WEBVTT - Can you sail on light? 0:00:09.600 --> 0:00:12.280 Hey, Daniel, you like the outdoors. You're an outdoorsy kind 0:00:12.280 --> 0:00:14.800 of person. Are you a fan of sailing? Oh? Man, 0:00:14.840 --> 0:00:17.919 I love sailing. There's so much to appreciate, the wind, 0:00:18.320 --> 0:00:21.920 the quiet, But mostly it's because it's about applied physics. 0:00:22.160 --> 0:00:23.799 That's the part you love the most about it is 0:00:23.880 --> 0:00:26.279 the physics of sailing. Yeah. You know, you've got the 0:00:26.280 --> 0:00:28.120 wind coming in one way and the boat is pointing 0:00:28.160 --> 0:00:30.840 another way, and you have the you know, the keel 0:00:30.960 --> 0:00:34.120 underneath and the rudder. It's a it's a big complicated calculation, 0:00:34.200 --> 0:00:37.040 all happening in real time under you. Yeah, and you 0:00:37.120 --> 0:00:39.279 might die or or get strounded out and see if 0:00:39.320 --> 0:00:41.839 you if you mess it up, that's right, that's right. 0:00:41.880 --> 0:00:45.479 So physics can save your life. It's good to understand vectors. 0:00:45.560 --> 0:00:47.600 But no, yeah, I always find it really confusing. You know. 0:00:47.680 --> 0:00:49.199 It's like if you want to go one way, you 0:00:49.240 --> 0:00:51.440 actually have to point the boat the other way. But 0:00:51.440 --> 0:00:53.479 then you have to move the sail in line with 0:00:53.600 --> 0:00:55.800 the wind, and so there's like the Bernoulli effect that 0:00:55.840 --> 0:00:57.880 I just I found it. What we're really confusing? It 0:00:57.960 --> 0:01:00.520 is confusing basically, Um, you know, all you need to 0:01:00.560 --> 0:01:02.080 know is if you want to go one way. Make 0:01:02.080 --> 0:01:04.520 sure you point the boat a different direction, right, That's 0:01:04.560 --> 0:01:07.240 the only way to get there. Never never point to 0:01:07.280 --> 0:01:26.880 where you're going. No, that's classic groupie mistake. Him Orgey, 0:01:26.880 --> 0:01:29.800 I'm a cartoonist and the creator of PhD Comics. Hi, 0:01:29.920 --> 0:01:33.119 I'm Daniel. I'm a particle physicist and the co author 0:01:33.160 --> 0:01:36.240 of our book Together We Have No Idea, A Guide 0:01:36.240 --> 0:01:39.080 to the Unknown Universe. Right now, you're listening to our podcast, 0:01:39.160 --> 0:01:42.600 Daniel and Jorge Explain the Universe, a production of I 0:01:42.760 --> 0:01:47.120 Heart Radio, in which we try to find weird, crazy, wacky, interesting, 0:01:47.160 --> 0:01:50.240 amazing things about the universe that will blow your mind 0:01:50.320 --> 0:01:52.160 and explain them to you in a way that makes 0:01:52.160 --> 0:01:55.080 you understand them and also laugh along the way. That's right. 0:01:55.120 --> 0:01:57.400 We take you to all the corners of the universe 0:01:57.440 --> 0:02:02.320 in rockets, in spaceships, in warp drives potentially, and also 0:02:02.400 --> 0:02:06.200 maybe using sailboats. That's right. We want to navigate your 0:02:06.240 --> 0:02:09.160 brain from here to there and all around, and we're 0:02:09.160 --> 0:02:12.320 willing to do in any sort of mental capsule that's possible. 0:02:12.400 --> 0:02:14.080 And so today on the program, we're going to be 0:02:14.080 --> 0:02:17.440 answering a listener question, who was wondering if there are 0:02:17.560 --> 0:02:21.360 better ways to travel through space. That's right. You guys 0:02:21.400 --> 0:02:23.880 might be familiar with the question of how do we 0:02:23.919 --> 0:02:26.399 get from here to there? Right? And if you want 0:02:26.400 --> 0:02:28.880 to fly from Earth to Mars, or Earth to Jupiter, 0:02:29.120 --> 0:02:32.239 or even do another star, you gotta push yourself there, 0:02:32.320 --> 0:02:35.040 or you gotta get your ship going at a certain speed, 0:02:35.080 --> 0:02:38.440 and that requires energy. And most of the technologies that 0:02:38.480 --> 0:02:41.560 we have currently are basically just like a fire spewing 0:02:41.560 --> 0:02:43.799 out the back, and that requires some sort of fuel. 0:02:44.000 --> 0:02:46.240 That's