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I'm not the down-voter, but I think you were likely down-voted because this article/discussion is not about time travel. And your first statement is that "you

by nlh 14y ago

I'm not the down-voter, but I think you were likely down-voted because this article/discussion is not about time travel. And your first statement is that "you can't have faster-than-light travel..." is precisely what this paper discusses -- that with certain loopholes in physics (and consistent with General Relativity), faster-than-light travel is at least theoretically possible.

nessus42 14y ago
Faster-than-light travel allows you to travel backwards in time. This is an essential part of Special and General Relativity. Those who don't understand this and who are not ready to address its consequences, should refrain from speculating on what is and isn't possible.
- ryandvm 14y ago
  > [Those] who are not ready to address its consequences, should refrain from speculating on what is and isn't possible Really? Do you hear yourself? I hope you're taking down badge numbers because I'm not sure that all these guys are qualified to address the consequences of faster-than-light travel.
  - nessus42 14y ago
    Badge numbers? Are you talking about the badge numbers of the authors of the original article? If so, I'm sure they are quite aware that their proposed drive violates causality. Some scientists are willing to bite that bullet. It's some people on HN who don't seem to understand the chose-two-out-of-three principle when it comes to Relativity, FTL, and causality, and want to willfully ignore it.
- Evbn 14y ago
  Is FTL the same as warping space? what happens in a (reduced dimensions for intuitiveness) scenario where a universe is like a line segment, and gets bent into crossing itself, allowing jumps from one point to another? Then there is a long way and a short way to send a message, kind of like travelling through vacuum is faster than traveling through water.
  - nessus42 14y ago
    FTL is not the same thing as warping space in the same way that speeding is not the same thing as driving a Maserati. But if you can warp space at your will to give you the power to effectively get from point A to point B faster than a beam of light would, then you will also be able to construct "closed time-like loops", which will allow you to travel backwards in time.
- gizmo686 14y ago
  I have very little experience with post newtonian physics, so could you explain why FTL implies time travel. Also, doesn't quantom entanglement imply that data travels faster than light?
  - pvarangot 14y ago
    I don't know the specifics about quantum entanglement, but any means of making information travel faster than light that can work reliably in two different inertial frames (thus communicating four different points, two not moving relative to each other in space in each) can be used to break causality or relativity. This is achieved by constructing a loop in which if the second pair of devices is used to disable the first you have a time paradox. This is the clearest place explaining it I'm aware of, but I bookmarked this a while ago and maybe now some video or animation explains it better: http://www.theculture.org/rich/sharpblue/archives/000089.html http://www.theculture.org/rich/sharpblue/archives/000089.htm...
  - codehotter 14y ago
    I keep hearing about faster than light communication with quantum entanglement. It seems to be a very persistent misconception. The same "communication" as with quantum entanglement can be done in the classical universe. You can easily create two entangled envelopes. People's minds are blown just because we put the word "quantum" in there. Take two indistinguishable envelopes. Put a green card in one and a red card in the other. Shuffle the envelopes so that you do not know which card is in which envelope. Have a friend take one of the envelopes many kilometers away. Your envelopes are now entangled. If you now open your envelope, and it contains the red card, you instantly know your friend's envelope contains the green card. Did information travel faster than light? No, it did not, since in order to communicate by this method you still need to tell your friend what it means to have the green card. You still need to send slower than light information that Red is 1 and Green is 0 which you can only do once you've measured your own envelope, after which you've destroyed the entanglement of your envelopes. Quantum entanglement is a phenomenon where you can tell something about the other part of the entangled pair by measuring one part. Just like with the entangled envelopes, you cannot communicate anything by this since you don't know in advance what you're going to measure.
dhughes 14y ago
I think the "faster than light" part wording seems a bit off since from what I gather the point is not to go fast to get to a location but to get there through warped space-time. I imagine a 100 km long and 1km high brick wall, you're in the middle but want to get to the other side of the wall. Option #1 is to travel as fast as you can 50km to one end and then 50km back to the spot on the other side. Option #2 tunnel through the wall. Option #1 is fast but the option #2 is faster although you didn't exceed the speed of option #1.
- nessus42 14y ago
  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

by nlh 14y ago

nessus42 14y ago

Faster-than-light travel allows you to travel backwards in time. This is an essential part of Special and General Relativity. Those who don't understand this and who are not ready to address its consequences, should refrain from speculating on what is and isn't possible.

