A lot of people think the simple fact that we exist is somehow "special." These people are stupid. If anyone ever tells you that the Universe is fine-tuned to support intelligent life, you need to punch him in the face immediately. Look at the Universe - just fucking look at it! It's not "for us" by any stretch of the imagination, unless your imagination is dumb. Most of it, even on the medium scale we're used to, is cold, sterile, empty space. There's a quarter-million miles between the Earth and the Moon, and only a tiny bit of that is habitable by life as we know it. Beyond that, it's unremarkable empty space in all directions for millions of miles, unless you happen to run into an asteroid, or head in the direction of Mars or Venus (even then, they'd have to be at least vaguely aligned with the Earth in order to be anywhere even remotely close to our neighborhood). Farther out, things get even worse: beyond our solar system, there is nothing but the darkness between the stars, until you get to Proxima Centauri. In all that space, the only place we know that there's life is a thin, hollow, semi-spherical volume comprising Earth's upper crust and atmosphere.
And yet some people claim that the Universe is fine-tuned for intelligent life. What is wrong with these morons?!
Looking at the Earth itself, the picture is hardly prettier. Pick any spot on the planet at random, for example by spinning a globe and then shooting it with a gun, and you'll probably wind up in the motherfuckin' ocean. For those of us who aren't marine biologists, most of the ocean is sterile saline. It's like a desert, except rather than being dry and teeming with life just out of sight, it's fucking soaked and harbors no life whatsoever - look, I don't know what it is with people and thinking deserts are especially lifeless, you'd have to ask them. If you managed to find a spot that did have life, congratulations: you've got fucking phytoplankton, which, while being more intelligent than your average Creationist, hardly qualifies as intelligent life. Sure, there will be stuff that eats the phytoplankton, and stuff that eats that other stuff, and so on and so forth up the food chain. You might wind up catching some humans in the act of fishing, or perhaps diving or in a submarine. Maybe a dolphin counts as intelligent when it's beating a baby porpoise to death - smart enough to hate, so why not?
When we up the scale, and look at things on a galactic level, the picture becomes even more disheartening. That's a nice way of saying, "People who think the Universe is fine-tuned for intelligent life do not qualify as intelligent life." Look at the Hubble Deep Field image: that area of sky, from Earth, looks pitch black, and is about the size of a dime held at seventy-five feet. It's fucking packed with galaxies, though! As far as we know, every single one of those galaxies is sterile. The light from them is probably so old that, at the time it was emitted, life may not have had time to get started yet even if the conditions were right. However, for life to arise organically, consider all that must happen: a star has to form, live its life, and burn out. It has to burn out in such a way that it's able to form a second-generation star, and then that fucker has to have enough dust orbiting it (not ejected, not consumed, just hangin' out) to accrete into planets. It will also need at least one gas giant to sweep up would-be meteors, but that gas giant has to leave the Earth-like distances relatively untouched. Then a rocky world needs to build up with a rotating, metallic, liquid core to generate a magnetic field to protect against the deadliest forms of solar radiation; it also needs a moon to stabilize its axis, or else it can "roll flat" along its orbit, with extreme polar seasons producing too much of an environmental variance for anything to tolerate; and it needs to be in a damn-near-circular orbit so it doesn't alternately freeze and bake during the seasons.
On top of all that shit, it also needs to have the right chemistry! Carbon-based life, boring as it may be to sci-fi writers, seems to be the only way that life can come about - that's because carbon is the shit. As for sulfur-based life, just look at the hydrothermal vents at the bottom of the ocean: plenty of sulfur there, and sulfur-based life could easily have gotten started along with or instead of the carbon-based variety. But it didn't (or, if it did, carbon-based life simply outcompeted and then ate it). Now look at Venus, a planet with a motherfucking ass-load of sulfur in its atmosphere, and what does it do? Oh, shit, son! All the sulfur is tied up in compounds that are inimical to life! Specifically, sulfur dioxide and sulfuric acid would in all likelihood break down any would-be replicators (more specifically, their distant chemical precursors) before they could really get started. As for silicon-based life... look, I'm willing to grant that some silicon-based life could be designed, I'm saying that it's even less likely for silicon-based life to evolve on its own. I had a million fucking footnotes here, but really, the whole paragraph just needs its own. So here1.
These are the preconditions of life: a ruthlessly narrow range each of possible stellar pedigree, planetary arrangement, and homeworld configuration (which by looking at the Universe we can tell come in all sorts of life-preventing flavors) all have to come together before we even say the word Go. Whether or not there is in fact life elsewhere in the Universe is incidental at this point - the deck is already stacked the Hell against it! The Universe is not in any meaningful sense "fine-tuned" for life, intelligent or otherwise; it's fucking hostile and we're fucking lucky. The End.
