When 0 = 1000

Why does one of the most familiar numbers on a nutrition label turn out to be far more complicated than it looks? What can a can of fizzy drink teach us about thermodynamics, human metabolism, and the strange ways scientists measure energy? Professor Hannah Fry and VSauce’s Michael Stevens dive into the weird science of calories. From century-old experiments involving fire, body heat, and human digestion to the hidden quirks of modern food labelling. Do “negative calorie” foods really exist? Where does burned fat actually go? Why chewing matters more than you’d think, and how your body is constantly leaking energy out into the universe. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit https://www.cancerresearchuk.org/our-research/rest-is-science⁠⁠ 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 Assistant Producer: Lucy Lipscombe 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. Today, we're gonna be field notin'.

• 0:06Hannah Fry?

  Field hootin', tootin', notin'.

• 0:08Michael Stevens?

  Yeah, we're doing like a whole field journey. I've brought some specimens. Not biological specimens, don't worry. But I'll just start, I'm gonna dive right into this.

• 0:17Hannah Fry?

  Okay, let's do it.

• 0:18Michael Stevens?

  Here's Exhibit 1. Exhibit 1 is an American Coca-Cola Zero can.

• 0:24Hannah Fry?

  You spoil us, Michael, you really do.

• 0:26Michael Stevens?

  Well, it's empty, I've already drank it. It's just a can.

• 0:30Hannah Fry?

  Can I, can I?

• 0:31Michael Stevens?

  You can touch it.

• 0:32Hannah Fry?

  Is there anything special about it?

• 0:33Michael Stevens?

  There's nothing special about it. It is exactly how it comes when you buy one in America.

• 0:39Hannah Fry?

  You know, honestly, I thought we'd get through a few more months before we completely ran out of material.

• 0:44Michael Stevens?

  Well, hold on. This is gonna be cool. It's cooler than you think.

• 0:54Hannah Fry?

  This episode is brought to you by Cancer Research UK.

• 0:57Michael Stevens?

  Here's something strange. Your DNA contains more ancient viral fragments than genes. The genes that build our cells make up only 2% of our DNA. And for years, that is what scientists focused on. They treated the rest, the ancient viruses and stuff, as junk.

• 1:18Hannah Fry?

  But now we know that that hidden majority, sometimes called the dark genome, influences how our biology works and how diseases like cancer behave.

• 1:28Michael Stevens?

  It's a reminder that progress rarely comes as a single breakthrough. It builds gradually. Cancer Research UK plays a central role in that progress, supporting decades of research into over 200 types of cancer, work that's helped double survival in the UK over the past 50 years.

• 1:47Hannah Fry?

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

• 2:00Speaker 02

  Hi, this is Gary Lineker from Goalhangers, the rest is football. This episode is brought to you by Wise. It's only when you start moving money between currencies that you really think about the exchange rate, the fee, and what might be hidden away in the small print. Whether you're living abroad, paying someone overseas, or just trying to manage your money across borders, you want a fair exchange rate, an easy transfer, and no surprises along the way. Wise keeps things simple. Wise is a smart way to move the currencies you need around the globe. It works in more than 160 countries and with over 40 currencies. Most transfers arrive instantly. Wise uses the mid-market exchange rate, like the one you see on Google, with no markups or hidden fees.

• 2:44Speaker 02

  So when money needs to move, you can see the rate, know the fee, and get on with it. Join millions saving billions on hidden fees by downloading the Wise app today. Be smart, get wise, t's and c's apply.

• 2:57Speaker 03

  Are you looking for support in your weight management journey? Zepbound, terzepatide, may be able to help. Zepbound is a prescription medicine used with a reduced calorie diet and increased physical activity to help adults with obesity, or some adults with overweight who also have weight-related medical problems, to lose excess body weight and keep the weight off. Zepbound is approved as a 2.5, 5, 7.5, 10, 12.5, or 15-milligram injection. Zepbound contains terzepatide and should not be used with other terzepatide-containing products or any GLP-1 receptor agonist medicines. It is not known if Zepbound is safe and effective for use in children. Don't share needles or pens or reuse needles.

• 3:40Speaker 03

  Don't take if allergic to it, or if you or someone in your family had medullary thyroid cancer, or if you've had multiple endocrine neoplasia syndrome type 2. Tell your doctor if you get a lump or swelling in your neck. Stop Zepbound and call your doctor if you have severe stomach pain or a serious allergic reaction. Severe side effects may include inflamed pancreas or gallbladder problems. Tell your doctor if you experience vision changes before scheduled procedures with anesthesia. If you're nursing, pregnant, plan to be, or taking birth control pills. Taking Zepbound... That found with a sulfonal urea or insulin may cause low blood sugar. Side effects include nausea, diarrhea, and vomiting, which can cause dehydration and worsen kidney problems. Talk to your doctor.

• 4:20Speaker 03

  Call 1-800-545-5979 or visit zeppbounds.lily.com.

• 4:35Michael Stevens?

  So you look at this can and you'll notice a few things. First of all, Coca-Cola Zero. What's the zero refer to?

• 4:41Hannah Fry?