right, you need fuel, And unfortunately there are no 0:02:46.360 --> 0:02:49.200 gas stations between here and Mars, and so that you 0:02:49.240 --> 0:02:50.800 kind of have to bring it all with you. But 0:02:50.840 --> 0:02:53.560 there might be Tesla supercharger stations for all we know. Right, 0:02:53.600 --> 0:02:56.000 isn't that Elon Musk's plan? How does that company doing 0:02:56.080 --> 0:02:59.360 these days? I haven't really checked my stock portfolio, but 0:02:59.800 --> 0:03:02.320 you know, the guy thinks big. So probably as SpaceX 0:03:02.360 --> 0:03:04.720 goes to Mars, he's gonna stop along the way and leave, 0:03:04.760 --> 0:03:07.079 you know, charging stations. Yeah. So to the end the program, 0:03:07.080 --> 0:03:10.200 we'll be talking about an interesting idea about traveling to 0:03:10.240 --> 0:03:18.959 the stars. We'll be talking about solar sales. How do 0:03:19.040 --> 0:03:23.320 they work? Do you really sale our solar cells on sale. Right, 0:03:23.400 --> 0:03:25.280 how did what does this thing even mean? That'd be 0:03:25.360 --> 0:03:28.120 nice if they're on sale, everyone can get one, that's right. 0:03:28.680 --> 0:03:31.160 That's right, more than just our listeners in Delaware. Remember 0:03:31.160 --> 0:03:33.160 that podcast when we were going to cover the state 0:03:33.160 --> 0:03:35.680 of Delaware with solar cells. Oh? Yeah, do we get 0:03:35.680 --> 0:03:40.200 any feedback from delawareans? Oh? Actually we did. Um. First 0:03:40.240 --> 0:03:42.960 of all, they commented that we need to also include Maryland. 0:03:43.480 --> 0:03:45.640 And they weren't defended at all. Actually, they were just 0:03:45.680 --> 0:03:47.760 glad to have any sort of Delaware shout out. They 0:03:47.800 --> 0:03:50.720 say that they don't often get mentioned. Never happens. I 0:03:50.720 --> 0:03:54.840 guess exactly. So we love you, Delaware. Keep listening. Yeah, 0:03:54.880 --> 0:03:57.320 so it's kind of an interesting idea that you can 0:03:57.480 --> 0:04:02.000 make a sale to sale all the deep blue blackness 0:04:02.000 --> 0:04:04.360 of space. Yeah, it's really kind of an awesome idea. 0:04:04.600 --> 0:04:07.120 I mean, you're we're familiar with the wind, right, and 0:04:07.400 --> 0:04:09.720 the wind is a wonderful way to use a sailboat 0:04:09.760 --> 0:04:12.040 because you don't have to bring any fuel with you. Right, 0:04:12.320 --> 0:04:14.080 you go on a motor boat, you've got to bring 0:04:14.080 --> 0:04:16.040 all that fuel with you. It makes your boat heavier, 0:04:16.120 --> 0:04:19.560 it's loud, it's noisy, is obnoxious. Right, One of the 0:04:19.600 --> 0:04:22.360 things I love about sailing is that it's quiet. Right. 0:04:22.480 --> 0:04:23.960 First of all, you don't have to fuel up because 0:04:23.960 --> 0:04:26.360 your fuel is just the wind. And then when you're sailing, 0:04:26.360 --> 0:04:29.719 there's no obnoxious motor sound to listen to. So the 0:04:29.760 --> 0:04:32.720 idea of traveling from one planet to another through space 0:04:33.240 --> 0:04:37.040 using something similar like being propelled without bringing along your 0:04:37.040 --> 0:04:39.440 own fuel, it's a beautiful idea. Yeah, it's kind of 0:04:39.440 --> 0:04:42.480 cool to think that you can ride something out in space, right, 0:04:42.480 --> 0:04:45.719 Like there's something already going there and you can just 0:04:45.760 --> 0:04:47.479 kind of latch onto it and will push you to 0:04:47.520 --> 0:04:49.080 where you want to go. That's right. And you might 0:04:49.120 --> 0:04:52.680 be tempted to say, what's pushing the sail, Like obviously 0:04:52.720 --> 0:04:55.360 on Earth here it's air, But what's pushing your sail 0:04:55.400 --> 0:04:57.520 out in space? Because there's no air in space and 0:04:57.520 --> 0:04:59.960 you're right, right if we're not sailing in that same way. 0:05:00.480 --> 0:05:02.360 And then you might be tempted to say, what about 0:05:02.400 --> 0:05:04.560 the solar wind? These guys have told us about all 0:05:04.560 --> 0:05:07.359 the particles shooting out