The Physics Of Thermodynamics

Is the kitchen home to some of the most extraordinary technology humans have ever invented? Professor Hannah Fry and Michael Stevens explore the science of everyday appliances, from the strange physics of coldness to the wartime origins of the microwave. They explore how humanity learned to trap 'coolth', beam heat into leftovers, and turn the most ordinary room in the house into a high performance laboratory! From ice merchants and exploding eggs to magnetrons and magnetic fridges, this is the surprising story of the science hiding in plain sight. ------------------- 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 Oakley + Jack Meek Animator: Sam Benson Video & Social: Bex Tyrrell Producer: Simona Rata Senior Producer: Lauren Armstrong-Carter Head Of Digital: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Michael Stevens?

  Hello and welcome to The Rest Is Science. I'm Michael Stevens.

• 0:04Hannah Fry?

  And I'm Anna Fry. Michael, what is your favorite room in the house and why is the answer the kitchen?

• 0:09Michael Stevens?

  Oh my gosh, we're jumping right in. My answer has to be the kitchen. Is this a setup for your episode?

• 0:13Hannah Fry?

  It's the correct answer.

• 0:15Michael Stevens?

  Okay, I want to tell the audience, this is an episode where Hannah has come to talk to me about something that is, dare I almost say annoyingly, close to her heart. Before we record episodes, she's always talking about refrigerators. And I'm like, Hannah, one of these days.

• 0:31Hannah Fry?

  One of these days, my time will come.

• 0:32Michael Stevens?

  Get it out of your system.

• 0:33Hannah Fry?

  My time will come.

• 0:34Michael Stevens?

  No, I'm really excited to hear this. And of course, my favorite room in the house is the kitchen. If that's going to help move things forward.

• 0:40Hannah Fry?

  I'm not, see, this is the thing. I've managed to, I've managed to expand from not just my love of fridges, but I'm going to do, I'm going to do other, other household items in the kitchen too, Michael. This is, this is going to, this is going to be a little justification as to why the kitchen is the room that contains all of the most interesting, high-performance scientific equipment in your house.

• 1:08Hannah Fry?

  This episode is brought to you by Cancer Research UK.

• 1:10Michael Stevens?

  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.

• 1:30Hannah Fry?

  And different tissues read that same rulebook in different ways. A skin cell doesn't behave like a lung cell.

• 1:36Michael Stevens?

  And cancer can begin when those instructions change. Not one dramatic moment, but through small, gradual edits over time.

• 1:44Hannah Fry?

  Now, cancer isn't one disease. It is more than 200 types shaped by where those changes to the rulebook happen and how cells respond.

• 1:54Michael Stevens?

  Cancer Research UK is the world's largest charitable funder of cancer research, backing studies across all types of cancer.

• 2:02Hannah Fry?

  Work that takes years of very careful, steady progress to deliver each breakthrough.

• 2:07Michael Stevens?

  For more information about Cancer Research UK, their research, breakthroughs, and how you can support them, visit cancerresearchuk.org/the rest is science.

• 2:20Speaker 02

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• 2:50Speaker 03

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• 3:24Hannah Fry?

  I suppose I should probably start by saying why I like fridges so much.

• 3:27Michael Stevens?

  Well, yeah, I mean, look, I love fridges too. But, but your love is unique and I want you to describe it for me.

• 3:33Hannah Fry?

  It's sort of a philosophical love, you know? It's, it's like, okay, the thermodynamics is delicious. The history of it, sumptuous, right? You're gonna love all of that stuff. But I think there's something that is, is just really strange to imagine that before the invention of fridges, before the ability of humans to artificially cool things down, there were areas of the world where, I don't know, people had literally never tasted a cold drink before, right? Like, you don't get this. In the, if you look across the universe, temperature gradients are these smoothly changing things, right? You don't get these little bubbles of anomalies

• 4:17Hannah Fry?

  of like frozen temperatures in amongst things that are many, many, many degrees high. It just doesn't happen.

• 4:24Michael Stevens?

  Right, we definitely have pockets of high heat. Sure. Because of gravity, we've got stars.

• 4:31Hannah Fry?

  Yeah.

• 4:31Michael Stevens?

  But there's no natural phenomenon that creates big balls of coldness.

• 4:36Hannah Fry?

  Coolth, coolth, I like to call it.

• 4:38Michael Stevens?

  Coolth.

• 4:39Hannah Fry?

  You know, you've got warmth, why not have coolth?

• 4:41Michael Stevens?

  I mean, black holes, they get really hot around them because matter gets squeezed together and it's a vibe. But in the middle of a black hole, I'm not even sure temperature makes sense. So really, we don't have any cool balls.

• 4:54Hannah Fry?

  No, there are no cool balls apart from in your kitchen, which which I think is kind of interesting. I mean, the other thing is the thing that's also kind of important to say here is that cool, not only is it not a word, it also isn't really a thing, right? Like cold, cold doesn't really exist. Cold is just the absence of heat. You can't, you can't actually cool something down. You can only take away the heat from it.

• 5:16Michael Stevens?

  So would you say it's like darkness? Darkness isn't a thing. It's the absence of light.

• 5:20Hannah Fry?

  Exactly.

• 5:22Michael Stevens?

  Cold.

• 5:23Hannah Fry?

  Cold.

• 5:24Michael Stevens?

  Coldness is just the absence of heat energy.

• 5:27Hannah Fry?