  The fact that it hasn't got any sugar in it.

• 4:43Michael Stevens?

  No sugar. In fact, it says zero sugar. That's the official name, Coca-Cola Zero Sugar. And down here, significantly, it says zero calories.

• 4:52Hannah Fry?

  Yeah.

• 4:52Michael Stevens?

  So how many calories does it contain?

• 4:55Hannah Fry?

  Well, you'd assume zero.

• 4:56Michael Stevens?

  Zero. And if you look at the nutrition facts, calories zero. Okay?

• 5:00Hannah Fry?

  Yeah.

• 5:00Michael Stevens?

  It says it right there. Zero calories. Now, let me show you a UK can of Coke Zero. Here it is. Now, this one doesn't look that much different, except notice the size difference.

• 5:14Hannah Fry?

  Whoa, hang on. Because this one's 12 fluid ounces.

• 5:17Michael Stevens?

  Yeah, which is about 355 milliliters. But in the UK, a can is only 330 milliliters.

• 5:24Hannah Fry?

  Is this why obesity is so much more of a problem in the US? Just literally down to that difference?

• 5:28Michael Stevens?

  It's part of it. Yeah, it is part of it. However, when it comes to obesity, these are sugar-free, calorie-free, apparently, items.

• 5:37Hannah Fry?

  Mm-hmm.

• 5:38Michael Stevens?

  If you look at the UK can, it also, down at the bottom, says, it doesn't say zero calories. It says no calories.

• 5:45Hannah Fry?

  I mean, they're synonyms, aren't they?

• 5:47Michael Stevens?

  Right? They're synonyms. Zero calories, no calories. They both have zero calories. But if you look at the UK can that says no calories, and then you look at the nutrition information here, it says that actually this contains... One kilocalorie of energy.

• 6:05Hannah Fry?

  That's a thousand calories.

• 6:06Michael Stevens?

  A thousand calories. Now, I don't, I'm not a mathematician.

• 6:10Hannah Fry?

  Hey.

• 6:10Michael Stevens?

  But there's a big difference between zero and a thousand.

• 6:13Hannah Fry?

  I am a mathematician. I can confirm your suspicions are correct.

• 6:16Michael Stevens?

  But zero does not equal 1,000.

• 6:18Hannah Fry?

  Hey.

• 6:18Michael Stevens?

  So why are they able to say no calories right here? And then over here, they say, well, actually, there's a thousand.

• 6:25Hannah Fry?

  Is there an answer to this, or is this just?

• 6:27Michael Stevens?

  There is an answer.

• 6:28Hannah Fry?

  Is there?

• 6:28Michael Stevens?

  There's two answers. So first of all, the formulations are the same. It's not like they sneak some calorie thing into the UK version. First of all, the UK can doesn't really contain a thousand calories. A calorie is a measure of energy.

• 6:45Hannah Fry?

  Hmm.

• 6:46Michael Stevens?

  And one calorie is the energy it takes to warm up a milliliter of water, 1 degree Celsius.

• 6:52Hannah Fry?

  Mm hmm.

• 6:54Michael Stevens?

  The food that we eat gives our bodies a lot more energy than that. And so we actually measure dietary calories in kilocalories, thousands. But in America especially, we use the word calorie when what we really mean is thousands of calories.

• 7:11Hannah Fry?

  Yeah. I mean, that's always been something that's confused me quite a lot. People use calories, kilocalories, kind of interchangeably.

• 7:17Michael Stevens?

  Right. In Europe, you'll see KCAL, K-C-A-L, all the time. It's kilocalories. But in America, we just call them calories, but we actually mean kilocalories.

• 7:28Hannah Fry?

  Well, you've managed to make the mathematics so that 1,000 equals 1.

• 7:32Michael Stevens?

  Yeah.

• 7:33Hannah Fry?

  That's a pretty good party trick already, but you're going to have to keep going to get it down to zero.

• 7:37Michael Stevens?

  So, so yeah, still, even if we agree that like, okay, well, we won't use the word kilocalories. We'll just use calories. Why does this can get to say, well, legally, like technically, we've got one calorie of food energy in this beverage, but we're allowed to say it has none? That's because in the US and the UK, there are rounding amounts that food manufacturers are allowed to use. Usually they have to go to the nearest five. That's actually the law in the United States. In the UK, if something contains less than four calories, kilocalories, per 100 milliliters, they're free to just say none.

• 8:16Hannah Fry?

  Okay, so actually, that's getting in quite a long way under that bar, right? Because four per 100 mil, it's a, what is it, 330?

• 8:25Michael Stevens?

  30.

• 8:25Hannah Fry?

  30 milliliter can. So, you know, it could have 12, 13, 14 calories and still be fine.

• 8:31Michael Stevens?

  That's right. So a diet soda has about the same calories as like a little baby carrot. But I think the spirit of the law is that you don't want to mislead consumers. And so if you told them, you cannot say your beverage has no calories because technically the whole can has one. Like, honestly, I think it probably takes more than one calorie, kilocalories, just to warm that cool beverage up to your body temperature. So if a consumer thinks, oh, this has calories, I should be able to survive somewhat by only drinking it, they'd be wrong. So you better just tell them it has none. No nutritional food calories, no energy will be taken in by your body by drinking this.

