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Book Review: The Janus Point, Julian Barbour

March 6, 2021
The Janus Point: A New Theory of TimeThe Janus Point: A New Theory of Time by Julian Barbour
My rating: 4 of 5 stars

This book is largely about an attempt to reenvisage the concept of entropy to fit it into a view of the universe as, due to the constant expansion, being more like an open system, rather than a closed system like a box with walls that particles can bounce off. Entropy is normally viewed in relation to this latter view of things. Now this can work well for localised thermodynamic systems, but is misapplied to the universe as a whole, according to Barbour.

As a result this allows him to think more positively about how entropy may apply to the universe overall, in which the arrow of time does not lead us to a heat death style conclusion to the universe, of things becoming more disorganised and equilibrating, like in an isolated thermodynamic system, but instead the arrow of time means continual expansion as in the big bang, but locally also it leads to perpetual complexification of island like entities within that expanse, such as planets, galaxies etc. It suggests this local internal complexification can continue without end into the future.

Part of the way he shows this is through viewing space and time in a purely relational manner, true to Leibniz’ insight and concern all those years ago in his argument with Newton over the fact that absolute space and time disobeys the principle of sufficient reason and the principle of identity of indistinguishables. Barbour aims to work in line with these principles to try and provide a different way of envisaging what the big bang means, and what an origin to the universe could mean. This is what the Janus point is meant to represent.

He tries to work in line with these principles, to provide a background independent understanding of the basic “being” of the cosmos, as opposed to the at times ad hoc “past hypothesis”, relied upon by many in the standard interpretation of times arrows in line with typical closed-box entropy, and the work of those in string theory that is not background independent and relies only on the principle of non-contradiction, allowing them to end up with many different consistent and mutually exclusive interpretations of what basic reality may be, making it seem more like a mathematical game or model, rather than dealing with fundamental reality of the cosmos.

Part of the way he goes about it all, gets into complex mathematics in relation to N-body and 3-body problems, and kepler pairs, in which out of basic triangular relational snapshots of what he calls shape space, a system can develop to allow our regular notions of time and space to emerge. I couldn’t comment much on this more purely mathematical aspect. Only to say it would be something of importance to see more experts in this field look into and check over and verify or falsify some of his results.

In the larger philosophical picture and physical picture, I find this idea of returning to certain basic principles of reason very attractive in our envisaging of the cosmos. As opposed to relying on arbitrary starting points of something from nothing, or ad hoc postulation of principles to fill gaps in the reasoning, like with the standard account of the big bang and the past hypothesis. However, there are some issues remaining, such as quite what he means by this “law of the universe”, preceding the more regular and emergent laws of nature and physics we commonly see, that he evokes often to defend his position, and what experimental proofs or falsifications of his theory there could be, because not many are supplied.

Unlike Roger Penrose, who suggests a more clear empirical test of this kind in relation to his conformal cyclic cosmology. I was also surprised that he did not contrast his view with the view of Penrose, for all he says is that he sees Penrose’s “closed box” account of entropy and thermodynamics as misguided in line with the standard model. But does not talk of his CCC at all. At times, he seems to be taking some digs at Roger Penrose in general, without himself offering something much clearer. And really it seems to me these two should be finding much common ground in their views of reality and of mathematics.

It would be interesting to see Roger Penrose’s response to this cosmological perspective of Julian Barbour and the Janus point, however, given he does not seem much taken by the idea of going for a purely relational view of space and time, it may be hard to reconcile their approaches from the very foundations.

A lot to ponder, and certainly it addressed some of the concerns I have always had with the standard account of the big bang, past hypothesis and heat death of the universe, where, aside from the negative consequences for our future being, it seemed to rely on arbitrary and unproven elements and misguided extrapolations from localised phenomena.

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