The Elegant Laminar Flow of Moroccan Tea

0:00 You are here today to show us something very

0:02 cool about tea and I don't know what it is.

0:05 It's not my exploration.

0:07 It's your it's your reveal.

0:10 It's your exploration into my mind.

0:12 That's right.

0:13 I will be exploring your mind while you spill

0:16 the tea as they say or used to say.

0:19 I'll be honest with you.

0:20 I I'm on holiday in Marrakech staying at La

0:23 Mamounia this beautiful hotel and I have become

0:25 completely obsessed with Moroccan teapots and and so

0:30 I've insisted I've insisted basically that's where we start.

0:33 Let me just let me just going to get

0:34 this going to get this tea sitting behind me.

0:36 Hold on one second.

0:36 It comes in a teapot that is absolutely scorching hot that looks like this.

0:41 I think by the end of this you're going

0:42 to know why I'm obsessed with this teapot, okay?

0:44 Cuz it is basically a masterclass in fluid dynamics,

0:49 chemistry and the evolution of design.

0:51 All right, so it's like the whole world in a teapot.

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2:19 Okay, now I'm going to try and do this without burning myself.

2:22 The key thing about Moroccan tea is it's like it's like a green

2:25 tea that they stuff with mint leaves and like an insane amount of sugar.

2:31 But crucially when they pour it, they do this really really big pour.

2:36 Now I was anyone who is actually Moroccan is going to look at what I

2:39 did there and think it was a pathetic

2:41 a pathetic version of what the professionals do.

2:44 I've got a video for those of you who are watching

2:47 on YouTube of of an actual professional doing this for me at breakfast.

2:50 Okay, so we're outside and we're watching a waiter pouring tea

2:53 into a cup that's on a tray and he starts low,

2:57 but then he lifts the pot up all the way above his head and the stream is just

3:01 falling falling falling right into the cup and I

3:04 can see that sloshing the air getting mixed in.

3:07 By the way, we're outdoors.

3:08 This is beautiful.

3:09 We got a nice blue sky.

3:10 Looks delicious.

3:12 I should say if anyone watching or listening

3:14 to this is themselves a pro at pouring Moroccan tea,

3:18 then send us in your video and we can judge it.

3:20 So the key thing to notice is that when you pour this tea,

3:24 you end up like this this down here

3:26 is all like you know tea color, fine, boring.

3:29 But what you have on the top is these really foamy bubbles.

3:33 Can you see that?

3:34 There is a good reason why you would want this on your tea.

3:37 It looks like the head of a beer.

3:39 It's a foamy, but it's the tea like air has been mixed in, right?

3:43 Is that what causes it?

3:44 Exactly.

3:45 It looks like it looks like a porter lager essentially [laughter] like

3:49 a bubbly lager and the story goes that the reason why you would have

3:53 this in Morocco is because if you are out in the desert and you're

3:56 drinking tea and there's sand kind of flying around all over the place,

4:00 what this does I mean this shows just how pathetic mine is.

4:03 When when the professionals do it,

4:04 it's a really foamy head of head of tea that stays there for absolute ages.

4:08 Mine is already puffing.

4:10 Demonstrates I'm not very good at this.

4:12 But the idea then is that if there is sand

4:14 floating around in the wind and it gets onto your tea,

4:17 it will get trapped inside these glossy bubbles

4:20 on top and then you can either blow them

4:23 off to get rid of the sand or if you kind of drink in a particular way,

4:27 then the the sand will will stay within the bubbles

4:29 and you can get access to the liquid but not below.

4:32 But even though it starts off having this really practical reason behind it,

4:36 it's also this foam is now considered as this visual indicator

4:41 that it's good hospitality and it's good quality tea and that you've been

4:44 served correctly because where it comes from I mean if you pour

4:48 normal black tea that you get in in in Britain for example,

4:51 you don't end up getting this foam and where this comes from is

4:55 this like chemical process that is going

4:58 on inside the tea because green tea leaves,

5:01 they contain this thing called saponins which is like this natural

5:06 soap-like molecule and essentially they are amphiphilic I think is the word.

5:12 Basically this molecule ends up half the molecule

5:14 one end of the molecule loves water, the other half hates it.

5:18 So it ends up orienting itself to make these kind of bubbles.

