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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

#131

Post by amorphid »

CWIZO wrote: post #10

As much as it pains me to say this, but I think we have to invent some more advanced weapons before we start poking our heads out of our galaxy. Don't get me wrong, this is fantastic and I'm all tingly from excitement (this is the first time I've read about warp drives in the context of real science) ... but like I said, taking a stroll trough the galaxy with our bombs and finding a hostile alien world. Well we'd be…

I have no doubt that research into warp will also inspire idea on how to blow stuff up.

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

#132

Post by cygx »

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…

Tachyons do not necessarily violate causality if you actually take the time to derive the laws of tachyonic kinematics consistent with special relativity.

Sure, tachyons will be strange (different observes won't agree on direction of travel or charge of a tachyonic particle - if we are even able to localize the particle at all; there will be frames of reference where a tachyon won't have energy but will still have momentum, ...), but not really any stranger that what we deal with in quantum mechanics and field theory, and the laws of physics will still hold in all frames of reference.

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

#133

Post by powertower »

I don't understand how the warp-bubble would itself travel through space-time faster than C (it's effects are inside of it), only that the space-craft traveling through that warp-bubble would. But the space-craft is stationary / in the center of it?

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

#134

Post by nessus42 »

pessimist wrote: post #119
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…

In General Relativity, Faster-Than-Light travel is only prohibited locally. Its possible for space-time itself to expand and shrink faster than light. This is why distant-enough galaxies are receding from us at faster than the speed of light. Mathematically, the structure of the proposed warp-drive is such that the spaceship is moving at http://www.icarusinterstellar.org/daydreaming-beyond-the-sol...

Nowhere does he state that causality is never violated.

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

#135

Post by teamonkey »

nessus42 wrote: post #109
teamonkey wrote: post #102

Earlier quoted context omitted.

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…

> 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.

Not true. It also implies uniformity of space-time in all inertial frames and the space between them. Since the theoretical purpose of the warp drive is to create a non-uniformity by definition SR does not apply.

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

#136

Post by sentientbicycle »

nessus42 wrote: post #126
sentientbicycle wrote: post #117

Earlier quoted context omitted.

OOoohhhh. I totally get it now. You are an unpublished internet stranger and the Alcubierre drive has been scrutinized by some of the top minds in physics. But your criticisms are more important for some reason I don't know. Mkay, going to bed now. Edit: By the way. I did read the thing about point A and B and understand it completely. The thing is, it doesn't matter. This is why I'm absolutely sure now that you have…

Where do any of these top minds of physics say that this drive does not violate causality??? They DON'T! If they asserted such a nonsensical thing, they would be the laughing stock of the scientific world and would no longer be considered any kind of mind, other than a quack. The only reason that you don't see much talk about this violation of causality is that it's just a fact that all physicists know. One physicist…

Alcumbierre himself states that it does not violate causality. from: http://www.npl.washington.edu/av/altvw81.html > The possibilities for FTL travel or communication implicit in the Alcubierre drive raise the possibility of causality violations and "timelike loops", i.e., back-in-time communication and time travel. Alcubierre points out that his metric CONTAINS NO SUCH CLOSED CAUSAL LOOPS, and so is free of their paradoxes. However, he speculates that it would probably be possible to construct a metric similar to the one he presented which would contain such loops.

    So either he's a laughing stock and nobody is talking about that or (more likely) you are wrong.

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

#137

Post by nessus42 »

Steuard wrote: post #128
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…

[Background note: I'm a physics professor with a background in string theory and relativity.] You're raising a sensible point, and most of the objections raised here are invalid. But it nevertheless turns out (surprisingly, to me!) that your argument doesn't work. This topic came up a lot during the short-lived superluminal neutrino excitement last year, and one good discussion of it by Sean Carroll can be found at:…

I would certainly defer to your much superior knowledge of physics. Mine is only that of an MIT student who was thoroughly indoctrinated with Special Relativity as part of MIT's general science education, and who sat in on an undergrad course on GR taught by cosmologist Max Tegmark.

