This is sometimes known as the design explanation for the fine-tuned universe. A life supporting universe is intrinsically unlikely, or so it is argued. But if there is an intelligent Creator, then that would explain everything. Random chance would only raise the question as to why this universe could be so "lucky" as to have precise conditions that support life (at least here and for the time being). But if everything were designed according to some intelligent plan, then this mind boggling precision would be exactly what to expect.
A rival explanation is the Multiverse-hypothesis, according to which there is a whole bunch of universes -- not just galaxies within our own universe, but complete universes. Given a string of universes, one would expect the various combinations of parameters for basic physical factors to show up in endless combinations. That one combination is suitable for life should not surprise anyone."If there is a large stock of clothing, you're not surprised to find a suit that fits," in the words of Martin Rees. "If there are many universes, each governed by a differing set of numbers, there will be one where there is a particular set of numbers suitable to life. We are in that one."
Well, of course our universe would have to be fine-tuned, given that we live in it. But how does that so much as begin to explain why it is that [our universe] is fine-tuned? One can't explain this by pointing out that we are indeed here—anymore than I can "explain" the fact that God decided to create me (instead of passing me over in favor of someone else) by pointing out that if God had not thus decided, I wouldn't be here to raise that question. It still seems striking that these constants should have just the values they do have; it is still monumentally improbable, given chance, that they should have just those values; and it is still much less improbable that they should have those values, if there is a God who wanted a life-friendly universe.There are difficulties here. Whether or not this God-hypothesis is more probable than other explanations depends, as John Perry argued in a teaser for a recent Philosophy Talk, on what is required for the existence of such a God. "Wouldn’t that in turn require the existence of a Creator-friendly universe, or proto-universe, with parameters set to allow for the development of such a powerful and wonderful Being, capable of setting the parameters for our universe?" A clever question, no doubt; but I am sure Plantinga would have an answer ready and argue that intelligent design nevertheless is the more plausible hypothesis. I am not writing this to take sides. In fact, I am not sure what the discussion is all about. Arguing over which explanation (for why the universe is suitable for life) is more probable, looks like an argument where language has gone on holiday. Probability is something we normally talk about within the universe -- when unlikely things happen, we ask for explanations -- but here the question is how probable the universe itself is? How unlikely is a life-supporting universe? And how unlikely is that to develop by sheer coincidence? Unlikely, compared to what?
I am not sure I see why there is something here to explain either. Consider the following quote from Bill Bryson's A Short History of Nearly Everything:
To be here now, alive in the twenty-first century and smart enough to know it, you also had to be the beneficiary of an extraordinary string of biological good fortune. Survival on Earth is a surprisingly tricky business [...] Not only have you been lucky enough to be attached since time immemorial to a favoured evolutionary line, but you have also been extremely -- make that miraculously -- fortunate in your personal ancestry. Consider the fact that for 3.8 billion years, a period older than the Earth's mountains and rivers and oceans, every one of your forebears on both sides has been attractive enough to find a mate, healthy enough to reproduce, and sufficiently blessed by fate and circumstances to live long enough to do so. Not one of your pertinent ancestors was squashed, devoured, drowned, starved, stuck fast, untimely wounded or otherwise deflected from its life's quest of delivering a tiny charge of genetic material to the right partner at the right moment to perpetuate the only possible sequence of hereditary combinations that could result -- eventually, astoundingly, and all too briefly -- in you.Of this, I am tempted to say, if things had gone differently, I simply wouldn't have been here to raise the question at all. I fully agree that that doesn't explain anything, but I do not share Plantinga's (and other's) need for an explanation. Reading Bryson's tale fills me with amazement too, momentarily at least. Of all the things that could have gone wrong, none did! It is incredible that I got here at all, yet here I am! But there seems to be a certain (mischievous?) picture here -- of a tiny charge of genetic material that has made it safely through 3.8 billion years of continuous narrow escapes in order to make me. This looks like quite an accomplishment. When a package reaches its final destination unscathed, despite having faced earthquakes, avalanches, blizzards, mine-fields and so on, then that might make us look for an explanation. Calling it chance will hardly satisfy our need. (That's because chance isn't really an explanation at all, but rather something we appeal to when there are none.) Intelligent design (or Providence or Destiny) might look like much better options.
However, I cannot settle with this picture, mainly, I guess, because I cannot see any sense in saying that if things had been a little different and my parents hadn't met, then I would have been a package forever lost in the mail, as it were. One can say (and some do), how amazing it is that my mother, of all the men in the world, happened to meet my father. What were the chances!? But to me this sounds confused. It does make some sense to praise yourself lucky that your parents met and fell in love. But the sense is not that it would have been very unfortunate if they hadn't met, because then you would never have been born. One cannot say, bad luck for all those whose parents never meet.(Though that seems to be exactly what Plantinga is saying, when claiming that God, in creating me, somehow decided not to pass me over in favour of someone else.) When one say, how very lucky I am to be alive, this is normally a way of expressing one's gratitude, not a probabilistic judgement.
Your parents did meet, of course. Good for you, but is it more than that? Is it amazing? Today your father, of all the people in the world, sat next to this particular odd person on the bus. Why should the first be more in need of an explanation than the second? The first strikes you as wondrous because it was crucial for your existence. But if your father hadn't met your mother on that day, say, if he had gone to the movies instead of the beach, possibly to fall in love with someone else, and father, not you (you simply wouldn't exist) but someone else. Would that have been amazing too?