The warp drive of the Star Trek starship Enterprise could become a reality much sooner than we thought. Or at least that's what can be deduced from a paper recently published in Classical and Quantum Gravity by a team of researchers from the Applied Physics group, which specializes in advising governments and businesses on scientific and technological issues.
In their study, the researchers openly announce the first feasible model of a warp drive, one based on the idea proposed more than 20 years ago by Mexican physicist Miguel Alcubierre, who has explicitly supported the research.
"Many people in the scientific field," says Alexey Bobrick, the first author of the article, "are familiar with the Alcubierre drive and believe that warp drives are not possible in the physical world due to the need to use negative energy. But this, however, is no longer the case."
The Alcubierre drive, the starting point
In 1994, Miguel Alcubierre published an ingenious solution to the equations of the General Theory of Relativity in the same journal (Classical and Quantum Gravity). Since then, known as the 'Alcubierre metric,' his idea allowed a spacecraft to travel at over 300,000 km/s—that is, faster than the speed of light—without violating any laws of physics.
To achieve this, Alcubierre proposed that the ship travel inside a space-time warp bubble. Behind the ship, space-time would stretch, pushing the bubble, while in front of it it would shrink, bringing the target ever closer. The ship, inside the bubble, would remain motionless in flat (unwarped) space and therefore would not violate the law against faster-than-light travel. It would be similar to a person standing still on a fast-moving conveyor belt.
Photo. The graphic shows a space-time warp bubble, inside which (yellow) a ship would remain in a flat space. The bubble would expand the space behind the ship and compress it in front of it, allowing for high-speed travel.
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Gianni Martire (Applied Physics)
In fact, the ship proposed by Alcubierre would be transported by the bubble at superluminal speeds, but it would be space, not the ship, that would 'move' with its repeated expansions and contraction. Relativity, in fact, prohibits any object from traveling faster than the speed of light through spacetime, but it says nothing about the maximum speed that spacetime itself can reach. With his idea, therefore, Alcubierre took a major first step toward the famous 'warp drive' of the 'Star Trek' series, which, incidentally, served as inspiration for his work.
The problem, however, is that to create the space-time warping bubble that provides the drive, you would have to use negative-density, or exotic, matter to obtain negative energy, which doesn't exist, leaving the Alcubierre drive completely out of reach. The more negative energy there is in the bubble, the greater its propagation speed would be, easily exceeding that of light.
For these reasons, the physics community had long since dismissed the Alcubierre drive proposed, and the general idea was that humanity would never build propulsion systems based on the warping of spacetime. NASA itself, researchers indicate, has been unsuccessfully attempting to design physics warp drives since 2012 at the Eagleworks laboratories at the Johnson Space Center in Houston, Texas.
A solution without negative energy
But the new study has managed to avoid that problem. Bobrick explains: "We went in a different direction than NASA and other researchers. Our research has shown that there are actually several other types of warp drives in General Relativity. In particular, we have formulated new classes of warp drive solutions that do not require negative energy and can therefore occur in the physical world."
Giving up the negative energy proposed by Alcubierre, however, comes at a price in terms of speed. The warp drive proposed by the researchers, in fact, "is subluminal and, at least in principle, can be built based on the physical principles known to humanity today. It cannot exceed the speed of light, but it comes close," the researchers write.
In any case, they add, "we have shown that all the criticisms of the famous Alcubierre drive are irrelevant because there is a whole variety of other curvature drives that are physical and can be used. Therefore, the Applied Physics team has demonstrated that curvature field mechanics is not stillborn, but is a viable, physical science."