Speaker 1: Hey, Daniel, you like the outdoors. You're an outdoorsy kind
Speaker 1: of person. Are you a fan of sailing? Oh? Man,
Speaker 1: I love sailing. There's so much to appreciate, the wind,
Speaker 1: the quiet, But mostly it's because it's about applied physics.
Speaker 1: That's the part you love the most about it is
Speaker 1: the physics of sailing. Yeah. You know, you've got the
Speaker 1: wind coming in one way and the boat is pointing
Speaker 1: another way, and you have the you know, the keel
Speaker 1: underneath and the rudder. It's a it's a big complicated calculation,
Speaker 1: all happening in real time under you. Yeah, and you
Speaker 1: might die or or get strounded out and see if
Speaker 1: you if you mess it up, that's right, that's right.
Speaker 1: So physics can save your life. It's good to understand vectors.
Speaker 1: But no, yeah, I always find it really confusing. You know.
Speaker 1: It's like if you want to go one way, you
Speaker 1: actually have to point the boat the other way. But
Speaker 1: then you have to move the sail in line with
Speaker 1: the wind, and so there's like the Bernoulli effect that
Speaker 1: I just I found it. What we're really confusing? It
Speaker 1: is confusing basically, Um, you know, all you need to
Speaker 1: know is if you want to go one way. Make
Speaker 1: sure you point the boat a different direction, right, That's
Speaker 1: the only way to get there. Never never point to
Speaker 1: where you're going. No, that's classic groupie mistake. Him Orgey,
Speaker 1: I'm a cartoonist and the creator of PhD Comics. Hi,
Speaker 1: I'm Daniel. I'm a particle physicist and the co author
Speaker 1: of our book Together We Have No Idea, A Guide
Speaker 1: to the Unknown Universe. Right now, you're listening to our podcast,
Speaker 1: Daniel and Jorge Explain the Universe, a production of I
Speaker 1: Heart Radio, in which we try to find weird, crazy, wacky, interesting,
Speaker 1: amazing things about the universe that will blow your mind
Speaker 1: and explain them to you in a way that makes
Speaker 1: you understand them and also laugh along the way. That's right.
Speaker 1: We take you to all the corners of the universe
Speaker 1: in rockets, in spaceships, in warp drives potentially, and also
Speaker 1: maybe using sailboats. That's right. We want to navigate your
Speaker 1: brain from here to there and all around, and we're
Speaker 1: willing to do in any sort of mental capsule that's possible.
Speaker 1: And so today on the program, we're going to be
Speaker 1: answering a listener question, who was wondering if there are
Speaker 1: better ways to travel through space. That's right. You guys
Speaker 1: might be familiar with the question of how do we
Speaker 1: get from here to there? Right? And if you want
Speaker 1: to fly from Earth to Mars, or Earth to Jupiter,
Speaker 1: or even do another star, you gotta push yourself there,
Speaker 1: or you gotta get your ship going at a certain speed,
Speaker 1: and that requires energy. And most of the technologies that
Speaker 1: we have currently are basically just like a fire spewing
Speaker 1: out the back, and that requires some sort of fuel.
Speaker 1: That's right, you need fuel, And unfortunately there are no
Speaker 1: gas stations between here and Mars, and so that you
Speaker 1: kind of have to bring it all with you. But
Speaker 1: there might be Tesla supercharger stations for all we know. Right,
Speaker 1: isn't that Elon Musk's plan? How does that company doing
Speaker 1: these days? I haven't really checked my stock portfolio, but
Speaker 1: you know, the guy thinks big. So probably as SpaceX
Speaker 1: goes to Mars, he's gonna stop along the way and leave,
Speaker 1: you know, charging stations. Yeah. So to the end the program,
Speaker 1: we'll be talking about an interesting idea about traveling to
Speaker 1: the stars. We'll be talking about solar sales. How do
Speaker 1: they work? Do you really sale our solar cells on sale. Right,
Speaker 1: how did what does this thing even mean? That'd be
Speaker 1: nice if they're on sale, everyone can get one, that's right.
Speaker 1: That's right, more than just our listeners in Delaware. Remember
Speaker 1: that podcast when we were going to cover the state
Speaker 1: of Delaware with solar cells. Oh? Yeah, do we get
Speaker 1: any feedback from delawareans? Oh? Actually we did. Um. First
Speaker 1: of all, they commented that we need to also include Maryland.
Speaker 1: And they weren't defended at all. Actually, they were just
Speaker 1: glad to have any sort of Delaware shout out. They
Speaker 1: say that they don't often get mentioned. Never happens. I
Speaker 1: guess exactly. So we love you, Delaware. Keep listening. Yeah,
Speaker 1: so it's kind of an interesting idea that you can
Speaker 1: make a sale to sale all the deep blue blackness
Speaker 1: of space. Yeah, it's really kind of an awesome idea.
Speaker 1: I mean, you're we're familiar with the wind, right, and
Speaker 1: the wind is a wonderful way to use a sailboat
Speaker 1: because you don't have to bring any fuel with you. Right,
Speaker 1: you go on a motor boat, you've got to bring
Speaker 1: all that fuel with you. It makes your boat heavier,
Speaker 1: it's loud, it's noisy, is obnoxious. Right, One of the
Speaker 1: things I love about sailing is that it's quiet. Right.
