancer before it starts. The first stage of the trial starts this year focusing on people at higher risk. It shows what long-term research makes possible.

For more information about cancer research, UK, their research breakthroughs and how you can support them, visit cancer researchuk.org forward slash the rest is science. Square knows that in hospitality, efficiency is everything. That's why their system lets you take payments. Track sales, handle inventory, manage staff, send invoices, and keep up with finances all in one place. Fly through orders with zero mistakes.

Get the data you need and keep everything working together. So you're ready for whatever's next. Learn more about their customized little plans That's squareup.com Okay, when I sell my business, I want the best tax and investment advice. I want to help my kids, and I want to give back to the community.

Ooh, then it's the vacation of a lifetime. I wonder if my out-of-office has a forever setting. An IG private wealth advisor creates the clarity you need with plans that harmonize your business, your family, and your dreams. Get financial advice that puts you, you at the center. Find your advisor at IGPrivatewealth.com. All right, we're back. I'm going to write a wrong. Okay. Because I found out that I do not follow you on YouTube. And I noticed like three weeks ago and I'm like, I'm going to wait for a field notes episode to do it.

And so everyone can watch. Here I am. I'm. Here's my little like channel page. I'm going to search for fry squared. Fry R squared. It's a math joke, Michael. Come on. Oh, it's fry R squared. I don't. even know the name of your YouTube channel. Fry R squared is so much better than fry squared. Isn't it? I was choosing between that and E to the I fry. That's really clever. Oh my gosh.

All right. Now here's the proof. Here I am logged in as Vsauce. And the subscribe button is ready to be clicked. We're going to watch it all together. Boom. Is this the point that I should admit that yesterday I realized I also didn't subscribe to Vsos? Oh, and do you now?

secretly, just quickly press the button. I want to see how many people you follow. Hold on. Let's have a look. There's one, I don't know who it was, but someone I followed years ago, they just changed their name. Or someone bought the channel and it's now called like totally nude massage. Something like that. And there's this whole debate about like, why is Michael subscribed to this channel? It's because that wasn't what it was originally called.

Hey, look, I think lean into it. I want to own it. I want to be like, yeah, you guys keep wondering why. Because if I unsubscribe, it's like I was embarrassed or they caught me at something. This is true. This is true. I think just keep teasing it and maybe in 2035 release a video on Tolly Thune Massage. Yeah, a little collaboration.

Hey, why not? Why not? You know, I was thinking during the break that people can be resurrected, but can someone be resurrected? Because to resurrect means to be re-sorrected. Like, oh man, I was just resurrected again. It's a bit like, the one that people always talk about is whelm, right? Where it's like you can be underwhelmed or overwhelmed, but never whelmed.

You can be under the weather. But you can't be over the weather. No. Can you be the weather? I'm going to try later today after the recording. Be the weather. I'm full of questions, but I want to hear questions from our viewers. Yeah, okay, so we have a little mailbag, little mailbag entry here.

Lucy has asked, if you couldn't live on Earth, which planet would you like to live on and why? Or moon. I'm going to expand it to moon. Fair enough. There are some quite fun ideas. I mean, one of them's got some rain's diamonds, doesn't it? Yeah, but I'm going to say Venus, but I would want to live on like a blimp up in its atmosphere where the pressure, the atmospheric, pressure is safe. And gravity would be like pretty similar to Earths. They're like twin planets Venus and Earth. I couldn't handle having less gravity on Mars. I think that would be,

even though Mars is a fun one, even if we terraformed it, made its atmosphere breathable, it would still just not have enough gravity for the muscle strength I want to build. To be hench. Just to, yeah, just to, I don't know, I'm worried about that. I feel like even my lungs wouldn't be strong enough. And I feel like if I stayed on Mars too long, I would never be able to come back to Earth. Yeah. What about the other way around? If you went someone with more gravity and then just did loads of weight training, you could come back to Earth and be like extremely buff. Yeah. I mean, there's a limit to how strong a human can get. But yeah, I've heard from people who've done the vomit rocket thing. Have you done that? No, never. Okay, the zero G flights where you go up in a

plane and then the plane just drops. And you're in free fall inside the fuselage of the plane. So it's like you're in in a free fall orbit around the earth. Your legs are one of the biggest hindrances you have. Really? People have a tendency to go, oh, I want to move and they'll kick themselves to move like they're swimming. But there isn't the resistance of water around them. And they fly across the room. And if you watch videos of people doing this, you'll notice that they can't control how powerful their legs are. So if you could go and live on, I mean, Jupiter's too much. but, you know, in the atmosphere of Jupiter, far enough away that the gravity was twice or three times Earth's, came back to Earth, you would be, like, demolishing your shoes.

