In short
Why color is taught as a wheel (artists) instead of a line (physics), using Crayola crayons to demonstrate spectral vs psychological colors, camera/screen limits, fluorescence, and infrared.
Guests
None. Hosts: Hannah Fry and Michael Stevens (Michael’s “guest” is his own crayon experiments).
Key claims
Violet/magenta (“purple”) is not a spectral color; it’s a brain construct from overlapping short- and long-wavelength cone responses, since there’s no “purple cone.” Color wheels help artists place hues by perception, not by physical wavelength. Some Crayola neon colors use optical brighteners that convert UV to visible light, making them brighter than normal objects; phone cameras often fail to reproduce their real appearance. Infrared is invisible to humans but visible to cameras (e.g., TV remotes, night-vision doorbells).
Notable examples
“Outrageous Orange,” “Neon Carrot,” “Atomic Tangerine,” “Maroon,” and “Shadow” crayons; remote-control purple glow on a phone; Face ID/doorbell infrared flash.
Written by AI. May contain mistakes. Listen to the episode to check what was said.
Chapters
Tap a time to open that second in VOMichael's Crayon Revelation
0:46 to 2:54
Michael shares his newfound obsession with color theory through crayons.
“But it's just based on the skew of the products.”
The Color Spectrum Dilemma
4:11 to 6:01
Exploration of why artists use color wheels instead of linear spectrums.
“And this struck me as I was driving around yesterday.”
The Mystery of Purple
6:02 to 8:45
Discussion on the psychological nature of purple as a color that doesn't exist physically.
“In addition, which is sort of the same thing, you know, if you ask a physicist what the primary colours are, they will tell you that it is red, blue and green.”
The Limitations of Color Representation
8:46 to 13:14
Examining how cameras fail to capture certain vibrant colors like outrageous orange.
“And so that's why we're able to do starting at red, increase the wavelength until all of a sudden, boom, you're at violet.”
Michael's Favorite Crayola Colors
13:15 to 14:00
Michael discusses his favorite Crayola colors and their unique properties.
“This is just the regular orange that you would get in an eight pack, you know, at a restaurant.”
Exploring Crayon Colors and Perception
14:00 to 22:40
Learn how different crayon colors and their properties affect our perception of color.
“not muted tones their loudness is why i love them i don't know what is going on but the maroon crayon is like paint.”
Understanding the Tea Leaf Paradox
22:40 to 28:05
Discover the science behind the tea leaf paradox and fluid dynamics.
“It is now time for us to dive into questions from you all.”
Fluid Dynamics in Cooking
28:05 to 29:09
Learn how stirring techniques affect the dissolution of substances in liquids.
“Because this is what I do when I need to like get salt to dissolve in pasta water.”
The Concept of Wetness in Water
29:10 to 30:18
Explore an unusual theory about the varying 'wetness' of tap water.
“Our next question is actually a little bit about water as well.”
Water and Firefighting Techniques
30:19 to 33:12
Discover how water's properties can be manipulated for firefighting efficiency.
“I didn't know how to answer this, but I had to look into it, and I had to go all the way back to 1946.”
Show all 17 chapters
Surfactants in Biology
33:13 to 34:33
Understand the role of surfactants in human lungs and their importance for breathing.
“I'm also thinking, are there surfactants in your lungs?”
Exploring Definitions of Wetness
34:34 to 36:48
Discuss the different meanings of 'wet' and how they apply to various contexts.
“Do they put it in the, like when they're sort of there with the hose, are they pumping out wetter water?”
Communication with Space Probes
36:49 to 39:07
Learn about how NASA communicates with satellites and the security challenges involved.
“Because, you know, what does your boyfriend do?”
Recent Satellite Hacking Incident
39:08 to 42:00
A significant hacking event impacted satellite communications during a critical time.
“Ironically, though, the modern satellites, which are much closer to Earth, they sort of makes them slightly easier targets.”
Exploring Hacking Satellites and Quantum Computing
42:00 to 43:12
The hosts discuss the implications of quantum computing on encryption and the playful idea of hacking satellites for personal uses.
“Complete coincidence and complete mystery.”
Engaging with Listener Questions
43:12 to 43:29
The hosts reflect on the joy of answering listener questions and encourage more submissions from their audience.
“You guys bring us not just fun questions to answer, but the learning behind how we kind of approach them is just so fun.”
Concerns About Knowledge Overload
43:29 to 44:07
A light-hearted conversation about the potential for becoming know-it-alls and the worry of being unable to be stumped by unusual questions.
“Do you worry that your brain is going to get to a point where it's like, no, I'm actually full now?”
Transcript
Automatic transcript. May contain errors.0:00Hannah Fry:Welcome to The Rest of Science. I'm Hannah Fry.
0:03Michael Stevens:And I'm Michael Stevens.
0:04Hannah Fry:And this is Field Notes, our weekly exposition into the mind this week of Michael Stevens.
0:10Michael Stevens:All right. So what's going on in my mind? I'll tell you, I got to apologize. I've gotten really into something brand new once again. This time it's Crayola crayons. So I'm still a mechanical pencil guy. Don't get me wrong. Sure. But I visited my mom a few days ago and she had this box of 152 crayons she'd bought for this coffee shop. Turns out they didn't need them. She was going to return them. And I'm like, well, I'll take them. And they don't come ordered by any sort of color theory that exists in human knowledge. Right. It looks random. It isn't. But it's just based on the skew of the products.
