A team of physicists has discovered that it is possible to build a real, physical warp drive and not break any known physics rules. One caveat: the ship performing the warp can’t exceed 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.
Moving without movement
Einstein’s general theory of relativity is a set of tools for solving problems related to gravity that connects mass and energy with warps in space-time. In turn, those spacetime warps tell mass and energy how 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 wonder how those objects warp space-time and what the subsequent evolution of the system should be.
But it is also possible to run Einstein’s mathematics in reverse, imagining some desired motion and asking what kind of warping of spacetime can make it possible. This is how the Mexican physicist Miguel Alcubierre discovered the physical basis of a warp drive, which for a long time was a basic element of the system. Star Trek franchise.
The goal of a warp drive is to get from A to B in the time between commercial breaks, which typically involves faster-than-light movement. But special relativity expressly prohibits speeds faster than light. While this never bothered the writers of Star Trek, that irritated Alcubierre. He discovered that it was possible to build a warp drive through clever manipulation of space-time, arranging it so that the space in front of a ship shrank and the space behind the ship stretched. This generates movement without, strictly speaking, movement.
It sounds like a contradiction, but that is just one of the many wonderful aspects of general relativity. Alcubierre warp drive prevents light speed limit violations because it never moves through space; instead, space itself is manipulated to, in essence, bring the spaceship’s destination closer to it.
Although tempting, Alcubierre’s design has a fatal flaw. To provide the necessary space-time distortions, the spacecraft must contain some form of exotic matter, typically considered matter with negative mass. Negative mass has some conceptual problems that seem to challenge our understanding of physics, such as the possibility that if you kick a ball that weighs negative five kilograms, it will fly backwards, violating the conservation of momentum. Furthermore, no one has ever seen any object with negative mass in the real universe.
These problems with negative mass have led physicists to propose various versions of “energy conditions” as complements to general relativity. These are not built into relativity itself, but they are necessary add-ons because general relativity allows for things like negative mass that don’t seem to exist in our universe; These energetic conditions keep them outside the equations of relativity. They are scientists’ answer to the disturbing fact that vanilla GR allows things like superluminal motion, but the rest of the universe doesn’t seem to agree.
Zero warp factor
The energy conditions are not proven experimentally or by observations, but they are statements that agree with all observations of the universe, so most physicists take them quite seriously. And until recently, physicists had considered those power conditions to make it absolutely 100 percent 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 research, among many other things, into warp drives.) In an article accepted for publication in the journal Classical and quantum gravityResearchers delved deeper into relativity to explore whether some version of a warp drive could work.