Trespassing on Einstein's Lawn (6 page)

As I paged through Smolin's book on the subject, one section caught my attention. The universe, he wrote, has to be considered a closed system.
“It is true that the universe is as beautiful as it is intricately structured. But it cannot have been made by anything that exists outside it, for by definition the universe is all there is, and there can be nothing outside it. And, by definition, neither can there have been anything before the universe that caused it, for if anything existed it must have been part of the universe. So the first principle of cosmology must be ‘There is nothing outside the universe.' ” I couldn't help thinking that the same principle would have to apply to my father's H-state, since nothing, by definition, was infinite and unbounded. It had no outside.

My father gave up reading around 4:00
A.M.
, but I made it through the night and in the morning wrote the best email I could manage on no sleep, offering a breezy, off-the-cuff explanation of loop quantum gravity.

But something was nagging me. At the Wheeler symposium, Markopoulou's talk had been about more than atomic geometry—it had been about the meaning of observers in a quantum universe. “A physical cosmological theory must refer to observers inside the universe,” she had said, echoing Smolin's first principle. Rather than a single description of the universe from the outside, the best we can get is a vast array of partial internal views. Quantum gravity, she said, ought to be a set of rules for translating between them. Markopoulou's internal cosmology,
built of observers' limited perspectives, reminded me of Wheeler's suspicion that observers play some part in the creation of the universe. Did her loop quantum world have something to do with Wheeler's self-excited circuit? I knew if I could get the
Scientific American
article, I'd have my chance to find out.

I was sitting at my computer at
Manhattan Bride
when the email from Phil popped up in my in-box. I glanced over my shoulder and made sure Rick was engrossed in the layouts he was fiddling with on his computer screen before opening it:
Hi
,
Amanda. Thanks for this. Would you be interested in writing a profile of Fotini Markopoulou?

I called my father, huddling over the phone, my hand covering my mouth so Rick couldn't hear. “I'm writing for
Scientific American
,” I whispered. “We're in.”

I made a plan to meet Fotini Markopoulou a few months later when she would be visiting New York. The following morning, I walked into the office and quit.

“It's not personal,” I told Rick. “It's just that I want to write about physics.”

“Maybe I could find a way for you to do that here,” he said.

I blinked. “For a bridal magazine?”

An hour later I was back on the subway headed for Brooklyn. As the train made its way downtown toward Wall Street, it dawned on me that quitting my job might have been impulsive. One article was not going to pay the bills, and neither was my quest for ultimate reality, no matter how impassioned. But by the time we hit the East River, I was sure I had made the right call. In my bones I knew that this was the start of something big. That there was a leap to be taken, that adventures would ensue. That if we were going to do this thing, we needed to take it all the way.

My excitement descended into nervousness when I called my parents. “I know it wasn't the most fiscally responsible decision,” I said sheepishly. “But it felt right.”

“You've got to trust your gut,” my father said. “Money is useful. But this thing is
important.
”

I heard my mother sigh. “You better hope you can marry a doctor.”

Without a day job to worry about, I dedicated all of my time to reading and thinking about physics. Unfortunately, to my friends and to the boyfriend I was living with at the time, “thinking about physics” looked awfully similar to “doing nothing.” When I explained myself, everyone nodded politely, but their questions betrayed a deep conviction that I had officially lost my mind. “It's just that, well, do you think it might be difficult to devote your life to physics when you've never taken a single physics class?” they'd ask.

“Nah,” I'd say. “It'll be a piece of cake.”

To keep me in cash, I worked a few nights a week in my brother's Manhattan nightclub as a coat-check girl. It was a good gig. Amidst the deafening thump of hip-hop, in my miniskirt and high heels, I'd sit on the floor, lean back against a mountain of designer coats, and silently read about the universe.

When the weather warmed, I spent my afternoons sitting outside on the stoop with Cassidy, my black Labrador retriever, soaking in the sunlight and thinking about reality in preparation for my meeting with Fotini Markopoulou.

I knew that physicists needed a theory of quantum gravity because general relativity and quantum mechanics couldn't manage to peaceably coexist in a single universe. But what exactly made them so hopelessly incompatible? Everywhere I looked I found technicalities—the world of relativity is continuous and the quantum world discrete; relativity regards positions in spacetime as well defined, while quantum theory renders them fuzzy. They were obstacles, sure, but they struck me as mere couple's squabbles, not deep, unbridgeable rifts. It was like relativity preferred chocolate and quantum theory vanilla—not like relativity was a Protestant and quantum theory was a duck.

Relativity, at its core, was about what space and time mean to different observers. It began with a simple question that obsessed a sixteen-year-old Albert Einstein. What would a light beam look like if
you were flying at the same speed alongside it? Would it appear to stand still, the way a car in the next lane looks like it's not moving if you're cruising alongside it at exactly the same speed? James Clerk Maxwell's equations of electromagnetism demanded that electromagnetic waves, otherwise known as light, always travel at 186,000 miles per second. Einstein immediately saw the problem. For an observer traveling at 186,000 miles per second, light's speed would drop to zero. And what then? Would electromagnetism cease to exist? Would the universe crumble?

Einstein realized that for the universe to hold together, and for the laws of electromagnetism to apply equally to every observer, there couldn't be any frame of reference in which light stood still. And while it seemed impossible, he knew there was only one way to make that rule hold: observers must always measure light to be moving at a constant 186,000 miles per second,
regardless of how fast the observers themselves are moving relative to the light.
No matter how fast you run you can never catch a light beam. Even if you were speeding alongside it, it would still stream away from you at a relentless 186,000 miles per second, a horizon that recedes just as quickly as you approach.

