# Faster than light travel!

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jedishrfu
Mentor
Ryan_m_b
Staff Emeritus
What jed said. There are a plethora of published papers on warp drives and wormholes but all rely on unobtanium that at best isn't impossible but there's no reason to think it exists and at worse violates an energy condition.

What I've never gotten about these types of propulsion methods is that if they contract space in front of the ship and expand it behind the ship to make it move whilst staying still, doesn't that mean that when space returns to normal (space in front expands and space behind contracts) the ship will be in the exact same spot it was before.

Like putting a dot on a half stretched rubber band, stretch it behind, and let it contract in front. Yes, it is closer to the destination, but once the band goes back to the way it was and the dot is in the exact same position.

Or if the ship actually does move in a pocket of "normal" space, doesn't that mean that the contracted space in front has to normalize in that pocket that the ship is passing through making it so the ship has to travel the same distance anyways?

Or if they ship passes through the contracted space, as the ship is still a part of the universe, would then contract itself, and thus, have to pass through the same distance again.

Kinda makes this method of propulsion seem useless to me, unless I'm missing something.

Just some questions here - firstly, how does "exotic" matter make this Alcubierre warp effect possible? Are we talking about dark matter here? I thought its existence hasn't even been definitively proven. And even then, what exactly does dark matter do that regular matter doesn't? I'm told that it would have "negative mass" - meaning it produces a gravitational field that repels matter instead of attracting it. How does this get you moving faster than light?

From what I've read, this Alcubierre concept is to produce expanding space behind you and contracting space in front of you, while you are motionless inside the span of space between. So you are sitting motionless in this "patch" of space, while the "patch" slides along very quickly like a magic carpet. This is then supposed to circumvent any lightspeed limitations.

The original concept apparently had prohibitively high mass-energy requirements, but now recently further calculations show that it could be achieved with a more practical amount of mass-energy.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023492_2011024705.pdf

So I was reading that thing, which doesn't seem like a real physics paper, and it talks about a "warp field interferometer" (ie. a laser interferometer attuned to detecting tiny perturbations in spacetime). So is a "warp" a transient perturbation in spacetime, or a lasting distortion? Is it again the natural gravitational field created by ordinary matter and alleged exotic dark matter? Can ordinary matter be said to generate a "warp field"? If a "warp" is a perturbation, then are we talking about gravity waves here?

There are already large gravity wave detectors like LIGO. So how do these "warp" researchers intend to detect waves or perturbations any better than those setups? Can they somehow create a "warp" artificially, without the use of exotic matter?

What really is a "warp field" and how is it created?

The point of the matter is "feasibility".
Is or will it be feasible given the required energy and technology to achieve spacetime warping for travel? If the numbers add up and such technology although unattainable at present should be available in the future then obviously it will be implemented. But, I am interested if it is even theoretically possible.

Ryan_m_b
Staff Emeritus
If the numbers add up and such technology although unattainable at present should be available in the future then obviously it will be implemented.
Short on time but quickly wanted to point out that this is fallacious. Not only because possible-in-theory is not a synonym of possible-in-practice but also necause possible-in-practice is not a synonym of will-be-practiced.

Through further surfing, I see that White says they plan to use their laser interferometer to produce the warp effect as well as detect it. So I'm very curious on how they plan to do this.

I've been reading lately about how "attosecond pulse" lasers are being used to push the bounds of physics, and study the nature of quantum phenomena in greater detail. I'm wondering if such lasers could be used to manipulate spacetime (or rather the virtual particle sea underpinning it)

Well, Alcubierre's warp drive concept is based within the framework of known theoretical physics, and what he is saying is that while there is a speed limit on how fast matter can travel through space, there is no similar limit on how fast space can travel through space.

But Alcubierre's idea depends on some kind of exotic matter with "negative mass", but White's current efforts are seeking to create some kind of tiny space warp in the lab, using lasers instead of the exotic matter.

Well, from what I interpret, this "warp" idea seems analogous to an "exciton" (electron-hole pair), in the sense that it's like a dip-and-peak in the spacetime fabric. So the idea is that you have the dip in front of you (contracting space) and the peak behind you (expanding space), with you in between the two. You are then traveling through space like a ripple (trough-and-peak). We already know that such dips and peaks exist in spacetime in the form of vacuum fluctuations, but this warp thing would be a macroscopic version perhaps. Or if you think of gravity, that is all dip, but the warp would be a dip-and-peak.

Or if you think of gravity, that is all dip, but the warp would be a dip-and-peak.
How can a gravity wave be all dip with no peak? Don't you need both to propopage a wave?

JesseM
Alcubierre’s original paper didn’t address the issue of how a warp bubble could be created, it just analyzed a spacetime where one already existed. I wonder, has White or anyone else actually found an exact solution to the equations of general relativity where a warp bubble is created in a previously bubble-free region of space, perhaps using a theoretical model of the "White-Juday Warp Field Interferometer" that Harold White & co. are using to try to create one? If there are no exact solutions, are there numerical simulations that show this happening? If neither, I’m skeptical that there’s much good basis for the claim that the White-Juday Warp Field Interferometer might plausibly be used to create one (I would imagine the argument would be fairly “handwavey” as physicists like to say).

