Friday, 30 August 2013

Rebirthing Pains

[From Science, 30 August 2013; full details and link to published version]

Lee Smolin likes big targets. His last book, The Trouble With Physics, took on the string theorists who dominate so much of contemporary theoretical physics. It was my engrossing in-flight reading on a trip to the Perimeter Institute a few years ago, where I first met its rather engaging author in person. I thoroughly enjoyed that battle, from my distant philosophical vantage point – “Pleasant is it to behold great encounters of warfare arrayed over the plains, with no part of yours in the peril,” as Lucretius put it (1). But now things are more serious: in Time Reborn Smolin has my team in his sights, and some part of mine is certainly in the peril, if he emerges victorious. Should I now be feeling sorry for the string theorists?

I’ll come back to that question, but first to the dispute itself, which is one of philosophy’s oldest feuds. One team thinks of time as we seem to experience it, a locus of flow and change, centered on the present moment – “All is flux”, as Heraclitus put it, around 500BC. The other team, my clan, are loyal instead to Heraclitus’s near contemporary, Parmenides of Elea. We think of time as it is described in history: simply a series or “block” of events, lined up in a particular order, with no distinguished present moment. For us, “now” is like “here” – it marks where we ourselves happen to stand, but has no significance at all, from the universe’s point of view.

Which side is right? Both teams have supporters in contemporary philosophy, but we Parmenideans claim powerful allies in modern physics, commonly held by physicists themselves to favour the block picture. Einstein is often quoted as one of our champions. In a letter to the bereaved family of his friend Michele Besso, Einstein offered the consoling thought that past, present and future are all equally real only from our human perspective does the past seem lost: “We physicists know that the distinction between past, present and future is only an illusion, albeit a persistent one,” he wrote. (For this, Karl Popper called him “the Parmenides of modern physics”. Smolin, too, quotes this letter, though he also claims evidence for a more Heraclitan Einstein, in some remarks reported by the philosopher Rudolf Carnap.)

On the other side, some Heraclitans are so sure of their ground that they insist that if Einstein is right – if the distinction between past, present and future is not objective – then time itself is an illusion. Accordingly, they interpret the block view as the claim that time is unreal. In a celebrated paper from 1951, the Harvard philosopher D. C. Williams (following Wyndham Lewis) called these folk the “time snobs”: “They plume themselves that . . . they alone are ‘taking time seriously’,” as Williams puts it (2).

To Parmenideans such as Williams and myself, this attitude is just linguistic imperialism, cheeky and rather uncharitable. Of course we believe that time is real, we insist. (It is as real as space is, the two being simply different aspects of the same four dimensional manifold.) What we deny is just that time comes carved up into past, present and future, from Nature’s point of view. On the contrary, we say, “now” is just like “here”: it all depends where you stand.

I’ve mentioned this because Smolin is a classic time snob, in Williams’ terms. When he says that he is defending the unpopular view that time is real, he means time in the time snobs’ proprietary sense. This makes him sound like a defender of common sense – “Of course time is real, what could all those clever folk have been thinking?”, the reader is being invited to think – whereas in fact the boot is on the other foot. It is Smolin’s view that trips over common and scientific sense, denying the reality of what both kinds of sense take for granted.

To explain why, and to bring these issues down to earth, suppose that I ask you to tell me what you did last week. You give me some of the details, telling me a little about what happened to you, what you did, on each of those seven days. I can press you for more details – the conversation might go on for a long time! – but can I complain that you haven’t told me which day (or minute, or second) last week was the present moment? Obviously not: each moment was present when it happened, but they all have this feature in common – no single moment is distinguished in any way from all the others. Have I denied that there was time last week? Again, obviously not. Like any other week, after all, it contained 168 hours of the stuff! And the week wasn’t static – events happened, things changed.

So we can make perfectly good sense of time without picking out one moment as the present moment. We do it all the time, when we think about other times. And there’s nothing more radical to the block universe view than the idea that science should describe reality in the way that we just imagined describing last week, leaving out altogether the idea of a present moment, and hence a division between past and future. For the universe, as for last week, this is perfectly compatible with thinking that time is real, that events happen, and all the rest of it.

Again, D. C. Williams was beautifully clear about this, in his challenge to the time snobs. Here he is, pointing out that nothing that matters is missing from the block view:

Let us hug to us as closely as we like that there is real succession, that rivers flow and winds blow, that things burn and burst, that men strive and guess and die. All this is the concrete stuff of the manifold, the reality of serial happening, one event after another, in exactly the time spread which we have been at pains to diagram. What does the theory allege except what we find, and what do we find that is not accepted and asserted by the theory? 

Thus the block picture is simply a view of time from no particular time, just as a map depicts a spatial region from no particular place. (In both cases, we can add a red dot to mark our own position, but the map is not incomplete without one.) It no more makes time unreal than maps make space unreal.