from the Sun, Is that the 0:05:07.400 --> 0:05:09.880 solar wind that a solar sale would be riding. But 0:05:09.960 --> 0:05:12.479 that's not even the case. It's not it's not the 0:05:12.520 --> 0:05:15.200 solar wind that a solar sale works off of though 0:05:15.200 --> 0:05:18.400 that would be some sort of poetic you know, beautiful parallel. Wait, 0:05:18.440 --> 0:05:20.880 so it's not the solar wind that you would sail 0:05:20.920 --> 0:05:24.160 on in space. No, it seems tempting, right, you'd like 0:05:24.200 --> 0:05:27.679 to have a solar sail boat using the solar wind 0:05:27.920 --> 0:05:31.080 for this beautiful analogy for our whiskey fueled adventures on 0:05:31.120 --> 0:05:33.800 the high seas here. But it's not actually the solar 0:05:33.839 --> 0:05:36.320 wind that pushes along a solar sail. Oh man. The 0:05:36.320 --> 0:05:39.200 solar wind does it give you a sunburn and chapped 0:05:39.200 --> 0:05:43.479 lips at the same time? That's right, It gives you 0:05:43.520 --> 0:05:46.400 that solar wind touseled hair. Also you have deep fried 0:05:46.680 --> 0:05:51.800 probably exactly not recommended, folks, not recommended. It's like a 0:05:51.800 --> 0:05:55.560 Brazilian blowout. But um, Chris here, if you're listening to 0:05:55.600 --> 0:05:57.719 this podcast on the space station, do not stick your 0:05:57.760 --> 0:06:01.080 head at the window to get a solar wind tewseled look. Yeah, instead, right, 0:06:01.160 --> 0:06:02.880 is because that'd be really cool to hear from you, 0:06:03.200 --> 0:06:06.520 exactly exactly. Yeah, So we'll be talking to me about 0:06:06.560 --> 0:06:10.600 the solar sales, the idea that you can go between 0:06:10.640 --> 0:06:14.000 planets or stars or galaxies using a sale to catch 0:06:14.200 --> 0:06:16.800 something out there in space to take you there. And so, 0:06:16.839 --> 0:06:19.239 as we mentioned, this question came to us from Derek 0:06:19.320 --> 0:06:22.400 from Cleveland, and so here is Derek asking his question. Hey, 0:06:22.480 --> 0:06:25.880 Daniel Jorge, this is Derek from Cleveland, Ohio. My question 0:06:25.960 --> 0:06:28.840 is how does solar sales work if photons are massless? 0:06:28.920 --> 0:06:31.440 How can they impart momentum to a satellite? And how 0:06:31.560 --> 0:06:34.760 is the conservation of momentum upheld? I quickly want to 0:06:34.800 --> 0:06:36.680 say hi to my brother in law, Tim, who I'm 0:06:36.720 --> 0:06:39.080 sure we'll listen and discuss your answer with me later. 0:06:39.360 --> 0:06:41.480 Thanks guys, All right, thank you Derek. That's a pretty 0:06:41.520 --> 0:06:44.719 interesting question. I mean, it's it's sort of um. It 0:06:44.760 --> 0:06:46.840 sounds like he's heard of solar sales and he knows 0:06:46.920 --> 0:06:50.680 they work by catching light, but his question was how 0:06:50.680 --> 0:06:53.160 does that work if photons have no mass? Yeah, so 0:06:53.160 --> 0:06:55.560 many good questions here, right, like how does the solar 0:06:55.600 --> 0:06:58.440 sale work? He seems to understand that it catches light, 0:06:58.680 --> 0:07:01.920 but it doesn't understand like does light half momentum because 0:07:01.960 --> 0:07:06.040 he's probably thinking that momentum is mass times velocity, right, 0:07:06.080 --> 0:07:09.160 which is the case for slow moving massive objects. So 0:07:09.200 --> 0:07:11.840 he's wondering if the mass term is zero, how can 0:07:11.880 --> 0:07:13.720 you have any momentum, Like, how do things with no 0:07:13.840 --> 0:07:16.240 mass have any momentum? And if they have meantum, if 0:07:16.240 --> 0:07:18.320 they don't have momentum, how can they push along a 0:07:18.400 --> 0:07:20.680 solar sale? It's a great question, right, I mean, I 0:07:20.720 --> 0:07:23.160 think it means, like, you know, if light has nothing 0:07:23.280 --> 0:07:25.800 to it in terms of like mass, how can it 0:07:25.880 --> 0:07:28.840 push you? Exactly? That's the question. And so I was 0:07:28.920 --> 0:07:31.800 wondering what people thought about this. So people aware of 0:07:31.800 --> 0:07:34.840 solar sales do they understand photons and momentum and all 0:07:34.840 --> 0:07:37.200 this kind of stuff. And so I went around and 0:07:37.240 --> 0:07:40.360 I asked people, um what they knew about solar sales. 