  Exactly. And we are so blasé about the cool that we have created because, I mean, okay, the very first time that people really started to notice that actually this desire that humans have for for coldness, for ice in particular, and how it could be monetized was this guy called Frederick Tudor. So he lived up in Massachusetts. Now Massachusetts is somewhere where it's got this gigantic temperature gradient between summer and winter, right? Really frozen in the winter, really hot in the summer. So so what people had done, and this is like for thousands of years, and in China, people have been doing it for thousands of years. When it would snow in the winter, they would dig out these ice houses. And then they would cut up ice from lakes and shove it in in these ice houses.

• 6:12Hannah Fry?

  I mean, it's it's literally the opening sequence to Frozen, right? Disney's Frozen, okay?

• 6:17Michael Stevens?

  Oh, that's true. Yeah, yeah, yeah. I've also seen really great reels on TikTok where people are like, we're gonna make ice cream this summer. The old fashioned way.

• 6:24Hannah Fry?

  Oh, wow.

• 6:25Michael Stevens?

  They make an ice house. They like dig a trench, build a structure over it. And in the winter, they cut big cubes of ice and they fill this pit inside the ice house with straw. Put the ice cubes in the straw, cover it in more straw. And literally, four months later, middle of the hot days of summer, they're like, hey, there's still some ice left. And they use it to make ice cream.

• 6:49Hannah Fry?

  Oh, that sounds amazing.

• 6:51Michael Stevens?

  Yeah.

• 6:52Hannah Fry?

  That sounds amazing.

• 6:54Michael Stevens?

  So it was possible, but you had to have access to ice in the first place.

• 6:57Hannah Fry?

  Exactly. It was a geographically anchored. I mean, you, you had to be in a place which, which, which had that temperature gradient. So there are places, you know, like cross Africa, across the Caribbean, you know, loads of South America. Where, where it's just, I mean, forget it, right? There's no, you, you'll have never seen ice. You will have never touched anything that is, that is zero, like zero degrees. It would just will never have happened, which is just mind boggling to me. Anyway, this guy Frederick Tudor, he was like, okay, all of these people, these fancy people doing with their ice houses. Can I not just follow that same logic? Can I not just get loads of ice, chuck it in a ship, sail down south? And then I can be on the beach selling ice creams to all of these people.

• 7:38Michael Stevens?

  When did he have this idea? Put me in historical context here.

• 7:42Hannah Fry?

  We're talking very, very early 1800s here. Okay.

• 7:45Michael Stevens?

  Okay.

• 7:46Hannah Fry?

  So, so really before the industrial revolution has got underway in full swing.

• 7:50Michael Stevens?

  Right, but Massachusetts is a state of the USA, no longer a colony of the British.

• 7:55Hannah Fry?

  Correct.

• 7:56Michael Stevens?

  But industrial revolution is about to take off.

• 7:59Hannah Fry?

  Meanwhile, New York is this up and coming city, which has less access to ice. So he starts off doing a little run down there and it works pretty well, right? You can, you can sell ice to people down in New York and that's, that's, that's nice and great. So he decides to ship ice to, to Martinique, okay? Where, you know, no one had ever seen ice before in their lives. And everyone thought that this was an absolute joke, like who would try and make a business out of something that melts? Right? This is, and it did melt, by the way, his first boat turned up, there was as much water inside the ship as there was outside. It was.

• 8:30Michael Stevens?

  Oh, no.

• 8:30Hannah Fry?

  This total disaster.

• 8:32Michael Stevens?

  That's the punchline to the joke of the guy who tries to sell ice to, well, no, the, the joke is selling ice to the Inuit. But Martinique, by the way, is in the Caribbean. It is an island down southwest of Florida.

• 8:46Hannah Fry?

  Super warm, essentially.

• 8:47Michael Stevens?

  Super warm.

• 8:48Hannah Fry?

  All year round.

• 8:49Michael Stevens?

  Giant mountains that raise up high enough an elevation that you've got snow at the peak. So yeah, we're talking about an ice free zone.

• 8:55Hannah Fry?

  We're talking about an ice free zone and we're talking about Frederick Street outside it in a sad, wet, empty boat. That's what we're talking about. But he doesn't give up. So, so he goes back up to Massachusetts. And this time he uses the straw trick. He, he's like, right, and you just need to insulate it better. And he realizes that if he goes around to local timber mills, take all of their sawdust off their hands, he can pack it around the ice. He's just at this moment where it's like, he thinks it might actually work. But what he does is very clever. He goes down to places like the Caribbean, you know, Cuba, Jamaica, even actually across to India. He gets people to sign these contracts and he essentially makes it so that he has the sole rights to sell ice

• 9:38Hannah Fry?

  in that country, region, wherever it might be. So he knows that he's going to make it work. It's not quite there yet, but he's like, because no one believes him. They're like, yeah, yeah, yeah, yeah. Sure. Fine. You can do this. Go right ahead. He does this other thing where he would go into bars and he would give free samples. He would let patrons experience how refreshing a chilled beverage would be. I mean, the first time ever that these people have drunk a cold drink, which is just incredible to imagine. Anyway, he makes it work. The, the sawdust is the thing and he ends up making so much money, so much money. He becomes known as the ice king of the world. Okay. So, so we know even eighteen hundreds, we know that there is this like incredible demand,

• 10:22Hannah Fry?

  not just for, for preserving food, but for the enjoyment of having an ice cube in your glass.

• 10:28Michael Stevens?

  I want to say this guy really seems like a forerunner of this modern mentality where he's not just an inventor or an engineer. He's also a salesman.

• 10:37Hannah Fry?

  Yeah.

• 10:38Michael Stevens?

  And he's also a legal wizard. He's out there signing contracts to exclusively sell ice to your country before he really knows that he can do it. He wants to sell something not because people need it, but because it's joyful and fun.

