Saturday, March 14, 2009

Earth: Rare, or Dime-a-Dozen?

On March 6, a Delta II rocket lifted off from Kennedy Space Center in Florida, carrying the Kepler space telescope towards an Earth-trailing Solar orbit. Kepler's mission is to look for Earth-like planets circling other stars. Metaphysically speaking, this is related to the biggest question left that Science has a fighting chance of answering: Are we alone? (The bigger ones, like "Is there a God?" or "Is there an afterlife?" are beyond the purview of Science, as most of us understand the term.)

I'm not really sure what to expect. Frank Drake once developed a famous equation to estimate the number of civilizations in the Galaxy. One can work backwards from that to get a hack at how many Earth-like planets there are, making the rather bold assumption that intelligent life can only develop on Earth-like planets. If you make some generous assumptions, then it seems likely that the Galaxy is as jam-packed with ETs as the Cantina from Star Wars.

Or maybe not. I read the book Rare Earths by Ward and Brownlee back when it came out in 2000, and the argument looked like it carried some weight. Basically, Ward and Brownlee argued that although single-celled life may be near-ubiquitous in the Universe, the leap to multi-celled life was a darned chancy thing, and may have only happened rarely. It's definitely a point to ponder, even if you don't necessarily agree with the premise. It's always dicey to make statistical inferences from a sample size of one, and Earth is the only habitable planet we know of. The Kepler mission will hopefully add some grist to the discussion. Because, when we start talking about ETs, the question inevitably comes up, "Where are they?"

Fermi's Paradox: if you can't swing a cat in the cosmos without smacking an ET upside the head, why haven't we seen any real traces of them?

We're left with a number of possibilities: (a) They exist, but won't make contact; (b) They exist, but can't make contact, or (c) They don't exist. There are several different flavors of (a) and (b).

One: They are prohibited by their own law from contact. Think "Prime Directive" from Star Trek. I find this reason slightly fatuous. Although it would explain why putative ETs have taken such great pains to avoid contact. They're not afraid of our cops or military. They're very afraid of their own. The ones who actually strut their funky stuff down here are poachers.

(As an aside, I tend to be very skeptical of claims of ET visits, especially in modern times. The reason is that any form of travel that involves a large change in velocity will invariably also involve a large amount of waste heat. This is elementary First Law of Thermodynamics stuff. Energy cannot be created or destroyed. Therefore, if you shed a boatload of kinetic energy, it's gotta go somewhere. You can't just wave a magic stick at it and make it go away. So, the easiest thing to do is radiate it away into space as waste heat. Which would be a gigantic HERE I AM beacon to anyone with an infrared telescope... Someone's bound to notice, I'm just sayin'. Given that no one has, I'm inclined to think it hasn't happened. Anyway...)

Two: They're not prohibited from contact, but refrain anyway because we're so incredibly gauche. This, I can believe. "OK, I'm off to study the natives of Sol III." "What? Are you mad? They still fling poo at each other, don't they?" "Well, I don't suppose I actually have to go all the way there..."

Three: Interstellar travel is rather harder than we've been led to believe. In the stories, heroes flit around the Galaxy like we drive over to the Stop-N-Go for a Slurpee. It ain't that easy, folks. Interstellar travel is, in my professional opinion, somewhere between damn hard and practically impossible. The easiest part is navigation. And that's not all that easy. When you're out far enough away from the Sun, you have no reliable position references. You can get a red-shift from the Sun, and a blue-shift from your target star, and figure out how fast you're going. And if you can get angle measurements from four widely-separated stars, you can triangulate your position, with some fat margin for error. If you're not careful, you can miss the star you're shooting for, and then you're in a whole world of trouble. But with care and attention, you can get the details right, and at least theoretically arrive in the right place. But then, there's the issue of propulsion to consider. We know we can't exceed the speed of light in normal space. So, if we want to fly to another star within a human lifetime, we have to do it at a fairly high speed. Here's the problem. Let's say we've got a 1000-ton ship moving at 99% the speed of light. How much energy does that take, relative to how much energy we produced in toto this year? The kinetic energy of this spacecraft is ten thousand times greater than the world's entire energy output in 2005. Chew on that for a second. How in the roaring purple Hell do we get that much energy in one place at the same time? Well, there's always antimatter ... but brother, that much antimatter all in one place is a damn scary prospect. And understand that this is coming from a guy who wouldn't sweat too much from living next door to a nuclear power plant. I'm not sure I want to live on the same continent as an antimatter fuel plant! That crap's dangerous. One fuel leak, just one, and foom! Your ship just became a blue flash. (Someone once said that gamma-ray bursts were high-tech industrial accidents. I'm not sure he was wrong...)

Now, we humans are extraordinarily stubborn. If something's physically possible at all, one of us is bound to try it eventually. No matter the hardships, no matter the obstacles, one of our descendants will be hard-headed enough to make it so. But, not all creatures are quite so obstinate. It wouldn't surprise me at all to see our would-be visitors look at the vast deeps of interstellar space and say, "Hell with that. I've got better things to do."

Four: We're not alone alone, but intelligence is sufficiently sparsely distributed that we're alone for all practical intents and purposes. If there are only two or three intelligent ET species in our Galaxy, and they're on the other side, it's gonna be quite some time before we see any of them face-to-face. By "quite some time" I mean some thousands of years.

In any case, it's going to take Kepler a while to scan its assigned areas of local space. Hopefully we'll find something interesting. But even if we do find an Earth-like planet elsewhere, we're still stuck with the one we've got for the foreseeable future. None of us are going anywhere anytime real soon.

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