The Rest Is Science - Why We Need Zip Lines On The Moon

Episode Date: April 1, 2026

Why would a zip line be the best form of transport on the Moon? Why exactly can your feet still feel other textures right through your socks? Hannah and Michael tackle the spectacular physics of extreme commutes and everyday biomechanics. They unpick the orbital chaos and terrifying vacuum of space, proving why a lunar theme park ride is essentially a brilliant, fiery death trap. Back down on Earth, they dive into the hypersensitive neurology of touch, revealing how your brain decodes microscopic vibrations through layers of cotton to perfectly map the floor beneath you. To top it all off, Hannah shares her very old school, steam punk esq, mechanical calculator. ------------------- 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. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton + Oli OakleyVideo & Social: Bex TyrrellProducer: Simona RataSenior Producer: Lauren Armstrong-CarterHead Of Digital: Samuel OakleyExec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Welcome to The Rest is Science. This is filled notes, which is our Thursday edition, our podcast expedition diary, as it were. That's right. We answer questions from you, which you can submit by emailing the rest is science at goalhanger.com. Now, after the break, I have got what I like to describe as a steampunk iPad. That's one I've got for you today. This episode is brought to you by Cancer Research UK. If you wanted to type out the entire human genome, you would have to type at 60 words a minute for eight hours a day for about 50 years. Okay, that's the scale of the DNA rulebook inside each one of your cells, telling it when to grow, when to divide, and when to stop. And different tissues read that same rule book in different ways. So a skin cell doesn't behave like a lung cell.

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Thoughtful, meaningful, uniquely hers. Give more than a gift for less. Give AncestryDNA. Visit Ancestry.ca today. Offer ends May 10th. Terms apply. First, we're going to go to some of your questions. And we're going to begin with this one from Chris and Oliver Hornsby.

Me and my lad, Oliver, are thinking of starting a zip line business from the moon to Earth. Assuming the budget was infinite, what problems might occur, how can we overcome them, and what other considerations should we take into account? Good luck and we'll offer you 5% of the business for free each, which is very generous. That's pretty generous because I feel like we are not going to solve their lunar zipline business problems on this podcast. And yet we each get 5% of it. That could be a very valuable business. It certainly could.

Sending something on a zip line between the earth and the moon would save so much money. You could just build a robot that climbed the zip line to get from the earth to the moon, and it would take so much less fuel, so much less energy, and it could carry such heavy payloads. That would really change human society. So this is not a new idea. This isn't necessarily just a silly idea. There are some silly things that we need to avoid, right? Like, first of all, the moon and the earth are always moving, right? The earth is turning.

The moon is orbiting the earth, which means that they're not all. always facing the same points to the same points. If you had a tower on the earth and a tower on the moon connected by a cable, uh, well, sometimes the moon's at the horizon and that cable's coming straight across and it might hit your roof. Uh, but then as the moon climbs up higher,

that cable on the earth tower goes up higher and then it comes down, it lays flat on the ground, cuts the earth in half. No, really the cable is just going to snap. But just for the moment, let's assume that we fix that. we get the Earth and the moon to just face each other.

Because the budget is infinite, he said. If the budget is infinite, then let's change the moon's orbit so that it's just always at the same point in the sky. So it becomes geostationary? So it's geostationary, which means that half of the world never sees the moon. For half of the world, it's always right above. And for people on the edge, it's always right at the horizon. You get it. We could string a cable between the two.

And if you're on the moon side, you could, you really could zip line down to the earth. I mean, you'd have to have a little bit of a push to escape the gravity of the moon. But Earth has a lot of gravity. That's why the moon doesn't go away. The Earth's always pulling even that far away. So you're going to fall to Earth. And problem is that it's a long distance. Like, you're not going to just zip on down.

It takes, you know, five minutes and what a ride. it's going to take more than five days. Okay. Five full days, like night and day, you're going to be accelerating the whole time. You know, that's one good thing, except it's not really that great because by the time you reached Earth, you'd be going seven miles a second. Wowza. So you're going to need protective gear for reentry, or I guess entry, into Earth, and you're going to need to slow down. So it's going to probably, I think it would take like a week, just ball.

parking, like you got to speed up and then you got to slow back down for a safe arrival. It would be very boring. I think that you can't just hang on to like a tea bar and zip down. You're going to need to build a gondola that the passenger can sit in and, you know, watch TV and read books and bring friends with them. Because, again, this is like a week-long trip. But that's assuming we change the moon's orbit and steal views of the moon from half of the earth so that the moon is.

