The End of Time: The Next Revolution in Physics

The three-dimensional snapshots I have in mind could be constructed if many different people took ordinary two-dimensional snapshots of a scene at the same instant. Comparison of the information in them makes it possible to build up a three-dimensional picture of the world in that instant. That is what I mean by a Now. It is very remarkable that such completely different two-dimensional pictures can be reconciled in a three-dimensional representation. The possibility of this ordering is what leads us to say that things exist in three-dimensional space. It leads to an even deeper ‘knitting together’ over and above the directly experienced sense of being aware of many different things at once (it is this that enables us to know instantly that we are seeing, say, six distinct objects without counting them individually). I regard space as a ‘glue’, or a set of rules, that binds things together. It is a plurality within a deep unity, and it makes a Now.

You may object that no experience is instantaneous, just as snapshots require finite exposures. True, but we can still liken instants to snapshots. It is the best idealization I know. It allows us to begin to get our hands on time, which is otherwise for ever slipping through our fingers. As instants, rather than an invisible river, time becomes concrete. We can pore over photographs, looking for evidence in them like military intelligence analysts studying satellite pictures. We can imagine ‘photographing’ our successive experiences, obtaining innumerable snapshots. Using them, we can identify the most important properties of experienced time.

THE PROPERTIES OF EXPERIENCED TIME

Suppose that the snapshots are taken when we are witnessing lots of things happening, say people streaming past us in a street, and that the snapshots (either two-dimensional, as directly experienced, or ‘three-dimensional’, as explained above), once taken, are jumbled up in a heap. A different person, given the heap, could relatively easily, by examining the details in the snapshots, arrange them in the order they were experienced. A movie can be reassembled from its individual frames. My notion of time depends crucially on the details that the ‘snapshots’ carry. It requires the richly structured world we do experience.

This imaginary exercise brings out the most important property of experienced time: its instants can all be laid out in a row. They come in a linear sequence. This is a very strong impression. It is created not by invisible time, but by concrete things.

It is harder to pin down other properties. I have already mentioned the difficulty of saying precisely what the powerful impression of moving forward in time consists of. We also have the intuition of length of time, or duration. Indeed, seconds, minutes, hours dominate our age, though you may not know how these precise notions have arisen. That is an important issue. Finally, there is the remarkably strong sense that time has a direction. A line traced in the sand does not by itself define a direction. If time is a line, it is a special one.

The evidence for time’s direction is in the ‘snapshots’. Many contain memories of other snapshots. We can do a test on time. We can stop at one of our experienced instants laid out in a line, and see that it contains a memory. We locate the remembered instant somewhere in the line. That defines a direction – from it to the memory of it. We can do this with other pairs of instants. They always define the same direction. Many other phenomena define a direction. Coffee cools down unless we put it in the microwave; it never heats up. Cups shatter when we drop them; shards never reassemble themselves and leap back up onto the table as a whole cup. All these phenomena, like memories, define a direction in time, and they all point the same way. Time has an arrow.

Thus, experienced time is linear, it can be measured and it has an arrow. These are not properties of an invisible river: they belong to concrete instants. Everything we know about time is garnered from them. Time is inferred from things.

NEWTON’S CONCEPTS

In 1687, Newton created precise notions of space, time and motion. Despite major revisions, much of his scheme remains intact. It is still close to the way many people, including scientists, think about time.