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A team of physicists has discovered that it is possible to build a real, actual, physical warp drive and not break any known rules of physics. One caveat: the ship doing the warping can’t go faster than the speed of light, so you won’t be getting anywhere interesting anytime soon. But this research still represents an important advance in our understanding of gravity.

Movement without movement

Einstein’s general theory of relativity is a set of tools for solving problems involving gravity, which relates mass and energy to deformations in spacetime. In turn, these spatiotemporal deformations instruct mass and energy how to move. In almost all cases, physicists use the equations of relativity to understand how a certain combination of objects will move. They have some physical scenario, like a planet orbiting a star or two black holes colliding, and they ask how these objects deform spacetime and what the subsequent evolution of the system should be.

But it is also possible to do Einstein’s math in reverse by imagining some desired motion and asking what kind of spatiotemporal deformation might make it possible. That’s how Mexican physicist Miguel Alcubierre discovered the physical basis for warp drive, long a staple of the Star Trek franchise.

The purpose of warp drive is to get from A to B in the time between commercial breaks, which usually involves going faster than light. But special relativity explicitly forbids speeds faster than light. Although this never bothered the writers of Star Trek, this really irritated Alcubierre. He discovered that it was possible to construct a warp drive through the clever manipulation of space-time, arranging it so that the space in front of the ship contracted and the space behind the ship expanded. This generates motion without, strictly speaking, motion.

It sounds like a contradiction, but this is just one of the many wonderful aspects of general relativity. Alcubierre’s warp drive avoids breaking the light speed limit because it never moves through space; instead, space itself is manipulated to essentially bring the spaceship’s destination closer to it.

Although irritating, Alcubierre’s design has a fatal flaw. To provide the necessary space-time distortions, the spacecraft must contain some form of exotic matter, usually thought of as negative-mass matter. Negative mass has some conceptual problems that seem to contradict our understanding of physics, such as the possibility that if you kick a ball that weighs minus 5 kilograms, it will fly backwards, violating the conservation of momentum. Plus, no one has ever seen a negative mass object exist in the real Universe.

These problems with negative mass have led physicists to propose various versions of “energy terms” as additions to general relativity. These are not included in relativity itself, but are necessary additions because general relativity allows for things like negative mass that don’t seem to exist in our universe – these energy conditions keep them out of the relativity equations. They are scientists’ answer to the disturbing fact that vanilla GR allows for things like superluminal motion, but the rest of the universe seems to disagree.

Warp factor zero

The energy conditions have not been proven experimentally or observationally, but they are statements that are consistent with all observations of the universe, so most physicists take them quite seriously. And until recently physicists viewed these energy conditions as absolutely 100 percent clear that you couldn’t create warp drive even if you really wanted to.

But there is a way around this, discovered by an international team of physicists led by Jared Fuchs of the University of Alabama in Huntsville. (The team is also affiliated with the Applied Physics Propulsion Laboratory, a virtual think tank dedicated to researching, among many other things, warp propulsion.) In a paper accepted for publication in the journal Classical and quantum gravityresearchers delved into the theory of relativity to investigate whether some version of warp drive might work.

The equations of general relativity are extremely difficult to solve, especially in complex cases such as warp drive. So the team turned to software algorithms; instead of trying to solve the equations by hand, they examined their solutions numerically and checked that they satisfied the energy conditions.

The team did not actually attempt to construct a propulsion device. Instead, they explored various solutions to general relativity that would allow point-to-point travel without the craft undergoing any acceleration or experiencing any massive gravitational tidal forces within the craft, much to the comfort of all imaginable travelers. They then checked whether these solutions adhere to energetic conditions that prevent the use of exotic matter.

Researchers have indeed found a solution to warp propulsion: a method of manipulating space so that passengers can move without accelerating. There’s no such thing as a free lunch, however, and the physicality of this warp drive comes with a big caveat: the ship and passengers can never travel faster than light. Also disappointing: the fact that the researchers behind the new work don’t seem to have bothered to figure out what configurations of matter would allow the distortion to occur.