5:22 The sort of water hating tails stick out into the air bubble

5:26 while the water loving heads of this molecule stay inside the tea

5:29 and that creates this kind of protective skin around the air which effectively

5:34 lowers the surface tension and makes these bubbles form in the first place.

5:37 But also you add a shedload of sugar

5:39 to increase the viscosity of this of this liquid so

5:42 that the bubbles stay for a while and then because

5:45 you've got loads of peppermint in there and loads of mint,

5:48 you have these these kind of essential oils

5:50 which then stabilize the the bubbles even further.

5:53 So okay, it's it's good to keep sand out and it lets you know

5:57 that it's sweet enough and the and you're

6:01 you're you're you're not you're not cheating.

6:02 You're not using like dried mint basically.

6:04 You're using like the fresh good stuff.

6:06 Okay, hang on one second.

6:06 I'm actually just going to have a little sip of tea.

6:08 Hold on.

6:08 Is this only true for teas that are made with things like mint leaves?

6:12 Would you not get this from a traditional

6:14 black tea and English breakfast tea for example?

6:18 I don't know actually.

6:19 I'm not sure.

6:20 That's a good question because black tea and green

6:22 tea are from the same plant, aren't they?

6:24 They're just the way that they the way

6:27 that they process them ends up being quite different.

6:29 So I'm not sure, but definitely the aim

6:32 of black tea is not to create these bubbles, right?

6:35 No, it isn't, but it's cool that the the purpose the stated original purpose

6:42 of the bubbles is to keep out debris because the first thing I thought was oh,

6:46 that's how soap works.

6:48 Soap creates bubbles.

6:49 Surfactants create these bubbles that then lift out debris like particles

6:55 and dust and that's literally what they're being used for in the tea.

6:59 You're literally drinking soapy tea.

7:02 I mean it is a surfactant that that you're that you're doing.

7:05 Yes.

7:05 Okay, the real reason why I'm obsessed with this, right?

7:08 Is when I I mean tea is delicious, sure that's great.

7:12 But when I saw the teapots,

7:14 I immediately spotted the fluid dynamics that's going on inside

7:18 this thing cuz this is a very particular shape.

7:21 It's like the size of a pretty big coffee mug,

7:23 but of course it's a it's a jar shape

7:25 with a with a like a bell shaped kind of lid,

7:28 but the spout is starting from very low.

7:31 The other thing to [laughter] the thing to notice about this spout

7:35 because this doesn't look like a British teapot.

7:37 Okay, like a British teapot, you have the spout starts maybe halfway up the pot.

7:42 Sometimes a little lower,

7:44 but but around about halfway and the spout just curves upwards.

7:47 It's like a U-shaped spout.

7:48 This spout is S-shaped and that is

7:52 absolutely critical to getting these bubbles to form.

7:55 If you want to get proper bubbly tea,

7:58 what you need to do is you need to be able to pour

8:02 this tea from a real height like arms length away from the cup.

8:06 You want it to gather up all of the speed

8:08 and momentum and when it plunges into the liquid,

8:13 you want it to take in all of the air from around it with it.

8:16 So it's kind of like plunging right to the bottom

8:19 of the glass and creating these big bubbles and and foamy surface.

8:23 Now in order to do that, in order to be able to pour this tea from a height

8:27 which by the way has the added advantage of cooling it down to make it sippable.

8:30 Oh, sure.

8:31 Yeah, yeah.

8:32 You know, even though in the pot it's absolutely boiling.

8:35 What you need is you need the tea

8:38 to leave the spout in what's called laminar flow.

8:41 It needs to be extremely neat, extremely slippery,

8:45 extremely well-behaved tea so that you can get this stream that will behave

8:51 all the way down and you can direct it perfectly into your cup.

8:54 If it wasn't laminar,

8:56 it would spread out too much over this long falling distance

9:00 and you would just get it would rain tea all around the cup.

9:04 It would be boiling tea soap rain.

9:07 Yes, exactly.

9:08 Okay, doesn't [laughter] that sound delicious?

9:11 All right, so to get laminar flow then,

9:13 what you have got here is all of the things that you noticed.

9:17 So for starters, the fact that this the spout

9:19 starts right at the very bottom of the teapot.

9:22 This means that you are at the the the point

9:25 of the liquid that is that's under pressure, right?

9:28 You've got like the highest density.

9:30 You've also got a lot of dense tea leaves down there.

9:32 Sort of the the flavor of the tea is going to be best down there.

