The constants of Nature give our Universe its feel and its existence. Without them, the forces of Nature would have no strengths; the elementary particles of matter no masses; the Universe no size. The constants of Nature are the ultimate bulwark against unbridled relativism. They define the fabric of the Universe in a way that can side-step the prejudices of a human-centred view of things. If we were to make contact with an intelligence elsewhere in the Universe we would look first to the constants of Nature for common ground. We would talk first about those things that the constants of Nature define. The probes that we have dispatched into outer space carrying information about ourselves and our location in the Universe pick on the wavelengths of light that defined the hydrogen atom to tell where we are and what we know. The constants of Nature are potentially the greatest shared physical experience of intelligent beings everywhere in the Universe. Yet, as we have followed the highways and by-ways of the quest to unravel their meaning and significance, we have come full circle. Their architects saw them as a means of lifting our understanding of the Universe clear from the anthropomorphisms of human construction to reveal the otherness of a Universe not designed for our convenience. But these universal constants, created by the coming together of relativistic and quantum realities, have turned out to underwrite our very existence in ways that are at once mysterious and marvellous. For it is their values, measured with ever greater precision in our laboratories, but still unexplained by our theories, that make the Universe a habitable place for minds of any sort. And it is through their values that the uniqueness of our Universe is impressed upon us by the ease with which we can think of less satisfactory alternatives.
John Barrow, The Constants of Nature: From Alpha to Omega, London, 2002, pp. 290-291