Warp Drive May Be More Feasible Than Thought, Scientists Say • Hacker News Board

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#101

Post by stickfigure » Tue, Sep 18, 2012, 4:26 AM UTC

chii wrote: post #86

pyre wrote: post #81

Earlier quoted context omitted.

It takes two to tango, so to speak. No matter how peaceable we are as a race, if the other guy has bigger weapons and is itching to use them, it might not make any difference.

Theoretically, it isn't possible to stop an advanced alien race that has mastered ftl travel from being able to destroy earth. There is this concept called relativistic bombardment - your "artillary" is set to travel so fast, that the light that comes off it only arrives moments before the actual shell, and thus, there is little to no warning. The only way to stop this sort of attack is a shield that is impenatrable.…

If my (admittedly rough) understanding of relativity is correct, there's a problem with this weapon: From the recipient's perspective, the shell would never arrive.

Basically, as the shell accelerates to C relative to the target, time in the target's reference frame expands relative to time in the shell's reference frame. A shell traveling at C would instantaneously travel from origin to destination (from the shell's perspective) but would take infinite time (from the target's perspective).

Of course, an impact at 1% C would still make one hell of a bang.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#102

Post by teamonkey » Tue, Sep 18, 2012, 4:32 AM UTC

nessus42 wrote: post #64

enraged_camel wrote: post #59

Earlier quoted context omitted.

>>You are not correct. If anything with information travels faster than the speed of light, then there are frames of reference in which that information arrived at the destination before it left the origin. No. If you send a radio signal to Mars, and then warp to Mars to find yourself there 0.1 seconds later, you are still 0.1 seconds after the moment on which you sent the signal from the point of origin. You are tra…

Nothing you just said contradicts my statement, which was, "there are frames of reference in which that information arrived at the destination before it left the origin." I suspect that you don't know anything at all about Special Relativity, in which case, there's not much more I can tell you except to go educate yourself.

Special Relativity only applies to cases where there is uniform relative movement in two or more inertial frames of reference. That is not the case with this theory - the relative movement is clearly not uniform and although I've not read the paper I'm certain that the time warp provides a non-inertial frame.

TL;DR - ignore Special Relativity completely, General Relativity is the only thing that applies here.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#103

Post by spullara » Tue, Sep 18, 2012, 4:35 AM UTC

nessus42 wrote: post #89

spullara wrote: post #85

Earlier quoted context omitted.

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.

>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.

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.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#104

Post by codehotter » Tue, Sep 18, 2012, 4:52 AM UTC

gizmo686 wrote: post #93

nessus42 wrote: post #49

Earlier quoted context omitted.

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.

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?

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.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#105

Post by Dn_Ab » Tue, Sep 18, 2012, 4:54 AM UTC

gizmo686 wrote: post #93

nessus42 wrote: post #49

Earlier quoted context omitted.

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.

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?

No, quantum entanglement does not allow Information to travel faster than light. Classic channel is needed to know what if any unitary transformations are needed. Otherwise requiring roll of massively many sided dice. Check out No Communication Theorem.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#106

Post by nessus42 » Tue, Sep 18, 2012, 4:55 AM UTC

gizmo686 wrote: post #93

nessus42 wrote: post #49

Earlier quoted context omitted.

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.

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?

I can't provide a coherent explanation of Relativity in one little HN box, but what I can say is that Special Relativity is pretty easy to learn and understand if you're willing to put in a bit of effort and deal with some high-school level algebra.

General Relativity is much much more difficult, but once you understand Special Relativity, a lay-person's understanding of GR gets the job done for most purposes.

Re quantum entanglement, no it doesn't imply that data travels faster than light. The versions of QM where the probability waves collapse might, but in the Many Worlds interpretation, which is probably the most popular interpretation now among physicists and philosophers of science, the probability waves never collapse, and so there is nothing to transmit.

In the Copenhagen interpretation, one might argue that the probability wave collapsing transmits information all along that wave instantaneously, but if so, this happens under the covers of the universe. There's no way for anyone to use this feature of QM to transmit usable information from one place to another at faster than the speed of light.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#107

Post by nessus42 » Tue, Sep 18, 2012, 5:02 AM UTC

ryandvm wrote: post #96

nessus42 wrote: post #49

Earlier quoted context omitted.

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.

> [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.

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.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#108

Post by nessus42 » Tue, Sep 18, 2012, 5:04 AM UTC

spullara wrote: post #103

nessus42 wrote: post #89

Earlier quoted context omitted.

>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.

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.

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.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#109

Post by nessus42 » Tue, Sep 18, 2012, 5:11 AM UTC

teamonkey wrote: post #102

nessus42 wrote: post #64

Earlier quoted context omitted.

Nothing you just said contradicts my statement, which was, "there are frames of reference in which that information arrived at the destination before it left the origin." I suspect that you don't know anything at all about Special Relativity, in which case, there's not much more I can tell you except to go educate yourself.

Special Relativity only applies to cases where there is uniform relative movement in two or more inertial frames of reference. That is not the case with this theory - the relative movement is clearly not uniform and although I've not read the paper I'm certain that the time warp provides a non-inertial frame. TL;DR - ignore Special Relativity completely, General Relativity is the only thing that applies here.

Special Relativity applies ANY TIME that you transmit information from one point A in an inertial frame to another point B in an inertial frame.

If you can use your warp drive to transmit information from A to B, then Special Relativity applies.

If you cannot use your warp drive to transmit information from A to B (e.g., from Earth to Mars), then what good is it?

(I've mentioned several times in this thread that you might be able to come up with some sort of FTL drive that doesn't violate causality if you put enough constraints on it to make it useless.)

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#110

Post by jlgreco » Tue, Sep 18, 2012, 5:14 AM UTC

fungi wrote: post #69

MBlume wrote: post #37

Earlier quoted context omitted.

Find one with a halting oracle on board and you're set.

seems unlikley. if only we had some kind of improbability engine.

I doubt an improbability engine would be good for much more than party tricks. An infinite improbability drive would be much more useful, but such a thing would be virtual impossibility...