Alcubierre drive

Since 1993, the Mexican-born physicist, Miguel Alcubierre, had set about solving for solutions to Einstein's equations. The usual constraints hold. No ship can exceed the speed limit, particularly lightspeed. The ship's passengers should also not feel any abrupt jolts or find that onboard clocks begin to misbehave.

Since Einstein first developed general relativity--particularly the idea that mass itself can distort space and time--a number of exotic solutions and paradoxes have arisen. Arranging the stars themselves in just the right pattern often produces unusual--if not highly realizable--special effects. But since Alcubierre published his results in an article entitled, "The warp drive: hyper-fast travel within general relativity," the physicists are getting better at this stellar chess game.

If chess were played, say, on a sheet of rubber matting, with the moves possible for all chesspieces changing as the rubber sheet itself warped under a knight's or king's weight, one might get a sense of the challenges presented just to understand the rules of the game.

To understand clearly the proposition, the Alcubierre warp drive rides a bubble on space time itself, a ripple built up by pulling in regions in front and expelling them in back--a kind of 'push-me, pull-me' approach to interstellar travel.

The novelty is supraluminal travel becomes possible with an added bonus: the passengers would remain relatively unaware of the massive accelerations going on around them. Their bubble moves with them and defines all internal rules to its own captain's logs and stardates.

Right: A Possible View from Above. Space-time expands behind and contracts in front, which becomes a mathematical wave on space-time itself, a warp bubble. Highly unrealizable, or as physicists might understate as 'non-trivial', the consequences of this warp bubble allow unusual solutions. One such solution is this 'push-me, pull-me' approach to space travel. The energetic costs can be suboptimal, even if just the proper conditions seem arrangeable.

But as Dr. Chris Van Den Broeck says in his follow-on warp-drive paper in the journal, General Relativity and Quantum Cosmology: "This does not mean that the proposal is realistic."

Whether such solutions as published by Alcubierre (and now refined by Van Den Broeck) build on themselves could actually hinge more on astronomy, not engineering, and how over time, like the mathematics of black holes and wormholes themselves, keen observers start looking for what previously could neither be imagined nor predicted.

Above: As imaged by the Hubble Telescope, this ring structure found in galaxy NGC 4261, is suspected to originate from a core with super-massive gravitational pull on its surrounding cool gas. Photo credit: HST/Hubble Space Telescope Institute Left:Super-Massive Stellar Distortions of Space Time

To see a kind of proposed natural counterpart to the warp-drive concept, almost all of the bright objects in this Hubble Space Telescope image shown below are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it. As a result, multiple images of these background galaxies are distorted into faint stretched out arcs - a simple lensing effect analogous to viewing distant street lamps through a glass of wine. The Abell 2218 cluster itself is about 3 billion light-years away in the northern constellation Draco

Whether these proposals occupy more than physicists and astronomers however is far from being determined: many impossible or otherwise exotic kinds of matter are needed to put a wrinkle in space-time.

But as scientists study the conditions for fast transits, the next generation of star-watchers will have to become even more imaginative. For example, the often depicted view of blurring or distorting zoom motions shown to accompany faster-than-light travel is not consistent with known physics. Since lightspeed is constant, independent of the observer, faster-than-light travellers would not get the opportunity to see any zoom forward from their view. The light would neither speed up nor hit the observer's retina with any such apparent velocity boost.

In this thread

Published physics

M. Alcubierre, "The warp drive: hyper-fast travel within general relativity," Class. and Quantum Grav., vol. 11, p. L73 (1994)

Ken Olum, (1998),"Superluminal Travel Requires Negative Energies", Physical Review Letters,81, 3567-3570

Morris, M., and Thorne, K.S. (1988) "Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity", Am. J. Phys., Vol. 56, No. 5, pp. 395-412.

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