If I understand Bob Geroch properly (much of his paper is Sanskrit to me, but I think I understand the parts that are in English), he acknowledges that FTL particles would seem to allow you to set up "closed causal curves" (i.e., violate causality in a way that would allow you to try to generate a time paradox), but he asserts that you would never actually be able to achieve this goal due to something like the "Novikov self-consistency principle", although he doesn't mention this principle by name.

This is similar to the position that many physicist think about the existence of closed time-like loops in GR. Sure, in some sense they are possible, since GR shows you how to set them up, but something like the Novikov principle would either prevent you from setting one up or from doing anything nefarious with one.

So, if I understand things correctly, Geroch's claim doesn't really different too much from assertions that I made elsewhere in this thread, that sure you might be able to build an FTL drive, but if the universe lets you do this, it's not going to let you make good use of one, like, for instance, creating an FTL space-liner fleet, because if it did, you'd generate a time paradox soon enough. Or if the universe were so kind as to let us do that, we'd end up finding ourselves in a very strange world where Novikov's principle was mucking with our daily affairs in a very creepy manner.

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

#138

Post by nessus42 »

twoodfin wrote: post #127
codehotter wrote: post #104

Earlier quoted context omitted.

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 i…

But isn't the essential difference (and what makes the QM effect seem like spooky action-at-a-distance) that it's been proven that it isn't like the envelope example? Namely, there's no definite "redness" or "greenness" to the entangled particle before you examine it (unlike the envelope, which contains a red or green card the whole time). Whether you have a "red" or a "green" quantum part isn't decided until you loo…

If the Many Worlds interpretation of QM is true, then there is no wave collapse.

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

#139

Post by nessus42 »

sentientbicycle wrote: post #136
nessus42 wrote: post #126

Earlier quoted context omitted.

Where do any of these top minds of physics say that this drive does not violate causality??? They DON'T! If they asserted such a nonsensical thing, they would be the laughing stock of the scientific world and would no longer be considered any kind of mind, other than a quack. The only reason that you don't see much talk about this violation of causality is that it's just a fact that all physicists know. One physicist…

Alcumbierre himself states that it does not violate causality. from: http://www.npl.washington.edu/av/altvw81.html > The possibilities for FTL travel or communication implicit in the Alcubierre drive raise the possibility of causality violations and "timelike loops", i.e., back-in-time communication and time travel. Alcubierre points out that his metric CONTAINS NO SUCH CLOSED CAUSAL LOOPS, and so is free of their pa…

He has only stated that there are no closed causal loops for one particular use-case of his drive. He never stated either that causality was not violated from the point of view of a distant observer in a different frame of reference. Nor did he state that such a drive would not allow closed causal loops to be generated. In fact, he implied the opposite.

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

#140

Post by nessus42 »

stryker wrote: post #124
nessus42 wrote: post #100

Earlier quoted context omitted.

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.

I'm going to ignore your condescension. I'm also going to assume you didn't read the rest of my post, because you presented no arguments to counter my points. I'd like to point out that the wikipedia article on the Alcubierre drive writes at length to show how this warping process does not violate causality: http://en.wikipedia.org/wiki/Alcubierre_drive . I know you feel strongly about people not understanding specia…

You're simply closing your ears and exclaiming "special relativity" which only applies locally (if you want an appeal to authority, I talked about this with a former physicist who worked with Stephen Hawking).

If you come up with a mathematical "proof" and I can use its conclusion to prove that 1 + 1 = 3, then I have shown your proof to be incorrect via contradiction, no matter how hard you continue to argue for it.

Special Relativity does not only apply locally. It applies to any system where information can be transmitted between two points that are in inertial frames.

The universe expanding at faster than the speed of light is neither here nor there, since you cannot use the expanding universe to transmit information between two points in at FTL speeds. On the other hand, you CAN use an FTL drive to transmit information between two points in inertial frames at FTL speeds.

QM spooky action at a distance does not let you transmit information between two points at FTL speeds.

This is all you need to do to show that any FTL scheme violates Special Relativity: Information transmitted between two points in inertial frames at FTL speeds. If you can do that, you've either disproven causality, or you've disproven Special Relativity.

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