just always in one place in the sky. Funny enough, this is still a serious idea because, again, like I said, it would change everything about how accessible the moon was. Of course, we wouldn't attach a tower on the moon to a tower on Earth. We would attach a tower on the moon with a cable with a counterweight somewhere up above Earth, like near high Earth orbit. So you would only get that close to the Earth, and then from there you could enter, like, space shuttle style maybe. I don't know. I'm not an astrophysicist or an astronaut, but

my head is in the clouds, but I'm shooting for the stars. The point is, this is a real proposal because it's not as hard to get things into these Earth orbits. It's still expensive, but you could couple a zip line that went almost to the Earth with a space elevator that went from the Earth up really high. Which is a serious proposal. Which is a serious proposal. And I think it's absolutely shameful that we aren't already planning such a thing because that's going to be our number one chance to start mining asteroids and just

changing the entire world. I mean, what are asteroids made out of? Like literally platinum, gold, iron, nickel. Like, it's all just sitting right there. But the problem is that we have to burn tons and tons of fuel to get there. and it's so expensive. But with a space elevator that went up from Earth or a zip line from the moon close to Earth,

you could literally just put stairs on it and you could walk all the way up into Earth orbit. And you'd have to take a couple of breaks, but you wouldn't need giant fuel tanks or anything. Michael, I had to take a couple of breaks going up the Eiffel Tower. I think it's more than a couple of breaks. Okay, well, look, Alex Honol can be employed by NASA to do all of this asteroid mining back and forth climbing.

But the point is that a space elevator, also I just want to say, like, it sounds a bit ridiculous because what, the Birch-Khalifa is the tallest building. It's not even a kilometer tall. But if you build tall enough, the centrifugal force that fictitious force that pulls things away from a spinning object starts to help you out.

You build a tall enough building and its top is actually flying away from Earth. And if you build it just right, it doesn't even have to touch the earth. It can just float above it, you know? You can put a counterweight up at the top that's swinging and lifting the thing up so that its foundation doesn't have as much weight on it. That's why, you know, we're also not doing it because this is a huge project. We're talking an enormous amount of material and where do you build it? Because you don't want it to fall during construction.

It would literally be as wide across as like Kansas, you know. So it's got to be, you know, it's a bit. It's a hard problem. I mean, this is the reason why satellites are possible that they can stay in this same level of orbit. I mean, that's the effect that you're talking about. They are these massive objects effectively. And they are, I mean, depending on what frame of reference you're talking about, sort of suspended in the sky. Right.

So it is possible. You could have, you know, ladders hanging down from them. If you get it perfectly right, it is possible. It's just hard. Yeah. And it would be really a great way to. teach physics as well, because you could take a field trip with your fifth grade class up the steps of the space elevator. And even when you got up as high as the International Space

Station orbits, Earth's gravity is still like 89% of its strength at the surface. So you could still walk around. You might feel a bit lighter, but you would not feel like, whoa, you wouldn't be floating. You wouldn't be experiencing zero-g because the International Space Station astronauts feel it because they are falling. Luckily, they're also moving to the side so quickly that by the time they fall a little bit, the Earth is curved away from them, so they never hit.

But if you climbed the space elevator stairs, you really could just step off it and you would fall. You would fall to Earth. It would take a while, especially if you climbed all the way to the moon. It's going to take, like we said, five days. I want to mention, though, that zip lines in the moon are even more seriously considered as a method of transportation on the moon

from one place to another. Because the moon is very dusty. And using wheels or anything that's going to contact the surface is this whole problem. The moon dust is really abrasive. It clogs things up. It makes things dirty. It cuts things up. It's like really, you know, nasty stuff.

And the moon's surface is, you know, it's got all this like rough terrain. And there's all these landmarks. And of course, if we start driving all over it, we change the way it looks so that research can't be done anymore on how the moon was before we messed it up. But if we connected bases and launch pads with zip lines, you don't touch the ground. And it's not like you whiz by the ground

and you kick up a breeze that messes it up. There's no breeze. There's no atmosphere. There's no friction from the atmosphere. And you can just zip around the moon on zip lines. So maybe we should put this in the description. I found an entire proposal from NASA digging into the advantages of zipline transportation on the lunar surface as we try to spend more and more time there due to the Artemis missions. Very exciting stuff.

But overall, to answer your question, I think what you need to be worried about is how boring the trip would be if you ever figured it out. So Chris and Oliver Hornsby, great question. And good luck. What you also need to be worried about now is how you're going to sign over that 10% to me and Michael. That's the other main issue you should be concerned about because, you know, my lawyers can be pretty feisty. Look, Hannah, don't worry about it. It's already in writing. Like, we've got the email.

This is true. This is very true. All right, let's do another question. This one comes from Jade. Is it just me or do some numbers give off better vibes than others? For example, the number 12 feels like a benign grandfatherly number. If 12 was a person, it would smell of peppermint and hand out Werther's originals. 17, on the other hand, feels like a three-pin plug to the soul of a bare foot.

What do you think? Well, actually, I think, Jade, you've probably got a type of synesthesia. The most common version of this that you hear is that people think that different words have colors or there was one guy who I spoke to once who said different tube stations were associated with a different smell in his mind and not just because the smell that he remembered when he was in those places,

but Notting Hills smelled like sort of summer roses, you know, that kind of thing. It's called ordinal linguistic personification. And it's something that just happens where a certain number of people, quite a small number of people, end up sort of their brain assigns character or some characteristic to things that ordinarily wouldn't.