9:36 But it means that you've got the weight

9:38 of all of the tea all of the liquid sitting

9:41 on this on this exit as you're pouring so that you're

9:44 kind of pushing down on it as much as possible.

9:46 Then what happens is this spout starts off

9:49 reasonably wide and then it gets thinner and thinner

9:51 and thinner and thinner and thinner all the way

9:53 to the end which means you're you're reducing the aperture,

9:57 you're speeding up the tea effectively.

9:59 You are accelerating this tea all the way through

10:02 the spout to get it go faster and faster.

10:04 And what is that?

10:04 Is that like Bernoulli's principle or something?

10:07 Like the liquid speeds up as it's the cross-sectional area of the tube shrinks.

10:13 Yeah, you've got Bernoulli which is talking about the pressure,

10:15 talking about the the size of the aperture.

10:17 There's like Reynolds number stuff going on here.

10:19 There's the Venturi effect.

10:21 There's like the There's all sorts of like

10:23 really delicious fluid dynamics going on here.

10:25 The thing is is that normal teapots with the U shape,

10:28 they're doing the same thing.

10:29 They're accelerating the tea out of the end.

10:32 But this S shape is absolutely critical because if you imagine

10:35 that you were going on a slide, like a water slide,

10:39 and you kind of come round and the slide bends in one direction,

10:44 you're going to go up the slide,

10:45 you're going to be slopping about all over the place as you exit that slide.

10:50 So, crucially, this S bend, so it curves one way and then curves the other,

10:55 essentially straightens out all of these water molecules

10:59 so that when they exit from the tip, they're all pulling in the same direction.

11:03 You haven't got any little tiny little eddies or like bits

11:06 of bits of turbulence that are hiding inside of the spout.

11:09 Right.

11:10 All essential for laminar flow.

11:12 Then, you've also got this extremely sharp tip.

11:15 So, um in the '90s, there was this this group of of fluid dynamicists who

11:22 won the Ig Nobel Prize for working out how to um stop a teapot from dripping.

11:29 They did all of this unimaginable rich mathematical analysis.

11:35 Uh and the answer that they came to essentially was

11:38 what the Moroccans had already found hundreds of years ago,

11:41 which is to just have this sharp corner on the end.

11:44 And this I think brings me to what I really really like,

11:47 the reason why I find this kind of design so interesting and exciting.

11:52 Because I could literally spend maybe 4

11:56 years writing the equations for this teapot, right?

11:59 I could I could work out these extremely

12:02 sophisticated computer simulations demonstrating that this is the optimal

12:06 way to create laminar flow that behaves in this way

12:09 to to to create bubbles exactly like that.

12:13 But here's the thing, this teapot,

12:15 there was literally no maths or physics that was involved in the design of this.

12:20 And so I think this is one

12:22 of the most gorgeous demonstrations of how the evolution

12:27 of design manages to land on totally optimal

12:33 physics solutions without ever having touched an equation.

12:38 I think that's really cool.

12:40 It's beautiful.

12:40 It just It emerges through natural selection in a way,

12:44 except the pressure is our desires to have laminar flow, foamy tea.

12:51 And you try things out and then boom,

12:53 you've solved the equations, but you never had the equations.

12:56 But you never had them.

12:58 And you see this I mean, you do see this over and over again, right?

13:01 Roman arches is a really good example of like

13:04 finding this optimal way to support a structure.

13:07 You see this in Japanese steel in the way

13:09 that they heat the when they're making knives and blades,

13:13 the way that they heat it is actually this You know,

13:16 to understand what they're doing requires

13:18 this incredibly deep understanding of the material

13:21 science of the structure of of the the the materials that they're working with.

13:25 But actually, they just chanced upon it through many

13:29 many many many many iterations of design over numerous generations.

13:34 Yeah, that's right.

13:35 I love the the folk physics of it.

13:37 The like, "Look, if you warm the metal up and then you cool it down quickly,

13:42 it's going to be softer." And we call that annealing.

13:45 And today, you can look up a bunch of videos

13:47 about exactly what's happening at a molecular level and why,

13:50 but before that was really understood,

13:52 before atomic theory, before molecular theory, it was just like,

13:56 "The metal has a personality and you have to treat it this way.

13:59 You have to be mean and then tender." And I can see how much

14:02 more alive the world was when you had to just make everything an animal.

14:05 And yet, you it still gave you the right answer.

