Trespassing on Einstein's Lawn (60 page)

“In classical physics you can find out the state of a system, and then someone else can come along and find out the state of the same system, and you'll both agree,” Zurek had told us. “In quantum mechanics, that's generally impossible.”

I understood now why it was impossible. Making a quantum measurement amounted to choosing a reference frame. In the non-Boolean superposition of every possible point of view, there's no differentiation, no information. Quantum interference makes sure of that. When you make a measurement by selecting a single point of view, a Boolean logic, yes or no, you break the symmetry of the superposition and create, at random, a bit of information. “That's the participatory business,” Zurek said. “That's a hint of how this universe is built.”

“If the world wasn't quantum mechanical,” I said to my father, “then it couldn't possibly have arisen from nothing. I don't mean that in the usual way people mean it, like quantum mechanics takes some state that you call ‘nothing' and then uses the uncertainty principle to transform it into something. That's trivial. That's assuming quantum mechanics from the start. What I mean is that if the world weren't described by quantum mechanics, then logic would be Boolean, and reality would be invariant. All observers would agree on the truth-value of propositions. They'd agree on what's real. There would be no interference between their perspectives; physics would be classical. But when you have invariance, you have
something.
Something you can't explain away. There would be a reality that's ontologically distinct from nothing, and then you'd be stuck with this unbridgeable divide that logic can't fix. It doesn't make sense to say that the universe came from nothing but is now something—there's no way to get from one to the other. It does make sense if the universe
is
nothing. But if the universe is nothing, then only nothing is ultimately real. Nothing is invariant. And that lack of invariance shows up, to us, as quantum mechanics.”

“So a universe that had some kind of real existence, a universe that was
something
, wouldn't be described by quantum mechanics?”

“That's my hunch,” I said. “Wheeler always knew that the quantum was a clue. I think it's a clue to the observer-dependence of reality. To the fact that everything, at bottom, is nothing.”

“You know the story of Plato's cave?” my father asked. “All the prisoners are chained up in the cave and they can't see the real world outside, only the shadows on the wall? That's supposed to be a negative thing, like they'll never know reality. But the truth is, you have to
be stuck inside a limited reference frame for there to be any reality at all! If you weren't chained to your light cone, you'd see nothing. The H-state.”

I nodded. “You'd have no information. You need the broken symmetry, the shadow, to have information and information gives rise to the world. It from bit.”

I couldn't help but grin with excitement. The message was clear: having a finite frame of reference creates the illusion of a world, but even the reference frame itself is an illusion. Observers create reality, but observers aren't real. There is nothing ontologically distinct about an observer, because you can always find a frame in which that observer disappears: the frame of the frame itself, the boundary of the boundary.

“If physicists discover an invariant someday, the game will be up,” my father mused. “That would rule out the hypothesis that the universe is really nothing.”

That was true. But so far, at least, every last invariant had gone the way of space and time, rendered relative and observer-dependent. Spacetime, gravity, electromagnetism, the nuclear forces, mass, energy, momentum, angular momentum, charge, dimensions, particles, fields, the vacuum, strings, the universe, the multiverse, the speed of light—one by one they had been downgraded to illusion. As the surface appearance of reality fell away, only one thing remained. Nothing.