0:51Michael Stevens:Like they just shoved together the eight pack, the 16 pack, the 24 pack. So it's a mess. And I'm like, I got to arrange these. But it's 152 distinct colors. 152 distinct colors. And I'm like, I got to arrange these. That means I've got to learn color theory. And that began what has now consumed my life. I've had to get special paper to do swatches. Oh my gosh. This is amazing. So, because I'm looking at the wax going, okay, but what is the difference between scarlet and red? Okay.
1:25Hannah Fry:For the purpose of those of you who are joining us in audio only, first of all, what are you doing? Secondly, you are missing Michael holding up what looks like one of those fancy spiral bound artist notebooks. Except instead of it being some sketch of a building or a face, he has laid out every colour crayon that he has in his pack. And each one he has labelled with the name of that crayon. He's also done a gradient from very dark, extremely heavy crayon all the way through to very light. But what is interesting about this also that I already noticed is that this is not a linear progression of colours.
2:06Hannah Fry:They appear in a grid. I think there's something going on here. And genuinely, I say this without any humour whatsoever, I am thrilled that this is the subject today.
2:17Michael Stevens:I should show you that I've got piles of different crayons. I had to buy different packs because some of them don't give you exactly that. You can't finish the spectrum unless you get the colors of kindness pack. And the 96 has a dandelion in it, but the 152 doesn't. Anyway, I've learned so much. And so today I want to show off a couple of cool things about color, but especially I want to show you some things that I can't show you.
2:45Hannah Fry:Oh, I'm so excited.
2:54Hannah Fry:This episode is brought to you by Cancer Research UK.
2:57Michael Stevens:Our bodies are incredible machines, whirring away, making more and more DNA to build the proteins that keep us alive.
3:05Hannah Fry:In fact, in the last minute, your body has made over 200 million new cells and enough DNA to stretch to the moon and back. To the moon and back.
3:15Michael Stevens:That's so much DNA that if you compared it to the size of the cell it fits into, That would be like squeezing the London Underground into a suitcase.
3:23Hannah Fry:By the age of 50, you have copied almost 6 trillion miles of DNA. But every time that your body copies DNA, it risks making mistakes. And over time, those mistakes can accumulate and that collection of errors can lead to cancer.
3:38Michael Stevens:But incredibly, Cancer Research UK scientists can spot these errors. And by finding them, they've helped double UK cancer survival over the last 50 years. and are driving even more discoveries that could tackle over 200 types of cancer.
3:53Hannah Fry:For more information about Cancer Research UK, their research and breakthroughs, and how you can support them, visit cancerresearchuk.org slash rest is science.
4:10Michael Stevens:Okay, so we'll start with the biggest mystery. And this struck me as I was driving around yesterday. Literally, this is how fresh this whole thing is. I was like, wait a second. The electromagnetic spectrum, okay, which is how we lay out all the different energies light can have, makes sense to me. I get it. You've got radio waves. You make them more energetic. Oh, whoops, now they're microwaves. Eventually, you get into visible light that our eyes can see. And if you crank up the energies there, you go from red light to orange, yellow, green, blue, violet, and then ultraviolet all the way up to x-rays, gamma rays.
4:48Michael Stevens:It's a line, okay? A linear scale. Yeah, you either have more energy or you have a longer wavelength than, say, 700 nanometers or less. It's one way or the other along one line. And yet, artists are always telling us about color wheels. What the heck? Come on, you guys. You guys, it's a line. It doesn't connect back on itself. It's not like when you reach violet, you add more energy and it's red again. Why is it a wheel? I'm holding up a color wheel, by the way. This is just a classic artist's coloring wheel. You might see this in like elementary school even where the teacher wants to talk about, you know, how the colors mix and how they change where they fall on the spectrum.
5:29Michael Stevens:And this helped me sort my crayons really well because I just did not know when I looked at a red, Does that red have more orange in it or yellow? So this allowed me to like add more red to yellow orange and be like, oh, I hold the crayon up. And then if it was a tone or a shade or a tint, I can use the back to kind of determine where it should go. I can sort the grays, you know. Anyway, why do artists use a color wheel, but scientists use a color spectrum that's a line?
6:01Hannah Fry:Right. This is generally this is something I've always wondered. In addition, which is sort of the same thing, you know, if you ask a physicist what the primary colours are, they will tell you that it is red, blue and green. But if you ask an artist, they'll tell you it's red, yellow and blue. And I'd never understood. What? What? How? Why?
6:20Michael Stevens:Look, it depends what artist you ask. I think if you ask an artist who has also become obsessed with this, they will say there are no primary colours. It's all made up. You can choose any group of colours to be your primaries. It might not be as helpful, but it's not like the universe at the Big Bang was like red, blue, green. Oh, my gosh. Look at all the other stuff that you can make out of this. No, that's not how it works. Okay. The reason we put color in a wheel, even though physically it lies on a line, is that purple does not exist. Excuse me? Yeah. Here's the problem. So you've got a spectrum of color.
