Faster-than-light (FTL) travel is commonly thought to be impossible. Einstein established this in his Special Theory of Relativity in 1905. The speed of light, he said, is an unbreakable constant. FTL travel will never exist if his theory is to be accepted—and it is, almost universally. However, gravity is a tricky thing. It changes our perception of time, bounds the current model of the universe, and twists itself into wells of darkness called black holes, which alter spacetime. So maybe it is no surprise to learn that by manipulating space in a similar way, an unmoving starship might slide from one side of the galaxy to another at more than one hundred times lightspeed.
To do this, future scientists will need to play with gravity. Gravity is one of the four fundamental forces that govern the universe, along with electromagnetism and the strong and weak forces. “Four forces?” a reader might ask. “Why not one?” This same question toyed with the minds of Einstein and other pioneering researchers. Why not express all physical forces in terms of gravity, or electromagnetism, or the strong or weak force? After all, they thought, gravity and electromagnetism have infinite range and similar mathematical forms. Electromagnetism and the weak force become the same “electroweak” force at high energy levels. It seemed perfectly natural to consolidate things under a Grand Unified Theory. Yet now, the least plausible approaches to such a task seem to be the most effective, and gravity, despite its deep similarities to electromagnetism, will probably be the last force to fit into such a theory.
In other words, gravity is an oddball. It causes all mass, including you and I, to bend spacetime a little. The heavier the object, the more spacetime is warped, until we encounter the extreme scenario of hyperdense black holes, which dilate time near their dark spheres, pulling inexorably into a negative, sunless horizon. But here’s the odd part: objects near Earth fall at the same speed, but farther away, the force due to gravity depends very much on mass. In fact, every mass in the universe exerts a gravitational force on you and me—most are just too far away to have much effect. Since heavier objects have more effect on spacetime, a very dense material would prove helpful—even necessary—in a warp drive.
What might this material look like? What exotic substance could undo and reweave the tapestry of the universe? The short answer is that we don’t know. However, Mexican physicist Miguel Alcubierre proposed a craft surrounded by a ring of such unknown material, which, when supercharged with energy, could warp the fabric of the universe. If the proper material exists, the Drive would create a bubble that expands space at the back and contracts space at the front. Oddly enough, this would funnel the craft through the universe, sliding it down a slope of altered spacetime.
A prospective spaceship might slide down a slope of spacetime. (Say that five times fast.)
Because the ship doesn’t actually move—only the space around it moves—normal side effects of faster-than-light travel are negated. This means no user of the Alcubierre Drive will end up millenia in the future or past, as is sometimes thought. However, they just might annihilate their destination in an explosion worthy of the Death Star.
Here’s why: space isn’t empty, but full of tiny energy particles and radiation. A warp bubble such as the one created by an Alcubierre Drive could catch these particles, building a deadly store of energy. Although the ship itself would probably be safe to travel in, exiting the surrounding warp bubble would expel heat in a cone-shaped blast. If the journey is long enough—and space voyages generally are—enough energy could be gathered during the trip to annihilate an entire star system upon arrival.
So perhaps these Drives would work best with missiles rather than spaceships. For now, it seems best that there are no extrasolar human civilizations that could be targeted by such weapons. But that’s not to say there’s no hope of colonizing nearby star systems. NASA’s math puts a warpspeed journey to Alpha Centauri, our solar system’s closest neighbor, at about two weeks’ time—a travel speed greater than 113x that of light. Perhaps not enough to reach a long time ago in a galaxy far, far away, but fast enough for real life… as long as we can reconstruct our destination when we get there.
Sources
Nave, R. “Einstein’s Effort toward Unification of Forces.” HyperPhysics, Georgia State University Department of Physics and Astronomy, hyperphysics.phy-astr.gsu.edu/hbase/Forces/einun.html#c1.
Whitwam, Ryan. “The Downside of Warp Drives: Annihilating Whole Star Systems When You Arrive.” ExtremeTech, 16 Nov. 2012, https://www.extremetech.com/extreme/140635-the-downside-of-warp-drives-annihilating-whole-star-systems-when-you-arrive.
Williams, Matt. “What Is the Alcubierre ‘Warp’ Drive?” Universe Today, 22 Jan. 2017, https://www.universetoday.com/89074/what-is-the-alcubierre-warp-drive/.
Images courtesy of Lawrence Berkeley National Library and AllenMcC.