Can we travel to the stars? The answer to that question is “yes,” provided we don't care how long the journey will take. According to Einstein's special theory of relativity, nothing with mass can accelerate to light speed, much less past it. Since the closest star is about 4 light-years away, it would take a great deal longer than four years for any spaceship based on known technology to reach it. At its present speed, Voyager 1 would require several thousand years to get to another star system—and it's one of the fastest spaceships we have.
That's where research by NASA engineer Harold “Sonny” White comes in. White claims he has found a way to build a faster-than-light warp drive, based on a simple mathematical relation in Einstein's general theory of relativity. While the idea is inspired by Star Trek, the basic concept behind the design is grounded in physics.
However, the information that's publicly available about White's work would make Mr. Spock's klaxon sound. The warp drive design appears to be based on an exotic form of matter that nobody has seen experimentally, in combination with a quantum effect too small to work in a device the size of a spaceship. As if that weren’t enough, White's research is largely unpublished, and he claims he can’t reveal the details because they are covered by nondisclosure agreements. Despite that, the media coverage of the warp drive has been largely uncritical, taking White's claims of his own research at face value.
Here's what we do know. In general relativity, it's possible to have a warped bubble of space-time that can move faster than light because it isn't made of matter. Think of this bubble like a moving sidewalk: It carries you faster than you can walk, but your leg muscles still dictate how fast you can walk on the rubber surface. In the case of the space-time bubble, the “sidewalk” is moving faster than light, while objects inside that bubble still obey the speed limit.
The “warp bubble” is a mathematical solution to Einstein's equations discovered by Miguel Alcubierre in 1994, and it is now included in at least one college-level general relativity textbook. However, solutions to equations are conditional: If the universe is configured in a particular way, then the solution describes how (for example) a spaceship can travel. Alcubierre's solution shows that a warp bubble exists if there's a region of space-time with negative energy density. All forms of matter and light possess positive energy density, which is why they create an attractive gravitational field. Even dark energy, which drives the accelerating expansion of the universe, has positive energy density.
Because nothing ordinary can make negative energy, that leaves only exotic options. One uses hypothetical particles with negative mass, but those have never been observed experimentally—and there's good reason to think they don't exist. The other idea is based on the Casimir effect: When two metal plates are placed in a vacuum, they experience an attractive force thanks to quantum fluctuations in the cavity between them. In some calculations, the Casimir effect exhibits negative energy in the region between the plates, but no matter how you interpret it, it's a tiny amount relative to the size of the apparatus. To make a spaceship-size warp bubble using the Casimir effect, you'd need the equivalent of converting all of Jupiter's mass into energy.
So how does White get around these limitations? We don't know. We can't know, because White won't tell us. The technical details of his experimental setup aren't published, and his public appearances have focused on big ideas rather than practical realities. When Popular Science writer Konstantin Kakaes asked White how his design works, the response was revealing:
“[White] explains that he has signed nondisclosure agreements that prevent him from revealing the particulars. I ask with whom he has the agreements. He says, ‘People come in and want to talk about some things. I just can’t go into any more detail than that.’ ”
The apparatus uses a set of ceramic capacitors in a ring, so it sounds like it's based on a cavity, such as one might use for Casimir effect experiments. In his appearance at the Starship Congress last week, White mentioned that his device also uses exotic matter of an unspecified nature that exploits quantum effects for propulsion. As physicist Richard Easther points out, even the details of White's experiment to test his device are sketchy.
The difficulty is clear. From what physicists have learned about the universe and its contents, White's warp drive can't work, period. If White has found a new method for generating negative energy, he hasn't published it, which means there's no way for other scientists to test his claims experimentally—or even check his calculations. Science requires its practitioners collectively to keep each other honest. For all the flaws in peer review and academic publishing, true suppression of ideas is rare. Until White publicizes the details of his research, our best option is to assume that what we know about quantum physics is correct—and his warp drive is still science fiction.