Wednesday, August 9

On the Recentness of What We Know


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, Corona Borealis, Lyra, the red light of Arcturus in the west, the diffuse band of the Milky Way 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 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.

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" 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 or great chunks of Dickens. 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 and the various anthropic principles. I’m never sure what’s going to set me off. It could be a news item about a flyby of Saturn or a new photograph from the Hubble Space Telescope 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. The authors walk you, step by step, through the sequence of astronomers who have taught us about the cosmos—Copernicus, Galileo and so on. What you learn about the nature of the universe in a history like that is less important, at first, than what you learn about the decay of dogma and improvements in scientific methodology and equipment.

There are good reasons for telling the story this way. You get a feel for the passion of discovery, and you confront one of the basic cosmological questions —"How do they know that?" But as the pages turn and the chronicle nears the present, the story changes. Suddenly, it’s no longer a history of the development of science, a book about the human capacity for learning. It turns into a book about the nature of the universe we actually live in. The night sky never looks quite the same again.

* * *

The last time I lost myself in a good book about cosmology, just a few months ago, I counted down, as always, from the past to the present—from Aristarchus to Einstein to Weinberg. Usually, the dates in the history of science seem abstract, almost equidistant in the past: 1543, 1632, 1905 — it’s all ancient history. But this time, for some reason, I found myself weighing the dates of various discoveries—the ones that define our present idea of the age and dimensions of the universe—against the time-scale of my own life and the lives around me. I tried to picture what the universe looked like — or rather what it was thought to look like — around the year my dad was born — 1926 —- or the year I was born — 1952.

It was like going the wrong way in one of those analogies meant to convey the immensity of time. You know the ones. “If the age of the earth is the distance from the Golden Gate Bridge to the Empire State Building , then mankind originated in the Garment District.” The current picture of the universe rests, of course, upon the ancientness of what we know—the long series of carefully tested assumptions that make each new accession of knowledge possible.

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.

In 1923, working at the Mount Wilson Observatory, near Pasadena, Edwin Hubble discovered a Cepheid variable star in the nebula called Andromeda, the first ever found in a nebula. Thanks to Henrietta Leavitt’s research on these stars — which vary in brightness over a period of time, with a predictable ratio between the two — Hubble was able to calculate the distance to the Andromeda Galaxy, as we call it now. It was vastly more distant than anyone had guessed. By his calculations, Andromeda was 900,000 light years away — well outside the Milky Way. In a sense, Hubble had turned the universe inside out.

Hubble was wrong about one thing. Andromeda is the closest galaxy to us, but it is actually 2.5 million light years away, not 900,000. You can see it with the naked eye if you look just below and to the right of the constellation Cassiopeia on a very dark, clear night. It’s worth knowing, somehow, that in another 3 billion years Andromeda will collide with the Milky Way. Perhaps "violently intersift" is a better way of putting it.

* * *

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 the years since, there have been many, many discoveries more astonishing than Hubble’s path-breaking calculation of Andromeda’s distance, including his discovery, several years later, that the universe is expanding. But measuring that Cepheid variable in Andromeda fascinates me. It’s tempting to construe its effect solely in human terms, to say, with a vainglorious sniff, that it diminishes the place of humans in the universe. Ah, well. There is no end to that. One of the central problems of cosmology all along has been getting a true sense of scale. The age of the universe, its size, its origin, whether it’s static or expanding or contracting — these things are all interrelated, and they all depend on being able to measure distance accurately out to the far reaches of the universe. The more we know, the smaller we humans seem to loom against the universal backdrop. Luckily, what matters isn’t how big or important we are. It’s how interesting the universe we live in is.

My maternal grandfather, who was born in the 1880’s, used to marvel at the fact that in his lifetime humans had gone from horse-drawn carriages to the moon. I like to think of it a different way. He was born about the time astronomers finally proved that the ether — the peculiar light-carrying substance through which all celestial bodies were supposed to move — does not exist. He was married around the publication of Einstein’s theory of general relativity. He died a few years after Arno Penzias and Robert Wilson found the lingering echo of the Big Bang with a radio telescope in New Jersey. I cannot imagine that my grandfather was aware of any of these discoveries. And yet within his lifetime, the dimensions of the universe increased by a factor I am not mathematician enough to work out. Call it ten to the plenty.

* * *

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.

* * *

Science is mostly a tale of continuity. Scientists today are working within the same professional framework — the same idea about how they do what they do, what hypotheses are, what evidence is — as scientists a century ago. That is the strength of the endeavor. The change from one picture of the universe to another is incremental, based on work that obeys the self-regulating, international standards of the scientific enterprise. But I find myself marveling at its discontinuity, too. What has changed, of course, is the technologies available to scientists, which have exploded at a revolutionary pace. The result is that you don’t have to go far back in time before the best idea of what the universe looks like is very different from the idea we have now.

In 1920 there was one galaxy and now there are one hundred billion.

In 1955 the universe was 5.5 billion years old. Now it is believed to be two and a half times older — an estimate with a considerably higher degree of precision.