ryandvm 14y ago
> [Those] who are not ready to address its consequences, should refrain from speculating on what is and isn't possible Really? Do you hear yourself? I hope you're taking down badge numbers because I'm not sure that all these guys are qualified to address the consequences of faster-than-light travel.
- nessus42 14y ago
  Badge numbers? Are you talking about the badge numbers of the authors of the original article? If so, I'm sure they are quite aware that their proposed drive violates causality. Some scientists are willing to bite that bullet. It's some people on HN who don't seem to understand the chose-two-out-of-three principle when it comes to Relativity, FTL, and causality, and want to willfully ignore it.
Evbn 14y ago
Is FTL the same as warping space? what happens in a (reduced dimensions for intuitiveness) scenario where a universe is like a line segment, and gets bent into crossing itself, allowing jumps from one point to another? Then there is a long way and a short way to send a message, kind of like travelling through vacuum is faster than traveling through water.
- nessus42 14y ago
  FTL is not the same thing as warping space in the same way that speeding is not the same thing as driving a Maserati. But if you can warp space at your will to give you the power to effectively get from point A to point B faster than a beam of light would, then you will also be able to construct "closed time-like loops", which will allow you to travel backwards in time.
gizmo686 14y ago
I have very little experience with post newtonian physics, so could you explain why FTL implies time travel. Also, doesn't quantom entanglement imply that data travels faster than light?
- pvarangot 14y ago
  I don't know the specifics about quantum entanglement, but any means of making information travel faster than light that can work reliably in two different inertial frames (thus communicating four different points, two not moving relative to each other in space in each) can be used to break causality or relativity. This is achieved by constructing a loop in which if the second pair of devices is used to disable the first you have a time paradox. This is the clearest place explaining it I'm aware of, but I bookmarked this a while ago and maybe now some video or animation explains it better: http://www.theculture.org/rich/sharpblue/archives/000089.html http://www.theculture.org/rich/sharpblue/archives/000089.htm...
- codehotter 14y ago
  I keep hearing about faster than light communication with quantum entanglement. It seems to be a very persistent misconception. The same "communication" as with quantum entanglement can be done in the classical universe. You can easily create two entangled envelopes. People's minds are blown just because we put the word "quantum" in there. Take two indistinguishable envelopes. Put a green card in one and a red card in the other. Shuffle the envelopes so that you do not know which card is in which envelope. Have a friend take one of the envelopes many kilometers away. Your envelopes are now entangled. If you now open your envelope, and it contains the red card, you instantly know your friend's envelope contains the green card. Did information travel faster than light? No, it did not, since in order to communicate by this method you still need to tell your friend what it means to have the green card. You still need to send slower than light information that Red is 1 and Green is 0 which you can only do once you've measured your own envelope, after which you've destroyed the entanglement of your envelopes. Quantum entanglement is a phenomenon where you can tell something about the other part of the entangled pair by measuring one part. Just like with the entangled envelopes, you cannot communicate anything by this since you don't know in advance what you're going to measure.

dhughes 14y ago

I think the "faster than light" part wording seems a bit off since from what I gather the point is not to go fast to get to a location but to get there through warped space-time. I imagine a 100 km long and 1km high brick wall, you're in the middle but want to get to the other side of the wall. Option #1 is to travel as fast as you can 50km to one end and then 50km back to the spot on the other side. Option #2 tunnel through the wall. Option #1 is fast but the option #2 is faster although you didn't exceed the speed of option #1.

nessus42 14y ago
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