14:08 I mean, maybe it didn't allow you to fiddle with numbers

14:10 a little bit and develop whole new like hardnesses of steel,

14:15 but you would discover them on accident and it was like a blessing.

14:18 Exactly.

14:19 I think this is it actually.

14:20 You know, the sum total of of human

14:24 knowledge even without science is just really profound.

14:29 There's this Japanese idea actually that in a single cup of tea,

14:34 you'll eventually discover the truth of 10,000 forms in the universe, right?

14:40 Like this idea that you can you can you can

14:43 observe all of humanity in a single cup of tea.

14:46 And it's not that far off.

14:48 A single cup of tea gives us thermodynamics, fluid dynamics,

14:53 it gives us history and botany and human culture and tastes and flavors.

15:01 It's all there.

15:02 It's all there.

15:02 Okay, Michael, that's me spilling the tea.

15:04 Maybe less juicy than than you might have been expecting,

15:07 but um more fluid dynamics.

15:09 Hannah and I are now going to delve into questions that you all have sent us.

15:13 We certainly are.

15:15 Should I go first, Michael?

15:15 I took the first half.

15:16 Yeah, I'll go first cuz I love this question from Louis Taylor.

15:19 The question is the boiling point of water is affected by your altitude,

15:24 which we tend to measure as a height above sea level.

15:27 But if sea level changes outside of its normal range,

15:30 will that change the time it takes to boil water and therefore eggs?

15:34 And I love this because one,

15:36 it's very personal to me because I spend time pretty much at sea level in LA,

15:41 but also up over 5,000 ft in Boulder, Colorado.

15:46 And you notice a difference.

15:47 I have to now remember two different times for soft-boiled eggs.

15:53 Like here in LA, it's like 5 minutes.

15:55 We're getting We're going to It's too far.

15:57 But I need to do six and a half in Boulder.

16:00 And you can measure the water temperature and it's like, "Oh, wow,

16:03 this boiling water is not 212, you know, it's like Let me see.

16:08 Temp of boiling water, Boulder, Colorado." Yeah,

16:12 the water boils in Colorado in in Boulder at 203° Fahrenheit.

16:17 Translate that into sensible system, Fomikiji.

16:20 In C is 95.

16:22 Woah.

16:23 So, water boils at 95° Celsius in Boulder.

16:28 And that means that to cook an egg, like to soft-boil or hard-boil it,

16:32 it just needs to be in that water a lot longer,

16:34 like a couple minutes longer at least.

16:36 And pasta is the same way.

16:38 You know, normally pasta instructions would be like 10 to 12 minutes.

16:42 Boil this to be soft.

16:43 And I would go just to like 10 or even under the minimum.

16:47 But in Boulder, I've got to go past

16:49 the maximum and it's still not even al dente.

16:51 It's still like too hard.

16:54 I think that you would I think you'd particularly notice that, too,

16:57 given that for some strange reason, Americans don't have kettles.

17:02 I've always found that the weirdest thing about your country.

17:04 I can't say too much about it though because my mother had a kettle.

17:08 Oh.

17:08 My wife I married a Kiwi who lived in England for decades,

17:13 so she's got an electric kettle in our house and we use it all the time.

17:16 So, I Look, I get what you're saying though.

17:19 Um it takes even longer to boil water when

17:22 you don't have like a super fast turbo electric kettle.

17:26 But um yeah, I think constantly about how my altitude is

17:31 a is is the reason the water's taking longer to boil.

17:34 Long story short, there's just less air above

17:36 you when you're already up in a mountain.

17:39 And it's that water's that Sorry,

17:41 it's the air's weight that's pushing down on the water molecules saying,

17:45 "No, you cannot leave your liquid state.

17:48 You cannot leave this container." And if you go up high enough,

17:51 there's so much less weight from that air squeezing

17:54 on top that the water molecules can get out more easily.

17:56 They don't have to have as much energy to leave the liquid state.

18:00 So, that it boils with a lower temperature, with less kinetic energy.

18:05 And uh I always think of my altitude

18:09 in terms of a number like 5,000 ft or whatever.

18:14 And that's from sea level.

18:15 But if sea levels go up, like let's say I live at 5,000 ft.

18:20 If the sea levels rise by a foot, do I now live at 4,999 ft?

18:26 Technically, I do.

18:28 But what happens to the actual air pressure effect on boiling?

18:34 And I think that's a lot more complicated.

