The universe is evolving toward loneliness. In the first moments of our universe’s life, the matter and energy were so dense that not even light could travel more than an atom’s length before being absorbed into the willing heart of an atomic nucleus. Like a too-large family in a too-small house, every one of those nuclei was constantly bumping into another. But as the moments and the millennia have passed, the universe has expanded, and the space between the atoms has grown from microns to megaparsecs.
With this expansion, encounters have become much more rare and light can now travel unimpeded from one side of the universe to another. This expansion comes at a cost; in the distant future, the universe will grow to the point that any remaining life will stare out into emptier skies. All the other galaxy clusters will move beyond the visible horizon as the stars around us begin to one-by-one wink out.
A Magical Time
The moment in which we live is a somewhat magical time. The Universe is old enough that heavy elements—the iron in your blood, the calcium in your bones—have come to exist in sufficient amounts that life is possible. At the same time, the universe has evolved enough that galaxies are safe places. Deadly objects like quasars are few and far between. As we look out across the sky, we see our place in our solar system of eight planets, and we see our solar system’s place in this immense Milky Way galaxy. With telescopic eyes, we can reveal our home in the small “local group” of galaxies, and see how we are falling into the gravitational arms of the nearby Virgo Cluster. As we look and look across the heavens, we begin to see our place in a vast lace of galaxies and galaxy clusters that trace out the shape of space.
Had we been born earlier, ignoring the lack of elements needed to form our bones and blood, these structures wouldn’t have had time to achieve this beautiful structure, and we would have seen nothing more than a lumpy universe of still-coalescing forms. Had we come later, ignoring the slow blinking out of the stars, we would have found a structure stretched so much that only our small piece—the much merged future version of the Local Group and the Virgo Cluster we’re falling toward—would remain within the visible universe. All the other galaxies and clusters are being carried away by the expansion of space—a process that can ignore relativistic speed limits and cause the distance between objects to grow faster than light can travel. Someday the galaxy clusters will be so distant that their light will be unable to reach our galaxy and we will only see those things to which we are gravitationally bound.
An Isolated Time
The universe is evolving toward loneliness, but even today the vast distances of space mean that humanity, limited by our far-less-than-the-speed-of-light technology, is isolated on the Earth.
The immense distances of space are almost impossible for a human to grasp. In school we learn the Sun is eight light minutes away or about 150,000,000 kilometers distant. These are just large numbers, though, and we don’t really have a sense of them. If I say his large blue eyes are 4in (or 10cm) apart, depending on your culture, you can see what I see in your mind. Up to a few kilometers or miles, you can feel out the distance with your feet. But what does 150,000,000 km feel like to the lonely astronaut traveling on an interplanetary journey? The fastest interplanetary spacecraft built to date, New Horizons, is traveling toward Pluto at 58,536 kilometers per hour. This is the equivalent of traveling 2.3 times around the Earth’s circumference every hour! To this speedy spacecraft, 150,000,000 km is 107 days of travel; 107 days of nothing. Yes, one might encounter Venus. Yes, Mercury could be on the path from here to the Sun. Yes, maybe even an asteroid or comet could get in the way, but probably not. On any given day—on most given days—the path from us to the Sun is much more likely to be utterly empty.
The Sun is eight light minutes away. The next nearest star, Proxima Centauri, is 4.243 light years farther off. The nearest large galaxy is 2.52 million light years away. The distance to the nearest cluster of galaxies is 59 million light years. And the distance to the current edge of the visible universe is 46 billion light years.
Our fastest spacecraft would take more than 1,820 years to get to Proxima Centauri.
What We Have and What We Dream
Space is vast, and, mostly, space is empty. Today we know of no way to burrow through the distances between here and some distant where without facing the speed of light limitations of relativity. There are those who hope we will learn to tunnel like an electron through space, expanding our wave functions out to collapse somewhere new in an instant. But no one knows where to begin the experiments that will get us to teleportation technology. There are those who dream of stable wormholes, but the math says no mass may enter these theoretical one-way tunnels to nowhere. There are those who speak of warping, folding, or otherwise employing a tesseract or Holzman effect to get the space here and there brought together for a moment so we can simply step across the vastness of space. But this is still just science fiction and finds no support in science fact.
We are limited by the human lifetime to our own solar system for now and mostly until the next bright new genius is born to change our scientific paradigm in the ways of Newton, and Plank, and Einstein.
So we sit here, alone on Earth, watching the Sun and the stars and the galaxies shine down. But in our isolation we can at least cherish the knowledge that we have that Sun, and those stars and distant galaxies shining there in our sky. Someday, those will all be gone and we will be alone on whatever remains of our terrestrial perch.
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