Exhibition: Philosophy in the Open

Williams and Sciama debate how far the notion of time as it occurs in physics may depart from the common-sense conception of time. Williams holds that there are certain common-sense beliefs about the features of time that are so fundamental that if we say time does not have these features, we aren’t really talking about time at all. Sciama says he does not set too much store by common sense. Some of what common sense tells us about time just has to go, he argues. On some points, Williams agrees. He would be ‘jolly silly’, he says, if he didn’t accept that special relativity erodes the common-sense idea of absolute simultaneity. Nevertheless, the notions of before and after, he proposes, are elements of the common-sense conception that seem partly definitive of time. If physicists dropped these notions, they wouldn’t be talking about time at all. Sciama thinks Williams begs the question. We cannot ask, of the parameter physics offers a characterisation of, ‘But is that really time?’, for the issue is what time really is.

 

This segues into a discussion of the Gödel universe, in which it would be possible for an object to take a journey into its future and arrive in its own past. Each time in such a loop is both before and after itself. Williams thinks this is ‘demonstrably self-contradictory’. For example, a person who at some time travels in a spaceship both has and has not travelled in a spaceship yet.  Whilst there are points on which Williams and Sciama agree, they disagree over whether the application of the concepts ‘before’ and ‘after’ that the Gödel-universe demands is coherent. Ordinarily, we think these relations are transitive, asymmetric and irreflexive. If A is before B and B is before C, A is before C; if A is before B, B is not before A; A is not before A. Williams mistakenly says the Gödel-universe would abandon transitivity – in fact, it abandons asymmetry and irreflexivity. But his point remains the same: without before and after as we know them, there can be no such thing as time.

 

Sciama holds that ‘before’ and ‘after’ have local application – isolate any one ‘stretch’ of the loop, such as the life of a particular creature, and we can treat time as if linear. He does, then, have a satisfactory answer to the challenge Williams pushes, of what makes the parameter physicists are talking about time (or at least time-like, as opposed to space-like). But to demonstrate that there is something time-like in the Gödel-universe, Sciama appeals to its local conformity to a common-sense conception – just as Williams argues we must. Interestingly, Sciama seems to prefer to describe the Gödel-universe as having no global before and after, rather than to countenance the idea of before- and after- relations that are symmetric and reflexive. He seems to share Williams’ thought: that way, contradictions lie. In this way, he implicitly concedes much to Williams’ position.

 

Perhaps both overestimate the specificity of common sense concerning time? If time behaves locally as linear in the Gödel universe, and the local, which informs common sense, is all any creature experiences, then common sense holds only that time may as well be linear, so far as everyday ends go. Likewise, Williams and Sciama are both quick to take the abandonment of absolute simultaneity as doing violence to common-sense. But does common sense have an opinion on this? Common sense is informed not by the assumption that there is absolute simultaneity, but by the fact that there may as well be so far as most everyday ends go.