It's easy to miss how insane a statement that really is. Speed is a measure of how much space something crosses in a particular amount of time. For light to always move at the same speed regardless of how fast an observer is moving when measuring it,
space and time themselves
have to vary from observer to observer to make up the differences. The total distance in space and time
combined
remains the same for everyone—a unified four-dimensional spacetime that observers slice up in different ways, choosing some coordinates to call “space” and others to call “time,” according to their individual points of view.

Einstein knew that there had to be some way of translating between all the different points of view, some prescription for figuring out how the same spacetime appears to different observers, since presumably there's only one universe. When he found it, he named it special relativity—“special” because it only provided translations for observers in uniform motion. It did not contain the rules for translating between a uniformly moving, or inertial, observer and an accelerated one—suggesting that a guy cruising down Bedford Avenue at a constant
speed would find himself in a different universe than the guy who's picking up speed in the car next to him, even though they're both in Brooklyn.

For Einstein, this was nothing short of tragedy. He believed deeply that the true nature of the universe shouldn't depend on an arbitrary choice of coordinates. That reality was unified and singular, transcending our fragmented perspectives. That there was some way in which the world
really was
, in and of itself, regardless of who was looking or how they were moving as they looked. He was desperate to peel back the layers of false appearances and get at the truth that lay beneath. That meant finding a way to translate between what an inertial observer sees and what an accelerated observer sees. It was a mission that led him to create his masterpiece: general relativity.

I thought back to the night when general relativity had finally made sense to me. I'd been in high school and it was late at night; I was hunkered down at the kitchen table with my father. It was one of those perfect gestalt moments when something in the brain clicks and nothing is ever the same.

I had read all the usual explanations. That space and time are sewn together by the constant speed of light into a four-dimensional spacetime. That mass or energy in this spacetime causes its metric properties to warp, laying a landscape of slopes and valleys that we call the gravitational field. That what appears to us as the force of gravity is really space's hidden geometry.

Okay, so gravity isn't a force, it's the curvature of spacetime. Everyone said that as if it were to be followed by the sound of my kneecaps hitting the floor. But I didn't see what the big deal was. Sure, “the curvature of spacetime” sounded mysterious and arcane, but so did “the gravitational force.” It was like replacing one phantom with another.

“Think about it this way,” my father said, flipping to a fresh sheet of paper in one of those yellow legal pads he was always writing in. “This is a diagram of the universe,” he said, drawing an L-shaped coordinate system, labeling the vertical axis
time
and the horizontal
space.
“This area in here,” he said, sweeping his hand over the empty yellow expanse framed by the two axes, “is four-dimensional spacetime. Let's
say I'm moving through spacetime at a constant speed. So here's me.” He traced out a straight line, cutting a diagonal across the paper. “And you're moving at some different but also constant speed, so here's you.” He traced a second straight line, drawn at a slightly different angle. “But we're both looking at the same world. It might look different to each of us, we'll each measure different distances and times, what looks like space to you might look like time to me … but ultimately it's just one world described by two different points of view, right? So special relativity gives you the equations that allow you to rotate my path here in spacetime until it aligns with your path. That's a Lorentz transformation. You can move one until it lines up perfectly with the other—that tells you that we're looking at one and the same world.”

“Okay,” I said, curious to see where this was headed.

He flipped up the yellow paper to reveal a fresh sheet, quickly scratching out new coordinate axes. “Okay. Here's me again,” he said, drawing another straight line at an angle. “But this time, you are moving at a changing speed, you're accelerating. An accelerated path in spacetime is a curved line, right, because you keep crossing more space in less time,” he said, drawing a curve that swept up toward the right-hand corner of the page, then slowly arced back downward. “Now, imagine rotating your curve until it matches up perfectly with my straight line.”

I thought for a minute. “It's impossible,” I said. “A curve can never match up with a straight line.”

“But it is possible,” he said. “Einstein knew it
had
to be possible, because there's still only one universe. If you can't get that curve to match up with that line, it means that you and I see entirely different worlds just because I'm moving at a constant speed and you're accelerating.”

“Einstein figured out how you can make a curve match up with a straight line?”

“Yup.” My father looked at me, grinning. “Bend the paper.”

Suddenly it all became illuminated in what I can only describe as a religious experience. Somewhere a choir was singing “Hallelujah.”
Bend the paper!
If you wrinkle the paper in just the right way, you can turn a curve into a line. The wrinkles are gravity. They connect the
world. General relativity is at once incredibly profound and incredibly simple, a classic case of thinking outside the box. “That Einstein was some kind of freakin' genius, huh?” I said.

“The bending of the paper—of spacetime—is called a diffeomorphism transformation,” my father said. “You have to be able to curve spacetime to ensure that everyone sees the same reality. Here in the lower-dimensional world of space and time, we see the curvature as gravity.”

General relativity is about how we can stitch reality back together when it's broken into pieces by our various points of view. We
can
translate between the perspectives of inertial and accelerated observers—we just need gravity. An inertial frame with a gravitational field is indistinguishable from an accelerated frame without a gravitational field. That means there's nothing fundamentally unique about acceleration, and that all observers, regardless of their state of motion, are on equal footing. The universe looks radically different from one perspective to the next, but at the end of the day there's just one ultimate reality.

Quantum theory was a little more complicated. All the physics books I read told me not to feel discouraged if my brain blew a fuse while trying to comprehend it.
If quantum theory seems bat-shit crazy
, they'd say,
don't worry. It is.
Then they'd try to make me feel better by quoting a handful of brilliant quantum physicists talking about how no one understands quantum physics, and in case that wasn't enough to console me, they'd toss in some objections from Einstein to boot.