First, let’s talk about physical necessity. As I just explained, according to this alternative the universe has to be life-permitting. The constants and the quantities had to have the values that they do. It is literally physically impossible for the universe to be life-prohibiting. It is physically necessary that the universe be a life-permitting universe.
On the very face of it, this is an extraordinarily implausible explanation of the fine tuning. It would require us to say that a life-prohibiting universe is physically impossible – such a thing could not exist. And that is an extremely radical view. Why take such a radical position? The constants, as we have seen, are not determined by the laws of nature. Nature’s laws could hold, and the constants could take any of a wide range of values, so there is nothing about the laws of nature that require the constants to have the values that they do.
As for the arbitrary quantities, remember those are completely independent of the laws of nature – they are just put in as initial conditions on which the laws of nature then operate. Nothing seems to make these quantities necessary in the values they have. The opponent of design is taking a very radical line which would require some sort of evidence, some sort of proof. But there isn’t any proof that these constants and quantities are physically necessary. This alternative is just put forth as a bare possibility; and possibilities come cheap. What we are looking for is probabilities or plausibilities, and there just isn’t any evidence that the constants and quantities are physically necessary in the way that this alternative imagines.
The first option, physical necessity, is the easiest to dismiss. The idea that it was physically impossible for the universe to have been created in any way other than in a manner that would support life is neither logically necessary nor scientifically plausible. As Barr notes, “In the final analysis one cannot escape from two very basic facts: the laws of nature did not have to be as they are; and the laws of nature had to be very special in form if life were to be possible.” Our options, therefore, are between chance (the anthropic coincidences truly are coincidences) or design (the parameters needed for life were purposely arranged). While it cannot be established with absolute certainty, we can, I believe, determine that design is the most probable explanation.
Paul Davies, Information, and the Nature of reality , page 86:
Given that the universe could be otherwise, in vastly many different ways, what is it that determines the way the universe actually is? Expressed differently, given the apparently limitless number of entities that can exist, who or what gets to decide what actually exists? The universe contains certain things: stars, planets, atoms, living organisms … Why do those things exist rather than others? Why not pulsating green jelly, or interwoven chains, or fractal hyperspheres? The same issue arises for the laws of physics. Why does gravity obey an inverse square law rather than an inverse cubed law? Why are there two varieties of electric charge rather than four, and three “flavors” of neutrino rather than seven? Even if we had a unified theory that connected all these facts, we would still be left with the puzzle of why that theory is “the chosen one.”