Published 10 February 2016 in New Scientist. 

Mary-Jane Rubenstein writes that modern physics considers it strange to find our universe so hospitable to life, when nearly any other values for the fundamental constants would not have allowed life to form (19/26 December 2015, p 64). A proposed solution to the problem is offered by a multiverse containing many different values of physical constants.

While this is a fair description of contemporary debates in physics, the fact is that we don't know whether there is any meaning to the notion of “fine-tuning” of physical constants. Indeed, if there is only one universe, in what sense can we give meaning to the notion of “fine-tuning of constants”?

An empirical approach fails, because there are no other universes to observe for comparison. A probabilistic approach fails because, at the level of the universe as a whole, probability is not well defined, nor can it be empirically verified.

Whatever we may mean by fine-tuning of constants, it must be rooted in mathematical, aesthetic, philosophical or theological assumptions. 

For example, we may be assuming that the mathematical form of physical laws remain fixed when considering alternative values of physical constants. This gives a privileged status to the physical laws that they need not necessarily have.

There is a clear affinity here between modern physics and philosophical-theological inquiry, fertile ground for asking deep questions about chance, necessity, naturalness, meaning, causality, creation and existence.