• 10:53Hannah Fry?

  Yes, you're so right.

• 10:54Michael Stevens?

  How much more modern of a combination constellation. Kind of elements can a single person have?

• 10:59Hannah Fry?

  Gosh, you are so right. How perfectly, perfectly put. The thing that ends up putting him out of business, by the way, is the fridge, right? The fridge and freezer, it's essentially the same technology, it's just set at a different level.

• 11:09Michael Stevens?

  I could see that coming, yeah.

• 11:11Hannah Fry?

  That's the kind of great point, but he's the person, he's the person that makes us want it. But going back to your people who are making ice cream in the summer, the old fashioned way, one thing that you can also do, you can make ice yourself. Wherever you are in the world, there is a way that you can do this, actually quite easily now. I should probably put an actual disclaimer on this. Um, don't actually, don't actually try this. Okay? I mean, do, but don't actually.

• 11:37Michael Stevens?

  Don't actually?

• 11:39Hannah Fry?

  This is something I've done. You have to be quite careful and I would definitely do it outside because it is a little bit explodey.

• 11:45Michael Stevens?

  Oh, okay. What, what am I, what do I need to use?

• 11:49Hannah Fry?

  Okay, you need a can of butane.

• 11:51Michael Stevens?

  Okay, yeah, I've got one at home.

• 11:52Hannah Fry?

  Which you can, you can get is lighter fluid or camping, camping gas. Okay, the thing about butane is that it exists as a gas at room temperature. It has this boiling point of about naught point five, sorry, minus naught point five degrees C. Okay, so below the freezing temperature of water. And it's put in these really pressurized containers and it's stored in liquid form in these pressurized containers. And so when it gets released into the air, it desperately wants to become a gas. It's squirted out as a liquid and it desperately wants to get out as a gas. And to do that, to make that transition from liquid to gas, it needs a little kick of energy. Um, specifically this thing called latent heat of vaporization.

• 12:35Hannah Fry?

  It will draw that energy from its surroundings. It will kind of steal the, the thermal energy from anything that it's in contact with. So if you get like a little glass of water and you place it in a bowl. And then pour liquid butane into that bowl surrounding the glass of water. What will happen is that liquid butane is going to really quickly boil. And it looks like that too. It looks like a pan of boiling water, right? There's bubbles on the surface. And to fuel all of that boiling, it's sucking the thermal energy right out of the water, dropping the temperature of that water so that the water will then flash freeze into ice in a matter of seconds.

• 13:15Michael Stevens?

  Wow. So you've got the yin and the yang. You've got the boiling butane and the freezing water.

• 13:20Hannah Fry?

  Exactly.

• 13:21Michael Stevens?

  I think you could probably also do this with a can of compressed air. If you didn't want an explosive gas sprayed everywhere. I know that when you spray compressed air, like from a keyboard cleaner, you can get streaks of ice. And I don't know if that's

• 13:33Hannah Fry?

  You can.

• 13:35Michael Stevens?

  moisture from the air or if it's from the air in the can or from the air around you.

• 13:39Hannah Fry?

  This idea of evaporative cooling of anything that's from a liquid transitioning into a gas, you do get this effect of like stealing the thermal energy. I mean, it's the same thing as if you come out of a swimming pool in the summer and you've got droplets of water on your arm, those drops of water are going to evaporate. And then you feel really cool. It's not like, it's not like the wind affects you differently when you're wet. It's that those molecules of water are stealing your energy, stealing your thermal energy as they're escaping.

• 14:06Michael Stevens?

  Yeah.

• 14:06Hannah Fry?

  Exactly. So it is the same effect. I just don't know whether you'd actually be able to make a chunk of water freeze using something which had a higher, oh, yeah, I don't know, actually.

• 14:18Michael Stevens?

  Well, do the experiment at home, any adults out there listening. Uh, you're at your own risk and let us know.

• 14:26Hannah Fry?

  Just hold gaseous butane on our arms, okay?

• 14:30Michael Stevens?

  I'd rather suck on an ice cube made with compressed air than compressed butane. Just for the flavor of it all.

• 14:37Hannah Fry?

  Just for the flavor of it all. But you know, this is, this is something where I think is quite fun to do when you go camping, right? It's like, let's make our own ice cubes.

• 14:46Hannah Fry?

  And the thing is, the way that fridges work, okay, they sort of seem like they're magical, but they're using the exact same trick. That's it. That's the only thing that they're doing. Except instead of letting the liquid butane like float off into the atmosphere, they Just keep it all in a pipe. Also, technically, they use isobutane, which has a boiling point that's lower. It's minus eleven point seven degrees, but but it's the same, the the the main trick is exactly the same. Is that you you spray in a pipe, you spray it in there in liquid form. It's the fridge is like five degrees, which for the isobutane is mega, mega hot. So it instantly boils, steals all the the thermal energy from the inside of the fridge. And then it exits down the bottom of the fridge, still in the same pipe.

• 15:29Hannah Fry?

  And then that's sort of the the the cold bit of the fridge, as it were. And then round the back, all you ought to do is get this this gas now, this hot gas into a colder liquid. So you compress it and you put it through a condenser at the back. All of the heat escapes out into the room and then it's back into a liquid again. And I mean, that's all you do is just a loop, the loop, the loop, the loop, the loop, this butane, isobutane, going round and round and round for the entire lifecycle of this fridge. I don't know, man. I think there's something so amazing about that, this idea that you are just recycling this liquid round and round and round and round and round, giving it energy, stealing energy, you know, moving the energy. You're pumping the energy out of this little box. I think that is, and and as a result,

• 16:15Hannah Fry?

  we can all have cold drinks all over the world. I think that's really cool.

