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Inspired by this great answer.

There is a planet with:

  • Floatium, a superconductor that behaves as such at 0 ºC and is found in nature.
  • A stronger magnetic field than Earth's.

In really cold areas I imagine people seeing that Floatium floats after being impacted by a lightning. After that they would try to take big rocks of that material, force a lightning to land on them (maybe through metal rods) and build their cities there.

Would it be plausible to create floating cities this way?

I'm afraid that maybe the force needed to push the rock up would be too much to be really feasable. Or that the whole thing doesn't have any sense.

I'm interested also in how low the technology level can be and still those floating cities be possible.

PS: An alternative which seems viable had been asked in v2 of this scenario, thanks to Karls' answer.

Masclins
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  • why would low tech people want to live somewhere that is always below zero? What do they eat? Makes more sense to use it as transport, perhaps refridgerating a vehicle. but not a city – Kilisi Jan 16 '19 at 09:22
  • @Kilisi I would work that out depending on how feasible is this and how low the technology level can be so it can be done. – Masclins Jan 16 '19 at 09:31
  • @L.Dutch as I understood superconductors, it becomes blocked in the magnetic field, so I should stay stationary. – Masclins Jan 16 '19 at 09:35
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    @Kilisi 0°C does not mean no food. Mamouth, Elk or any animals living well under 0°C. And you said : why would low tech people want to live somewhere that is always below zero? Many reason: Cause there is more food ? Cause they can't stay elsewere ? Cause stuck by some climatic event, etc – Dorian Turba Jan 16 '19 at 09:48
  • Do not forget that in order to use supraconductor material, you need electricity. With electricity, you can do... a lot of things. It's not very very low tech level for me. – Dorian Turba Jan 16 '19 at 09:50
  • @DorianTurba That's where I thought a lightning might solve it. A single lightning strike would be enough so it behaves as intended. Well, at least that's a huge part of what I want to reality-check. – Masclins Jan 16 '19 at 09:54
  • ".. floats after being impacted by a lightning" Why the twist with the lightning? Superconductors are always repelled by a magnetic field gradient! @DorianTurba Check any picture you find on google when you search for "superconductor": You need no wires to see the Meissner effect. – Karl Jan 16 '19 at 10:02
  • No wire ? The floating thing is a magnet. The supracondutor is under. – Dorian Turba Jan 16 '19 at 10:51
  • @DorianTurba OK, got me with that one. Sorry for supersimplifying. :-| But the superconductor in these pictures is simply submerged in a small beaker full of liquid nitrogen. It's not connected to any battery or other electrical circuit, but just lying there. – Karl Jan 16 '19 at 11:43
  • For me, supraconductor material do nothing if no electricity. It's not magic, not even magnetic. You need electron traveling in the supraconductor material in order to repel magnet. Maybe I'm wrong but last time I read something about it, that was the case. – Dorian Turba Jan 16 '19 at 13:25
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    And of course, event if there is a superstrong magnetic field on the planet, it's not in the rock, but created by the iron core of the planet. So the supra conductor have to be in the island. And admit such a powerful magnetic field exist (it's impossible), the supraconductor material have to be extremly powerful, or your little rock will stay near the ground. Once again, if not magic, it can't happen. Even with great lightning hit. – Dorian Turba Jan 16 '19 at 13:29
  • @DorianTurba A superconductor is the ideal diamagnetic substance. If a magnetic field line tries to cross its surface, it creates ring currents in the material that are exactly strong enough to make an opposing magnetic field that cancels the external field. That's called the Meissner Ochsenfeld effect. So, yes, there is an electric current, but it has no source and no voltage, no external wire and no electric field. – Karl Jan 16 '19 at 22:35
  • @Dorian Turba: Re "Mamouth, Elk or any animals living well under 0°C", they don't live at that temperature for the entire year. They either survive on what grew during the summer (if not carnivores), or they hibernate. Even Antarctic penguins get their food from the (slightly) above 0°C ocean. – jamesqf Jan 17 '19 at 01:12
  • Well, in order to get a city in the sky... Sorry I don't know the math for this, but for me, it's nearer fantasy than science. That's cool but needs a certain amount of suspension of disbelief. Maybe I'm wrong of course, that's why I don't answer ^^ – Dorian Turba Jan 17 '19 at 03:08

2 Answers2

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Impossible: The Meissner effect creates a force on a superconductor in a magnetic field gradient, that is in the direction where the field becomes weaker.

On the lengthscale of a few meters or even a kilometer, the magnetic field of a planet is practically constant, so you will get no repelling force worth mentioning.

The magnetic field of the planet would have to be extremely strong before the superconducting rock can even lift itself, and such a strong field usually destroys superconductivity again.

One more (it always gets worse ;-): The magnetic field gradient itself weakens even slower with distance from the ground. So the repelling force is more or less constant, which means your superconducting rocks would keep accelerating, and might just pop out of the atmosphere and vanish into space. Now that's a valuable target for asteroid mining. ;-)

Karl
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  • Would it be different if the magnetic field of the planet is earth-like, the mountain is a superconductor and I try to suspend a magnet on it? I feel like I might missunderstood some of the stuff regarding superconductors and this might help. (If so, I'll create a new question changing this things) – Masclins Jan 21 '19 at 09:59
  • @Masclins If the mountain is superconducting, a magnet would float on it! (Actually it would topple off the side. You want a ring mountain, like a superconducting crater. Let's hope you never get a storm that pushes your city over the brim ....) – Karl Jan 21 '19 at 10:16
  • would not the premise of their story be restored if instead of Meissner repulsion it was flux pinning and the people of the story did some engineering to successfully "pin" their planets magnetic field lines to the rock – Sidharth Ghoshal Jan 08 '24 at 19:56
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Assuming you can the rocks 'hover' (not entirely unimaginable), you can have your technology level as low as you'd like, as long as they have the means to build weather-proof shelters on these rocks and somehow have a way of moving between the rock and earth.

Higher up one usually finds stronger winds, which could move the rocks, if the rocks are not tethered, and damage abodes. Hail, snow, or rainfall may have similar results, though this may also push the rock towards the ground temporarily. Freshwater lakes could be present from the rainfall, and simple flora could exist on the rock.

Shelters may be in the form of artificial caves or lightweight structures to prevent the rock from tipping.

Settlements might bind the rocks to the earth, perhaps having a religious connection to them or using them for transport (similar to a hot-air balloon, but harder to control), while nomadic tribes may use a retractable rope to hop down and gather resources while preventing predators or vermin from climbing onto the rock.

'Capturing' the rocks could come from daring leaps from mountains to ensnare bypassing rocks, ballistic anchors (perhaps multiple sets of longbows) or trained creatures of flight, similar to hunting birds.

Rocks discovered in the ground could have a net thrown over them before being 'mined'.

For most of these tasks and challenges bronze-age technology would be more than sufficient, and while potentially unrealistic from a physical standpoint could bring a lot of unique features to your world.

A Lambent Eye
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