There have been many books about the paradoxes of time, but this one is far and away more paradoxical than most, for its thesis is that time doesn't exist at all. This idea is explored in great detail, mostly in relation to physics but the philosophical and even the theological implications are touched on in an Epilogue. In fact, Barbour himself is something of a paradox, for he is a respected theoretical physicist who has remained independent, supporting himself and his family by translation while working on his ideas about time whenever he could. However he has continued to keep in touch with mainstream physics and he acknowledges help from a number of well-known scientists, including Lee Smolin among others.
The book, he tells us, is intended to interest that fabled beast, the "general reader", but he also expects his colleagues to look over his shoulder. He mentions Roger Penrose and Richard Dawkins as other scientists who have written similar types of books, and his own will certainly bear comparison with theirs. Like those authors, Barbour is an excellent writer, and his interests include philosophy, art, and literature as well as science so that his view of his subject is multidimensional; no nonsense about "two cultures" here.
In the first part of the book, Barbour sets forth a number of basic ideas which are then progressively elaborated in later parts. The central mystery that he confronts in his first three chapters is best described in his own words.
"The main aim is to introduce a definite way of thinking about instants of time without having to suppose that they belong to something that flows relentlessly forward. I regard instants of time as real things, identifying them with possible instantaneous arrangements of all the things in the universe. They are configurations of the universe. In themselves, these configurations are perfectly static and timeless. But how and why can something static and timeless be experienced as intensely dynamic and temporal?"
These instants of time Barbour calls "Nows" or "time capsules". Examples include long-term memory stored within the brain, fossils and geological records, and the human body, which contains within itself more time capsules nested one within another (cells, genes). The universe is composed of things like this, and it exists within what Barbour calls Platonia, which is an unimaginably vast configurational space. To help us understand what this means, Barbour uses the analogy of Triangle Land: the different ways that triangles can be arranged in a configurational space. Much poring over of diagrams is needed here and elswhere in the book if his argument is to be grasped, and my attempt to do so wasn't helped initially when a Necker cube illusion made me think that a diagram was meant to represent a solid cube whereas it's really supposed to be hollow. A note in the legend might have made this clearer.
In fact, this book does demand close attention from the reader, in spite of the beautiful clarity of the text. The difficulties are of at least two kinds. One comes from the complexity of the physics. The theory that Barbour advances has profound implications for both quantum mechanics and general relativity, and these implications are examined in considerable depth. Part of Barbour's thesis is that his approach will reconcile these two fundamental scientific theories, something that ultimately baffled Einstein and has still not been achieved. Certain more technical or more peripheral sections are enclosed in boxes, so the reader can skip them if necessary, and other material is placed in the notes at the end. Even so, Barbour pays his readers the compliment of thinking that they are willing to come to terms with some pretty deep ideas.
The other. and even more profound, kind of difficulty arises from the nature of the theory itself. We feel as if we have our being in time. If there is no time, what meaning can we attach to the notions of past or future, and - even more difficult to accommodate - our peception of motion? Barbour suggests that what we see as motion, in a leaping cat or a diving kingfisher, is really a series of still photographs, which are somehow brought together by the brain to produce an illusion of movement. Of possible relevance here is the very interesting fact that in certain kinds of brain damage the ability to perceive objects in motion is lost. Barbour mentions this, but not the equally interesting observation, recorded by Oliver Sacks, that some patients suffering from post-encephalitic Parkinsonism found themselves frozen in time for years, until released from this state, though only temporarily, by the drug levodopa.
Trying to picture oneself in a timeless state is probably something like a fish would feel if it tried to picture itself out of the water. Our language, of course, has no vocabulary to describe this, and Barbour finds himself repeatedly forced to use temporal language to describe his theory, even though he acknowledges that this is just shorthand. Indeed, even if he is right, will it ever be possible to feel that he is? The analogy that comes to mind here is with the shift from a geocentric to a heliocentric universe that took place in the sixteenth century; no doubt many people, and not only churchmen, found that hard to come to terms with, but the imaginative shift from a time-based to a timeless universe would be incomparably bigger.
But is Barbour right? This is a mainly technical question for physicists and cosmologists, but he does suggest some ways in which the theory can be tested; in other words, it is intended to be physics, not metaphysics. Neverthless, profound metaphysical questions are inevitably raised. Does free will exist? Is there room for a Creator? Where is Heaven (and Hell)? Is time travel possible? Doesn't the denial of motion and change take all the joy out of life? Some of these are old chestnuts, of course, but they would need to be radically re-evaluated if Barbour's theory were to become widely accepted. And, of course, the field is open for anyone who wants to have a go; Barbour merely opens the way for us to think about the implications. For himself, he finds that his ideas, like those of Lee Smolin (see his The Life Of The Cosmos), tend towards pantheism. "The whole universe ... is the closest we can get to a God."
I've read few books that have made me think as much as this. If ever I find myself on that legendary desert island, I probably now know which book I'd choose to have with me.
See also Julian Barbour's website and the Edge interview with Barbour.