• 16:19Michael Stevens?

  Yes, socially, refrigeration really is a big deal. And today we take it so for granted that I'm I'm remembering, I think back decades ago, there was a Fox News segment about people living in poverty in the United States and how it can't be that bad because eighty five percent of them have refrigerators. And you watch that today and you go, wow. Yeah, I mean, first of all, they don't own them, like probably the landlord does. But like a refrigerator is just such a ubiquitous part of our lives today that even if you're living paycheck to paycheck, like you've got a fridge. And that wasn't always the case.

• 16:59Hannah Fry?

  Really wasn't.

• 16:59Michael Stevens?

  Time when having a fridge meant you were hoity-toity fancy pants McGee.

• 17:04Hannah Fry?

  Because I hear that number and I hear fifteen percent of people didn't have a fridge. Which makes me wonder about food preservation. It also makes me wonder about medication. I mean, vaccines is the is the perfect example of this. The only reason why we are able to, you know, vaccinate vast populations across the entire world is because of the invention of fridges. Without it, these like very complex solutions that are made just can't, they're too fragile to remain active, you know, before they reach your arm. I mean, it's really incredible what the fridge has enabled us to do, and we just don't even consider it. There is a jump, I guess, between butane and the modern fridge. So the first ever ice maker

• 17:46Hannah Fry?

  was made in Australia. This is like eighteen fifty five. Okay, so you know, we're only fifty years after the Ice King has has been giving people the delights of a cold drink.

• 17:58Michael Stevens?

  So that's all he had. He had fifty years and then an invention was made that could just do it on site.

• 18:04Hannah Fry?

  Yeah, I mean, he his monopoly lasted a bit longer than that. It took some time for this for this this engine to to make its way across the world. Also, the first one, by the way, was absolutely massive. It's like the size of, I mean, the size of a room. It's absolutely gigantic. I think the other really big difference that the fridge has made is giant societal change. You know, before fridges, back to those, what was it, eighty five percent of people having fridges and fifteen percent not. It was only with the invention of the fridge, the the sort of particularly the fact that fridges became commonplace in people's kitchens, that leftovers were a thing, right? Or that like ready meals were possible. All of this stuff is just like a direct consequence.

• 18:49Hannah Fry?

  The time-saving nature of this, I think you can't really underestimate.

• 18:54Michael Stevens?

  Oh, yeah. And I just looked it up. Today in America, ninety nine point eight percent of people have a fridge, have access to a fridge. It is just like air almost. Now, ninety nine point eight isn't a hundred percent, but when you think about the standard of living and how that's changed and what it just means to live a routine life in America and a lot of the world, it's incredibly different than it was back when the only ice you could get had to come on a ship from Massachusetts.

• 19:25Hannah Fry?

  Yeah, yeah. I mean, this is it, right? Life expectancy aside from medically, yes, is gigantically different from then. And, you know, these two things are not unconnected. The fridge has made a big difference to quality of life as well as the length of it.

• 19:41Michael Stevens?

  I mean, you know those videos where people show their water of the day? And they fill a cup with water and then they mix in all these flavors and different waters? A person from, you know, seventeen ninety-nine would watch that and go, "Oh, that's like eighteen million dollars worth of ice." "Are you a witch?" And today, we're like, oops, one of them fell off. Better throw it in the sink so it can go away annoyingly. It's like a bother to us.

• 20:08Hannah Fry?

  I have to say, actually, during the, um, during the gold rushes, so the Australian gold rush and the Cana- and the Californian gold rush. You know, this is the point when ice is the absolute ultimate luxury, either whether it's come down from Massachusetts or whether it's been built in this absolutely giant honking machine. People would say that if you had a good day, if you'd gone out in the gold rush and you'd found a lot of gold, if you had a good day, you would come back to the bar and you would buy everybody a whiskey. But if you had a really good day, you would buy people whiskey with ice.

• 20:40Michael Stevens?

  Yeah.

• 20:40Hannah Fry?

  Big money times.

• 20:43Hannah Fry?

  And now they're chucking it on the floor for TikToks.

• 20:45Michael Stevens?

  The expanding butane, cooling down and then compressing it, it warms up. That whole procedure is pretty well known. Like, we all kind of have this intuitive idea of, oh, yes, I learned in high school, when a gas expands, it cools. An almost opposite, seemingly paradoxical thing happens with rubber bands. I'm sure you've played with a rubber band before and noticed that if you stretch it real fast and strong, it gets warmer. Like, it warms up. You can, you can take a rubber band, if you have one with you right now or later, stretch it fast and stick it on your lips, which are very sensitive to temperature. Do you have one?

• 21:23Hannah Fry?

  No, I don't have one. No, yeah, I have some downstairs, but go on, this is my joint.

• 21:26Michael Stevens?

  Okay, so you'll just have to trust me. The experience of stretching rubber band and then putting it on your lips to feel that warmth is, is, is pretty common. But if you stretch a rubber band. And leave it stretched, like you just keep pulling it, you keep it stretched. It'll eventually cool down to room temperature. Won't take that long. You can even blow on it if you're impatient. Then let it collapse back down, put it on your lips. It will feel cold.

• 21:51Hannah Fry?

  Right.

• 21:52Michael Stevens?

  It gets colder than room temperature. It's like a extremely simple refrigerator. And yet it doesn't seem to make a lot of sense because when the rubber band shrinks, isn't it compressing? Shouldn't it heat up? And shouldn't it cool down when you expand it like a gas? Obviously, something very different is going on. The rubber band is not a gas. It's made of solid molecules. The, the whole reason rubber bands even snap back is that essentially they've got, and this is, I'm borrowing from Richard Feynman's explanation, by the way, as

• 22:28Hannah Fry?

