FTL travel g-forces

[Iroscato]

Hello, I'm quite new to this forum and I have a question that should be able to be answered here. This may be a silly question, but if we were one day able to develop ships that could travel faster than light, how would we be able to counteract the g-forces involved in acceleration?

As far as I know (from my extremely limited military knowledge), pilots can't really get past mach 5 without blacking out, so to even go to 1% of the speed of light would cause instant death, surely?

Please help me out, this has bugged me since I was 10

[Ryan Thunder]

Acceleration is not the same thing as speed.

[Eternal_Freedom]

An important thing to remember is that the "g-forces" you mention are acceleration, not the result of a speed. And in space, speed is faintly irrelevant. It's the acceleration, the change in velocity that matters.

Yes, slamming from 0 to 5% of lightspeed would kill you, but if you accelerated there gradually at 1g (9.81 metres per second squared) it would feel no different than being on Earth. It would take a while, but it wouldn't kill you.

I won't pretend to know enough to comment on military pilot endurance, but I hope that helps clear up the matter.

[Batman]

Going to 0.01c would NOT cause instant death. It would merely take quite a bit of time (at 1 g, approximately 85 hours).
As Ryan says, it's not the speed that matters, its the acceleration. You can get to high fractional c on a billionth of a g if you keep at it long enough.

As for going FTL, g forces cease to matter because it's impossible to go FTL by simply pouring on acceleration regardless of rate. You're never going to go faster than c no matter how hard or long you step on the gas. You either have the magic trick that allows you to go FTL or you don't.

[Korto]

Batman got there first, but yeah. Any worries about surviving the g forces going faster than the speed of light take second place to explaining just how you went faster than the speed of light in the first place.

Anyone care to suggest a time frame for Freedom's "slamming" from motionless to 5% c, just so we can work out the g-forces, and laugh at the thought of the ship surviving, let alone anyone inside? I wonder if it could crush it ito neutronium, or even a singularity? Or am I just completely off the rails?

[Eternal_Freedom]

Try working it out for, I dunno, 0.1 seconds

[Iroscato]

Interesting, so we could theoretically travel at close to light and be fine, as long as we accelerated slowly? And yeah, I guess we need to actually invent a FTL ship before we start worrying about the mechanics of it

[Korto]

OK, just using v=u+at (don't ask me to do anything Einsteinian Relativistic, for God's sake)

v=5% c, u=0, t=0.1

We get an acceleration of 15.3 million g.

Assuming I'm right, someone with more knowledge on materials can tell us what that'll do to the structure, but unconsciousness is the least of the pilot's worries.

[Batman]

Or am I just completely off the rails?

Yes?
Anything capable of that kind of acceleration will pretty much inevitably have the technobabble means to enable it to survive this (acceleration compensators, inertial dampeners, inerters, whatever you want to call them).
And about 1.53E7g if I haven't fucked up the math once again.

Interesting, so we could theoretically travel at close to light and be fine, as long as we accelerated slowly?

Err-yes? Or at least the g forces wouldn't be the problem?

[Korto]

Technobabble, Shmecknobabble. Since the OP was wondering about the effect of the acceleration on the pilot, it seemed reasonable to assume an absence of magitech. And far more fun.

I am off the rails, anyway, since a neutron star apparently has a surface gravity four orders of magnitude higher than the g forces I calculated, making it reasonable to assume that neutronium wont happen.

[Iroscato]

Thanks for the answers everyone, I knew this forum wouldn`t let me down

[Sea Skimmer]

For a benchmark, the space shuttle accelerates at a constant 3gs going up, this is less then the rockets are physically capable of moving it; anything much higher then that would be severely taxing to human endurance and 1g is the realistic limit for multi day accelerations. Fighter pilots can take up to about 5-7gs somewhat reliably without a G suit, G suits allow for 9-11gs and bursts above that, but we are talking about seconds and fractions of a second of time at that force. After a dogfight a pilot may not even be able to lift himself out of the cockpit.

[Kuroneko]

I am off the rails, anyway, since a neutron star apparently has a surface gravity four orders of magnitude higher than the g forces I calculated, making it reasonable to assume that neutronium wont happen.

