Trespassing on Einstein's Lawn (11 page)

All the data were in rather spectacular agreement. As for inflation, WMAP had confirmed its most generic predictions. The temperature fluctuations didn't exhibit any characteristic scale, and the hot and cold spots were distributed randomly. Plus, a flat universe was exactly what inflation had ordered, because even if it were curved, the radius of curvature would be blown up to such large proportions that it would look flat anyway, just like the Earth looks flat around my feet. The physicists were so pleased with WMAP's vindication of inflation, they
were practically glowing. There were rumblings that Guth would win a Nobel Prize.

But beneath the celebratory mood, something wasn't quite right. One piece of the WMAP puzzle didn't add up. Inflation predicted that the temperature fluctuations would occur at all scales, but at scales larger than 60 degrees across the sky, they abruptly stopped. Whenever this problem, known as the “low quadrupole,” was mentioned, every physicist's face seemed to darken with worry, and while I wasn't sure why, I had the sense that it might be a bigger problem than they were letting on.

If there is one larger-than-life superstar, a Michael Jackson of physics, it's Stephen Hawking. Seeing him in the flesh was surreal. Even the other physicists, many of whom had known him for years as a colleague and a close friend, seemed a bit slack-jawed in his presence.

During one of the lectures, I sat directly behind Hawking. I was trying my best to pay attention to the speaker, but I found myself mesmerized by the words flashing on the computer screen mounted to the arm of his wheelchair. Paralyzed to the brink by a motor neuron disease, Hawking had one last functioning muscle, in his cheek, and by twitching it he could control the cursor on his monitor. The cursor constantly scrolled through a catalog of Hawking's most commonly used words, and with a properly timed twitch he could select one from the list. Twitch by twitch, Hawking could slowly, arduously build sentences, which were then sent to a speech synthesizer that spoke the words for him in a robotic voice that lacked not only a sense of humanity but also, as Hawking lamented, a British accent.

Seeing him there in front of me, his body slumped over in his wheelchair like a deflating balloon, I found myself in even greater awe of all he'd been able to accomplish. And as I watched the words flash across his monitor, knowing full well that they were nothing more than random lists, I couldn't help thinking that if I watched them closely enough, I'd glimpse the answers to the universe.

* * *

When the meeting broke for lunch, everyone headed outside. Lunch wasn't provided, so we were free to go off on our own. I noticed Lisa Randall, the Harvard physicist, standing on her own, likely waiting for someone, so I approached and introduced myself. In her talk, Randall had pondered the mysterious origin of the inflaton field, which I was glad to hear, as I was sitting there pondering it myself. The inflaton, in its false vacuum condition, was responsible for triggering inflation and spawning the large, uniform, star-speckled universe we know and love—but what had spawned the inflaton? Some other mysterious field? And behind that? Was it turtles all the way down? I was about to ask her when a few other physicists approached. “We found a restaurant. Let's go get lunch.”

Chatting with Lisa Randall at UC Davis
Dan Falk

They seemed to be speaking to me, too—or at least they hadn't specifically asked me
not
to come, which I figured was as good as an invitation. So I tagged along and soon found myself at a long table in a casual Italian restaurant with Sir Martin Rees, Britain's Astronomer Royal; David Spergel, a Princeton physicist who played a key role in analyzing the WMAP results; Randall; and a few legit journalists.

After everyone placed their orders, the conversation turned to the dreaded A-word—dreaded but looking less avoidable by the day, given its ability to explain the inexplicable.

Like dark energy. Physicists knew from the supernova data, and now from WMAP, that dark energy is extremely sparse, a meager 10
^-23
gram in every cubic meter of space, barely a whisper in the dark void of the vacuum, but a whisper that builds with distance and at large enough scales crescendos to an audible howl.

That's because the most likely identity of the dark energy is the energy inherent to the vacuum of space itself, christened by Einstein as the “cosmological constant.” Its power lies in its constancy—as space grows, everything in it gets diluted out,
except
for the dark energy, whose density remains constant. More space, more dark energy: the kind of feedback loop that takes off running.

You'd think that physicists could have predicted the observed strength of the dark energy, given everything they already know about the quantum vacuum. Quantum field theory provides all the tools you need to calculate the vacuum's energy. Unfortunately, the calculation comes out wrong.
Really
wrong. According to the theory, the vacuum energy should be infinite. Clearly it's not infinite, otherwise we'd all have been ripped to shreds by the blazing expansion of space. Since objects aren't spontaneously combusting all around us, the vacuum must be a reasonably calm place, at least at atomic scales and bigger. So if it's not infinite, physicists had figured, it ought to be zero.

That sounded like a weirdly big leap, but zero and infinity are more similar than you'd think. They are the simplest and most elegant quantities to calculate. It's far tidier to come up with a theory that suggests that some number should be zero or infinity as opposed to, I don't know, 3,746. Finite numbers can seem pretty random. So if infinity was off the table, zero seemed like the next best choice. Physicists figured that there could be some feature of the vacuum with positive and negative contributions in equal numbers, canceling out to a perfect zilch.

But that was before astrophysicists traded pencils for telescopes and actually measured the value of the dark energy, finding that it was almost zero, but not quite. It was the worst kind of number: tiny but finite. Getting the right value would require some mechanism that could take quantum field theory's infinity, cancel it to zero out to 120 decimal places, and then miraculously stop, leaving some minuscule crumbs behind. Crumbs that could hijack the universe.

