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Humans can survive maybe 3-10 $g$'s sustained acceleration when applied to their backs, like in a rocket launch. This question is not about that.

I'm wondering about alternative theoretical future ways humans might be able to be accelerated faster than that. What kind of exotic gravitational, electromagnetic, or other physics could be used to accelerate something in a way that doesn't put major stresses on the accelerated body?

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closed as off-topic by user10851, Brandon Enright, user36790, John Rennie, Ryan Unger Dec 18 '15 at 11:16

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  • $\begingroup$ the acceleration strength is not important if it is applied a long time ... $\endgroup$ – user46925 Dec 18 '15 at 3:12
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    $\begingroup$ I'm voting to close this question as off-topic because it's about human ability to resist acceleration not physics $\endgroup$ – John Rennie Dec 18 '15 at 7:04
  • $\begingroup$ @JohnRennie Actually, the question is NOT AT ALL about a human's ability to resist acceleration. I see that many people focused on the part of my question intended to fend off those kinds of answers. I'll try to make it clearer. $\endgroup$ – B T Dec 18 '15 at 8:11
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I am not sure there is such a theoretical limit. Yes, under ordinary conditions, high acceleration kills humans, however, if all points of the body have the same acceleration, I do not think such acceleration would kill, due to the equivalency principle - the body will actually be in weightlessness. Therefore, I guess a human body can survive a free fall in high homogeneous gravitational field (if there is no air drag, the body is protected by a space suit from vacuum and has a supply of air:-) ) However, you need to conduct such experiments near some giant star:-), so this is not very practical:-)

EDIT (12/22/2015): Let us make some estimates. The free fall acceleration at the surface of the Earth is $a_i=G\frac{M_i}{r_i^2}=g$. The tidal force is approximately $a_t=G\frac{M_i}{r_i^2}-G\frac{M_i}{(r_i+d)^2}\approx G M_i\frac{2 d}{r_i^3}=g\frac{2 d}{r_i}$, where $d\approx 1 m$ is the dimension of a human body. So the tidal force is extremely small, less that one millionth of g. Let us then increase the radius of the Earth by a factor of $k$ and the mass of the Earth by a factor of $k^3$, so the density will remain the same. The free fall acceleration at the surface will increase by a factor of $k$, whereas the tidal acceleration will not change.

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I'll take your question to mean, "what is the highest acceleration a person can experience without dying".

It depends on the duration, health, and whether a G-suit and/or other help is provided. A person can fall a few meters onto a hard surface while oriented horizontally and usually survive, and that is 100G+ for a millisecond or two. About 10G continuously (many minutes) may be survivable if the person is rotated regularly (1-2 RPS)to maintain fairly even blood and lymph flow, which can be done while immersed for more comfort. Of course, the person should be horizontally oriented. Otherwise blood flow in the brain will be totally lost.

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  • $\begingroup$ good analogy idea but it's worse than 100G+ ! $\endgroup$ – user46925 Dec 18 '15 at 3:50
  • $\begingroup$ Yeah, I think you're right. Maybe that's what it is for a meter drop, or so. $\endgroup$ – Digiproc Dec 18 '15 at 3:52
  • $\begingroup$ That's interesting about rotating the body to even out blood flow, but my question explicitly asked about alternatives to traditional acceleration using a pushing force. So this isn't really an answer to my question. $\endgroup$ – B T Dec 18 '15 at 5:22
  • $\begingroup$ @BT : higher accelerations imply bodies death. Else consider frozen travellers or some futuristic digital storage $\endgroup$ – user46925 Dec 18 '15 at 5:44
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Freefalling would not be considered accelerating. Standing on the surface of the earth is equivalent to being accelerated at 1G. If you were free falling that's equivalent to no gravity. The sudden stop of landing on a sidewalk would be equivalent to extreme acceleration.

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  • $\begingroup$ While I mostly agree with you, this isn't an answer. If you want to comment on something someone else said, please write a comment, not an answer. Also, if you could somehow move the gravitational field as you accelerate toward it, it could in fact accelerate someone. $\endgroup$ – B T Dec 18 '15 at 5:34
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    $\begingroup$ You're right I got off on the train Of thought and forgot what I was answering. Your comment about moving the gravitational field made me realize something. I guess technically freefalling is not the same as weightlessness because acceleration due to gravity would be slightly accelerating you, until you stopped at least. $\endgroup$ – Bill Alsept Dec 18 '15 at 5:45
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The theoretical fastest way is a uniform force with no distance component. The force on every cell and every sub particle was the same. A force that creates no internal stress in the body. A super-gravity with no distance component. There is no known force like that today and not likely to be discovered or created.

You asked for "theoretical fastest way" and that is the answer. You dismissed practical limits in a comment to akhmeteli.

Once the body got near the speed of light you would run into some issues but that is whole different theoretical problem. That is getting into this time travel thing.

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  • $\begingroup$ But if there is no known force like that, then that isn't even a theoretical possibility, right? I'm looking for things that we know are possible, while ignoring the economic feasibility of such things. How about a giant accelerating planet you can ride the gravitational pull of? Or a spinning cylinder that accelerates things via gravitomagnetic force. That's the kind of thing I'm hoping people will bring up. $\endgroup$ – B T Dec 18 '15 at 8:17
  • $\begingroup$ Lot of rules. Just because it is not know mean it is not possible. A cure for cancer is not know - does that mean it is not possible. You literally asked "exotic gravity". $\endgroup$ – paparazzo Dec 18 '15 at 12:05
  • $\begingroup$ A cure for cancer is possible within the realm of theoretical physics and theoretical medicine. "super-gravity with no distance component" has absolutely no theoretical merit. You might as well say "super-acceleration with no momentum component". Neither has an hint of existing. I meant exotic like things we don't think of or see everyday, not as in completely made up (which is not what exotic means anyway). $\endgroup$ – B T Dec 20 '15 at 7:59
  • $\begingroup$ @bt Now more rules. Can you prove it has no theoretical merit? Exotic means something we don't think of everyday? So exotic gravity is limited to gravity? You might as well say gravity. $\endgroup$ – paparazzo Dec 20 '15 at 8:18
  • $\begingroup$ The fact that you have no reasons that it does have theoretical merit is proof enough that it doesn't. The burden of proof is on you if you're claiming something has merit. $\endgroup$ – B T Dec 22 '15 at 6:22

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