• 9:12Hannah Fry?

  Is this like the idea of chewing through celery ends up costing you more energy?

• 9:15Michael Stevens?

  Yeah, and I've looked into it and it's not totally agreed to be the case. There's an urban legend that eating celery actually causes you to burn calories because it takes more calories to chew, swallow, and digest and warm it up than you actually get from it. And that is not totally proven. A lot depends on how you chew, okay? If you like really work at it and chew each bite like 50 times and you eat frozen celery, then yes. But for the most part, the way we normally eat celery, it's pretty close and you could still gain from it. Now, negative calorie foods exist, like chewing gum, okay?

• 9:59Michael Stevens?

  Chewing gum, you get like nothing, sugar-free chewing gum, you get nothing from, but you're like working your muscles potentially for like an hour or more. So basically, I just find this fascinating because of that rounding error and because we interchangeably use the word calories and kilocalories, a can can say it contains no calories when it actually contains a thousand.

• 10:23Hannah Fry?

  Let me make sure I understand this, though. So are you sort of saying here that Coke Zero, especially if it's like ice cold, is the drink equivalent of frozen celery?

• 10:33Michael Stevens?

  Yeah, um, I kind of am. And I got really into this a few years ago. I thought, dang, I'm just gonna drink ice water all day.

• 10:42Hannah Fry?

  Yeah.

• 10:43Michael Stevens?

  And

• 10:43Hannah Fry?

  Get really thin.

• 10:44Michael Stevens?

  Yeah, if you drink like eight liters of ice water a day, you do burn about a hundred calories just warming all that water up to your body temperature.

• 10:55Michael Stevens?

  It's only a hundred calories.

• 10:56Hannah Fry?

  Sure.

• 10:56Michael Stevens?

  But I'm like, oh, I may as well. And I did this. Um, and then it like hurt my throat. Like, I actually got like, not throat damage, but like a sore throat from drinking so much ice cold water every day. So I stopped.

• 11:11Michael Stevens?

  Basically, just eat what intuitively makes you happy is my guidelines. But in America, they don't even have to admit that there's at least one calorie in that can. They can just say, nope, it's got zero.

• 11:22Hannah Fry?

  You're done. You're okay.

• 11:23Michael Stevens?

  Cause it's under five per serving, when a serving is a can. So they're allowed to say zero.

• 11:28Hannah Fry?

  This does remind me a lot of alcohol free, what you're allowed to to claim as alcohol free. I think if I remember rightly, the the rule in the UK is anything other under half a percent counts as alcohol free. And the reason why this came up was because I was in a long discussion with with someone about whether it's okay to have a glass of wine when you're breastfeeding, knowing that some alcohol will be passed through your bloodstream to your milk, to your baby.

• 11:58Michael Stevens?

  Yeah.

• 11:58Hannah Fry?

  And I ran the calculations and worked out that for your breast milk to not be labeled as alcohol free, okay, so for the amount, the percentage of alcohol in your breast milk to go over half a percent, I can't remember the exact thing, but you basically would have had to drink about 20 bottles of wine.

• 12:18Michael Stevens?

  Wow. I would say, though, in the defense of that rule of thumb, that alcohol free to a baby is probably different than the 0.5% rule.

• 12:30Hannah Fry?

  Yeah, I mean, to be clear, I generally don't think, you certainly don't want to be drinking 20 bottles of wine when you're breastfeeding a baby, you're in charge of a child.

• 12:39Michael Stevens?

  No, but 19, you're good to go. In fact, the rest of science recommends, just don't finish the last sip from your 20th bottle and you're good. No, that's a joke.

• 12:48Hannah Fry?

  Oh, your breast milk and blood alcohol level being 0.5%. To be clear, 0.08% is the legal driving limit, 0.15% is severe intoxication, loss of motor control and vomiting.

• 13:01Michael Stevens?

  Right, so 0.5% in your breast milk, you're dead.

• 13:05Hannah Fry?

  You're typically at the threshold for death due to respiratory arrest. Yeah, so, you know, you've got bigger problems.

• 13:12Michael Stevens?

  Yeah, so again, 19 bottles only. But the way calories are calculated is also something that fascinates me because, remember that I said a calorie is the amount of energy required to heat a milliliter of water, 1°C? But from where to where are we going? From 0°C to 1°C? Or from 50 to 51? That's different. And it takes a little bit more or less energy, I forget which way it is. So there are, when you get into the science of it, it's like, okay, the amount of calories in this, or the amount of calories that this contains, depends on whether you're measuring this in like room temperature water or ice cold

• 13:56Michael Stevens?

  water. And of course, our bodies aren't perfect converters of mass into energy. We don't have nuclear reactors inside of us. And so, the system that we use for dietary food calories is both complicated and also incredibly, like, flimsy. It's based on some work that was done by a scientist named Atwater, many, many decades ago, who had people eat food, and he measured the energy content of the food in a laboratory by burning the food in a bomb calimeter. This is like a big glass ball that's in a big vat of water, and you burn the food so that you turn it into heat energy, and you're left with just all the carbon. And you look at how much you've raised the temperature of the water.

