Time is pretty mysterious stuff – almost as elusive and hard to pin down as conscious awareness itself. It seems to flow – ‘like an ever-rolling stream’ – but what is it that does the flowing? We have the feeling that the present is the only instant of time that actually exists. The past is a shadowy memory, the future a vague uncertainty. Physicists don’t see it like that. The present has no privileged status in their equations. Some modern physicists have gone so far as to describe the present as an illusion, a product of the observer’s mind.
For poets, time is anything but an illusion. They hear its wingèd chariot hurrying near; they aspire to leave footprints on the sands of it; wish there was more of it – to stand and stare; invite it to put up its caravan, just for one day. Proverbs declare procrastination to be the thief of it; or they compute, with improbable precision, the ratio of stitches saved in it. Archeologists excavate rose-red cities half as old as it. Pub landlords announce it gentlemen please. We waste it, spend it, eke it out, squander it, kill it.
Long before there were clocks or calendars, we – indeed all animals and plants – measured out our lives by the cycles of astronomy. By the wheeling of those great clocks in the sky: the rotation of the Earth on its axis, the rotation of the Earth around the sun, and the rotation of the moon around the Earth.
By the way, it’s surprising how many people think the Earth is closer to the sun in summer than in winter. If this were really so, Australians would have their winter at the same time as ours. A glaring example of such Northern Hemisphere chauvinism was the science-fiction story in which a group of space travellers, far out in some distant star system, waxed nostalgic for the home planet: ‘Just to think that it’s spring back on Earth!’
The third great clock in our sky, the orbiting of the moon, exerts its effects on living creatures mostly to a lunar calendar. The Pacific Palolo worm, Palolo viridis or Eunice viridis, lives in crevices of coral reefs. In the early mornings of two particular days during the last quarter of the moon in October, the rear ends of all the worms simultaneously break off and swim to the surface for a breeding frenzy. These are remarkable rear ends. They even have their own pair of eyes.
The same thing happens twenty-eight days later, in the last quarter of the November moon. So predictable is the timing that the islanders know exactly when to go out in their canoes and gather up the squirming rear ends of Palolo worms, which are a prized delicacy.
Notice that the Palolo worms achieve their synchrony not by simultaneously responding to a particular signal from the sky. Rather, each worm independently integrates cycles registered over many lunar cycles. They all do the same sums on the same data, so like good scientists they all come to the same conclusion and break off their rear ends simultaneously.
A similar story could be told of plants synchronizing their flowering seasons by integrating successively measured changes in day length. Many birds time their breeding seasons in the same way. This is easily demonstrated by experiments using artificial lights put on and off by time-switches to simulate artificial day-lengths appropriate to different times of the year.
Most animals and plants – probably all living cells – have internal clocks buried deep in their biochemistry. These biological clocks manifest themselves in all kinds of physiological and behavioural rhythms. You can measure them in dozens of different ways. They are linked to the external astronomical clocks, and normally synchronized to them. But the interesting thing is that if the biological clocks are separated from the outside world, they carry on regardless. They truly are internal clocks. Jet-lag is the discomfort we experience when our own internal clocks are being reset by the external Zeitgeber* after a major shift of longitude.
*The use of the German word for time-giver or synchronizer in the scientific literature reflects the fact that much of the classic work in the field was done in Germany.
Longitude is, of course, intimately linked with time. John Harrison's winning solution to the great longitude competition of the eighteenth century was nothing more than a clock that stayed accurate even when taken to sea. Migrating birds, too, make use of their own internal clocks for similar navigational purposes.
Here’s a lovely example of an internal clock. As you know, worker bees have a code with which they tell fellow hive members where they have found food. The code is a figure-of-eight dance, which they perform on the vertical comb inside the hive. There is a straight run in the middle of the figure of eight, whose direction conveys the direction of the food. Since the dance is performed on the vertical comb, whereas the angle of the food is in the horizontal, there has to be a convention. The convention is that the upward direction on the comb in the vertical plane stands for the sun’s direction in the horizontal plane. A dance with a straight run straight up the comb tells the other bees to leave the hive and fly dead towards the sun. A dance with the straight run 30° to the right of the vertical on the comb tells the other bees: Leave the hive and fly at an angle 30° to the right of the sun.
Well, that is remarkable enough, and when Karl von Frisch first discovered it, many people found it hard to believe. But it is true.* And it gets even better, and this brings us back to the sense of time. There’s a problem with using the sun as a reference point. It moves. Or rather, since the Earth spins, the sun appears to move (from left to right in the Northern Hemisphere), as the day advances. How do the bees cope?
