Stephan’s Quintet

Today at APOD there’s a Hubble photo of Stephan’s Quintet, four gravitationally interacting galaxies (and one much closer in the foreground that just looks like it’s part of the group). This is one of those photos that prior to Hubble would have been a fairly unimpressive set of blurry galaxies, but with Hubble, is a sign of the truly awesome size of the universe. Because with the exception of a few foreground stars (the one with diffraction “starbursts” around them in the photo), just about every speck in the photo is an entire galaxy, with hundreds of millions to trillions of stars. Note the stars and lanes of dust being scattered into the abyss as a result of the gravitational interaction of several of the galaxies.

Any civilizations on planets orbiting these stars would be physically unharmed by this “collision,” but as the stars scatter, the night skies would gradually, over periods of tens of millions of years, grow darker and more featureless. Instead of a sky like ours, with thousands of naked-eye stars and the band of the Milky Way reaching all the way around the dome of the heavens, on a such a world there may be only a few dozen naked-eye stars, and their equivalent of the Milky Way would be a dimmer band that would reach only partway across the sky, eventually fading to a distinct, but small and faint, separate galaxy. For a civilization that comes to technological maturity on a world that has been flung out of its galaxy, interstellar travel may never even be so much as a dream. Without nearby stars to visit in anything remotely resembling a reasonable timeframe, they might not even bother trying. And who could blame them… humanity can hope, with current engineering and physics, to eventually attain speeds in excess of ten percent the speed of light. This would put the nearest stars within the grasp of a  single lifetime. But on a star a hundred lightyears from its nearest neighbor, and fifty thousand lightyears from the bulk of its original galaxy, sub-light travel would seem a ridiculous notion at best.

Of course, a civilization such as this might also be more motivated to truly plumb the depths of arcane physics to develop a faster than light propulsion system. A civilization that has, say, instantaneous travel from a distant lone world to a galaxy tens or hundreds of thousands of lightyears away would be in a potentially unique position: the galaxy would be open to exploration and exploitation, but so long as their ships could not be tracked, and they never told anyone else where they came from… who would ever find their homeworld?

Some people see such pictures and understand the implications, and it gives them the cliched impression of “it makes me feel so small.” While I can understand that, my own response isn’t to feel small, but to feel a part of something truly vast. Something that Mankind can claim as ours, if we put our minds to it. Even if we never exceed ten percent lightspeed, the furthest reaches of our own galaxy are only a million years away. While this would be a ridiculously long trip for a single ship, think of it instead as the result of a vast colonization effort. If we can travel at 0.1 C, the average colonizable star might be, say, less than 10 lightyears away (100 years travel time). This means 10,000 or so “jumps” to the other side of the galaxy. If we proceed *really* slowly, with a new world taking one thousand years to develop and grow bored and decide to send out more colonies, that’s 1,100 years per jump, or 11,000,000 years to cover the galaxy. A doable prospect, I should think, given that each “jump” would essentially reset the civilization doing the jumping.

If we can bump speeds up to 0.5C (travel time: 20 years), and time to get bored drops to 100 years, then the other side of the galaxy is only 1,200,000 years away.

Of course, exploration and colonization will not proceed at such a static pace. There wil be trips of greater range than 10 lightyears, and there will be worlds that will sprout colonies faster and at higher rates than others. In less time than  it took for Homo Erectus to turn his gaze to the stars and produce a people who can understand how to actually get to them, we could fill this galaxy with life.

Getting to other galaxies, like those of Stephan’s Quintet, may take a little longer. But by the time we’ve filled up this galaxy, I’m reasonably confident that we will have come up with a way to cross the vast gulf between galaxies. Perhaps faster than light travel; perhaps sublight worldships, perhaps sublight *worlds.* A million years from now, it may be a trivial engineering exercise to cause a star to accelerate itself towards a distant galaxy, dragging with it a retinue of planets and asteroids and space colonies, to arrive, tens of millions of years later, in another galaxy. And perhaps we might send ships no bigger than a Pomeranian at speeds vanishingly close to the speed of light; not filled with people per se, but filled with information. Upon arrival, the ship would set up shop on a promising world, using inconceivable technology to transform it into the likeness of a terrestrial world, complete with terrestrial ecosystems… and intelligence.

Sadly, I expect I probably won’t be around to see it. But of all things to dream of… humanity and our children, whoever they may be, surviving into the depths of space and time is one hell of a dream.