Here’s a question: could aliens come to earth and kidnap humans with the intent of sticking non-descript metal things up their butts? (Last time I put this post up a commenter asked what else the aliens might want to look at, other than our butts. The commenter basically undid my entire post by asking that question; when I read her comment my girlfriend of the time was wondering around in her underwear, and I honestly couldn’t think of a single thing I’d rather have been looking at…)
Maybe we should break that down. First of all, could aliens—as part of a complex civilisation—exist? To answer that we need to take moment to consider the size of our universe.
Our galaxy is a disc, one hundred thousand (100,000) light years across and three thousand (3,000) light years in thickness. Conservative estimate imagine there to be to one hundred billion (100,000,000,000) stars in our galaxy alone. Each star has the potential to have its own orbiting solar system with planets. That is unimaginably vast.
There are also between two hundred- and four hundred billion (200,000,000,000 to 400,000,000,000) galaxies in the known universe. Each galaxy is of at least comparable size to our own. Some are much larger.
Another way of looking at this is to do the following thing: on a clear night (a true clear, cold, beautiful night) get out of the city and look up at the sky. Every tiny dot is a star like our own sun. Each one represents a chance at life somewhere else. And that’s not even all of them.
So it’s possible aliens could exist. For the sake of the thought experiment, let’s say they do. How would they get here?
It takes time to travel vast distances. No life that we are currently aware of lives long enough to make these kinds of journeys. So far that I can tell, life that does make these journeys has limited options as to how they can:
Space pirates: these would be aliens without a home planet (although they would have a planet of origin). In order to travel immense distances the entire civilisation lives on the spaceship. The lifespan of an individual doesn’t matter because a society can, in principle, exist indefinitely. These ships would be travelling for hundreds of thousands of years.
Biological stasis: The lifetime of an alien individual can be put into stasis and the ship can travel as long as it wants and wake up its crew upon arrival at a desired planet. Anyone who sets up this mission and stays on the planet will be a fossil before the ship returns home.
Near-light speed: light speed is just marginally faster that Einstein’s theory of relativity says anything with mass can travel. The reason this is an answer is not because travelling particularly fast shortens your travel time (although it does). The answer is much more amazing than that. At near light speeds time for the person-travelling-very-fast slows down. If you travel at the speed of light you travel a light year in distance instantly. But to a stationary observer it takes you a year. This is the weird stuff of Einstein’s theory of relativity. So a ship travelling at near-light speed can make the journey across the Milky Way (100,000 light years) within an individual’s life time aboard the ship, however their home planet would have aged by just over 100,000 years.
Knowing now the massive technological feats that need to take place to send an individual across space, and knowing that no one on the home planet will ever live to see the results of the voyage, are they really going to come here to get a good look at our butts? I’d set up a space program to look at my ex-girlfriend’s butt… but with the exception of her, really?