Talking Points - On the Recentness of What We Know by Verlyn Klinkenborg - New York Times
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 and the moons of Jupiter through a small telescope of my own when I was a boy in Iowa. I spent part of a summer watching meteors 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 crossing the sky—is the state of my knowledge.
* * *
The same could be said for the whole of humanity. Besides a supernova 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.
But I am overwhelmed by the recentness of what we know.
* * *
Take, for instance, a relatively fundamental set of facts, something "everybody knows." Earth belongs to the solar system, and the solar system, with the Sun at its center, belongs to a galaxy called the Milky Way, which is about 100,000 light years across. The Milky Way is one of perhaps a hundred billion galaxies in the observable universe, each one containing perhaps a hundred billion stars. But until 1925, many astronomers believed — on the available evidence — that the Milky Way contained the whole of the observable universe, and that our galaxy was thus the only galaxy. Astronomers had seen and catalogued plenty of galaxies — they were called nebulae in those days — but there was no way to know how far away they really were.
To a casual naked-eye observer on Earth it makes no practical difference whether the universe is the size of the Milky Way or much, much bigger. In fact, it makes little difference whether we’re looking up at stars scattered across empty space or at an empyrean of concentric crystalline spheres. The night sky overhead would look the same.
Or would it? Actually, I don’t think so.
What we see when we look up into the darkness of a summer night isn’t just a pattern of pinpoint lights. We’re also looking up at the state of our knowledge and the contents of our imagination. Does our own galaxy encompass the whole observable universe? Or is it only one among a huge number of galaxies in a vastly larger universe? The difference is enormous. Both are theories. One was plausible before 1925. The other is now true. The revolution in imagining who we are, or rather where we are, is nearly Copernican.
In 1931, Edwin Hubble concluded that the universe was 1.8 billion years old, a nonsensical number since geologists had already shown that the rocks on earth are nearly twice as old. (Recent knowledge in itself!) In 1952, the scale of distance was recalculated with greater accuracy, and suddenly the age of the universe doubled to 3.6 billion years, much older but still a problematic figure. In 1955, the universe aged another 1.9 billion years overnight, again thanks to a clearer understanding of the things that shine in the dark. In the past 80 years the universe has expanded faster and aged faster — in the minds of humans — than it is doing in actuality. The current age of the universe, as measured in 2003, is now 13.7 billion years, give or take 200 million. That is another way of saying that the distance to the edge of the observable universe is 13.7 billion light-years.
What astronomers are seeing when they look at a galaxy like Abell 1835 IR1916 — 13.2 billion light years away — is light (or radiation) that was emitted 13.2 billion years ago, light that is about 3 times older than the planet we live on. Imagine a galaxy just a little farther away, at the extreme edge of what astronomers can observe. Suppose that it emits light even as you’re reading this sentence. How far away will the edge of the observable universe be when that light reaches us? The answer is somewhere between 78 and 90 billion light years. In fact, we — that is, "they" — have no idea how much of our universe lies beyond the threshold of observability. There is even sober speculation that our universe is merely one of a possibly infinite series of universes, that we live in a multiverse. Oddly, one of the best arguments for the multiverse is the simple fact that we exist....