18:37 And I think first of all, the ice And you tell me if I'm wrong

18:40 because this is just me kind of noodling through it.

18:44 The ice that melts that then causes the sea level

18:48 to rise took up more volume than the water does.

18:53 I know that a lot of glacial ice is much more

18:55 dense than the typical ice that we'll put in a drink.

18:59 But I think that overall,

19:01 the amount of space taken up by solid matter on Earth goes

19:04 down when sea levels rise because you've exchanged some liquid water You Well,

19:11 you've exchanged some solid ice for some liquid water.

19:15 Which is a smaller volume.

19:17 But crucially, you have a hell of a lot of water

19:22 in glaciers on land that could be added to that total.

19:26 Yes, but if a glacier on land melts, Mhm.

19:30 the total volume of solid material on Earth has

19:34 gone down cuz it's turned from ice to water.

19:37 Mhm.

19:38 And so in that way, the average height of Earth,

19:44 like what we call mean sea level, Mhm.

19:47 would Well, but mean sea level is based on where the oceans are floating.

19:53 But you got to imagine that all the solid stuff on Earth is displacing the air.

19:58 And when the solid stuff that's displacing

20:00 the air gets smaller, you now have what?

20:04 A thicker atmosphere or a thinner?

20:07 I see where you're going with this.

20:09 Isn't there an additional complicating factor,

20:11 which is that there is a huge amount of gas also trapped within glaciers?

20:18 So that once that ends up melting,

20:22 there's a higher amount of air of air overall.

20:26 Right.

20:27 Let's just do like a toy model and let's imagine that the Earth becomes smaller,

20:33 like half the diameter, but it has the same amount of air.

20:37 Now we're really exaggerating this change.

20:40 But that same amount of air is now going to be much thicker everywhere.

20:45 The The atmosphere is thicker because it's got a a smaller um surface to cover.

20:51 Hang on, let me make sure I'm following you.

20:52 You take you take the sphere of Earth

20:55 and you shrink it so that it's half the size.

20:57 Yeah, and it you keep all the same air around.

21:00 All the same air?

21:02 So air Are we saying that the outer like the Karman line, as it were,

21:06 effectively, is like is in the same place or is the whole thing shrinking?

21:11 I think that the only the solid part of Earth shrinks.

21:15 So I think the Karman line would go up

21:19 because you've got the same amount of air Okay,

21:21 so imagine you've got like a a cake that's a that's

21:24 really big and you've got a one jar of frosting,

21:27 you can cover the whole cake, but it's a thin layer.

21:29 Now you make the cake half the diameter,

21:32 but you have the same amount of frosting, it's going to be a thicker layer.

21:35 So air pressure frosting pressure in our example here is

21:39 going to be greater now at each point on the cake

21:42 surface because there's a higher column of frosting above you

21:46 than when you were a big cake with a thin layer.

21:49 Let us know in the comments below what

21:51 I'm getting wrong because I am just noodling

21:55 on this and I'm thinking that if the total

21:59 volume of solid stuff that Earth is made up shrinks,

22:03 like the the total amount of mass I'm imagining it stays the same,

22:06 the volume gets smaller, the air pressure would increase,

22:09 but I think there's also so many complicating factors,

22:12 like could the atmosphere become thicker or is it going

22:15 to start getting picked off more quickly by solar wind or something?

22:18 Like I think when we talk about sea level rising 1 ft,

22:21 we're probably talking about such a small

22:23 change that other consequences might compensate.

22:29 Extra air released from melting glaciers,

22:32 thicker atmosphere being pulled off by solar wind,

22:35 I there might not be much of a change,

22:36 but if all that happened was that Earth technically had a smaller volume,

22:41 I think that the boiling point of water would go up

22:45 regardless of the fact that your altitude above sea level went down.

22:49 I like this so much.

22:50 This feels like this almost feels like a um [snorts]

22:54 you know, when they do those incredibly hard interview questions.

22:57 Yes, the Yeah, how many ping pong balls are here in New York City?

23:01 Yeah.

23:01 Right, exactly.

23:03 Or like if you were a flea trapped in a blender, how would you get out?

23:07 Like that if you were shrunk down to the size

23:09 of a flea and put into a blender, right?

23:10 That kind of thing, you know?

23:12 Yeah, this is I I want to think about this.

23:14 I want to think about this.

23:14 Maybe maybe in the comments as well,

23:16 you can [laughter] you can tell us your answers.

