A popular religious claim is that "the universe has been fine-tuned for our existence." The argument goes something like this: If the fundamental constants of the universe differed even slightly from their observed values, then life as we know it could not exist. Examples of these constants are the mass of elementary particles, the strength of the strong nuclear force, and the gravitational constant.
As the Christian apologist William Lane Craig put it, "If any one of these numbers were altered by even a hair's breadth, no physical, interactive life of any kind could exist anywhere. There'd be no stars, no life, no planets, no chemistry." The conclusion, of course, is that a god is responsible for this fine-tuning. There are several problems with this argument.
First off, how have they determined that these constants are free to vary? Or how do they know to what degree they can vary? Since we only have our one universe to observe, drawing conclusions about the possible range of conditions seems to be nothing more than speculation. Given our inability to observe the singularity that created our universe, such a claim seems hard to justify.
Another thing to point out is that this may not be the only universe. There may, in fact, be many universes. And these could differ from one another in their fundamental constants. So the apparent fine-tuning of our universe could just be a consequence of there being a large number of universes which differ from one another. And we would, of course, inhabit the rare universe that has our exact constants. Imagine, by analogy, that I had a safe that required the input of a five-digit code on a keypad to open. If one robber came in and typed in a single random guess, and happened to get it correct, this would be pretty amazing. But if all 7 billion people on earth took a guess, we would be less impressed to find out that one of them got it correct.
Another problem with this argument is that it focuses exclusively upon our lifeforms. Maybe there are other combinations of these constants that would allow entirely different self-replicating, conscious creatures to come about? And we can imagine these lifeforms concluding that their completely different universe was fine-tuned for their existence. In fact, maybe there's another universe out there where—right now—there's a slimy, green version of William Lane Craig with tentacles and 15 eyeballs who's arguing that his universe was designed by his god.
This argument also fails to take into consideration the big picture within our universe. Yes, our universe permits the formation of stable stars, the fusion of atoms into higher elements, and, ultimately, allows life to arise. But it also allows gigantic stars to undergo supernova explosions. It also allows black holes to form.
I can't help but wonder if there has ever been an intelligent, extraterrestrial lifeform that arose in our universe, and that made the fine-tuning argument, only to have their entire planet obliterated by a nearby supernova explosion, or swallowed up in a black hole. I hope that if such a thing ever did happen, there was a skeptic among them to say "Where's your god now!?!" But I'm sure they'd have explanations ready at hand: "We're being swallowed up by a black hole because we allowed gay aliens to marry." I digress.
The point is: Yes, our universe is compatible with life and happiness and enjoyment. But it's also compatible with death and misery and destruction. "Some design!", as Christopher Hitchens used to say.
Another thing to point out is that this is an extremely arrogant and self-centered argument. We live in a vast universe, with hundreds of billions of galaxies, all of which have billions of stars. Life happened to arise here on one rocky, watery sphere orbiting one star on the outskirts of one galaxy. And certain members of one primate species here have the audacity to claim that all of this—this entire universe, with its billions of galaxies and stars—was created specifically so that they could be here. It's amazing to me that anybody can say this with a straight face and take themselves seriously.
Of course, this self-centered view of the universe is nothing new. Carl Sagan argued in his book The Pale Blue Dot that the fine-tuning argument is just another way that humans are desperately trying to make themselves feel significant.
Over time, there have been a series of what he called "great demotions." Early on, people believed that earth was at the center of the universe. Then once they learned that earth actually orbited the sun, they thought that at least our solar system was at the center of the universe. Close enough, right? But once they found out that it was actually at the outskirts of the galaxy, they thought that at least our galaxy was at the center of the universe. Now that this notion has been dispensed with, people are claiming that the universe itself was created specifically so that we could be here.
As time goes on and we continue to learn more and more about the universe, the fine-tuning argument is likely to join its obsolete cousins and be remembered as just another one of our childish attempts to cling to the idea that everything revolves around us.