So for me, I don't have this at all, right? I don't have, I don't really feel like some numbers are nicer than others. Do you have it? I think that what Jade is describing is more relatable than synesthesia to me. I'm always like, five is brown. Give me a break. But this whole like, yeah, 12 is like a powerful number. And 17, see, it gets personal.

I used to live on the 17th floor of a building, so I love 17. I think it's also my sister's favorite number, but I think the vibes of a number I definitely get. But I don't have sensory associations with the numbers. Okay. So I think I could understand it in terms of what the numbers do and how the numbers are. I mean, like 12 is a really, 12 is a cool number.

It's what we call highly compound because it's got so many different factors. I mean, we absolutely, we've mentioned this before, but we absolutely should be working in base 12. The fact that we are stuck on lame-o-based 10 is a travesty for all humanity. Yeah. I mean, look, 10 is pretty cool, right? I can divide it in half.

I can divide it by five. Oh, shoot. Besides one in 10, we're done. But 12 is like, divide me into thirds. Divide me in half. Divide me into quarters. Divide me into sixths. I'll do it all.

Almost all. Yeah. Which is a bit grandfather-like in a lot of ways, you know? That is quite, you know, being flexible and wise. I like that. Yeah. 17, meanwhile, prime number, extremely obtuse, refuses to go into anything. So I can see that.

I can see that sort of what the numbers themselves are doing can relate to their personalities. It does seem, and I think this might be the words we used for the numbers, but it seems like 17 is a sharper number, whereas like 12 is kind of a blob. It's like Kiki and Bobo. Mm-hmm. So Kiki and Bobo is this very famous experiment where you draw two shapes, one of which is very spiky, sort of like a misshap in star, and the other one is more like a cloud, very round around the edges. And then you go across the world and you say one of these is called Kiki, one of these is called Bobo,

and almost universally people think that Kiki should be the sharp shape. There's no real reason why that should be the case, but it's sort of, it just, it's, something that feels right among all of us. Yeah, just the sound of Kiki is very percussive, whereas Bobo is very blobbed out and soft. The actual physical motion of your mouth, regardless of your culture or language, they're parallel. One thing I will say, Jade, is that you, if you do have this ability to see characters in numbers, to assign characters to numbers, you're in good company because some really amazing mathematicians, had exactly the same thing.

Notably, Ramanujan, who we did an entire podcast about a few months ago now, this is an incredible Indian mathematician self-taught. But he had this incredible ability to sort of feel the character of numbers. And for him, it would make sense in the way that numbers fit together. So there's the amazing story about a conversation he has on his deathbed of the number 17. 29 and he immediately comes up with the way that it's constructed from other numbers, a sort of sequence of numbers cubed and so on.

And he was doing that ultimately because his brain was able to assign character to each of these numbers and then in the way that they related to each other, it meant that his mental arithmetic essentially had this gigantic shortcut. Yeah, which makes sense. I feel like it's hard to remember bare facts, but it's easy to remember people's personalities. So if numbers have a personality because of their properties, then sure, you'd remember them better, right? Yeah, yeah, absolutely. Feynman, Richard Feynman also appears to have had this.

He said that when he sees equations, he can see letters and colors, essentially. He's seeing pictures of vessel functions and with light tans and violet blueishes and dark brown exes and all of that floating around. and it meant that he had more of a emotional connection to the things that he was manipulating than maybe the rest of us do. Wow. So yeah, maybe you should really lean into that, Jay. That's, I think, where I'm going with this one.

Definitely embrace it. Yeah. All right, another question we had in. This is from Elliot, who says, I read the curious incident of the dog in the nighttime about 20 years ago, and I remember the Monty Hall problem being described in it, and I could not get my head around the maths of it.

Is there any chance that you could explain it like I'm five? Michael, ever to you. There is. And look, I chose this question, Elliot, even though, like, before we recorded, Hannah was like, oh, no, the Monty Hall problem. Everyone's talked about this over and over again. And I was like, Hannah, look, this is a joint project. And, yes, even I have made a 14-minute-long video on the Monty Hall problem.

And I'm one of 18 billion people who have done videos on it, and mine is not even the best. but I feel like 14 minutes was an obnoxious amount of time to spend on it. Yeah, I don't well. I now feel like the Monty Hall problem is one of the least mysterious things, and we keep making it mysterious because of language. We just describe the problem too imprecisely, and it makes it confusing, but I think all the confusion simply comes down to the rules about what the host can do. And it's never made clear when you read a description.

So here we go. What I'm going to do is I'm going to actually read the famous Monty Hall. And again, I don't want to spend a lot of time on this because it doesn't need a lot of time. This is the Monty Hall problem as it was proposed, as it was written by Marilyn Vassavant in her famous Ask Maryland Parade Magazine column in 1990. I'll tell you, why was it famous? Because no one thought she was right. I mean, some people did. But the vast majority of people, when shown this problem, make the wrong decision and they cannot be convinced that they're wrong.

