Travel by bubble might seem more appropriate for witches in Oz, but two physicists suggest that a future spaceship could fold a space-time bubble around itself to travel faster than the speed of light.

We're talking about the very distant future, of course.

The idea involves manipulating dark energy — the mysterious force behind the universe's ongoing expansion — to propel a spaceship forward without breaking the laws of physics.

?Think of it like a surfer riding a wave,? said Gerald Cleaver, a physicist at Baylor University. ?The ship would be pushed by the spatial bubble and the bubble would be traveling faster than the speed of light.?

In theory, the universe grew faster than the speed of light for a very short time after the Big Bang, driven by the dark energy that represents about 74 percent of the total mass-energy budget in the universe. Dark matter constitutes 22 percent of the budget, and normal matter (stars, planets and everything you see) makes up the remaining 4 percent or so.

Strange as it sounds, current evidence supports the notion that the fabric of space-time can expand faster than the speed of light, because the reality in which light travels is itself expanding.

Cleaver and Richard Obousy, a Baylor graduate student, tapped the latest idea in string theory to devise how to manipulate dark energy and accelerate a spaceship. Their notion is based on the Alcubierre drive, which proposes expanding space-time behind the spaceship while also shrinking space-time in front.

String theorists had believed that a total of 10 dimensions exist, including height, width, length and time. The other six dimensions exist largely as unknowns, but everything is based on hypothetical one-dimensional strings. A newer theory, called M-theory, suggests that those strings all vibrate in yet another dimension.

Manipulating that additional dimension would alter dark energy in terms of height, width, and length, Cleaver and Obousy theorize. Such a capability would permit the altering of space-time for a spaceship, taking advantage of dark energy's effect on the universe.

"The dark energy is simultaneously decreased just in front of the ship to decrease (and bring to a stop) the expansion rate of the universe in front of the ship," Cleaver told SPACE.com. "If the dark energy can be made negative directly in front of the ship, then space in front of the ship would locally contract."

This loophole means that the spaceship would not conflict with Einstein's Theory of Relativity, which states that objects accelerating to the speed of light require an infinite amount of energy.

However, the Baylor physicists estimate that manipulating dark energy through the extra dimension requires energy equivalent to the converting the entire mass of Jupiter into pure energy — enough to move a ship measuring roughly 33 feet (10 meters) by 33 feet by 33 feet.

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

The workaround solution may leave fans of Einstein pleased. But for now, faster-than-light travel remains, like Oz, a pleasant fantasy.