FTL Travel Methods

Discussion in 'Setting Development' started by The Crazy Kakoos, Sep 28, 2012.

  1. xhawkeyex

    xhawkeyex New Member

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    I believe that the use of extreme gravitational pulls have been known to zip objects across space at nearly the speed of light. Something such as a black hole, which can bend light, could probably make it pretty close, however you'd have to be really far away to avoid getting sucked in, then use the gravity to orbit around such as like the planets do with the sun. Another possibility would be to include gamma rays as a source of energy considering that they can launch across space at nearly the same speed as light. Possibly combining both could result in a giant burst of speed
     
  2. jsipprell

    jsipprell New Member

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    Gamma rays are electromagnetic energy, they are light, just in a very high frequency portion of the spectrum that is invisible to humans (as most of the EM spectrum is). They have zero rest mass and thus always travel at C in a vacuum.

    I'm not quite sure how one would use photons, of any wavelength, as a "source of energy" in a fashion that wouldn't be immediately perceived as pseudo-science nonsense.
     
  3. daydreams

    daydreams Member

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    The best bets right now might be the Alcubierre drive or wormholes. Neither violates relativity, but they are impossible for other reasons right now.
     
  4. jsipprell

    jsipprell New Member

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    Then why not just use magic?

    Because scifi has to be constrained to the arena of plausibility, otherwise it's fantasy (which, admittedly, much softer scifi actually is). If we are constrained by plausibility then we need to at least try to obey natural laws, such as the speed of light, or offer plausible explanations as to how we are "breaking" them.

    In the past 700 years there has been massive cultural and technological revolution which has significantly altered the very way we think about things. This doesn't automatically mean that the same thing will happen in the next 700 years (and if it does, that probably means you can't write scifi, as distinguished from fantasy, that would be meaningful in any way).
     
  5. jsipprell

    jsipprell New Member

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    Wrong. All adhoc* FTL transmission of information causes a causality violation according to special relativity.

    * I use "adhoc" because you can prevent causality violations if you restrict the reference frames involved; i.e. if you only allow FTL in specific directions/circumstances.
     
  6. Cogito

    Cogito Former Mod, Retired Supporter Contributor

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    As long as an FTL vessel follows a continuous path across real space (i.e. if you interrupted the flight at any point, the locus of all emergent points would form a continuous path in normal space), it violates special relativity. Only if the path constitutes a discontinuity in normal space is there any possibility of not violating special relativity.
     
  7. minstrel

    minstrel Leader of the Insquirrelgency Supporter Contributor

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    Just a quick note: Einstein was the biggest party-pooper in the history of the science-fiction community.
     
  8. Cogito

    Cogito Former Mod, Retired Supporter Contributor

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    Nah. He made things a lot more interesting - and more challenging.

    Besides, if it hadn't been him, it would have been someone else, or several someones. Too many people were seeing the flaws in the Newtonian model, and the same equations were spreading like cracks in a windshield. The discoveries were inevitable.
     
  9. jsipprell

    jsipprell New Member

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    Don't blame Einstein, he just was the first to discover that the universe wasn't exactly how we classically thought it to be. These discoveries might be a bit uncomfortable to some, but reality is what it is.

    Also, as many people know, General Relativity is incomplete due to lacking a theory of quantum gravity. That means it's probably an approximation, a very good approximation in most cases, but not the final word on the matter. For scifi writers that means there is a bit of leeway in the theory. If you can posit some future where a better theory exists, one that fully supports the predictions made by GR/SR, but also accounts for gravitational singularities (which we have recently learned are an important part of the large-scale structure of the universe) then perhaps some mechanism for rapid transit becomes available.

    (*Note that such a theory could also solve the "missing mass" problem -- without resorting to dark matter)
     
  10. jsipprell

    jsipprell New Member

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    If you mean that any two points connected by a space-like interval cannot be traversed FTL without some possibility of violating SR, then yes, that's correct.

    If you mean that instantaneous translation from one reference frame to another might be okay, well, then that's technically not true (with a caveat). Any transmission of information superluminally (in a cyclic nature) between two reference frames connected by a space-like interval will result in some reference frames existing that observe events occurring in an order which violates causality.
     
  11. Cogito

    Cogito Former Mod, Retired Supporter Contributor

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    Note that I only stated one test for an FTL that is sure to violate special relativity. I was careful not to say that avoiding that particular trap would make your FTL possible.

    Instantaneous travel implies that two widely separated events can be simultaneous, but special relativity does not allow simultaneity. The order of two events depends on the reference frame.

    About the best you can do is place an upper bound on the travel time from the perspective of the origin or the destination frame.
     
