Trespassing on Einstein's Lawn (28 page)

No single objective description of the universe? Markopoulou had suggested we need some kind of observer-dependent logic to deal with the fact that each of us occupies a different portion of the universe. Now Hawking was suggesting that we might need an observer-dependent theory of everything?

I pulled the crumpled IHOP napkin from where it was tucked inside my notebook and scanned the ultimate reality ingredient list.
Particles/​fields/​vacuum. Spacetime. Dimensionality. Strings. The universe. The multiverse. The speed of light.

Shit. My thesis. I had spent months completely bogged down in my research. The discovery that particles weren't ultimately real was a major breakthrough in our quest, and in all my excitement I hadn't actually gotten down to the business of writing. It was due in two days.

I collected all of my notes into a huge pile and sat down to write my thesis: “The Observer-Dependence of Horizons and the Ontology of Matter.”

When I had first arrived at the London School of Economics, one
of my professors had pulled me aside after class to issue a strange warning. “I know you are used to writing for magazines,” he said, to my surprise. “But when you write an academic paper, it shouldn't sound like it's written for a popular audience.”

“I know that,” I said. “I would never make an academic paper that understandable.”

A few days later, a second professor stopped me in the hallway. “Be careful your papers don't sound like magazine articles,” he cautioned, looking preemptively disappointed in me.

“They won't,” I promised. “I am going to make them as dry and humorless as possible.”

So when I finally sat down to write a paper, I conjured what I imagined to be the voice of an old British man wearing a brown tweed jacket with suede elbow patches sitting next to a weathered globe and puffing haughtily on a pipe.
Indeed, as I shall argue in the passages that follow, Duhem's holism thesis does in fact undermine the hypotheticodeductive method of confirmation. Puff, puff. Cheerio.
I littered my sentences with conjunctions and jargon; I combed them for any stray morsels of color or joy. I outlined and reiterated my arguments at every stage.
Here is a summary of what I just said. Here is what I am now saying. Here is what I'm about to say.
I used words like
normative
and
aforementioned.
My professors were duly impressed.

Now that it was time to write my thesis, I conjured the old man and wrote for forty-eight hours. Straight.

In the world of classical Newtonian physics, matter was an objective entity that existed independent of its observers
, I began.
Its ontology seemed firmly rooted in the world of absolute space and time. Both quantum theory and relativity shook those ontological foundations, challenging our conceptions of matter. In quantum theory it became clear that, for instance, an electron exists in a superposition of possible states defined by probabilities, and only “collapses” into one particular state when an observer makes a measurement. Thus the observer became a participant in defining the properties of matter. In relativity, it became clear that our perception of matter is determined in part by our frame of reference, and that two observers will not always agree on, for instance, the length of an object. Again, observers were made participants of some kind, and one
could no longer provide a description of matter without first establishing a particular reference frame. Nonetheless, neither of these theories entirely undermined the classical view of the ontology of matter. In both relativity and quantum theory, the
properties
of matter may be in some sense observer-dependent, but the very
existence
of matter is not. Here we will argue that the quantum properties of horizons in general relativistic spacetimes take that final step in rendering matter entirely observer-dependent, not only in its observational properties but in its very existence. This has profound implications for ontology, and is a direct product of the cutting-edge physics that have begun to unite general relativity, thermodynamics, and quantum theory.
Blam.

I continued, explaining the physics of black hole, Rindler, and de Sitter horizons. I defined their temperatures and entropies, detailing the equivalences between horizon mechanics and thermodynamics. Then I paused to consider whether the three types of horizons were equivalent or merely analogous.
Physically they seem like significantly different situations
, I wrote.
In one you've got a black hole sitting there, the heap of bones of a dead star. In another you've got an observer bolting through empty space. In another the entire universe is ballooning outward. How could they possibly be the same?

From the standpoint of a structural realist, however, those stories didn't matter. What mattered was structure. Math. And from the math's point of view, there was no difference among the three horizons.

The physics of horizons—the radiation they produce, for instance—results from the relationship between the frame of reference of the observer and the geometry of the spacetime
, I wrote.
This relationship holds equally for all three cases under consideration: in the black hole case, gravity defines the geometry of the spacetime; in the de Sitter case, the cosmological constant defines the geometry of the spacetime; and in the Rindler case, the observer's acceleration defines the geometry of the spacetime. But the physics stem not from gravity, nor the cosmological constant, nor acceleration in and of themselves, but from the relationship between geometry and observer. This relationship defines the “structures” of interest, and they are all equivalent. In adopting this position we follow
suit with Einstein, whose equivalence principle states that gravity and acceleration are not merely analogous, but equivalent.