23:19 And um and maybe we'll come back to this in another episode of Field

23:22 Notes and we'll we'll compare cuz I

23:24 think there's an argument that it's the opposite,

23:25 but you know, there's I want to I want

23:27 to get my equations on before I before I commit.

23:30 Yeah, yeah, yeah, using no equations or anything,

23:32 just straight up what I know about stuff

23:35 and comparing stuff to cake sometimes very helpful.

23:38 I think that all else being equal,

23:41 if sea levels rose because of melting glaciers and ice caps, technically,

23:47 the boiling point of water everywhere would be

23:49 a little higher despite the fact that your your altitude

23:52 above sea level will have gone down because

23:54 mean sea level will be closer to you.

23:56 I'll tell you what, there was a question I really like

23:58 the look of by Alistair That's my best possible attempt at the pronunciation.

24:04 And I think this links in quite nicely with this because here's a question.

24:08 I was watching some climbing videos on YouTube

24:10 and it made me wonder what percentage

24:11 of naturally occurring vertical surfaces on land that are

24:16 on land have actually been traversed by humans.

24:19 Well, great question.

24:20 So I had a little go at this uh at calculating it.

24:25 And a sort of related question that I have wondered so many

24:31 times is how much of horizontal surface has ever seen a human footprint.

24:37 Like when you go out and you're kind of walking the land,

24:42 how much of Earth has no human footprint ever laid upon?

24:48 This is sort of I mean,

24:49 this question by Alistair is like the vertical version of this, I guess.

24:52 And that one does have a clear answer, right?

24:54 So I'll I'll tell you this well, clearish answer.

24:56 Because I think that humans you sort of I think it's very easy to feel

25:02 like we're spread out all over the place

25:03 that we've kind of dominated the entire planet.

25:06 But the reality is we're actually a really huddled species.

25:10 So if you take all urban infrastructure,

25:12 everything that we've built and live in, it's actually only 1% of of land.

25:18 It's tiny teeny teeny tiny.

25:20 Which is an even smaller percentage of Earth's surface.

25:24 Exactly.

25:25 So everything every number I'm going to say here,

25:27 you have to you have to basically cut it by 30 you know,

25:32 cut it to 30% of the number because as you say,

25:34 70% of the Earth's surface is is ocean.

25:37 Um even our agriculture, which is way way way way way bigger than

25:41 than the urban infrastructure is only 37% of Earth's landmass.

25:48 Managed forest is about 10%, but wilderness dominates.

25:51 I mean, you think about the Sahara Desert or you know,

25:54 the Arctic, the Antarctic, it's 52% of the of the landmass.

25:59 So if you go through and you make some assumptions about you know,

26:03 I think you can you can assume that in an urban landscape,

26:06 100% of the land, you can't you know,

26:08 you're not going to find a single patch where people haven't stepped on it.

26:12 Um which decreases as you go further down.

26:15 So in agriculture, some bits of agriculture maybe it's going to be 80%,

26:18 some bits maybe slightly less, more like 20%.

26:21 But in the wilderness, I mean, almost none of it has been stepped on by humans.

26:26 So when you kind of go through and calculate this, it's

26:29 about 15% of the Earth's surface have ever seen a human footprint.

26:34 Um which as you say, uh that's sorry, that's of land.

26:38 And then when you consider that that's only

26:41 a third of the surface because of the oceans,

26:44 5% of the Earth's total surface has ever had a human footprint on it.

26:49 Amazing.

26:50 That's amazing.

26:52 Yeah, cuz it's easy to get so sad about how there's no new frontiers.

26:57 There's there are no far-off distant lands that we've never, you know, visited.

27:01 I I was thinking about that today.

27:03 You're coming from Marrakech.

27:05 Just 200 years ago, I would have read about it in a book,

27:08 but I would never even probably correspond with any from one from there.

27:11 Now it's like, oh, we're both going to be

27:13 talking live from Los Angeles and Marrakech simultaneously.

27:18 Piece of cake.

27:18 Now are you factoring in like the the actual surface area of a footstep?

27:23 Because I could walk in a field, but I haven't walked on the entire field,

27:27 but I've, you know, been near and seen a lot.

27:30 Oh, I was cheating slightly.

27:31 I did I did some I did some rule of thumbs.

27:35 So I said that if it's a field, then it's about 80%.

27:38 80% of that would have been covered.