  12. jsipprell

    jsipprell New Member

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    I realize that "instantaneous" runs afoul of the relativity of simultaneity. It was a poor word choice. Rather, what I meant was some method of traveling from one frame to another without transiting the intervening space. Say, a worm hole of some type which allows one to translate from one frame to another but with no appearance of motion between the two end-points outside of the area near the entrance and exit.

    I understand what you mean by some methods having the potential to not violate causality while others clearly do no matter what. If you place restrictions on the reference frames involved, it's possible to technically "violate" SR but not have it matter. If someone is unable to determine the correct ordering of events but this fact doesn't seem to be causally problematic for them (i.e. they can never do anything useful with this information), does it really matter? (Obviously this requires the universe to take on special properties when there is no evidence of such)
     
  13. Paradigm-shift

    Paradigm-shift New Member

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    For some hard Science
    Quntum Entanglement (I'm sure it wouldn't be hard to expand this into some sort of drive tech)
    for not hard science
    I went with a jump drive, it eliminates the need for keeping track of travel time. Now I just don't have my ship jumping all over the milky way, so there are some time and resources restraints to track. Nothing to bad, Also my story takes place deep in the future so a progression of technological development is required.
     
  14. Khaelmin

    Khaelmin Active Member

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    Even though I like reading about the limitations and advantages of possible and impossible FTL drives, the higher mathematics needed to fully understand these issues (or try to) is beyond me. So, I take the quick and dirty solution and use hyperspace. I may not call it that, but it's hyperspace alright. I find it neater and a little more logical(but not necessarily correct, I know) than the other solutions. Opening a tiny, ship sized tear in the fabric of space-time seems more feasible in terms of required energy than say... bending space? Also, it gives the impression to most people that it still obeys Einstein's mechanics by not going over the 360.000 km/s speed limit.
     
  15. jsipprell

    jsipprell New Member

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    But your jump drive doesn't actually eliminate time travel unless you have some other restrictions in place on where/when you can jump.

    (This is a bit repetitive/pedantic, but there is a lot of misinformation out there: Quantum Entanglement doesn't allow transmission of information FTL, so there is no conflict with special relativity)
     
  16. Paradigm-shift

    Paradigm-shift New Member

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    I you all think to hard, it's science fiction.
    Anyways QE would be FTL even if the two entangled partical are pulsing moris code back and fourth, if one entangled partical was on Earth, and the other was on the other side of the galaxy. The instant pulsing of moris code from one partical to the other would be FTL.
     
  17. jsipprell

    jsipprell New Member

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    (It's about 3.0x10^8 m/s, not 3.6 :))

    Is it more plausible that some sort of universal reference frame (hyperspace) exists, which would completely invalidate general relativity, or that space-time is malleable as per GR?

    We have easily observable evidence of space-time distortion, such as the fact that Mercury's orbital periapsis moves rotationally around the sun faster than it should in a "locally flat" space-time (by about 43 arc-seconds per century). That would seem to give it a pretty significant plausibility edge.
     
  18. jsipprell

    jsipprell New Member

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    You cannot use entanglement to send information, period. To put it most simplistically, you need to examine both entangled particles to extract any information, and thus you need some form of communication using normal mechanisms between the two before you actually get usable "FTL" information.

    Causality remains intact despite the best efforts to disrupt it. ;)
     
  19. Khaelmin

    Khaelmin Active Member

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    Oy, this is embarrassing. I used to take pride in the fact that I know some elementary notions of astrophysics. I really don't know why I was so certain it's 360kps and not 300.

    All plausibility aside, as this is science fiction after all, it still makes more sense to me that an advanced race would find a way to cheat GR by developing something like hyperspace. What would be the alternative? It takes a mass of ~2x10^30(a-HA! I do occasionally take time to fact check stuff, after all) to accelerate Mercury's rotation speed by 43 arc-seconds per century. What would the energy requirements be, in order to bend space-time by light years or tens of light years? Of course, scaled down to the mass of a starship, not an object as massive as Mercury. Also, even if it were ever possible, how would that be feasible? It would disrupt the orbit of every object in a very wide radius.

    (It just occurred to me that I may be talking out of my ass. Feel free to ignore it if it's dumb. But if you have the patience to explain why it is indeed dumb, please do.)
     
  20. jsipprell

    jsipprell New Member

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    So I thought of a highly boiled down simplistic method of contemplating why FTL communication via QE (or any mechanism) doesn't make any sense. Boiled purely from the perspective of a part of special relativity; w.r.t. QE there's a whole different quantum mechanism that makes it problematic.

    First off, for this contemplation to work, you have to limit yourself to only one perspective: your own.

    Instead of thinking of the speed of light being some big cosmic speed limit sign just begging to be ignored, think of it as the speed of "right now". That is to say the speed that your "now" propagates through space relative to you.