• 14:41Michael Stevens?

  And that tells you how many calories of energy are in the thing. But our bodies don't burn the food in combustion style when we eat it. So you have to make some kind of estimates of like how efficient the human body is at getting energy out of its food. But he got really specific. He not only fed people the food, he then collected their urine and feces and burned that to see, okay, I put this much energy into you and you excreted this much energy. So the difference is how much your body used. And he would also put people in big water baths and feed them food and have them not move and see how much their bodies warmed up the water.

• 15:22Michael Stevens?

  And from that, we get what we currently use as the tools for estimating the calorie content of food.

• 15:29Hannah Fry?

  Okay.

• 15:29Michael Stevens?

  He found that fats contain about nine kilocalories per gram.

• 15:36Hannah Fry?

  Okay, I mean, that's energy dense.

• 15:38Michael Stevens?

  Yes, proteins and carbohydrates, about four kilocalories per gram. And when I say kilocalories, remember that in America, we just call that a calorie. And he found that alcohol contains about seven kilocalories per gram.

• 15:52Hannah Fry?

  Wow.

• 15:53Michael Stevens?

  So today, when you submit a food for nutrition fact information, the numbers on the nutrition label aren't calculated through an experiment. They're calculated through the manufacturer saying this many carbohydrates, fats and proteins are in each serving.

• 16:08Hannah Fry?

  I'm a bit disappointed. I sort of, I sort of wanted that to be a laboratory somewhere where they were just setting light to, you know, chocolate eclairs and like, you know, foie gras.

• 16:17Michael Stevens?

  No, they, and you'll notice this if you look at a nutrition package and you look at the fats, carbohydrates and sugars inside of it and you multiply the, you figure out how much per gram that would mean, and then you multiply the fats and protein, or sorry, the carbohydrates and proteins by four and the fats by nine, you'll get the calories per serving.

• 16:36Hannah Fry?

  Okay.

• 16:36Michael Stevens?

  That's just how it's done. But it's been found that that's like a little bit too vague.

• 16:43Hannah Fry?

  I mean, it's quite a simple method, really.

• 16:45Michael Stevens?

  It's very simple because we don't. Our bodies don't get food energy from this, some, from all fats equally. And not every body works the same way either. I think the most conclusive proof of this is by studying the amount of energy people got from pistachios. And it totally depended on how much they chewed them. If you like barely chew a pistachio and swallow it, you actually mainly get nothing from it. But if you chewed it for a full minute before you swallowed, you got almost all the food energy out of it. So the, the, this was, I, I forget why they were looking into this, but they were trying to figure out how many calories were in pistachios. And it was like, whoa, it really depends on how they chew them.

• 17:25Hannah Fry?

  That's interesting. What, so that if it's un, un chewed, if it's sort of un-macerated in your mouth, then once it gets to your stomach, your stomach acid isn't as able to extract the energy from it as possible.

• 17:34Michael Stevens?

  Yeah, I mean, chewing is, is the first step in digestion and your spit helps break things down. So that you can then get all the nutrients, including the, the fats, the carbohydrates, the proteins, the things that give you energy. It requires that, that chewing process first. So if you just swallowed a bunch of pistachios whole, like a pill, it's almost like nothing.

• 17:55Hannah Fry?

  I tell you what, though, you are coming up with quite a good diet going on here. Next time I feel, you know, I've got like a bit peckish and I want to eat something, but know that I shouldn't. I'm just going to drink ice cold Coke Zero and swallow pistachios whole.

• 18:08Michael Stevens?

  Wash pistachios down with ice cold water. No, I don't want to encourage eating disorders. You're all beautiful. And again, you should eat what you want to eat and, and, and be mindful. But if you want to hurt yourself, yes. The worst diet I've ever heard of was the Sleeping Beauty Diet. Have you heard of this one? This is just, well, you can't eat if you're asleep.

• 18:28Hannah Fry?

  Okay. I sort of feel like I've been following that one for my entire life.

• 18:32Michael Stevens?

  Yeah, right. Well, I think that if you really are dedicated to the Sleeping Beauty Diet, you take medicine to keep yourself asleep for like days.

• 18:41Hannah Fry?

  No.

• 18:42Michael Stevens?

  Mm hmm. Yeah. Now, it, I don't know if it's ever actually been done by somebody, but it's been like a joke that's been around for decades.

• 18:49Hannah Fry?

  Drop the weight real quick.

• 18:50Michael Stevens?

  Drop their weight quick by just letting your body not eat. And it won't bother you because you'll be asleep or unconscious.

• 18:58Hannah Fry?

  Yeah. Or going back to your previous advice, just, just eat what you want.

• 19:03Michael Stevens?

  Yeah, maybe just try that one.

• 19:05Hannah Fry?

  Just like, listen to what your body needs.

• 19:06Michael Stevens?

  Yeah, yeah.

• 19:07Hannah Fry?

