In the wake of the announcement of gravitational-wave signatures from inflation in the cosmic microwave background, I was invited to contribute a piece to The Stone section of the New York Times, on “naturalness” and how it’s used in physics. Mostly The Stone is devoted to philosophy, but occasionally they’ll let an outsider opine about a philosophical-sounding topic.
The hook is obviously the fact that inflation itself is motivated by naturalness:
Cosmic inflation is an extraordinary extrapolation. And it was motivated not by any direct contradiction between theory and experiment, but by the simple desire to have a more natural explanation for the conditions of the early universe. If these observations favoring inflation hold up — a big “if,” of course — it will represent an enormous triumph for reasoning based on the search for naturalness in physical explanations.
I conclude with:
Naturalness is a subtle criterion. In the case of inflationary cosmology, the drive to find a natural theory seems to have paid off handsomely, but perhaps other seemingly unnatural features of our world must simply be accepted. Ultimately it’s nature, not us, that decides what’s natural.
I like to capitalize “Nature,” but nobody agrees with me.