Here's what's going on. I'm going to read you what she wrote. Let me just say very, very briefly, for any of you who have not come across the Monty Hall problem, because I believe that there is still a small percentage of people who fit into this category. This is a puzzle about a game show host, some goats and some cars, that has become infamous, I would say, because everybody, when they first hear it, gets extremely, confused about the answer. And there have been untold arguments about this very problem. But

anyway, over to Michael, who's about to explain it. Here's the problem. And again, I'm quoting from Marilyn Vassavans article. So this is like an official, famous way it's been described. Suppose you're on a game show and you're given the choice of three doors. Behind one door is a car. Behind the others, goats. You pick a door, say door number one. And the host who knows what's behind the doors opens another door, say number three, which has a goat. He then says to you, do you want to pick door number two? Is it to your advantage to switch your choice? Even that description, I think, is confusing.

Because here's the answer. It is always best to switch. Many people say, well, it doesn't make a difference. It's still, you know, at that point, it's, you know, it's the same. nothing's changed. And then when you tell them, no, no, no, if you switch, you will win two thirds of the time. They're like, what? No, I mean, it seems like he's revealed where one goat is, and then there's the door I picked,

but it's just a 50-50 now, right? Whether I pick the money or the goat or, you know, whatever. But that's not true. You should always switch. And the reason you should always switch is very simply that the host not only knows what's behind each door, but the... the host is required to always open a door that has a goat behind it. And that is an assumption that Marilyn Vassavant later on admits is required because what's happening is not that you're choosing a door and then the host is randomly opening one of the other two doors.

The host will never open a door to show a car and say, nah, okay, I guess it's a draw, you know, you lose. Basically, when you choose a door, the host is then required to look at the two remaining closed doors and open one that has a goat behind it. One third of the time, you have already picked the car. You've already picked the winning door. And so the host can just randomly open one remaining door or the other. But most of the time, two thirds of the time, you have not picked the car. And the host is faced with two doors, one with the car, one without. And the host goes, well, I got to open the one that has a goat behind it.

So two thirds of the time, the one door that remains unchosen was unchosen because there's a car behind it. So choose that one. switch. I think that's exactly right. The only way that you will not win by switching is if you are lucky enough to do it to pick the car right at the very beginning. And that will happen a third of the time. One third of the time. Every other scenario, you're better off switching, which happens two thirds of the time. Yeah. So actually, once it boil it down in that way, it is really super duper simple. But my goodness me. You know, actually, right, like, so let's say maybe 2011, 2011, 2012, I went for a screen test at a production company, which is this thing that they do when

they're trying to work out if they're going to include you in a documentary or whatever it might be. Anyway, they showed me this clip of how they were like doing lots of cool maths. And the clip that they had was James May. Did you ever come across him? He was like, Dup-duper famous. I've worked with him on a Vsos video. Oh, he's great. He's a really great guy. I like him a lot.

But he was explaining the Monti-Hul problem. And then he had an explanation at the end, which was absolutely categorically wrong. Oh. And they had shown this. They had like filmed this. They'd put it out on TV already. They were sort of showing me the clip to kind of demonstrate the type of stuff that this production company were doing. And how, you know, interesting it might be for me to work with them.

And then I was like this quite young I was like 28 years old or something I'd just finished my PhD and I was sort of sitting there in this production company and I had no idea what to do I had no idea whether to tell them that they were wrong or not so I didn't say anything

but then when I got back to you know my office later I was like you know what I need to tell them that they they just yeah they absolutely but to that explanation that was terrible like that was just completely misunderstood it So I wrote them this email just saying in the kindest way possible, I'm really sorry, but the clip that you showed me is wrong. Like you shouldn't show that on TV ever again.

The head of the production company replied to me telling me that they had fact-checked it by someone very serious and important and I was completely mistaken. And then I never worked with them. So was their explanation wrong or was it just suboptimal? No, I think it was wrong. Dang, wow. I can't remember exactly in what way they got it wrong, but I think that they had said that the chances, I think they said the chances of winning by switching were a half,

because at that point you have two doors. Maybe that's why I don't like doing the Monty Hall problem, because actually I think it delayed my TV career by about five years. It's personal with you. It's personal. It's personal. It really demonstrates how much it confuses people, though, right, that you could have TV level production, someone as amazing as James May, who will himself

be the first to admit that he's not a mathematician, right? Oh, sure. And I guarantee you there are going to be a lot of comments on this video saying, oh, no, I still don't believe you, or endless analogies of like, but what if they're not doors? What if they're marbles in a bag? Or what if there's a hundred doors? And 99 of them are opened and blah, blah, blah. And it's just like, no, 98 of them are opened.

And it's like, guys, we could talk about this for 14 minutes. I already did. And after that, my like go-to when I'm driving, when I was commuting in L.A. from work to home, it was to talk out loud about the Monty Hall problem. And I just realized, man, a lot of breath is being wasted on what is otherwise pretty clear if you describe it well. Look, let's just move on. Here's a question from Lucas. How many calories do we burn while giving blood?

All right. So I've done some calculations, as I take every opportunity to do every single week on this stuff. The thing is, is that when you're just sitting there, kind of none. I mean, you're just, it's sort of like your base rate calorie usage. But the problem is you've got to go away, a remake all of the stuff that's in your blood. There's four kind of main components here. You've got your red blood cells, which are like these, I mean, they're basically like little inner tubes effectively that are carrying around hemoglobin, hence oxygen. in 500 mil of blood, you've got 2.5 trillion red blood cells.