0:07:40.640 --> 0:07:42.720 And before you listen to these answers, think to yourself, 0:07:42.800 --> 0:07:45.000 do you know how a solar sale works? Do you 0:07:45.080 --> 0:07:47.880 understand how light can have momentum if it doesn't have mass. 0:07:47.920 --> 0:07:50.080 Here's what they had to say. I feel like I've 0:07:50.120 --> 0:07:51.600 heard of it, but I'm not sure. I mean, I've 0:07:51.640 --> 0:07:54.920 seen like six once, but I haven't seen I know 0:07:54.960 --> 0:07:58.600 that they're kind of transitioning like testas doing the roof 0:07:58.720 --> 0:08:01.360 tiles and stuff that I was sore, but I don't 0:08:02.120 --> 0:08:05.800 I don't know if I've seen a big pike. I 0:08:05.840 --> 0:08:08.720 guess kind of like sheet of sunlight. Yes, actually I 0:08:08.800 --> 0:08:12.120 have a solar sale is basically a really big sale 0:08:12.360 --> 0:08:14.880 that doesn't get pushed by wind. It gets pushed by 0:08:15.120 --> 0:08:18.400 energy from the sun. So basically energy has a little 0:08:18.440 --> 0:08:22.160 bit of movement in it, and that big movement, a 0:08:22.200 --> 0:08:24.640 little bit of movement can push it because it's not 0:08:24.720 --> 0:08:27.440 too much movement, but it's a lot of energy in 0:08:27.880 --> 0:08:30.560 a big area that that will push it. I'm honestly 0:08:30.560 --> 0:08:33.320 not sure. I couldn't even I couldn't mean guess like 0:08:33.520 --> 0:08:36.760 maybe the stilted price on solar system or something like that. 0:08:38.559 --> 0:08:41.280 All right, I love these answers or I feel like 0:08:41.280 --> 0:08:46.199 they're all correct. Like is it a boat powered by 0:08:46.200 --> 0:08:50.000 solar power? Yes, technically that would be a solar That 0:08:50.000 --> 0:08:52.160 would be like a boat with an electric engine on 0:08:52.200 --> 0:08:56.040 it that's powered by solar cells. That's pretty cool. Yeah, sure, yeah, 0:08:56.080 --> 0:08:59.319 that's like a solar boat for sure. Or like a discount, 0:08:59.480 --> 0:09:02.040 I don't think is it? Is it like a discount 0:09:02.040 --> 0:09:04.880 on solar panel? I think like a solar sale. I 0:09:04.920 --> 0:09:06.720 think that guy might have thought I was actually trying 0:09:06.720 --> 0:09:09.240 to sell him solar panels, like he looked kind of wary. 0:09:09.280 --> 0:09:12.480 He's like, are you another one of those shady solar 0:09:12.520 --> 0:09:18.000 salesman discounts. They are pretty shady quote unquote, that's right exactly. 0:09:18.120 --> 0:09:20.160 Their business wouldn't stand up to sunlight. You have to 0:09:20.160 --> 0:09:23.120 be pretty bright. And there was one folk, one guy 0:09:23.120 --> 0:09:25.559 who actually had a pretty solid answer. Was this your 0:09:25.640 --> 0:09:29.200 physics student sale and slash sale instructor? It was not. 0:09:29.720 --> 0:09:32.080 Actually that was my eleven year old son, who I 0:09:32.120 --> 0:09:35.160 think overheard me talking about solar sales to somebody else 0:09:35.200 --> 0:09:37.360 before I asked him, so he had a preview of 0:09:37.400 --> 0:09:40.120 the answer and just wound wanted to sound smart. You're 0:09:40.160 --> 0:09:44.000 saying your son cheated, I'm saying I asked him the question, 0:09:44.000 --> 0:09:45.720 and he knew the answer, and so he answered it. 0:09:48.800 --> 0:09:51.079 That's right, it's it wasn't a test. Yeah, he had 0:09:51.120 --> 0:09:53.200 a bit more of a head start than the rest 0:09:53.200 --> 0:09:55.200 of the other folks that we asked. So, um, it's 0:09:55.200 --> 0:09:56.880 not something that a lot of people seem to know 0:09:56.920 --> 0:09:59.679 about or recognize the name of. That's right. It's not 0:09:59.720 --> 0:10:01.640 a in concept. And that surprised me a little bit 0:10:01.720 --> 0:10:05.280 because I thought that people had heard more about like 0:10:05.320 --> 0:10:07.600 how to