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Can We Turn Earth Into a Spaceship?

Beautiful isn't it? The only home we've ever known. But what if the only way to save the Earth was to push it somewhere else? Could we do that? Let's get technical. It is freezing out here. (upbeat music) Life, as we know it, dependson two million septillion kilograms of mostly hydrogen and helium that forms an almost perfect sphere that we humans call the sun. And because we are sodependent on the suns energy, life on Earth has a time limit. In a little over seven billion years, the sun will have burnedthrough enough of its hydrogen and helium fuel that it'll move into another stage of itslife, the red giant stage, and expand so much so that the Earth and all the inner planets will be consumed by just its radius. And that, as they say, will be that.

How could we escape such a scorching fate? Well that is the centralquestion in the novella and recent Chinese blockbuster,"The Wandering Earth". And that story's solution is to construct thousands of rocketstaller than Mount Everest and just push Earth toanother solar system. This would get us out ofthe way of a red giant, but is this even close to feasible? What kind of engineering would this take? Could we make a spaceship Earth? Let's begin with the (humming), let's begin with a simple case. Using rockets to fling theEarth out of the solar system.

The Earth goes around the sun more or less in a circle because we aregravitationally bound to it. To change where or how theEarth was orbiting then, something would have to fight against this constant gravitational force and add energy to the entire system. We are now describinggravitational potential energy and the more we wanted tomove something like a planet through a gravitational field away from a gravitational influence,like giving it a larger orbit, the more energy we would have to put in. But just how much energywould we have to put into the Earth's orbit in order to fling it out of the solar system? Well, if we gave the Earthenough kinetic energy to equal or exceed thegravitational influence of what it's bound tothe sun, by say changing its velocity, it's orbitwon't just increase and get larger, it willjust fly off into the cosmos never to return, always slowing down, but never falling all the way back into the suns gravity well.

So let's set gravitationalpotential energy and kinetic energy equal toeach other and do the math. We know the mass of theEarth, the mass of the sun, how far the Earth and sunare apart from each other, and we know Newton'sgravitational constant. So if we solve for V here, wecan get the escape velocity from an Earth-like orbit. Do this and you get anescape velocity for Earth from the sun of 42 kilometers per second, an absolutely blisteringspeed that could take you, for example, from New York to Los Angeles in just 95 seconds.

The good thing though,is that we do not need to get Earth moving at this ludacris speed because we're already movingat an absolutely crazy clip. Do you feel like you're moving right now? Well probably not, butyou've always been moving. Since you were born everysingle molecule of you has been absolutely racing around the sun. And because of this, you've never felt it. Earth's orbital velocityis already a substantial 30 kilometers per second around the sun. And so if we wanted to pushEarth out of the solar system all at once, we wouldn'thave to add 42 kilometers per second, we'd only haveto add the difference, around 12, and then Earth would be on its way to Alpha Centauri. However, because the planin "The Wandering Earth" specifically, an understandable plan, is to slowly push the Earthout of the solar system over the course ofdecades, we need to change the Earth's velocity by a lot more than 12 kilometers per second. In a slow, constantspiraling outwards burn for example, where the sunis always pulling on you the entire time, youneed to instead exchange all of this orbitalvelocity and kinetic energy for potential energy.

You are spiraling outwardsgetting further and further away from the sun, slowingdown, down, down, down until you escape thesuns influence with zero, or there about zero, kilometers per second and you have no orbital velocity because you are no longer orbiting. However we actually accomplishthis, this all means that we would need to cancelout a full 30 kilometers per second of ancient orbital velocity to escape the suns influence. Kind of like slowly gettingoff a cosmic merry go round when it's slow enoughand safe enough to do so. And doing all of thiswould be the greatest feat of engineering ever attempted. In 2006 we launched theNew Horizon's space probe with a velocity that would takeit out of the solar system, so we have done this kind of thing before. The problem with doing it with Earth is Earth is so dang heavy.

The Earth is obviouslyhuge relative to us, but just think about fora second how much of Earth do we actually interact with? All of the forests, all of the oceans, every living thing you've ever seen, all of human civilization,all of the human experience has existed in a volumeof Earth that is less than 1% of the whole. If we had to move the Earthto another solar system and we wanted to maintain some semblance of life as we know it,we couldn't just move 1% that is the biofilm that we call life. We would have to move 100% of Earth to maintain the biosphere, the geology, the magnetosphere, ourgravity, everything. 100% of Earth is sixtrillion trillion kilograms, six with 24 dang zeroes after it. And if wanted to move allof this with some relative speed in some time frame,we would have to provide a lot of thrust, which wouldhave to come from our rockets.

Back in the envelopethough, using a simple force equals mass timesacceleration equation, the mass of Earth and theorbital velocity we have to cancel out, along with the time frame, let's say something like 15years like "The Wandering Earth" uses, we get a thrust value that has 20 zeroes after it, that's a lot. So now we have to look uphow our rockets stack up. Slow burn baby, slow. Now, the simplest wayto, ope, still thrusting. There we go, the simplest,most straight forward approach to turn Earth into a spaceship would be to first stop therotation of the planet, which would cause anatural disaster unlike we've ever seen before, butlet's ignore that for a second, pick one hemisphere ofearth because we want the thrust point in one direction for pretty much the entire time, and then dot as much of that hemisphere as we can with rockets.

