If the universe is “finely tuned,” that is, if the constants of nature are so finely tuned that they sustain life here on Earth, then it behooves us to look for a cause. It’s a big “if”, as I’ll get to in a minute, but let’s first admit that it’s settled really well.
For example, if the cosmological constant, a measure of the rate of expansion of the universe, were slightly greater than what we currently measure, galaxies (and therefore stars and planets) would not form, that is- ie not from us. The electromagnetic force – which dictates how atoms work, is dictated by the fine structure constant; change it up a bit, and there’s material: again, not from us. And so on, through 24 other constants of nature, all seemingly fine-tuned to allow us to be here, not to mention (by the way!) the rest of the universe as we observe it.
God’s solution is that he fixed these constants so much at the time of the Big Bang… and here we are, nearly 14 billion years later. It seems a little uncertain – what did she/he/she slightly misunderstand one of the constants? (And anyway, who or what adjusted God?) The problem with God’s solution is that it leads nowhere. All questions can be answered with “God did it,” and there’s your curiosity about, well, anything. In other words, God’s solution is
a scientist: science has nothing to say about it. Then there is…
The multiverse solution. If there are millions of universes – perhaps an infinite number of them – all with different constants, you would naively expect one of them (at least) to have the constants we find in our universe. The multiverse was imposed upon us not by fine-tuning, by the way, but as the logical outcome of the inflationary model of the early universe. The idea is that it went through a short period of incredibly rapid expansion to give us not only the universe we see now, i.e. our
universe, but it would have spawned other universes, like a non-stop bubble machine.
Curiously, these two solutions, God and multiverse, have this in common: they are both unverifiable — articles of faith, if you will — and therefore unscientific. Science, which is essentially a process for testing hypotheses (the empirical method) has nothing to say about either.
The third answer, which happens to be the one I favor, is to ask, “How would we know if the universe is fine tuned or not?” Of course, it may seem so because of our expectations, but how do we know what to expect? We have no other universes for comparison. With a sample size of just one, we can’t say anything about the likelihood or unlikelihood that these 26 constants of nature have the values they do.
Or, to put it another way, “What fine tuning?”