move through space or the kinds of engines 0:10:07.679 --> 0:10:10.000 you might use. But I guess not which makes an 0:10:10.040 --> 0:10:12.880 excellent topic for today's podcast. Yeah. Well, I have to 0:10:12.920 --> 0:10:16.960 admit my only reference to a solar sale powered spaceship 0:10:17.240 --> 0:10:19.480 is from Star Wars. Do they do solar sales? And 0:10:19.520 --> 0:10:21.200 Star Wars? I don't even remember that. I thought they 0:10:21.240 --> 0:10:24.720 all had ion engines and stuff. Yeah, I know. I mean, 0:10:24.760 --> 0:10:27.800 if you if you've watched the prequels, which I'm sure 0:10:27.880 --> 0:10:30.720 we can get into a whole episode about. But count 0:10:30.720 --> 0:10:33.640 Dooku with that character has rise around in a ship 0:10:33.760 --> 0:10:36.840 that has solar sales or what looks like what looked 0:10:36.880 --> 0:10:38.960 like solar sales. Oh my gosh. Why you have like 0:10:38.960 --> 0:10:41.920 an encyclopedic knowledge of all the ships in every science 0:10:41.920 --> 0:10:46.120 fiction movie ever. That's that's impressive. And I have an 0:10:46.200 --> 0:10:50.719 encyclopedic knowledge of all NERD movies. So that's what That's 0:10:50.760 --> 0:10:52.360 what you do it for In the afternoon when you're 0:10:52.480 --> 0:10:54.400 not feeling in the mood to do cartooning, it's like 0:10:54.679 --> 0:10:57.800 turn on some science fiction movie. Yeah, isn't that what 0:10:57.840 --> 0:11:02.719 everybody does? Yes, yes, that is exactly what everybody does 0:11:02.760 --> 0:11:05.520 in the middle of the afternoon. Um, no, but you're right, 0:11:05.600 --> 0:11:07.959 these things are in science fiction. Um. I've read lots 0:11:08.000 --> 0:11:11.400 of books with solar sale powered chips in them. Uh, 0:11:11.440 --> 0:11:13.840 it's a pretty common idea in terms of like how 0:11:13.880 --> 0:11:15.120 to get from here to there. And you know what, 0:11:15.160 --> 0:11:17.400 we don't have that many ideas for how to get 0:11:17.480 --> 0:11:20.160 from one planet to another or one star to another, 0:11:20.640 --> 0:11:22.679 and so it's on a pretty short list. Well, this 0:11:22.720 --> 0:11:24.480 is how it kind of worked in Star Wars. So 0:11:24.600 --> 0:11:27.600 count get on this ship. He takes off, he flies 0:11:27.679 --> 0:11:30.880 up into orbit or space, and then he like unfurls 0:11:30.960 --> 0:11:35.199 this huge giant sail, this like giant sheet that looks 0:11:35.280 --> 0:11:37.640 kind of like it's made out of gold, and then 0:11:37.679 --> 0:11:40.280 then he starts going. So it's like he's it's like 0:11:40.280 --> 0:11:43.120 he opened a giant umbrella and then that pushed him forward. Yeah, 0:11:43.160 --> 0:11:46.680 that's basically a solar sales are giant umbrellas. Podcast over, 0:11:47.000 --> 0:11:53.600 you nailed it Star Wars for the wind. Yeah, let's 0:11:53.600 --> 0:11:55.760 get into it, Daniel. What is a solar sale? So 0:11:55.800 --> 0:11:59.200 a solar sale is an enormous flat sheet, just like 0:11:59.240 --> 0:12:01.600 a sail on a sale boat. Um, and the thing 0:12:01.640 --> 0:12:05.079 that it captures is not wind like in air, because 0:12:05.080 --> 0:12:07.079 there is no wind in space and it's not the 0:12:07.120 --> 0:12:10.360 solar wind because the solar wind member is protons being 0:12:10.360 --> 0:12:13.520 shot out by the Sun and those could push the sail, 0:12:13.559 --> 0:12:15.520 but there's just not that much of them. There's just 0:12:15.559 --> 0:12:17.320 not that many of them. There's not enough of them. 0:12:17.640 --> 0:12:20.880 What is capturing is light. So the light from the 0:12:20.920 --> 0:12:23.520 sun is zooming out from the Sun and it's carrying 0:12:23.600 --> 0:12:25.680 energy with it, and we'll dig into that in a moment. 