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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 laws of physics. One caveat: the warp craft can’t exceed the speed of light, so you won’t be getting anywhere interesting anytime soon. However, this research still represents an important advance in our understanding of gravity.
Movement without movement
Einstein’s general theory of relativity is a toolkit for solving problems related to gravity that relates matter and energy to deformations in spacetime. These distortions of space-time in turn instruct matter and energy to move. In almost all cases, physicists use the equations of relativity to determine how a particular combination of objects will move. They have some physical scenario, such as a planet orbiting a star or two black holes colliding, and they ask how these objects warp space-time and what the subsequent evolution of the system should be.
But it’s also possible to do Einstein’s math in reverse by imagining some desired motion and asking what kind of space-time warping it might allow. This is how the Mexican physicist Miguel Alcubierre discovered the physical basis of warp drive – the long base Star Trek franchise.
The goal of warp drive is to get from point A to point B in between commercial breaks, which usually involves traveling faster than light. But special relativity explicitly forbids speeds faster than light. Although the authors never minded Star TrekThis irritated Alcubierre. He discovered that it was possible to construct a warp drive by cleverly manipulating space-time and arranging it so that the space in front of the craft would shrink and the space behind the craft would stretch. This creates movement without, strictly speaking, movement.
It sounds like a contradiction, but that’s just one of the many amazing aspects of general relativity. Alcubierre’s warp drive avoids exceeding the speed limit of light because it never moves over space; instead, space itself is manipulated to essentially approximate the spacecraft’s target.
Alcubierre’s performance has an irritating but fatal flaw. To provide the necessary space-time distortions, a spacecraft must contain some form of exotic matter, usually considered negative mass matter. Negative matter has some conceptual problems that seem to defy our understanding of physics, such as the possibility that if you kick a ball that weighs minus 5 kilograms, it will fly backwards and violate conservation of momentum. Furthermore, no one has ever seen any object with negative mass existing in the real universe.
These problems with negative mass have led physicists to propose various versions of “energy terms” as supplements to general relativity. These aren’t baked into relativity itself, but additions are needed because general relativity allows for things like negative mass, which don’t seem to exist in our universe – these energy conditions keep them out of the relativity equation. They’re scientists’ response to the disturbing fact that vanilla GR allows for things like superluminal motion, but the rest of the universe doesn’t seem to agree.
Warp factor zero
Energy conditions are not experimentally or observationally proven, but they are claims that are consistent with all observations of the universe, so most physicists take them rather seriously. And until recently physicists considered these energy conditions absolutely 100% clear that you couldn’t build a warp drive even if you really wanted to.
But there is a way around it, 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 Propulsion Laboratory of Applied Physics, a virtual think tank dedicated to researching, among many other things, warp drives.) In an article accepted for publication in the journal Classical and quantum gravityresearchers delved deep into relativity to investigate whether some version of warp drive might work.
The equations of general relativity are notoriously 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 examine their solutions numerically and verify that they are consistent with 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 overwhelming gravitational tidal forces within the craft, for the convenience of any imagined passengers. They then checked whether these solutions obeyed the energetic conditions that prevented the use of exotic matter.
Indeed, scientists have discovered a solution to warp drive: a method of manipulating space so that passengers can move without accelerating. However, there is no such thing as a free lunch, and the physicality of this warp drive comes with a major caveat: the vessel 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 for deformation.