In my mind, these conclusions were greeted by a sudden fanfare. Lights flashed and balloons and confetti came pouring down from the ceiling, like we were the hundredth customer in the grocery store checkout line. Throngs of cheering people filled the restaurant and crowded around us, applauding. Looking out into the crowd, I noticed some familiar faces. There, in a flowing skirt, was Fotini Markopoulou, and next to her I saw Carlo Rovelli and Lee Smolin. Alan Guth was there with his giant yellow backpack, as was James Ladyman, dreadlocks spilling down his back. Timothy Ferris stood dangling his car keys from his finger, and Andy Albrecht was laughing and waving his hand as if to say,
Don't worry about it!
Off to one side I spotted the Panama hat: Brockman and Matson were there. Behind them I saw Phil, from
Scientific American
, and for a minute I swore I caught a
glimpse of Rick from
Manhattan Bride.
Through the commotion I heard Susskind's Bronx inflection, and I looked over to see him standing with Raphael Bousso and Tom Banks. Joe Polchinski was there, too, as was Ed the Head, and next to him, in his wheelchair, was Stephen Hawking. I spotted Kip Thorne in the back donning a Star Trek uniform, and I saw a crop of bushy hair that I presumed to be Zurek. Scurrying happily around everyone's feet were seven rats tittering and shouting, “Gotcha!”—one of them sporting a large X-shaped bandage where the base of its tail would have been. Suddenly the crowd grew quiet and parted, creating a path for an older man who slowly made his way toward our table. As he neared I saw that it was Wheeler. He shook my father's hand, then mine. He smiled, a perceptible gleam in his eye. “I told you persistence would be rewarded.”

In real life, the restaurant was quiet, the world still littered with unanswered questions. In real life, we clinked our glasses together, smiled, and drove home.

Back in my old bedroom, I curled up in bed with my notebook, my eyes retracing those clues.

My father's definition of nothing had made it possible to cross that ontological divide between nothing and something, and the radical observer-dependence of every ingredient of reality down to reality itself made it possible to cross back. We had found the universe's secret: physics isn't the machinery behind the workings of the world; physics is the machinery behind the illusion that there
is
a world.

Still, so many questions remained. It wasn't clear yet what the new paradigm in cosmology would bring—Hawking and Hertog's top-down cosmology, Banks's holographic spacetime, or something else altogether. It wasn't clear what new ingredients might still be buried among the dualities of M-theory. A positive cosmological constant seemed to be required to ensure that nothing would look like something, but would an ultimate theory ever uniquely determine its value, or was its value irrelevant in the same way that the particular values of the speed of light or Planck's constant were? How would the mystery of dark matter be resolved? Would some new twist in the data appear in the
tunnels of the Large Hadron Collider or the patterns mapped by the Planck satellite that would send everything we know spinning on its head?

Personally, I was glad for all the unanswered questions—they meant my father and I weren't done yet, that we were still in it together. For me, chasing the mysteries of the universe and growing up had always been one and the same, and I wasn't ready to be done growing up just yet.

We are each the author of our own universe
, I wrote in my notebook,
but it's comforting to know that there is some other reference frame in which my father and I are both characters, side by side, partners in crime.
It was my last sentence on Earth, just in case I needed it.

I thought back to that day in Princeton when we first crashed the party. I thought about Wheeler's four questions and how we might answer them after everything we'd learned. It from bit? Yes, but each observer creates different its from the same bits, bits that are themselves observer-dependent and arise from the asymmetry wrought by a finite reference frame. A participatory universe? Participatory, yes; a universe, no. It was one participatory universe per reference frame, and you can only talk about one at a time. Why the quantum? Because reality is radically observer-dependent. Because observers are creating bits of information out of nothingness. Because there's no way things “really are,” and you can't employ descriptions that cross horizons. How come existence? Because existence is what nothing looks like from the inside.

It was time to start writing my book. From a justified line into the margin. I took a deep breath.

It's hard to know where to begin. What even counts as a beginning? I could say my story begins in a Chinese restaurant, circa 1995, when my father asked me a question about nothing. More likely it begins circa 14 billion years ago, when the so-called universe was allegedly born, broiling and thick with existence. Then again, I've come to suspect that
that
story is only beginning right now. I realize how weird that must sound. Trust me, it gets weirder.

I cannot express the depth of my appreciation to the many physicists who have patiently and generously offered me their time and wisdom over the years, and who have no idea what a profound influence they've had on my life. I'd especially like to thank Lenny Susskind, Raphael Bousso, Fotini Markopoulou, Joe Polchinski, Alan Guth, Tom Banks, Carlo Rovelli, Wojciech Zurek, Kip Thorne, Lee Smolin, and James Ladyman.