Speaker 1: First of all, you don't have to fuel up because
Speaker 1: your fuel is just the wind. And then when you're sailing,
Speaker 1: there's no obnoxious motor sound to listen to. So the
Speaker 1: idea of traveling from one planet to another through space
Speaker 1: using something similar like being propelled without bringing along your
Speaker 1: own fuel, it's a beautiful idea. Yeah, it's kind of
Speaker 1: cool to think that you can ride something out in space, right,
Speaker 1: Like there's something already going there and you can just
Speaker 1: kind of latch onto it and will push you to
Speaker 1: where you want to go. That's right. And you might
Speaker 1: be tempted to say, what's pushing the sail, Like obviously
Speaker 1: on Earth here it's air, But what's pushing your sail
Speaker 1: out in space? Because there's no air in space and
Speaker 1: you're right, right if we're not sailing in that same way.
Speaker 1: And then you might be tempted to say, what about
Speaker 1: the solar wind? These guys have told us about all
Speaker 1: the particles shooting out from the Sun, Is that the
Speaker 1: solar wind that a solar sale would be riding. But
Speaker 1: that's not even the case. It's not it's not the
Speaker 1: solar wind that a solar sale works off of though
Speaker 1: that would be some sort of poetic you know, beautiful parallel. Wait,
Speaker 1: so it's not the solar wind that you would sail
Speaker 1: on in space. No, it seems tempting, right, you'd like
Speaker 1: to have a solar sail boat using the solar wind
Speaker 1: for this beautiful analogy for our whiskey fueled adventures on
Speaker 1: the high seas here. But it's not actually the solar
Speaker 1: wind that pushes along a solar sail. Oh man. The
Speaker 1: solar wind does it give you a sunburn and chapped
Speaker 1: lips at the same time? That's right, It gives you
Speaker 1: that solar wind touseled hair. Also you have deep fried
Speaker 1: probably exactly not recommended, folks, not recommended. It's like a
Speaker 1: Brazilian blowout. But um, Chris here, if you're listening to
Speaker 1: this podcast on the space station, do not stick your
Speaker 1: head at the window to get a solar wind tewseled look. Yeah, instead, right,
Speaker 1: is because that'd be really cool to hear from you,
Speaker 1: exactly exactly. Yeah, So we'll be talking to me about
Speaker 1: the solar sales, the idea that you can go between
Speaker 1: planets or stars or galaxies using a sale to catch
Speaker 1: something out there in space to take you there. And so,
Speaker 1: as we mentioned, this question came to us from Derek
Speaker 1: from Cleveland, and so here is Derek asking his question. Hey,
Speaker 1: Daniel Jorge, this is Derek from Cleveland, Ohio. My question
Speaker 1: is how does solar sales work if photons are massless?
Speaker 1: How can they impart momentum to a satellite? And how
Speaker 1: is the conservation of momentum upheld? I quickly want to
Speaker 1: say hi to my brother in law, Tim, who I'm
Speaker 1: sure we'll listen and discuss your answer with me later.
Speaker 1: Thanks guys, All right, thank you Derek. That's a pretty
Speaker 1: interesting question. I mean, it's it's sort of um. It
Speaker 1: sounds like he's heard of solar sales and he knows
Speaker 1: they work by catching light, but his question was how
Speaker 1: does that work if photons have no mass? Yeah, so
Speaker 1: many good questions here, right, like how does the solar
Speaker 1: sale work? He seems to understand that it catches light,
Speaker 1: but it doesn't understand like does light half momentum because
Speaker 1: he's probably thinking that momentum is mass times velocity, right,
Speaker 1: which is the case for slow moving massive objects. So
Speaker 1: he's wondering if the mass term is zero, how can
Speaker 1: you have any momentum, Like, how do things with no
Speaker 1: mass have any momentum? And if they have meantum, if
Speaker 1: they don't have momentum, how can they push along a
Speaker 1: solar sale? It's a great question, right, I mean, I
Speaker 1: think it means, like, you know, if light has nothing
Speaker 1: to it in terms of like mass, how can it
Speaker 1: push you? Exactly? That's the question. And so I was
Speaker 1: wondering what people thought about this. So people aware of
Speaker 1: solar sales do they understand photons and momentum and all
Speaker 1: this kind of stuff. And so I went around and
Speaker 1: I asked people, um what they knew about solar sales.
Speaker 1: And before you listen to these answers, think to yourself,
Speaker 1: do you know how a solar sale works? Do you
Speaker 1: understand how light can have momentum if it doesn't have mass.
Speaker 1: Here's what they had to say. I feel like I've
Speaker 1: heard of it, but I'm not sure. I mean, I've
Speaker 1: seen like six once, but I haven't seen I know
Speaker 1: that they're kind of transitioning like testas doing the roof
Speaker 1: tiles and stuff that I was sore, but I don't
Speaker 1: I don't know if I've seen a big pike. I
Speaker 1: guess kind of like sheet of sunlight. Yes, actually I
Speaker 1: have a solar sale is basically a really big sale
Speaker 1: that doesn't get pushed by wind. It gets pushed by
Speaker 1: energy from the sun. So basically energy has a little
Speaker 1: bit of movement in it, and that big movement, a
Speaker 1: little bit of movement can push it because it's not
Speaker 1: too much movement, but it's a lot of energy in
Speaker 1: a big area that that will push it. I'm honestly
Speaker 1: not sure. I couldn't even I couldn't mean guess like
Speaker 1: maybe the stilted price on solar system or something like that.
