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Warp Drive May Be More Feasible Than Thought, Scientists Say

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

#91

Post by gizmo686 »

jxcole wrote: post #84
nessus42 wrote: post #35

You can't have faster than light travel without violations of causality. And while the equations of General Relatively allow for universes where causality is routinely violated, the probability that we are in such a universe seems vanishingly small. E.g., just because you can violate causality does not mean that you can go back in time and kill your grandfather. If you were to try, something would stop you, as a univ…

A lot of people responding to this thread do not understand relativity. The OP is correct, the fundamental problem is causality, relativity and FTL do not mix. The common way of saying it is that you can have two of the three: FTL, causality, or relativity. You cannot have all three. Here is a very nice explanation of why: http://thebestforumever.com/community/threads/tachyon-pistol... Also, I've never understood how…

I remember reading a paper that dealt with this issue. The setup was that a spherical mass hit another one into a wormhole that sent it back in time. The velocity was such that it would deflect the first mass before the initial collision, creating a casual paradox. If I remember correctly (and it has been years since I read the paper), they found that the second mass was garaunteed to come out of the wormhole with a velocity that would cause the first mass to hit the second in a way that would result in the new velocity, leading to a consitent system; however the final velocities were probabalistic, not deterministic, of the initial conditions.

Again, I have not seen that paper in years, so my memory might have just made half of that up.

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

#92

Post by gizmo686 »

jxcole wrote: post #84
nessus42 wrote: post #35

You can't have faster than light travel without violations of causality. And while the equations of General Relatively allow for universes where causality is routinely violated, the probability that we are in such a universe seems vanishingly small. E.g., just because you can violate causality does not mean that you can go back in time and kill your grandfather. If you were to try, something would stop you, as a univ…

A lot of people responding to this thread do not understand relativity. The OP is correct, the fundamental problem is causality, relativity and FTL do not mix. The common way of saying it is that you can have two of the three: FTL, causality, or relativity. You cannot have all three. Here is a very nice explanation of why: http://thebestforumever.com/community/threads/tachyon-pistol... Also, I've never understood how…

I remember reading a paper that dealt with this issue. The setup was that a spherical mass hit another one into a wormhole that sent it back in time. The velocity was such that it would deflect the first mass before the initial collision, creating a casual paradox. If I remember correctly (and it has been years since I read the paper), they found that the second mass was garaunteed to come out of the wormhole with a velocity that would cause the first mass to hit the second in a way that would result in the new velocity, leading to a consitent system; however the final velocities were probabalistic, not deterministic, of the initial conditions.

Again, I have not seen that paper in years, so my memory might have just made half of that up.

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

#93

Post by gizmo686 »

nessus42 wrote: post #49
nlh wrote: post #47

Earlier quoted context omitted.

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.

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?

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

#94

Post by nessus42 »

sentientbicycle wrote: post #90
nessus42 wrote: post #61

Earlier quoted context omitted.

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.

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

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!

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

#95

Post by gizmo686 »

Ygg2 wrote: post #67
huffman wrote: post #31

Earlier quoted context omitted.

Are you trying to tell me that Stargate has been lying this whole time?

Yes, rules of cinematic narrative outweight the need to tell a faithful story. I.e. in Stargate universe it would be really boring if the Goa'uld just came, slaughtered everyone and take the rest prisoners for experiments within the first 5min-1hr.

Exept all humanoid life in the modern galaxy was the result of an Ancient experiment, when they seeded their genetic code through a wave traveling through the stargate network. I am not aware of any research on the topic, but I suspect that would scew the odds of humanoid civilizations being at a relativly equal level. Then, it could be argued, that the Goa'uld only get their technological advances from the host species, humans, so they cannot be that far beyond us.

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

#96

Post by ryandvm »

nessus42 wrote: post #49
nlh wrote: post #47

Earlier quoted context omitted.

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.

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.

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

#97

Post by pvarangot »

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 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.htm...

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

#98

Post by stryker »

nessus42 wrote: post #35

You can't have faster than light travel without violations of causality. And while the equations of General Relatively allow for universes where causality is routinely violated, the probability that we are in such a universe seems vanishingly small. E.g., just because you can violate causality does not mean that you can go back in time and kill your grandfather. If you were to try, something would stop you, as a univ…

I feel like a lot of people here misunderstand the speed of light as a cosmic speed limit. The speed of light as a speed limit is a local constraint. On a larger scale there is no such speed limit. Just because you travel faster than light on a non-local scale does not mean you break causality.

For example, light "travels" more slowly through water than vacuum. Well, actually, photons travel at c always -- it's just that light gets bounced around by water molecules, getting absorbed and reabsorbed many many times before arriving at the destination. It's like driving to a destination as opposed to running to it. If the roads are curvy enough, the runner will win because he is not constrained by roads. Could it be that the Alcubierre drive gets past the roads of empty space in a way light cannot?

