We Still Don’t Fully Understand Time

6 minute read
Rees is Astronomer Royal, former President of the Royal Society, Fellow (and former Master) of Trinity College, Cambridge, and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge. His latest book is If Science Is to Save Us

In our everyday lives, time is a precious commodity. We can gain or lose it. We can save, spend or waste it. If our crimes are revealed, we risk having to do time.

To scientists, time is something we can measure. Clocks have, over the centuries, been the high tech artifacts of their era—the water clock, the pendulum clock, Harrison’s chronometer, and so forth up to the incredible precision of atomic clocks—marvels of modern technology, albeit without the evident aesthetic quality of more traditional timepieces. (Though engineering friends tell me that, viewed through a microscope, there’s beauty in the intricacies of a silicon chip.)

Before there was a reliable calendar—or any records, or artifacts that could be reliably dated—the past was a ‘fog’. But this didn’t stop efforts to impose fanciful precise chronologies. Most precise of all was that worked out by James Ussher, Archbishop of Armagh, according to which the world began at 6 pm on Saturday, 22 October, 4004 B.C. Right up until 1910, bibles published by Oxford University Press displayed Ussher's chronology alongside the text.

Even in the 17th-century, Ussher's estimates ran into problems. Jesuit missionaries returned from China, telling of detailed historical records dating back to dynasties before 2350BC—the proclaimed date for Noah's Flood. Many were sceptical that the entire history of Earth's mountains, rivers and fauna could be squeezed into 6000 years. Sir Isaac Newton, in his old age, had abandoned science, and was obsessed with completing his own 'Chronology of Ancient Kingdoms'. He did not contest Ussher's dating of human origins, but conjectured that the six 'days' of Genesis could each be a prolonged era.

In the 19th-century, Darwin's genius was to recognise how "natural selection of favoured variations" could have transformed primordial life into the amazing varieties of creatures, now mainly extinct, that have crawled, swum or flown on Earth. But this emergence—a higgledy-piggledy process, proceeding without any guiding hand—is inherently very slow. Darwin guessed that evolution required not just millions but hundreds of millions of years. He was mindful of supporting evidence from geology. He estimated, by an argument that was actually flawed (and which he cut from later editions of his book) that to carve out the Weald of Kent took 300 million years. If he had seen the Grand Canyon he could have made a more convincing estimate.

Precise radioactive dating now tells us that the Sun and its planets condensed 4.55 billion years ago from interstellar gas in the Milky Way—itself a galaxy that, along with billions of others, is part of a still vaster cosmos that emerged from a fiery "beginning" about 13.8 billion years ago. Ever richer data from giant telescopes has allowed cosmologists to developed a credible scenario of our expanding universe. The timechart can be confidently extrapolated back to an era when everything was squeezed as dense as an atomic nucleus. At that time the universe had been expanding for only a millisecond. But that first millisecond—when crucial features of the universe were laid down—is still mysterious and speculative; the densities and temperatures were far higher than can be achieved in a lab, and so we lose our foothold in experimentally-tested physics

And what happened ‘before the beginning’? On this fundamental question, we cannot do much better than St Augustine in the 5th-century. He sidestepped the issue by arguing that time itself was created with the universe. Some modern cosmologists say that time closes up on itself, and the question is like asking, What happens if you go north from the north Pole? The 'genesis event' remains in some ways as mysterious to us as it was to St Augustine.

So cosmic history, we now believe, extends over billions of years. Our time-horizons have hugely extended back into the past. But our concept of the future has stretched even more. To our 17th-century forbears, history was nearing its close. Sir Thomas Browne wrote "The World itself seems in the wane. A greater part of Time is spun than is to come."

But that hardly seems credible to an astronomer—indeed, we are probably still nearer the beginning than the end. Our Sun is less than half way through its life; it will shine for another 6 billion years before the its nuclear fuel runs out. It then flares up, engulfing the inner planets. And the expanding universe will continue—perhaps for ever—destined to become ever colder, ever emptier. To quote Woody Allen, eternity is very long, especially towards the end.

The traditional view, even among those who accept Darwinian evolution, is that we humans are necessarily the culmination of the evolutionary tree. But in the perspective of a vastly prolonged cosmic future, it’s more reasonable to conjecture that we haven’t even reached the half-way stage in the progressive emergence of complexity in the cosmos. Any creatures who witness the death of the sun (having long before then developed the technology to escape to a safe distance) may be as different from us as we are from slime mould.

But even in the immensely concertinered timescape that modern cosmology reveals, extending billions of years into the future as well as the past, this century is special. It’s the first in the 45 million centuries of Earth’s history when one species, ours, can determine the entire planet’s fate. We’ve entered what’s sometimes termed the ‘anthropocene.’ The collective ‘footprint’ of humans on the Earth is heavier than ever; today’s decisions on environment and energy, empowered by our scientific knowledge, resonate centuries ahead and will determine the fate of the entire biosphere, and how future generations live.

Despite our awareness of the aeons lying ahead, our planning horizons have shrunk because our lives are changing so fast. The political focus is on the urgent and immediate, and the next election. Medieval cathedrals took a century or more to complete. There are few efforts by public or private sectors to plan more than two or three decades ahead—or to build structures that will, as the cathedrals have done, offer inspiration for a millennium.

Even more crucial is the possibility that humans will acquire the capability to redesign or ‘enhance’ themselves via genetic modification; or to deploy ‘cyberg’ tchniques that enable them to implant in their progeny the advantages of electronic computers. This evolution via ‘secular intelligent design’ could operate faster than Darwinian selection.

Perhaps our remote descendents will have a much-enhanced lifespan; they might even become near-immortal. Such entities, whose mental powers and attitudes are beyond our grasp—perhaps even beyond our imagination, would surely not feel ‘prisoners of time’, as we mortals do. Would they, like us, ‘spend and save’ it as a scarce resource? Or would an over-abundance lead to ennui? Only time can tell.

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