Thread by @anderssandberg

#FridayPhysicsFun - I wrote an answer on Physics Stack Exchange about moving the Earth outwards to compensate for solar brightening. physics.stackexchange.com/questions/7227…

The first consideration of how to move the planet was made by Archimedes boast: "Give me a place to stand and with a lever I will move the whole world." physics.stackexchange.com/questions/4831…

Christoph Grienberger in 1603 proposed gearing powered by a treadmill, allowing it to be raised veeeerrryyy slowly. He got the rough number of gears right by modern reckoning. bbc.com/future/article…

These ideas of course assume that Earth is somehow resting in a gravitational field like Earth's surface, and that you have fixed pivots and gear axles. Practicality was never the point.

The next earthmover I know of was Victory Hugo, who in his 1866 novel The Toilers of the Sea have a character suggest a version of Archimedes:

Jules Verne discussed using a giant cannon to change the tilt of the Earth in the novel The Purchase of the North Pole (1889). I wonder if he read the Hugo novel? en.wikipedia.org/wiki/The_Purch…

He correctly noted that it was not practical. Still, this is something that could in principle be done: unlike the previous ideas it is consistent with mechanics.

It is not hard to calculate that to move Earth out to 1.3565 AU (keeping it in the life zone for the next 5.4 Gyr) we need 6.4240e32 J of energy. A lot... but just 3.7697e15 W, 2.1% of the total solar energy falling on Earth.

One proposal due to M. Taube was to construct 24 batteries of 30 km tall rocket towers around the equator. Around local noon they would fire 10000 tons of hydrogen per second into space at 300 km/s.

The reason for the towers is to keep the hydrogen from interacting with the atmosphere, and the timing prevents effects on Earth's rotation. The reaction mass would be imported from Jupiter, in the end reducing its mass by 10% for this particular scenario.

I get the feel he liked Jules Verne. Later he had a more serious paper about how to do it. arxiv.org/abs/0811.4052

That builds on Korycansky, Laughlin, & Adams' idea of using asteroids slingshotting past Earth and Jupiter to transfer momentum to Earth, moving it into a higher orbit. arxiv.org/abs/astro-ph/0…

Colin R. McInnes didn't like having big asteroids passing by, and noted that we could also use a big solar sail that acts as a gravity tug: it hovers outside Earth, gently pulling on its mass. link.springer.com/article/10.102…

David Brin was also not a fan of asteroid streams, and suggested an electrodynamic tether on the moon. It needs a lot of solar panels but may have far more graceful failure than the other proposals. davidbrin.blogspot.com/2014/11/lets-l…

There are other issues here, like avoiding getting into orbital resonance with other planets (or exploiting it!)

There are more ideas (I need to leave some surprises in my book) but basically we know methods that could be scaled to move planets. Not now, but given that we are talking planning horizons of hundreds of million years, there is time to work them out.

https://twitter.com/anderssandberg/status/1517120190399528960

The idea of moving earth is preposterous. Yet it is irresistible once you know physics: the equations scale all the way up to planets! Human ability to move large masses have also grown exponentially with no end in sight... science.howstuffworks.com/engineering/st…

Deep down, what makes us so powerful is that we can move matter purposefully. Our muscles are not that strong, but if we know how we can make matter channel energy and move other matter for us. This can be used to move more matter, and so on.