  Just do that instead.

• 19:09Michael Stevens?

  So anyway, I just wanted to show you this because every time I'm in the UK, I, I can't stop but like, looking to make sure it's still the fact that it says, it says no calories on it and yet it contains a thousand.

• 19:21Hannah Fry?

  Okay, this is what I quite like though, the way, as you were talking, ah, okay. I thought that the, um, cause the UK, we have this like traffic lights system, right? Where you break it down, you have energy, fat, saturates, sugars and salts. I thought for a second there, you could just do like a straight up calculation from that of how many calories are in everything. But it's a little bit more complicated than that. But if you go to the ingredients, the nutritional information. Hey, that's a fun little project. I mean, for my children, when I go to the supermarket, that's, that's one way I can torture them.

• 19:50Michael Stevens?

  Yeah.

• 19:51Hannah Fry?

  Calculate how many calories are in this.

• 19:52Michael Stevens?

  Yeah, yeah, yeah.

• 19:53Hannah Fry?

  See if you're correct.

• 19:54Michael Stevens?

  Cover that part up and then make them do the arithmetic.

• 19:57Hannah Fry?

  Yeah.

• 19:57Michael Stevens?

  It's just four times the, how many grams of carbohydrates and proteins are in a serving?

• 20:02Hannah Fry?

  Yeah.

• 20:02Michael Stevens?

  And then nine times.

• 20:03Hannah Fry?

  The fat.

• 20:04Michael Stevens?

  The fat.

• 20:05Hannah Fry?

  And seven times the alcohol.

• 20:06Michael Stevens?

  And seven times the alcohol. Now, again, because manufacturers can round to the nearest five for, for small items, they can round to the nearest 10. If there's a lot of, of, of calories in the, in a serving, uh, you'll be within five or 10 of the, the, the answer on the box.

• 20:22Hannah Fry?

  Amazing.

• 20:23Michael Stevens?

  Yeah.

• 20:23Hannah Fry?

  Yeah, that was very fun. I enjoyed that.

• 20:26Michael Stevens?

  Goodness. Okay. Well, look, we've got a question about calories coming up after the break from you guys. So we're going to get to your questions when we come back.

• 20:39Hannah Fry?

  This segment is brought to you by Cancer Research UK.

• 20:41Michael Stevens?

  We've all become used to technology measuring and improving our lives, right? It's the story of human history. We've now got watches that monitor our heart rates and count our steps. But what happens when that same technology is turned on cancer?

• 20:55Hannah Fry?

  Cancer Research UK is backing the research that harnesses new tools and technologies to help find cancer earlier, treat it more precisely and ultimately save and improve lives.

• 21:06Michael Stevens?

  And so today we're asking, what becomes possible when our? Our technology sharpens its senses.

• 21:12Hannah Fry?

  Right, so a big part of all of this is that with cancer, timing can change everything. If you find cancer really early, then treatment has a much better chance of working. It's much less invasive. But if you find the cancer later, it may have already spread or it may have changed. It makes it much harder to treat. So you really want to catch it as soon as possible. I mean, it's a bit like a bank robbery, right? If you imagine that you've got the police that are really slow to come when the alarm rings, the robbers are already gone. It's really hard to track down, really hard to work out what's going on. But if you get an immediate response as soon as there's any problem, the police kind of surround the building before anyone can get away and you just have a much better chance of getting the bad guys. And Cancer Research UK, they have played an incredibly important part in the breast

• 21:57Hannah Fry?

  screening programme that we have here in the UK. One of the many ways that they've helped to double breast cancer survival in the UK over the last 50 years. One of the difficulties is that in the UK, while mammograms save about 1,300 lives a year, for some people, there can be real barriers to accessing them, particularly for people who have disabilities. So what Cancer Research UK scientists have been doing is they've been working to bring cancer detection to people who struggle to access mammograms. So what they've invented, Michael, is a smart bra, right?

• 22:30Michael Stevens?

  Finally.

• 22:31Hannah Fry?

  Finally. It's a wonder that I got this section rather than you. Okay, so the smart bra, what it does is it uses this electronic textile that is stitched on to the inside. It sends electrical signals through the breast tissue and then reads how they come back. And that data can then be fed to your smartphone. So whereas and clinicians can be alerted if you get any concerning changes. Now, I have to tell you, the way that they've tested this technology, it turns out that something that closely mimics the electrical properties of cancerous tissue is carrots. And there are, you know, they've been using carrots in the bras as part of the testing. Unconfirmed reports that people were actually walking around with carrots in their bra.

• 23:15Hannah Fry?

  But I mean, the promise of this is amazing because this technology can Spot tumours that are as small as five millimetres. And by the way, one centimetre tumours is the current benchmark for early detection. So this is like much earlier than that. The long term goal here is if you can make detection more accessible, easier to engage with, then one day breast cancer screening could happen in somebody's home and you can get the cancer at the earliest possible opportunity.

• 23:44Michael Stevens?

