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It finally happened. The inhabitants of Metropolis, the capital of Our Nation, have finally had enough of the swampy lands, suffocating summers, freezing winters, spring floods, risk of surprise invasion by sea and whatever other nastiness the local geography had in store for them.

They have decided to move Metropolis. Since Our Nation is a glorious empire with vast, vast resources at our disposal, we will literally uproot the entire city and move it some place we like better (about 161 km away -- 100 miles away).

How do we go about moving a city of 5 Million?

How much time, how much energy would it take? Can it be done in bulk, whole blocks at a time? Can you literally float it, in the air or on a river?

A few details:

  • I would prefer near-future technology, but I won't get upset if your solution needs to specify otherwise, i.e. literally float-up into the air the whole darn city at once, as long as you can show your work (energy calculations etc).
  • Metropolis has about 5.5 million people in the greater urban area, and is the seat of administration of Our Nation. Edit: The area is 176.9 km² or 68.3 mi².
  • By law, no building in the city can be taller than the Giant Phallic Symbol of Power, a monument 169 m tall. Only a handful are taller than 60 meters.
  • The move should be as quick as possible and cause as little disruption as possible to government and the lives of the inhabitants.
  • As a real-life historical near-precedent, Chicago has literally been lifted off the ground, with 19th century tech at that.
  • The reason we can't go the normal route (just build a new city) is because we're vainglorious and, frankly we have the technology and we want to show off.
  • I softly encourage hard science answers, but if you feel you have a brilliant idea but lack the time or the maths to flesh it out, please share it anyway.
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    $\begingroup$ Oh, and a few question to clarify. How much space does the city take up? Do you care what happens to the suburbs? How about all the land between Start and Destination? Do you mind leaving a huge crater behind? $\endgroup$ – guildsbounty Mar 18 '15 at 16:36
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    $\begingroup$ When I first came here, this was all swamp. Everyone said I was daft to build a city on a swamp, but I built it all the same, just to show them. It sank into the swamp. So I built a second one. And that one sank into the swamp. So I built a third. That burned down, fell over, and then sank into the swamp. But the fourth one stayed up. And that's what you're gonna get, lad: the most powerful city in this land. $\endgroup$ – Samuel Mar 18 '15 at 16:56
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    $\begingroup$ Does a Simpson episode count as historical precedence? $\endgroup$ – Twelfth Mar 18 '15 at 17:42
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    $\begingroup$ @Twelfth Only if you include the Lost City of Atlanta from Futurama. $\endgroup$ – Samuel Mar 18 '15 at 17:56
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    $\begingroup$ Personally, I think I'd drain the swamp, dredge canals, let the ocean in and make Venice... How tall are the buildings? What are they constructed of? Are we moving something like New York? Is the place they are moving to along the coast too? $\endgroup$ – AndyD273 Mar 18 '15 at 18:13
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This is probably the most destructive, tyrannical, and least glamorous answer you are going to see.

We can already relocate structures...it's simply a matter of building a metal framework solid enough to support the structure underneath the foundation. Jacking this framework up off the ground, and then putting wheels on it and pushing it to wherever you want to drop it off. The entire process must be done very, very slowly so as not to damage the building.

In order to relocate something like a Skyscraper (which has a very high center of gravity, generally compensated by affixing the structure to bedrock) you are going to be at a risk of it tipping over unless you can build a sufficiently massive framework to stabilize it.

From there, it is simply a matter of scale. Stronger frameworks, more/stronger jacks, more/bigger wheels. Heck, if you can build something strong enough, you might be able to carve out the bedrock that the city is built on, jack THAT up, and relocate the whole thing in one go.

But here's the catch. Anything between Point A and Point B is going to have to go. Anything that is not nice, flat ground. This means towns, cities, mountains, lakes, etc. The smaller of pieces you move the city in, the less widescale obliteration you need to unleash. Trying to take a skyscraper up a hill would end in a tipped-over skyscraper.

You're probably also going to have some repairs to make, regardless of how careful you were, because things are going to shift and move while being relocated. Hopefully not to the point of anything falling down entirely, but you'll have cracked walls, damaged floors, etc.

I'm sure someone else will come up with a more fantastic answer, like orbital lifting or somesuch...but I figured I would toss up the simple 'we already do this on a smaller scale' answer.

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  • $\begingroup$ For reference, the heaviest building ever relocated like this was the Fu Gang building in the Guangxi Province of China, weighing in at 15,140 tons, standing 6 stories tall. It took 11 days for the entire process that moved it a mere 36 meters. $\endgroup$ – guildsbounty Mar 18 '15 at 17:02
  • $\begingroup$ So to move the OP's entire city would probably take an ungodly amount of time. $\endgroup$ – JDSweetBeat Mar 18 '15 at 17:44
  • $\begingroup$ Not necessarily. Economies of scale would apply to the time, both for the mass and distance moved. It wouldn't be "fast" by any definition, but "ungodly" might not be accurate either. This is because increasing either mass or distance is very much "more of the same" kind of change. $\endgroup$ – Ville Niemi Mar 19 '15 at 6:35
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Space Elevator.

I once wrote a story which involved that.

There's an elevator into space in the center of the city. The city needs to be moved (built on a volcano that was inert but the strain from the elevator reactivated it, and it will erupt soon), and they decided to use the technology in place to move the city.

First, reinforce the supporting ground through building tunnels and drawing cords of the same material as the space elevator through them, making the clump of stone and earth not fall apart from the stress. Then reinforce the elevator to support the whole mass, adding extra ropes. Then pump a lot of water up beyond the Geostationary orbit, forming a counterweight of ice in space.

