"Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." -- Douglas Adams, The Hitchhiker's Guide to the Galaxy
There have been a lot of articles lately about the "Goldilocks Planet," known officially as Gliese 581g, that a group of American astronomers claim to have found last month. This planet is reported to be in what astronomers call the "Goldilocks Zone"--neither too close nor too far from its star to have liquid water on its surface. On Earth, where there is liquid water there is life. So the unconfirmed possibility of liquid water on Gliese 581g suggests the even less confirmed possibility of life on Gliese 581g.
That's fascinating stuff, even if you're careful to avoid the hype from overenthusiastic journalists and even from one of the scientists on the study, who pegged the chance of finding life on Gliese 581g at "100 percent" (calm down there, Sparky).
If you want to read more about it you can do so at :
http://blogs.discovermagazine.com/badast
or
http://www.independent.co.uk/news/scienc
The point of my post is not how fascinating the discovery of Gliese 581g is, though. It's not even about the later reports that dispute the very existence of Gliese 581g (http://www.space.com/scienceastronomy/d
We're the Special Kids
Since the discovery was announced, at least two bloggers of my personal acquaintance, and I imagine numerous others, have written at length about all the marks against the likelihood of life on Gliese 581g (and there are several, it's true, even beyond the chance that the planet might not be there in the first place--not least that its orbit and rotation are likely such that it always shows the same face to its little red dwarf star much as the Moon always shows its same face to us). These bloggers have gone on to make the claim that because there are factors that make it unlikely that there is life on Gliese 581g or on any of the other "Goldilocks Zone" planets that have been discovered so far, it must follow that life--especially intelligent life--is unique to Earth. Further, the uniqueness of life to Earth must prove that a god--and further still, the particular god these two bloggers happen to share--must have created the Universe, and life, and us.
Such claims are, frankly, nothing short of outlandish and absurd.
Yes, for you and I to be having this conversation via blog, an astounding number of events had to happen just so, when it was staggeringly unlikely that they would do so. On that much I think we can all agree. But had any one of those events--from the formation of the Earth in the Sun's "Goldilocks Zone" to the first cells' mitosis to the fall of the dinosaurs to the advent of Homo sapiens sapiens to our respective parents' meeting and successfully reproducing--not happened just as they did, we would not be here to have the conversation about how unlikely any of it was. So it strikes me as a bit moot to harp on how unlikely it all was. It happened. Everything between the first moment in which the Earth existed to my writing this now happened. And here we are.
A Series of Unlikely Events
Does the fact that all those exceedingly unlikely events happened so that I might be writing this and you might be reading it necessitate the conclusion that it was a god who made it all happen? No, of course it doesn't. No matter how unlikely an event may have been before it happened, after it happened the probability jumped immediately to 100%. Unlikely things do happen--if not, those things would be called impossible rather than unlikely. I don't think we have anywhere near enough evidence to draw any conclusion as to why particular unlikely events actually happen. But given enough time---whether on one try or thousands of tries--they do happen. After all, when the amateur sinks that full-court basket at the basketball game publicity stunt and we call it a "million to one shot," we don't literally mean that it took him a million tries to make that shot. No. He made one shot that managed to have the unlikely result. Is everything that had to happen just so for us to be here an unlikely result? Certainly. Did it happen? Yes. Can we draw any absolutely necessary conclusion about why we got our unlikely result? No. Probability doesn't work like that. It doesn't tell us whys or hows. It simply tells us what to expect of events how likely or unlikely an event is before it either happens or doesn't. It doesn't mean much to call an event or series of events unlikely in retrospect. They've already happened. We can marvel at the fact that we got such an unlikely result, but that doesn't necessitate any particular why or how.
Our Solar System has eight planets and one planetoid. In a quick search I've found mention of three exoplanets that at least at the time of their initial discovery were thought to be "Goldilocks planets." That's four "Goldilocks planets" counting Earth. Now, we do know about other exoplanets besides the three "Goldilocks" ones (Universe Today reported 342 known exoplanets as of March 9, 2009). So okay, we'll use the 342 number. So far none of these planets is definitively enough like Earth to conclusively make it an excellent candidate for life--let alone a confirmed life-bearing planet. This seems to fuel the fire of those who say that life is unique to Earth by a god's design.