7:02Michael Stevens:That means a spectrum of energies light can have that causes our brain to experience different colors from red all the way up to the really small wavelength and high energy blues and violets. Now, violet is a spectral color. That means it's created from light. It's a real thing that has physical properties. And our eyes, the human eye, is only sensitive to basically the short, the medium, and the longs, okay? If your eye receives short and medium wavelengths, then the perception in your brain is that it must be somewhere in between. So maybe it's orange. OK. If you get a bunch of middles and a bunch of longs, then your brain goes, well, we'll give you the experience of blue.
7:47Michael Stevens:OK. Or maybe like a blue green.
7:48Hannah Fry:Because you only have the three cones, right? In your eyes, you have the three cones, which are like, is there any red there? Yes or no? I mean, and how much yes and how much no? is there any blue there? Is there any green there? You haven't got an orange cone. You're right. There isn't one. There isn't a purple cone.
8:05Michael Stevens:But we can see orange because our brains are able to process, hey, the shorts and the mediums are firing. So let's call it orange. And by call, I mean it creates the experience of orange on that object in the world for you. But here's the the big question, what happens when your eye is receiving both short and long? It doesn't give you middle as a perception because that would be triggering the middle guys. It'd be green. So instead, our brains have created a color that does not physically exist, and it is the color purple or magenta. That is purely a psychological phenomenon, not a spectral color.
8:49Hannah Fry:Wow, I never thought about this.
8:52Michael Stevens:This is so good. This is so good. And so that's why we're able to do starting at red, increase the wavelength until all of a sudden, boom, you're at violet. And then it goes back because in between the violet and the red, we have a combo that we experience as a mental construct. And that is purple or magenta type colors. Okay. So then I'm chronicling my crayons. I'm taking photos. Uh-oh. Phone camera sensors cannot recreate every color that Crayola makes. Go on. Let me show you a color. This one. Okay.
9:35Hannah Fry:This is like a, it's orange, but it's like a reddy orange. Sort of like the color of a tomato as it becomes ripe. but before it goes into that deep red.
9:48Michael Stevens:Wrong. This color does not look anything like what you just described. To me, seeing it with my own eyeballs. What does it look like? You're seeing it only as the camera and your computer screen can show it to you. This is a color that Crayola calls outrageous orange. And it is brighter than safety orange. It's like a high-vis, shocking, hurts-your-eyes orange. And yet on camera, it looks like, oh, that's a tomato. Yeah. Or, you know, it looks almost creamy. It's almost like a salmon to me on my screen. But in real life, this thing is outrageous orange. That's the perfect name for it. And you cannot photograph this the way it actually appears because it's fluorescent.
10:34Michael Stevens:That's the problem. The way this works, the reason this color is so bright in real life. And if you ever stumble upon a box of crayons, just open it up, pull out an outrageous orange. And you'll see what I mean. Basically, Crayola has added special optical brightener chemicals to this that take in ultraviolet light, which is coming in from all kinds of sources, especially the sun. And those chemicals convert that invisible ultraviolet light down into visible light that we can see that's re-emitted. And so the crayon is brighter than it should be. It is brighter than any normal thing in the world because it's actually producing, it's reflecting more light than is landing on it that we can see.
11:16Michael Stevens:Hold on, hold on. Can I see some of it on the page? Can you draw some on the page? I can show you this corner up here. I'm going to show my swatches again. So outrageous orange is right there. Right. And it looks a lot more like a carrot. It's a little bit more brown. There are three colors here on my swatches that really do not come across on screen. The three are Outrageous Orange, Neon Carrot, and what's this one called? Atomic Tangerine. So these three look almost more like an earth tone on a screen. Outrageous Orange does look a little lighter than natural. It still looks ready.
11:56Hannah Fry:It doesn't look like Hazard Orange at all. It just looks like a sort of a reddy orange smudge.
12:04Michael Stevens:I know. And so this is what's sort of disappointing about this episode. So if you're listening only, it doesn't matter. The people watching aren't seeing anything different because the camera cannot capture this. Now, Neon Carrot is really interesting because Neon Carrot is another neon fluorescent color that has optical brighteners in it that make its color brighter than physically possible without light being literally changed in energy levels. But neon carrot on screen looks almost exactly like regular old orange. So can you tell which one? They clearly are different, but which one of these is the fluorescent neon carrot and which one is just standard orange?
12:48Hannah Fry:Okay, so you're holding two up to the camera. I mean, honestly, they look almost identical. They both look sort of traffic cone orange. One of them is slightly redder than the other. I'm going to go for the, I think the slightly redder one is normal orange. Okay, this one, this one, you're wrong.
13:12Michael Stevens:This one is neon carrot. Okay. And this one almost looked brighter. This is just the regular orange that you would get in an eight pack, you know, at a restaurant. This is just regular orange. But to me, actually in front of these crayons, this one that you thought was regular orange, this one is bright. This is a high-vis. You would never miss it. You could spot it across the room kind of orange. Side note, because all you guys are going to be wondering, what are Michael's favorite Crayola colors? These are them, and they do appear on screen exactly the way they appear in real life.