For a better example, consider the expansion of the universe. Link: http://curious.astro.cornell.edu/question.php?number=575. I quote:

The fact that galaxies we see now are moving away from us faster than the speed of light has some bleak consequences, however. Astronomers now have strong evidence that we live in an "accelerating universe," which means that the speed of each individual galaxy with respect to us will increase as time goes on. If we assume that this acceleration continues indefinitely, then galaxies which are currently moving away from us faster than the speed of light will always be moving away from us faster than the speed of light and will eventually reach a point where the space between us and them is stretching so rapidly that any light they emit after that point will never be able to reach us.

In other words, vacuum fills in between us and far away galaxies faster than light can traverse it. Again, locally, the derivative of position with respect to time is c, but the universe is able to "cheat" by messing around with the definition of position. If the Alcubierre drive messes with the fabric of the universe in a similar way, I don't see any reason why it cannot succeed.

Here's a related link: http://curious.astro.cornell.edu/question.php?number=56. I quote:

Technically speaking, the speed of light limit only applies when you are in an "inertial frame" -- that is, sitting where you are, without any forces acting on you, and measuring the speed of an object that moves past a ruler and clock that you are holding in your hand. Across the large distances in the universe, however, we have a very different set of circumstances. No one is in an inertial frame, because everyone is being accelerated with respect to everyone else, due to the universe's gravitational field and the fact that the universe is expanding. In effect, the universe's expansion isn't really due to galaxies moving "through space" away from each other, but rather due to the stretching of space itself, which isn't governed by the same limits that we are.

I'm not sure whether the Alcubierre drive contradicts causality, but if it does, I highly doubt that it is because of the arguments presented on this forum.

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

#99

Post by nessus42 »

jxcole wrote: post #84
nessus42 wrote: post #35

You can't have faster than light travel without violations of causality. And while the equations of General Relatively allow for universes where causality is routinely violated, the probability that we are in such a universe seems vanishingly small. E.g., just because you can violate causality does not mean that you can go back in time and kill your grandfather. If you were to try, something would stop you, as a univ…

A lot of people responding to this thread do not understand relativity. The OP is correct, the fundamental problem is causality, relativity and FTL do not mix. The common way of saying it is that you can have two of the three: FTL, causality, or relativity. You cannot have all three. Here is a very nice explanation of why: http://thebestforumever.com/community/threads/tachyon-pistol... Also, I've never understood how…

> Say, for example, you set up a pool table with a pool ball and hit it through a time machine such that it went back in time and hit itself, making it miss the time machine? Would the pool ball be suddenly acted on by some invisible force? Would it explode? Would the universe just end?

No, none of these. Well, something would prevent this from happening, but whatever happened would have a perfectly reasonable explanation at the time.

You have to understand, firstly, that in GR, the universe doesn't start at the beginning of time and slowly evolve until it reaches the end of time. Instead, all of space and time that ever was or ever will be, exist now and forever. And this one big constant eternal space-time is one of many possible solutions to the equations that constrain the universe.

If a potential universe does not satisfy those equations, then it can't exist and therefore it won't exist.

A universe in which your pool ball goes back in time and deflects itself, is not a solution to those equations, and therefore, that will never happen in any GR compliant universe.

So, what might happen instead? Well, you might get bored with the experiment and give up before you get it working. Your girlfriend might come along and tell you that you are neglecting her. Burglars might steal your time machine. Or most likely, you might never invent the time machine to begin with.

It's quite conceivable that in some sense a time machine is theoretically buildable, but the reason our universe is one of the solutions to GR is that no one ever actually builds one in the history of the universe.

Why not, you ask? Because if they did, that universe is much less likely to be a solution to the equations, so we just so happen to find ourselves in one of the more likely universes.

Another way to think about this is that perhaps all possible universes actually exist. In that case, we have to find ourselves in one of the existing universes. We can't find ourselves in a non-existing universe, since non-existing universes don't exist.

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

#100

Post by nessus42 »

stryker wrote: post #98
nessus42 wrote: post #35

You can't have faster than light travel without violations of causality. And while the equations of General Relatively allow for universes where causality is routinely violated, the probability that we are in such a universe seems vanishingly small. E.g., just because you can violate causality does not mean that you can go back in time and kill your grandfather. If you were to try, something would stop you, as a univ…

I feel like a lot of people here misunderstand the speed of light as a cosmic speed limit. The speed of light as a speed limit is a local constraint. On a larger scale there is no such speed limit. Just because you travel faster than light on a non-local scale does not mean you break causality. For example, light "travels" more slowly through water than vacuum. Well, actually, photons travel at c always -- it's just…

I'm not sure whether the Alcubierre drive contradicts causality, but if it does, I highly doubt that it is because of the arguments presented on this forum.

The Alcubierre drive most certainly does violate causality, and this follows from just the most basic amount of Special Relativity that you might learn if only you'd spend your time learning real things, rather than spreading disinformation.

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