But wait a minute. It's a question of scale here. We're talking about 342 planets, a good percentage of which are gas giants because they're the easiest to find. Just 342. The most commonly reported number for the number of stars in our galaxy is 100 billion. I read an estimate based on Hubble Space Telescope observations that there may be 125 billion visible galaxies in the Universe--and mind you, that's just the visible ones. Based on those numbers, that would mean that there are 1.25 X 10^22 stars just among those that we can potentially see. If even ten percent of those stars had planets at all (a purely arbitrary estimate) and if even three percent of those stars had Goldilocks planets (another arbitrary estimate), that would still be potentially 3.75 X 10^19 stars with Goldilocks planets. Needless to say, even if my arbitrary numbers are exceedingly generous, three not-so-great candidates out of all the potential Goldilocks planets is hardly a big enough sample upon which to base any conclusion. Mathematically that's far worse than going up to a haystack, picking out a single piece of hay that is not a needle, and concluding that there absolutely must not be any needles in that stack. You just don't know yet one way or the other. Three or eight or eleven or even 342 planets compared to all the planets that might be out there isn't even a hydrogen atom that makes up one of the water molecules that makes up a drop in the bucket. We just don't know yet.
Let's take another look at how scale impacts the likelihood that life could have arisen here on Earth, and perhaps elsewhere, without divine intervention. Imagine you flip a coin. Each time you flip the coin you have a 1 in 2 chance of having the coin come up heads. If you flip the coin 35 times in a row, the chance of having the coin come up heads all 35 times is 1 in 34,359,738,368. That's pretty seriously unlikely. Well, if you were to flip the coin only 35 times, you could be pretty confident that you almost certainly wouldn't get heads every time. But what if you flipped the coin 35 trillion times? That's 3.5 x 10^13 times. Well now, given the chance of getting 35 heads in a row and given your number of trials, you could reasonably expect that somewhere in your 35 trillion flips you could have somewhere in the neighborhood of 30 strings of 35 heads in a row. In other words, it starts to become likely that somewhere in all your trials you're going to see your extremely unlikely result not just once but somewhere around 30 times. If you were to do your 35 coin flips 3.75 x 10^19 times, you could expect to see 35-head strings around 1 x 10^9, or one billion, times.
Maybe Not So Unlikely, Maybe Not So Special
For everything to have happened here on Earth just so for life to form--let alone intelligent life such as us--is indeed staggeringly unlikely. And if you think on the small scale of just Earth, or just our Solar System, then yes it does start to seem unbelievable that such a chain of events could have happened without some omnipotent help. But if you think on the scale of all the planets orbiting all the stars in all the galaxies that may be out there, it starts to look downright likely that it would have happened somewhere at least once. We know it has happened once, and we're on that planet right now. So yes, we happen to be on the one planet on which we know this unlikely chain of events occurred. If we weren't, though, we wouldn't be here to talk about being here. But with numbers on the scale of the Universe, maybe it did happen elsewhere too. Whether we're alone or not, on the scale of the whole Universe it ceases to be quite so surprising that Earth sank that full-court basket and got 35 heads in a row so that we could be here to sink full-court baskets and to write and read blogs. Space, as Douglas Adams said, is vastly, hugely, mind-bogglingly big. Toss the planetary coin enough times to "fill up" space, and who knows what might happen?
Gliese 581g is only 20 light-years away (if it's there at all--but the star Gliese 581 is definitely there and it's 20 light years away). It's practically our next-door neighbor, as these things go. Recent analysis of Martian rocks has revealed what sure looks like--but has not yet been conclusively identified as--fossilized bacterial cells in mid-mitosis. In all our study of the Universe and in all the 342+ exoplanets we've found so far, we've not yet even started to start to start to start to scratch the surface. When one considers how little looking we've done and how close to home we're finding even the suggestion of planets that might now or might once have had life on them, one must confront the suggestion that potentially life-bearing planets might not actually be all that uncommon after all. Or maybe they're exceedingly rare. Or maybe we really are unique here on Earth. Whatever the case, we simply don't know enough to make the determination yet, and we certainly can't make any conclusive statements as to why life is common, uncommon, or unique.
Next, we'll take a look at the leap that people make between "the Universe and life are too unlikely to have arisen by chance" and "therefore, my particular god must have created the Universe and all life."
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