13:49Hannah Fry:okay that was not the colors i thought you were going to go for um for those of you who are listening uh michael is holding up two pens that these are you know apparently his favorites one of them is a gray brown the other one is a red brown yeah i um look they're muted tones they're
14:06Michael Stevens:not muted tones their loudness is why i love them i don't know what is going on but the maroon crayon is like paint. It gets so thick. You put a line on a sheet of paper, you'd see it from a mile away. I don't get it. I can show you this on the swatches. Yes, please. Okay, so maroon is this one that's screaming at you right there. You see that? Oh, yeah. Yeah, there is a lot has come down there. A lot comes down. It is such a pleasure to draw with. It is like drawing with blood. I don't know. It can't just be the pigment unless the pigment is chemically changing the wax a little bit, but it's night and day.
14:49Michael Stevens:There's no other crayon like it. The browner one, this one, this is called Shadow. Right. And it's pretty fun to draw with, but it is so confusing. Try to draw with a Shadow Crayola. And it's not a mix of brown and green. It's sometimes brown, sometimes green, depending on where you decide to look. It is so strange. I can't wrap my head around it. I've been thinking about it every day.
15:16Hannah Fry:Well, depending on the light that's hitting it.
15:18Michael Stevens:No, it depends on, like, maybe it depends on the way the wax is structurally on the surface. Because I'll show you the swatch. Okay, here's shadow. Shadow is this one.
Read the full transcript
15:32Hannah Fry:It does look green. It looks very green on camera.
15:35Michael Stevens:It looks pretty green on camera. But it looks like, you know, where it's thicker, it becomes browner. But sometimes for no reason whatsoever, it looks more green in areas than others.
15:45Hannah Fry:Do you think this is intentional part of the design of it?
15:48Michael Stevens:I think someone there was like trying to make a greenish brown and then they made this and it scared them so much they called it shadow. The one Crayola they all feared. I've got one more thing to show you. This is something that I'm sure you've seen many times before. But phone cameras and screens can also pick up infrared colors that we cannot see. And they pick them up and then they convert them and display them as colors that we can see. The most easy way to see this is to use a television remote control or any kind of remote control that uses infrared light to communicate with a device. So if you look at the emitting light bulb on your remote and you push buttons, nothing happens.
16:32Michael Stevens:It looks like it's off. but point it at your phone and look at how it shows up on your phone screen or I'll point it at the camera right now and you guys can see.
16:40Hannah Fry:We can see it. There it is.
16:42Michael Stevens:A little purple light. And that purple light is infrared light that the cameras can pick up on. They go, oh, there's light there. And then they render it as usually that kind of purplish color.
16:53Hannah Fry:The version of that that I really enjoy is I have one of those doorbells, the smart doorbell things with the camera on it. and the one I really enjoy is when it's night time and the camera switches on as somebody comes home you know whenever someone's coming home from they're getting a taxi home or whatever and they open their phone if you have face ID on your phone you essentially does an infrared scan of your face that's essentially how it's like a depth measurement of your face that it's doing and when you watch somebody on something like a door camera that's in night vision mode, where it is essentially doing the same thing, as they open their phone, you can see it's flashing onto their face.
17:37Hannah Fry:This very bright light flashes onto their face that in real life, you do not ever see that at all.
17:43Michael Stevens:Yes, that's another great experiment to do. It shows you how much of the world we don't see that's happening. But then when it comes to the fluorescent colors, the neon colors, there is a world that cameras still can't capture and show us that you have to see in real life. And I've got a whole short about neon colors and using how they work to create neon brown. What would neon brown look like? And as it turns out, the definition of brown is basically, it can't be neon. Neon means more light is coming out than is even available in the environment. But brown means that there's so little light coming out that it looks dim.
18:26Michael Stevens:Take an orange, dim down the amount of light coming off of it, it's going to look brown. So brown is not only not neon, it's like the opposite. It's knee off.
18:35Hannah Fry:So neon and knee off together doesn't work. You've got to choose one. This is a light switch situation. Going back to your color wheel, can I tell you the reason why I was so excited about this episode? Because there is one time where understanding color theory comes up on an almost daily basis for a lot of people, which is in makeup. Do you know about this? okay so um i know that like makeup feels like quite a girly subject but i'm just going to go with it for just a moment because i think this is absolutely i personally think makeup is very very interesting and exciting for these exact reasons for these exact reasons that you are using the color wheel the entire time and you are essentially changing the whole point of makeup is that you are changing lightness and darkness on your face in order to correct or give the illusion that your face is doing something different than it actually is yeah so so for instance i have like these little blue um uh my skin is like basically translucent so you can kind of see the veins just underneath my eyes and so every morning i wake up in the morning and because i know the color theory i get a tiny bit of orange like a tiny tiny little bit of orange and i paint a bit of orange on top of the blue because they are opposite on the color wheel and then sometimes i get a little bit of red around here so i get some green and i put some little bit of green around here but there are now these people on uh on tiktok on on instagram who uh call themselves color theory witches and they i don't know if you've ever seen this michael it's so amazing but they will start off with their completely clear place and they will chuck on like some vivid green and then like a blodge of purple and then like a tiny little bit of yellow and they'll just mix it in and it will perfectly match like perfectly match the color of their face yeah i I find this so endlessly phenomenal and impressive.
20:27Michael Stevens:It's impressive. And it's impressive, but it's reality. Yeah. Because your skin is not one color. It's not like a pure peach or whatever was put on you. Instead, all the colors are there. And if there's a lot of them, then you wind up with something that's very light in color because it's approaching whiteness, right? white light containing all the wavelengths. And so you can combine green and orange and all these colors and make something that looks like it doesn't have any green in it at all to a naive perspective.
