I think I agree with atheists in saying that the existence of the universe doesn't necessarily imply there's a creator behind it. Theists tend to like the watchmaker argument: if you found an old watch lying on the ground, picked it up and examined it carefully, seeing the marvelous intricacies of its mechanism, you would naturally ask, "Who made this?" Since all scientists, whether they believe in God or not, cannot but marvel at the amazing structure and patterns in our universe, shouldn't they all be asking, "Who made this?"
But we are embedded in a universe of time and space, and can conceive of nothing outside it. Who knows if there's a larger picture we are part of, one which we can't even begin to fathom? And why can't what we see be all there is? Is saying the universe simply exists a worse explanation than saying there's a purposeful intelligence who brought it into existence?
And atheists all see where the Christians are headed as they try to drive the thin edge of this wedge into the debate. Even if there is some intelligence behind it all, why should it be personal? And even if it's personal, why should it bear any resemblance to the God of Abraham, Isaac, and Jacob? There are so many different beliefs about God! Isn't it crazy (and presumptuous) to think that Christians have got it right, and everyone else is wrong?
Now, I used to be an atheist: everything we see is just matter in motion, laws of chemistry and physics. We are the way we are because genetic variation, the struggle to survive, and some random, dumb luck let our ancestors survive hard times, and live to reproduce. If we examine ourselves, looking for reasons we are the way we are, the question to ask is what survival advantage this gave our ancestors? Everything else is just accident, like the experiment on foxes in Siberia, where decades of breeding solely for tameness has led also to shorter snouts and softer coats---a more dog-like animal. And so, all the most prized qualities of being human, even wondering about this question of an intelligence lying behind what we see, must be unintended byproducts of a brain evolved to give us and our offspring a competitive edge in the harsh ancient world.
This seems to me "remarkably accidental." We can see the function of song in animals: birds announcing their identity in the forest, claiming territory, or advertising for a mate; ape troupes whooping it up on the tree tops to warn they're the biggest bad-asses in the jungle, and to reinforce group membership. Somehow this leads directly to a concert hall filled with a thousand people sitting quietly, enthralled by a single person playing a violin. Bach's Chaconne in D minor is simply piggy-backing on our mechanism for sound processing that has a back-door to the amygdala, stirring deep emotions. For example, we are hard-wired to respond to the sounds of baby cries (the survival advantage of this is obvious). Music simply exploits these pathways. All the thousands of shades of colour we experience in music, from elation to deepest grief, and everything in between, in various mixes, are all a result of a system evolved with the sole purpose of survival.
And beyond music, what about our sense of beauty? What's the survival advantage of climbing to the top of a mountain? Or watching a sunset? Or arranging flowers? Or our sense of humor? Or our love of stories? It seems to me many of the things we prize most about being human have a rather tenuous connection with the survival imperative. And so the only conclusion is that they are accidental byproducts of a process flowing along a course that had nothing to do with these things, but was simply a matter of getting more of our genes to the next generation than the competition.
Unless you're going to admit the possibility of interference in the evolutionary process by superior aliens, or some divine being, then this is the only game in town. There must be a natural explanation. And indeed, the progress in this has been remarkable. For example, people used to say the human eye is such a complex thing, one that fails to work if any one of a myriad of components is not functioning, that it is foolish to imagine it evolving from simpler structures. But biology has shown that, in fact, we see a continuous gradation of complexity of eye structures in the world around us today, from the simple photoreceptors in the skin of worms that tell them when they are exposed to sunlight, all the way up to our own. And so, if we see something amazing and improbable, it is far better to assume that an evolutionary pathway for it exists, but simply hasn't been discovered yet.
After all, what's the alternative? When you have a theory that explains so much, are you going to look at the few things left to be explained and suddenly claim a special, divine creation was necessary for it? Or an alien presence, like the monolith in 2001: A Space Odyssey? When everything was ticking along nicely, why did God have to step in at various spots to give the system a kick? Couldn't he have gotten it right in the first place? No, the Big Bang, the laws of physics and time were all that was needed. No need of bringing in God here. The case for atheism rests.
But let's consider for a moment what is being claimed here. At about a millionth of a second after the Big Bang, all we had was quark-gluon plasma in a rapidly expanding universe. No structure. Just an undifferentiated soup of sub-atomic particles, and the handful of physical laws that govern matter and energy. Now, let the clock run: the universe evolves, matter prevailing over antimatter; hydrogen clouds coalescing into stars; heavier elements forming in dying massive stars, which explode, scattering dust unimaginable distances; that dust gets captured into galaxies, made up of billions of stars, and eventually captured by a star, joining an orbiting disk of dust, from which it joins a planet that happens to be just the right distance from the Sun to have liquid water on its surface; that planet has a collision with another planetoid which becomes the Moon, locked in a close orbit that stabilizes Earth's wobbles, and steadies the climate enough so that the Permian extinction doesn't freeze all but the most basic organisms; and even though the most basic living thing we know of is way more complex than any space ship we have ever built, out of the "primordial soup," the laws of chemistry and time led to the right combinations of atoms snapping together to build living creatures; and then time, and the survival of the fittest, led to ever-greater complexity of life, until the planet was ruled by fearsome dinosaurs; but then an asteroid hit the earth, one big enough to change the climate for a while, but not big enough to kill everything, and that wiped out the dinosaurs and made room for the ascendance of mammals, and eventually us.
At this point, you may be thinking I'm going in the direction of "this is way too improbable, so God must have been intervening, or nudging it along at points, to keep it going in the right direction." But that's not it at all. I'm quite happy to say that all one needed was the laws of physics and time to make us happen. Because that means that the basic physical structures of the universe are so amazingly put together that out of the chaos of the quark-gluon plasma, just running the clock produces all the life on planet Earth.
Atheists and I are all nodding our heads, looking at the exact same thing, but for me it's evidence for theism, not atheism. Math and science have found the most amazing, unlikely, unexpected, beautiful structures all around us. In all these things I see the signature of the Artist, the Designer. What a vast, complex, rich and beautiful mind that could write out a few physical laws, set it in motion with the Big Bang, and have it all result in us frail, fragile humans, turning in wonder and questioning to find the One behind it all! The poetic account of creation in Genesis, where God brings order out of chaos, and breathes life into the dust of the earth, suits the overall picture rather nicely, I think.
As I finish up this post, I'm again struck by how weak rational argument is. Atheist and theist can both look at exactly the same thing and claim it as strong evidence for their own position.