27:40 Interesting.

27:41 Okay.

27:41 I mean, I'm get I basically I'm guessing, Michael, at this point.

27:44 Oh, you get down deep enough, you're always guessing at everything, frankly.

27:48 Um but so there's some some estimation going on.

27:51 But to do this for the vertical surface, which is was the question, right?

27:55 This I mean, if we're if we're talking

27:57 about 5% of the horizontal surface of the Earth,

28:00 the vertical surface is almost nothing.

28:04 So [snorts] I I looked it up,

28:05 there's about a million established rock climbing routes around the world.

28:11 I mean, I was I I like I'm doing one significant figure here.

28:15 That is like again, this is some serious estimation going on here.

28:19 And then when you think about them, I was like, what do you reckon?

28:23 About 30 m?

28:24 I mean, most of them are not going to be on average about 30 m,

28:27 maybe about 2 m wide.

28:30 So once you once you run these numbers,

28:33 you're talking 60 square meters of climbing

28:36 surface for each of these million routes.

28:40 I mean, this is it's a rounding error.

28:43 We've done none of it.

28:45 Literally none of it.

28:46 Wow, we could have not climbed anything and still

28:49 pretty much touched the same amount of Earth.

28:52 It's so small in comparison.

28:53 Wow.

28:54 We think of ourselves as an invasive species.

28:56 We've we've barely got started, Michael.

28:58 We It really depends on what you mean by invasive, doesn't it?

29:02 Because we've got satellite imagery of so much,

29:05 our our emissions surround and touch so much,

29:10 but yet our flesh has touched so little.

29:13 Almost nothing.

29:14 Yeah.

29:14 And I used the word flesh just there, but usually we're wearing shoes.

29:19 And when you're climbing, you you'll well, you'll have the chalk on your hands,

29:23 but you know, I'm saying that shoes and gloves are different, too.

29:26 I've always been like, no one's really touched the moon.

29:28 No one's run on it barefoot.

29:30 Yeah.

29:31 Does it count if you there's fabric in between your skin and the moon surface?

29:38 You're you're counting contact we've made wearing shoes with the Earth.

29:42 You are absolutely right.

29:43 Let's get out there and touch grass, everybody.

29:46 Yeah, for s- for real.

29:49 Because you're right, you'd have to I mean split this by a massive fraction.

29:55 This is actually a perfect segue to a question that came in from Andrew.

29:59 So, Andrew asked, "While lying in bed,

30:02 I ran my foot along my bed cover and noticed

30:05 I could feel the fluffiness of it through my sock,

30:08 but I could also feel my sock.

30:10 It made me think about all the times I was able

30:12 to discern a texture through my socks or my socks and my shoes.

30:16 How am I able to feel and discern all

30:18 these separate textures?" I know exactly what you're talking about,

30:21 Andrew, because I got I really tripped out when

30:24 I was at Derek Muller's wedding in uh Portugal.

30:30 This is Veritasium.

30:31 Veritasium got married and I was there.

30:34 I was very honored to be there and I was walking around the streets

30:37 of Lisbon and the stones there uh that line the streets are very smooth,

30:43 but sometimes they weren't and I could tell the texture,

30:49 like the microtexture of the stones through my socks and shoes.

30:55 I don't know if this if anyone else has

30:56 experienced this, but I could like immediately tell, "Wow,

30:59 these stones are different," but they looked identical and I'd

31:01 reach down and feel them and I'd be like,

31:03 "Oh, these aren't polished as smooth," but I couldn't tell

31:07 with gross motor movements whether it was slippy or not.

31:10 It wasn't obvious.

31:11 It was something different and I think

31:13 it might have been even like the vibrations, like the microvibrations,

31:17 and that reminded me of a study I saw that looked

31:21 into how we measure how heavy things are and that it's

31:25 not as simple as we hold it and we just look

31:27 at how much our our our muscles are having to work.

31:31 We we really do feel like thousands of little micro motions.

31:35 We're sensitive to them when we reach out and grab something before we even lift

31:38 it that tell us how easy it's going to be to change this thing's velocity,

31:44 how easy it's going to be to accelerate, to pick up,

31:47 and we can tell that before we even hold it.

31:50 And as I dove deeper into this, Andrew,

31:52 I found that there's all kinds of ways to trick your sense of weight.

31:56 You can actually make things vibrate so that they feel heavier.