These rockets would haveto be engineering marvels like the world has never seen. And to get an idea of just how much thrust each one would produce, let's look to "The Wandering Earth" againand say we use 10,000 rockets. If all of our Earthengines needed to add up to our total estimatedthrust, then every single one of them would have to produce 37, wait, wait, wait a second. Thousand trillionnewtons of thrust, crazy. And if we choose a prettybeefy boy in terms of thrust like the Raptor engine from SpaceX, you can see that even though it produces a lot of thrust, itwould still take billions of Raptor engines just to equal one of our Earth moving engines. And all of these engineswould take up a lot of space. (dramatic music) Let's assume that because our scenario is a literal doomsdayscenario, we as humans are willing to put as manyrockets as we can possibly fit on one half, or one hemisphere of Earth. How much construction,looking at this map, do you think we'd need to do?

I have indicated here with a single dot a surface area required for a number of SpaceX Raptor engines. Not any of the infrastructurewe would probably have to build around them,just the thrusty bits. Looking at this dot, how many other dots do you think we wouldhave to draw on this map? Take a second to guess, I will wait. I will give you a hint,it's not this many dots. It's this many. Using current technology,the number of rockets that we would need to slowlypush out of the solar system would literally cover every square inch of one half of Earth. Every square centimeter of ocean, every square meter of land, everything. Our wandering Earththen would have to look something like this, whichis objectively super awesome, but shall we say totallyand completely implausible. I think we need to go sci-fi. We would have to cover literallyhalf the planet in rockets.

So I don't think chemicalpropulsion is the way to go. So what about nuclear fusion? Oh, that's where that was. To it's credit, "The WanderingEarth" doesn't suggest that regular old chemicalrockets are the solution to the Earth movingproblem, instead saying that they use giantnuclear fusion engines, taller than Mount Everestas their Earth pushers. And this makes everythinga bit more believable because one of theadvantages of a theoretical nuclear fusion rocket is the speed at which they can throwfuel into the void. However, even if fusion enginescould turn Earth's crust directly into fuel throughthe fusion process, even if all of thesefusion engines could fit on one half of Earth, andeven if they could provide the required thrust in total, fuel would still be a big problem. This may be the most famous equation in all of rocket science.

The very cleverly named Rocket Equation. It is able to take what we want to change, in terms of velocity for our space craft and relate that to theexhaust velocity coming out of that spacecraft and how much mass we started off with and howmuch mass we finally end with. This change in mass ishow much fuel we need. If we now give our nuclear fusion rockets an absolutely ridiculous exhaust velocity thanks to the millionsof degrees plasma created in these fusion reactions, then we can use our change velocity we wanna give to Earth to solve for what percentage of Earth we want to use as fuel. To move our spacecraftout of the solar system under all of our assumptions,we would only need to use .3% of its total mass in terms of fuel, but remember that our spacecraft is Earth. Let's remember thateverything you know and love accounts for less than1% of Earth's total mass. So in that context, this.3% number is more like 30% of everything you've ever seen.

To power these futuristicnuclear fusion reactors, yes we would only need to use.3% of Earth's total mass, but not all of Earth's total mass is readily available to us. So we would need to throwinto these fusion reactors the equivalent of 13 times the mass of all the world's oceans combined. Even if we could make reactors like this and move Earth with them,we might not have the fuel to supply them or the ability to. And we don't even havefusion engines right now nor do they seem to be onthe technological horizon. Using current technologylike SpaceX Raptor engines and the rocket equation, wecould calculate that we would eventually have to throw theequivalent mass into space from our spaceship, whichis Earth, of 98.98%, and if we had to dothat, just to push Earth out of the solar system,just .02% would remain, meaning that everything, eventually, all the animals, all ofhumanity, civilization, plants, geology, everything,would have to fit on a spaceship Earth thesize of a large asteroid.

Because we'd have to usethe majority of Earth's mass as fuel, just a few years after launching spaceship Earth towards Alpha Centauri, we would run out of spacefor pretty much everything. The rockets, the animals,the plants, the food, us, I don't know if we wannamake a spaceship Earth. So could we turn theEarth into a spaceship to escape a dying sun? Well, using today's technology,we would have to make trillions of our best rocketsand then move everything on one hemisphere of Earthin terms of resources to one side, and then dotthat entire other side with rockets, literallyevery square centimeter, and then use so much of Earth as fuel that by the time we gotto where we were going, we would be reduced to thesize of not a planet anymore. Obviously all of thisis totally improbable, if not completely impossible. Using fusion engines wouldmake everything easier, but space and fuel wouldstill be a problem.

For now, the only trip thatthe Earth will be taking around a star is another one around the sun, because science. I'm taking this. (upbeat music) And I should say there'sa lot of other ways that you can approachthis kind of calculation. You can change the trajectory,you can change the engines or orientation, the power requirements, but what I will say is that basically any combination ofvariables that you pick, it still is completely implausible to do. Either it would take you,with current day technology like millions or billionsof years to leave the solar system and thenit's gonna be too late and you're gonna be engulfed by the sun, or the power requirementis so crazy for you to launch yourself out of the solar system like New Horizons that it's just something we probably won't ever createin terms of engineering. So that's, that doesn't work so much.

But "The Wandering Earth"does get a lot right from having to slow downand stop the rotation of the Earth, and populationdie-offs and all that stuff. It's pretty fun and Iappreciate the science in it. Thank you so much for watching today and a huge thank you Doctor Ethan Segall and Matter Bean for theirhelp on this episode. If you enjoyed this episodeof "Because Science" about spacey stuff, youcan check out some of the other videos that we've done like what would happen if youactually pulled the moon to Earth like in Majoras Mask,and why you definitely why you do not want Superman to reverse the Earth's rotation. You can follow us @BecauseScience here on these social media platformswhere I take suggestions for future episodes, and hey, thanks. (upbeat music) 

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