  First of all, I love that technology, but also I love that fact. Next time I eat a carrot at dinner, you know, the electrical conductive properties of this carrot are kind of like cancer, but I will also talk about surgical micro robots. So when you're a surgeon who's removing a tumour, one of the big difficulties is that tumours are made of cells. Cells are incredibly tiny and you want to remove every one of those cancerous cells and you want to remove as few healthy cells as possible. And so now there are these tiny robots that give live information to the surgeon about what the cells are that are being operated on.

• 24:24Michael Stevens?

  What it does is it shoots a laser at a cell and then the cell burns up and the robot essentially sniffs the smoke from the burned up cell. Looking at the chemical signature of that smoke, the robot can learn all kinds of things about the metabolism properties of the cell, the cell's makeup and can guide the surgeon in knowing where to stop, where to keep going. And then even after the surgery, all this information about the nature of that tumour can be used to help with, you know, what kind of steps should be taken next. So that's just an incredible little like team of tiny robots and normal sized people doing amazing things. And that level of accuracy can change and save lives.

• 25:08Michael Stevens?

  So by investing in this kind of breakthrough research, we're turning high tech ideas into real world precision, making cancer medicine smarter, more targeted and more effective.

• 25:19Hannah Fry?

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

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• 26:02Speaker 05

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• 26:38Michael Stevens?

  Okay, welcome back. Hannah, you're going to be reading the questions because you've got them right there in front of you.

• 26:43Hannah Fry?

  Yeah, I've got them right here.

• 26:43Michael Stevens?

  Okay.

• 26:43Hannah Fry?

  And the first one links in perfectly to what you were talking about. This is from EPO. Where do the calories I burn actually go? I assume I get rid of some of them through urine and stool, but does part of it evaporate? And if those calories evaporate, does the earth lose weight too?

• 26:58Michael Stevens?

  Hmm, hmm, hmm, hmm. Yes, I love this because it is weird to think like, okay, wait a second. I turned my food into energy, but then where does it go? And it does, in a way, evaporate away. Ultimately, it turns into wasted heat. Like your body takes that food apart, it takes the molecules it needs and it uses them through primarily the ATP process to produce the energy you need to be warm, to move your muscles, beat your heart, breathe, think, all of that stuff. And ultimately that causes motion, right, of your limbs, of your heart, of your lungs, which is a kind of mechanical energy. It also produces heat energy that is released into the world. And

• 27:41Michael Stevens?

  Ultimately, this whole like mass can be turned into energy thing does not lead to a change in the amount of like mass. Well, I mean, it changes, it changes the amount of matter, but the mass doesn't change. A compressed spring weighs more than a loose spring.

• 28:01Hannah Fry?

  Hmm.

• 28:02Michael Stevens?

  I mean, it's calculatable, but not really measurable. But that energy that I put in really does, the potential energy that that spring has really does affect its mass. It does actually weigh more. A phone weighs more when it contains a lot of photos because we've got a higher energy state in the electrons, I think, or a different.

• 28:22Hannah Fry?

  I think it's the other way around, isn't it? It's the same as punch card. So in a punch card, no hole is a one and a hole is a zero. In hard drives, very simply, it's zero if you've got a charge in it and it's a one if you make a hole and remove that charge.

• 28:39Michael Stevens?

  Oh, interesting.

• 28:40Hannah Fry?

  Right.

• 28:41Michael Stevens?

  Ones are no charge.

• 28:43Hannah Fry?

  Ones are no charge.

• 28:45Michael Stevens?

  Yeah. In that case, then, yeah.

• 28:47Hannah Fry?

  Yeah. So when you get it, it's all zeros, right? So charge is in the hole.

• 28:52Michael Stevens?

  Right.

• 28:52Hannah Fry?

  Effectively. And then one electron weighs, I think it's 27 zeros, right? Not point no, no, 27 zeros, one. When you add in a one, you're taking the electron away, you're making the thing lighter. And so full USB drives weigh less than brand new ones.

• 29:10Michael Stevens?

  Interesting.

• 29:11Hannah Fry?

  Yeah.

• 29:12Michael Stevens?

  Now, your body does not act like a USB drive.

• 29:15Hannah Fry?

  No.

• 29:15Michael Stevens?

  But we can account for all of the mass that you put into your body through breathing, drinking and eating by, by finding that either in excreted out of your body through urine, feces and your exalted breath.

• 29:29Hannah Fry?

  Right. Because the exalted breath is actually a really big component of this because the ATP process that you're describing, where you take glucose and oxygen, the two things that give your, your, your body energy, and they break down into water, energy and CO2.

• 29:45Michael Stevens?

  Right.

• 29:45Hannah Fry?

  So the question about where does a lot of it go? It's actually that you breathe it out, right? You breathe out most of it.

• 29:53Michael Stevens?

  Yeah. And if you compare everything put in and everything that comes out, you will still find a deficit because some of it was turned into the energy of motion, of heat. And some of it still exists in your body as chemical energy. Like, in many ways, fat contains chemical energy. There's the potential for it to be turned back into energy for motion and for heat if your body needs to do that. Burning fat is turning that back into energy. So that's where it all goes. But it's all accounted for. None of it just magically evaporates. If we had enough time, we could extract all the energy that was in that Snickers bar that you ate.