Good, I thought; who could argue with Einstein? Or with a narrator who speaks in a royal “we”?

I explained the meaning of entropy, the derivation of Hawking radiation, and the inequivalent metrics of the observer-dependent vacuum states, finally concluding,
The presence of a horizon indicates a degeneracy of vacuum states, with no preferred field modes definable. The ontological consequences of this are
fucking crazy!

Reading it back to myself, I suspected that the last sentence might not be looked upon as “academic” enough. I tapped the delete key, then tried again.
The ontological consequences of this are dramatic shifts in our concepts of “particles” and “fields,” which are shown to be intrinsically characterized by reference frames.

Better.

Save, print, submit, sleep.

School had ended and my six-month editorship at
New Scientist
was up. I was itching to get back to the States. To see my family and friends and the Sun. To live in a Newtonian apartment. At the same time, my
New Scientist
gig had opened up a new universe of possibilities. It had given me steady access to physicists and the ultimate alibi for pursuing the nature of reality. I wasn't about to give that up. So I convinced my superiors to keep me on as an editor back in the United States, where I'd work in their satellite office in Cambridge, Massachusetts.

Heading back across the Atlantic, I knew that I needed to find out more about event horizons. So many questions were still bugging me. How was it possible that you can map the entropy of the vacuum onto the area of an event horizon, even though the horizon has one less dimension? What did it mean for cosmology that we live in a de Sitter universe, an impassable event horizon lurking in our future? And why had the de Sitter horizon led Hawking and Gibbons to believe, as Bousso put it, that “quantum gravity may not admit a single, objective, and complete description of the universe,” but that “its laws may have to be formulated with reference to an observer—no more than one at a time”? I was sure that the answers would help us figure out what was invariant. What was ultimately real.

Back in the United States, I settled into life in Cambridge. The
New Scientist
office was located in Kendall Square, which was basically like physics Disneyland. Within a few blocks of the office were a street called Galileo Way, a restaurant called MC
²
, a bookstore called Quantum Books, and a bar called The Miracle of Science. I got an apartment on the edge of the MIT campus overlooking the Charles River.

The only thing missing was Cassidy. I was thankful that my parents had taken her in while I was in London, but now that I was back in the States I couldn't wait to get her back. My mother, however, was holding her hostage. The very same woman who had reeled at the thought of having an animal in her house was now refusing to return her to her rightful owner. And Cassidy, whom I had raised to live the fast-paced life of a New York City dog, had apparently grown accustomed to suburbia, with all its “space” and “grass.” What's more, the little traitor adored my parents now. She still wiggled with delight at the sight of me, but she gazed at them like they were home.

Portrait of an editor: my dream job at
New Scientist
's office in Cambridge, Massachusetts
W. Gefter

To help fill the void, I adopted a stray kitten. “You've been hired to deal with any rodent intruders,” I told him when I brought him home. “Quantum or otherwise.” He purred.

The next order of business was to go to Santa Barbara. Just before leaving London I had received an advance copy of
The Cosmic Landscape
by Leonard Susskind. Susskind, a physicist at Stanford, was one of the originators of string theory.

Over the past few years I had been piecing together a basic understanding of string theory. The premise was simple: every particle—every electron, photon, quark, and all the rest—is a different vibration of the same tiny, undulating strings. Rather than the diverse zoo of particles, the theory said, the world was made up of just one animal: the string. About 10
^-33
centimeters in length, strings vibrate like the strings of a guitar, playing the various particles like musical notes, including one that sounded just like gravity.

When I first heard about the theory, the whole idea of strings seemed pretty random. I mean, why strings? Why not stars or spirals? But, looking into it further, I learned that strings weren't random at all. In fact, they had been spotted in experimental data.

Before physicists knew that hadrons such as protons and neutrons were composed of quarks, they had been confused by the results pouring out of particle accelerators in the 1960s. At the time, an approach to particle physics called the S-matrix was becoming increasingly popular. The idea was that rather than trying to describe how two particles interact when they collide at a given point in spacetime, you can describe them solely by the starting and ending points of their travels. The
S
stood for
scattering
, and it went something like this. Step one: from their starting positions and velocities, two particles head toward each other. Step two: they collide, and the energy produced in their collision spawns new particles that decay into other new particles that interact to form still more particles, all of which are surrounded by swarms of virtual particles, which in turn interact with other virtual particles, which in turn … ad infinitum. Step three: somehow just a few particles emerge from the mess.