The Janus Point: A New Theory of Time by Julian Barbour
My rating: 3 of 5 stars

Thinking Outside The Box

I have no doubt that Barbour is a polymath of considerable renown for his work in the history and philosophy of science. His insights are thrilling in their originality and import. His ability to make connections not just among diverse areas of science but also with literature, philosophy, myth and religion is remarkable. His aphorisms are memorable. The consequence is that his writing is dense to the point of impenetrable obscurity.

Unless you are prepared to engage with the details of such things as phase space, shape spaces, minimal model, root-mean-square lengths, Poincaré recurrence, the Boltzmann brain, Abelian gauge theory, the N-body problem, Kepler pairs, and invariant variations, you will not find much to linger on in The Janus Point. This is unfortunate since it is a self-proclaimed paean to the universe, a sort of celebration of all that is. But it’s a celebration much like an Oxford commencement, in which the orator gives his often lengthy speech entirely in Latin. Snippets are intelligible to many in the audience but only the experts in ancient rhetoric understand the content.

The snippets that I comprehend in The Janus Point centre on his chief concerns: 1) the apparent reversibility of the laws of physics which is contradicted by all experience, and 2) the necessity within current cosmological theory for postulating inscrutable ‘special conditions’ for the universe at the moment of the Big Bang. Both these issues he perceives as deficiencies in cosmological theory involving a misconception of time and a related mistake in the application of the second law of thermodynamics. In his exposition, Barbour critiques not just the historical ‘greats’ in Physics - Newton, Boltzmann, Leibniz, Thomson, Mach, and Einstein among others - but also more recent ‘heavies’ like Penrose, Feynman, and Hawking. Throw in a bit of Shakespeare, Augustine, and Wagner and the result is density bordering on that of a black hole.

Barbour’s response to his two main concerns is, after considerable discursive detours fore and aft in the text, is literally to “think out of the box.” By this he means to consider the universe as what it is: not an experimental enclosure in which the established laws of thermodynamics reign, but an un constrained, expanding space in which certain concepts like entropy and especially time must be re-defined. He proposes an entropy-like concept which he calls entaxy, and which is measured in terms of ‘shape-complexity.’

If I understand him correctly (and this is questionable), Barbour claims that the inevitable increase in the entropy of the universe, and its consequent heat-death, masks a simultaneous process of increasing shape-entaxy. Such entaxy is a potential for order in an otherwise chaotic universe. It is just such entaxy which allows the structure of galaxies, planets, and biological life, including ourselves to emerge from such background chaos. In a sense we already live in the cosmic end-times since “the total entropy of the black holes known to exist within the observable universe dwarfs the entropy of all the matter outside them.” Yet cosmic structures continue to thrive.

So Barbour wants to define time as the growth in complexity rather than the increase in entropy. And according to him (with such complexity that I do not understand it) this implies that the experience of time ‘emanates’ as it were from the point of the Big Bang. But, crucially, it does so in two directions, thus making the Big Bang a so-called Janus point. The ‘line’ on which the arrow of time travels is thus infinite in the past as well as the future. Only what we consider as the past on our side of the Janus point is future on the other side!

Lest I misrepresent what Barbour has to say, let me use his summary: “... the claim this book makes. It is not just that it proposes a new theory of time and with it a first-principles explanation of its arrows; it also aims to overturn the doctrine that it is entropic disorder on a cosmic scale that puts the direction into time. The claim is this: the direction gets into time not through the growth of disorder but through the growth of structure and complexity.” That much I understand.

But I must say that I don’t understand anything more about time that I did before the agony of reading The Janus Point over the last several days. Barbour claims that time is “... ultimately a measure of the difference of shapes, both on the cosmic scale and within well-isolated emergent subsystems.” Really? And as a human being I perceive this how? I’m sure it’s very important to understand. That I don’t is a burden I must endure.

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