0:12:25.720 --> 0:12:28.079 But photons have momentum, and so what happens when they 0:12:28.280 --> 0:12:31.240 hit the sail is that they give it a little push, 0:12:31.440 --> 0:12:34.160 and you get enough little pushes and you can actually 0:12:34.200 --> 0:12:36.320 get going somewhere. So this is a real thing, like 0:12:36.400 --> 0:12:41.160 people have built these, Like there are functioning solar wind 0:12:42.040 --> 0:12:44.760 sailboats out there in space. Um, yes, this is a 0:12:44.840 --> 0:12:47.400 real thing. It's like physics says, there's no reason why 0:12:47.440 --> 0:12:51.079 I shouldn't work. People have big plans to make huge 0:12:51.080 --> 0:12:53.320 solar sales that can go all around the Solar System 0:12:53.400 --> 0:12:57.000 or maybe even to other stars. And somebody has actually 0:12:57.040 --> 0:12:59.160 built one of these things and made it work. The 0:12:59.280 --> 0:13:03.079 Japanese they launched one um several years ago and showed 0:13:03.080 --> 0:13:05.520 that it actually worked. Like the physics isn't just theoretical, 0:13:05.600 --> 0:13:08.280 Like there is one thing out there that's solar sailing 0:13:08.360 --> 0:13:13.000 right now, that's pretty cool the Japanese. The Japanese, nice job. 0:13:13.320 --> 0:13:16.920 But the thing about solar sales is that it's gentle, right, 0:13:17.160 --> 0:13:20.600 It's not really really powerful winds of light out there 0:13:20.640 --> 0:13:22.920 for you to capture with your sales. So if you 0:13:22.960 --> 0:13:26.800 have like even a really big sale, like eight hundred 0:13:26.840 --> 0:13:30.080 meters by eight hundred meters, which is you know, enormous, right, 0:13:30.559 --> 0:13:33.760 then that only gets five newton's of force, And five 0:13:33.760 --> 0:13:36.679 newtons is not that much. It's like how much you know, 0:13:36.960 --> 0:13:39.800 a fourth there isn't like a one pound object on Earth, 0:13:40.280 --> 0:13:43.440 So like a one pound rock, you know, think about 0:13:43.440 --> 0:13:45.400 how much that feels in your hand. That's the force 0:13:45.800 --> 0:13:48.280 of the Earth's gravity on a one pound rock. That's 0:13:48.280 --> 0:13:51.199 the same amount of force that the Sun would push 0:13:51.320 --> 0:13:54.720 on a eight hundred meter by eight hundred meters sail 0:13:55.000 --> 0:13:58.200 about the distance from of the Earth, which is huge, right, 0:13:58.240 --> 0:14:00.920 I mean it's a several city blocks. Yeah, that is 0:14:00.960 --> 0:14:04.160 not a small thing to build and to unferral and 0:14:04.200 --> 0:14:07.040 to keep from getting shredded right by like micro meteorites 0:14:07.120 --> 0:14:10.360 or whatever. But you're saying if I made a tarp 0:14:10.960 --> 0:14:14.959 that was about a kilometer on each side over Manhattan, 0:14:15.679 --> 0:14:17.600 it would get pushed down not just by the weight 0:14:17.600 --> 0:14:20.400 of it, but also by the sun that's hitting it. Yes, exactly, 0:14:20.640 --> 0:14:24.400 And every time a photon hits you, you're getting pushed. Like. 0:14:24.440 --> 0:14:29.000 Photons are actually pushy. They are kind of rude, aren't they. 0:14:29.240 --> 0:14:31.280 They just like zoom along wherever they want to go. 0:14:31.360 --> 0:14:33.840 They don't ask questions, they don't take turns, or they 0:14:33.880 --> 0:14:37.600 just going straight lines wherever they need to know. Photons 0:14:37.680 --> 0:14:40.320 care momentum, and every time they hit something, they give 0:14:40.360 --> 0:14:42.200 it a little push. So when you turn, when you 0:14:42.200 --> 0:14:44.640 flip the switch and turn on the light, you get 0:14:44.680 --> 0:14:47.440 pushed down a tiny little bit. And you might think, what, 0:14:47.680 --> 0:14:50.040 I can't feel it, And you're right because it's a 0:14:50.040 --> 0:14:53.120 small effect, which is why solar sales are very gentle, 0:14:53.200 --> 0:14:55.360 and you need a huge one to add up to 0:14:55.400 --> 0:14:58.480 any measurable force. Well, let's step us through a little 0:14:58.520 --> 0:14:59.880 bit of how this works. I mean, so you're saying, 0:14:59.880 --> 0:15:02.080 if I take a flashlight and I flash it at you, 0:15:02.360 --> 0:15:05.440 I am technically kind of pushing you with it. You're 0:15:05.440 --> 0:15:09.840 basically punching me in the face with light. Yeah. Yeah, 0:15:09.880 --> 0:15:11.880 that's that's