Tim Maudlin in Aeon:
Can it be mere chance that there are galaxies at all, or that the nuclear reactions inside stars eventually produce the chemical building blocks of life from hydrogen and helium? According to some theories, the processes behind these phenomena depend on finely calibrated initial conditions or unlikely coincidences involving the constants of nature. One could always write them off to fortuitous accident, but many cosmologists have found that unsatisfying, and have tried to find physical mechanisms that could produce life under a wide range of circumstances.
Ever since the 1920s when Edwin Hubble discovered that all visible galaxies are receding from one another, cosmologists have embraced a general theory of the history of the visible universe. In this view, the visible universe originated from an unimaginably compact and hot state. Prior to 1980, the standard Big Bang models had the universe expanding in size and cooling at a steady pace from the beginning of time until now. These models were adjusted to fit observed data by selecting initial conditions, but some began to worry about how precise and special those initial conditions had to be.