You would, the steps would just crumble at your feet. So wait, I really want to understand that comet rocket thing. So wait, when they're pushing off from something, not just like kicking in the air, right? Yeah, kicking in the air does nothing. But if they're pushing off from something, they're suddenly extremely strong. Yeah, they'll be like, oh, I want to move away from the wall. And they just push themselves as you. you might if you were in a rolly chair or if you were underwater, but that winds up being

20, 30 times the force they need and they just, and also the force doesn't die down, right? They just keep moving. And so if you kind of tap yourself to move into the middle of the plane, nope, you're going to hit the wall. Okay, but the reverse of that then is that if you did go and live on Mars, you would feel like a kangaroo? Yes, you would. That would be pretty cool. That would be very fun. I think it's more of a theme park ride than a home and I'm looking for a home. Mm-hmm. You've got to actually live there. I do always think when people talk about, you know, terraforming Mars, and it's like, oh, all we've got to do is add in some atmosphere and then da-da-da-da-and-da-da. It's like, you know, guys, there are inhospitable places on Earth that are way more hospitable than that.

Like, why don't we just go and, I don't know, the Sahara, for example, all it needs a little bit of water and you're fine. But it's got, it already checks off a lot of boxes. It's got the right amount of gravity. It's got the right kind of air. Yeah. I guess a place where the wet bulb thermometer temperature. gets up to a certain point, that would be a fun challenge. You know wet bulb temperature?

Go on. So this is not the air temperature that a thermometer reads. It's the temperature as measured by a thermometer that's wrapped in a wet towel. So it shows you what evaporative cooling is able to do. Oh. And if the wet bulb temperature gets above 95 Fahrenheit or 35 Celsius, that's not that high. That's too high for your body to cool down. and you will die.

Hold on, hold on, hold on, hold on. Right. If you wrap a wet towel around a thermometer and then take it outside on, I mean, we can still do this on earth. Yeah. If that goes above 35 degrees, you will die. Yeah.

Because your body will not be able to maintain body temperature. Evaporative cooling cannot save you. Which of course is how you cool yourself down, right? Which is how you cool yourself down. And so if you have cold water, if you've got refrigeration, if you've got an air conditioner, you will be okay. But we are finding more and more places on earth that are exceeding that wet bulb temperature. Sometimes just for a day, but the longer you stay in that zone, the more people die. They have to escape. They cannot

keep their bodies at a safe temperature at that level. Wow. Yeah. That's extraordinary. Yeah. What's the hottest place you've ever been? Oh, the hottest place I've ever been is Death Valley, which by the way it keeps setting records for highest temperature dry bulb and I think if you went out there with enough like equipment you could detect a record high number in August you could hold the record is that what you're saying? Yeah right right right right right so I've always wanted to do that as a YouTube video I'm like just in August like get a couple of weeks stay out in Death Valley

and you can record the hottest temperature ever recorded they're happening out there all the time this does feel like a quite a high risk way to get a record Michael It's worth it though It's worth it Died doing what he loves Setting records I wouldn't die But if I did

Think about how many views the video It's all content baby Yeah Yeah Tell you where I wouldn't want to live In the solar system I think Triton is the absolute worst place

imaginable Triton is a moon of Neptune That's far away Mm-hmm Super cold It's got geysers that run on liquid nitrogen you know, spouting out minus 230 fountains into this sky. Also, it orbits backwards.

Oh. Yeah. Just to really mess with you. I think Triton would be beautiful, though. Doesn't it possibly have oceans of like methane or something? Yeah, I think so. I think so. That could be cool.

Oh, no, wait, isn't methane on Titan? That's the one with the methane lakes. I think there the atmosphere is so dense that you could pretend to, actually fly? Yes. Yes, I've heard this. By flapping your arms. Because the atmosphere is very thin, but the gravity is so low that human arms they've calculated could flap and you could fly. That would be pretty cool. That would be very cool. I mean, it would stink. Okay, you're not going to take a helmet off, I think. You're just going to wear your spacesuit. And like, yeah, on the moon, gravity is very low, but there's no atmosphere. So moving your arms doesn't displace enough mass to

move your mass. But on Triton, that's where you can... Titan, I think. On Titan. I mean, look, they all end up being the same, don't they really? Titan, Triton, the moon. How funny that the moon is just called the moon. Yeah.

It just doesn't have a... Does it have a name in any other languages? I don't know, you know. There must be cultures that are like, oh, no, it doesn't have the general name for a satellite around a planet. It's called, you know... Jeremy or whatever. Maybe the Martians called it something different.