A number that fine-tuned is rare, to say the least, and physicists hadn't been able to dredge up a single good explanation. In desperation, they turned to the
A
-word. As it happens, dark energy's bizarrely fine-tuned value fits squarely in the narrow range that would allow
atoms, stars, carbon, and eventually life to exist. A little larger or a little smaller and our Goldilocks existence would be shot. In itself, that observation makes the whole situation worse—now not only is it an incredibly unlikely value, it's also, coincidentally, exactly the kind of unlikely value that life requires. Lucky us. It was the kind of coincidence that carried the unpleasant whiff of fate and teleology. But there was a catch. Dark energy's value is only a coincidence so long as our universe is the only universe around, and according to inflation, getting a single isolated universe is virtually impossible. Once you inflate one, you're stuck with an infinite number of them, a vast and varied multiverse. If every one of those infinite universes has a different amount of dark energy, then the tiny amount in ours is not only more likely, it's inevitable.

It was an answer, but not the kind physicists were hoping for, an explanation that placed disturbing limits on the very nature of explanation. Physicists want the laws of physics to be beautiful, basking in unity and inevitability. They want to perform elegant calculations, derive singular solutions, and know that the world had to be exactly as it is because it reflects the harmony and order that permeates a cosmos built of Platonic perfection. No one wanted to think that it was all a fluke, a petty accident of location. It was depressing.

Rees, who was extraordinarily polite and appeared to be carved of wax, explained that he takes the multiverse idea seriously and believes that anthropic reasoning is not only justified but necessary. Still, he said, physicists should go about their work as if it isn't, otherwise they risk getting lazy. They should still keep on trying to calculate physical laws from first principles, even if it's not going to happen. Spergel wasn't so enthused. Anthropic reasoning, he said, was nothing but scientific surrender.

Sitting there quietly, I couldn't help thinking back to something Wheeler had once written:
“If an anthropic principle,
why
an anthropic principle?” For Wheeler, the
A
-word wasn't an explanation, but a
clue
—a clue to the role of observers in the origin of the universe, a clue to the nature of ultimate reality.

I was building up the courage to bring this up when Rees suddenly
steered the conversation to politics, bioterrorism, and nuclear war. Over paninis and espressos, he explained that humanity has a fifty-fifty shot of destroying itself by the end of the twenty-first century. For a knight, he was a serious buzzkill.

Of all the brilliant people gathered at the conference, I was most intimidated by the prospect of talking to Timothy Ferris. Maybe it was because Ferris was a writer, not a physicist. His book
Coming of Age in the Milky Way
was one of my all-time favorite physics reads. When it came to the physicists, I was in awe. With Ferris, I was a fan.

So the next day, as everyone filed into the auditorium for a lecture and I spotted Ferris taking a seat in the front row, I quickly slid into the seat behind him, hoping that I would eventually think of something brilliant to say to him. I didn't. But when the lecture ended, Ferris turned around and asked, “How are you getting to the banquet tonight?”

The conference organizers had planned a banquet at the California Railroad Museum, about a half hour away in Sacramento's historic district. “I think they're busing us out there,” I said.

Ferris gave me a look as if to say,
Do I seem like the kind of guy who rides a bus?
“I have my car here,” he said. “I'll have to get directions. I don't want to get stuck there waiting for a bus. These conferences are great for the physics, but for social events …” He gave me a knowing smile. “If you decide you want to cut out early, just look for me. I'll give you a ride back to Davis.”

I was itching to find out more about the worrisome low quadrupole, and during a coffee break I found my chance. As everyone milled around outside enjoying the California sun, I introduced myself to Lyman Page, a Princeton physicist and one of the lead investigators on the WMAP team.

“What's so problematic about the quadrupole?” I asked him.

Page explained that the lack of temperature fluctuations at scales
larger than 60 degrees seemed to imply some kind of cutoff on the size of space itself.

That made sense. The temperature fluctuations had been formed when the hot plasma of the early universe was compressing and expanding, and that cosmic accordion was playing throughout all of space. If there were no fluctuations at scales larger than 60 degrees on the sky, it was as if there was no
space
at scales larger than 60 degrees on the sky. As if the universe were finite. Of course, those 60 degrees corresponded to the size of the universe at the time the CMB photons were first released. That region of universe has since undergone 13.7 billion years' worth of expansion. So the question was, if the size of space back then was capped at 60 degrees across today's sky, where does space end now?

The answer was shocking. Not only did the low quadrupole imply that the universe is finite, it implied that it's
small
—claustrophobic by cosmological standards. Stranger still, it implied that it was almost
exactly
the size of our observable universe. That if we could somehow peer just beyond the edge of our light cone, there would be nothing there to see.

“Could it be a glitch in the data?” I asked.

“No,” Page said. “It's there. It's there to stay. It was there in the COBE data, too, but the signal-to-noise ratio wasn't high enough. Seeing it in the WMAP data is a wake-up call that there's really some potentially new stuff going on.”

I had to wonder about inflation. The whole idea behind the theory was that spacetime gets stretched out far beyond our cosmic horizon, blowing up to such a huge size that monopoles disappear and curvature becomes negligible. “If that's true, and the universe really is small,” I asked, “what happens to inflation?”

“Ninety percent—well, I'm leaving out Linde here—but ninety percent of inflationary guys would say, now we need a different model because a finite universe is just too weird,” Page said. “It would mean the whole mechanism is off. I think it bothers all of us.”

I was curious to know why Page had singled out cosmologist Andrei Linde as the one guy who wouldn't give up on inflation even in the face of a finite universe, so when I spotted him standing in the courtyard, I headed his way. I thought perhaps he had an idea of how inflation
could explain such a phenomenon—I had no clue that it was simply because Linde was some kind of inflationary fundamentalist.