*How it arose in evolution is a fascinating question. Von Frisch and his colleagues have compared the dance to various more primitive equivalents in other species of bee. Some nest out in the open and signal the direction of food by repeating a ‘take-off run’ in the horizontal plane, pointing directly towards the food source that they have discovered. Think of it as a kind of ‘follow me in this direction’ gesture, repeated several times to recruit more followers. But how did this get translated into the code used on the vertical comb, where ‘up’ (against gravity in the vertical plane) stands for ‘direction of the sun’ in the horizontal plane? There’s a clue in an odd quirk of the insect nervous system, demonstrated in insects as distantly related to each other as beetles and ants. First, a piece of background information (not the quirk): as I mentioned, many insects use the sun as a compass, flying in a straight line by keeping the sun at a fixed angle. This is easily demonstrated using an electric light to simulate the sun. Now for the quirk. Experimenters watched their beetle, or ant, as it walked over a horizontal surface, maintaining a fixed angle to an artificial light source. They then switched off the light, simultaneously tilting the horizontal surface into the vertical. The insect continued to walk, but switched its direction so that the angle to the vertical was the same as the previous angle to the light. I call it a quirk because the circumstance is unlikely to arise in nature. It is as though there is some kind of wire-crossing in the insect nervous system, which was convenient for exploitation in the evolution of the bee dance.
Von Frisch tried the experiment of trapping his bees in his observation hive for several hours. They went on dancing. But he noticed something which really is almost too good to be true. As the hours advanced, the dancing bees slowly turned the direction of the straight run of their dance, so that it would continue to tell the truth about the direction of the food, compensating for the changing position of the sun. And they did this, even though they were dancing inside the hive and therefore couldn’t see the sun. They were using their internal clocks to compensate for what they ‘knew’ would be the changing position of the sun.
What this means, if you think about it, is that the straight run of the dance itself rotates like the hour hand of a normal clock. But anticlockwise (in the Northern Hemisphere), like the shadow on a sundial. If you were von Frisch, wouldn’t you have died happy, to have made such a discovery.
The interesting thing is that if the biological clocks are separated from the outside world, they carry on regardless
Even after clocks were invented, sundials remained essential for setting clocks and keeping the synchronized with the great clock in the sky. Hilaire Belloc’s famous rhyme is, therefore, rather unfair.
I am a sundial, and I make a botch
Of what is done far better by a watch.
It is less well-known that Belloc wrote a whole series of verses on sundials, some humorous, some sombre, more in keeping with the ‘Fighting Time’ theme of our exhibition:
How slow the Shadow creeps: but when ‘tis past
How fast the Shadows fall. How fast! How fast!
Creep, shadow, creep: my ageing hours tell.
I cannot stop you, so you may as well.
Stealthy the silent hours advance, and still;
And each may wound you, and the last shall kill.
Save on the rare occasions when the Sun
Is shining, I am only here for fun.
I am a sundial, turned the wrong way round.
I cost my foolish mistress fifty pound.
You may think of this last verse when you look round the exhibition and see the exquisite little pocket sundial. It has a built-in compass, without which it would be useless.
When I talked of the great clocks in the sky, I did not go out beyond one year, but there are potential astronomical clocks of hugely longer period. Our sun takes about two hundred million years to complete one rotation around the centre of the galaxy. As far as I am aware, no biological process has become entrained to this cosmic clock.*
*Indeed, I would be very surprised if one were ever found.
The longest timekeeper that has been seriously suggested as being influential on life is an approximately twenty-six-million-year periodicity of mass extinctions. The evidence for this involves sophisticated statistical analysis of extinction rates in the fossil record. It is controversial and by no means definitely demonstrated. There is no doubt that mass extinctions happen, and at least one of them is pretty likely to have been caused by the impact of a comet, sixty-five million years ago when the dinosaurs perished. More controversial is the idea that such events rise to a peak of likelihood every twenty-six million years.*
*My speech made mention of a hypothetical astronomical clock to account for it, but I have deleted it from this reprinting because modern astronomers mostly discount it and there is no direct evidence for it. Briefly, the suggestion was that the sun mutually rotates around a binary companion star, called Nemesis, with a periodicity of about twenty-six million years. The gravitational effect of Nemesis was supposed to disturb the Oort cloud of planetesimals and increase the probability of one hitting Earth.
Another suggested astronomical clock longer than a year is the eleven-year sunspot cycle, which might account for certain cycles in populations of Arctic mammals, such as lynxes and snowshoe hares, as detected by Charles Elton, that great Oxford ecologist, in fur-trapping records of the Hudson’s Bay Company. This theory, too, remains controversial.