32:02 If you take a little device and you have it vibrate side to side,

32:06 not even up and down, but side to side, people will think it's heavier than

32:10 it really is because it's well we don't know why.

32:13 One hypothesis is that it's using more muscles and the brain goes,

32:17 "Ooh, it's taking a lot more muscle activity to hold this.

32:20 It must be heavier," um even though of course it isn't.

32:23 Um we know for certain that you can have something vibrate up and down,

32:27 especially asymmetrically, like a bigger vibration down down.

32:30 It has to be pretty fast.

32:32 Like 30 hertz, I think is like the the the real

32:35 sweet spot for making something feel heavier because of its vibrations.

32:39 And so basically, we I think learn through experience

32:44 how to tell the textures of things through other things.

32:50 You can poke uh an object with a stick

32:54 and learn if it's rough or smooth even if you're blindfolded.

32:57 And I think we learn that through time and it's very

32:59 trippy to think that it's an extension of our body, really.

33:02 We learn how to feel through sticks and um walking sticks and socks and shoes

33:10 and gloves um as though they were part

33:13 of our bodies with sensory receptors on them.

33:17 Though of course they're not, they're inert.

33:19 And we our bodies don't have to be this big, they can be large.

33:23 Yeah, you do hear that about blind people in particular where

33:26 the stick essentially becomes an extension

33:28 of their body exactly as you describe.

33:30 But in a way, I mean your it's the same

33:34 story in the sense that your brain is receiving signals,

33:39 it's receiving some data, some some input [snorts]

33:42 and it's interpreting it's it's making an interpretation

33:46 based I mean I I I sort of feel like almost every week we come back

33:50 to this idea that like reality is not reality,

33:53 it's just our brain's interpretation of it,

33:55 but it sort of feels like it's the same thing.

33:57 a little show your brain puts on for your awareness.

34:00 Like my glasses, right?

34:01 I wear these all the time and I don't think I'm looking through glasses.

34:06 This is just the world.

34:07 So, these have become part of my eyes as far as my brain is concerned.

34:11 They're not there.

34:12 They are a prosthetic that is almost all the time completely fused with my body.

34:18 Or yeah, I mean you could say for people who don't wear glasses this kind

34:21 of the opposite way around that your nose

34:23 is permanently in your field of vision.

34:26 You just don't bother noticing it.

34:28 We yeah, we ignore it just like you can

34:30 ignore that the sock is there and go, "Oh yeah,

34:32 I can feel the fluffiness of my duvet through the sock."

34:35 No one ever looks at a beautiful view and says "Oh,

34:38 let me describe this for you.

34:39 So, first of all, there's this like nose down here

34:43 and there's like the li- the bar of my glasses,

34:47 so imagine that's going over the top, you know, second fifth.

34:51 No, no, they just describe the view.

34:52 We can ignore these things.

34:54 I feel like the uh classic painters [laughter]

34:59 they really should they really missed a trick, you know?

35:02 I think it would have been so much more beautiful if you saw the Mona

35:04 Lisa and you just had Da Vinci's nose in the middle of the canvas.

35:08 Right there.

35:09 Yeah.

35:10 Yeah, he erased himself.

35:11 He did.

35:12 You know, let's embrace that.

35:14 Let's put in the like weird overgrown eyelashes that are kind of down there

35:19 and the little dust on the glasses that you keep ignoring or the floaters.

35:24 For those of you who don't use I mean I see floaters, too,

35:26 but you know, even without glasses, you've still got artifacts in your vision.

35:30 Maybe I'll stop into the Louvre on the way home on the way home from Marrakech

35:34 and just break in at midnight paint Da Vinci's nose on top of the Thank you,

35:39 I'd appreciate that.

35:40 I'm sure there's some famous works of art

35:41 in Morocco that would be easier for you to vandalize.

35:44 Do you know what else too?

35:45 That's also that's also true.

35:46 I'm also obsessed with Moroccan tiles, by the way.

35:48 Expect to see me do a video on that for a for for the internet very shortly.

35:53 I can't wait to see you talk about that.

35:56 So, anyway, I'm I'm glad that we get to touch

35:58 you guys all through your ears every single week.

36:01 Send us in your questions.

36:02 Like I said, therestisscience@golhanger.com.

36:06 Or you could sign up for our free newsletter,

36:08 therestiss.com/science and we will see you next week.

36:12 See you then.

36:15 [music]