really me because we don't think of light 0:15:11.920 --> 0:15:14.600 as having substance to it, right, Like you I mean, 0:15:14.640 --> 0:15:17.200 we know we sort of associated with energy and heat 0:15:17.280 --> 0:15:20.520 and warmth, but not um force. That's right. We don't 0:15:20.520 --> 0:15:23.120 think of photons is having mass because they don't, but 0:15:23.160 --> 0:15:26.160 they do have energy, right, Photons are energies is just 0:15:26.360 --> 0:15:29.960 pure energy. And if you have energy, that means you 0:15:30.040 --> 0:15:33.520 have momentum. And it's complicated because we're only used to 0:15:33.560 --> 0:15:36.360 thinking about things having momentum when they have mass. We 0:15:36.400 --> 0:15:39.320 think about you give something momentum because it's heavy and 0:15:39.360 --> 0:15:41.320 it's hard to get going, and once you've pushed it, 0:15:41.320 --> 0:15:44.760 it keeps going. It has momentum. Right, So something that's 0:15:44.800 --> 0:15:47.840 like light and fluffy and you know, weighs nothing, it's 0:15:47.840 --> 0:15:50.240 hard to understand how that can have momentum. Well, I 0:15:50.280 --> 0:15:52.240 think I think we're all pretty familiar with like if 0:15:52.280 --> 0:15:54.720 I shine a flashlight on you or a laser, like 0:15:54.800 --> 0:15:57.960 your body is gonna absorb that energy or you know, 0:15:58.040 --> 0:16:00.360 warm up a little bit or something. But you're saying 0:16:00.400 --> 0:16:02.600 that if I have an atom on my skin and 0:16:02.880 --> 0:16:06.040 you're flashing a flashlight on it, the photons actually sort 0:16:06.040 --> 0:16:07.880 of hit it and the atom wants to go the 0:16:07.920 --> 0:16:11.440 other way. Yes, exactly. Think about what happens with a mirror, right, 0:16:11.680 --> 0:16:13.840 it's a little bit more complicated when the light gets absorbed. 0:16:13.840 --> 0:16:15.800 So let's think about a mirror where the light gets reflected, 0:16:16.240 --> 0:16:18.720 the light zooming in one direction, it hits the mirror, 0:16:18.760 --> 0:16:21.200 and the lights going in the other direction. Right, how 0:16:21.240 --> 0:16:24.680 does the light change direction? Right? What changes the direction 0:16:24.680 --> 0:16:27.840 of the light. It's the mirror. Instead of thinking about 0:16:28.280 --> 0:16:30.160 light in a mirror, think about a ping pong ball 0:16:30.200 --> 0:16:32.680 and a paddle. Right, if you get hit. If a 0:16:32.720 --> 0:16:35.400 ping pong paddle gets hit by the ball, then the 0:16:35.440 --> 0:16:38.040 ball bounces the other direction, but the paddle gets pushed 0:16:38.040 --> 0:16:41.720 back a little bit. Right, That balances the momentum. Momentum 0:16:41.760 --> 0:16:44.360 is conserved. So in the same way, when the light 0:16:44.440 --> 0:16:46.800 hits the mirror, it gives that mirror a little push, 0:16:46.800 --> 0:16:49.560 and the mirror pushes back, and that's what turns the 0:16:49.680 --> 0:16:52.360 light the other direction. And so when light reflects off 0:16:52.360 --> 0:16:55.240 of something, it's giving it a little push. So pure 0:16:55.320 --> 0:16:58.800 energy can push you basically exactly. It can result in 0:16:58.960 --> 0:17:01.800 something wanting to move the other way. That's right. And 0:17:01.800 --> 0:17:03.560 this is one of the cool things in physics when 0:17:03.560 --> 0:17:06.080 you learn that a concept you thought you had a 0:17:06.119 --> 0:17:09.320 firm grasp on, like momentum, is actually just a special 0:17:09.359 --> 0:17:11.919 case of sort of a larger concept. Like we're familiar 0:17:11.960 --> 0:17:15.480 with momentum is mass times velocity. But that's not it's definition. 0:17:15.520 --> 0:17:19.480 That's just how you calculated for slow moving things with mass. 0:17:20.040 --> 0:17:22.480 You can calculate momentum for things that don't have mass, 0:17:22.520 --> 0:17:26.080 because momentum is a larger concept. It's just it captures 0:17:26.119 --> 0:17:29.320 like the quantity of motion of something, not just it's 0:17:29.359 --> 0:17:31.639 mass times velocity. It's just that it's more like the 0:17:31.640 --> 0:17:34.399 total energy. Yeah, but it's fascinating because energy is just 0:17:34.440 --> 0:17:37.199 a number. It doesn't have a direction, right, and physics 0:17:37.320 --> 0:17:40.359 energies is a scaler, not a vector, like it doesn't 0:17:40.400 --> 0:17:43.880 have a direction, just a magnitude, whereas momentum has a direction. 