Finding your place in the universe. Literally.
A friend once asked me if there are any scientific words of comfort to give someone experiencing a bereavement. Can a person’s life somehow leave a meaningful imprint on the cosmos long after their corporeal exit? I thought hard and finally said that each time we stand under a clear sky some of the sunlight reflecting from our bodies races up through the Earth’s atmosphere and into the universe. That light, as streams of photons, can even be quantified, totaling octillions over a human lifetime””octillions of little bits of energy that were once uniquely modified by kissing our bodies.
Perhaps a few of these photons will impinge eventually on some other place: a star, a planet, a speck of interstellar dust. Conceivably, one day, another species determined to find out if it’s alone in the universe might even register a little of this light in some unimaginably sensitive telescope and puzzle over its meaning. But most photons will just keep going, carrying a lifetime of our images with them. So rather surprisingly, we can indeed leave an imprint on reality that will persist long after our consciousness evaporates.
As uplifting as this thought might be, it hides a deeper, more challenging reality. The phenomena that make all of this happen actually have very little to do with any kind of permanence, personal or cosmic. Quite the contrary.
When you or I move through the world we are dragging around atoms born out of a chain of tumultuous processes that began within a few hundred million years of the start of it all””the Big Bang. That origin, a ferociously hot and dense exhalation of energy, matter, and space, remains at the hairy edge of our grasp of fundamental physics. But what came after that origin is understood today with an astonishing level of detail.
Within moments of the universe’s existence it underwent a sequence of transitions as it expanded and cooled. Matter that was once a soupy mess started to condense into the things we call protons and neutrons, the essential ingredients of atomic nuclei. A few hundred million years later some simple nuclei found themselves jostling together inside the agglomerations we call stars. So vigorous was the jostling that they started fusing with each other, forging heavier and heavier elements. In the blink of a cosmic eye these stars became supernova, explosively throwing many of their old and new elements out into space. Time and time again gravity gathered up these elements into new stars, even planets, and eventually, in at least one place, a curious animation of matter called life.
A piece of life like a human is endlessly swapping out its complement of these star-forged elements. The cells lining your stomach must renew every couple of days. Red blood cells operate for around two weeks before degrading. Fat cells, I’m sorry to say, live for around ten years, a similar timescale to the regeneration period for your bones. Neurons and tooth enamel may be the most lasting components in our bodies. But in most respects, the you of today is not the you of yesterday. Atoms come and go with scant regard for our sense of unique identity.
The sunlight that bathes your wayward parts on a bright day also exists because of change. Like the generations of stars before it, the center of our Sun is filled with atomic nuclei at a density over ten times that of solid gold. Their fusion releases energy that takes about a hundred thousand years to propagate through these thick solar innards to finally escape as photons of visible light. The light you felt this morning originated in nuclear events at a time when Neanderthals roamed the world, oblivious to their eventual extinction. That light is also a sign of the Sun’s nonstop evolution toward an end some five billion years in the future. There is no such thing as a permanent star.
Stellar death and rebirth are what produced a planet we call Earth four and a half billion years ago. That world was a chemical incubator, full of pent up energy and potential. In ways that we still do not understand, Earth’s youthful conditions drove the start of more complex chemistry. Eager-to-connect molecules began enveloping themselves in proto-cells, propagating and exchanging information, and embarking on a cascade of experimentation that is still ongoing, billions of years later.
Central to that experimentation is a precarious balance between order (boring) and chaos (unruly). Natural selection is what increases the odds that a particular biological experiment will be able to keep on grasping at permanence. But without change and variation there is no natural selection. At the same time, the universe throws endless curveballs. Ecosystems collapse by sheer bad luck. Asteroids smash into small blue ocean worlds. What’s left of life refills the gaps, but often with entirely new inventions””fresh, exuberant experiments in novelty. Even at the dullest of times the Earth doesn’t sit still. Its axis wobbles, its orbit shifts back and forth from circle to gentle ellipse, all driving climate cycles and biological change across the eons.
Finally, even that hopeful stream of photons, the record of your time on Earth, will not and cannot remain intact. Not because of interception, or degradation, but because the universe itself is evolving. With every passing moment space itself is expanding, and it appears to be expanding at an accelerating rate. Consequently, a mere hundred billion years or so from now this expansion will take place at a rate that effectively isolates entire galaxies from one another. Not just in the sense of travel distance but in absolute causality””there literally will be no way to see the light from other parts of the cosmos. By this time your personal photons, long since departed from our Milky Way, will be lost, not just unseen but unseeable forevermore.
Yet if the universe were a place of permanence, all that has occurred to enable our species to briefly emerge from cosmic embers might not have happened. Impermanence is not simply a dispiriting fact about the nature of existence, it appears to be an essential part of the reason for existence. In that we may take some solace.
About the Contributor
Caleb Scharf is director of astrobiology at Columbia University, where he leads efforts to study the nature of life and planets across the universe. His books include Gravity’s Engines, The Copernicus Complex, and The Zoomable Universe. He writes the blog Life, Unbounded at Scientific American and is on Twitter @caleb_scharf.
Photographs by Anton Surkov via Getty Images and Tim Foster via Unsplash