Trespassing on Einstein's Lawn (53 page)

I body-checked my way into a seat, and Witten's lecture finally began. He was a strange character—unnervingly tall and broad-shouldered, with a large rectangular head that had inspired my father to refer to him as “Ed the Head.” But despite his looming presence and intellect, Witten spoke in a soft, whispery, high-pitched voice, an incongruity that lent him an air of otherworldliness. (M is for
mother ship
?) He was widely considered the smartest man alive.

Actually, this was the second time I had seen Ed Witten. The first was many years earlier, about a month after the Davis conference in 2003, when the American Physical Society held a meeting in Philadelphia. I had scored myself a press pass and my father had snuck in to watch with me as Wheeler was awarded the Einstein Prize. Afterward, we were taking an escalator down to the ground floor when we noticed Witten standing a few steps ahead of us. We had watched as he stepped off the escalator and into a revolving door. He attempted to push the door clockwise, and when it didn't budge, he inexplicably continued pushing it for several seconds before deciding to turn around and try pushing it the other way. My father and I had looked at each other, trying not to laugh out loud. We were thinking the same thing: that is the smartest man alive.

Now, at Harvard, I watched as he scribbled incomprehensible equations on the blackboard, his pants covered in chalk. I had no idea what he was talking about. It wasn't just that the subtleties of his argument were lost on me, or that the math threw me off—I couldn't even figure out what the topic was. Everyone else, however, seemed thoroughly engaged. Even the blind guy was following along. I had grown accustomed to the feeling that I could see through the equations to the concepts beneath, but today they were an opaque reminder that, no matter what Smolin said, I
was
on the outside of this universe, circling its periphery like someone locked out of her house, sizing up the interior, pathetically trying to find a way in.
M
is for
mediocre.

When the talk ended, I approached Witten, introduced myself, and asked if he might have some time to talk with me while he was in town. He paused. What seemed like minutes passed. He paused for so long that I began to wonder if I should just walk away, and I was about to when he said, “I can do it at my hotel, the Inn at Harvard, tomorrow after I've finished my breakfast at eight-thirty
A.M.
”

Eight-thirty
A.M.
? There were very few people on the planet for whom I'd be willing to be anywhere at that hour. Johnny Depp, probably. Fiona Apple. A resurrected Albert Einstein. And, apparently, Ed Witten.

I nodded, and before I could say another word, he turned around to talk with someone else.

The following morning, at the crack of dawn, I made my way into the Inn's dining room, which sat beneath a vaulted glass atrium, bathed in the painfully early morning glow. I spotted Witten and awkwardly joined him at his table, hoping to God he remembered our ten-second conversation the day before and didn't think I was some weirdo off the street hoping to polish off his yogurt.

It was more than a little intimidating, talking to Ed the Head in person. It was obvious that he had no interest in small talk and that I should jump right in with questions. “What the hell were you talking about yesterday?” seemed like a bad way to start. But what was a good way? What exactly does one say to the smartest man alive?

M
is for
mute.

“What are you working on these days?” It was the best I could come up with.

“I'm working on an application of physics ideas to math, particularly to understanding knots better,” he said in that surreal whisper.

Knots? Was that what yesterday's lecture had been about?

We discussed knots for a bit before I transitioned into dualities and their erosion of ultimate reality. I was eager to get his perspective on M-theory's elusive ontology. (
M
is for
missing.
)

“Initially, when people talked about string theory, they said okay, point particles are really just strings,” I said. “Then with the second
revolution, with M-theory, we found there weren't just strings but branes of every dimension. And now with dualities we see that strings are equivalent to particles again in certain situations. Is there a fundamental entity that everything is made of?”

“The dualities would contradict that idea, because in each description a different aspect of the theory is fundamental and other things are derived,” Witten said. “There are fundamental ideas rather than fundamental physical objects.”

Fundamental ideas rather than fundamental physical objects.
It was like structural realism meets Berkeley's
esse est percipi.
(
M
is for
mind-dependence
?)

