There are really two different anthropic principles; the ‘strong’ one and the ‘weak’ one. The latter is pretty much a tautology. If the most basic laws of the Universe would different, then the Universe itself would look differently. There’s not much controversy there, it’s pretty straightforward. So here I’ll be focusing on the ‘strong’ anthropic principle.
As you might’ve guessed, the strong anthropic principle goes a bit further than the weak one. Lurking behind it is this assumption that the balance of natural laws in such a way as to produce life (specifically our own lives) must be maintained by some intelligent entity with a plan for humanity, as if it somehow knew we would exist some 13.7 billion years before our time when the physical constants were established. The physicists/cosmologists John D Barrow and Frank Tipler expressed this in their 1986 book, The Anthropic Cosmological Principle:
There exists one possible Universe ‘designed’ with the goal of generating and sustaining ‘observers.’
Now we know that even just with materials found here on Earth and without any intelligent input whatsoever, natural processes can produce things which look very much like they have a purpose or a goal. For example:
That looks like it was designed by humans in order to accommodate travel from one area to another. But the reality is that it formed naturally without any intelligent input. The point here to remember is that we should be careful to avoid being deluded into seeing a goal or a purpose where there isn’t any. The fact that there are living things in Virginia which can use the natural bridge pictured above doesn’t necessarily mean that it was created for that specific goal. Similarly, we can’t assume that our existence was presupposed just because we happen to exist.
The only reason we can even think about an anthropic principle is because we’re already here. If different physical constants could also produce life in different Universes, then they’d be wondering the same thing. It’s only by necessity that we only hear about how great our Universe was to produce us. Other Universes in a multi-verse could also produce life by saying how awesome their own particular physical constants were to produce them.
The late British science fiction author Douglas Adams had come up with one of the best responses along these lines:
“[I]magine a puddle waking up one morning and thinking, ‘This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn’t it? In fact it fits me staggeringly well, must have been made to have me in it!’ This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it’s still frantically hanging on to the notion that everything’s going to be all right, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for.”
The point that Adams got to towards the end of that quote is what makes the strong anthropic principle not just nonsense, but dangerous nonsense. If the Universe or a God or whatever had us in mind as the lead in some epic cosmic plan, then we don’t really need to worry about environmental destruction or extinction by meteors or anything like that. It takes that responsibility out of our hands – and we as a species seem to like not having much responsibility in general.
Even against our own interests, we’re predisposed to accept the strong anthropic principle (or anthropo-centric principle, as Carl Sagan put it). We’d like to be special and the pinnacle of existence, and at the same time we’d like for a Big Brother to protect us from dangers, even dangers we might inflict upon ourselves. We’re so compelled by this combination of protection and self-aggrandizement that even unscrupulous leaders in politics, religion, and economics who might not have even heard of the anthropic principle make some crude use of it for their own purposes.
For more on the history and problems on these issues, I’d reccommend Massimo Pigliucci’s recent writings on the subject.