Scientific cosmology is slowly revealing a universe that is incredibly fine-tuned. We are beginning to realize that fundamental constants in our universe – the unexplained numbers that seem to occur in nature for no particular reason e.g. the speed of light, the charge of the electron and the gravitational constant – are all ideal for the development of life (as defined by our limited human experience on Earth) in the universe. Any slight tweaking of any of these numbers produces a universe that would be totally devoid of life. These observations are summed up in the weak and strong anthropic principles.
Weak Anthropic Principle (WAP): What we can expect to observe must be restricted by the conditions necessary for our presence as observers.
Strong Anthropic Principle (SAP): The universe necessarily has the properties requisite for life, life that exists at some time in its history
The WAP is non-controversial, and all it does is state the obvious. The SAP however, demands an explanation, as it opens up a whole pandora’s box of philosophical and metaphysical questions. Was our universe designed to be this way by a Supreme Being (the theistic principle)? Or was the universe brought into existence by the presence of observers? Are there an infinite number of universes, most of them barren, of which we happen to live in one that had the conditions suitable for life?
There are many ideas floating around about how there can be multiple universes and multiverses, many being spawned from some of the peculiarities of quantum mechanics, taking into account also the special role of the observer e.g. the cat being both dead and alive in Schrodinger’s thought experiment, with the universe splitting into two universes once the box is opened and the probability waves collapse, one in which the cat is alive, the other in which the cat is dead.
Consider an ensemble of self-contained universes covering all possible values of the fundamental constants of physics. Suppose that all these universes are ‘virtual’. That is, they all exist in potential form, and each only becomes ‘real’ by observation by conscious life. because each is self-contained, the only possible observations are by internal forms of life. Thus only those universes are real in which the fundamental constants are compatible with the existence of life. What happens in a universe such as our own that passes through an early lifeless age? In the early stage there exists no conscious life to observe it; does it exist? Presumably, it evolves in a virtual state and becomes real by observation when conscious life comes into existence. This seemingly weird picture of virtual (potential) versus real (actual) is common in the theory of quantum mechanics. A wavefunction consists of many evolving, parallel, virtual states, all of which are potential candidates for a final observed state in the real world. ~ Edward Harrison, Cosmology: The Science of the Universe
But are concepts regarding other universes and multiverses still scientific? Are these hypotheses falsifiable? Or have they crossed into the realm of metaphysics?
Cosmology is a workshop in which experimental universe are invented and investigated as potential representations of the Universe. In this sense cosmology is a science. But when cosmology invents a plurality of physical universes, and claims that each is self-contained and real in its own right, it ceases to be a science. Cosmology takes on metaphysical aspects and the notion of containment becomes vague. Once again cosmology is at the mercy of metaphysics, as in earlier ages. ~ Edward Harrison, Cosmology: The Science of the Universe
Why is the universe the way it is? Because we exist. But why do we exist? Because the universe is the way it is. The circularity of the argument is broken in the theistic principle at the cost of introducing a supreme being, and in the anthropic principle at the cost of introducing an ensemble of universes. ~ Edward Harrison, Cosmology: The Science of the Universe
I am also personally a bit wary about using the fine-tuning of the universe as pointing to a Cosmic Designer, as many Christian scientists such as Owen Gingerich and even John Polkinghorne have done. I am concerned that this may turn out to be another God-of-the-Gaps argument. The fact that we do not understand how these fundamental constants appear to be so fine-tuned does not mean we will not find out in the future. As cosmologists and particle physicists continue to search for a grand unified theory, it may turn out that these constants may not be free parameters but are instead embedded into the laws of the universe. The anthropic and theistic principles may serve merely as makeshift principles while we await for a more complete theory of the universe. String theory anyone?
The fundamental constants have values that are either intentional (theistic principle) or fortuitious (anthropic principle), and otherwise are inexplicable. But science forever advances by explaining what previously was thought to be inexplicable. Perhaps in the future the constants of nature will have rationally explained values that are neither intentional nor fortuitious. ~ Edward Harrison, Cosmology: The Science of the Universe