Speaker 1: All right, I love these answers or I feel like
Speaker 1: they're all correct. Like is it a boat powered by
Speaker 1: solar power? Yes, technically that would be a solar That
Speaker 1: would be like a boat with an electric engine on
Speaker 1: it that's powered by solar cells. That's pretty cool. Yeah, sure, yeah,
Speaker 1: that's like a solar boat for sure. Or like a discount,
Speaker 1: I don't think is it? Is it like a discount
Speaker 1: on solar panel? I think like a solar sale. I
Speaker 1: think that guy might have thought I was actually trying
Speaker 1: to sell him solar panels, like he looked kind of wary.
Speaker 1: He's like, are you another one of those shady solar
Speaker 1: salesman discounts. They are pretty shady quote unquote, that's right exactly.
Speaker 1: Their business wouldn't stand up to sunlight. You have to
Speaker 1: be pretty bright. And there was one folk, one guy
Speaker 1: who actually had a pretty solid answer. Was this your
Speaker 1: physics student sale and slash sale instructor? It was not.
Speaker 1: Actually that was my eleven year old son, who I
Speaker 1: think overheard me talking about solar sales to somebody else
Speaker 1: before I asked him, so he had a preview of
Speaker 1: the answer and just wound wanted to sound smart. You're
Speaker 1: saying your son cheated, I'm saying I asked him the question,
Speaker 1: and he knew the answer, and so he answered it.
Speaker 1: That's right, it's it wasn't a test. Yeah, he had
Speaker 1: a bit more of a head start than the rest
Speaker 1: of the other folks that we asked. So, um, it's
Speaker 1: not something that a lot of people seem to know
Speaker 1: about or recognize the name of. That's right. It's not
Speaker 1: a in concept. And that surprised me a little bit
Speaker 1: because I thought that people had heard more about like
Speaker 1: how to move through space or the kinds of engines
Speaker 1: you might use. But I guess not which makes an
Speaker 1: excellent topic for today's podcast. Yeah. Well, I have to
Speaker 1: admit my only reference to a solar sale powered spaceship
Speaker 1: is from Star Wars. Do they do solar sales? And
Speaker 1: Star Wars? I don't even remember that. I thought they
Speaker 1: all had ion engines and stuff. Yeah, I know. I mean,
Speaker 1: if you if you've watched the prequels, which I'm sure
Speaker 1: we can get into a whole episode about. But count
Speaker 1: Dooku with that character has rise around in a ship
Speaker 1: that has solar sales or what looks like what looked
Speaker 1: like solar sales. Oh my gosh. Why you have like
Speaker 1: an encyclopedic knowledge of all the ships in every science
Speaker 1: fiction movie ever. That's that's impressive. And I have an
Speaker 1: encyclopedic knowledge of all NERD movies. So that's what That's
Speaker 1: what you do it for In the afternoon when you're
Speaker 1: not feeling in the mood to do cartooning, it's like
Speaker 1: turn on some science fiction movie. Yeah, isn't that what
Speaker 1: everybody does? Yes, yes, that is exactly what everybody does
Speaker 1: in the middle of the afternoon. Um, no, but you're right,
Speaker 1: these things are in science fiction. Um. I've read lots
Speaker 1: of books with solar sale powered chips in them. Uh,
Speaker 1: it's a pretty common idea in terms of like how
Speaker 1: to get from here to there. And you know what,
Speaker 1: we don't have that many ideas for how to get
Speaker 1: from one planet to another or one star to another,
Speaker 1: and so it's on a pretty short list. Well, this
Speaker 1: is how it kind of worked in Star Wars. So
Speaker 1: count get on this ship. He takes off, he flies
Speaker 1: up into orbit or space, and then he like unfurls
Speaker 1: this huge giant sail, this like giant sheet that looks
Speaker 1: kind of like it's made out of gold, and then
Speaker 1: then he starts going. So it's like he's it's like
Speaker 1: he opened a giant umbrella and then that pushed him forward. Yeah,
Speaker 1: that's basically a solar sales are giant umbrellas. Podcast over,
Speaker 1: you nailed it Star Wars for the wind. Yeah, let's
Speaker 1: get into it, Daniel. What is a solar sale? So
Speaker 1: a solar sale is an enormous flat sheet, just like
Speaker 1: a sail on a sale boat. Um, and the thing
Speaker 1: that it captures is not wind like in air, because
Speaker 1: there is no wind in space and it's not the
Speaker 1: solar wind because the solar wind member is protons being
Speaker 1: shot out by the Sun and those could push the sail,
Speaker 1: but there's just not that much of them. There's just
Speaker 1: not that many of them. There's not enough of them.
Speaker 1: What is capturing is light. So the light from the
Speaker 1: sun is zooming out from the Sun and it's carrying
Speaker 1: energy with it, and we'll dig into that in a moment.
Speaker 1: But photons have momentum, and so what happens when they
Speaker 1: hit the sail is that they give it a little push,
Speaker 1: and you get enough little pushes and you can actually
Speaker 1: get going somewhere. So this is a real thing, like
Speaker 1: people have built these, Like there are functioning solar wind
Speaker 1: sailboats out there in space. Um, yes, this is a
Speaker 1: real thing. It's like physics says, there's no reason why
Speaker 1: I shouldn't work. People have big plans to make huge
Speaker 1: solar sales that can go all around the Solar System
Speaker 1: or maybe even to other stars. And somebody has actually
Speaker 1: built one of these things and made it work. The
Speaker 1: Japanese they launched one um several years ago and showed
Speaker 1: that it actually worked. Like the physics isn't just theoretical,
Speaker 1: Like there is one thing out there that's solar sailing
Speaker 1: right now, that's pretty cool the Japanese. The Japanese, nice job.
