Recent observations of the rotation of individual galaxies have shown that the visible matter in galaxies is insufficient to account for their rate of rotation. It is therefore easy to calculate that there must be a huge amount of matter which we cannot see, some of which will be made of particles with which we are already familiar (such as neutrinos), but most of which will be made of as yet undiscovered "exotic" particles.

It is customary to refer to these particles as "dark matter".

However, quite separate observations of the universe as a whole, and not of its rotation but of the change of its apparent rate of expansion, have shown that although "dark matter" can account for the rotation of galaxies, it is insufficient to account for the expansion of the universe as a whole.

Two schools of thought have emerged: the broad-brush approach of looking for "dark energy", which (since mass is energy and vice versa) would have to make up 70 per cent of the mass of the universe: and quantum loop chronology, which completely rejects the classical structure of space-time and replaces it with relationships between events

Classical (Einsteinian/Minkowskian) space-time regards four-dimensional space-time as fundamental: it is the structure on which events happen. This structure has "wrinkles" (because "matter tells space how to curve"), and string theory even assigns it eleven dimensions instead of four, but it is still fundamental.

Quantum loop chronology regards space-time (whether four- or eleven-dimensional) as a large-scale approximation of the true fundamental building-blocks of nature: pairwise relationships between events. These relationships form a network, and just as a fishing-net is made of one-dimensional string whose joins give it (from a distance) a two-dimensional structure, so the network of one-dimensional pairwise relationships between events appears, on the large-scale, to have the familiar four-dimensional structure (or the less familiar eleven-dimensional structure) of classical space-time.

Events are the structure on which space-time exists: a particular place at a particular time does not exist unless an event happens there.

Since pairwise relationships have to be one-dimensional, it is natural to associate them with the unique dimension of time. Space is then only the inevitable result of the loops of time.

Events, or groups of events, whose only relationships are with themselves, and therefore do not interact with other events, are thought to correspond to the free chronicles of the equivalent classical theory, quantum chronodynamics.

These apparently pointless events are sometimes referred to as "dark time", or "wasted time", and are believed to make up about 70 per cent of the time in the universe.

B.P. 2007