TT Journal, ISSUE 7, September 2024
A cosmologist’s quest to experience more-than-human timescales
by Roberto Trotta
The little train rattled down the steep incline at a good clip, among the gasps of excitement of my fellow passengers. The tunnel ceiling was so low that the tallest among us ducked instinctively between the puddles of light flowing from miners’ lamps incrusted in the sides at regular intervals. My son grinned as he turned in his seat: we were being ferried into the bosom of the Earth.
As the slope fell away, the tunnel emerged into an immense vault constellated with spiky stalactites, scintillating in a myriad beams, bejewelled with crystals of all colours and shapes. As the rail track sneaked among stalagmites as tall as a tree, with a gird that five people holding hand could scarcely embrace, a collective exclamation of surprise exhaled from the open-top carriages: a glass chandelier hung suspended in mid-air, the heavy chain that kept it there disappearing into the dark for an unknowable length. The electric light bulbs radiated the brightness of a cluster of pure white suns, mysteriously shining cold in the depths of the Earth – a Viennese ballroom in the reign of Hades. It was striking, incongruous, and beautiful.
I had come to the Postonja caves in Southern Slovenia -the longest cave systems in Europe, and the only one boasting a railway line, built over 140 years ago- in search of an elusive experience. For many years I had been considering the question of how to relate with and draw meaning from larger-than-human scales. As a cosmologist, I deal every day with ineffably large and old objects of study: galaxies billion of light years away; dark matter particles created right after the Big Bang; light beams that crossed the universe for over 13 billion years before hitting our detectors. Yet, all of this remains a purely intellectual experience, mediated by mathematical analysis, crunched through artificial intelligence systems, and ultimately resulting in a precise but utterly unrelatable number: what does it mean to us, human beings with a lifespan of 4,000 weeks (give or take), to know that the Big Bang happened 13 billion and 787 million years ago?
I came to be interested in deep time -timescales so unfathomably long that vastly outstrip our ability to experience them- when researching my last book, Starborn – How the stars made us (and who we would be without them)[i]. In Starborn, I ask the question of how the sight of the stars has shaped the course of human history, from prehistory to AI, and how everything would be different had we not been blessed with the sight of the heavenly bodies in the sky, for example had we evolved on a planet permanently shrouded in clouds. I realized then the intimate connection between the twin horizons that for millennia foreclosed our view of the wider landscape in which Homo Sapiens arose. Marooned on the tiny island of our own mental confines, we could not conceive of the wild extent of deep time, nor of the immense expanse of space beyond our immediate view.
When the true extent of the cosmos around us became clear, it was a shock: Newton’s estimate that Sirius is a million times farther than the Sun opened up an immense vista onto the abysses of space, which was further expanded by Hubble’s discovery in 1928 that the Andromeda galaxy is, in turn, 100,000 times farther away than Sirius. At the beginning of the 20th century, while Hubble stretched the astronomers’ ruler into the millions of light years, geologists and evolutionary biologists were clamouring for vast quantities of a key ingredient that physics seemed unable to provide: time. In the biblical six thousand years since the creation, the peacocks’ feathers could never have evolved from a T. rex, nor humans from mice; and if mountains had arisen from oceans, and the world had been moulded by wind and water as geologist Charles Lyell maintained, the Earth had to be millions of years old.
“The geological age plays the same part in our views of the duration of the universe as the earth’s orbital radius does in our views of the immensity of space,” wrote Irish geologist John Joly in 1915[ii]. Late-nineteenth-century physicists had a hard time granting the geologist and the evolutionist the unfathomable stretches of time they needed. Lord Kelvin was adamant—and correct—that if the Sun’s energy was provided by gravity, “unless sources now unknown to us are prepared in the great storehouse of creation,” our star could not be older than twenty million years[iii]. The mystery would only be cracked with the discovery of radioactivity, which allowed geologists to date the age of the Earth to several billion years, and the establishment of nuclear fusion as the energy source of the Sun in the 1930s.