You've got to make one of those from scratch. It's a lot of protein. It's a lot of lipids. It's a lot of work to do. You've got platelets as well, which is essentially they're like little irregular cell fragments that break off from these giant cells in your bone marrow. And these are the things that are waiting to stick together to clot if there's a tear in your blood vessel. you can need 150 billion of them.

So far, far, far less than your red blood cells, but that's still, I would say, quite a lot. These are big numbers, but they're small things. These are big numbers, but small things are great. You're also going to need white blood cells, the sort of rarer mix. You need about a couple billion of them, barely any, really. They're quite rare in comparison.

And then you've got the plasma, which is all the water and so on. So in total, all of those together, you're losing about 110 grams of protein. And manufacturing proteins from raw amino acids, that's really where the energy intensive work is going to come in. So in total, that's about 500 calories. And then probably an extra 150 or so to get all of the blood glucose that you've lost,

the kind of cellular energy reserves, the lipid bilayers. So that's what you're looking at, about 650 calories. That's a lot more than I. expected. It is quite a lot, isn't it? The thing is it's spread out over a period of time. So in the first 24 hours, you're going to get the volume replacement. That's really just where your body's going to pull water from other tissues. Mostly to replace your lost blood plasma. And then it's over the next one to four weeks, which is when these blood cells start being made. That's really when you're kind of spending those 650 calories.

But what I will say is they give you sort of, you know, a glass of orange juice and a biscuit to say, thank you very much. You're kind of already there, really. Just on eating those, you're kind of back up to zero. Well, yeah, especially if it's sugary juice. Exactly. So, wait, how long does it take for your body to replenish everything that was donated? About four weeks. Four weeks.

Yeah, which is quite a long time. Oh, man. Here's what I was thinking. If you were sitting there and instead of giving you, some orange juice to drink. What if instead you sort of became a bit of a vampire and drank a pint of blood instead?

Ah. Because here's what's interesting. Half a litre of blood, it might take 650 kilocalories for you to make it, but it only contains about 450 calories. That is fascinating.

Isn't it? So gulping down blood isn't a good way to bulk up? Gulp down blood is not a good way to bog up. So here is what I was thinking was like, okay, if you, I mean, sure, there's like, that's still some good calories in there.

But what if you connected yourself up? So you basically made yourself a sealed, a sealed tube. Oh, yeah. Where you were continually drinking your own blood, right? How would that work out? Probably not well. The answer is definitely not well.

So there's a few issues here. The first is that you would almost certainly die from heavy metal poisoning because a single pint of blood also contains 250 milligrams of pure iron. And if you are drinking that continually, you're going to be forcing your digestive tract to absorb these massive toxic doses of iron, which is going to overwhelm your liver. Oh, wow. So it's obviously that iron got in there naturally and healthily,

but to have it so concentrated. Exactly, is generally not a good idea. Wow. What you could do, though, is if you were, if you're allowed to drink water, I'm going to assume that you're allowed to drink water, how long would it take you? You're running this calorie deficit. It takes you 650 calories to make the blood, but you're only getting 450 calories from drinking it. How long would it take you to waste away, to wither away?

So we're talking here, you know, you've got your, you've got your base metabolic rate as well. that's all going on. And then you've got this deficit that you're running at. Essentially, I work it out as you're running at a deficit of about 2,190 kilocalories a day. I reckon you would wither away in 87.6 days. Almost three months. That is also longer than I expected. So if you tell someone to go eat themselves, it's like telling them to go die in three months.

Yeah. Yeah. Now, what I will say is I'm not a medical professional, and I wouldn't recommend this as a way to be. And it does also assume a steady supply of water, okay, because you're kind of losing water at every stage of this process. Yeah, you've got to replenish that. But wow. Okay, so donating blood means that over the next month, you will have an extra 650 calories. You're going to have to burn just to make back that blood.

How often can you give blood? I think it's about every three months for men and every four months for women. Oh, interesting. It's different. I guess because if you're menstruating, presumably that comes into it too. Gosh, only every like three or four months. And a pound of fat, roughly, everyone's body is different. But it takes like, that contains like 3,500 calories. So for your body to eat a pound of its own fat to compensate for the blood loss from the donations,

would take how many months, seven times four, like 28 months, basically two years to lose a pound just by donating blood at a healthy rate. Not worth it, guys. Now, this is reminding me of a question that I'd always wondered and I finally tried to look it up this morning and it was, you know, I don't grow hair up on top of my head anymore. And I'm like, how many extra calories am I not burning because my body is. isn't physically producing hair out of these follicles. Like, is that something to be, you know, worried about?