21:05Hannah Fry:But it goes back to what you were saying earlier, that you've got, you know, your brain is only like, is it short, medium or long? And how much short, medium and long photons, essentially, are there that are hitting the back of my retina at this exact moment? That's literally it. That's all there is to it. Yeah, that's great.
21:21Michael Stevens:Yeah, so I've got a lot more to learn about color. One of these days I will have my crayons arranged in, it's going to have to be a 3D shape because we've got three things going on. We've got how much gray, how much black, how much white. That's one spectrum. And then what the hue is. But I'm excited to show that off once I've got it.
21:41Hannah Fry:Okay, this is good. I'm looking forward to this. Also, can I just say, what an absolute delight to get a little insight into the way you spend your time, Michael. This is really genuinely, I'm endlessly fascinated by you.
21:55Michael Stevens:Well, Hannah, I'm glad. I'm glad that I have someone to share it with, not just you, but the listeners out there, because otherwise I'm just sitting alone talking to myself at night being like, ah, oh, okay, so is the atomic tangerine more red or orange? And then I try to like use my camera phone, realize that doesn't work at all because it's a neon, and boom, podcast episode.
22:19Hannah Fry:I'll tell you who else I'm endlessly fascinated by, Michael. Our listeners and their questions, which we will come to after the break.
22:39Michael Stevens:All right, welcome back. It is now time for us to dive into questions from you all. And you were ready to jump in, Hannah? You bet I am because the first one's about fluid dynamics, Michael. I know. I know. I know. I love this one. So this comes from Patrick Farrell. He emailed this question in to us. By the way, if you want to do that, you can email us at therestisscienceatgoalhanger.com. Please do so, just like Patrick did. Patrick asks, when I stir a cup of tea, the leaves collect in the center of the bottom rather than being flung to the edges, which to me feels backwards since everything spinning should be pushed outward.
23:13Michael Stevens:I've read that Einstein once wrote about this and that the same effect explains why rivers erode their banks the way they do.
23:19Hannah Fry:What's actually going on in the cup? Patrick, I don't believe for a second that you don't know the answer to this, but I think that you're here to amuse me because you've given yourself away in the question that you know so much about this already. But I love it and I'm very, very excited to get to talk about this. Okay, this is called the tea leaf paradox. Have you come across this before, Michael?
23:41Michael Stevens:Yeah, I have. But I don't remember enough about it. So I'm just like Patrick. Well, no, I'm not like Patrick. Patrick probably knows the answer. He's like, well, Einstein wrote about it. But I think he wants to hear how you explain it. And so do I. Right.
23:57Hannah Fry:OK, so he's absolutely right. If you stir a cup of tea, I mean, frankly, you should be straining the cup of tea before it ends up in your cup. But fine. If you end up with leaves in your tea and you stir it, then the leaves, you expect they should get pushed out to the sides because the whole of the fluid is sort of rotating in your cup. And you should expect they get kicked out to the sides, but they don't. They end up clustering in the middle. It doesn't make any sense. People have been like, what the hell is going on for a really long time? since the 1850s essentially and uh the key thing the key reason why this happens is because the top of your cup is not the same as the bottom of your cup because the bottom of your cup has a bottom and the top of your cup is free to the air the the the level of the fluid is free to the air and so essentially what's going on here is friction is causing this great big kerfuffle because as you have friction at the bottom you get something called a boundary layer this by the way was quite literally what my PhD was in Bangelea and fluid dynamics so you you get like right next to the uh to the physical surface of your cup you it's completely jagged it's like a mountain range if you zoom in so the fluid cannot be moving at that point and yet a little bit further up where your spoon is spinning around it's going really fast so what happens is you have this like this range of flow speed from zero to very fast at the bottom and it's sort of like it drags along the bottom right it's sort of like it kind of it goes slowest along the bottom and then sort of slower slower slower and then and then kind of speeds up as it goes up up towards the top um so all around the sides of the cup and all around the bottom you've got this this boundary layer this friction is kind of like dragging fluid so what that ends up meaning is you have this like rotating fluid it ends up there's a secondary flow so the dominant flow is round in a circle but the secondary flow is that it kind of goes up and then it has to go back down and around the sides you know your your spinning t is pushing outwards but near the bottom of the cup it's slower so you end up with this hidden circular movement and the thing is is that once it gets down to the bottom that is like so much more dominant than the spinning that's going on at the top and so you end up with these leaves being pushed along by that that secondary circular circulation so this is this it is the same thing as goes on in rivers thank you so much Patrick but as rivers go round corners you end up with essentially the same thing you have like fast flow on one side then you have all of the the like friction along the bottom and so you end up with this secondary circulation that ends up dumping loads of sediment on the inside is that right yes on the inside of the the rivers so you should be able to tell if I just take a photograph of a river, you should be able to tell based on the riverbank, which is the sort of inside and the outside bend, even if you can't fully see the bend.
26:58Hannah Fry:If I show you a cross section of a river, you can tell just from that because of this effect, essentially. Anyway, fluid dynamics is just really great. And thank you for letting me have three or four minutes on it. It was worth all the training.