Oh, yeah. You know that thing about life on Mars, right? Which thing? I mean, just the idea of whether it exists or not. Or was there, yeah. I got to go and see Curiosity before it launched. Oh, you did?

I did. It was amazing. That is so cool. I wasn't allowed in the vacuum lock thing. So you weren't able to touch it. I wasn't able to touch it. I mean, they're extremely careful about who touches it. But I got to go and see the mock-ups of it in the Mars basically robot playground where they kind of move it around and

learn how to navigate. A couple of things that were really amazing about it. When they're checking for life on Mars, the idea is that what curiosity is going to do is it's going to drill into the rock and then take these samples that can be analysed for signs of previous microbial life. And in particular, they chose a spot on Mars, which they think isn't a really old riverbed where they think they used to be water flowing. And the idea behind that is that then when they're sampling in that space, they're not just sampling, oh, here's a patch of land. They're sampling something which has had land come in from all across the region. Great. Yeah. Which is just really, really smart, right? But the thing that is, I found so amazing about curiosity in this like process

to analyze whether there's life or marks is as they're drilling in the rock, they're not like running the analysis on the samples, they've got another mission planned to go and get those samples and then another one to get them into orbit and then another one to come back to Earth to sort of analyze them. So at the moment, what curiosity does

is it drills into the rock kind of puts these samples in these like basically testes and then she chucks them on the ground. Yeah. Just litters the surface of Mars with these like scientific samples. Waiting for us to do a mission to pick them up. Yeah.

And then it's like, well, have you got, do you know how are you going to do that? And they're like, no. No, no idea yet. You know, sort of many billions of pounds later. That's so cool. So, yeah, because I hadn't heard any results from it, but it's because we, curiosity didn't analyze the samples.

No, just chucked them on the ground. Chucked them on the ground. Yeah. The other thing is they're very careful about who gets to go in and touch the rover, of course. Yeah. But they're also extremely careful about the engineers who do get to work on it, not leaving their mark on it. Because I think in the early days, they found people had like, you know,

maybe with the Sharpie, just like written their child's name on it or whatever. And they have this like blanket rule, you're not allowed to do that. But then they found that some people had started soldering or soldering, if you're in the American. Sodering, thank you. You like our silent L's. It blows my mind that you call it sodering. Anyway, had like soldered in to the electrical circuits in this like microscopic way,

the names of their children. But they're really like, no, this is from all of Earth. Yep. This is not coming from you as the engineer. I like that. I like that. I mean, obviously, you want to avoid contamination of biological agents because you touch the rover and some virus stays on there dormant until it gets to Mars.

And then there could be life there, very simple life, completely unprepared for that virus. And you've literally extincted the whole planet. But then to not even put a little message your child's name on the rover. I like that because, right, the anonymity of the individual but the power of the species. This is from humanity. But we'll put an American flag on it. But it's from humanity. One small step for a man, one giant leap for mankind.

American flag. There is no earth flag, though. And there should be. And there will be, I think, soon. Yeah. And once there is, then maybe the moon will get a proper name. Mooney. Mooney McMoon face. Mooney McMoon face. If the Brits have a say, the Americans would probably call it something like...

Freedom Rock. The 51st state. Amazing. Would be pretty American. That would be pretty American. I think they would call it something like the Great American Skyball. Skyball. New Texas.

This episode is brought to you by. cancer research UK. You know when the moon landing happened? There was all of this spin-off technology that made everybody's lives better, right? Napis, cat scanners, memory phone, one big grand challenge that sparked all kinds of scientific innovation.

I do. And things like that happen, not just in space exploration, but even in cancer research. Like, I don't know what the analogy to a moon landing in cancer research would be, but the coolest thing I've learned recently is that the old idea that,

Well, cancer is what happens when there's damage to your DNA. It just hasn't really turned out to always be the case. The Cancer Grand Challenges team, mutographs. They looked at 7,800 cancer samples. And they found that there's this thing that they're calling dark carcinogens. Go on. Okay, these are molecules that cause cancer without leaving any scar on DNA at all. Right.

I mean, that's completely against the previous theories, though. Yeah, so the new hypothesis, or one new hypothesis is the promoter hypothesis, that there are other kinds of molecules that promote the expansion of mutated cells. And without those promoter molecules, mutated cells would just like stay dormant. Okay, so the mutated cells are still there, but it's like they need a little friend to help them. That's right. Just an evil friend who causes cancer. Exactly.