And it turns out probably not. I found a forum on the straight dope where this user called squink, which how can you not trust squink? Squint is like, really loved this question and got obsessed with it. But the only data squink could find was the amount of energy sheep need to grow their wool. And so Squink's conclusion is that if a person is like a sheep, well actually, squink is talking about beards specifically, to grow a beard for a day, just a day's worth of beard growth is only 2.28 calories. Is that it? That seems really low, but I know our bodies are really efficient. I mean, if that's true, then it kind of explains why when people go bald, they don't suddenly go, wow, my metabolism is so different.

That sort of feels worth it, actually. I mean, if you're thinking of the cost-benefit analysis, right? I'm like, I will pay you 2.2 calories for a day of beard. That seems worth it. Depends how much you want to have a beard, I guess. Balding is a better comparison because you can't stop growing a beard. and if you pluck or shave all your hair off, it keeps growing. You're still spending those calories every day.

But once you actually go bald or have the follicles destroyed, then that's when the weight loss begins, guys. Over time, it starts to build up. Yeah. I mean, you can also shave off all your hair for like a weigh-in. If you want to weigh like an ounce less, you could remove some weight that way. Speaking of which, if you look behind me,

there's a Ziploc bag on the board. Let me bring this closer. Yeah. Here's some of my beard hair. Honestly, Michael, I think sometimes a tour around your office, you would be confused as to whether it was the office of the great V-source or a serial killer. But go on. Or both. Yeah, it is weird.

But, you know, I shaved it all off once for charity and we had more than we needed. So I'm like, I can't throw this out. It's like a reminder of my beard before it turned completely white, which will happen when. day soon. And so I just, I just have it. When I was, I don't know, maybe about eight years old or something, I got into a big fight with my sister. And she pulled out a great big handful of my hair. And my mom, who has a sort of strange approach to punishment, she kept it in a zip-block bag and put a little note in it saying, this is what happened on this day. And she still has it, still has this little handful of hair.

And the two things that I've noticed in viewing it as an adult is one, my goodness me, my sister has got a good grip strength because it was an astonishing amount of hair to pull out of a child's head. But secondly, my hair color has not changed at all my entire life. Oh, see, that's why it's so great that your mother did that. It's not punishment. That's being an archivist. Like, I understand.

I've done that too. I've still got my daughter's umbilical cord the little bit that like you had to wait for it to fall off. And I've got clippings from her first haircut. I've got the wristband that they put on to her and us at the hospital when she was born. And I've given them all dates. I'm trying to remember. I might have like her first fingernail clipping. And they're all in like envelopes in my bedside table.

It's like a whole, you know, Hannibal Lecter drawer. But it's actually beautiful. Yeah, it is. It is. Life through off cuts. Yeah. Okay, should we go to a break? Let's take a break, and when we come back, I want to see this steampunk iPad.

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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 cancerchukuk.org forward slash the rest is science. And we are back. Hannah, you've got some kind of, I'm assuming like a mechanical calculator, but not an abacus, something in between then and now. I do have, I do have a mechanical calculator. So this was, um, my, uh, sister gets really good gifts for me for Christmas. And this is my Christmas gift this year. Um, and it's a thing of, it's very beautiful.

Look at this. So, oh, it's, um, it's brass, uh, or looks like brass anyway. And, um, it is, it sort of fits in your hand. And, uh, it's got a fractometer written across the top. It has feet inches and 16ths And basically it's an addition system With a subtraction system Hiding on the back

Right, it's quite flat It's definitely iPad scale kind of a thing Like a very thin little book But it's made of metal And it's got grooves on it With what look like Divots or something Little holes that you can use

I cannot wait to see how this works Because believe it or not There's something similar to that at the thrift store next door to my office. And I could not figure out how to move the numbers or the pieces inside of it. Do you need to have a stylus or a pencil? A pencil, exactly right. Okay, so I just want to sort of like picture the world at this point. So this particular one is made by a German company.

They started making them in the 1920s. But these continued to be popular even after the invention of the calculator. Essentially, this is like a pre-calculator world, right? And you have to imagine that if you are doing complicated sums, so either you are an accountant and you're totting stuff up all day long, or worse, you're an engineer trying to build a bridge or an aircraft, actually, do you know what? I don't know when the actual digital calculator was invented.

I know that my grandparents got one, I think, in the early seven, They got it for free for looking at some property, like real estate. And they just, they drove like all day just to do this tour with no intention of buying because they wanted the free digital calculator. Do you know what? Your grandparents are my kind of people, frankly. So the first electronic desktop calculator was in 1961. But as you said, they were not widely available.

Texas instruments who are sort of the kind of the calculator kings, they weren't releasing them until the late 1960s, 1970s. So we're talking about there are spotnickets in space. We've got, you know, attempts to get to the moon. While people are running the calculations on all of the orbits, on how to build everything, they're running them on these kind of things here, these like these mechanical systems where,

There's no electronics involved, right? When you stop to think about it, they're like constructing nuclear bombs with mechanical calculators. They're sending people into space with mechanical calculators. Just they're discovering general relativity and quantum mechanics with mechanical calculators. This is just wild to me. I can't even do five times eight anymore without checking it on electronic.

calculator. Yeah. Show me how this works. Okay, let me show how it works. All right. So this particular one, the fractometer, the thing that makes this special and the thing that made it outlast electronic calculators is because it can handle fractions of an inch. Okay, so if you go run on top here, this is all about distance. Can you use this for simple addition and subtraction, or is it for working within the imperial system of feet and inches? So you can, use it for integer addition and subtraction if you want to. But when it comes to the decimal points, then you're locked into the imperial system. Okay.

