The Problem of Time

One of my favourite films is The Truman Show. It tells the story of a young man’s growing realisation that his whole life has been scripted, and he is in fact the unwitting star of a reality television show about his own life. When the creator of the show, Christof, is asked in an interview about why he thinks Truman has never suspected anything, the response is illuminating: “We accept the reality of the world with which we are presented”. We assume that what appears to be true about our world is. It is only when we notice glaring anomalies, when the weight of the evidence against our assumptions can no longer be explained away or ignored, that we revolutionise our paradigms.

We tend to accept that inhabited time is real time. Yesterday happened, we are living now and tomorrow is yet to come. Children grow into adults. Summer gives way to winter.  Days turn into weeks, turn into months, then into years. Things persist for a while and eventually end. Our lives seem to follow a very simple trajectory through time, from birth to death.

Only time is not quite that simple. When you begin to delve into Physics, it becomes apparent that we have to draw a very definite distinction between time and our experience of it. The history of physics has repeatedly compelled us to reshape the way we understand time. And whenever we have done so, the universe has become a little stranger.

For Newton, time was an absolute, flowing independently of everything else.  If space was a stage, time was the clock hanging above it. The actors strut and fret their hour upon the stage, full of sound and fury, signifying nothing. Time, in Newton’s universe, is the great equaliser.  

But Einstein’s theories of relativity changed everything. The stage and the clock are the same thing. No two actors will experience time in precisely the same way because they move differently and are located differently on the stage. There is no universal “now”. If we are able to assume simultaneity it is because we occupy roughly the same position on the stage – the same planet, orbiting the same star within the same galaxy. The differences in our individual rates of movement through space are negligible, so our “now”s seem similar. Star Trek never accounted for how starkly different our experiences of time would be from those we left behind if we were to boldly go off at warp speed.

Imagine you must move 1 kilometre in any direction. If you moved directly north, the co-ordinates of your end location would contain no east bearing at all. You would achieve the maximum possible northerly bearing of 1 km north. If you moved directly east, there would be no northerly bearing at all and you would attain the maximum possible easterly bearing of 1 km east. If you moved anywhere in between, you would divide your 1 kilometre between northward and eastward motion and arrive at a bearing somewhere in between, neither fully 1 kilometre north nor fully 1 kilometre east.

Movement through time and space works in the same way. Everything moves through spacetime at the same invariant rate. A massless particle directs all of that motion through space, so none of it is directed through time. A massive object always directs some portion through time. And the more it directs through space, the less remains for time.

Since a photon is massless, it moves through the vacuum of space at the maximum possible rate (what we have come to term ‘the speed of light’). And since it moves at the maximum rate through space, this means that at the speed of light there is no time. From the perspective of a photon, if a photon could have a perspective, light leaving a distant galaxy would arrive at earth at precisely the same instant that it left. The instant of emission and the instant of absorption would be identical.

Relativity presents us with a four-dimensional spacetime, where events have a location in both space and time. The most common philosophical interpretation of this among physicists is the “block universe”, where the past, present and future are all parts of the four-dimensional structure.  In much the same way that Cape Town and New York exist simultaneously at different locations in space, my childhood and my adulthood can be understood as different locations in spacetime.

But if time is a block, why do we seem to move in one particular direction? Why do we remember the past but not the future?  If many fundamental laws work the same way whether backwards or forwards, why do we experience the flow of time only as from past to future? Why do people grow old? Why do stars inevitably burn out and die? If the fundamental laws of physics do not distinguish between the past and the future, why does the universe seem to do so?

The answer, it would seem, is entropy. Statistical asymmetry, not any fundamental direction in the laws, is why stars burn out and people age. The arrow of time is not written into the equations; it emerges from the overwhelming probability of certain configurations over others. Systems evolve toward macrostates that have more available microscopic configurations: there are many more possible configurations corresponding to a shattered glass on the floor than to an intact one on the table.

Quantum mechanics observes that at a fundamental level the building blocks that make up the universe operate probabilistically. A photon moving from point A to point B does not do so simply by going in a straight line, Feynman notes. Rather, it takes every possible path there simultaneously. It exists in every possible position until it is measured. It will move along an infinite number of possible paths all at the same time. But most of these paths interfere with each other and cancel out, so that the observable paths are the ones in the narrow band where they do not.

We have two Truman Show moments: Einstein’s general relativity that compels us to reconsider our experiences of spacetime, and quantum mechanics that suggests a frankly quite disturbing redescription of physical reality. In both cases, the world we thought we inhabited turned out to be a stage, and we the unwitting actors. Physicists have spent decades trying to bring these two enormously successful theories into a single framework. Once you have seen the spotlight falling from the sky and noticed the routine patterns in your morning commute, you need to find a new story that makes sense of your world.  

In 1967, two physicists, John Wheeler and Bryce De Witt, met for coffee at the Raleigh-Durham airport in North Carolina and tried to do just that.  Wheeler had time to kill between flights and invited his friend to join him in this endeavour. While most mere mortals would pass the two-hour layover time by doing a crossword or enjoying a nice piece of carrot cake, John Wheeler decided to reconcile general relativity with quantum mechanics. To each their own.

The result was an equation describing the wave function of the universe that contains a startling feature: there is no external time parameter. This has become one of the central puzzles in quantum gravity, known as “The Problem of Time”. One plausible interpretation is that time may not be a fundamental property of the universe at all, but one that emerges from a deeper level of physical reality. The fundamental equation of the universe could describe a timeless state that does not evolve or change but simply is.

Which brings me back to the eddy. And the essence of my third fragment: perhaps a life is like an eddy: a pattern that persists at a specific location in spacetime. But spacetime, certain interpretations of the Wheeler-De Witt equation suggest, may itself be a pattern that emerges from something more basic. And if time is emergent rather than fundamental, then the sequence from birth to death would be a feature of the emerged level, not the fundamental one. Perhaps neither things nor time are quite as fundamental as our experiences would suggest.

Would it be fair of me to suggest, then, that death is not the end of a thing travelling through time, but the ending of one particular pattern within a reality whose deepest nature may lie beyond time altogether? And if that is indeed the case, if we are temporary patterns within a reality deeper than the time we experience, what is this peculiar kind of pattern that can not only exist, but know that it exists?