World Building 101: Today's Topic: Holy Magnitude!

Space is huge. Really huge. Mind-bogglingly, oh-my-gawd huge. Trying to wrap your brain around just how huge space is is a daunting task. But we'll give it a try.

Why does one need to know just how huge space is? Well, it allows you to do something amazing. Winning the lottery sort of amazing. You can imagine your world just about anyway you want, and if it can theoretically exist, then chances are it does, or did, or will. The numbers are on your side.

Our solar system is comprised of our lonely sun, a single star, and eight decently large planets, four rocky and four slushies, and a multitude of smaller icy planetoids. (Nine? You say? Well, not really, since Pluto hardly qualifies... but I digress).

How many more stars are out there in our galaxy? About 200,000,000,000. That's two hundred billion suns in our local Milky Way galaxy alone. And how many galaxies are there? Well, current estimates put the value around 100 to 300 billion galaxies. Our Milky Way is considered pretty large on the ol' galaxy scale, so we can't use it as an average, but assuming an average of only 1 billion stars per galaxy we end up with 100,000,000,000,000,000,000 stars in the known universe! That is a lot of stars! That is ten raised to the twentieth power, also called a hundred quintillion.

So, assuming for the moment that only one percent of those stars have planets in stable orbits, and assuming only one percent of those have been around long enough for life to form on the planets, and further assume that only one percent of those actually have planets in the right orbital temperate zone, and assume that one percent of those have the right collection of elements to start life, and in the right proportions. How many planets does that give us? That reduces our huge number solar systems by eight powers of ten, leaving 1,000,000,000,000 planets that have all the right stuff for life. One trillion planets. Odds are, one of them fits your profile.

Now, my 'one percent' assumption could be off, it could be off a lot, but even if it's off several magnitudes, we still have plenty of life producing planets to choose from. (This thought experiment is brought to you by something called the Drake Equation.)

What I'm getting at is that a fantasy writer doesn't have to worry about the odds of a habitable planet existing. Chances are, it does. Somewhere out in the vastness that is space, a planet probably exists with that blue sun, three distinct rings, and two moons that you want.

The real problem is distance. Space is huge, as I've said. And most of it is filled with nothing (or dark matter, which is still mostly nothing). Traveling from one solar system to another is a monumental undertaking.

Most stars are light years apart. A light year is about six trillion miles.

How long would it take to travel a light year? Well, Voyager 1, our own unmanned space probe sent out 28 years ago (in the summer of '77 - and still running, I might add!), is now 8,700,000,000 miles away. That's about 0.15% of a light year. At that speed (about 38,000 mph), it will be another 18 thousand years before Voyager 1 is one light year away.

Even assuming you made a craft that travels a thousand times faster than Voyager 1, it would still take you a good 18 years to get one light year. And our nearest neighbor, Alpha Centauri, is four light years away! That's 72 years at 38 million mph. And, of course, once you got there and tried to phone home, you'd have to wait four years for the signal to reach Earth, and another four years for the answer to come back. It's hard to carry on a conversation with an eight-year lag time! Can you hear me now?

And, traveling very fast creates new problems, problems that are weird and spooky, which I'll save for a some future lecture.

All this humongous distance of space is the reason why sci-fi writers invented warp drive. Flying from star system to star system via faster-than-light space travel is de rigueur. It is so much nicer to be sitting around playing holographic chess for a few hours while hurtling through space at super-light speed rather than waiting a whole lifetime just to reach your stellar neighbor.

In summary, space is huge and empty, yet contains billions and billions of stars, some of which probably have a habitable planet orbiting it that can be your fantasy world. But good luck getting there.