Also, this blog entry by a physicist gives another reason to be skeptical it would be possible even with the necessary exotic matter:
In a quite recent paper, Stefano Finazzi, Stefano Liberati and Carlos Barceló (see here) show that Alcubierre drive is unstable with respect quantum effects: Indeed, if you go faster than light, Hawking radiation will kill you.
And another physicist writes here:
did my doctorial stuff in General Relativity. When I was in Austin for Armadillocon, last August, I asked my adviser, Richard Matzner, about the Alcubierre deal, since Richard does a lot of numerical GR he knows Alcubierre (who is an ace numerical GR guy), says he never heard him talk about his warp drive. Richard is not much interested in it either, thinks the solution is Lyapunov unstable. I have seen some works from Italy about Alcubierre and other ‘exotic matter’ warp solutions that show the models are unstable. Richard said he thinks Kip Thorne is no longer interested in it. I have never seen a really ‘heavy hitter’ like Hawking or Thorne, or a whole lot of other first string GR theorists ever remark on Alcubierre or the other recent solutions. There was a ‘name’ relativistist, William A. Hiscock, who did, he felt the solutions were not physical, but he thought people should keep trying. Alas that guy died young, only a few years ago.

Ah, the Huffington post... a source of reliable, objective science information??
Who knew??

JesseM
Ah, the Huffington post... a source of reliable, objective science information??
Who knew??
Well, the story that NASA is funding this research is true. And the story has been reported a bunch of other places as well:

http://www.wired.com/wiredscience/2012/09/warp-drive-plausible/
http://www.space.com/17628-warp-drive-possible-interstellar-spaceflight.html
http://www.msnbc.msn.com/id/49064028/ns/technology_and_science-space/#.UFur_67x9H4
http://techland.time.com/2012/09/19/nasa-actually-working-on-faster-than-light-warp-drive/

ANd from NASA itself:

www.jsc.nasa.gov/roundup/online/2012/0712.pdf

Here's Harold White's paper on why he thinks it could be possible to produce warp bubbles (doesn't seem to have much detail on the question I asked above about the theoretical argument for thinking they could be produced in a region of space that didn't have them already):

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936_2011016932.pdf

So what I gather so far is that Harold White's lab apparatus will consist of a capacitor ring and laser interferometer. The capacitor ring is what will produce the "warp" and the laser interferometer will measure/detect it.

So it sounds like what's being inferred here is that the potential gradient from an electric field will warp space - ie. it will cause a measurable difference in path length that can be detected with an interferometer.

Is such a belief reasonable, and consistent with known physics?

The trouble with only going ten times the speed of light it is still going to take a hell of a long time to get anywhere outside the solar system.

It might take you a few years to get somewhere really interesting, but that's still better than centuries. Obviously, we are looking for travel on human timescales.

Still, who believes that voltage can warp space? That means every time I use my camera flash bulb, I'm doing some "warp field engineering" :P

Can electric capacitors really produce a measurable path length difference that can be detected by an interferometer?

MTd2
Gold Member
Isn't the cosmological inflation, or even the concept of expansion of the universe, a kind of isotropic warp drive? As for the inflation, if there was a way to deflate space ahead and inflate behind, wouldn't that be a warp drive?

Isn't the cosmological inflation, or even the concept of expansion of the universe, a kind of isotropic warp drive? As for the inflation, if there was a way to deflate space ahead and inflate behind, wouldn't that be a warp drive?
Well, that's exactly what Alcubierre's Warp Drive concept proposes - a bubble with contracting space in front and expanding space behind, in order to achieve FTL.

MTd2
Gold Member
Well, that's exactly what Alcubierre's Warp Drive concept proposes - a bubble with contracting space in front and expanding space behind, in order to achieve FTL.
Yes, I know. But I am actually thinking about a feasible mechanism. What was the energy density by the end of inflation? If we could compress matter at least that much, maybe we could do warp drive.

Yes, I know. But I am actually thinking about a feasible mechanism. What was the energy density by the end of inflation? If we could compress matter at least that much, maybe we could do warp drive.

Yeah, that would be a prohibitively high mass-energy requirement, which Alcubierre calculated as a Jupiter-sized mass. Impossible to do. But Harold White has recently come up with revised calculations that say it can be done with a mass of 800kg, which is much more manageable - and possibly even lower mass requirements if the warp field is modulated.

MTd2
Gold Member
Yeah, that would be a prohibitively high mass-energy requirement, which Alcubierre calculated as a Jupiter-sized mass. Impossible to do. /QUOTE]

What I am saying is something different. They use negative mass to achieve that. I am talking about using usual matter to deflate space, the opposite of inflation. Is it possible, to deflate space?

JesseM
So what I gather so far is that Harold White's lab apparatus will consist of a capacitor ring and laser interferometer. The capacitor ring is what will produce the "warp" and the laser interferometer will measure/detect it.

So it sounds like what's being inferred here is that the potential gradient from an electric field will warp space - ie. it will cause a measurable difference in path length that can be detected with an interferometer.

Is such a belief reasonable, and consistent with known physics?
Presumably the point of the capacitor ring is to produce negative energy density (exotic matter) in the space between the plates by the Casimir effect? Still, like I said I don't think the belief is "reasonable" unless someone has actually shown mathematically (by finding an exact solution or by numerical solution) that merely producing a ring of negative energy density is sufficient to cause a "warp bubble" to form--while Alcubierre showed that exotic matter was necessary to sustaining an already-existing bubble, he did not address the question of what would be necessary to form a bubble in the first place.

Somehow, I'd always imagined that "warp coils" might be coils with some kind of superfluid flowing through them, where the movement of the superfluid matter then produces gravity waves, and these waves could then be concentrated by the helical coil shape, in the same way that an electrical coil can then concentrate electric and magnetic fields through its shape.

In principle, would it theoretically be possible to concentrate gravity waves through a helical coil shape, just as we do with an electromagnetic coil?

If so, then why can't we run a superfluid like ultra-cold helium through such coils, to achieve this? Wouldn't this perhaps result in a space "warp"?