It's not just let's pin this on DNA damage. Kind of like you can't pin a mudslide on rain. There's also other factors like deforestation and, There's other causes that all combine together. So it's more than just damage to DNA. Because, for example, you would think, okay, well, if this damage can like randomly happen, then an animal with more cells should get more cancer. Like elephants, for example.

Exactly. Elephants, giant whales, right? They've got so many more cells than us. If each cell is like a lottery ticket and some of them, unfortunately, win the cancer, well, then we should see more cancer in bigger animals, but we don't. Does that also help to explain then why you have these patterns in the way that cancer appears across human populations around the world that can't totally be explained by mutations alone? That's right. It does. And it also leads us perhaps towards better ways of preventing cancer in the first place. Because you can target the promoters, not just the cells themselves.

That's right. And so, you know, there's been a lot of follow-up on this. One team prominent is now chasing down what these newly. identified promoters could be. This is like a clear demonstration that even if you haven't yet cured cancer, just doing the research is giving you all of this extra, these extra kind of hooks to latch on to. The more you know about it, the more you know about how it arises, the more chances you have of being able to develop a weapon that helps defend against it. That's exactly right. And for more information about Cancer Research UK, their research breakthroughs and how you can

support them, visit cancerresearchuk.org forward slash rest is science. All right, here's a question from James. He asked, I'm curious to know how we determine the age of water on Earth. Because we mentioned this in our water episode, right? We said that it was older than the sun, and then we gave no receipts. Yeah, how do you know? Okay, so there's a few different ways that you can tell. It works in a similar way to carbon dating effectively, which is that different atoms have different numbers of neutrons in them, right? So inside an atom, in a nucleus of an atom, you have the number of protons and that tells you what type of atom it is. And in hydrogen, for example, you can just have one proton on its own, or you can have a proton and a neutron, or you can even have a proton and two neutrons. Duterium. Absolutely. Like two with a block nose. Wait, two neutrons would be tridium, wouldn't it? Correct, yes. All right.

So you have one on its own, hydrogen atom, which is just a proton. Just normal hydrogen. If you have something else stuck to it, a neutron, deuterium. Duetarium, two particles in the nucleus. Tu terrium. But it's still hydrogen. Still hydrogen. Still hydrogen.

Yeah. Right. Add another one in tritium. Still chemically hydrogen. Still chemically hydrogen. But it's called tritium. Absolutely. Now the thing is, is that over time this hydrogen atom sort of doesn't like the neutrons

sticking around too much. So over time it will like kick them out. Sort of be like, yeah, I'm not interested in you. And we know the rate at which it kicks them out. And it's slow. It's slow. Like millions of years slow. Right.

And there are a lot of hydrogen atoms in a tiny bit of water. Absolutely. So the thing is, is that when water is formed, there's like a particular fraction of them that have deuterium, tritium. And then you can take a chunk of water and go in to look at how many of them of each of, of, you know, normal hydrogen, deuterium and so on. And that can give you a good clue as to how old the water is. And there are a few other versions of this, right? So oxygen also has that same trick, right? You get heavier oxygen with more neutrons in it. And what you can do is you can tell when that oxygen was formed as part of the hydrogen bond. And there's particular ratios that sort of match the

the ratio that you found in the earliest earth, this mixture of molten rock and then the big, was it Thea that came in and sort of? Yeah, that's the name for the proposed. I think it's quite popular as a theory. The name of the thing that crashed into Earth to create the moon, Thea. It's probably about the size of Mars. Wow.

Yeah. And the moon is just a little offshoot, a little splash. Yeah, it's made out of the guts of Earth and, I guess, Thea, too. Absolutely. So we know that some of the world. water on earth predates our moon because we know that from the oxygen isotopes. Then there's also that ancient water has dissolved noble gases in it. So things like xenon, argon, that kind of thing.

And when that water has been locked inside sort of minerals in the mantle, so locked inside the rock kind of underneath the surface of earth, when you analyse that, you can see that there are xenon, there, for example, which has isotopes that you can tell how old is from that. And then finally, zircon crystals, which are, by quite a long stretch, my favourite gemstone, zircon forms effectively like a cage, right, as it solidifies into crystal structure, and can trap water in there. And so we know there's very, very, very old zircon crystals that have been found in Australia

that tell us how old the earth is, 4.3 billion years old. And we know that that rock could only have been formed in the presence of liquid water. So James, there you go. If anyone else out there has questions, please send them to us. You can email us at the rest is science at goalhanger.com. Or you can join our newsletter. And we're going to be back every Thursday with a new edition of Field Notes. And on Tuesday with our normal episode.

Yeah, that's right. So we will see you then and there.