The Blundering Earth

When I commented in a Facebook thread recently that the new Netflix production, The Wandering Earth, was beautiful but oh so stupid, someone responded,

why do you think this? The physics was sounder than 75% of sci fi films

The answer is longer and requires more formatting than can fit in a comment, so I’m responding here. If you enjoy the film, that’s fine, I can’t argue with that. But don’t go around saying the physics is sound because that will start a fight.

• My computer has biometric login. A few decades from now, that will still be possible and far more ubiquitous. You can’t just steal someone’s key card and use it to make off with valuable equipment.
• For that matter, you can’t make a fake ID tag. It’s in the freaking computer, and anyway the computer can recognize your face. Especially in China.
• The Sun doesn’t change appreciably in the span of a few centuries. Especially not because of climate change on Earth.
• Planets do not have “gravity spikes”. That’s why they’ve been in the same orbits for billions of years.
• Fifteen years is a ridiculous amount of time to work in space without switching out the personnel. They have supply runs. What the hell?
• The stated purpose of the station is absurd. It’s supposed to provide communication for the people on the Earth? I mean obviously they can’t have regular communication satellites in orbit, but everyone lives under the engines, which are on the opposite site of the planet from the station. They need a complete ground communication network to talk to the station, and if they have that, they don’t need the station for communication, do they?
• The other purpose of the station is navigation. The what? What navigation can they do from there that can’t equally well be done from the leading end of the planet? Especially since that part of the Earth would have practically total vacuum, excellent for observation, and lots of rock for protection from cosmic rays and micrometeorites.
• You can’t move the Earth by mounting fusion engines on the planet and using the local rock for fuel. There are several reasons for this.
  1. The Earth isn’t a boulder; it has a chewy center under a relatively thin crust. The crust isn’t terribly stable once you start pushing on one side of the planet hard enough to move it. Not a comfy place to live.
  2. There’s not enough local rock, you can’t just scoop it up — at least not enough to keep going for years let alone centuries. You’d have to mine it and bring it in from far away.
  3. How much fuel would you need? People who study realistic fusion engines for space travel talk about fuel in the neighborhood of 90% of the total vehicle weight. The planet moving project is in less of a hurry, so let’s say they only need to burn 70% of the Earth as fuel. During the couple hundred years of acceleration, you’d need to mine, say, 47% of the Earth’s mass to use as fuel (you need less for deceleration because by that time you have less mass to decelerate). So that’s 2,820,000,000,000,000,000,000 metric tonnes, over 200 years, or just 14,100,000,000,000,000,000‬ tonnes per year. For comparison, the total output of all mineral mining currently is about 3,600,000,000 tonnes per year (and that’s 98% sand and similar loose stuff).  To fuel those engines, we’d have to increase our mining activity by a factor of 4 million. And we’d run out of loose stuff pretty quickly. We’re talking solid rock, baby. We’d need to increase solid rock mining production by a factor of 200 million. And magma. Ever mined magma? Wear good boots.
  4. To put these numbers into perspective, the population of the US is around 300 million. I don’t remember what proportion survive the original disaster but let’s say 150 million. More than one person works in solid rock mining in the US. We need to multiply that workforce by 200 million. Do the math.
  5. I know, these engines are different. They burn a different, heavier fuel. However, they also have to move a heavier fuel supply, so it’s pretty much a wash. Still, maybe I’m wrong. Say the fusion engines of 25 years from now are 1,000 times more efficient than those of today. You’d only have to up the mining production by a factor of 200,000. And still grow food, make air, raise kids, etc.
  6. In summary, you’d need somewhat more fuel than you could move with a few dozen trucks and a few shovel cranes per engine.
• Repair parts for the vitally important engine are kept hundreds of miles away?
• The big engines on the equator are especially stupid. What are they supposed to do? We don’t need thrust in that direction.
• Nobody wants to live right under a tremendous fusion reactor whose PURPOSE is to spew out radiation in unbelievable quantities.

I am done. I could say more but I think I’ve made my point.