  As we so often do.

• 22:29Michael Stevens?

  As we so often do. There are really long rubber molecules in a rubber band. And when the rubber band is relaxed, they're all crinkled up like this and they're kind of floppy. But when you stretch the rubber band, they get pulled really taut and straight. But there are other molecules in there that have a temperature. That means they're moving, they have kinetic energy and they're bouncing into these long polymers. And they're like hitting it, trying to like crinkle it up. That's where that force of, of, of compression comes back in. It's literally the, just the motion of molecules in the rubber band trying to kink up these long polymers that you've stretched out. So what happens is that when you stretch the rubber band, those rubber molecules get

• 23:11Michael Stevens?

  really taut and they're like, like extremely powerful trampolines. And so the, the whole thing heats up. But when you release it, now suddenly these molecules that are bouncing around, they're hitting like mud, like quicksand, like sloppy slop. And they're just like losing energy when they hit it rather than going boing and bouncing right off, they go and they get caught and they slow down. And a lot of their kinetic energy goes into just moving around

• 23:37Hannah Fry?

  Right.

• 23:38Michael Stevens?

  floppy rubber polymers. So the temperature drops and Ben Crasno over at Applied Science on YouTube took

• 23:46Michael Stevens?

  That idea to the practical extreme by building a rubber band powered refrigerator. No isobutane for him. He, but he had to do the same thing where, you know, you're, you're going to have to compress or you're going to have to reset the rubber bands, just like the refrigerator has to reset the gas outside of the box. So he built basically like a disc that would stretch rubber bands outside and then rotate them into a little box and compress them. And then take it out of the box and stretch it. And it did this with a whole chain of rubber bands. And he was able to drop the temperature like a degree or two.

• 24:24Hannah Fry?

  That is amazing. That is amazing. I like that so much. There is this amazing company that I got to go and visit once as part of my obsession with fridges called Camfridge. And they have this idea. It's, it's like, it's kind of similar to your elastic band thing, but they're using magnets. So there are some materials, I think gadolinium is one of them, these rare earth materials that really, they exhibit this really strong effect when you bring them near magnets that they, they do the, I mean, look, I'm going to simplify slightly, but they, it, it's, it's essentially the same effect that it heats up and cools down. You put them in, they heat up, you leave it in there, let it get down to room temperature and then take it out.

• 25:08Hannah Fry?

  And then it cools down to below room temperature. So they have a similar thing where you have this spinning magnet. And that feels like really cheating the universe, you know? That all you're doing is, and, and this works, by the way, they have this as commercial fridges. It's like unbelievably green technology because all you're paying for in energy terms is just to rotate this magnet. And that is like, what a trick that is to just put a magnet in, take a magnet out. Ice. You know?

• 25:39Michael Stevens?

  Yeah, magnets already seen magic, as we've discussed before, but then to use them to make a refrigerator or a freezer seems like you're treading pretty close to too much magic.

• 25:52Hannah Fry?

  Too much.

• 25:53Michael Stevens?

  And yet you're not. It's real.

• 25:54Hannah Fry?

  It's it's definitely an approximation of wizardry. I think that's.

• 25:58Michael Stevens?

  Are they like super expensive or something at the moment? Because current refrigerators are really affordable for what they what they do, but they they are. Yeah, they're using like a gas that's not so great.

• 26:10Hannah Fry?

  Yeah, because this is the thing at the end of the life of a fridge, that isobutane is pretty nasty stuff. You know, you don't really, you don't want it like floating around. You don't you don't want that kind of in the environment. I think that at the moment, their main focus is on like, I don't know, drinks companies, for example, who have a ton, a ton, a ton, a ton, a ton of fridges all over the world. And for them, you know, decommissioning fridges is like a really serious financial burden. So, but I mean, yeah, this is like a fridge that never, never runs out of juice, essentially.

• 26:45Michael Stevens?

  It doesn't even use juice.

• 26:46Hannah Fry?

  Doesn't even use a juiceless fridge, a juiceless fridge.

• 26:50Michael Stevens?

  Dry fridge.

• 26:51Hannah Fry?

  Absolute wizardry. Okay, so we've done, we've done the fridge. I'm gonna say, I've got other parts of the kitchen to take you to, Michael. So my tour will continue after the break.

• 27:00Michael Stevens?

  Woo hoo.

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• 28:08Speaker 05

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• 28:46Hannah Fry?

  Okay. From cooling things down, Michael, I'm gonna, I'm gonna go straight into hitting things up. Do you, do you know how a microwave works?

• 28:54Michael Stevens?

  Well, I mean, I've never investigated one because I'm scared of them, but I, I feel like I could say some things about a microwave. Like if my daughter asked how it worked, I would just say, well, okay, so microwaves are a kind of light that we can't see, but it, it has energy and you can shoot this kind of light at food. And I think the microwaves that microwave ovens use are like sized just right to especially wobble around water molecules. What happens when a molecule wobbles more? It means it's hotter. So they just do that. And so unlike an oven that it's going to only just like touch the outside with heat, the microwave can make everything, all the water inside hotter all the way through.

• 29:38Hannah Fry?

  We don't need to do anything else. I've got, I'm nothing else to add.

• 29:43Michael Stevens?

  I do feel a connection to the microwave because there's this cool thing that I do every so often on X, formerly known as Twitter. If you search the word, not microwave, but search the word Michael wave, you will find a lot of people who use Michael wave when they mean microwave.

• 30:04Hannah Fry?