This book would not exist without the help of my kickass agents, Katinka Matson, John Brockman, and Max Brockman, who now (embarrassingly) know just how long I've dreamt of working with them. I want to thank them for taking a chance on me and for helping me to find my voice.

It has been a joy and privilege to work with the editorial team at Random House, and particularly with my editor Mark Tavani, who took on this project when others fled and who always remained in my corner. This book would have been a mess if it weren't for the genius copyeditor, Sue Warga, and the ever-helpful production editor, Loren Noveck. Thank you also to Luke Dempsey—wherever you are—for believing in this book from the start.

My extreme gratitude goes to the library staff of the American Philosophical Society, and particularly to Charles Greifenstein, for affording us access to the John Wheeler journals and for preserving a priceless piece of intellectual history.

I owe a special thanks to the brilliant, kind, and hilarious Maggie McKee, who graciously read the entire manuscript and offered invaluable guidance, and to Hester Kaplan, for encouraging me to tell stories.
Thank you to Dan Falk for reading a bulk of the book and for ten years of friendship and physics.

A huge thank you to Philip Yam at
Scientific American
for giving me my start as a journalist, and to all the talented editors and science journalists I've had the pleasure of working with since. I am forever indebted to the entire
New Scientist
family, and especially to Michael Brooks, Michael Bond, and Valerie Jamieson for fighting for me and supporting me over the years.

Thank you to Samantha Murphy and Rebecca Rodriguez, my 24/7 lifelines and the best friends a girl could have. To Winston Loach for believing in me, and to Joe Kitsch for the inspiration. To Christina Shock Weiss, Stephanie Dresner, Kevin Kerrigan, Natasha Wehrli, Katherine Tomkinson, and all the friends who have lived with and encouraged my insanity over the years.

My family, and especially my grandmother Winnie Gefter, mean the world to me. I'd like to express my enduring admiration for William Gefter, who never underestimated the power of ideas, and my inexpressible love to Harry and Marion Bergelson, who are no longer with me but who helped me grow in ways I'm still discovering today.

This journey would never have gotten off the ground without the unfailing support of my mother, Marlene Gefter. She and my brother, Brian Gefter, have been my inspirations and my best friends—and for enduring countless hours of physics conversations at the dinner table they deserve some kind of medal.

Finally, a shout-out to Hunan Restaurant in Ardmore, PA, where my cosmic adventure first began. I'll never forget the cashew chicken.

Accelerated observer
An observer whose speed or direction of motion is changing. Goes by the name Safe. Can be found outside black holes.

Acceleration
The rate of change in velocity with respect to time.

AdS/CFT
Juan Maldacena's breakthrough 1997 discovery that string theory (with gravity) in an anti–de Sitter space with five large and five tiny dimensions is exactly equivalent to a conformal field theory (without gravity) on its four-dimensional boundary. What look like strings on one side of the equivalence look like particles on the other; what look like five large dimensions on one side look like four on the other. Because neither description is more real, this introduced ambiguities in the nature of reality, and was the first convincing example of the holographic principle in action.

Anthropic principle
The seemingly tautological statement that features of our universe must be compatible with our biological existence. Why? Perhaps we live in a multiverse in which features vary from one universe to the next, and we find ourselves, unsurprisingly, living in the one we can live in. Or perhaps, as John Wheeler suggests, observers play a role in creating the universe that created them.

Anti–de Sitter (AdS) space
A space in which a negative cosmological constant bends space like a saddle at every point, distorting geometry in such a way that light can travel to spatial infinity and back in a finite amount of time. In AdS space, every observer's light cone overlaps, so everyone sees the same universe.

Antiparticle
A particle with the same mass but opposite charge as its ordinary counterpart. Or, equivalently, an ordinary particle moving backward in time.