Oh, but wait, we still got lucky. Christ on a bike, that's fucking right! Give that cock-sucker a cookie! (I'm gonna go eat a cookie now. Wait here, I'll be right back. ... OK, I'm back2.) We got lucky, and so we're here to sit and think about all of that - and isn't that special? Well, define "special," shit-for-brains: if you just mean "statistically unlikely," then yeah, you've just defined your way to victory. Congratulations, asshole (no, really, it's OK - I define my way to victory all the time). You've won yourself a trivial tautology and nobody gives a cunt-suck. Or do you mean metaphysically special, like some kind of "cosmic significance" besides the idea that if you roll a die enough times, then it will eventually punch you in the kidneys? Doesn't it "mean something," in the warm-and-fuzzy sense, that we're here on this rock and not some other, much shittier rock?
Of course not, dumbass! What, do you think we were fucking planted here or some shit? Eat me. It's like this: if intelligent live does in fact evolve at all, then of fucking course it's going to evolve on a planet that meets the preconditions for that to happen! Fuckin' DUH! Did you think humans just sprang whole from the fabric of reality out in the dead of space? I didn't think so. You're damn right we can only come about to think about these questions on planets where this sort of thing can happen in the first place - that's fucking elementary. Yeah, Sherlock Holmes called (I have his induction on loan, which is why he's been stuck with deduction all this time), and he left a message for you: LRN 2 INFERENCE, NOOB. For any event, it is trivially and obviously true that it can only come to pass if the necessary preconditions are met - what shithead needs to be told this?! Did you know that bread can only be baked if the necessary preconditions are met, too? Does baking bread now also have cosmic significance? Fuck me running, this is getting stupid!
This bullshit line of reasoning touches on what's called "the anthropic principle," and in short, it's the idea that intelligent life can only contemplate its origin in a Universe which is capable of supporting intelligent life in the first place. We're doing that thing, so therefore we have to be in that sort of place - and that's exactly as far as it goes. What you don't get to say is whether it "ought" to be one way or the other, or whether that has "special meaning" aside from the fact that we got lucky. Jesus titty-fucking Christ, what is so hard to understand about this?
As for the likelihood of such a thing occurring, in the first place, it's purely incidental: no matter the chances of this sort of Universe happening, it did happen, and that's that. Count your lucky stars, if you're the simple-minded superstitious type. Feel good just 'cuz if you're not. In the second place, sorting out just what the odds are, as it turns out, is a tricky goddamned proposition. See, here's the thing: we don't have a lot of experience with Universes. Just the one, really. So whatever sexy math and pretty words we'd like to spout about initial conditions and variant laws and mutable constants, at the end of the day, we don't fuckin' know. Maybe there are other Universes, maybe it's just the one; maybe the Universe could have been otherwise, maybe it couldn't have; maybe there's a fucking multiverse and we only see one facet of it, maybe this is all there is to reality. We don't fuckin' know.
Now, don't get me wrong: all that sexy math is still sexy, and all those pretty words are still pretty. What we've been able to find out about the Universe just by looking at it carefully is, in a non-trivial sense, sphincter-clenchingly stupendous! But we need to be extra-special careful when we go about speculating on things beyond our ken, because it's still just speculation and these matters are still beyond our ken (at present, anyway). But I swear to porn, if any motherfucker tries to say that the mere fact of our existence indicates anything beyond the fact that our Universe is capable of producing that existence, I will pee on that guy's soul. And that's a stain that don't wash out.
1. Yeah, yeah, I'm doing the same fucking thing here that I'm yelling about throughout the rest of this post, with one big BUT. Sure, sure, we all know that we're carbon-based life and all our retrospective stuff (which the parent paragraph to this footnote is based on) is only in the context of "looking at what carbon-based life does and/or needs." Fair enough. Still, I maintain that it is more rational to remain skeptical of S/Si-based life being possible until something shows that it in fact is. Could it be designed? Surely, and in a number of creative ways. But until or unless we can construct some causal story with some manner of empirical oomph behind it (and here, I'm not gonna be picky, so if there's anything out there on this, please send it my way!), I'm going to say it's more rational to remain skeptical of the possibility. All my yelling above is more or less to show reasons to remain skeptical, in a kinda-sorta analogous way to how we ought to be skeptical of life actually existing on other planets until we find it.
2. Damn, that was a tasty fuckin' cookie!