I'm always a little reluctant to respond to the worst arguments when there are good arguments to respond to. I don't want to be accused of going after low-hanging fruit. But sometimes, like today, I'm motivated to respond to an argument because it's popular, and not because it's worth responding to on its own merits.
Today, I'm going to respond to an argument that has come up multiple times in conversations I've had and conversations I've witnessed about fine-tuning. It came up one time in a meet up group I was a part of. At the time, I thought the guy was joking, and maybe he was, but a lot of people are serious about it.
Fine-tuning is the idea that the free parameters in our physics equations have to fall within extremely narrow ranges before life can even be possible in our universe. Since there is such a narrow range of values the constants of nature have to fall into so the univere can be life-permitting, the probability that our universe would be life-permitting is extremely small.
The objection that sometimes comes up is that the probability that our universe is life-permitting is 100% because if it wasn't life-permitting, there wouldn't be any life, yet here we are. I don't mean to insult anybody, but people do make this argument seriously and think it's a good response to fine-tuning.
The problem with the argument is that it's looking at the wrong probability. The question for fine-tuning isn't whether our universe actually is life-permitting. Of course it is! The probability is 100% that our universe is life-permitting. The question, rather, is what the probability is that our universe (or any universe) would be life-permitting if it didn't have to be.
Let me use a lottery analogy. Since there are a large number of possible outcomes, there's a very small probability that any given ticket will have the right numbers. That's why you have such a small chance of winning the lottery. But suppose I won the lottery, and I said to my friend, "Wow! What are the chances that I would win the lottery?" And my friend said, "It's 100% probable because you won." We would know immediately that my friend was confused because I wasn't asking what the chances are that I did win the lottery, but what the chances are that I would win the lottery given all the possible outcomes? The answer to my real question is whatever the odds were that any given ticket would have the winning numbers.
The same thing is true with fine-tuning. The question isn't, "What are the odds that our universe is life-permitting?" but "What are the odds that our universe would be life permitting?" What are the chances that any random universe would be life-permitting given that there's a large range of possible values the constants could take and only a small life-permitting range? That's the question.
This seems so obvious to me that I wonder, of all the people who raise this objection to fine tuning, how many of them are being serious and how many are joking? I would likely think they were all joking if it weren't for the fact that people will dig their heels in about it and others will congratulate them for bringing it up. This might be the silliest argument I know against fine-tuning.