27:11Michael Stevens:That's really cool. Yeah, I didn't know the answer was so sort of complicated.
27:15Hannah Fry:Oh, okay. Maybe I explained it complicatedly.
27:18Michael Stevens:No, no, no. What I mean is I thought that there was some like, oh, it's because of, you know, gravity.
27:23Hannah Fry:Well, it's all because of friction. It's all because of friction.
27:26Michael Stevens:It sort of slows it down. When did we figure out the tea leaf paradox?
27:32Hannah Fry:1857. It's, yeah, 1857. Like all of this stuff was going on. You know, all of this boundary layer stuff was going on around this time. Late 1800s, early 1900s. It's like this explosion in like how fluids flow. I should tell you one other thing, actually, when it comes to a cup of tea. If you are stirring your tea in a circle because you're like, oh, I want to get, you know, I really want to get this sugar stirred in really quickly. Terrible idea. Don't do it that way. Because actually the sugar will dissolve much better in a turbulent, turbulent fluid, right?
28:04Michael Stevens:Oh, OK. Hold on. Let me, let me, let me guess. Because this is what I do when I need to like get salt to dissolve in pasta water.
28:12Hannah Fry:As quickly as possible, yeah. Don't do a circle. Don't do that.
28:14Michael Stevens:Well, hold on. I'll do a circle this way and then I'll do a circle the other way really quickly. So it gets all like, you know, turbulent. And it feels like at least that fixes the problem of salt congregated in the bottom, just like tea leaves.
28:28Hannah Fry:Absolutely. You can also, I stir tea like this. Like for people who are watching, just listening, it's sort of an erratic, just do an erratic shape with your teaspoon. You look completely insane.
28:42Michael Stevens:Like you're just bouncing back and forth off the walls randomly. Yeah. It's like, oh, let's just, you know, wiggle it around a bit.
28:48Hannah Fry:It's much quicker. It's much quicker. Also, I should probably give up having sugar in my tea. But I'll tell you what, we should definitely do an episode on the effect of sugar on your brain. And because it's not good. It's not good.
29:00Michael Stevens:Oh, I would love to. Yeah.
29:02Hannah Fry:One for another time. But for now, sugar fans, until then, you can carry on enjoying the fluid dynamics of what's going on behind the scenes. actually i've just been reliably informed by neil who was watching the world porridge making championships that's a kind of caliber of human who works who works on our show michael correct and uh he's uh he's told us that actually when it comes to stirring porridge you need to do it
29:24Michael Stevens:with your right hand because that keeps the devil out oh we forgot about the devil that's right whoops continue stirring with your right hand probably clockwise because well i mean what do You want Satan to, like, come bother you or do you want sugar that's not quite dissolved? Okay? Your choice. All right. Well, you know what? Our next question is actually a little bit about water as well. This one comes from our subreddit, The Rest is Science, where JessXX underscore says, so my boyfriend has this really weird theory proposing that water can be differently wet. He doesn't mean in terms of hardness.
30:02Michael Stevens:He means sometimes tap water is more wet than other days. Honestly, I just want to prove him wrong, but apparently no one has ever asked a question like this, so I can't find any studies on it. Can water get more wet? I loved that. I didn't know how to answer this, but I had to look into it, and I had to go all the way back to 1946. Go on. And as it turns out, do you know where this is going? No. So I had to go all the way back to 1946 to Fire Engineering Magazine. They wrote about this problem that firefighters have had for a long time, which is that sometimes water isn't wet enough. What? So before I explain what that means, let's look at like what causes fire.
30:52Michael Stevens:Okay, fire is a chemical reaction, and you need three, maybe four things to really have a fire start. You need the fuel, but you also need oxygen, and you also need heat. It's that third leg, the heat, that water fixes. Water absorbs heat so well that it cools stuff down to the point at which the chemical reaction of combustion can no longer happen. The water isn't like washing away the elemental particles of fire. It's just cooling down the fuel to the point where it no longer combines with oxygen and combusts. Okay, here's the problem. A bale of cotton on fire is very hard to put out because as soon as you put that water on and you need that water to seep into the cotton and cool it down, the cotton on the top, the surface, absorbs the water.
31:41Michael Stevens:And it stops the water from penetrating deep into the cotton to cool down the entire bale, especially in the middle. And this 1946 article is like, honestly, it's been shown that kerosene can put out a cotton bale fire faster than water.
31:57Hannah Fry:No.
31:59Michael Stevens:Because it slips through. Because it slips through. Kerosene, being this hydrocarbon, it just slips right into the cotton. And if you have enough kerosene, yeah, it's flammable. But if its temperature is low enough, it'll drop the temperature of the cotton all the way through. So quickly, combustion stops. The fire is out long before water could do it. And so they had to come up with ways to make water wetter, to reduce its surface tension, to reduce the extent to which it sticks to things and itself. And they do this with all kinds of chemicals nowadays. They do it with like glycols and surfactants, obviously basically soaps.
32:39Michael Stevens:And these make the water wetter. Yeah. And so let me send you, this is a hilarious link where you can buy like firefighting products. This is a product called wetter water. The water extender. And it is water that's more wet. It wets things, it clings to things and seeps through them faster than regular water.
