The idea that an acceptable cosmological theory needs to be formulated in a framework different from that of the so far successful theories of physics is not new. There is a tradition of critique of Newtonian physics, which leads to what is often called the relational position on the nature of space and time. Relationalism is associated with Leibniz [15], Mach [16],and Einstein [17] and, in the present period, Barbour [18], Rovelli [19], and others. Much of the critique concerns issues that only arise if you aspire to a theory of the whole universe rather than a part of it. General relativity is partly – but only partly, as I will explain – a response to that critique.

The roots of relationalism

We can draw criteria for a truly cosmological theory from that tradition of critique. The starting point is Leibniz’s great principle:

My view is that we should take the PSR as an aspiration and a goal, perhaps never to be completely reached but, nonetheless, a beacon illuminating the direction in which we are to search for the answer to cosmological questions. We can state this as follows:

In this form the PDSR is best used as a means to evaluate progress (has sufficient reason increased?) or to judge the likelihood of success of competing research programs. It is especially useful in judging the promise of novel research programs.