• 30:31Hannah Fry?

  And in terms of the Earth getting lighter over time?

• 30:33Michael Stevens?

  Oh, yeah. Well, so the Earth's mass, if it was in a completely sealed system, would not change. Even, even the, the fact that you've heated up the air by, by being warm-blooded and by moving in it, that does make up for the matter that is now missing because you digested it.

• 30:52Hannah Fry?

  Yeah. Sorry, Earth. The Coke Zero diet won't work for you.

• 30:55Michael Stevens?

  The Coke Zero diet might make a person lighter, but it will not make the Earth lighter. This really depends on the Earth being in a sealed system. Because if you are turning Coke Zero or full sugar Coke into heat energy, some of it is radiating into space.

• 31:12Hannah Fry?

  True.

• 31:13Michael Stevens?

  So technically, Earth will lose some of it. But I'm, I'm, I'm assuming that the Earth is like a closed system and everything that's on Earth or leaves it is still part of the system. So, but technically, yes, the Earth does become lighter just because of the, the heat that we radiate away that leaves space. It's gone from Earth now.

• 31:33Hannah Fry?

  Yeah. Because actually, if you think about it, if you were sitting on a, I don't know, like a spaceship some miles out in space, like, you know, if you, let's say, half a light year or whatever, and you had an infrared camera, an extremely sensitive infrared camera, you would be able to see your body on the surface of the Earth. And the only way that that's possible is because there is, as you described,

• 31:54Michael Stevens?

  Some of it's left.

• 31:55Hannah Fry?

  Yeah, exactly. In fact, there is an entire cone of your energy floating out in space right now.

• 32:01Michael Stevens?

  Yeah, you're welcome, aliens.

• 32:02Hannah Fry?

  You're welcome. You're welcome. Okay. All right. Next question. This one came from Luke FTF. I've heard NASA turned Velcro into a household name after it was widely used in the Apollo 11 mission. Are there any technologies that have come from space science that we are now using in our daily lives without realising it? It's a myth, it's not.

• 32:22Michael Stevens?

  That, that, that hook and loop fastener wasn't popularised by the space programme?

• 32:26Hannah Fry?

  I mean, it was popularised by it, but it wasn't invented by them.

• 32:28Michael Stevens?

  Sure, yeah.

• 32:29Hannah Fry?

  Um, it was actually invented in the forties, a Swiss engineer called George de Maestral. Okay, so I did a programme, I actually can't remember which programme this was in, but anyway, there was a bit about the invention of Velcro. And what, his story was that he noticed these burdock burrs that were sticking to his dog's fur. So for this story, for this TV programme, we were like, okay, here's what we'll do. We'll get a dog, we'll go for a walk with the dog and then there'll be burrs sticking to the dog and then it'll be great and we'll take them off and it'll be fine. Anyway, it was hilarious because this dog was very happy, right? The dog was having a great old time. But the exec producer was so worried that we would get complaints about there being

• 33:09Hannah Fry?

  burrs on the dog, um, that we had this entire, like, I mean, days of conversations, days of conversations about whether this counted as animal cruelty on TV.

• 33:18Michael Stevens?

  Yeah, wow.

• 33:18Hannah Fry?

  Anyway, turns out it obviously isn't, uh, but that is where Velcro came from. But it was popularised by NASA, that one's, that's fair to say. Um, but there are nonetheless, some really amazing technology that has come directly as a result of the, of the, um, space programme. Pixel sensors being one. I mean, the only reason why we have smartphone cameras is a direct result. Um, this is from the 1990s. They, uh, had these giant spacecraft cameras, but they wanted to shrink them down. So they essentially came up with this digital version, a way, uh, that you can, I mean, they needed something lightweight, it needed something low power. Um, so they came up with these active pixel sensors that are now in smartphones everywhere. Uh, another example, braces.

• 34:01Hannah Fry?

  So you know Invisalign, the ones, I'm sure other brands are available.

• 34:05Michael Stevens?

  I, I know they are. In fact, you can 3D print your own, uh, plastic.

• 34:09Hannah Fry?

  Your own?

• 34:10Michael Stevens?

  Tooth fixer braces, yeah. I was just reading about this, I forget where it came from, but this guy was like, yeah, I, I, I just printed, he had to print like a new one every week or so to get it smaller and smaller and tighter, but it fixed his teeth.

• 34:22Hannah Fry?

  But then, hold on, is it not quite a sophisticated process to work out the sort of trajectory you want your teeth to?

• 34:28Michael Stevens?

  Oh, yeah, yeah, yeah. I would still say go to a doctor.

• 34:30Hannah Fry?

  I would say.

• 34:31Michael Stevens?

  But you don't have to.

• 34:35Hannah Fry?

  I think the key one about this is the fact that the material is completely see through. So you can't always tell that that people are wearing.

• 34:43Michael Stevens?

  Oh, no, but this guy's thing, you could tell he was wearing a 3D printed mouth guard. Yeah, I mean, yeah.

• 34:50Hannah Fry?

