One of the fathers of the Big Bang was sitting across the aisle from me on the train, so I introduced myself. I had seen P.J.E. Peebles speak at a conference in Washington that afternoon at the National Museum of Natural History, and now we made small talk about this and that: the weather, a mutual acquaintance, the end of the universe. Then we shook hands and went our separate ways. But for the rest of the ride between Washington and Princeton, where he got off, I couldn’t help glancing across the aisle every so often and marveling at how recent our present conception of the cosmos is, that at any moment one of its founders might be sitting among us on a train, chatting with his wife and sipping a Budweiser.
It can be difficult to remember this when we look up at the night sky. Indeed, it is entirely possible to study the celestial vault and assume it to be eternally unchanging, as people did for thousands of years. It does change. We know that now. We watchers of the sky at the end of the twentieth century and the second millennium can take in stride that if we could see the heavens of 25,000 years into the future or into the past—or a million years, or a billion years—they wouldn’t look the same. Some parts would, of course, but others would be just enough out of alignment to seem more like glimpses into some seemingly identical yet maddeningly different parallel universe—which is, in fact, what they’d be. And that’s what’s easy to overlook on a day-to-day, or night-to-night, basis: The universe we inhabit is alive in time, a mutating organism, a work in progress complete with beginning, middle and, maybe, end. It was the end of the universe that had brought me to Washington on a warm, wet Sunday afternoon—specifically, a symposium on the eventual fate of the cosmos. I had invited my son to accompany me, and knowing that he’d find the conference itself dull, dull, dull, I’d planned a detour first, past something I imagined any seven-year-old would find irresistibly fascinating: dinosaurs.
I was wrong. We got to the museum early enough to stroll through the vast dinosaur halls at a leisurely pace, but after a few minutes my son was practically racing past the creatures, granting them barely a glance. It took me several more minutes to realize why. Partly it was because he’d seen dinosaurs on field trips to the American Museum of Natural History back home in New York. But partly he couldn’t react to these behemoths with what I considered the requisite awe and honor because he couldn’t comprehend the implications of their existence, and of their extinction. To him, they were neither freaks of evolution nor harbingers of mortality. They were just so many stuffed animals and stacks of bones from tens of millions of years ago—neat, to be sure, but hey, what’s next?
Then he saw the video monitor. (Of course, I sighed to myself, TV.) It was in the next room, a hall devoted to geological eras, and across the screen danced an animated reenactment of continental drift in reverse chronological order: This is what the Earth looked like 200 million years ago…400 million years ago…800 million years ago. My son drew nearer, watching as the familiar geographic shapes of today lost their moorings and began to drift, bumped together like boats in a harbor after a hurricane, until they finally fused into one single primordial land mass.
Is that still happening? he wanted to know. Are the continents still moving?
I saw my opening, and I seized it. I explained how the continents are in fact still moving, only so slowly that you can’t really see it except over time scales in the hundreds of millions of years, and how in fact it was only when people started finding fossils of dinosaurs, within the past couple of hundred years, that they began to consider the possibility of the Earth changing over time, and how once people started thinking about that—well, then the natural next step was to wonder whether the whole universe changes over time. In fact (I went on, pushing my luck), inside the very auditorium where we’re going to be sitting this afternoon for the symposium, a famous debate once took place between two astronomers about how big the universe is, and only since then have scientists figured out that the universe does indeed change over time—and that debate was only back in 1920.
I’d gone too far. His face was blank, his eyes beginning to wander. (What’s next? What’s next?) And then I realized why I’d lost him I’d given him a frame of temporal reference he couldn’t comprehend. So I gave him one he could. “Nineteen-twenty,” I said, “is the year that your grandfather—my father—was born.”
I stopped there. I didn’t tell him that what resolved the so-called Great Debate of 1920 was Edwin Hubble’s discovery four years later that at least some so-called nebulae, or what we today would call galaxies, are external to our own. Nor did I mention Hubble’s subsequent finding in 1929 that indicated that galaxies seem to be moving away from one another at speeds directly proportionate to their distance—that the universe is expanding. I didn’t tell him that in 1931 a Belgian Jesuit priest named Georges Lemaitre worked backward from this proposition, mentally running the universe in reverse in much the same way that the animation on the monitor had depicted continental drift, until he arrived at a single, compact, “primeval atom”; that a Russian-American physicist named George Gamow later endowed this concept with a mathematical basis, to which his partners, the Americans Ralph Alpher and Robert Herman, added the prediction of a still extant background radiation, the fossil record, in effect, from that moment of creation; and that in 1964—when I was slightly younger than my son—a team of researchers working in New jersey found the telltale radio waves from that initial period of creation, thereby providing the crucial validation for what by then had come to be known as the Big Bang.
The night sky hasn’t changed much since 1920—no more than usual, anyway. What’s changed instead is the way we think about it. Just like my son, we needed to adjust to a new frame of temporal reference, one that stretches back millions, then billions, of years. And now here we were, walking into an auditorium to hear two cosmologists—including Dr. Peebles, a member of that Big Bang team from 1964 and now Albert Einstein Professor of Physics at Princeton University—discuss what might be waiting at the other end of the creation continuum: the fate of the universe.
When we left the museum at the end of the day, I thanked my son for enduring what must have been a dull afternoon. He tried to assure me that it hadn’t been dull at all, but I told him I’d seen him napping and I didn’t mind; he didn’t need to be polite on my account.
“Well,” he said, sighing, surrendering to his exasperation, “it’s just—Big Bang, Big Bang, Big Bang. It’s all anybody wanted to talk about was the Big Bang!”
That’s just about right, I thought, as we tried to hail a taxi to take us to Union Station and what would turn out to be our ride across the aisle from Dr. Peebles. One generation—my father’s—arrives at a bold break-through interpretation of the universe. The next generation follows that interpretation to its inevitable conclusions. And now the members of the generation after that claim this knowledge as their birthright, carrying it in their bones, growing up with a sense of entitlement that allows them to demand of science and of the universe, with an impertinence that perhaps only a seven-year-old can muster: What’s next?
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