33:05Hannah Fry:So this here says lowers surface tension, cools faster, super concentrated, safe for pumps and seals. Wow, I had no idea about this.
33:15Michael Stevens:So as I dove into this, I saw a lot of people saying, oh yeah, you know, I'm a firefighter and we'll sometimes put soap into the water because it's going to soak through, especially fabric materials, absorbent materials faster and cool them down faster. So yeah, they use wetter water.
33:33Hannah Fry:I am so blown away by this. I'm also thinking, are there surfactants in your lungs? Have I remembered that correctly? ah to to help in what way to help so the inside of your lungs is basically like a wet balloon and surface tension would mean that they would collapse they're sort of covered in this very thin layer of water and because the water molecules are attracted to one another it continues to pull this little sack into a very tight little droplets so if your lungs just had pure water in there, then the surface tension would be so strong that every time you breathed out, they would collapse flat and they wouldn't open again.
34:13Hannah Fry:Right. So you've got this wetter water. In your lungs. In your lungs to make it so that you can actually breathe.
34:21Michael Stevens:So the tiny parts of your lungs don't just get stuck together by the water's surface tension. The water is wetter. It's thinner. It flows even more easily.
34:31Hannah Fry:Slipperier. Slipperier and less sticky.
34:34Michael Stevens:Slipperier.
34:35Hannah Fry:I've loved that so much. That is such a good question. I had no idea. Do they put it in the, like when they're sort of there with the hose, are they pumping out wetter water?
34:46Michael Stevens:Sometimes, not all the time. It depends on the type of fire, the type of fuel being burned. But it's a real thing. And so JessXX, I think I wouldn't have learned any of this. It wasn't for your question. I feel like, honestly, I haven't really answered your question because your boyfriend is talking about tap water. And I don't think any municipalities add surfactants and glycols to their drinking water in the tap. But that could go up and down day to day. Or even what's already on your boyfriend's skin might be mixing with that water and creating a more or less wet feel day to day. So that's my guess.
35:30Hannah Fry:But wouldn't it be the other way around though? because I think like feeling wet is about water sticking to you, no? Whereas we're talking about water slipping off.
35:39Michael Stevens:Well, I don't know. I would say that you're actually, you're right. Things get wet when water sticks to them. So a hydrophobic substance, like, you know, glass on cars coated with special things. So the water droplets just come right off. They don't get wet by the water where, you know, wet is this verb where wetting means to stick to. Some metals like gallium can wet glass, meaning they stick to it. And so the feeling of water being wet, does wetter water feel less wet? I think it would. I think we need to buy some and we need to try this out. And we need to feel and then you need to drink it.
36:21Michael Stevens:And tell me what it's like. No, but this is sort of two different definitions of wet being used here. One is how quickly does it penetrate materials? And the other is how much does it do the opposite, stick to them? And you're right. Wetting is more about sticking to things and staying on them through surface tension.
36:39Hannah Fry:We need more information from Jess at Sex. We need more, I think. We need, what does he actually mean?
36:46Michael Stevens:Yeah, does he mean that it feels thicker? Because, you know, what does your boyfriend do? He might be coming into contact with hydrophobic substances like fine dusts that then cause the water to just slough right off his skin and not wet his skin as much. That could be going on.
37:07Hannah Fry:Look, I feel like there's a follow-up episode on this coming. Are you?
37:11Michael Stevens:Yeah, I think there is. Okay, so yeah, keep us up to date and we will be following along on the subreddit. Here's a question that came from T. Sinri. How does space agencies such as NASA communicate with satellites, space probes and rovers in a way where they cannot be hacked? And has this changed over time such that older space probes may be more vulnerable to hacking? Are there any known instances of people hacking satellites?
37:39Hannah Fry:Okay, so I had a look into this, right? And I think you would imagine that the older ones would be easier to hack. So like Voyager 2, for example, because that was launched in 1977, which is, you know, before anyone was worried about cybersecurity, before all of this like modern encryption stuff was put out. And I, you know, you probably could. The only slight problem is that it's now 20 billion kilometers away.
38:05Michael Stevens:Yeah, you're going to need a really powerful antenna to like contact. I never thought about that, though. Like clearly NASA communicates it with probably radio waves. could I spoof that and tell Voyager to like come back or something?
38:19Hannah Fry:I mean, yes, but you're, I don't know if you could tell it to come back. I'm not sure it's got enough fuel on board, but you could, you, you, you would need to get into NASA's giant deep space network antennas that they have dotted around the world.
38:30Michael Stevens:That's the problem. Yeah.
38:32Hannah Fry:I mean, they are capable of transmitting these incredibly powerful beams, radio waves, exactly as you described with extraordinary precision, but you're, I mean, no, you're just not going to, you're not going to have one of them sitting around in your backyard. You're not going to be able to build one of them without anyone noticing. And even if you did, you would also need to know Voyager's original language, programming language, which would be, I mean, who even knows what it was? But it would be decades old. It would be really, I'm sure there would be details on it out there. But don't bother, basically.
39:02Hannah Fry:What I'm saying is the start-up costs are prohibitive and the output that you would get would be also quite limited. Ironically, though, the modern satellites, which are much closer to Earth, they sort of makes them slightly easier targets. The thing is, these do have much more standard technology, this sort of encryption that people have, you know, authentication because they know that they are easy to intercept. In fact, you know, I can't remember if I told this story in this podcast before, but you know Sputnik, when Sputnik originally was launched, it was a group of students in a bedroom who worked out where Sputnik was because Sputnik was giving out this beep.
