Ask a physicist to imagine a universe different from our own. Maybe gravity is ten times as strong. Imagine another one. There are 4 dimensions of space instead of 3. Maybe the charge on an electron is 10% bigger than what it is in our world.
When I was a grad student in the 1970s, I wanted to ask the question, "how many of these universes are capable of supporting life?" In other words, "how special is our universe?"
Before that decade, scientists assumed that the laws of physics were arbitrary and that life used them opportunistically. In fact most scientists and most people still think that way.
The laws of physics were imprinted on the universe at the Big Bang, and life originated when a particular configuration happened to be able to make copies of itself. All the rest is explained by Darwin. [the classic materialist perspective.]
That started to change in 1973, when a young Australian physicist named Brandon Carter wrote about an extraordinary series of what-ifs. If the gravitational force were just a little weaker, there would be no galaxies or stars, nothing in the universe but spread-out gas and dust. If the electric charge of the proton were just a bit bigger, hydrogen would be the only chemical element. If our world had four (or more) dimensions instead of three, there would be no stable orbits, no solar systems because planets would would quickly fly off into space or fall into the star; for that matter, there would be no stable galaxies in which solar systems might form in the first place.
When I proposed to my graduate adviser in 1979 that I wanted to write a dissertation on the question, "how special is a universe that can support life?" he told me the question was not yet ripe, that physicists did not have any way to interpret "special" by assigning probabilities.
But others have worked on the question. Now, forty years later, physicists are agreed that our universe is very special indeed. The vast majority of imaginable physical laws give rise to universes that are terminally boring. They quickly go to thermodynamic equilibrium = "heat death", so that nothing can happen. Or they Bang and then turn around and collapse so quickly that there's no time for anything interesting. Or they don't support chemistry, or anything like it. Or they produce starlight that is too hot or too cold to interact with chemistry, so there's no photosynthesis. Or".
So many things that can go wrong! The inescapable conclusion is that this universe that we live in is a rare gem. The probability of laws that can support life is infinitesimal. This has been called the Anthropic Principle.
Scientists mostly don't take account of this extraordinary fact; they go on as if life were an inevitability, an accident waiting to happen. But those who have thought about the Anthropic Princple fall in two camps:
The majority opinion: There are millions and trillions and gazillions of alternative universes. They all exist. They are all equally "real". But, of course, there's no one looking at most of them. It's no coincidence that our universe is one of the tiny proportion that can support life; the very fact that we are who we are, that we are able to ask this question, implies that we are in one of the extremely lucky universes.
The minority opinion: Life is fundamental, more fundamental than matter. Consciousness is perhaps a physical entity, as Schrödinger thought; or perhaps it exists in a world apart from space-time, as Descartes implied 300 years before Schrödinger; or perhaps there is a Platonic world of "forms" or "ideals" [various translations of Plato's είδος] that is primary, and that our physical world is a shadow or a concretization of that world. One way or another, it is consciousness that has given rise to physics, and not the other way around.
I prefer the minority view
I am a mystic as well as a scientist, and the minority view resonates for me. I worry that this is superstitious or even wishful thinking, so I examine the scientific evidence.
The argument for the majority view is in the nature of science. Science asks, "what about the world can we agree on?" Getting the observer out of the picture is the essence of science. Historically, the Enlightenment began, and with it the scientific age, when man was first willing to step aside from center stage long enough to describe an objective physical reality that exists independent of himself. We have worked for centuries to emerge from the prejudices and superstitions of religious beliefs. We don't want to let them creep in by the back door. It is to preserve the Copernican revolution that most scientists would rather imagine a large number of dead universes, rather than revert to the idea that man is special.
Of course, it is impossible to disprove the existence of gazillions of other universes, but it is also impossible to impute any evidence in favor of their existence. I find it inelegant for a theory to carry so much baggage, to assume so much in order to explain so little. It is an extravagant waste of universes. These are aesthetic objections to the majority.