  Oh, that's that's adorable.

• 30:07Michael Stevens?

  Like, I just searched it right now, and this is this is from last year in December. Someone wrote about like, is this microwave safe? And and because I'm my name is Michael, it's like they're saying hi to me. So one of my dreams is to collect a whole bunch of screenshots of people calling microwaves, microwaves and just show it all in a short. And then at the end, have myself waving and I'm like, I'm here, guys. Everyone's microwave safe.

• 30:29Hannah Fry?

  That is that is adorable. That is adorable.

• 30:32Michael Stevens?

  Isn't it adorable?

• 30:32Hannah Fry?

  Really adorable. I like that so much. I'm looking at a picture right now, which says someone has put their microwave outside their house and they've just written and signed on it saying, free Michael Wave.

• 30:44Michael Stevens?

  Yes.

• 30:45Hannah Fry?

  As there is like, free him, he's trapped inside.

• 30:48Michael Stevens?

  Free, free Michael Wave.

• 30:50Hannah Fry?

  Michael, Michael Wave did nothing wrong.

• 30:54Michael Stevens?

  I don't deserve this.

• 30:55Hannah Fry?

  Don't deserve this. Yeah, that is, that is absolutely adorable. I like that so much. I like that so much.

• 31:00Michael Stevens?

  So I love microwaves too, but for for a very personal reason.

• 31:03Hannah Fry?

  For that, I mean, that's a really great reason to love them. I I really like them, okay? I mean, all of the stuff about, sorry, you're you're wobbling water molecules using light in order to make your baked beans warm. Like, what? I think there's something really extraordinary about that. The other thing I like about them is that this is such one of the best examples about how often the precursor to a really revolutionary technology was not designed with that technology in mind. Okay.

• 31:38Michael Stevens?

  Oh.

• 31:38Hannah Fry?

  Because microwaves came to be, the path that they took to get to us is just so wild. You would, if you were plotting it out and were like, right, I want something that exists in everybody's kitchen to make their ready meals cook quicker. This is just, you would never plot this. Okay. I mean, the first thing is just really technical. People were like mucking around with electrons and they realized if you have a cathode and an anode, right? So one's positively charged, one's negatively charged, and you you sort of slot the anode around the cathode and you kind of a solid block of copper and you just chuck a load of holes in it. Some people realized that if you introduce magnets into that. Situation, you can tweak it so that the electrons want to run from the cathode to the anode.

• 32:19Hannah Fry?

  But the magnets affect their path, so they end up like swirling in and around between the two in this cloud. And as they go over the holes, it's a bit like when you blow over a bottle of, you know, a glass bottle and it sort of makes that sound, that resonance.

• 32:34Michael Stevens?

  Yeah.

• 32:34Hannah Fry?

  That's how you make the microwaves, right? That's how you do it is these electrons blowing past these holes. So, so people had like been mucking around with this being like, look, we can make microwaves, we can make this like this type of electromagnetic wave. And we can send it down a wire and, and, and like, you know, chuck it at stuff. Isn't this great? But it had absolutely no application whatsoever. People were like, there's nothing, this doesn't really do anything good or interesting. Um, and it was just something that existed in, in, in labs in the middle of nowhere. This is like nineteen hundred, right?

• 33:04Michael Stevens?

  Right.

• 33:05Hannah Fry?

  And then what happened in World War Two, Britain had radar, okay, which is like another type of electromagnetic wave. Where you bounce out, look at it bouncing back and you can, you can sense big objects that are obstructing it. Don't need to explain radar, I don't think.

• 33:23Michael Stevens?

  But so early radar or a radar today, I don't really know what they use, radio or?

• 33:29Hannah Fry?

  Yes, radio, yeah. Early radar use radio, which is.

• 33:32Michael Stevens?

  Okay.

• 33:32Hannah Fry?

  The wavelength of, of radio, radio waves is like meters long.

• 33:37Michael Stevens?

  Yeah.

• 33:37Hannah Fry?

  So they're really good if you're trying to spot a massive formation of bombers on the skyline. But if you want to see anything small, I mean, forget it. It's not gonna, it's not gonna capture anything. It's just gonna, you know, wrap around it, basically. It's not gonna say anything. And what was happening in, in World War Two, there was this huge stretch of the Atlantic Ocean. Where the, the Allied ships, they had no air cover. It was too far from land. Their planes couldn't, couldn't get that far. And what the Germans would do, their U-boats, which were diesel powered. But had these batteries that they used when they were underwater. Obviously you can't run diesel engines underwater. These U-boats would wait there, knowing that they couldn't be seen from the sky.

• 34:18Hannah Fry?

  And that they couldn't be detected by radar because radar was too, too big to pick up on, you know. If, if they surfaced, it was just, it wouldn't see them at all. So they would sit there on the surface at nighttime, recharging their batteries, like quite comfortable that they were never going to get attacked. And what the British realised was that you could use microwaves as a much smaller, much more precise version of radar. So they fixed it into the nose of their um of their aircraft and would fly out over the Atlantic.

• 34:54Michael Stevens?

  And microwave the ocean.

• 34:55Hannah Fry?

  And microwave, literally microwave the ocean, right? And it was sensitive enough that it could even pick up on like a periscope. It's just a U-boat periscope poking out of the water, it could spot it. Like it's absolutely amazing, you're ten miles away, you can see where the U-boat is. Anyway, all of a sudden, these U-boats are like just getting sunk left, right and centre, even when there's really heavy cloud cover and they've got no idea what's going on. I mean, they think, they think that it's like that maybe the Allies must be, I don't know, like using magic essentially.

• 35:28Michael Stevens?