Speaker 1: But the thing about solar sales is that it's gentle, right,
Speaker 1: It's not really really powerful winds of light out there
Speaker 1: for you to capture with your sales. So if you
Speaker 1: have like even a really big sale, like eight hundred
Speaker 1: meters by eight hundred meters, which is you know, enormous, right,
Speaker 1: then that only gets five newton's of force, And five
Speaker 1: newtons is not that much. It's like how much you know,
Speaker 1: a fourth there isn't like a one pound object on Earth,
Speaker 1: So like a one pound rock, you know, think about
Speaker 1: how much that feels in your hand. That's the force
Speaker 1: of the Earth's gravity on a one pound rock. That's
Speaker 1: the same amount of force that the Sun would push
Speaker 1: on a eight hundred meter by eight hundred meters sail
Speaker 1: about the distance from of the Earth, which is huge, right,
Speaker 1: I mean it's a several city blocks. Yeah, that is
Speaker 1: not a small thing to build and to unferral and
Speaker 1: to keep from getting shredded right by like micro meteorites
Speaker 1: or whatever. But you're saying if I made a tarp
Speaker 1: that was about a kilometer on each side over Manhattan,
Speaker 1: it would get pushed down not just by the weight
Speaker 1: of it, but also by the sun that's hitting it. Yes, exactly,
Speaker 1: And every time a photon hits you, you're getting pushed. Like.
Speaker 1: Photons are actually pushy. They are kind of rude, aren't they.
Speaker 1: They just like zoom along wherever they want to go.
Speaker 1: They don't ask questions, they don't take turns, or they
Speaker 1: just going straight lines wherever they need to know. Photons
Speaker 1: care momentum, and every time they hit something, they give
Speaker 1: it a little push. So when you turn, when you
Speaker 1: flip the switch and turn on the light, you get
Speaker 1: pushed down a tiny little bit. And you might think, what,
Speaker 1: I can't feel it, And you're right because it's a
Speaker 1: small effect, which is why solar sales are very gentle,
Speaker 1: and you need a huge one to add up to
Speaker 1: any measurable force. Well, let's step us through a little
Speaker 1: bit of how this works. I mean, so you're saying,
Speaker 1: if I take a flashlight and I flash it at you,
Speaker 1: I am technically kind of pushing you with it. You're
Speaker 1: basically punching me in the face with light. Yeah. Yeah,
Speaker 1: that's that's really me because we don't think of light
Speaker 1: as having substance to it, right, Like you I mean,
Speaker 1: we know we sort of associated with energy and heat
Speaker 1: and warmth, but not um force. That's right. We don't
Speaker 1: think of photons is having mass because they don't, but
Speaker 1: they do have energy, right, Photons are energies is just
Speaker 1: pure energy. And if you have energy, that means you
Speaker 1: have momentum. And it's complicated because we're only used to
Speaker 1: thinking about things having momentum when they have mass. We
Speaker 1: think about you give something momentum because it's heavy and
Speaker 1: it's hard to get going, and once you've pushed it,
Speaker 1: it keeps going. It has momentum. Right, So something that's
Speaker 1: like light and fluffy and you know, weighs nothing, it's
Speaker 1: hard to understand how that can have momentum. Well, I
Speaker 1: think I think we're all pretty familiar with like if
Speaker 1: I shine a flashlight on you or a laser, like
Speaker 1: your body is gonna absorb that energy or you know,
Speaker 1: warm up a little bit or something. But you're saying
Speaker 1: that if I have an atom on my skin and
Speaker 1: you're flashing a flashlight on it, the photons actually sort
Speaker 1: of hit it and the atom wants to go the
Speaker 1: other way. Yes, exactly. Think about what happens with a mirror, right,
Speaker 1: it's a little bit more complicated when the light gets absorbed.
Speaker 1: So let's think about a mirror where the light gets reflected,
Speaker 1: the light zooming in one direction, it hits the mirror,
Speaker 1: and the lights going in the other direction. Right, how
Speaker 1: does the light change direction? Right? What changes the direction
Speaker 1: of the light. It's the mirror. Instead of thinking about
Speaker 1: light in a mirror, think about a ping pong ball
Speaker 1: and a paddle. Right, if you get hit. If a
Speaker 1: ping pong paddle gets hit by the ball, then the
Speaker 1: ball bounces the other direction, but the paddle gets pushed
Speaker 1: back a little bit. Right, That balances the momentum. Momentum
Speaker 1: is conserved. So in the same way, when the light
Speaker 1: hits the mirror, it gives that mirror a little push,
Speaker 1: and the mirror pushes back, and that's what turns the
Speaker 1: light the other direction. And so when light reflects off
Speaker 1: of something, it's giving it a little push. So pure
Speaker 1: energy can push you basically exactly. It can result in
Speaker 1: something wanting to move the other way. That's right. And
Speaker 1: this is one of the cool things in physics when
Speaker 1: you learn that a concept you thought you had a
Speaker 1: firm grasp on, like momentum, is actually just a special
Speaker 1: case of sort of a larger concept. Like we're familiar
Speaker 1: with momentum is mass times velocity. But that's not it's definition.
Speaker 1: That's just how you calculated for slow moving things with mass.
Speaker 1: You can calculate momentum for things that don't have mass,
Speaker 1: because momentum is a larger concept. It's just it captures
Speaker 1: like the quantity of motion of something, not just it's
Speaker 1: mass times velocity. It's just that it's more like the
Speaker 1: total energy. Yeah, but it's fascinating because energy is just
Speaker 1: a number. It doesn't have a direction, right, and physics
Speaker 1: energies is a scaler, not a vector, like it doesn't
Speaker 1: have a direction, just a magnitude, whereas momentum has a direction.