Yet, as our scientific understanding of time and distance scales expanded, our personal relationship with these concept began to slip away. Beyond our own life story, few of us are blessed with knowledge of their family tree spanning more than a few generations – often disappearing into the fog only one or two generations ago. Human life is no match for deep time. On a collective level, recorded history takes us back a mere 5,000 years (a kitchen clock when measured on the lifetime of the stars!), and the existence of our very species, Homo Sapiens, only stretches back to 50,000 years ago. But today connecting with more-than-human timescales is becoming of planetary importance. As we face a devastating ecological crisis due to human-induced climate change, irreplaceable loss of biodiversity on vast areas of Earth, and scarcity of resources, we must change our decision making to take into account not only our immediate needs, and worries about the next electoral cycle, but also those of the other life forms we share the planet with. To take a less human-centric view means to stretch our imagination to what it may be like to exist as a thousand-year old redwood tree; to ponder the oceans from the point of view of a species, such as sharks, that has inhabited them for two hundred million years; to consider Homo Sapiens as a temporary visitor to Earth, a guest among many, not its absolute overlord.
The stars can help us achieve such a consciousness by virtue of what author Samantha Harvey has called “the reverse overview effect”[iv]. The “overview effect” refers to the powerful, lasting impression that seeing our planet from space has left on many astronauts since the dawn of the space age. William Shatner -the actor who played the legendary Captain Kirk of the starship Enterprise– was at long last beamed up into space in the flesh in 2021, setting the record for the oldest person to reach orbit, aged ninety. When turning his gaze back toward the Earth and appreciating the contrast between our beautiful blue planet and the inhospitable cosmic void, he “discovered that the beauty isn’t out there, it’s down here, with all of us. Leaving that behind made my connection to our tiny planet even more profound. . . . [A] sense of the planet’s fragility takes hold in an ineffable, instinctive manner.”[v] While this kind of space-born transcendence is not available to all of us, a similar sense of awe can be experienced by simply looking up at night, and letting ourselves float among the infinite cosmic darkness above – the “reverse overview effect”.
Among the otherworldly stone landscapes of Postonja , I was searching for a similar sense of smallness, translated from the spatial to the temporal: what would it be like to count time not in weeks, but in aeons? Could a trip inside the Earth stimulate a new awareness of our true temporal scale, just as looking up into the universe does for our size? As we disembarked the red and yellow train at the deepest point, over a hundred meters below the surface, and continued the tour on foot, I admired the glittering surface of mighty stalactites, raising for up to five meters from the floor. They were made of rock, of course, but gave the misleading impression of waxworks. A steady dripping of water kept adding to their height even as I contemplated them – one millimetre every century.
When it hit me, it was fleeting, but powerful: as I descended along broad concrete steps, flanked by a metal banister, I saw the scene in front of my eyes from the perspective of the cave. A group of creatures clad in garish colours, walking down steps that would soon crumble, the bright electric light a flash, here now, but gone in the next frame. I reached out to hold on to the banister to steady myself against this vision, and for a moment my hand grasped not metal, but the perfectly smooth and polished rock, like cold flesh, that will envelope it in just a few million years, droplet after dripping droplet. In the blink of an eye, with the chattering bipeds gone, the cave will then be returned to the dark, unseen place it had been since the beginning, and deep time will resume its silent flow, untroubled.
[i] Trotta, Roberto, Starborn. How the stars made us (and who we would be without them, London and New York: Basic Books, 2023.
[ii] Joly, John. The Birth-Time of the World and Other Scientific Essays. London: T. Fisher Unwin Ltd., 1915, p3.
[iii] Quoted in Darwin, George. H. “Radio-Activity and the Age of the Sun.” Nature 68, no. 1769 (1903): 496-496, p496.
[iv] Harvey, Samantha, BBC Radio 4 Start of the Week, aired Nov 27th 2023.
[v] Shatner, William. “William Shatner: My Trip to Space Filled Me with ‘Over- whelming Sadness.’” Variety. October 6, 2022. https://variety.com/2022/tv /news/william-shatner-space-boldly-go-excerpt-1235395113.
Roberto Trotta is professor of theoretical physics at the International School for Advanced Study in Trieste, Italy, where he is the head of Data Science, and a visiting professor at Imperial College London, where he was professor of astrostatistics. His research focuses on cosmology and machine learning. An award-winning author and science communicator, he is the recipient of the Annie Maunder Medal 2020 of the Royal Astronomical Society for his public engagement work. His new book, STARBORN – how the stars made us (and who we would be without them), named BBC Radio 4 book of the week, is out now. www.robertotrotta.com