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One of the limitations to human space travel is acceleration limits. We'd really like to just shoot spaceships out of a cannon to 99% the speed of light, but the resulting pressures on the human body would crush them. Even for rockets, greater acceleration is more efficient.

Notice though that the problem is pressure: if the entire body is accelerated at the exact same rate, this feels the same as weightlessness. That's why floating in deep space and floating in orbit feel the same.

So a potential solution is to just accelerate the entire human body at the same rate. If your spaceship is accelerating at $a$, instead of pushing the human through their skin, use diamagnetic levitation to accelerate their entire body at $a$. (If you want to simulate the experience of earth gravity, use enough diamagnetic levitation that we would accelerate to $a - g$. The remaining acceleration caused by being pushed against the back of the spaceship will induce the same internal pressures as the ground on earth.)

However, there is a catch: although diamagnetic levitation can affect every location in a region equally, it does not affect all materials equally! In particular, $O_2$ is not diamagnetic at all!

So my question, how much acceleration from diamagnetic levitation can a human handle?

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  • $\begingroup$ all materials are diamagnetic. O2 is also paramagnetic so the attraction goes the other way.. $\endgroup$
    – camelccc
    Apr 25, 2023 at 20:38
  • $\begingroup$ You don't actually save that much time by accelerating faster when the distances are really large. A couple of gravities for a couple of (ship frame) years gets you as close to the speed of light as your ship can probably survive in the interstellar medium, so we're talking about doing some really wild engineering space magic to save just a few years of spaceship time and barely any station time. $\endgroup$
    – g s
    Apr 26, 2023 at 2:57
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    $\begingroup$ @gs the problem isn't time, it's the tyranny of the rocket equation. $\endgroup$ Apr 26, 2023 at 4:10

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Only about 1 g

And 1 g may already be unsafe.

Based on this safety sheet, 2 Tesla is the magnetic field strength "whole body ceiling limit"; whole-body exposure to a magnetic field stronger than this is considered unsafe. 5 Tesla is the "extremity ceiling limit"; it is considered unsafe to even expose an extremity to a magnetic field stronger than this.

The risk is apparently that the magnetic fields will generate electric currents in the body which may stimulate nerves and muscles, potentially causing cardiac arrest.

The levitating frog needed 16 Teslas to counteract gravity. Based on this post a human would need an even higher magnetic field intensity, tens of Tesla, to counteract gravity. However, this is already an unsafe amount according to the safety sheet. So, people shouldn't really do much more than that.

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