So let me show you like an additional, a really straightforward addition on this. Okay. So what you do? So for those of you who are listening, let me try and describe what you're looking at here. So you have, you've got this panel of numbers and they're arranged, as you might expect. So you've got some of units, tens, hundreds, et cetera, et cetera, et cetera. And then over to the far right-hand side, you have inches, and then you have fractions of an inch right over on the far right-hand column.

Okay, so if you want to add, the thing is, if you just want to add, let's go here, right? So in the ones column. If you want to add, say, four, so you slide it down to the number four. You see the number four appears here. Right. You've stuck your pencil into the hole for the number four, and you've dragged an internal rail downwards. Exactly.

So if you want to do something simple like 4 plus 2, I've done the 4 and then I can do the exact same process for 2. I put my pencil in the 2 and I drag it down. And then you've moved the internal mechanism six spaces. Okay, that's really super easy. Where things become difficult is when you take a number that then requires you to carry over into the next column. This has always been the thing that makes it tricky.

So what you do in that case, so I now have six. If I want to add a number to six, let's say you want to add eight to six. Instead of going down, you go up and over, which effectively moves this block, moves the block that you were originally in by eight spaces. but it also carries over to the following column. So it's like you're effectively like minusing two from this column and adding 10 to the next. And it's doing it all simultaneously. And so this is the bit that makes this super clever

is that you can, rather than the rail just going up and down and up and down, when you carry over, your pencil physically moves the next column of units. Right. I was wondering why they had that candy cane shape. And it's because you have to go up and then drag over to notch one more on the next place. So the slider that you're sticking your pencil into, it's mainly silver, but eventually you start seeing red numbers. And if it's red, you need to pull up, I guess, is the rule. Exactly.

Because adding eight is the same as saying minus two plus 10. or minus two to this column, add one to the following column. This is why I think devices like this should be in schools, not because I love old-fashioned things, but because it shows you how numbers work with each other and what the goal is and the different ways to get there. When you just are taught memorize five times eight or memorize this particular strategy for multiplying two-digit numbers, it just, becomes, I don't know, like you do it by rote, and you don't go, ah, place value matters and I

get why we're carrying over or whatever. Yeah, because you are literally carrying it. I mean, you're physically carrying it over to the next column. I think that's exactly right, exactly right, that you get this kind of intuitive physical feeling for it that you don't get when you're just dealing with an electronic calculator alone. The really nice thing about this one, so all of these, where you're in the feet columns, you're just going one to ten. So this all makes, you know, perfect sense. Because it's in Imperial, once you get over to the inches,

it no longer is 1 to 10, or nought to 9, I should say. It suddenly becomes nought to 11 in the inches column. Right. It still allows you to carry over, but it takes into account the fact that there are 12 inches in a foot. Right. So it's the 12th that moves into the next place. The next column, quite right. when you're over here on the 16th of an inch

this is where it has an advantage if you're having to deal in feet and inches and 16th of inches and so on all the time in imperial metrics and you're building bridges and whatnot this is where this has an advantage to an electronic calculator because let's say that you want to do okay three eighths of an inch hang on let me do a little reset clear all thank you

oh it shows how it resets it's got a little like bar on top it does have a little bar and you pull it up and it resets all of the numbers. Isn't that cute? I love that. So let's say that you had three eighths of an inch and you wanted to add to it 11 sixteenths of an inch. If you're doing it on a calculator,

you've first got to convert everything to 16ths. You've got to add it up. It gets a bit complicated. Then you've got the imperial to metric conversion, or sorry, the imperial to decimal conversion. It's all really complicated. But with this situation, you can just go, okay. Actually, it's just 15th, 16th. Easy peasy. That's really nice. So these actually, as I say, lasted

on in time. These were still being used well into sort of late 70s, early 80s, just because they had this advantage to it. I wanted to ask how subtraction works. Do you just reverse the rule? You move silver up and you move red down? You don't just reverse the rule, my friend. You reverse the side. What? It's the exact same internal mechanism. It's just you're moving it up on one side down on the other effectively because it's it's flipped over. Right. So you don't need a new thing. You can just add and subtract and subtract and subtract and it can tally the entire thing as you go.

So you could be adding some things together, flip it over, subtract them. So you flip it over. It's got the answer you currently have, the running total, and then you can start subtracting from it on the other side. Exactly. That's beautiful. Isn't it gorgeous? And this is the thing. Okay.