Speaker 1: Like you know, pointed in one direction is different from
Speaker 1: pointed in the other direction. Right, Uh, light has momentum.
Speaker 1: Light has momentum, has energy, and it has momentum and
Speaker 1: it has no mass. One way that some people like
Speaker 1: to think about it is you can think about momentum
Speaker 1: sort of the difference between the energy and the mass.
Speaker 1: Right because in real and relativity we think of the
Speaker 1: total energy as the energy store in the mass plus
Speaker 1: the energy of the momentum. So you can sort of
Speaker 1: invert that equation and say the momentum is the difference
Speaker 1: between the total energy and the mass. And in the
Speaker 1: case of the photon, there is no mass. Momentum just
Speaker 1: comes from the energy, whereas in the case of another particle, right,
Speaker 1: it has a bunch of energy. Some of that is
Speaker 1: in the mass and some of it is in its motion.
Speaker 1: But for the photon, all the energy is just in
Speaker 1: its motion, so it just has momentum and no mass.
Speaker 1: All right. Solar sales are a real thing, and they
Speaker 1: work by taking the momentum that's in light, absorbing it
Speaker 1: and then using that to push you along in space.
Speaker 1: That's right, And it's the light from the Sun that's
Speaker 1: doing this, not the protons from the solar wind. And
Speaker 1: everybody actually can see this if you just have seen
Speaker 1: a comet. You know, comet is just a big ice
Speaker 1: ball and it falls towards the Sun and as it
Speaker 1: does so it gets a big tail, right, and that's
Speaker 1: the tail of it, like the stuff melting and dripping
Speaker 1: out the back, and the tail points in a specific
Speaker 1: direction away from the Sun, not in the direction of motion.
Speaker 1: People think, like, you know, it's like a fuzzy lines
Speaker 1: behind something that's moving fast. But the commet actually always
Speaker 1: points away from the Sun, and that's because of this
Speaker 1: effect of light. That's light pushing the tail of the commet. Really,
Speaker 1: it's not like a trail of a dust that you
Speaker 1: leave behind. No, Because as the common is moving towards
Speaker 1: the Sun, the tail is behind it. But as the
Speaker 1: comet goes around the Sun and then leaves, the tails
Speaker 1: in front of it. Wow, so it shouldn't be called
Speaker 1: the tail once again? Yeah, I guess. Or maybe it's
Speaker 1: like backing away from the Sun as it leaves. It's
Speaker 1: like whoa, that was close. All right, let's get into
Speaker 1: will it work and how how can we make it work?
Speaker 1: But first let's take a quick break. All right. So
Speaker 1: that's solar sales Daniel. That's pretty cool. The question now,
Speaker 1: I think is does it work? If you build it,
Speaker 1: will it take us to other planets and maybe other galaxies? Yeah,
Speaker 1: it's it seems like it will. And you know, we
Speaker 1: know a lot about it. We can do these calculations.
Speaker 1: We know how much light there is, we can calculate
Speaker 1: how it will reflect and how much will be absorbed,
Speaker 1: and we know all the numbers we need. And so
Speaker 1: people have plugged all this stuff into calculations, and they said,
Speaker 1: if you build a solar sale that's like a kilometer
Speaker 1: by a kilometer and you have a really light ship,
Speaker 1: you know, not too heavy, how long would it take
Speaker 1: to get to Mars or to get to Jupiter. And
Speaker 1: the thing you have to understand is that the strength
Speaker 1: of the light, of course, gets weaker as you get
Speaker 1: further from the Sun. So the solar sale is very
Speaker 1: powerful close to the Sun because it's capturing more light,
Speaker 1: and then as you get further and further away from
Speaker 1: the Sun, it gets weaker and weaker. So solar sales
Speaker 1: are great for navigating around the inner parts of a
Speaker 1: solar system. Well, the question I have is, you know
Speaker 1: these sales are catch the rays from the Sun, right,
Speaker 1: they catch the light from the Sun and push it
Speaker 1: get pushed away from the Sun. But what if you
Speaker 1: want to travel towards the Sun are perpendicular to the Sun.
Speaker 1: How would you do that? If you want to move
Speaker 1: towards the Sun, It's not hard, right, you just need
Speaker 1: to use gravity. Right, the Sun is going to pull
Speaker 1: you towards the Sun, so that part is not hard.
Speaker 1: But the only way you can use the sail to
Speaker 1: build energies is moving away from the sun. So you
Speaker 1: can play this game of gravity versus the solar sail
Speaker 1: depending on which way you want to go. If you're
Speaker 1: facing the sun, can you go side? What can it
Speaker 1: push you sideways? Because gravity is pushing me towards the
Speaker 1: sun and the solar sales pushing me away from the sun.
Speaker 1: How do how do I gain speed sideways? WHOA, that's
Speaker 1: a really good question. I haven't even thought about that.
Speaker 1: How do you steer it? Because the photons are only
Speaker 1: coming out from the sun, so can you move in
Speaker 1: a direction that's not out away from the sun. My
Speaker 1: first thought is, let's think about how a sale works
Speaker 1: on a sail boat. Right, on a sail boat, you
Speaker 1: can move in a different direction than the wind if
Speaker 1: you put the sail across from the wind. But the
Speaker 1: problem is a sailboat has a keel, right, has something
Speaker 1: underneath it that keeps it from sliding sideway is and
Speaker 1: so it can only use the part of the wind
Speaker 1: that it wants by pointing in the right direction. A
Speaker 1: solar sale, of course, on a spaceship doesn't have a keel,
Speaker 1: So I first thought you might think, oh, a solar
Speaker 1: sale can only take you in the direction the photons
Speaker 1: are going. Right. Well, let's think about it for a moment.
