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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.

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  • $\begingroup$ 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 $\endgroup$
    – Kilisi
    Jan 16, 2019 at 9:22
  • $\begingroup$ @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. $\endgroup$
    – Masclins
    Jan 16, 2019 at 9:31
  • $\begingroup$ @L.Dutch as I understood superconductors, it becomes blocked in the magnetic field, so I should stay stationary. $\endgroup$
    – Masclins
    Jan 16, 2019 at 9:35
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    $\begingroup$ @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 $\endgroup$
    – Dorian Turba
    Jan 16, 2019 at 9:48
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    $\begingroup$ 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. $\endgroup$
    – Dorian Turba
    Jan 16, 2019 at 13:29

2 Answers 2

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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. ;-)

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  • $\begingroup$ 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) $\endgroup$
    – Masclins
    Jan 21, 2019 at 9:59
  • $\begingroup$ @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 ....) $\endgroup$
    – Karl
    Jan 21, 2019 at 10:16
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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.

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