Faster-than-light travel

Most science fiction stories depend on the concept of faster-than-light travel. The reason is simple-- the galaxy is immense. The central plane of our galaxy is about 50,000 light years in radius, and it has a halo of dark matter and globular clusters extends another 100,000 light years beyond that. The Earth orbits the galactic center at about 27,000 light years; the circumference of the Earth's orbit is therefore roughly 170,000 light years. The Earth traverses this immense distance once every 225,000,000 to 250,000,000 years. Hence the Earth is rotating about the galactic center at about 0.07% the speed of light.

It is believed that the Earth is situated in a torus-shaped habitable zone of the galaxy that is estimated to be roughly 6,000 light years in cross-sectional diameter. A spacecraft setting out to circumnavigate the galactic habitable zone would only be able to return to Earth within one year if it were capable of traveling at least 170,000 times the speed of light.

Einstein's Special Theory of Relativity states that no signal can travel between two points in the universe at a speed that is faster than that of light. This theory has been subjected to a large number of highly exacting tests and has never failed.

Certainly we have broken rules that seemed unbreakable before. It used to be believed that people would never be able to fly; and yet airplanes are a commonplace today. It used to be believed that any plane that attempted to go faster than the speed of sound would break apart in the turbulence of the sound “barrier;” and yet many planes and rockets routinely exceed that speed. Can breaking Einstein's speed limit be any different?

The problem with this idea is that Einstein's speed limit is something qualitatively different than the speed of sound. The sound barrier wasn't thought to be an actual speed limit. Rather, it was believed that the materials that were used to build planes couldn't endure the stresses imposed by the shock wave which would result when the speed of sound was exceeded. Einstein's speed limit is a formal restriction on the motions of physical objects in our universe, not simply a limit to the strength of materials. It is therefore a different kind of barrier than any previous limit to human ingenuity.

Quantum Mechanics allows for some types of particles to be interpreted as particles traveling faster than light. In certain scenarios, a positron can be viewed as an electron moving backwards in time. Particles that move backwards in time can be thought of as particles that are moving faster than the speed of light. So it would seem that Quantum Mechanics permits Einstein's speed limit to be broken, under certain conditions.

An embellishment of the Big Bang theory known as Inflation claims that the universe experienced a period of massive expansion during the very first moments of its life. During this time (known as the inflationary epoch) the universe purportedly grew in size by a factor of at least 1030 (1,000,000,000,000,000,000,000,000,000,000). The inflationary epoch lasted for less than 10-33 (1/1,000,000,000,000,000,000,000,000,000,000,000) seconds; hence the size of the universe expanded at a rate vastly greater than that of the speed of light. Surely that proves that it must be possible for objects in space to travel faster than the speed of light.

There are several problems with this kind of thinking. To consider the inflationary epoch, it was only space that was expanding at that time. Signals and particles within space were not traveling through space at a speed faster than light. So not even the theory of inflation violates the Special Theory of Relativity.

Although Quantum Mechanics allows particles to be interpreted as moving faster than light in some circumstances, no one has figured out how to adapt those circumstances to a human traveler voyaging across huge distances, such as the perimeter of the galactic habitable zone.

Star Trek's Enterprise was able to travel at speeds much greater than that of light by using “warp” drive. The idea was that the ship's engines were able to warp space itself, thereby circumventing Einstein's speed limit. The ship was effectively outside of space while under warp drive, so the normal rules of physical space and time no longer applied.

From the point of view of narrative stories, this is a clever idea. But it fails to answer how the ship was propelled through space. A ship with this sort of warp drive wouldn't be able to use a standard propulsion system, since the ship would be outside of normal space and time. Presumably under such conditions Newton's Third Law of Motion would no longer apply.

Neither could such a ship use an attractive force such as gravitation or electromagnetism. Even in normal space a ship cannot simply point some sort of gravitational antenna in the direction of travel and expect that it will somehow pull the vessel toward one's destination.

Furthermore, I fail to see how a ship with warp drive could pull itself through space. Space isn't tractable. There isn't a way to grab hold of it and pull oneself along. So a ship with warp drive might very well be able to create a warp bubble that would allow it to jump in and out of normal space and time, but it wouldn't be able to move from one point in space-time to another.

And finally we need to consider the power requirements of a warp drive ship. How much energy would be required to warp space around the Enterprise? Since no one has any idea how such a feat might be accomplished, it's rather difficult to estimate the power requirements. But we do have the example of a black hole. A black hole is an object that is truly outside normal space and time. Matter that is consumed by the hole cannot communicate in any way with any other object in normal space-time. And how much energy is required to manufacture a black hole? For a black hole large enough to subsume the Enterprise a star several times larger than the Sun would have to collapse in a supernova. That doesn't seem like a very satisfactory prelude to an interplanetary voyage.

So all in all, faster-than-light travel is a good way to sell novels, but a completely infeasible way to get from one point in the Galactic Habitable Zone to another.

  Copyright (c) 2011 by David S. Moore.  All rights reserved.