Through extending the network of tunnels, separate the city from the native rock. At certain point, the counterweight will pull stronger than the mass of the city. Multiple heavy ground vehicles provide a moving anchor, so that the city doesn't just float away. They move the city towards the destination, holding it with long ropes several hundred meters above the ground.

Then a stray asteroid hits the counter-balance, and the city falls, nearly flipping over, the elevator ropes snap, twisted as they were not meant to, and the city lands on one side of the mountain, houses of the other side hanging nearly upside down over the jungle below, providing arena for my story.

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  • $\begingroup$ Oh no, not the counter-balance! $\endgroup$ – Serban Tanasa Mar 20 '15 at 1:25
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Put the whole city on wheels

Do this as follows:

  1. Dig caverns into the bedrock under Metropolis.
  2. Build some very strong wheels with near-future technology. Carbon buckyballs may be useful. If necessary, you could use superconducting magnets in place of bearings.
  3. Quarry a pit of the right size and shape at your intended destination. Nuclear weapons may save time, if you don't mind a bit of radiation. Alternatively, design the wheels to be collapsible; when you arrive, they are crushed under the weight of Metropolis, which will then rest on a plateau above the surrounding landscape.
  4. Build a suitable roadway. You would need to dig away all the soil and expose the bedrock, then level the ground, creating a (relatively) shallow trench several kilometers wide.
  5. Very carefully dig away the last remaining pillars of rock beneath the city, so that the massive slab of bedrock rests on the wheels.
  6. Propel the city 100 miles inland.
  7. Wheel the city into the pit you have prepared. If the pit is very precisely shaped (requires some final precision digging, nuclear weapons not suitable) then the wheels will drop into individually prepared wells so that the slab of bedrock neatly comes to rest in its new home. (Or you can go with the plateau option above.)
  8. Celebrate with a huge party at the base of the Giant Phallic Symbol of Power.

Some engineering details

Metropolis has an area of 180 km^2. If it's roughly circular, it has a diameter of about 15 km. This is the width of the path you need to clear.

How much does the bedrock weigh? Ignoring the weight of the buildings, suppose we dig 1 km down into the rock, which is solid granite with a density of 2800 kg/m^3. One km^3 of granite is equal to 10^9 cubic meters, so 180 km^3 of granite weighs (1.8*10^2)*(10^9)*(2.8*10^3)*(10^3) = 5.04*10^17 grams.

Accelerating the slab to 1 m/s (a reasonable speed of 3.6 km/h) requires 5.04*10^17 joules of energy (kinetic energy being equal to mass times velocity^2). If we take 24 hours to get up to speed, this implies (5.04*10^17)/(8.64*10^5) =~ 10^12 watts of power to within an order of magnitude, or 1 thousand gigawatts. This is roughly equal to the total electricity grid output of the USA. So if Our Country is of similar size, you just have to ask the citizens to give up all electric power for a day, which I'm sure they will be happy to do for the greater glory.

Alternatively, you could use nuclear pulse propulsion to accelerate Metropolis, by building a large blast absorbing plate behind the city and setting off a number of nuclear explosions. This would leave a radioactive wasteland at the original location of Metropolis, which might be regarded as a drawback.

At 3.6 km/h it takes about 45 hours to move Metropolis. In fact it will take a little longer, allowing time for initial acceleration, and deceleration at the other end. Metropolis is presumably moving uphill; this may increase the energy requirements, but conversely you can use gravity to help with the deceleration.

For the most part, this method has the advantage of minimal disruption except when the city is actually in motion, which is only for a couple of days.

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  • $\begingroup$ Maybe 1km of bedrock is a bit too much? Given that the highest building is 169m high, you are basically moving a big chunk of rock with some little buildings on top of it. I feel like 100m should be enough to provide a good counterweight, and make the energy requirements a bit more bearable. This also made me think of how people move rockets en.wikipedia.org/wiki/Crawler-transporter $\endgroup$ – Maxime Lucas Mar 19 '15 at 13:03
  • $\begingroup$ @skysurf3000: 1 km was the first depth I thought of, but I also liked the fact that the entire power output of the USA would just about be enough to move it. You could probably get away with a thinner slab. Maybe you would want more than 100m, if Metropolis has nuclear bunkers, a metro rail system, and so on tunneled beneath its surface. (Typical depth of metro tunnels is between 50 and 70 m.) $\endgroup$ – Royal Canadian Bandit Mar 19 '15 at 14:00
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Float the city.

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Dig under it and put in structural bracing to support the buildings and then tons of pontoons. Then let the ocean in to let the city float up, and then tow it up the coast to the new destination. You haven't described the city at all (building height, materials used etc) so this may take some super materials to make possible.

Edit This gets you out of the swamp and 100 miles away into a better climate with hopefully milder winters, without having to level mountains. Which takes care of the seasonal flooding and malaria. Since everything is pretty solidly braced at this point, if you want to get out of the water to get to higher ground you could put wheels on the city boats pull them out. And because they are raised up, it would be pretty easy to put the utilities in underneath.
Or you could find a sheltered harbor and have a floating capital.

They'd still be near the coast, so maybe surprise attacks from the sea will still be a problem, but these are people with the technology to move a city. Seems like a fleet of warships to patrol the ocean and remove any surprises before they become a problem should be a small task.

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  • $\begingroup$ Though this may be the best way to move the city over great distances to a warmer climate, I don't really see how this could solve "the swampy lands, [...] spring floods, risk of surprise invasion by sea". $\endgroup$ – Maxime Lucas Mar 19 '15 at 13:59

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