Grace Weir
Published for Time tries all things, Institute of Physics, London 2019


Fay Dowker

There is a trope about physics — modern physics, quantum mechanics and relativity in particular — that it shows that the physical world is not as it seems. The crucial question being begged in the trope — how does the world seem? — is uncovered in this famous exchange between philosophers Elizabeth Anscombe and Ludwig Wittgenstein:

He once greeted me with the question: 'Why do people say that it was natural to think that the sun went round the earth rather than that the earth turned on its axis?' I replied: 'I suppose, because it looked as if the sun went round the earth.' 'Well,' he asked, 'what would it have looked like if it had looked as if the earth turned on its axis?'1

In the context of a world view in which we conceive of the earth as fixed, what we perceive is evidence of the sun going around the earth, but in the context of a world view in which the sun is fixed, what we perceive is evidence of the earth turning on its axis. We cannot analyse perception except in the context of the world view of the perceiver. Thinking a little further, the trope is revealed to be self-contradictory: a successful scientific theory, or world view, cannot be inconsistent with our experiences. If a theory cannot be brought into coordination with our experiences, then we give up the theory and look for a better one.

On the subject of “time”, however, there is no consensus on whether our perceptions can be coordinated with our current best scientific world view. We perceive time passing and make sense of our lives within the context of a fixed past that has happened and an open future that hasn’t happened yet. But the dominant view amongst theoretical physicists is that the Universe is a Block in which the future already exists and time doesn’t pass. The physical theory in question is General Relativity, Albert Einstein’s theory of gravity and spacetime, within which it is natural to adopt a Block view of the Universe as an unchanging, four-dimensional whole, including all past, present and future events.

There is a vast academic literature on attempts to coordinate our subjective perception of the passage of time with elements within a timeless Block in which the future is as real as the past. Many thinkers consider it has been achieved to their satisfaction. But some remain adamant that none of this work hits the mark. Philosopher of physics Tim Maudlin remarks that it is a strange world in which he can put food on the table by going around claiming that time really passes.

Can consensus be reached? We have to wait and see. In the case of the sun-earth system of the Anscombe-Wittgenstein exchange, one of the two world views is quantitatively, scientifically better than the other: the earth spins on its axis, we now agree. In the case of the debate over the nature of time, there is as yet no competitor theory to GR and we must now speculate about future physics: will there be, in the future, a quantitatively better way to understand spacetime than General Relativity, a new theory in which time does physically pass and the world is not a Block?

That this is a possibility is indicated by progress within one approach to the problem of Quantum Gravity, the problem of incorporating General Relativity and quantum mechanics into a unified theory. The approach, due to physicist Rafael Sorkin, is based on the proposal that, at very small scales, spacetime is granular and atomic, not smooth and continuous. The atomicity allows our four-dimensional spacetime to come into being, to grow, by accretion as it were, via a continual process of births of the individual spacetime atoms. It is this birth process, this Becoming, Sorkin suggests, that is the physical, objective correlate of our subjective perception of the passage of time.

We do not yet know if this physics of atomic spacetime will be successful. It requires new thinking along lines we probably can’t foresee. How do we break out of old ways of thinking and create new knowledge that yet remains disciplined by and true to all that we already know? We need to understand our current best theories, General Relativity and quantum theory, as well as we can. But we ought also to pay attention to different traditions of thought, to avail ourselves of the conceptual fruits of all of human intellectual labour across the centuries. Sorkin points out, for example, that the Vibhajavadin school within the Buddhist philosophical tradition contemplates the notion of accretive time and we would do well to consider whether such traditions offer us insights and further concepts we can use in our quest for understanding.

We can also look to art, music and literature to inspire and to challenge, to give us new worlds to contemplate. In Alan Moore’s novel “Jerusalem”, the first chapter is prefaced by the Anscombe-Wittgenstein exchange on the sun and the earth and the whole novel is, I believe, Moore’s vision of an answer to the question “How would it look, if it looked as if the Universe were a Block?” Grace Weir’s “Time Tries Truth” is both a sculpting in time and a weaving in dialogue which hints at the multiplicity of alternative histories for a quantum world, histories that interfere with each other to produce, by a process we do not yet comprehend, a world which might be an answer to every physical question we could possibly ask.

G.E.M. Anscombe “An Introduction to Wittgenstein’s Tractatus,” Hutchinson, London, 1959

2. I can’t resist pointing out that, from a Block world view, whether or not this is so is already the case in the really existing future. Does this mean that a Block view precludes one from considering even the possibility that there might be progress in physics which is not Block-y?