“You ushered in the second string revolution,” I said. “Do you foresee a third one coming?”

“My crystal ball is cloudier than when I was younger. By definition a revolution is hard to foresee. But in the mid-eighties and mid-nineties, before the second revolution happened, there were kind of hints that something was going to happen—I didn't know what, of course. I don't have that same feeling now, but perhaps other people do.… If I had my druthers I'd like to go deeper into what's behind the dualities, but that's really hard. Maybe that's the third string revolution. Or maybe it's something that won't be understood for a long time.”

My mind flashed back to the revolving door. “When you are doing everyday things—say, going to the grocery store or the dry cleaner's—are you thinking in eleven dimensions?” I asked. It seemed like a plausible explanation.

“Sometimes I'm able to continue thinking that way in my daily life and come up with key ideas while I'm doing an errand or something. Two of my key ideas came while I was riding on an airplane.”

I smiled. Then I asked
the
question.

“What does the
M
in M-theory stand for?”

“I didn't mean to confuse everyone with that,” he said. “The way I described it at the time was that the
M
stood for
magic, mystery
, or
membrane
, according to taste. But I thought my colleagues would understand that it was really for
membrane.
Unfortunately, it got people confused.”

So there it was.
M
is for
membrane.
Magical miracle mystery
solved. All that confusion just because nobody got the joke. To be fair, it was likely the first and only time Ed Witten had ever cracked a joke. But still.

The next steps involved polishing up the proposal, chatting with potential editors, signing a book deal, and, after six years more wonderful than I could have imagined or schemed, leaving my job as an editor at
New Scientist
to find out what would happen when I stopped pretending, sat down, and began to write.

Driving home from the
New Scientist
office on my last day of work, my mind flashed back to the family car trips we used to take when I was a kid. A few times a year we would drive from Philadelphia to Stamford, Connecticut, to visit my father's parents. My father would blast Bob Dylan, my mother would point out turns and exits as his mind inevitably wandered, my brother would put on headphones and sleep, and while the world passed by my window, I would curl up with a book and read.

My grandparents' home was a kind of autocracy that made our house look a hippie commune by contrast. My grandfather, a retired physician, was dauntingly strict and serious, with a piercing intellect and an insatiable appetite for knowledge. As a kid, I would stare with wonder at their looming library, at the hundreds upon hundreds of books on every subject imaginable: architecture, politics, art, ethics, religion, philosophy, science. My grandfather would find me standing
there, staring, and challenge me to a game of chess. Seated at the card table in the midst of the books, we would play, and with each move I made he would ask, “Are you sure you want to do that?” I would reconsider and change strategy and he would ask again until finally I found the proper move to satisfy him. While I studied the board for potential lines of attack, he would debate with me on matters of moral philosophy, speaking in a wildly grandiose vocabulary. Each time one of his words was met by a blank stare, he would send me over to the massive dictionary to look it up.

In his spare time, my grandfather wrote a treatise on biomedical ethics and composed crossword puzzles in Latin. In my spare time, I would wait until he left the room, move one of his countless trinkets not half an inch from its place, and then watch with perverse delight as he returned and, within seconds, adjusted it back to its initial position.

When it came to my grandfather, there were some things you just couldn't touch. One of them was Einstein. When I later wrote my article on Fotini Markopoulou, I showed it to my grandfather. As the piece was about loop quantum gravity and its attempt to reconcile general relativity with quantum mechanics, the
Scientific American
editors had titled the article “Throwing Einstein for a Loop.” My grandfather, glancing at the headline, declared it an insult to Einstein and dropped it on the coffee table, unread.

The pedestal on which my grandfather placed Einstein wasn't metaphorical. It sat next to a window, holding a large bust, Einstein's bronze eyes keeping watch over the living room. He wasn't the only one. Hanging over the television across the room was a sculpture of Homer in relief. As a kid, I would sit on the couch between them, looking at one and then the other, my eyes sweeping back and forth as if I were watching a tennis match, surveying those twin pillars of the world: words and ideas, story and science.

