Whenever you open your eyes, photons stream by the trillions through the four-millimeter-wide windows into your central nervous system otherwise known as pupils. Those photons—the bizarre yet ubiquitous packets of light that famously behave as both particles and waves—trigger an impossibly complex series of electrochemical signals that imbue emotion, meaning, and practical knowledge into our lives. They help us navigate, help us avoid danger, and help us fall in love. It’s in our eyes that light becomes thought.
But most light never gets seen. For every photon destined to end in the mind of a human being, countless others bounce banally into oblivion or streak across the cosmos into infinity. This is because we can only sense light that passes directly into our eyes—we often forget that a blazing array of light surrounds us at every moment, crisscrossing in every direction, much of it in spectra invisible to the human eye even when it does happen to smash into our retinas. Almost all the light from your desk lamp, let alone all the stars in our galaxy, sputters out into nothingness. For every 100 million photons our sun produces, only four crash into Earth, usually hitting some random part of the ocean or bouncing off the atmosphere. You have a better chance of winning the lottery 100 times in a row than a particle of sunlight has of winding up in your mind. A photon from a distant star? Forget about it.
Even then, most of the impossibly small percentage of photons lucky enough to thread the needle into a human retina usually gets ignored—our brains naturally dismiss most of our sensory input. From peripheral vision to the glare of the sun, to the time we spend spacing out, humans don’t pay attention to many of these lucky photons. But some photons have power (beyond providing the energy that powers almost every organism on the planet); they directly impact the behavior of humans. They help us catch a ball or know when it’s time to cross the street. Even fewer enter the hallowed halls of the hippocampus, where we etch the big moments to revisit time and again; our childrens’ smiles or our last glimpse of a perfect sunset we never want to forget.
Most photons experienced by humans were born in the last eight minutes, or much more recently. Light from our light bulbs reaches us in a few nanoseconds, while sunlight, having traversed 93 million miles of empty space, is only eight minutes old. Some photons, however, are much older and important for different reasons. They hail from far-flung locales in our galaxy or even from other galaxies; they’ve taken thousands or millions (or billions) of years to get here. They’re not important because of which talking ape they most recently bounced off of, but by virtue of where they came from and what they can teach us about the nature of reality. Pound for pound, ancient light from the night sky is some of the most critical to our understanding of who and where we are.
These rarest of photons have taught us that the sun is the center of our solar system, about the orbits of the planets, about the age and expansion of the universe, and even about the composition of planets orbiting other stars. Everything you’ve ever learned about astronomy was discovered by collecting these prized packets of information and studying them with the intensity they deserve.
Since the dawn of humanity, astronomers have sensed that there’s something special about starlight; the stories we tell about the lights in the sky aptly form the basis of creation myths across the planet. Starlight encourages us to think about our place within ourselves. This ancient light sets the scene for internal exploration and ubiquitously encourages humans to wonder who we are; why we are. It’s bright enough to light the way, yet gentle enough not to obscure the delicate details of the soul. In starlight, no one feels overexposed. What we’ve found in these photons forms the basis of our collective knowledge of ourselves.
Today, our species devotes significant resources to collecting and understanding them. We’ve created giant telescopes because our tiny pupils can’t take in enough at one time to answer the biggest questions. We use cameras and sensors to collect and store many photons over the course of time because our eyes and minds can only hold onto a moment’s worth. We now routinely see the sky through pupils several meters wide, through these telescopes we can view a week’s photons in an instant.
And when presented to us in the form of an image, these photons become iconic. Just last year, the first image of the event horizon of a black hole captured the world’s attention. To catch enough of these incredibly rare photons, scientists used a worldwide array of virtually aligned telescopes to create a mega-pupil–literally the diameter of our entire planet–to see the gaping maw. The photons represented in that image started their journey to Earth soon after the dinosaurs went extinct, when early mammals had just inherited the Earth. Eons passed and those photons traveled in a straight line until, at the very last moment, humans evolved. We looked up, captured those rare, ancient photons, and mainlined them into our collective memories and imaginations. There they will continue to live, ricocheting from one synapse to another in the infinite complexity of our minds, shaping our understanding of ourselves and of this experience we call reality. And for good reason; they are some of the most special light around.