You're on the right track, though. Neutronization won't be significant until the density is high enough for the electrons' Fermi energy to make up the difference between neutron and proton masses (which about two orders of magnitude higher than the Fermi energy of metals under normal densities), but at those accelerations, metals in general will undergo more stress than the electron degeneracy pressure.

Assuming the force is applied to one back of the ship (as rocket thrust would, though who knows for FTL engines), let's calculate the acceleration stress on a bit of matter of length L and density ρ. This could be an object on the floor of the ship, or even a strip of the ship's hull. The stress on the material is σ = ρaL, where a is the acceleration. The electron degeneracy pressure is on the order ~10GPa, so with this scale for σ, and ρ ~ iron, gives L ≲ 0.1m for a = 1E6g acceleration, and scales linearly from there.

In other words, although you're not going to see neutronium, there will be electron-degenerate matter in the situation you're worried about.

[LionElJonson]

As for going FTL, g forces cease to matter because it's impossible to go FTL by simply pouring on acceleration regardless of rate. You're never going to go faster than c no matter how hard or long you step on the gas. You either have the magic trick that allows you to go FTL or you don't.

True, but certain types of FTL like Alcubierre drives might still result in felt G-forces due to space-time distortions, if I understand how they work properly.

[RedHeron]

The real-life answer to this involves things which are only theoretically possible in physics... things like inertial collapse envelopes, which negate specific relativity by creating conditions which specific relativity didn't take into account (but which are not outside of the realm of possibilities in orthodox quantum physics). This concept negates both time dilation and G-forces, but there's a lot of maths involved which might not be well-understood by someone who isn't a quantum physicist (or at least intimate with some of the mathematics involved).

Until we're actually there, we can't know whether or not it's even possible to negate G-forces to a point that it makes FTL worthwhile.

[Kuroneko]

things like inertial collapse envelopes,...

???

... which negate specific relativity by creating conditions which specific relativity didn't take into account (but which are not outside of the realm of possibilities in orthodox quantum physics). This concept negates both time dilation and G-forces, but there's a lot of maths involved which might not be well-understood by someone who isn't a quantum physicist (or at least intimate with some of the mathematics involved).

'Specific' relativity? Every FTL proposal that has even an iota of realism happens within GTR, which definitely does not negate time dilation, nor does it mesh particularly nicely with QM. Orthodox QM does not explain how to get the conditions required in those proposals, and QM is not at all necessary to understand them if those conditions are simply assumed.

[RedHeron]

things like inertial collapse envelopes,...

???

Sorry, it's kinda like Star Trek's "warp envelope," and would require technology we don't have, but which is theoretically possible. Consider the idea of artificial gravity becoming a reality, and as soon as that occurs we can generate a "field" of gravity which essentially isolates the interior of the field from the outside, where inertia is concerned.

This isolation negates portions of Einstein's specific relativity, while leaving general relativity intact... or, I might have those reversed (it's been a few years since college, and QM wasn't exactly the primary field of study). However, I remember having this discussion with my professor, who said that the only solution is to "wait until we get there," because science has a tendency to come up with solutions to problems.

'Specific' relativity? Every FTL proposal that has even an iota of realism happens within GTR, which definitely does not negate time dilation, nor does it mesh particularly nicely with QM. Orthodox QM does not explain how to get the conditions required in those proposals, and QM is not at all necessary to understand them if those conditions are simply assumed.

Orthodox QM does permit the idea of negation of time dilation if there is some kind of super-science at work... such as gravity field generation.

It's a pity that after 300+ years there still isn't a solid grasp of what makes gravity work.

We can't assume that we know everything about science, or we hinder its progress.

[Kuroneko]

Sorry, it's kinda like Star Trek's "warp envelope," and would require technology we don't have, but which is theoretically possible. Consider the idea of artificial gravity becoming a reality, and as soon as that occurs we can generate a "field" of gravity which essentially isolates the interior of the field from the outside, where inertia is concerned.

Everyone calls them "warp drive/bubble". Both the physicists and Star Trek. "Inertial collapse" is a completely unrelated term phenomenon from fluid dynamics.

