The only FTL [faster than light] drive theory I know that hasn't been shot down (it appears there may be problems with the physics with the proposed quantum gravity theory) ...I was reading something that prompted me to finally link it.

Wikipedia: the Alcubierre drive.

In 1994 Alcubierre proposed a way of changing the geometry of space by creating a wave which would cause the fabric of space ahead of a spacecraft to contract and the space behind it to expand. The ship would then ride this wave inside a region of flat space known as a warp bubble, and would not move within this bubble, but instead be carried along as the region itself moves as a consequence of the actions of the drive. If this is so, conventional relativistic effects such as time dilation would not apply in the way they would in the case of a ship moving at a very great velocity through flat spacetime, relative to other objects. This method of propulsion would not involve objects in motion at speeds faster than light with respect to the contents of the warp-bubble; that is, a light beam within the warp-bubble would still always move faster than the ship. Thus the mathematical formulation of the Alcubierre metric does not contradict the conventional claim that the laws of relativity do not allow a slower-than-light object to accelerate to faster-than-light speeds. The Alcubierre drive, however, remains a hypothetical concept with seemingly insuperable problems: The amount of energy required is unobtainably large, there is no method to create a warp bubble in a region that does not already contain one, and there is no method to move from the warp-bubble once having arrived at a supposed destination.

More. Michael Szpir: Spacetime hypersurfing.

The key to Alcubierre's warp drive is something called exotic matter. Exotic matter has the curious property of having a negative energy density, unlike normal matter (the stuff that makes up people, planets and stars), which has a positive energy density. Two bits of matter that have the same energy density are attracted to each other by gravity. In contrast, bits of positive and negative energy matter would be repelled by gravity. It is the negative energy density of exotic matter that powers the warp drive. A negative energy density is not the nonsensical thing it appears to be. Indeed, in 1948 the Dutch physicist Hendrik Casimir first predicted that one could observe the effects of negative energy densities. He reasoned that if negative energy densities existed, two closely spaced parallel conducting plates in a vacuum would be attracted to one another. This phenomenon, now called the Casimir effect, was measured in 1958 by M. Sparnaay, and is usually taken to be a confirmation that negative energy densities are possible. Exotic matter of a slightly different type is also invoked in the modern theory of cosmology known as inflation. According to the theory of inflation, exotic matter in the early universe (moments after the big bang) had a positive energy density, but a very large negative pressure. The negative pressure was so large that it counteracted the effects of the positive energy density. The result was an expansion of spacetime so rapid that two observers originally very close to each other would be carried apart faster than the speed of light.

But it would take a lot of energy. Discovery News: Warp drive engine would travel faster than light.

While the theory rests on relatively firm ground, the next question is how do you expand space behind the ship and contract it in front of the ship?

Cleaver and Richard Obousy, the other coauthor, propose manipulating the 11th dimension, a special theoretical construct of m-theory (the offspring of string theory), to create the bubble the ship would surf down.

If the 11th dimension could be shrunk behind the ship it would create a bubble of dark energy, the same dark energy that is causing the universe to speed up as time goes on. Expanding the 11th dimension in front of the ship would eventually cause it to decrease, although two separate steps are required.

Exactly how the 11th dimension would be expanded and shrunk is still unknown.

"These calculations are based on some arbitrary advance in technology or some alien technology that would let us manipulate the extra dimension," said Cleaver.

What the scientists were able to estimate was the amount of energy necessary, if the technology was available, to change these dimensions: about 10^45 joules.

"That's about the amount of energy you'd get if you converted the entire mass of Jupiter into pure energy via E = mc^2," said Cleaver, an energy far beyond anything humanity can currently envision creating.

...or maybe not quite so much? - Chris Van Den Broek, Instituut voor Theoretische Fysica, Cornell U: A warp drive with more reasonable total energy requirements. Original paper [PDF] here.

I show how a minor modification of the Alcubierre geometry can dramatically improve the total energy requirements for a "warp bubble" that can be used to transport macroscopic objects. A spacetime is presented for which the total negative mass needed is of the order of a few solar masses, accompanied by a comparable amount of positive energy. This puts the warp drive in the mass scale of large traversable wormholes. The new geometry satisfies the quantum inequality concerning WEC violations and has the same advantages as the original Alcubierre spacetime.

Which still amounts to bunches of energy.

More here, Warp Drive Physics [home page]: Warp drive theory and Warp theory, the cons. John G Cramer [home page] ...of particular interest is the article The micro warp drive.

How does Alcubierre's metric manage to move an object faster than the speed of light? Isn't that in direct contradiction to Einstein's special theory of relativity? Actually, no. General relativity treats special relativity as a restricted sub-theory that applies locally to any region of space that is sufficiently small that its curvature can be neglected. General relativity does not forbid faster-than-light travel or communication, but it does require that the local restrictions of special relativity must apply. In other words, light speed is the local speed limit, but the broader context of general relativity may provide ways of circumventing this local statute. One example of this is a wormhole (see my AV columns, Analog 6/89 and 5/90) connecting two widely separated locations in space, say five light-years apart. An object might take a few minutes to move with at low speed through the neck of a wormhole, observing the local speed-limit laws all the way. However, by transiting the wormhole the object has traveled five light years in a few minutes, producing an effective speed of a million times the velocity of light.

Might it work? - Don't ask: I have no idea ...the physicists were impressed, at least.

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