The known universe is billions and billions of light-years across.
The entire universe may well be infinite.
In the midst of this incomprehensibly enormous cosmic canvas, there are galaxies like jewels in the dark, strung out across the void in a latticework of superclusters and great walls, a glittering spiderweb built on a scale the human mind is incapable of grasping.
Each of these galaxies, though many orders of magnitude smaller than the macrocosm itself, is still huge beyond the mind's ability to fathom. Each one is made up of billions of stars, from ancient, swollen red giants to hot young blue newborns, from middle-aged yellow like our own sun to exotic burned-out remnants like black holes or spinning pulsars that blink like lighthouses against the cosmic night. Though exponentially smaller than the entire universe, or even a single galaxy, these too run to scales the human mind cannot truly comprehend.
Smaller still than stars, we find asteroids, moons, planets, rocky islands drifting on the infinite sea of nothingness. Most of these - in fact, as far as we know, all but one of them - are dead places: cold, barren and frozen, or constantly boiling in the pitiless glare of hard radiation from too-near suns. Nothing lives there; nothing can.
We have looked out across the totality of creation, but found no one looking back at us. The radio signals we have transmitted into the depths of space have gone unanswered. There are no footprints but our own in the dust of our moon's surface. The robotic probes we have sent out, containing information and greetings we hope fellow minds will be able to understand, spin off endlessly past the solar system, and as far as we know, not one has ever been found.
In fact, there is only one place in all the cosmos where we know for certain that life exists: our own Earth, a green, blue and white haven orbiting peacefully third from its unremarkable yellow sun. By a stroke of miraculous luck - or perhaps not so miraculous; perhaps in the vastness of the entire universe, it was bound to happen somewhere - our planet evolved with just the right mix of chemical elements, just the right temperature to allow the existence of liquid water, just the right type of atmosphere to allow life-giving warmth in and keep dangerous radiation out.
And in the primordial seas of the young world, either at random or through some process not yet fully understood, the first few organic molecules linked up. Simple amino acids and proteins combined into self-replicating substances, growing ever more complex. And finally, somewhere between four or five billion years ago, the first primitive bacteria came into existence. They gained energy through photosynthesis, they grew, they lived, they evolved. Ever more complex forms arose. The precursors of fish swam in the planet's oceans. At some point, one lineage developed lungs, began to breathe oxygen and crawled onto land, and the process accelerated. Life spread to cover the planet, adapting to fill every ecological niche, branching and rebranching into a riot of exuberant biological diversity. Sixty-five million years ago, the dinosaurs dominated the Earth. Then, through some catastrophe, most likely a meteor hurtling in from outer space to crash into the planet, they were wiped out at one stroke. Most of the planet's species perished. But those that survived continued to grow and adapt.
No one knows exactly when the first ape-like creatures, when the first inquisitive and social and nurturing primates descended from the trees, when the first creatures that probably bore little resemblance to modern human beings began to walk upright, to use tools, to harness the power of fire, to talk, to think. But all of these things they did. All the species that had come before had various evolutionary advantages: sharper claws and teeth, better senses, stronger muscles, greater speed. But humankind had something new, something unique: the spark of intelligence, the ability to innovate. In a geological eyeblink, the human species spread across the globe, adapting to new environments and new challenges, using its intelligence to bridge the gaps that the plodding pace of natural selection had failed to fill. And humanity continued its upward climb, always seeking to improve its condition.
Stone axes gave way to bows and arrows, and technology continued to advance, each new invention bringing about the next one that much more quickly. The Iron Age, the Industrial Revolution, the Computer Age - ages of history came and went, faster and faster, like flipping the pages of a book. Today, human civilization dominates the globe, with a population six billion strong and technology that can work wonders early societies lacked even the ability to dream of. From the sky at night, our planet is covered by a spiderweb of glowing lights, testament to our ability to invent and innovate. Today, we are continuing to advance and grow, continuing to learn. Even today, we are taking our first tentative steps toward reaching out and exploring the universe, learning the truth behind those cosmic mysteries out of which we all emerged.
And yet, when it comes to the fundamentals of life, we are not that different from the ultimate ancestor of us all: that single bit of protoplasm, little more than a collection of complex molecules drifting in the primordial oceans of a young planet circling a yellow star in a remote corner of a spiral galaxy that is, after all, nothing more than a single gleam against the immensity of all the cosmos - a cosmos so vast that even the human imagination, possessed of a power unequalled in all the known universe, fails to grasp its magnitude.
Of course, this view is not shared by everyone.
Some people believe that there never were any primordial seas, indeed never any evolution. These people believe that the entire enormous spectrum of living diversity found on the Earth, as well as the Earth itself just the way it is now, were all created about six thousand years ago in a series of instantaneous miracles, like a vast magician waving his wand.
Some people believe that this unimaginably tiny and infinitely fragile dust mote where we live is the most important place in all of creation. At various times throughout our history, these people have tortured each other, killed each other, enslaved each other, committed every evil act and atrocity the human mind can conceive of to each other, all to possess miniscule fractions of it.
At this point it is worth noting that, until not too long ago, many of these same kinds of people believed that the Earth was the center of the universe around which everything else revolved. It is also worth noting that these same people attempted to silence, persecute, and in extreme cases execute anyone who dared to say differently.
In several hundred years, how much has changed? And how far do we have left to go?