Essays
Published in In my own time, Science Museum London, ISBN 978 1 900747 63 9

Time Moves On
Janna Levin

We all share a simple yet enigmatic observation about the universe. We all observe the unremitting, forward motion of time. I am sitting in the Denys Wilkinson Building on Keble Road in Oxford and it is raining. I am watching the rain fall. It is happening in time and time never flows the other way. The rain doesn’t drip back up. I remember having been here in this room in this building in this place in space before, years ago. In the past. My knowledge of the past isn’t perfect, granted, but it is knowledge. I know things about the past in a way that I will never know things about the future. Time separates irrevocably into a past and a future at an impermanent instant that pierces forward at an unstoppable pace. Time moves forward one second every second, one hour every hour, one billion years every one billion years.

In her film, A little bit of unknown, Grace Weir re-presents to me the theory of black holes. It’s a documentary. Or an experience. An observation. Or a suggestion. She walks up the stairs to the Denys Wilkinson Building on Keble Road in Oxford. She goes through the doors I have just gone through, takes the elevator I have just taken, alights at the seventh floor as I just have. Grace wasn’t there when I went through the doors, into the elevator and walked the corridors of the seventh floor because we were at here at different moments in time. I am unable to march backwards along that dimension of time and collide with her.

This is my lived experience of time. It is obvious and simple enough to describe. There is a basic commonality to this experience, although not every aspect of that experience is shared in common. An astronaut in a rocket ship traveling near the speed of light might experience the passage of one second for every one of my hours, one hour for every several days, geological time scales over the age of the universe. But still, to that astronaut, every second will seem like an ordinary second and every hour will be experienced as a regular hour. There will be an acquisition of an imperfectly remembered past and an unknowable future. And time will push forward every bit as ruthlessly as it does for me.

In that lived experience of time, my own mind becomes a kind of clock. I sense the passage of time from the passage of my thoughts, the firing of neurons, the change in a configuration, the alteration that ensures something is different and time has passed. Our minds are unable to hang on to the smallest moment – “A moment is the timeless border between past and future”. Unable to suspend a moment for inspection, Weir reminds us that even in the subtlest detection of the passage of time, the sequence of infinitesimal instants recorded in these films, “the question arises: `what is new?’” And we have a strong feeling for the order in which new things should occur. Time flows in the direction of increasing disorder. We all know this intuitively. If we watch a film of a moldy pulp of juice assemble into a fruit, we know that the film was running in reverse. If we watch a decayed ruin drift piece by piece into a pristine building, we know the film runs backwards. The natural direction of least effort is in the direction of the increase of disorder. Creation of order takes effort. Building a structure, assembling apparatus, arranging words on a page, all take effort.

In the film In my own time, Grace Weir insightfully picks out this significant and elegant physical principle: The principle of least action. She asks, `Does nature have an economic sense? Is there a minimum of effort involved?’ A bead of rain follows the jagged path of least effort along a wet window, mimicked by a car that rolls along a lumpy dirt path. All natural processes obey a principle of least effort. Weir films her own process, setting chairs in a field, fixing a laser with tape to a stand, and her movements are not rushed, the process obeying a simple principle of its own. Time is parsed out in our gestures, the simple actions, the effort to set up an experiment with lasers and mirrors, our experience of time measured in the duration of a film, the opening of a door, the milking of a cow.

Some of grace\'s films nearly defy the arrow of time. There are scenes in Grace’s film, A little bit of unknown, that could run equally well forwards or backwards. There is a scene out the window, it could be a still shot, until we see the trees swaying and the clouds drift to the left. Something is different. Something is new. But there is no way to know from the motion if the trees are swaying forward into the future or backwards into the past. Neither would seem to take more effort and neither shows distinct signs of an increase in disorder. In another shot, we look through the light into a dark stairwell at St. John’s College. It could almost be a still scene. One image with no passage of time. But then we see dust motes move randomly in the light. Time is passing. But we cannot know which way.

Then we see Paul Tod write on paper and we know that if there are more letters on the page then time has clicked forward, the letters taking effort to assemble. We hear his quietly expressed yet grand explanation of black holes and we recognize the effort to create a logical narrative from beginning to end and we know that time has moved forward. We watch Grace climb stairs and open doors and set a telescope in motion and we know from the effort which way time flows. But in the short timescale we have to watch them, not the trees, or the dust, or the clouds, or the sun, or the stars, gives us clues as to the arrow of time.

If we could watch for billions of years, the sun would expire as it runs out of the thermonuclear fuel that keeps it bright. Then we would know that the universe has aged. If one of the stars we see through the telescope’s lens at the end of the film was bigger, a few times bigger than the sun, then we could watch the formation of a black hole as the star died. The black hole becomes perfect and identical to every other black hole with that mass and spin. It is as perfect as a fundamental particle. As indistinguishable from every other black hole of that mass and spin as one electron is from another. It becomes ageless and timeless. (Quantum mechanics actually allows black holes to evaporate and so introduces an ageing process of sorts for black holes)

In Picture of a floating world, there are fewer clues. I could have been shown this film in reverse and I might not have sensed the distortion of the flow of time. I could have been suspicious of the petals that returned to the flowers from the ground, reordering themselves without effort – an impossibility we would all recognize as time running backwards. Unless the wind just kicked them back up into the trees, and the current pulled the fish back downstream, and the ducks floated on those same currents. The bubbles that frothed on the water like a solar system orbiting clockwise could equally well orbit counter-clockwise. But even the simplest reordering of events changes meaning. Is the woman pensive and calm as she contemplates the water, shifting to open and hopeful as she lifts her head and the blossoms disintegrate? Or does she move from contentment with the sun on her face, her eyes squinting, to a dark brood as she turns away and hangs her head?

In the animation A deep field for the time deaf, time measures distance, light traveling the path of least time. We wait in blackness for the light traveling nearly 3 hundred million meters per second to reach us from distant objects. First we see stars that are in our own galaxy and then we begin to see further – out to galaxies that are millions of light years away. Then we see the furthest, oldest objects whose light has been able to reach us in the entire age of the universe – early galaxies formed roughly a billion years after the big bang. We are seeing these galaxies as they looked in the past. We are separated from these islands of hundreds of billions of stars by vast distances in space and in time.

Outside my window the rain has cleared. I know it rained in the past precisely because of my knowledge of the rain. It’s a memory, not a future possibility. The trees are barely moving, maybe they are even the same trees as those in Graces’ film. The clouds move left but they could equally convincingly move right. From my view out these windows I can’t be sure that time is moving forward, other than my belief that it always has and so it is exceedingly likely that it is doing so at this juncture as well. But then, I’ve assembled words on a page that weren’t there before. It took some effort. It cost me some energy. I am slightly older as a result. My joints the tiniest bit more worn from the actions. The end of this page has definitely come after the beginning. And I know with certainty, as I could have predicted this morning, that time has inevitably moved on.