So just going back to the point that you made earlier about how having these old-school mechanical objects actually give you a much more intuitive feel for what the numbers are actually doing, even when you're doing simple things like addition and subtraction and multiplication. I think the same thing of good old-fashioned slide rules. You know, we're in boomer tech now. I love a good slide rule, but I love no slide rule more. the slide rule, Michael, that also happens to be a pair of chopsticks, which was a gift from you. Look at those. They look familiar. Yeah, we designed those, and they were in a curiosity box

a couple of years ago. And yeah, you can eat some food with your chopsticks, but then they also slide by each other, and you can do slide rule calculations. You can do addition subtraction, multiplication, division, as well as exponents. Yeah, to the power of two, to the power of three. We don't have time to go through it today, but learn how a slide rule works. Learn how that kind of, what the heck is that thing that you, what's it called in general, what you brought today? It's a mechanical calculator, but is it called like a slider or a... This one is called an adiator. Ah, yes, a slide calculator, also known as an addiator after the best known brand.

So the generic is slide calculator. I don't want the adiator people coming after us. They're their competitors. But the point is that learning how to... how these work gives you such a much deeper understanding of number theory. It's amazing. The reason why I think slide rules are really interesting is because they use this mathematical trick to make multiplication way easier. The thing that makes these unusual, the slide rule and the adiator, is that they're not using any turning because most mechanical calculators

would be based on a system of cogs where you would have one cog that would turn and turn and turn and and turn and then on the 10th would flip the next cog. That was sort of how they managed to handle carrying over a digit effectively. And there are all kinds of these that exist at various levels of complexity. One of them, which I think is probably the most beautiful, is called a curter. And these things, they get found in people's lofts, like stashed away in the stuff your grandparents owned, thinking they often get sort of chucked away, really, because people think that they're musical boxes that don't work anymore,

but they look like an old-fashioned sort of pepper mill. They have a handle on top that you can turn around to do the calculations. Like a pepper mill, yeah. Like a pepper mill, exactly. I know, I've seen videos about them, and I want one so badly. But look on eBay, they're all over $1,000. Over $1,000. They're wildly expensive.

And fair play, because they are an unbelievable masterclass in precision engineering. But the story about these curters is that it was actually invented by a prisoner of war during the Second World War, Nazi prisoner of war. And were it not for his clear talents in this area of engineering, then he almost certainly would have been murdered. But instead he managed to escape the camps and after the war launched this brand. and it was one of the most popular mechanical calculators for a number of decades. Wow. I want one of those so bad. I want one so bad.

All right. I'll put that on the Christmas list for Hannah. Kerta mechanical calculator. The fractometer, by contrast, I think is worth about 20 quid. Yeah, I was going to say the slide calculator next door is $3. Yeah. Buy it, though. I want to see a picture of it.

Yeah, I'll see if I could find it. You've inspired me, though. I think I'm going to go and play. with that with my kids. I was in the House of Lords last week talking about adult numeracy. This is the kind of stuff I do on days when I'm not with you, Michael. And they were saying, how can we improve numeracy in young people and adults in the general population? And it's really hard. But I think that you're right that actually having a physical connection when you're manipulating numbers is one of the really good ways to do it. Well, yeah, I'm sure you've seen people build those

mechanical counters that go up with binary. And like that shows how binary works so much better than reading the Wikipedia page. And you can build calculators with falling marbles and just little levers in the same way in base 10. And your understanding of what the heck numerals and our notation or what is a place value system, what that means, it makes everything so much clearer. I have a book that is, I haven't read it yet, but it's one of my ideas for like a long video in the future. And it's a book of all the different ways there are to multiply numbers and add them and subtract them. And by that it means all the methods. And in school, you usually learn the method that your country at the time has said, this is what we should teach.

So for like me multiplying, we did the whole like, okay, so you start at the ones digit and you go to the ones times the ones, the ones times the tens. and you label them out and add them up. But then you see these viral TikToks about in Japan, they use diagonal lines. And in China, they use dots or whatever. And everyone goes, what? Math should only go one way. And it's like, no, these are the methods for working with numbers. Sometimes it's more convenient to do it one way, sometimes the other.

But if you learn them all, you suddenly are like a wizard of numbers. I have a similar book downstairs, actually. It's speed arithmetic techniques. As you can tell by the fact that I need you calculate it to do four times eight, I haven't read it. But one day, Michael, one day I'm going to read it and then I'm going to blow you away. Oh, yeah. I fell down a rabbit hole of watching a math, a speed math person on Instagram or something. And I loved it because the guy was using very different methods. He was like, don't do the whole thing you learned in school. Like just take every number and break it apart. 72 times 48. You can do 70 times. 40 really quickly and you can do two times eight really quickly and then adding them together in your mind way easier to do mentally. Do you know what? I think we'd do another field notes have said where we just shout numbers at each other. Yes. I do definitely think an episode on like mental math

tricks could be useful. Like there are some, you know, like finding the square roots of certain numbers can actually be really easy. Squaring numbers and cubing them. There are shortcuts. And then the listeners will walk away going, hey, name a four-digit number. I can find its cube root in like a second. And your life will be the same. Okay, well, you can write to us and tell us if that is an episode that you would like to hear or the I'm very idea if it horrifies you. As ever send us anything, you would like us to answer to The Restiscience at Gohanger.com. Yes, please do. And join our newsletter at therestis.com slash science. Until next time, stay curious. You know,