DISTANCE, SPEED AND TIME
AUTHOR: Candice Vetter, Astronomy Diva

Star Trek and Star Wars and other great SF shows capture our imaginations partly because they appeal to the adventurers in all of us. Humans are natural explorers, which is one of the reasons our species covers the globe.

But the reality of distances to other stars is a great stumbling block to space exploration. It took Apollo 8 three days just to reach the moon. It takes unmanned probes years to reach the other planets in the solar system. Voyager I has just entered the termination shock, where solar wind slows, indicating the spacecraft is nearing the edge of the sun?s influence, and Voyager was launched in 1977.

Using the fastest technology existing today it would take 137,000 years to reach the nearest star to our sun, Proxima Centauri. Even if we could travel at the speed of light (In Star Trek terms ? Warp I) it would take 4.2 years to get there, because Centauri is 4.2 light-years away.

A light-year is the distance light can travel in one Earth-year, in a vacuum, which interstellar space mostly is. The speed of light ( c in equations) is 300,000 km per second (186,000 miles per second) and that?s pretty darn fast. That?s equivalent to flying almost to the moon in one second. An interesting problem, no?


And that?s one of the two main reasons the space race of the 1960s was abandoned. We simply can?t get anywhere fast enough to survive until we arrive. If the planets in our solar system had been hospitable to our type of life we would have explored and possibly colonized them. But they aren?t, and that?s the other reason we haven?t sent humans to, say, Mars. If someone else lived there the trip would be a lot more interesting.

Around other stars there may be planets that are just as habitable as Earth. In fact it?s quite likely, given the recent discoveries of extra-solar planets. But we come back again to the problem of distance. The solution is not as simple as building engines that go faster either. It is, in practical terms, impossible for objects of any significant mass (like, bigger than an electron) to travel that fast.

I?m not going to explain Einstein?s theories of relativity here, but in a nutshell, matter and energy coexist as variations of the same thing. Massless particles like photons (particles of light) are essentially particles of energy. Particles with mass (matter and anti-matter) change more the faster they travel. Time seems slower and slower until they are eventually frozen in time. Once they hit c, they?re stuck.

Even if very massive objects (such as people in spaceships) could go a tiny fraction of the speed of light (say, 1/50th) they would perceive time differently. Their friends and family waiting back home would age and die while they were gone for a few years.

So in a story with interstellar travel there has to be some trick.


Star Trek?s Enterprise just goes faster, exceeding the speed of light, which is shown when the ship blinks out of normal space. Gene Roddenberry chose to ignore the effects of faster than light travel. And that?s reasonable. The truth is, we don?t really know what will happen, everything predicted is theoretical, which means it could just as easily be wrong.

In Star Wars the Millennium Falcon enters hyperspace. Again, this works as a fictional device because other universes or dimensions do theoretically exist. Maybe we can enter them, travel a comparatively short distance, and pop out somewhere else. That would be nice.

Wormholes, like that used in Galaxy Quest, are useful, because a) they actually exist, and b) Einstein?s field equations, when plotted on a graph, show that they may connect distant parts of the universe or even other universes. It may be possible to enter wormholes via certain black holes. The part that doesn?t work is that speed of light thing again. As you cross a black hole?s event horizon and slide into the black hole, you approach c. You become stuck. Not only stuck, but dead, as your atoms are stretched infinitely.

Or you can accept the limitations of light speed and use other modes of travel, like automated ships with hibernating passengers, or generation ships holding whole cities and farms and travelling for thousands of years.


My personal favorite is the Firefly solution. Just assume we?ve left our solar system long ago and will never go back, but that we?ve found a new system with many habitable planets and moons. With a moderately faster propulsion system we could travel between closely spaced planets, moons, and dwarf planets over a few weeks or months. That is exactly what the crew of Serenity does and it works very well.

So the trick you use is up to you. But there has to be one. You can?t colonize the Centauri system otherwise.

Candice Vetter is an amateur astronomer and freelance writer who pines for the habitable Mars of Golden Age SF.