  Well, yeah, this, this seems related to a story that I should fact check, but it's the origin of the whole carrots are good for your eyes story.

• 35:36Hannah Fry?

  I fact checked this before, it's true.

• 35:38Michael Stevens?

  I heard that the Brits came up with that as a trick to, to explain away, no, no, no, don't, don't think it's technology, it's just that our pilots are eating a lot of carrots and they're becoming very good at seeing in the dark or just seeing in general. No need to do your own experiments and invent it simultaneously.

• 35:55Hannah Fry?

  But the quite funny thing about it is that actually it turns out that carrots has a vitamin in it that ends up being quite crucial for eyesight and seeing in the dark. So it's sort of true.

• 36:05Michael Stevens?

  Yeah, I love that when the, when the lie turns out to be a little bit true.

• 36:09Hannah Fry?

  Comes back around.

• 36:10Michael Stevens?

  And the liar didn't mean for that to happen and now they're a truth teller and the universe is whole again.

• 36:14Hannah Fry?

  Okay, so this up until, you know, like forties, this is, this is what microwaves are for. They're for finding U-boats in the ocean. And then Raytheon, this, this company that, that manufactured military items, they had all of these magnetrons sitting around, you know, they'd made loads of them. They're all just like sitting there, they're like, okay, well, we need to sort of, I don't know, get rid of them, do whatever. Anyway, this, this guy Percy Spencer, his job was to um to muck around with these, with these magnetrons, as they're called, right? The magnetron is the thing that creates the microwave.

• 36:46Michael Stevens?

  Right.

• 36:46Hannah Fry?

  They're submarine detectors essentially. And as he was working with them, he's, you know, sort of like mucking around with them. And as he stood in front of one while it was on, he noticed something really weird. He had a chocolate bar in his pocket and it. It had melted. He'd microwaved his own groin.

• 37:07Michael Stevens?

  Percy.

• 37:09Hannah Fry?

  Percy. And I could, thank goodness, something more serious didn't happen, but just this chocolate bar melted. And he was like, that's a bit weird. And I think a lot of people would see that and be like, you know, maybe my, maybe my pocket was too hot or whatever. But instead, he was like, I wonder what's going on here. So he went out, got a bag of popcorn, popcorn kernels, came in, held them, like dangled them in front of the machine, and then they just exploded all over the lap. And he was like, oh, I think I'm on something.

• 37:36Michael Stevens?

  Wait, no kidding. So microwave popcorn was one of the first deliberate foods.

• 37:41Hannah Fry?

  Yes.

• 37:41Michael Stevens?

  Created with a microwave.

• 37:42Hannah Fry?

  In terms of deliberate, it was the first, the absolute first. Next day, he goes off and he gets an egg. He's trying to microwave this egg with this, this magnetron, this military device. And the egg explodes in his colleague's face.

• 37:56Michael Stevens?

  Yeah.

• 37:56Hannah Fry?

  And yeah, but he, he's the person who realized, oh, wait, this is a way that it could cook food. So, so at that point, Raytheon, the, the company who had these military items, they start building these, these commercial units, right? They're like six feet tall. They're, you know, cost the equivalent of seventy grand today. You only see them in really, really high end kitchens. But meanwhile, over in Britain in the nineteen fifties, there is this ama-, one of my favorite YouTube videos of all time by our friend Tom Scott. Um, is about exactly this story. I think it's just so wonderful. Because, because what happens in Britain, there's a scientist called James Lovelock.

• 38:37Hannah Fry?

  And uh, he's doing these experiments on cryopreservation, right? Essentially whether you can, whether you can freeze something, you know, some tissue, some creature and bring it back to life. Okay.

• 38:52Michael Stevens?

  Right.

• 38:52Hannah Fry?

  And he's doing some experiments on hamsters. Okay. Which sounds, sounds pretty good. The, the hamsters are okay, by the way. It's important for me to say that. But what they were doing, they were freezing hamsters and then bringing them back to life and it works.

• 39:06Michael Stevens?

  And it worked.

• 39:06Hannah Fry?

  It works. But the way that they were doing it was that, you know, you have all these hamsters in the freezer. You get a hamster out and then they had to heat up a spoon and then put the spoon on the chest of the hamster to bring them back around to sort of warm up their heart. It worked, right? It was okay, but it wasn't very nice for the hamster.

• 39:23Michael Stevens?

  Yeah, it's a don't try this at home.

• 39:24Hannah Fry?

  No, it's a definite, definite do not freeze your hamster. I think they were doing it quite carefully as well. But he had read about this idea of a magnetron. He knew about it. He knew they were using them in America as, as, as, you know, the, the Raytheon were using thi- this radar range, this really amazing cooking device. And he was like, well, why don't we, why don't we try and get one that will sit on top of a desk, like a small one, and use it as a humane way to defrost hamsters? Why not? Why not? And so he builds one, and you can check out the Tom Scott video on this, because it's, as I say, it's an absolute delight. But he, uh, he builds one and it turns out that it works.

• 40:04Hannah Fry?

  And all of a sudden, there are these, these hamsters, you know, he tuned it perfectly so that it would exactly as you described, like vibrate the water molecules. And all of a sudden, these frozen hamsters are just like happily running around his lap.

• 40:16Michael Stevens?

  Coming back to life.

• 40:17Hannah Fry?

  Coming back to life.

• 40:19Michael Stevens?

  Okay, so the timeline of, uh, microwave, microwave cooking is chocolate bar, popcorn, hamsters.

• 40:27Hannah Fry?

  Baked beans.

• 40:28Michael Stevens?

  Baked beans, finally made it.

