The Absolute Now
- The Undivided Universe: An Ontological Interpretation of Quantum Theory by David Bohm, translated by Basil Hiley
Routledge, 397 pp, £25.00, October 1993, ISBN 0 415 06588 7
- Black Holes and Baby Universes, and Other Essays by Stephen Hawking
Bantam, 182 pp, £16.99, October 1993, ISBN 0 593 03400 7
David Bohm and Basil Hiley worked together for twenty years and between them developed a very unusual approach to quantum theory. Bohm died in 1992, but by then the book was almost complete. It is a magnificent monument to one of this century’s finest and most attractive minds.
Painfully shy, and finding few fellow physicists willing to give a hearing to his new ideas, Bohm struggled for four decades to get beyond the orthodox views that he had himself defended in his Quantum Theory of 1951, long the subject’s standard textbook, but which later put him in mind of Escher’s Waterfall, whose careful construction cannot hide the fact that the water must at some stage be flowing uphill. He found himself proposing that far separated events were correlated by influences which acted instantaneously. True, we couldn’t use these influences for faster-than-light signalling. Nevertheless, they would show that there was an absolute ‘now’, a uniquely correct way of splitting space from time, of the sort denied by Einstein’s special relativity.
Unpopular stuff, this. Yet Bohm made matters worse when he sprang to Einstein’s defence in an area where the great man was generally considered to have blundered – the blunder being summed up in the remark that God didn’t play dice. Bohm worked his way round to something very reminiscent of Louis de Broglie’s early approach to quantum theory. Particle positions, apparently just matters of chance, were in fact under the control of fully deterministic ‘pilot waves’. Over the years, Bohm and Hiley developed this theory in detail, guarding it against the criticisms which had led de Broglie to abandon it. Not even Bohm’s status as Fellow of the Royal Society and professor at Birkbeck could persuade many physicists to listen to a theory of this kind. And their tendency to block their ears was if anything made worse when he spoke of the ‘undividedness’ of the universe. While his reputation kept growing with the general public, swelled by such fine books as Wholeness and the Implicate Order (1980), physicists found something else to occupy their minds.
The Undivided Universe is Bohm’s final plea for their understanding. He and Hiley introduce their results in considerable mathematical detail, with difficult excursions into philosophy. Anyone likely to be put off by technical arguments – or the mere sight of mathematical equations – should read one of Bohm’s other books instead. On the assumption that some readers will be willing to give this one a try, I will concentrate here on one or two things to look out for.
To begin with, there is the ‘pilot-wave’ model of the famous double-slit experiment. Electrons fly towards two openings in a screen. Even if only one election is in flight at any one moment, ‘interference patterns’ are formed on the photographic plate on which they eventually land. It is as if the electrons were each of them a wave which traversed both openings. The two resulting waves would then ‘interfere’, reinforcing each other in some places and cancelling each other out at others. Always, however, such waves would finish by collapsing down to single landing places. The wave-patterns would control the likelihood that particular landing places would be chosen, but according to the orthodox ‘Copenhagen’ interpretation of quantum theory, there would be absolutely nothing that decided exactly which landing place would be chosen by any given electron. The waves might thus be considered ‘mere waves of probability’.
Bohm and Hiley instead hold that they are actual waves: waves which guide electrons to one place rather than another. The guidance, however, has results unpredictable by anyone. Think of the guidance given to a falling marble by a wall bristling with pegs: the slightest change in how you drop the marble makes it bounce down a different sequence of pegs, ending in a different spot.