Speaker 1: What happens if you tilt the sale so that it's
Speaker 1: not pointing um flat away from the sun right, if
Speaker 1: it's at an angle with respect to the photons. You
Speaker 1: might think, well, it doesn't really matter because the photons
Speaker 1: hit it and bounce off, and they're giving a push
Speaker 1: the direction they were going. Right. It's actually a tiny
Speaker 1: bit more complicated. If the photons hit it at an angle,
Speaker 1: then they also bounce off at an angle right. So
Speaker 1: if the photons are coming directly out from the sun
Speaker 1: and they hit flat on the solar sail, then they
Speaker 1: bounced back the opposite direction, and the momentum they have
Speaker 1: given is in the direction they were going. But if
Speaker 1: they come out from the sun and they hit the
Speaker 1: solar cell at an angle right, then they were flecked off.
Speaker 1: Think about light hitting a mirror right. It doesn't come
Speaker 1: back the way it was going. It reflects off at
Speaker 1: an angle, and so the push that it gives is
Speaker 1: actually in the direction that the solar sale was facing.
Speaker 1: So I think that means that you can steer a
Speaker 1: solar sale you just turn it through the way it
Speaker 1: wants to go, and it will catch that part of
Speaker 1: the photons momentum that pushes it in the direction it's facing.
Speaker 1: You can't just point in that direction and drive the
Speaker 1: way you came with your car. You have to take
Speaker 1: an account all these limitations. But you can do it,
Speaker 1: and you can take a pretty heavy load, you know,
Speaker 1: a few tons to mercury, and it just takes a
Speaker 1: few years. If you want to go to Venus, it
Speaker 1: takes you know, about a year. If you want to
Speaker 1: go the other direction, it starts taking longer because the
Speaker 1: radiation from the Sun drops, right, So if you want
Speaker 1: to go to Mars, it takes like a year and
Speaker 1: a half maybe two. Takes like two years to get
Speaker 1: to Jupiter, three to get to Saturn, and then like
Speaker 1: six years and nine years to get out to the
Speaker 1: outer planets. It's a lot of whiskey drinking on board.
Speaker 1: That's your fuel, after all, right, there's no there's no
Speaker 1: solar whiskey, and you'd be using it up. You could
Speaker 1: have burned it to evade that asteroid, but no, you
Speaker 1: had to drink it. Yeah, well, you know, it depends
Speaker 1: on how well you get along with your crewmates, depending
Speaker 1: that determines how much whiskey you have to drink. Can
Speaker 1: you imagine being stuck in a spaceship with your physics
Speaker 1: student for nine years? Tan? No, but I also can't
Speaker 1: imagine being a spaceship by myself for nine years, right, Like,
Speaker 1: what do you think would be easier to handle total
Speaker 1: isolation or being stuck with one person in a tin
Speaker 1: can for nine years? Oh? For me, would definitely be
Speaker 1: by myself. Yeah, you and a big stack of science
Speaker 1: fiction movies, right all you need and a cartooning pad, obviously,
Speaker 1: so I can document my descent into madness, your further
Speaker 1: descent into madness, you ment, surely, that's thank you for
Speaker 1: reminding me. But yes, but what about beyond the Solar system?
Speaker 1: Could you use the solar sale to leave the Solar system?
Speaker 1: You could a little bit. I mean what you can
Speaker 1: do is try One strategy is to just try to
Speaker 1: get going as fast as you can using solar sales
Speaker 1: and gravity, and then zoom off in the direction of
Speaker 1: another star. So you're like you sling shot around the
Speaker 1: Sun to get some speed up, and then as you're
Speaker 1: leaving the Sun, you unfurl your sails and it pushes
Speaker 1: you away from the sun is as hard as you can.
Speaker 1: But then once you leave the solar system, it's really
Speaker 1: going to stop pushing you very much, and so your
Speaker 1: speed doesn't pick up anymore. But you know, if you
Speaker 1: do it right and you have a light enough object,
Speaker 1: you could get up to a reasonable speed UM and
Speaker 1: head off in that direction. Yeah. I mean, at some
Speaker 1: point when you leave the solar system, it's like the
Speaker 1: there's no wind. It's like being on a sailboat with
Speaker 1: no wind. There's nothing to push you anywhere. Yeah, and
Speaker 1: you know there is radiation out there, and there are particles,
Speaker 1: but it's very low density. It's not enough to really
Speaker 1: really boost you. UM. One idea people have, and I
Speaker 1: love this idea because it's so crazy plus ambitious, which
Speaker 1: is my favorite combination, is to basically beam light at
Speaker 1: these things. Like if you're in a solar sailboat and
Speaker 1: you're leaving the solar system, maybe we could like build
Speaker 1: a huge laser and beam the energy at your solar
Speaker 1: sale to give you a push. What if you punch
Speaker 1: a hole through the sale with their laser? Yeah, exactly.
Speaker 1: It can't be too intense. UM. But you know these
Speaker 1: lass these sales will be very reflective, right. They are
Speaker 1: essentially the big sheets of aluminum or maybe plastic that's
Speaker 1: covered with aluminum so that they're super reflective. So if
Speaker 1: it's reflective enough, then even a really really powerful laser
Speaker 1: won't punch a hole, right, because punching a hole means
Speaker 1: the energy gets absorbed and so like melts and destroys
Speaker 1: the sail. If it's reflective enough, then you should be
Speaker 1: able to shoot even a really powerful laser and have
Speaker 1: all the energy to be transferred into the momentum of
Speaker 1: the sail. It's like blowing on a little sailboat. Yeah, exactly.