This isolation negates portions of Einstein's specific relativity, while leaving general relativity intact... or, I might have those reversed (it's been a few years since college, and QM wasn't exactly the primary field of study).

It's special relativity. And QM has little to do with what you're talking about; the only reason to bring it in is if you're worried whether the energy distribution and densities are consistent with it. But its effects and propagation are dictated by GTR rather than QM, partly because that's how they're constructed in the first place and partly because no one knows how to make any recognizable matter take on such properties or model it quantum-mechanically.

Orthodox QM does permit the idea of negation of time dilation if there is some kind of super-science at work... such as gravity field generation.

Not so. (Semiclassical) quantum field theory on a curved spacetime still respects the structure of that spacetime. What might be said is that nonrelativistic QM is incompatible with time dilation, but that's irrelevant, because nonrelativistic QM is simply wrong. You don't even need to relativistic regimes to see that--for example, the fine structure of the hydrogen spectrum shows that clearly. Although you can get the same result as a relativistic perturbation of nonrelativistic hydrogen, that implicitly admits that relativistic effects are correct and handwaves over the inconsistency.

We can't assume that we know everything about science, or we hinder its progress.

Non sequitur. You made claims about orthodox QM, which we do know quite a lot about and are in a position to evaluate. Those claims are incorrect. Whatever comes in some extreme case of a hypothetical future theory of quantum gravity, no one knows for sure, but such hypotheticals can't be called orthodox anything. Although if that theory happens to be string theory, then you would be incorrect there as well (if your claim was local).

[RedHeron]

What I'm talking about... yes, it is "special" relativity, and not "specific" relativity. I was taking something from a memory of almost 20 years ago and trying to apply it without sitting down for 6 or 8 hours to try to dig through boxes and boxes of notes from college (it's honestly not THAT important to me). Yet the professor I was speaking to seemed to believe that the time dilation effect of relativity didn't hold if inertia was completely suspended, and that much I remember solidly. Thus, if we develop something like artificial gravity, and envelop a space ship in something akin to a bubble of gravity with a high enough exterior density to negate inertia, it can travel at much greater than the speed of light without the specific relativistic perturbations... again, it depends on technology that is only theoretically possible and which doesn't have enough practicality to it to become technology. I might argue about the idea of a man-portable lightsaber from Star Wars, but the fact is that until we come up with a means of doing something even close to that, any discussion devolves into intellectual masturbation.

The essence of what I said remains, whether the science is there to back it or not, because it's all theory and philosophy until someone does it. I don't deal with this on a regular enough basis to know lots about it. So be that as it may, we can write anything we want to in fiction, because we really don't know everything there is about the universe or its rules... and if it bothers anyone so greatly that they can't suspend their disbelief for just a moment, I have a great little UFO report for you which might help you with such a suspension, if even for only a moment.

Just so we're clear, it demonstrates using both eyewitness accounts and radar data that a large, unidentified flying craft (object) did travel at over 2000 km/h over the course of 10 seconds, and while it was not demonstrated that it was a manned craft, I would remind you that electrical devices such as lights are still subject to the laws of relativity, and would necessarily break under sudden starting and stopping conditions which were both witnessed and measured. While we can't say that it was definitely an alien space ship (or whatever), we can say that the math my professor was talking about is borne out with a demonstration such as this.

Food for thought: we live in an energetic universe, as matter and energy are interchangeable. If we accept that E = mc2, then we accept that m = sqrt(c)E ... sqrt meaning "square root" of course.

Nobody's done that, so the key phrase here is:

"Until we're actually there, we can't know whether or not it's even possible to negate G-forces to a point that it makes FTL worthwhile."

Thus, this will be my last post on the topic, and I'll let the experts who seem to know everything about the universe have at it.

[RedHeron]

I lied... twice.

THIS is my last post.

And E = mc2, which I messed up the inverse equation of (a bit tired): m = E/c2 ... sorry for any confusion.