  Sure. I mean, you know, go to go to the dentist. I think that's better.

• 34:54Michael Stevens?

  But that came from NASA.

• 34:55Hannah Fry?

  It did. Yeah. So it's called translucent polycrystalline alumina. And yeah, they have these infrared antenna heat seeking tracker trackers essentially. And they needed this material that was really strong but transparent to be able to coat them. You know, transparent to specific wavelengths of light in particular. And yeah, they came they came up with this material and it can it can withstand supersonic flight. Right. And it turns out, you know, also can withstand being chewed on. The last one that I really like, well, I mean, there's loads, but this is one that I like is is memory foam mattresses. So when you are, you know, sending astronauts off into space,

• 35:39Hannah Fry?

  their seats are really uncomfortable. I mean, they get like thrown around really properly in their seats. And so they created this this foam that that molds to a warm body, but then returns to its original shape when when you remove the pressure.

• 35:53Michael Stevens?

  So memory foam is also a space technology originally. Wow. I didn't know that. And it was it was not like to protect the ship. It was for comfort.

• 36:01Hannah Fry?

  It was to protect their bus.

• 36:02Michael Stevens?

  Yeah. I wanted to show another space technology, which I do have in my bag. It's for a future Field Notes episode, though. Not today.

• 36:09Hannah Fry?

  Okay.

• 36:10Michael Stevens?

  Is this the Fisher Space Pen.

• 36:14Hannah Fry?

  Okay, so here's my guess. There's that thing that people always say, which is, oh, NASA spent forty squillion trillion dollars on making a biro that will write in space. And meanwhile, the Soviets just used pencils and it's often used on the internet as a really hilarious way to like slag off the research that goes into, you know, a high end products. But actually, the reality is using a pencil in space is a very, very, very bad idea. Because bits of graphite will flake off and get into the circuitry, short circuit stuff. It's just don't use them. Okay, all right, next question, hold on. This one is from Oscar Sedlak. Recently, I was listening to the episode about boredom and isolation and it got me wondering. There were multiple experiments regarding isolation which put individuals into some kind

• 36:59Hannah Fry?

  of chamber with no stimuli. But what happens if you put not one, but two people in such a room together? What are the effects of that?

• 37:07Michael Stevens?

  Dualitarian confinement. Oh, we have no idea. It's never been done. Yeah, there are no psychological studies of two people stored in sensory deprivation isolation together.

• 37:23Hannah Fry?

  I mean, it must have happened at some time. I'm thinking about prisons here, right?

• 37:27Michael Stevens?

  I know, but in prison, there just isn't a lot of history of like, oh yeah, we locked these two people together in solitary, which wouldn't be solitary, it would be dualitarian. Dualitarian confinement, by the way, is a word that you can search on Google and you get no results.

• 37:44Hannah Fry?

  A Google whack.

• 37:46Michael Stevens?

  Is that what they call it?

• 37:47Hannah Fry?

  I think so, yeah.

• 37:48Michael Stevens?

  Yeah, something that has absolutely no results on Google, I just love that. So the thing is, we don't know. I would predict that you would be likely to wind up with a folly ado sort of situation, where two people kind of lose their minds together and they mutually reinforce each other's delusional beliefs.

• 38:08Hannah Fry?

  Spiraling downwards together.

• 38:10Michael Stevens?

  Yeah, and so because of that, I think they're probably going to wind up getting along more than not. But what they get along in and what they both believe together and feel together and think together might be destructive. But I don't know if they would just wind up fighting and battling it out.

• 38:31Hannah Fry?

  I saw an episode of Mr. Beast where he did something quite similar to this, where he dug a bunker and locked two people in there for 100 days. It wasn't sensory deprivation, though. And also, once a week, he would go in with a big bag of cash, as he has a habit of doing.

• 38:46Michael Stevens?

  Right, so I think in those situations, it's not sensory deprivation. I think there have been a lot, like, yeah, Mr. Beast put two people down in a bunker together, but he also like visited and whatever, you know. But as far as two people locked into like a purely empty white room, or a dark room, or locked in a cave with nothing to do but be together, that's an experiment we've got to do. Soon.

• 39:13Hannah Fry?

  I'm not volunteering, to be absolutely clear. Okay?

• 39:16Michael Stevens?

  Oh, okay. So it won't be an episode of The Rest Is Science.

• 39:20Hannah Fry?

  It won't be an episode of The Rest Is Science.

• 39:22Michael Stevens?

  Well, I mean, or at least it'll, maybe if you guys want to volunteer for it. But it won't be Hannah and I.

• 39:27Hannah Fry?

  No, but if you do, I mean, you can write into us with your volunteering. The email address is [email protected]. As always, I mean, all your thoughts and questions and things you'd like us to answer. That's, you can do that instead, but, but really we want you volunteering to be put in a

• 39:44Michael Stevens?

  That's right. We love questions, we love comments, but we also love the third C, consent. Give it to us.

• 39:52Hannah Fry?

  Okay, I think that's about it for this week. We will see you next week with our usual episode on Tuesday.

• 39:57Michael Stevens?

  Thanks for watching.

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