6 ms·

That's not the scenario described in the OP. The FTL drive described in the OP is a traditional "warp drive", that allows you to travel faster than light by mov

That's not the scenario described in the OP. The FTL drive described in the OP is a traditional "warp drive", that allows you to travel faster than light by moving the space around you faster than light, while you continue to travel slower than light within your rapidly moving space bubble. You're still effectively traveling faster than light, however, and you'd still be able to use this to travel backwards in time.

spullara 14y ago
So, I haven't looked closely at it, but he does mention that your clock remains (almost) the same as an earth clock. That implies that there is no frame of reference that shows him traveling faster than the speed of light. I'm not sure that this can be used to violate causality.
- nessus42 14y ago
  >I'm not sure that this can be used to violate causality. If you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B before it left point A. It's really just as simple and plain as that. You need consider nothing further once you know the above facts.
  - spullara 14y ago
    Based on this effect though, it doesn't travel from point A to point B faster than the speed of light. Point A and point B are literally much closer together. Perhaps the space time distortion makes impossible to think of it in terms of static frames of reference.
    - nessus42 14y ago
      If you've somehow made A and B closer together, then you've made a wormhole, not a warp drive. Wormholes also come with "closed time-like loops", which allow for time travel.
      - spullara 14y ago
        I don't know. This isn't something covered by special relativity. You certainly don't need a wormhole though. http://curious.astro.cornell.edu/question.php?number=575 http://curious.astro.cornell.edu/question.php?number=575
        nessus42 14y ago
        Yes, there are parts of the universe traveling away from us at faster than the speed of light. In fact, it's quite likely that the universe is infinitely big and an infinitely large part of it is traveling away from us at faster than the speed of light. This fact, however, does not allow information to be transmitted between two points in space at faster than the speed of light. That's the important constraint here. Causality is only violated when you transmit INFORMATION between TWO POINTS at faster than the speed of light.
sentientbicycle 14y ago
I don't think you are understanding the concept here. http://en.wikipedia.org/wiki/Alcubierre_drive#Physics http://en.wikipedia.org/wiki/Alcubierre_drive#Physics
- nessus42 14y ago
  I understand it perfectly fine for the purposes of this discussion. Edit: I can't believe people down-vote irrefutable facts, so let me state this ONE MORE TIME: It is an irrefutable fact of Special Relativity that if you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B BEFORE it left point A. THAT'S JUST A FACT OF SPECIAL RELATIVITY. People can bitch and moan about whatever they want to, and come up with all sorts of creative ways to try to work around this FACT, but YOU CANNOT. c, it's not just a good idea--IT'S THE LAW!
  - sentientbicycle 14y ago
    I'm sorry, but I just can't find any sort of citation stating that the Alcubierre drive violates any of these principles. I also can't find any mention of paradoxes incurred by the drive and there is only one mention of where the meta-materials themselves would have to violate the light speed limit. Here is how I understand it (and correct me if I'm wrong), but it is not travelling in a vacuum, it is crunching that vacuum in front and expanding it in the back. This doesn't violate any laws because we know our universe is actually already doing this (expanding at a greater than light speed). If what you say is true then the galaxies that are currently moving away from us at those "super-luminal" (not actual super-luminal because we all know that's impossible) speeds shouldn't exist, but we know these do exist and we know why they appear to be doing so. Because of the expansion of the universe. http://curious.astro.cornell.edu/question.php?number=575 http://curious.astro.cornell.edu/question.php?number=575 So since this is already done naturally is it not feasible to do so artificially? But aside from all that it seems a little short-sighted to howl about how people can't do something. Time and time again nay-sayers have been proven wrong.

spullara 14y ago

So, I haven't looked closely at it, but he does mention that your clock remains (almost) the same as an earth clock. That implies that there is no frame of reference that shows him traveling faster than the speed of light. I'm not sure that this can be used to violate causality.

nessus42 14y ago
>I'm not sure that this can be used to violate causality. If you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B before it left point A. It's really just as simple and plain as that. You need consider nothing further once you know the above facts.
- spullara 14y ago
  Based on this effect though, it doesn't travel from point A to point B faster than the speed of light. Point A and point B are literally much closer together. Perhaps the space time distortion makes impossible to think of it in terms of static frames of reference.
  - nessus42 14y ago
    If you've somehow made A and B closer together, then you've made a wormhole, not a warp drive. Wormholes also come with "closed time-like loops", which allow for time travel.
    - spullara 14y ago
      I don't know. This isn't something covered by special relativity. You certainly don't need a wormhole though. http://curious.astro.cornell.edu/question.php?number=575 http://curious.astro.cornell.edu/question.php?number=575
      - nessus42 14y ago
        Yes, there are parts of the universe traveling away from us at faster than the speed of light. In fact, it's quite likely that the universe is infinitely big and an infinitely large part of it is traveling away from us at faster than the speed of light. This fact, however, does not allow information to be transmitted between two points in space at faster than the speed of light. That's the important constraint here. Causality is only violated when you transmit INFORMATION between TWO POINTS at faster than the speed of light.

sentientbicycle 14y ago

I don't think you are understanding the concept here. http://en.wikipedia.org/wiki/Alcubierre_drive#Physics http://en.wikipedia.org/wiki/Alcubierre_drive#Physics

nessus42 14y ago
I understand it perfectly fine for the purposes of this discussion. Edit: I can't believe people down-vote irrefutable facts, so let me state this ONE MORE TIME: It is an irrefutable fact of Special Relativity that if you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B BEFORE it left point A. THAT'S JUST A FACT OF SPECIAL RELATIVITY. People can bitch and moan about whatever they want to, and come up with all sorts of creative ways to try to work around this FACT, but YOU CANNOT. c, it's not just a good idea--IT'S THE LAW!
- sentientbicycle 14y ago
  I'm sorry, but I just can't find any sort of citation stating that the Alcubierre drive violates any of these principles. I also can't find any mention of paradoxes incurred by the drive and there is only one mention of where the meta-materials themselves would have to violate the light speed limit. Here is how I understand it (and correct me if I'm wrong), but it is not travelling in a vacuum, it is crunching that vacuum in front and expanding it in the back. This doesn't violate any laws because we know our universe is actually already doing this (expanding at a greater than light speed). If what you say is true then the galaxies that are currently moving away from us at those "super-luminal" (not actual super-luminal because we all know that's impossible) speeds shouldn't exist, but we know these do exist and we know why they appear to be doing so. Because of the expansion of the universe. http://curious.astro.cornell.edu/question.php?number=575 http://curious.astro.cornell.edu/question.php?number=575 So since this is already done naturally is it not feasible to do so artificially? But aside from all that it seems a little short-sighted to howl about how people can't do something. Time and time again nay-sayers have been proven wrong.