In a previous question on this site I asked about the side effects of a having ludicrously strong, permanent, static magnetic field on the surface of a planet, capable of pulling in non-magnetized ferromagnetic objects from a distance of many miles. Now, the world I have in mind has technology equivalent to Europe somewhere around 1300-1600, but I'm curious how a hi-tech society could take advantage of that field. For instance, could you put an electromagnet on a spacecraft, and use the magnetic pull to achieve escape velocity? Could you set up power stations inside the field (not too close to the center!) and generate electricity? Some other obvious exploit?


  • The magnetic field is coming from an object with some ridiculous level of coercivity. Don't worry about how it got magnetized that strongly.
  • The field is sufficiently strong to have a pull force of 10N on a 1kg iron ball at a distance of 100 km (I used 100 miles in the previous question; let's keep everything in metric here).
  • The field/magnet is stationary with respect to the planet's surface. Fairly sure this doesn't require handwaving--one answer to my previous question suggested the magnet would pull on the planet's iron core and sink (catastrophically) to the center of the earth, but my understanding is that ferromagnetic materials in the mantle or below would be too hot to remain magnetic.
  • The population of the planet survived the creation of the magnetic field (or the relevant population colonized the planet after the field was created).

Hope the question isn't too broad, and that it's acceptable to pose a question that isn't immediately of use to a story; happy to revise/close if it's a problem.

EDIT: To be clear, I'm looking for ways to exploit the magnetic field using modern knowledge and technology; the Renaissance period specified above is just for background. Based on the answers to my other question, some really wacky things start happening as you get close to a magnetic field that strong--I want to know if any of them would be useful.

  • $\begingroup$ Stationary with respect to what? $\endgroup$
    – L.Dutch
    Commented Apr 20, 2018 at 20:42
  • $\begingroup$ @L.Dutch With respect to the planet's surface; I'll add that to the question. $\endgroup$
    – rsandler
    Commented Apr 20, 2018 at 20:43
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    $\begingroup$ Not an answer, but a way to potentially improve the question and/or avoid any more answers along those lines - you cannot generate power from a stationary magnetic field. Motion through the field is required. That being said, a windmill dragging wires around perpendicular to the field would see powerful induced currents, so you could have a power plant, it just wouldn't be much easier to make than the normal sort. $\endgroup$
    – jdunlop
    Commented Apr 20, 2018 at 23:48

2 Answers 2


Something that pulls metal from that far away combined with a medieval/renaissance society? Torture, Prison, and maybe Hell come to mind.

As a gross over-simplification, in societies of that era especially the early end: magic was still a possibility, religion was a given, and science was quasi-heretical if you didn't agree with the local religion or offended someone important.


Remember the Rack? Arms tied at one end, legs at the other, and the victim was slowly stretched until something gave way. With a strong magnetic field of this nature, you simply need to anchor the person at one end, and attach some metal to the other end and let them hang. Sideways. Bonus points if you provide feathers.


Just encase them in metal, or give them metal boots and gloves and let them go. They won't be coming back. Think of a long walk off a short pier with concrete boots... only with metal and magnets!


Given the strength of that field, you get close enough, it might be able to pull the metal out of one's body, such as blood. Should that be the case, then you have a good candidate for the "Yellow Springs" to borrow an Asian metaphor for Hell. Anything which could slay a person invisibly by sucking the blood out of one would very likely give rise to the notion of demons and Hell, if they didn't already have the concept from mythology and/or religion.

As an added bonus, it would definitely interfere with birds and other creatures which rely upon geo-magnetism.

As another thought, once they discovered electricity, and the relationship between it and magnetism, you have the makings of an engine core.


Get a hula hoop, stick some cylindrical magnets into it (if your society has 1600's tech they can figure something with lodestones). The point is that the magnets should be aligned with the circle, like this:

Magnetic hula hoop

Take it to the insane magnetic field. Stick it to a structure through the hub someway, keep the circle standing vertically and aligned to the magnetic field. If it hasn't started spinning like crazy yet, give it a good, solid kick.

You've just got yourself a magnetic mill. You can use it to grind grains and stuff.

A high-tech society would be extracting energy from the magnetic field. setup above would look like a perpetual motion machine, but it would actually be draining the magnetic field (i.e.: it might take millions of years, but it would eventually stop). You could use the machine's motion to generate electricity.

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    $\begingroup$ Well then, you have invented a perpetual motion machine... The downside is that perpetual motion machines don't work. You cannot extract energy out of a static magnetic field because there is no energy there to extract. (Time-independent magnetic fields are conservative, meaning that the total work done by the field on a magnet moving on a closed path is zero.) $\endgroup$
    – AlexP
    Commented Apr 20, 2018 at 21:42
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    $\begingroup$ A static magnetic field can't be used for energy generation anymore than a gravitational field can. You can't 'drain' a gravitational field, why should you be able to drain a magnetic field? $\endgroup$
    – Samuel
    Commented Apr 20, 2018 at 21:55
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    $\begingroup$ @AlexP I'm not sure I understand why this wouldn't work. Surely the field would be expending energy on the magnet regardless? The implication is that this magnetic field is strong enough to overcome gravity. Therefore, any object effected by the field would necessarily draw energy as it repulsed or attracted objects in opposition to gravity. For that matter, the question does not actually specify that the field is static in the first place, only that it is ridiculously strong and generated by a geological object. $\endgroup$
    – Kaosubaloo
    Commented Apr 20, 2018 at 22:21
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    $\begingroup$ @Kaosubaloo: The point is that that the total work done by the field on a magnet which moves on a closed path is zero. You are right that the field would do work on part of the path; but that work will be exactly compensated on the return path. Think by analogy of Earth gravitational field; if you have an object falling the field does work, but if then you need to bring the object to the starting point you give back the exact same amount. $\endgroup$
    – AlexP
    Commented Apr 20, 2018 at 23:33
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    $\begingroup$ How about in an orbiting space-station? A simple magnet, for example, will continue to act like a compass and point at the planet, while the station orbits. From the station's point of view, (unless it happens to be rotating at exactly the same speed), the compass will appear to spin once per orbit. Surely power can be extracted from such a setup, no? $\endgroup$
    – Glurth
    Commented Apr 22, 2018 at 8:04

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