For many years, the Big Bang was a conceptual possibility, the logical implication of an expanding universe. (What happens when you run the film of an expanding universe backwards?) But in 1965, Penzias and Wilsonfound an evenly diffused radiation permeating the sky, with a temperature of 2.7 degrees Kelvin. They had discovered the Cosmic Microwave Background — residual radiation from the Big Bang.

The Cosmic Microwave Background has been measured again and again, most recently in 2003 by a satellite called the Wilkinson Microwave Anisotropy Probe, or WMAP, which occupies a stationary post 1.5 million kilometers from earth. Measurements from WMAP support a theory of inflation first proposed by Alan Guth in 1979 and since refined. It says — and the evidence confirms — that at an unimaginably short time after the Big Bang, the universe experienced an abrupt inflation, doubling in size over and over again until inflation stopped an unimaginably short instant later. The result is the relatively smooth and geometrically flat universe we find ourselves living in.

WMAP also suggests that the universe is made of 4 percent atoms (now called baryonic matter), 22 percent dark matter, and 74 percent dark energy. As an idea, dark matter first popped up in the 1930’s. Dark energy is the thought of the past few years. No one knows what either of them is, except that without them the behavior of the universe makes no sense. It’s worth remembering, too, that the modern idea of the atom — that is, the old-fashioned modern idea, well before quarks — only came together in 1932, when the neutron was discovered.

* * *

Someone, somewhere, is likely to be shouting, "Aha!" about now.

"You’re saying that our so-called scientific knowledge is only a projection of sorts and that there is no scientific truth, only relativistic assumptions — culturally created ideas — about the universe around us. Isn’t that what you’re saying?"

Thanks for asking. The answer is no. Science is a cultural enterprise, of course, like everything else humans do, and it sometimes suffers from characteristically human flaws. But the recentness — or, to put it another way, the evolution — of what we know about the universe around us doesn’t reveal the indeterminacy of science. It reveals the extraordinary intellectual and imaginative yields that a self-critical, self-evaluating, self-testing, experimental search for understanding can generate over time.

We know the universe to be a very different — and in every way more amazing — place than we did even a generation ago. We have no idea how much more surprising it will turn out to be in the years — not to mention the eons — ahead, should we manage to survive as a species that is able to do science. If what you want from life is a constant, fixed, unchanging truth, then the spate of fresh news from science can only seem bewildering. But the unchanging truths that people cling to in this inconstant world tend to rest on unexamined and untestable assumptions. At their best they are permanent ethical truths, which cannot be contradicted by the open-ended possibilities of scientific exploration. At their worst, they are mere dogma and deserve to be contradicted.

To me, the open-endedness of science isn’t its failing. It is its very beauty. Each answer is merely the prelude to the next question, and you never know when you’ll come upon an answer that forces you to rethink almost everything. This is as true in biology — itself overwhelmed by recent knowledge — as it is in cosmology. Yet many people can’t help hoping for a final set of answers. "So how old is it really — and how big is it really?" they ask about the universe, with an emphasis on "really." The fact that the answer depends on when you happen to ask it — 1931, 1955, 2003, today — seems to many people to imply that science has no answers worth giving.

But this is simply the bias inherent in living in the "now." Stated as a sentence, that bias goes like this: "We’re here now, so we expect some answers." Think about those analogies meant to convey the immensity of time. They always end in the present. Mankind emerges in the Garment District or at 11 seconds to midnight, and then what? The clock stops at the current time, as if the game is over. But there is no time limit on the questions science asks, and there is very little likelihood of a final set of answers. Humanity emerges, looks up at the stars, and soon there is a probe in space telling us that most of what exists is stuff we can’t identify. Who would want it any other way?

* * *

Thinking about the recentness of what we know is a way, I suppose, of thinking simultaneously about the strangeness of the past and the strangeness of the present — the reciprocal strangenesses that time brings about. I have a hard time trying to imagine the universe as it might have been in, say, 1920 — the whole of it packed into the Milky Way. But then I have an equally hard time imagining what it would have been like to be a hired hand on my grandfather’s farm in 1920. The changes in the way we live loom far larger in most of our minds than any changes in the theoretical model of a universe that most of us think about — if we think about it at all — only on a dark, clear night. But the changes go together.

I am at best the kind of cosmological reader who has to skip the math. As a result, my grasp on most of what astronomers have learned in my lifetime is largely esthetic. I admire the finished painting, but I have no real conception of what it means to apply the paint. And for me, in fact, the old forms of knowledge are hard enough. Not the ones rooted in dogma, but the ones rooted in a practical application of what astronomers have learned over the years. Understanding the motion of the moon through the sky is more complicated than it sounds, as I have discovered from trying to sort it out.

Knowing how and why the universe is expanding doesn’t change the rules of celestial navigation any more than it changes the stories people tell about the figures in the constellations. The recentness of what we know doesn’t annul the old knowledge; it transfigures it. Suddenly, what we used to know is now part of the story of how we go about knowing things and no longer a description of the universe around us. But go out on a deep summer night and there overhead are all the skies we have ever seen.