18 August 2008

Dark energy spacecraft could fly faster than light

Cosmos Online
A futuristic engine that uses dark energy to propel a spaceship faster than light is theoretically possible, and could revolutionise space travel, U.S. scientists say.
Warp drive

Full speed ahead: Warp field according to the Alcubierre drive. Image shows the opposing regions of expanding and contracting spacetime that propel the central region. Credit: Wikimedia

SYDNEY: A futuristic engine that uses dark energy to propel a spaceship faster than light is theoretically possible, and could revolutionise space travel, U.S. scientists say.

The idea, backed up by calculations made by physicist Gerald Cleaver and graduate student Richard Orbousy, both of Baylor University in Waco, Texas, was published online on the arXiv.org physics website.

Not as unlikely as it seems

Like something from the world of Star Trek, their theory says that a spacecraft could travel at ‘warp speed’ in a bubble of space-time by manipulating dark energy, the mysterious invisible force accelerating the expansion of the universe (see, More evidence for dark energy’s repulsive power, Cosmos Online).

The spacecraft would essentially remain in the same place, they said, while space-time ahead of the spaceship shrank, and expanded again behind it.

The warp engine is based on the ‘Alcubierre warp drive’, a mathematical model of a method of stretching space in a wave that was first proposed by Mexican physicist Miguel Alcubierre in 1994.

“Think of it like a surfer riding a wave,” said Cleaver. “The ship would be pushed by the spatial bubble and the bubble would be travelling faster than the speed of light.”

The concept is based on new predictions emerging from string theory (a branch of theoretical physics which states that reality is based on one-dimensional objects called strings). String theorists believe space has not three or four but 10 dimensions: height, width, length, time and others that are unknown (see, A way to ‘see’ extra dimensions, Cosmos Online).


M-theory, which is as yet untested, unifies the various string theories by adding a further, 11th, dimension. Manipulating this 11th dimension exploits a loophole in Einstein’s theory of relativity that says that travelling at faster-than-light speeds would take an infinite amount of energy.

“String theory suggests that dimensions are globally held compact by strings wrapping around them,” the researchers write in their paper. “If this is the case, it may be possible to locally increase or decrease the string tension,” they theorise, changing the size of the extra dimensions.

Theoretical astrophysicists think that at the beginning of time, dark energy may have driven the universe to grow at faster than light speed for a short time.

Vast quantities of energy

Even if it were possible, faster-than-light travel would still take an enormous amount of energy. It would consume the entire mass of Jupiter to move a spaceship 10 m at warp speed, the researchers said.

“That is an enormous amount of energy,” Cleaver said. “We are still a very long way off before we could create something to harness that type of energy.”

Theoretical physicist Peter Bouwknegt, from the Australian National University in Canberra, said that though travelling at speeds faster than light is an idea which “a lot of people would find hard to swallow” the new research “stems from serious physics”.

He said that while the idea that space-time itself can travel faster than the speed of light was a real possibility, he was sceptical about whether you could move spacecraft at faster-than-light speeds.

“It would turn the whole of physics around and there would be a whole lot of consequences – things like causality would go wrong,” he said. “When people make calculations in M-theory they necessarily make assumptions about the behaviour of the theory in certain limits – whether or not the assumptions are valid remains to be seen.”

More information:
The study on arXiv.org (PDF)
Alcubierre drive – Wikipedia
String theory – Wikipedia

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