Floating Cities and Superconductivity

[radienx000]

Is it possible to make floating cities from the concept of superconductivity? As the superconductor would exclude the external magnetic field and levitate. So this city might be able to float on our skies by having internal superconductive engines. Also if the superconductor was strong enough, it might be able to be sent into space where it can repel any space/celestial object that comes close to it. If this space object had a magnetic field of its own.

 

I see that we have not found a superconducting material that has a high enough critical temperature for us to use it without wasting our electricity and hence money on lowering to temperature to make the superconductor effective.

[insane_alien]

no its not possible.

 

it is true that it would repel the earths field(and they do that already) but there is one major problem. super condctors don't float. if it were possible for them to float on the earths magnetic field then they'd do so already.

 

we do know why the don't float though. the earths magnetic field is weak. very very weak.

 

effectively what you are asking is that we build a boat made from solid lead(no hollow hull). sure, when you put it in water there will be just as much buoyant force as there would be with any other material, but its too heavy to be supported by it and it'll sink like a brick. faster than a brick even.

 

it also wouldn't repel other objects in space unless they had a very strong magnetic field. and the super conductor will be repelled just as much as the other object is.

[timo]

From the most basic principles:

- Having something float does a priori not need energy, so that is possible.

- Lifting something needs energy, regardless of how advanced the method is. Presumably quite a lot for a whole city.

- Having to lift all goods and people going into the city doesn't sound too smart energy-wise, either.

 

In practice, energy consumption will of course be much worse than the E=mgh minimum because the mechanisms may not be fully efficient. Additionally, it's not clear if you find magnets strong enough, either. Living conditions in a city with a super-high magnetic field in it may be strange, too. And thousands other technical issues.

 

I tried finding a picture online but didn't. Anyways: In theory, just putting balloons on the city would seem much more efficient for lifting it than pushing from below with superconductors. The idea is not new but dates back to the days when balloons were invented. Somehow, the difference between theory and practice (which in practice is often bigger than in theory) somehow prevented this idea to become the mainstream solution for modern city design. So from the principle of superconductivity there is nothing that speaks against the idea. Only due to the interplay of this principle with reality it is pretty much impossible.

 

EDIT: Oh, and reading insane_alien's post: I was having a design with an artificially-created magnetic field on the ground in mind, not one using earth's magnetic field (in which case the strength of the field might or might not be a limiting factor even in theory).

[John Cuthber]

It would be spectacularly expensive and more than a little pointless, but yes, you could float a city on a superconductor.

You would need a couple of superconducting coils to generate two fields that repelled one-another. Then you would need some more to keep the system "stable".