The concept of the multiverse takes advantage of two principles, namely the Copernican Principle and the Anthropic Principle. This is intriguing for Carter introduced the Anthropic Principle as a reaction to the Copernican Principle.
The Copernican Principle states that the Earth, Sun, humans, life, do not occupy a special or unique vantage point or status. In the cosmological version it states that the universe is isotropic and homogeneous. The Earth was held once to have occupied a special place; we know that it does not. We thought in terms of one special galaxy or nebula, but we now know that our neck of the woods is nothing special. Nor is our local cluster of galaxies any special and so on.
The ultimate application of the Copernican Principle is to the universe itself. Our universe is not special, but one of many. One of many, many, many.
The Anthropic Principle is an observation selection effect. It states that the values of the physical constants, such as Planck’s constant, and other fundamental physical parameters are consistent with the evolution of life. If they took any other value there would be no life to observe them, but because we do observe them they must be as they are.
The idea here is to account for why the parameters take the value that they do without positing a fundamental physical mechanism, mainly because we don’t have any viable hypothesis or hypotheses as to why they take the value that they do. They don’t automatically spring from theory. We know the values through experiment, that is observation.
The problem with string theory is that there are many solutions to the theory, perhaps as much 10^500, which is problematical for a theory long seen as providing a unique and total picture of physical reality. One way of looking at this is to say that each solution describes a different universe with different laws of physics. The Anthropic Principle is invoked to assert that a certain subset of the possible solutions is consistent with the existence of observers or cognition and the physical parameters take the value that they do in our universe because we are here to observe them.
Much trades on what we mean by “life.” We actually don’t know what we mean by “life” so any theory that invokes the notion without adequately explaining what it is should be viewed with caution.
Say life emerges in any universe governed by physical law of any type. Evolution likes to take advantage of what nature puts on its plate. Say there are universal principles of self organised complexity, reproducibility and evolution at work so that life emerges in any universe governed by physical law. The form that life takes will differ as physical law differs, but life and evolution will take advantage of what is given and work its magic therefrom.
In that case there is no special subset of universes that possesses life. One cannot then say that the physical parameters in our universe take the value that they do because life evolved here. Life would have evolved no matter what value the physical parameters take.
Which still leaves the question; why do the values take the form that they do in our universe?
If you ruthlessly apply the Copernican Principle, then you can’t take advantage of Anthropic observation selection effects. If you limit or stop Copernican reasoning at some point, then you can invoke observation selection effects. However, I see no reason why you should and nor do I see why, a priori, it should be limited at some point rather than any other. Say, limit it at the point of the universe and forget about the multiverse altogether for instance.
It seems to me that there is a contradiction at work here. Unless, of course, I am missing something which I might well be as I only though/speculated about this whilst driving in some pretty heavy rain and fog this evening grrrrrrrh