Traveling faster than the speed of light has been a mainstay of science fiction for almost 50 years. Ever since the Starship Enterprise engaged warp speed in 1966, the idea of moving around the galaxy faster than light remained the construct of the show’s producer, Gene Roddenberry.
But in the real universe, traveling faster than light is just not possible. Albert Einstein told us so, though that could be changing.
Twenty-eight years after the original “Star Trek” series was launched, physicist Miguel Alcubierre watched one of its episodes and began to think about what it would take to make an object go faster than light speed without violating Einstein’s description of nature.
Back in 1905, Einstein described the odd effects that would happen as an object approached the speed of light: Time would stretch and lengths would contract. At the speed of light, time would stop and all lengths would shrink to zero. Not to worry, no object can ever attain the speed of light — that would take more energy than the entire universe could supply.
Then 10 years later, Einstein presented a new description of gravity, recasting this natural occurrence in terms of geometry. His novel account of gravity was the first since Isaac Newton portrayed gravity as a force reaching out from one object to act on another.
Fabric of universe
In his Theory of Relativity, Einstein united the three dimensions of space with that of time, calling it four-dimensional space-time, sometimes poetically referred to as the “fabric of the universe.”
Mass — how much material something is made of — causes space-time to twist, distort and warp. Space-time devoid of any mass is flat, but add mass and it becomes curved like a stretched-out bedsheet with a bowling ball placed on it. This is gravity according to Einstein.
(The notion of the gravity well comes from Einstein’s description. For our solar system, the planets “fall” down the sun’s gravity well and speed up; that additional speed enables planets to “climb” back up the well. This is similar to a coin placed in a toy gravity well but, unlike a planet’s orbit, the coin’s path deteriorates because of friction between its sides and the surface of the well. Eventually, the coin falls into the central hole — just like matter orbiting in a disk around a black hole!)
Alcubierre worked the problem backward. Instead of mass warping space, he proposed warping space to make an object move in such a way that it could move faster than light.
At first, this would seem to violate Einstein’s speed limit on matter. What physicists have come to realize is that Einstein’s limitations apply to objects that move in space-time but not to space-time itself.
Alcubierre proposed warping space-time so that it contracted directly in front of an object and expanded directly behind the object. The object, spacecraft or starship would be propelled, not by any propulsion system but by “surfing the space-time wave.” In this contrived situation, the thinking is that Einstein’s laws of relativity would not be violated nor would any of the strange effects of relativity be encountered.
Gravity is an attractive force and two objects only gravitationally attract one another, never repel one another. When Alcubierre first proposed his warp drive idea, he found that it would require what was then called exotic matter. Today, we call it negative energy.
Negative energy has the surprising property of being gravitationally repulsive. Instead of drawing space-time together, negative energy would push it apart. In front of the spacecraft, ordinary matter or positive energy — the kind that we are used to — would contract space-time — as nature ordinarily does — but behind the ship, negative energy or exotic matter would expand it.
Negative energy is not speculative; quantum physics predicts that it exists. In 1948, physicist Hendrik Casimir predicted that it would be possible to observe the effects of negative energy. In 1958, physicist Marcus Sparnaay observed and measured this Casimir effect. This finding is usually taken as evidence that negative energy is possible.
Faster-than-light expansion of space-time is believed to have happened in the moments after the Big Bang. The Inflation Theory explains that when the universe was the size of a pea, it expanded to the size of a grapefruit faster than a light beam could travel that distance.
Space observatories have shown that inflation is a necessary requirement in the early expansion of the universe because the temperature background of the universe has been found to be exceptionally smooth. A very fast expansion is required to even out any temperature irregularities in the emerging universe.
In addition, observations by the Hubble telescope made during the 1990s showed that the expansion rate of the universe is increasing over great distances. Astronomers call the repulsive force that is increasing the universal expansion “dark energy.”
Since the idea was originally published, other physicists have looked at the warp concept, and there has been some debate about whether any strange effects from relativity take place after all. Most outstanding is how, in practice, a device generates the negative energy required and then places it where it is needed.
Looking into it
Yet, NASA has taken the idea seriously enough to let a few scientists further investigate the warp drive concept as part of their ongoing research in advanced propulsion systems at the Johnson Space Center in Houston.
Maybe someday warp drive will allow humans to go beyond investigating the solar system with robotic explorers that travel at tens of thousands of miles per hour and free us to explore other stars and solar systems in our Milky Way galaxy.
Richard Monda is an astronomer living in the Capital Region.