THE OTHER NIGHT I took the dogs for a walk in the pasture. It was a cloudless evening with low humidity, a rare event in this damp, northeastern summer. I always look up at the stars when I'm outside in the dark, but all too often, even here in the country, they're obscured by haze. Not that night. They shone with a brightness, a clarity I'd almost forgotten. Cassiopeia (1), Corona Borealis (2), Lyra (3), the red light of Arcturus (4) in the west, the diffuse band of the Milky Way (5) arching overhead - their presence was overwhelming. And yet, somehow, when the stars look close to earth it's easier to imagine how far away they really are. It was a warm July night, but I could almost feel the chill of space.
I've been watching the stars for nearly half a century now. Not much has changed up there. The sky is a memory in itself. I stared at the rings of Saturn (6) and the moons of Jupiter (7) through a small telescope of my own when I was a boy in Iowa. I spent part of a summer watching meteors (8) while I was helping my family build a house in the foothills of the Sierra Nevada and part of a winter star-gazing from the top of a mesa on the Hopi Reservation, where somehow the smell of cedar mingled with the light of the moon. The only thing that has changed in all that time - apart from a few new satellites (9) crossing the sky - is the state of my knowledge.
The same could be said for the whole of humanity. Besides a supernova (10) here and there or a comet fluttering past, the night sky visible to the naked eye has barely changed as long as our species has been looking at it, unlike the stories we use to describe what we see up there. In a metaphorical sense, each human culture, separate in time or place, has lived under a different celestial roof. The metaphors for the heavens have changed over time, but not nearly as much as what we know about the universe itself.
I say "we," as in what "we" know. I really mean what "they" know astronomers, mathematicians, astrophysicists, cosmologists. Unlike scientists, most of us tend to live easily, almost unknowingly among our assumptions another word for our ignorance. But the business of science is to formally test assumptions, better known as hypotheses. You can feel the tension between these two ways of knowing in a few lines from the movie "Men in Black." (11) The scene is the Manhattan waterfront. Will Smith is still in shock after his first encounter with aliens. Tommy Lee Jones says to him, "Fifteen hundred years ago everybody knew the earth was the center of the universe. Five hundred years ago, everybody knew the earth was flat. And fifteen minutes ago you knew that people were alone on this planet. Imagine what you'll know tomorrow." Obviously, what everybody knows isn't a very high standard of proof. And things that can be proven - matters of scientific fact - don't always surface as common knowledge.
Every few years I go through a bout of cosmological reading, a reprise of what to me is now mostly a familiar story. In a way, it's like re-reading Raymond Chandler (12) or great chunks of Dickens. (13) The plot comes back to me as I go, but with a new ending every time. I started in childhood with an oversized, illustrated book about the solar system, a place where everything was just as we would like to believe it might be, a cozy people living in a handmade cosmos. The last time I wandered off into the universe, literarily speaking, I found myself, a little confused, on the far shoals of M-theory (14) and the various anthropic principles. (15) I'm never sure what's going to set me off. It could be a news item about a flyby of Saturn (16) or a new photograph from the Hubble Space Telescope (17) or even a walk with the dogs at night. But however it begins, it always turns into a desire to frame the small questions of life with the big question of existence itself.
Most books about cosmology for general readers begin by telling the story the way Tommy Lee Jones tells it in "Men in Black" - as the history of what we know. …