• 40:30Hannah Fry?

  Finally, finally made it to the top. Um, yeah, right? And, and like, this is it. It's just, I think this is why I'm describing that at no point in that history, when you're fixing them on the nose of an aircraft, is, is someone going to say, oh, okay. Well, obviously there's going to be a point where this belongs in almost every kitchen around the entire world.

• 40:51Michael Stevens?

  But that's what happened.

• 40:52Hannah Fry?

  But that's what happens. And it's the, is this, this, there's this notion and kind of the philosophy of innovation that I just really love about the adjacent possible, that it's almost like humans are navigating this, this great network of connected rooms. And every time you walk into a new room, there is, there is a new invention, there's a new thing to discover. But you have to have opened the room immediately before it in order to discover it. You can't leap straight ahead. And it's like, it's only because they had this U-boat device that any of this was possible. They opened the door that allowed the adjacent possible to be opened.

• 41:31Michael Stevens?

  Wow, yeah. So I'm still not a big fan of World War Two, but.

• 41:39Michael Stevens?

  It does mean that I get my hot dogs hot fast, faster.

• 41:42Hannah Fry?

  Yeah, I got to go to a microwave factory once, right? Because this is the kind of thing I do at my microwave instead of going to parties. And it was really amazing to be on the assembly line and all of these people who are, you know, doing, they're like doing their jobs. It's just the, the, the total difference between how mundane this object feels, how like little attention we pay it and how it's actually using incredibly high end particle physics to do something quite so boring. I just that there, there's something so delightful about that disconnect to me.

• 42:15Michael Stevens?

  Yeah, yeah. And it's cool to think that we all have a magnetron in our kitchens. Almost all of us do. And that we're using such a like space age sounding technology to do such simple things. Like, oh, I need to warm up my coffee. Ah, these leftovers are cold. Fix that really quick and you zap it with invisible light.

• 42:40Hannah Fry?

  Yeah, and there you go. Your toaster, by the way, meanwhile, guy, the guy looking for that, he was trying to do the opposite problem. He was trying to turn heat into electricity. And then he, he realized he stumbled upon ni chromium, which is basically the filament that you get in toasters, but also in ovens, in, in kettles, in, uh, you know, in, in air fryers, all of that.

• 43:01Michael Stevens?

  Right. It's the metal that turns orange hot.

• 43:04Hannah Fry?

  Yes, exactly.

• 43:05Michael Stevens?

  When electricity passes through.

• 43:06Hannah Fry?

  Because it does exactly the opposite thing, right? He was looking for something that turned heat into electricity and he discovered something that turned electricity into heat. Ends up being phenomenally useful, like phenomenally useful, like incredibly, incredibly useful. The first pressure cooker was invented in like the 1600s. Uh, unfortunately they, they were quite prone to exploding. It's the only thing, but it's like, you know, you change the pressure. It's a bit like trying to boil a kettle at the top of a mountain. You change the pressure, you can cook it, you know, incredible. If you can create this perfect seal and increase the pressure, it sort of changes the, changes the situation under which you can cook, right? You can, you can allow liquid water to reach temperatures of 120 degrees or so without, without boiling away.

• 43:46Michael Stevens?

  Yeah.

• 43:47Hannah Fry?

  Again, it's like. It's something that is just playing with the laws of physics in order to just make your your your weeknight meal a bit more easy.

• 43:56Michael Stevens?

  Yeah, so who knows what what new kitchen appliances are we going to get because of our upcoming missions to the moon? When am I going to have a, you know, nuclear fission powered kitchen implements that will allow me to, you know, peel an orange faster? Or today, my problem is opening packages. Okay, everything is packaged way too strong. And yes, I know this is also a problem because I'm becoming like an old person. But I'm like, guys, how come the bacon package is so hard to open? Like, give me a break. Come on, scientists, repurpose some crazy war machine to help me open my food.

• 44:35Hannah Fry?

  Just, just, we just want enough war that everyone gets on with it and does some good science, but not enough that anyone is harmed. Okay?

• 44:43Michael Stevens?

  Right, let's all, let's prepare the technology, get ready, and then suddenly become like, make a deal, no one got hurt. But what are we going to do with all this technology? Kitchen time, yes.

• 44:54Hannah Fry?

  Kitchen time, exactly. So there you go. I realize now that we've come to the end of Hannah's kitchen episodes, that all the people who has spent the last decade or so telling me that I belong in the kitchen. Well, actually, you were right all along, frankly.

• 45:08Michael Stevens?

  Well, yeah, because look at all the joy and insight you've brought us by taking us into the kitchen.

• 45:13Hannah Fry?

  Um, well, there you go. Thus thus ends my tour. That ends my scientific tour of of the high end science lab that each one of us has in our own houses.

• 45:25Michael Stevens?

  Well, I appreciate that, Hannah. Thank you very much. I mean, obviously, I like fridges. But now, because of you, I understand that they are both literally and metaphorically cool.

• 45:37Hannah Fry?

  Well, you can join us for our Field Notes episode later on this week. And next week on Monday or Tuesday, depending on which country you live in, we'll be back for our usual usual episode. As ever, you can email us, [email protected]. And I think we should finish with a microwave.

• 46:09Speaker 05

  Now at Kroger, your points add up to more ways to save every trip. Use them your way to take dollars off groceries at checkout or save at the pump. You can even save up to $35 on your next fill-up. Same points, more choices. And with low prices on fresh, quality food, plus digital and personalized offers tailored to how you shop, your dollar goes further. Redeem your points online or in the app. Kroger: Fresh for Everyone. Restrictions apply. See site or store for details.

• 46:39Speaker 02

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