Читать книгу What is Metaphysics? - John Heil - Страница 20

What are the options? Some philosophers, the presentists, agree with McTaggart that temporal passage requires the A series, but regard this as a feature, not a bug. Only the present is real, the only moments are present moments. The present moment is not something that arrives from the future and recedes into the past. Because the future and past are not on a par with the present, nothing could literally be in the past or future, no moment could be past, present, and future, so there is no incoherence.

Anyone who embraced the four-dimensional block universe would see this kind of response as profoundly inadequate. A proponent of four-dimensionalism could agree with the presentists that McTaggart was right, both in thinking that temporal passage required the A series and thinking that the A series is internally flawed. McTaggart’s mistake was to suppose that, without temporal passage, without the A series, nothing is left deserving to be called time. Four-dimensionalists would respond that, what is unreal, what is a mere appearance, is not time, but the passage of time.

You do not need to be a four-dimensionalist to find temporal passage baffling. If time passes, at what rate does it pass? One second per second? Could time speed up or slow down, or pause, and for how long? If time passes or flows, this would require something for it to flow through. A river flows because the water it comprises moves relative to the terrain through which it flows. What would play the part of the terrain in the case of time?

Space, maybe? Aside from worries about the physics of spacetime, this would seem to be at odds with the conviction that space, and its occupants, are themselves in time, participants in the flowing. If the terrain flowed with the river, however, in what sense would the river flow?

I shall have more to say about the status of time in chapter 7. For the moment – ha! – the discussion will have served its purpose if it has convinced you that the problem of reconciling appearance and reality is inescapable, not something cobbled together by philosophers engaged in unconstrained flights of fancy.

The problem confronts scientists no less than ordinary citizens. Scientists rely on the appearances to build, test, and deploy instruments designed to probe reality. But it is hard to square the universe revealed by those instruments with the appearances. Difficulties we encounter in making sense of the appearance of time’s passing and of accommodating this appearance to the physics of spacetime are just two small pieces of a much larger puzzle.