If you travelled through space at such a prodigious speeds you could return to Earth five hundred years into the future, having yourself scarcely aged at all
Director, you invited a biologist to perform this opening, so you will not be surprised to have been regaled with stories about bees and Palolo worms and snowshoe hares. You could have asked an archaeologist, and we’d all have been engrossed in tales on dendrochronology, or of radiocarbon dating. Or a palaeontologist, and we’d have heard about potassium-argon dating, and about the near-impossibility, for the human mind, of grasping the sheer vastness of geological time. The geologist would have used one of those metaphors with which we struggle – and usually fail – to understand geological deep time. My own favourite one I didn’t invent, I hasten to add, although I did use it in one of my books. As follows:
Fling your arms wide to represent the whole history of evolution from the origin of life at your left fingertip to the present day at your right fingertip. All the way across your midline to well past your right shoulder, life consists of nothing but bacteria. Animal life begins to flower somewhere around your right elbow. The dinosaurs originate in the middle of your right palm, and go extinct at your last finger joint. The whole story of Homo sapiens and our predecessor Homo erectus is contained in the thickness of one nail-clipping. As for recorded history; as for babylon, as for the Assyrian who came down like a wolf on the fold, as for the Jewish patriarchs, the legions of Rome, the Christian Fathers, the dynasties of Pharaohs, the Laws of the Medes and Persians which never change; as for Troy and the Greeks; as for Napoleon and Hitler, the Beatles and the Spice Girls, they and everyone that knew them are blown away in the dust from one light stroke of a nail-file.
If I had been a historian, I would have told stories of how different peoples have perceived time. Of how some cultures see it as cyclical, others as linear, and how this influences their whole attitude to life. Of how the Islamic calendar is based upon the lunar cycle, where ours is annual. Of how clocks used to be made, in the days before before Galileo used his own heart as a clock to work out the Law of the Pendulum, and engineer perfected escapements. I would have added that the Chinese had an escapement clock, driven by water, as early as the tenth century AD.
I would have remarked how the calibration of Egyptian water clocks had to be different at different times of year, because the Egyptian hour was defined as one twelfth of the time between dawn and dusk – so one summer hour was longer than one winter hour. Richard Gregory, from whom I learned this singular fact, remarks, mildly, that ‘this must have given the Egyptians a rather different sense of time from ours . . .’.
If I had been a physicist or cosmologist, my reflections on time would have been perhaps most remarkable of all. I would have tried – and probably failed – to explain that the Big Bang was not only the beginning of the universe, but the beginning of time itself. To the obvious questions, what happened before the Big Bang, the answer – or so physicists try in vain to persuade us – is that it is simply an illegitimate question. The word ‘before’ can no more be applied to the Big Bang than you can walk north from the North Pole.
If I had been a physicist, I would have tried to explain that, in a vehicle travelling at an appreciable fraction of the speed of light, time itself slows down – as perceived from outside the vehicle, though not within it. If you travelled through space at such prodigious speeds you could return to Earth five hundred years into the future, having yourself scarcely aged at all. This is not some therapeutic effect of high-speed travel upon the human constitution. It is an effect upon time itself. Contrary to Newtonian cosmology, time is not absolute.
Some physicists are even prepared to contemplate true time travel, going backwards in time – which I suppose must be any historian’s dream. I find it almost comical that one of the main arguments against this is the element of paradox. Suppose you killed your own great-grandmother!* Science-fiction writers have responded by giving their time travellers a rigid code of conduct. Every time traveller must swear an oath not to mess about with history. Somehow one feels that nature herself must erect stronger barriers than fickle human laws and conventions.
*You could do something far less drastic to change the course of history such that you would never be born. A sneeze would do it, given the prior improbability that any particular one out of billions of spermatozoa would succeed in fertilizing an egg.
If I had been a physicist, I would also have considered the symmetry or asymmetry of time. How deep is the distinction between a process running forwards in time and one running backwards? How fundamental is the difference between a film running backwards or forwards? The laws of thermodynamics seem to provide an asymmetry. Famously, you can’t unscramble an egg; and a shattered glass does not spontaneously reassemble itself.
Does biological evolution reverse the thermodynamic arrow? No, for the law of increasing entropy applies only to closed system, and life is an open system, driven upstream by energy from outside. But evolutionists, too, have their own version of the question whether time has an arrow of direction. Is evolution progressive?
Well, I may not be a physicist but I am an evolutionary biologist, and you had better not get me started on that fascinating question.
One of the things that any speaker can do with time is run out of it. The important business of the evening is to look at this exhibition ‘About Time’. I was privileged to be shown around it yesterday, and I can tell you it is fascinating – in all sorts of ways. It gives me very great pleasure to declare the exhibition open.