0:17:44.119 --> 0:17:46.800 Like you know, pointed in one direction is different from 0:17:46.800 --> 0:17:51.200 pointed in the other direction. Right, Uh, light has momentum. 0:17:51.320 --> 0:17:54.000 Light has momentum, has energy, and it has momentum and 0:17:54.040 --> 0:17:56.520 it has no mass. One way that some people like 0:17:56.640 --> 0:17:59.880 to think about it is you can think about momentum 0:18:00.040 --> 0:18:02.720 sort of the difference between the energy and the mass. 0:18:03.000 --> 0:18:04.960 Right because in real and relativity we think of the 0:18:04.960 --> 0:18:08.040 total energy as the energy store in the mass plus 0:18:08.080 --> 0:18:10.159 the energy of the momentum. So you can sort of 0:18:10.200 --> 0:18:13.200 invert that equation and say the momentum is the difference 0:18:13.440 --> 0:18:15.879 between the total energy and the mass. And in the 0:18:15.880 --> 0:18:18.439 case of the photon, there is no mass. Momentum just 0:18:18.560 --> 0:18:21.719 comes from the energy, whereas in the case of another particle, right, 0:18:21.720 --> 0:18:23.200 it has a bunch of energy. Some of that is 0:18:23.240 --> 0:18:25.040 in the mass and some of it is in its motion. 0:18:25.480 --> 0:18:27.919 But for the photon, all the energy is just in 0:18:27.920 --> 0:18:30.080 its motion, so it just has momentum and no mass. 0:18:30.320 --> 0:18:33.280 All right. Solar sales are a real thing, and they 0:18:33.320 --> 0:18:37.640 work by taking the momentum that's in light, absorbing it 0:18:37.800 --> 0:18:40.399 and then using that to push you along in space. 0:18:40.600 --> 0:18:42.760 That's right, And it's the light from the Sun that's 0:18:42.760 --> 0:18:45.239 doing this, not the protons from the solar wind. And 0:18:45.320 --> 0:18:47.560 everybody actually can see this if you just have seen 0:18:47.560 --> 0:18:50.080 a comet. You know, comet is just a big ice 0:18:50.119 --> 0:18:52.280 ball and it falls towards the Sun and as it 0:18:52.320 --> 0:18:55.280 does so it gets a big tail, right, and that's 0:18:55.320 --> 0:18:57.520 the tail of it, like the stuff melting and dripping 0:18:57.520 --> 0:18:59.960 out the back, and the tail points in a specific 0:19:00.000 --> 0:19:02.920 direction away from the Sun, not in the direction of motion. 0:19:02.960 --> 0:19:05.320 People think, like, you know, it's like a fuzzy lines 0:19:05.400 --> 0:19:08.200 behind something that's moving fast. But the commet actually always 0:19:08.200 --> 0:19:11.680 points away from the Sun, and that's because of this 0:19:11.800 --> 0:19:15.080 effect of light. That's light pushing the tail of the commet. Really, 0:19:15.119 --> 0:19:17.040 it's not like a trail of a dust that you 0:19:17.119 --> 0:19:19.560 leave behind. No, Because as the common is moving towards 0:19:19.600 --> 0:19:21.720 the Sun, the tail is behind it. But as the 0:19:21.760 --> 0:19:24.320 comet goes around the Sun and then leaves, the tails 0:19:24.359 --> 0:19:27.240 in front of it. Wow, so it shouldn't be called 0:19:27.280 --> 0:19:32.080 the tail once again? Yeah, I guess. Or maybe it's 0:19:32.080 --> 0:19:34.040 like backing away from the Sun as it leaves. It's 0:19:34.080 --> 0:19:36.840 like whoa, that was close. All right, let's get into 0:19:37.040 --> 0:19:40.400 will it work and how how can we make it work? 0:19:40.520 --> 0:19:55.040 But first let's take a quick break. All right. So 0:19:55.080 --> 0:19:58.000 that's solar sales Daniel. That's pretty cool. The question now, 0:19:58.040 --> 0:20:00.640 I think is does it work? If you build it, 0:20:00.640 --> 0:20:04.120 will it take us to other planets and maybe other galaxies? Yeah, 0:20:04.160 --> 0:20:05.919