# Explained: Physicists designed the first 'bending motor' to travel at the speed of light

The warp engine of the Star Trek starship Enterprise could become a reality much sooner than we thought. Or that is, at least, what is deduced from a recently published work in 'Classical and Quantum Gravity' by a team of researchers from the Applied Physics group, specialized in advising governments and companies on scientific and technological issues.

In their study, the researchers openly announce the first feasible model of a curvature motor, one based on the idea proposed more than 20 years ago by Mexican physicist Miguel Alcubierre , who has explicitly endorsed the research.

"Many people in the field of science" - says Alexey Bobrick, first author of the article - are familiar with Alcubierre's motor and believe that bending impulses are not possible in the physical world due to the need to use negative energy.

But this, however, is no longer the case.

Alcubierre's engine, the starting point

In 1994, Miguel Alcubierre published in the same magazine (Classical and Quantum Gravity) an ingenious solution to the equations of the General Theory of Relativity. Known since then as 'Alcubierre's metric', his idea allowed a spacecraft to travel at more than 300,000 km / s , that is, faster than light, but without violating any laws of Physics.

To achieve this, Alcubierre proposed that the ship travel inside a space-time warp bubble. Behind the ship, spacetime would stretch, pushing the bubble, while in front of it it would shrink, bringing the target closer and closer. The ship, inside the bubble, would remain immobile in a flat space (not deformed) and would not therefore violate the law that prevents traveling faster than light. It would be something like a person who stands still on a conveyor belt that is moving at full speed.

The graph shows a space-time warp bubble, inside (yellow) a spacecraft would remain in flat space. The bubble would expand the space behind the ship and compress it in front of it, allowing high-speed travel - 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, and not the ship, that would 'move' with its repeated dilations and contractions. Relativity, in effect, prohibits any object from traveling faster than light through spacetime, but it says nothing about the maximum speed that spacetime itself can reach. With his idea, then, Alcubierre took a great first step towards the famous ' curvature motor ' from the 'Star Trek' series , which by the way, served as inspiration for his work.

The problem, however, is that in order to create the space-time deformation bubble that provides the impulse, it would be necessary to use matter with negative, or exotic, density to obtain negative energy, which does not exist, which leaves the Alcubierre engine completely out of our mind. scope. The more negative energy there is in the bubble, the greater its speed of propagation, which would easily exceed that of light.

For those reasons, the physicist community had long since discarded the engine proposed by Alcubierre, and the general idea was that humanity would never build propulsion systems based on the warp of space-time. NASA itself , the researchers say, has been trying unsuccessfully since 2012 to design physical deformation units 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. In Bobrick's words: "We went in a different direction than NASA and other researchers. Our research has shown that there are actually several more types of bending momentum in General Relativity . In particular, we have formulated new classes of bending impulse solutions that do not require negative energy and therefore can occur in the physical world."

Giving up the negative energy proposed by Alcubierre, however, comes at a price in terms of speed. The curvature motor proposed by the researchers, in effect, "is subluminal and, in principle at least, can be built on the basis of physical principles known to mankind today. It cannot exceed the speed of light, but almost," the researchers write.

In any case, they add, "we have shown that all the criticisms of Alcubierre's famous motor are irrelevant because there is a whole variety of other units of curvature that are physical, and that can be used. Therefore, the Applied Physics team has shown that bending field mechanics is not dead before birth, but is a viable physical science."