Just when everything had fallen into place, the ground gave way beneath me.

It started one afternoon when I was browsing the physics papers
on the arXiv and spotted a new one: “Black Holes: Complementarity or Firewalls?”

Firewalls? I was intrigued. The paper was written by Joe Polchinski along with Ahmed Almheiri, Donald Marolf, and James Sully. I grabbed a cup of coffee and sat down to read.

In the paper, the authors once again sent Screwed plunging into a black hole, then compared his view of reality with Safe's. But rather than worrying about the illegal cloning of quantum bits, this time they were worried about entanglement.

To begin their thought experiment, Polchinski and crew waited until the black hole had evaporated away to less than half its original size. That was important, I remembered, because it's not until the halfway point that Safe can extract even a single bit of information from the Hawking radiation. Then they sent Screwed hurtling toward the horizon as Safe watched from afar.

Now consider, they said, a bit of information—call it B—just outside the black hole's event horizon. In Screwed's reference frame, B is part of the vacuum. Screwed, after all, is in an inertial frame, one devoid of boundaries, allowing all the positive and negative frequency modes of the vacuum—all those pairs of virtual particles and antiparticles, those uncertainty-born fluctuations of zero-point energy—to cancel out to a perfect zilch.

Guaranteeing their cancellation is entanglement, a form of quantum superposition in which two particles—such as a virtual particle and antiparticle pair—are described by a single wavefunction, a whole that's greater than the sum of its parts. Because the two particles form a single quantum state, their properties will remain correlated no matter how far apart they are. If, upon measurement, one is found to have a positive frequency, the other is guaranteed to have a negative frequency, a correlation that ensures everything adds up to zero and the vacuum remains a vacuum. The bit B, according to Screwed, is entangled with its opposite bit, A, deep in the black hole's interior.

Safe, however, disagrees. According to Safe, B is not a virtual vacuum mode but a real particle, a bit of Hawking radiation. That, I had learned back in London, was because the horizon restructures the vacuum, separating what was once a virtual particle from its antiparticle
mate, severing their entanglement, preventing them from canceling each other out and leaving instead a net positive gain, promoting B from virtual to real, transforming, bit by bit, what was once an empty vacuum into what is now a seething swarm.

No, Safe insists, B is entangled not with its counterpart inside the horizon but with another bit of Hawking radiation—call it R—that emerged earlier in the evaporation. That's required to prevent information loss. As Susskind had insisted—and Hawking eventually conceded—Safe will never see information vanish. Instead of disappearing into the black hole, Safe sees it burn up at the horizon, scrambled beyond recognition and then radiated back out. Because it's scrambled, the information no longer resides within a single Hawking particle, but in the entangled correlations among the radiation.

Thus, the paper's authors said, we have a paradox. Screwed says B is entangled with A. Safe says B is entangled with R. And quantum mechanics says that one of them has to be wrong. A bit can't be fully entangled with more than one other bit. Entanglement is monogamous.

As I sipped my coffee, I wasn't worried. The contradiction sounded exactly like the kind that Susskind's complementarity was designed to resolve. After all, complementarity allows you to describe either what's on one side of an event horizon or what's on the other—but never both. Just restrict your description of B to a single frame, Safe's or Screwed's, and entanglement will always appear monogamous, I thought. No problemo.

But as I kept on reading, problemo. Unlike the original cloning paradox, this one doesn't disappear upon restriction to a single observer's frame—because the measurement on B takes place outside the horizon for
both observers.
They are still in causal contact; they can communicate. Screwed can measure B, find that it's entangled with A, then turn around and tell Safe, who insists that, au contraire, B is entangled with R. The contradiction lives in a region where the two observers' light cones overlap. Complementarity prevented quantum cloning because by the time the duplication appeared, Safe and Screwed could no longer compare notes. In this case, they can.
“Complementarity,” the authors concluded, “isn't enough.”