[Kuroneko]

Yet the professor I was speaking to seemed to believe that the time dilation effect of relativity didn't hold if inertia was completely suspended, and that much I remember solidly. Thus, if we develop something like artificial gravity, and envelop a space ship in something akin to a bubble of gravity with a high enough exterior density to negate inertia, it can travel at much greater than the speed of light without the specific relativistic perturbations...

Yes, that's a somewhat literary way of describing a mathematically possible warp drive spacetime solutions of GTR. Hence:

Every FTL proposal that has even an iota of realism happens within GTR, ...

And QM has little to do with what you're talking about; ... its effects and propagation are dictated by GTR rather than QM, ...

To repeat yet again: QM does not "negate" relativistic concepts; what your describe happens in pure GTR.

The essence of what I said remains, whether the science is there to back it or not, because it's all theory and philosophy until someone does it.
...
Thus, this will be my last post on the topic, and I'll let the experts who seem to know everything about the universe have at it.

I've no idea why you've constructed this vast, elliptic strawman. No one here said or implied that we have any reliable knowledge about how FTL might be possible, and have in fact stated otherwise several times. Particularly since my exchange to you can be summed up as "we know even less about it than you have implied." By conscripting the support of orthodox QM, it is in fact you have have claimed more than our knowledge reliably supports.

No one will know with any certainty until there is a working theory of quantum gravity, i.e., beyond orthodox QM. Though possibly not even then.

[LionElJonson]

This isolation negates portions of Einstein's specific relativity, while leaving general relativity intact... or, I might have those reversed (it's been a few years since college, and QM wasn't exactly the primary field of study).

It's special relativity. And QM has little to do with what you're talking about; the only reason to bring it in is if you're worried whether the energy distribution and densities are consistent with it. But its effects and propagation are dictated by GTR rather than QM, partly because that's how they're constructed in the first place and partly because no one knows how to make any recognizable matter take on such properties or model it quantum-mechanically.[/quote]
IIRC, an Iranian physicist proposed using an array of tiny tubes to harness the Casimir effect to produce negative energy. I dunno how feasible that might be, though.

[Kuroneko]

IIRC, an Iranian physicist proposed using an array of tiny tubes to harness the Casimir effect to produce negative energy. I dunno how feasible that might be, though.

Normal matter won't get you Casimir plates anywhere near that fine. The closest thing I'm aware of is a proposal by to use the Casimir energy of compactified dimensions to locally vary the cosmological constant and hence the energy density of space. But this only makes sense in terms of a hypothetical M-theory. If you have something else in mind, then I'd be interested in looking at the paper if you can find it.

[LionElJonson]

IIRC, an Iranian physicist proposed using an array of tiny tubes to harness the Casimir effect to produce negative energy. I dunno how feasible that might be, though.

Normal matter won't get you Casimir plates anywhere near that fine. The closest thing I'm aware of is a proposal by to use the Casimir energy of compactified dimensions to locally vary the cosmological constant and hence the energy density of space. But this only makes sense in terms of a hypothetical M-theory. If you have something else in mind, then I'd be interested in looking at the paper if you can find it.

A bit of Google turned up these papers on arXiv. It looks like the papers of the guy that I remember; I don't know enough about the field to rate their quality, though.

[Kuroneko]

It's one of the standard results regarding traversable wormhole, warp drive, and Krasnikov tube spacetimes that the negative energy region must be extraordinarily thin in order to satisfy quantum inequalities, and you're not going to get that thin if your building blocks are something as large as atoms. Mind, they are based on a semiclassical treatment (QFT on a predetermined spacetime geometry), and so such thinness may be achieved in some other way or even the inequalities invalidated, but doing so goes into speculative physics. Which is quite fine, but isn't the disputed claim.

As for said theoretician in particular, I'm a bit wary of someone who states that the academia that doesn't accept his unpublished, un-peer-reviewed theory is "too slow" for him while trolling for investors to the tune of $10M. If someone has been at this for over half-decade, then they have the time to get published somewhere--and certainly incentive as well, as that would actually help with appearing legitimate to would-be investors. It certainly can't do worse than the "give me money and I'll build a warp drive; never mind the business plan" approach he's been going for so far. I've every expectation that it's a waste of time, though I can say that I'd love to be wrong about that.