Speaker 1: Or I'm sure I've seen some science fiction movie where
Speaker 1: somebody like reflects a laser blaster with a mirror. Right, Oh,
Speaker 1: you just have like a pure mirror shoot at it
Speaker 1: and then that pushes you forward. Yeah, if somebody shoots
Speaker 1: you with a laser blaster and you have a mirror,
Speaker 1: you can just reflect their you know, energy pulse or
Speaker 1: whatever back at them. All Right, Well, let's let's get
Speaker 1: into how you actually build a solar sale, even if
Speaker 1: it wasn't on sale. But first let's take a quick break.
Speaker 1: That would be a pretty awesome idea for merch like
Speaker 1: solar sale. Daniel and Jorge solar sale explore the universe
Speaker 1: instead of explain the universe. That'd be pretty cool. What
Speaker 1: do you mean, what will we sail sale sell? We'd
Speaker 1: sell the solar sale like you are. We have a
Speaker 1: shop where we sell t shirts and coffee mugs with
Speaker 1: you know, Daniel and Jorge is playing the universe on it.
Speaker 1: We should add to our Internet merch account a solar
Speaker 1: sale that you can buy. Okay, cool, done, let's do it.
Speaker 1: And then you just get a sheet of aluminum foil?
Speaker 1: Is that the idea? That one kilometer by one kilometers
Speaker 1: wherever loominum foil with your picture on it. There you go,
Speaker 1: and you can sail way into bankruptcy, right, and you
Speaker 1: can shoot a laser at that picture from Earth dual
Speaker 1: purpose aluminum foil. You can wrap your leftovers and go
Speaker 1: into space exactly. But that's basically what a solar sailing is. Right.
Speaker 1: You wanted to be really really big, but you also
Speaker 1: wanted to be really really light. You want your solar
Speaker 1: sailboat to be as light as possible so that all
Speaker 1: that momentum gets turned into speed um. The more massive
Speaker 1: your sailboat, the slower it's going to go for the
Speaker 1: same amount of momentum as you want it really big
Speaker 1: and really thin. I mean, does it matter in the
Speaker 1: long run how much here solar sail ways? Sure it does. Yeah.
Speaker 1: I mean you want to get up to like half
Speaker 1: the speed of light or a quarter of the speed
Speaker 1: of light or something, it's gonna take a lot longer.
Speaker 1: And if you don't have a laser push, then you
Speaker 1: have a limited amount of time to get energy from
Speaker 1: the sun as you want to get up to as
Speaker 1: high as speed as possible. Oh, I mean, but that's
Speaker 1: just in general the same for any acceleration, right, Absolutely,
Speaker 1: the lighter you are, the faster it is to go faster. Yeah, exactly.
Speaker 1: And that's like why people who you know, climb mountains
Speaker 1: on their bicycles or move every tiny little thing that's
Speaker 1: not necessary because they don't want to carry that mass
Speaker 1: up the mountain. You know, I met a guy who's
Speaker 1: climbing Matu Picchu and he like sawt his toothbrush in
Speaker 1: half because he didn't need the bottom half of it.
Speaker 1: And you didn't want to carry that thing up the mountain.
Speaker 1: So yeah, you wanted these your spaceship to be as
Speaker 1: light as possible so you can translate all of that
Speaker 1: momentum into speed. So basically that's all you need is
Speaker 1: just a thin aluminum foil. But usually they showed them,
Speaker 1: show them in movies and and pictures. Is gold It
Speaker 1: looks like gold foil. Does that give you a better
Speaker 1: advantage if it's gold or golden? No? Um, you can't
Speaker 1: just have aluminum foil because aluminium is too brittle. Like
Speaker 1: you try to make a huge sheet of aluminum foil,
Speaker 1: I mean, I can't even get like a one foot
Speaker 1: square of aluminum foil to stay together without tearing. And
Speaker 1: so you try to like fold and then unferral a
Speaker 1: one kilometer square of aluminum foil, It's not gonna work.
Speaker 1: So usually what they do is they have some sort
Speaker 1: of plastic and they spray aluminium coating on it. Um
Speaker 1: And so sometimes that plastic is gold. But I don't
Speaker 1: think there's a reason why that's gold. I think that's
Speaker 1: just to look cool. Right. Well, where are we at then,
Speaker 1: in terms of projects that are trying to use solar
Speaker 1: sales to get us out there? Yeah, So the best
Speaker 1: solar sale ever so far is the Icarus project. Launched
Speaker 1: in by Japan and they had a fourteen by fourteen
Speaker 1: meter solar sale and that sounds small compared to what
Speaker 1: we're talking about like eight eight hundred, but fourteen meters
Speaker 1: is not small, and that's like, you know, the size
Speaker 1: of an apartment. Can I just comment on their choice
Speaker 1: of names, like have they read the whole story of Icarus?
Speaker 1: Do they know how that story ends? I don't know.
Speaker 1: I love I love the hubris in choosing the name
Speaker 1: Icarus for a solar sale project. Right, it's they chose
Speaker 1: a story about Hubris and they did it kind of hubristically.
Speaker 1: They're like thumbing their nose in history. I love it.
Speaker 1: That's not going to happen to us. We're gonna fly
Speaker 1: really close to the sun and nothing bad is going
Speaker 1: to happen to Maybe they're trying to regain the name Acharis.