39:40Hannah Fry:Have I told you this story before?
39:42Michael Stevens:Yeah, yeah, yeah, yeah. But I guess Sputnik wouldn't have the ability to do anything. You couldn't like tell it to, you know, fall or change its orbit. It just kind of was there and was going to not be there eventually.
39:55Hannah Fry:Exactly right. But it really, I think, demonstrates how these young students were able to tune into it using their radios and to hear the beep that it was giving out. These things are overhead the entire time. It's really not that hard. It really wouldn't be impossible to create an antenna that could tune in to what they are putting out and have the original coded message. The problem is, is unencrypting it is going to be way, way harder because they're using modern techniques. There have been a couple of mishaps, though. There was a really famous one in 2022. 24th of February. This, by the way, is about an hour before Russian tanks crossed the border into Ukraine.
40:38Hannah Fry:So kind of a really critical moment. But attackers managed to reach the management network of Viasat's KASat system, right? Which is basically, it was a misconfigured VPN. And what they did is they pushed a virus effectively, a wiper called acid rain, out to tens of thousands of modern consumer broadband modems and just bricked them.
41:07Michael Stevens:It rained down. So it was like just a vector for this virus.
41:13Hannah Fry:Exactly right. Exactly right. You send it up, it sends it down, all of this thing goes. And so what it did was it took out the Ukrainian military satellite communications right at the beginning of the war. It also, incidentally, knocked out 5 ,800 wind turbines in Germany. I didn't even know about this. Viasat, who are the provider, they had to ship out 30 ,000 new modems. There was no recovering these things. And also the satellite itself was completely fine. You know, the attack sort of, it just was a little IT system that kind of went up and then disseminated to all of the terminals. But, I mean, no one knows who managed to do that.
41:54Hannah Fry:No one knows who carried out that attack. I don't have any suspects. I don't know about you. Not sure.
42:01Michael Stevens:No, no, no one's told me.
42:03Hannah Fry:Complete mystery. Complete coincidence and complete mystery. But, yeah, it does happen. It's just hard to do and you have to be, I think, quite motivated. Tell you what, though, quantum computing's coming and encryption's looking a bit ropey.
42:18Michael Stevens:Yeah, man. I never even thought about hacking a satellite. Like, could I get, is Hubble still up there? Could I get Hubble to like point down at my house? Send you pictures.
42:28Hannah Fry:Yeah.
42:28Michael Stevens:Take some family photos. I don't think Hubble does well with short distances, but you know what I mean. There are other cameras up there that are pointing at Earth. I could commandeer them and set up some fun photo shoots. that with quantum computing that could become a much bigger problem i i i guess you have to hope that encryption keeps up with the computing yeah there are ways to do it there are ways yeah i'll
42:52Hannah Fry:be honest with you mike you're starting to sound suspiciously like mark zuckerberg wanting to point a mirror to his house for today to give himself day during the night um yeah look i was kidding
43:03Michael Stevens:I don't really want to do a photo shoot from space.
43:07Hannah Fry:I knew you were. That was a joy. I really enjoyed those questions. That was a lot of fun.
43:12Michael Stevens:They were really good. You guys bring us not just fun questions to answer, but the learning behind how we kind of approach them is just so fun. So thank you. And please send in more. We've got our subreddit. The rest is science. And the rest is science at goalhanger.com.
43:29Hannah Fry:Do you worry, though, that we research for these every single way? Do you worry that your brain is going to get to a point where it's like, no, I'm actually full now?
43:37Michael Stevens:No, I don't think so. But I think that it might get so full that like, imagine that no one can stump us. They're just like, hey, what if human hair was made of spaghetti? And we're like, oh my gosh, this one again. Yeah, look, you know, every week you'd get 2000 calories of hair and blah, blah, blah, blah, blah, blah. And we would just become know-it-alls to a boring extent.
44:00Hannah Fry:I strongly suspect we might already be there, Michael, but I think there's still mileage in this. Thank you so much for joining us. We will be back with another few episodes next week. Bye bye. See you next week.
From the publisher
Colour wheel or colour line? Light itself runs in a straight line from red to violet, yet every colour theory chart bends that spectrum into a circle and the reason has nothing to do with physics.
Professor Hannah Fry and Michael Stevens (VSauce) dig into why human vision refuses to see colour the way light actually behaves, tracing the visible light spectrum from one end to the other and asking where all the "missing" colours, like magenta and purple, actually come from if they don't exist on that spectrum at all.
It turns out the colour wheel is less a description of light and more a diagram of a workaround your brain performs constantly.
Send your questions to therestofscience@goalhanger.com or find us at r/TheRestIsScience on Reddit.
Find the wetter water Michael discusses at - https://winsol.com/products/wetter-water
-------------------
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
Assistant Producer: Lucy Lipscombe
Producer: Simona Rata
Senior Producer: Lauren Armstrong-Carter
Chief Digital Officer: Samuel Oakley
Exec Producer: Neil Fearn
Learn more about your ad choices. Visit podcastchoices.com/adchoices