To deny this, to squeeze the obvious fact that we can talk about other times (like last week) into their peculiar present-centered cosmology, Heraclitans need to resort to desperate measures. They need to insist that when we seem to be talking about last week, or Einstein, or the history of the universe since the Big Bang, we are really talking about something in the present moment – our present evidence, perhaps.

Some brave Heraclitans are prepared to go this far, and Smolin may be inclined to follow them. As he puts it at one point, his view is that “the past was real but is no longer real. We can, however, interpret and analyze the past, because we find evidence of past processes in the present.” But this is a little slippery. What are we interpreting and analysing, exactly, and what is all this evidence supposed to be evidence about? Like other Heraclitans, Smolin faces a dilemma. If history – the study of the past – can be taken at face value, as attempting to describe something other then the present moment, then it’s a model for the block view of the universe, in the way I have indicated (and shows how misleading it is to say that such a view is timeless). If not, then the proposal is much more radically revisionary, much more out of line with common sense, than Smolin seems to appreciate.

True, Smolin would not be alone in going to this extreme. At the same meeting at the Perimeter Institute where I first met Smolin himself, I heard a distinguished quantum theorist insist that the past is just a model we invent to make sense of present evidence, and not to be taken literally (3). As I remarked at the time, this kind of attitude soon gets out of hand – I said that I felt myself tempted to conclude that the distinguished speaker, too, along with the rest of the audience, were just aspects of a model I had constructed to make sense of my own evidence (no more to be taken literally than talk of what we all did yesterday). The time snobs’ chauvinism of the present moment slides easily into solipsism.

So I have grave doubts whether Smolin’s version of the Heraclitan view is any more plausible than its predecessors. And yet it has a tragic quality that other versions of the view mostly lack, for Smolin regards it as the gateway to promising new physics. I haven’t said anything about these interesting ideas, which I’m not so well qualified to assess, but the tragedy lies in the fact that they seem entirely compatible with the block universe view, properly understood. The main idea is that the laws of physics can change from one time to another, and – leaving aside any special issues about the mutability of laws – we saw that the block universe can accommodate change as well as its rival. “Rivers flow, winds blow, . . . men strive and guess and die,” as Williams puts it. Laws change, too, perhaps, if Smolin is right, but this too would then be part of “the concrete stuff of the manifold, the reality of serial happening, one event after another.” If so, then Smolin’s campaign against the Parmenideans is entirely unnecessary, a great waste of energy and brain hours!

I think Smolin would reply that it is essential to his proposal that the way in which laws evolve not be deterministic, that there be genuine novelty, and that the block view doesn’t allow this. But although many people assume that the block picture is necessarily deterministic, this is simply a mistake (“albeit a persistent one”, as Einstein might have put it). There is no more reason why the block view should require that the contents of one time be predictable from a knowledge of another, than it is somehow a constraint on a map of the world that the topography at the Tropics be predictable from that at the Equator. I can think that there’s a fact about what I had for lunch last Tuesday – or will have for lunch next Tuesday – without thinking that there’s any decisive present evidence about these matters, such that Laplace’s demon could figure it out, based on what he could know now.

So Smolin is fighting an enemy with whom he has no real reason to disagree, in my view. He is opposing a conception of time that if not actually on his side, is certainly not in his way. And in waging this wholly unnecessary battle he is aligning himself with a team whose own weaknesses – and misunderstandings of their rival – have been apparent for many decades. If I’m right, then he’s shooting himself in the foot, big time. 

Coming back then to the question at the beginning, how do I feel? Do my parts feel in peril in Time Reborn, and should I now be feeling sorry for the string theorists? I wish I could say “yes”, but my main sense isn’t peril, but sadness: sadness for the reason just mentioned, the tragic unnecessity of Smolin’s campaign, but also sadness (and some embarrassment) that my home side – I mean Team Philosophy, now – has not succeeded in making these things clear. (“Must do better”, as a distinguished Oxford colleague put it recently (4).)


1. Lucretius, De Rerum Natura, W. H. D. Rouse, Trans. (Harvard Univ. Press, Cambridge, MA, 1975).
2. D. C. Williams. 'The myth of passage'. J. Phil. 48 457–472 (July 1951).
3. N. David Mermin. 'Confusing Ontic and Epistemic Causes Trouble in Classical Physics Too'. PIRSA:09090077 (Perimeter Institute, Waterloo, 2009).

4. T. Williamson. 'Must do better'. In Truth and Realism, P. Greenough, M. P. Lynch, Eds. (Oxford Univ. Press, Oxford, 2006), pp. 177–187.


This is the author’s version of this work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science, Vol. 341 no. 6149 (30 August 2013), pp. 960-961, DOI: 10.1126/science.1239717, and is accessible via these links: full text; reprint.

For some earlier thoughts on these topics, see this piece, written with my former Sydney colleague, Jenann Ismael.