Speaker 1: They're claiming it back, you know the way some people
Speaker 1: claim back bad words. That we're going to turn this
Speaker 1: new a positive stereotype. Now, they want to redeem Icarus himself.
Speaker 1: That's it exactly. Maybe they're like the descendants of Acharis himself. Yeah,
Speaker 1: so they they're building it. They build it. They're going
Speaker 1: to build it, they built it, they launched it. It worked.
Speaker 1: It's solar sailing. It's zooming around the sun right now. Really,
Speaker 1: it's out there. It's out there, sailing away. It's sipping
Speaker 1: whiskey and looking down on us. And that's the most
Speaker 1: successful solar sale so far. But it's not like a ship,
Speaker 1: right It's like a satellite or a little vessel. Yeah,
Speaker 1: it's it's a little vessel. It's basically just two experiments
Speaker 1: that can we do this thing. Let's see if it
Speaker 1: actually works. Because you know, sometimes in physics, you do
Speaker 1: the calculations, they sound great, and then you know it
Speaker 1: doesn't actually work the way you expected because you forgot
Speaker 1: to account for something. But in this case, it's pretty
Speaker 1: much worked as they expected. And that's a huge boost
Speaker 1: for all the solar sale enthusiasts. I didn't know that
Speaker 1: was such a thing. I'm a solar sale enthusiast. I'm
Speaker 1: a big fan. First of all, I love sailing, but
Speaker 1: I'm a big fan of anything that's going to take
Speaker 1: us to other planets or take us to other stars
Speaker 1: and it isn't going to require a huge ridiculous amount
Speaker 1: of fuel cool Well, uh, and then you were telling
Speaker 1: me there's another cool project called the Breakthrough star Shot project. Yeah,
Speaker 1: they have this awesome idea. They say, let's not send
Speaker 1: one big solar sale, let's build a hundred of like
Speaker 1: a thousand nano sales. So there would be a bunch
Speaker 1: of really small ones and they would push them along
Speaker 1: with lasers between here and Alpha Centauri. The problem with
Speaker 1: building a laser that pushes a big solar sales you
Speaker 1: need a big laser. So they were like, okay, well,
Speaker 1: let's just have a small solar sale that can be
Speaker 1: pushed by a small laser and then just have like
Speaker 1: a tiny little craft. And so they imagine that that
Speaker 1: it would take twenty years to get to Alpha Centauri
Speaker 1: with these little nano sailors, And so they would have
Speaker 1: a giant laser gun on Earth shooting at these things,
Speaker 1: pushing them along, a thousand laser guns pushing on them. Oh,
Speaker 1: each one has their own little laser gun. Yeah, exactly,
Speaker 1: each one needs its own little boost. But the cool
Speaker 1: thing about solar sailing is that you know it's a
Speaker 1: small effect, but it just adds up, and if you're
Speaker 1: traveling for a long time, it's just like more and
Speaker 1: more acceleration. Eventually these things can get up to a
Speaker 1: respectable fraction of the speed of light, you know, so
Speaker 1: they can cross the distances between stars, and then they
Speaker 1: would communicate back what they find. But they can't come back,
Speaker 1: can they. They cannot come back. No, because there's no
Speaker 1: laser system over there for to shoot them back. I
Speaker 1: mean that we're aware of. Maybe they'll get there and
Speaker 1: find Elon Musk has built some you know station over
Speaker 1: there for recharging your solar your solar lasers or something.
Speaker 1: But but no, they it's just a it's a one
Speaker 1: way trip. Well, that's cool. It's like instead of building
Speaker 1: a giant boat, you build a whole bunch of little
Speaker 1: rubber duckies into the river. Kind of exactly. That's gonna be.
Speaker 1: Humanity's first contact with an alien species is the equivalent
Speaker 1: of a rubber ducky. Hi, look at us, We're so impressive.
Speaker 1: This is a little squeezed toy. And then the aliens
Speaker 1: are like, this is a sign of war. That's sorry.
Speaker 1: Maybe the rubber ducky is like holy to them and
Speaker 1: it's offensive that we like through on in their face.
Speaker 1: Plus we probably all of our lasers will be like
Speaker 1: burning their eyeballs down for a twenty years while the
Speaker 1: while the natocrafts are getting there. But if we fill
Speaker 1: them up with whiskey, maybe they'll they'll like it. They'll
Speaker 1: either love it or hate it. They'd be like, what
Speaker 1: Scottish whiskey? I only drink irish? This needs war. Wars
Speaker 1: have been fought over less, I'm sure. All right. So
Speaker 1: that answers Derek's question, who wanted to know how do
Speaker 1: sol of our sales work? And hopefully you guys enjoyed
Speaker 1: that and are inspired to maybe think about taking off sailing.
Speaker 1: That's right, and you know, maybe someday we'll go out
Speaker 1: there and we'll sail among the stars. I think it's
Speaker 1: really beautiful and poetic to imagine using the life from
Speaker 1: the stars themselves to push ourselves from one to the other.
Speaker 1: I really wish that could happen. All right, Thanks for listening, guys,
Speaker 1: see you next time. If you still have a question
Speaker 1: after listening to all these explanations, please drop us a line.
Speaker 1: We'd love to hear from you. You can find us
Speaker 1: at Facebook, Twitter, and Instagram at Daniel and Jorge that's
Speaker 1: one word, or email us at Feedback at Daniel and
Speaker 1: Jorge dot com. Thanks for listening and remember that. Daniel
Speaker 1: and Jorge Explain the Universe is a production of I
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