    Given this personally relative concept of now+propagation: If you're standing/sitting in one place and not moving and you have a friend also stationary but exactly one light minute distant, what that really means is that their "now" is exactly one minute in the past. Again, you have to stick to your own perspective through all of this; when I say their "now" is exactly one minute in the past, I mean their "now" only from your perspective.

    If you want to send information to them instantaneously (*smirk*) via something like QE, what you're really saying is you want to send them information one minute ago. Absent some form of time travel, I suspect you'll have a difficult time doing so. It just makes no sense, how can you send information back in time?

    To wrap the concept up, realize that everyone else also has their own version of "now". Your friend one light minute away sees you as being one minute in the past, but neither perspective is more or less valid. They are on equal footing. In fact, all of the possible "nows" are on equal footing and there there is no real "now". What's more, out of all the possible "nows" the vast majority have absolutely no connection to your particular version. Fortunately, everyone's on Earth is effectively indistinguishable because we are all very close together and not in much relative motion.

    (Another way to think about this is that the speed of light is the natural speed that all information propagates through the universe absent something to slow it down.)
     
  21. jsipprell

    jsipprell New Member

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    You're right, it does currently seem to require vast amount of mass-energy to distort space-time in a meaningful way, but at least we know it can be distorted. There are highly dubious, yet still plausible, methods of distorting space as a means of propulsion and possibly exceeding C when observed from an external reference. There is a theoretical basis for wormholes.

    None of this is actually terribly plausible in the foreseeable future, but I still maintain it is at least better than something which requires completely throwing out General Relativity and introducing something else inherently indescribable. It's comparing one thing that we have only dreamy pie-in-the-sky ideas of how to actually achieve to another than we have absolutely no physics for. It's a portable personal transonic aircraft powered by some easily obtained, cheap, and clean fuel with an Isp of 900k vs … a magic broomstick.

    Plausibility must be grounded in our current understand of natural law, otherwise you're not writing science fiction.

    (Also, don't forget that generic FTL = time travel, a fact that must be dealt with by some type of hand wave.)

    • Sorry to add additional content after already posting, but a mild logical paradox just occurred to me: If you posit using some FTL mechanism, like hyperspace, which requires discarding General Relativity then the special cases version of it, Special Relativity, also goes. Without SR, there really isn't a problem with exceeding C, so why did you need hyperspace in the first place?
     
  22. jsipprell

    jsipprell New Member

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    I know you touched on large-scale problems with gravitational theory, but I would like to point out that the galaxy rotation problem is really significant and at a somewhat "meaningful" scale. I know it's in vogue to find extra special hidden mass, no matter what, to make the problem go away but given the host of other, (admittedly) almost entirely quantum, problems with GR and the fact that we now know that singularities are a significant and important part of the large-scale structure of the universe, there is clearly something "wrong" with our understanding of gravity. We are missing something very fundamental about the geometry of space-time and its relationship to mass-energy.

    I suspect that "observational" data regarding the environment in the vicinity of a supermassive blackhole will be, at first, highly confusing but then ultimately revealing.
     
  23. Ian J.

    Ian J. Active Member

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    I like to think about the 'long rod' conundrum - that is, if you take an improbably rigid, four light year long rod and point it towards Alpha Centauri system, then move it along just a millimetre in one second, you haven't exceeded the speed of light, but have just communicated faster than light to that system. Excluding the highly improbable nature of the rod, what is the argument against this idea, in theory?
     
  24. jsipprell

    jsipprell New Member

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    It ignores the fact that when you "push" on something, you're actually creating a pressure wave that propagates through the medium at some speed less than C. In other words, it requires a totally incompressible material that cannot exist absent something like "completely degenerate" matter (which wouldn't stay degenerate in SR's flat space-time due to the exclusion principle).
     
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  25. jedellion

    jedellion Member

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    Okay...
    first question... do you have to go faster than light. Orson Scott Card wrote some beutiful sci-fi with his Ender books using non FTL travel.

    Okay. so you need FTL.

    Two approaches I find that work well.

    One: do not even attempt to explain the science. The character sin the book know how it works and would not go explaining it to each other. So just 'show' it working, rather than explaining it.

    Two: If you have to explain it, you have to have a solid grounding in physics. There are some very possible FTL theories out there.

    I would recommend looking at Harold White's work on development of the Alcubierre drive. This is a very faesible potential exploitation of a loophole in relativistic theory. and the beauty of it is, all you need to do is use a ring shaped drive unit around a hull, and call it a White/Alcubierre Drive or WA drive.

    Incidentally, the Alcubierre drive is scarily close to how warp drive is supposed to work!

    Jed.
     

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