Physicist and Nobel laureate Steven Weinberg says the universe might remain eternally inexplicable, unless you believe it was designed for the emergence of intelligent life. Excerpt:
These bubbles may realize all the different solutions of the equations of string theory. If this is true, then the hope of finding a rational explanation for the precise values of quark masses and other constants of the standard model that we observe in our big bang is doomed, for their values would be an accident of the particular part of the multiverse in which we live. We would have to content ourselves with a crude anthropic explanation for some aspects of the universe we see: any beings like ourselves that are capable of studying the universe must be in a part of the universe in which the constants of nature allow the evolution of life and intelligence. Man may indeed be the measure of all things, though not quite in the sense intended by Protagoras.
So far, this anthropic speculation seems to provide the only explanation of the observed value of the dark energy. In the standard model and all other known quantum field theories, the dark energy is just a constant of nature. It could have any value. If we didn’t know any better we might expect the density of dark energy to be similar to the energy densities typical of elementary particle physics, such as the energy density in an atomic nucleus. But then the universe would have expanded so rapidly that no galaxies or stars or planets could have formed. For life to evolve, the dark energy could not be much larger than the value we observe, and there is no reason for it to be any smaller.
Such crude anthropic explanations are not what we have hoped for in physics, but they may have to content us. Physical science has historically progressed not only by finding precise explanations of natural phenomena, but also by discovering what sorts of things can be precisely explained. These may be fewer than we had thought.
UPDATE: Reader Carlo (who is a physicist) says I’ve misread Weinberg:
That not exactly what he is saying. Weinberg is an atheist and thinks that because of randomness during the initial inflation, certain physical parameters are essentially random and cannot be explained physically. The only reason we observe them is because they are the only ones that allow life. But that does not imply that the universe was “designed for the mergence of intelligent life.”
I disagree, but not because of the physics. The problem is that his understanding of “explanation” and “design” is positivistic.