The implication of new models arising from within science

Chris Clarke and John Kerr

1. The consistent histories approach to quantum mechanics

This is an interpretation of quantum theory that has become dominant in quantum cosmology - that is, in an area of physics where it is necessary to take a unified approach that embraces both microscopic processes (including comical processes in the very early universe) and us as macroscopic observers. In this approach, a history is a time-sequence of asserted propositions, such as the positions of all the galaxies given at a series of times; or, on a smaller scale, the position of radioactive source placed in a particle detector, followed by a succession of photographs that appear to depict particles. The idea is that "histories" is what science is about. pp On this approach (due to Hartle and Gel'man), the role of physics is not to embed these histories in a reductionist account of mechanical causation, linking one event in the history to the next; but rather to place constraints on which histories are consistent and which are not. In a consistent history, for instance, "snapshots" at times one second apart that show two widely separated bodies moving in empty space with separations first of 10 kilometres and then of 11 kilometres, are likely to be followed after one further second by a snapshot that shows them about 12 kilometres apart.

The point of this, from the viewpoint of the Drynachan discussion, is that it shifts the emphasis from the reductionist metaphysics of the atomistic programme (described in my other contribution) to a metaphysics in which the macroscopic world has a dominant role. Microscopic theories (and in physics all the available theories are microscopic) are allowed full play, but they need not be the whole story. Indeed, a considerable number of cosmologists recognise that in the context of this interpretation microscopic theories cannot adequately restrict the consistent histories down only to what is observed, so that there is a need for additional influences and constraints at the macroscopic level or, if we place histories within the human realm, at the level of human experience and consciousness.

2. Discrete approaches to space-time

Until recently, in all physical models events all happened in space and time (or in space-time), and causal effects were bound by the limitations of space and time. This made it particularly difficult to make sense of precognitive abilities, of altered states of consciousness accompanied by a synoptic view of space and time, or (to come to the theme of the discussion) of transcendent experience in which space and time were irrelevant or superseded. For one of the more promising (if not the more fashionable) attempts at quantum gravity, however, this is not the case: the loop space approach of Smolin and Rovelli.

In this, space-time is seen as arising from a more primitive level of physics at which the universe is represented as a knot (or, more exactly, as a braid: a knot made up of several different strings). The connection between knots and space comes through representing geometry in terms of the change that takes place in ones perceived position when one walks round a closed loop in space; this establishes a property associated with each loop, and then the way loops are interconnected is reflected in the behaviour of this property (speaking very roughly).

All quantum gravity theories must at present be regarded as speculative in their details. The point about this one, however, is that it is the first really successful implementation of an idea long canvassed by Penrose (and pursued with interesting, but tangential results in his Twistor theory) that any theory of quantum gravity would have to based on something more primitive than space-time. If we were to remain bound by the reductionist, atomistic view then this would be of no help. That view would have us develop the universe as a hierarchy, working from the smallest level upwards. In the first stages of the hierarchy, played out in the very earliest phases of the universe, the pre-space-time structure would somehow need to crystallise into the usual space-time that we experience, and from then on successively more classical entities would come to dominate, building up to an entirely mechanistic Newtonian realm by the time that structure was forming in the universe. If, however, we adopt the more "holarchical" approach (Seed 7) represented by the consistent histories approach to quantum theory, then things may be different. Here there is no unidirectional build-up of explanation, but all layers of reality may play a role in constraining the possible histories that constitute our experience. The classical world of a fixed space-time is only one possible outcome of the more primitive world of loop-space (or whatever might supersede it) and the additional freedom that this gives to the consistent histories may allow experiences that are not bound by space and time.

For the present, I would view all these speculations as having the role of freeing us up from the tyranny of a purely classical viewpoint, rather than as providing us with reliable concrete alternatives. Indeed, the appropriate alternatives could, if this thinking is correct, come equally well from an analysis of transcendental experience as from attempts to develop fundamental theories which have no physical manifestation except in the unobservably remote primordial structure of the origin of the universe. If this is to be a scientifically credible alternative, however, then we will need to develop with much greater clarity our understanding of realms at the very edge of human experience.