Trespassing on Einstein's Lawn (43 page)

“The theory of measurement,” Wigner wrote, “is logically consistent so long as I maintain my privileged position as ultimate observer.” From Wigner's point of view, quantum mechanics “appears absurd because it implies that my friend was in a state of suspended animation before he answered my question.” One way out of the absurdity, Wigner said, would be to contend that he himself was the only observer in the universe, a solution he just couldn't buy. “To deny the existence of the consciousness of a friend to this extent is surely unnatural attitude, approaching solipsism, and few people, in their hearts, will go along with it,” he wrote. Instead, Wigner took the paradox to mean that consciousness plays some special role in physics—that while atoms and photographic plates and obsessively organized notebooks can be in superpositions, conscious people cannot.

Hugh Everett, Wheeler's student at Princeton, likewise saw the
problem of the second observer as the central mystery of quantum mechanics. In his 1955 dissertation, written under Wheeler, Everett wrote,
“The interpretation of quantum mechanics … is untenable if we are to consider a universe containing more than one observer.” A possible escape route, Everett suggested, is “to postulate the existence of only one observer in the universe. This is the solipsist position, in which each of us must hold that he alone is the only valid observer, with the rest of the universe and its inhabitants obeying at all times [linear evolution of the wavefunction] except when under his observation. This view is quite consistent, but one must feel uneasy when, for example, writing textbooks on quantum mechanics, describing [the collapse of the wavefunction through observation] for the consumption of other persons to whom it does not apply.”

But Everett offered a solution that was the complete opposite of Wigner's: instead of privileging conscious observers, Everett gave up the notion of wavefunction collapse altogether. Instead, he said, we should assume that the universe, along with all the observers it contains, is described by a single wavefunction that never collapses. In that case, it
is
reasonable to consider Wigner's friend to be in a superposition. Then again, so is Wigner. So are all the rest of us. With every little decision we make—hit snooze or get up, eggs or waffles, Route 76 east or Chestnut Street—we evolve into increasingly complicated superpositions of having done and having not done everything we've ever done and not done. If we could stand outside the universe—and outside ourselves—we would see this tangled mess, this infinite repetition of our every possible variation, but since we can't, we inevitably see only a limited perspective, one in which it
seems
as though quantum wavefunctions collapse, one in which it
seems
as though we live out a single reality.

In 1957,
Reviews of Modern Physics
published a shortened version of Everett's dissertation along with an article by Wheeler analyzing its merits. Everett's interpretation of quantum mechanics, Wheeler wrote,
“does not introduce the idea of a super-observer; it rejects that concept from the start.” That's a good thing, Wheeler explained, because aside from Everett's interpretation “no self-consistent system of ideas is at hand to explain what one shall mean by quantizing a closed system like
the universe of general relativity.” There, again, was the central question of quantum gravity: if there's nothing outside the universe, how do you make sense of quantum mechanics from the inside? Now I realized it was just another way of asking, what happens when you have more than one observer?

Despite his endorsement of Everett's ideas, Wheeler leaned far more toward Bohr's point of view that the distinction between observer and observed is fundamental, even if “the line of distinction can run like a maze.” Reading his journals, it wasn't hard to see why. In quantum mechanics, Wheeler glimpsed a mechanism for creating reality out of nothing, bit by bit, through the posing of yes/no questions. But if observers are nothing special, just part of the system, ordinary physical objects, then there's no way they can have some special reality-building power. If the observers are stuck on the inside, they're subject to the same Gödelian uncertainty as everything else, helpless to decide the truth-values of propositions. In Everett's world, observers play no active role. With no need to go around collapsing superpositions, they're simply swept along by Schrödinger's wave. Genesis by observership short-circuits. You're left with a single, massive, universal wavefunction and no possibility of explaining where the hell it came from.

Still, Bohr's view, as Wigner made clear, held up only for a universe with one observer. So Wheeler knew he had three options. One: he could become a solipsist, rendering his propensity to go anywhere and talk to anybody just a tad insane. Two: he could accept Everett's parallel branching realities and surrender the hope of explaining existence through observership. Or three: he could maintain that consciousness was magically exempt from the laws of physics and yet mysteriously capable of affecting the physical world through wavefunction collapse. “About no feature of ‘It from Bit' do I feel less comfortable than
whose
bit,” he wrote.

At times Wheeler did veer toward solipsism, toward the idea that each observer was the sole enabler of wavefunction collapse in his or her own independent universe. It was a “many worlds” view, but not the kind that's been attributed to Everett. In Everett's view, each observer occupies their own branch of a single, shared wavefunction. In the solipsistic picture, there's one universe—one wavefunction—per
observer. Rather than all observers sharing a single reality, each has his or her own.

“Feeling I am wrong in looking for ‘one meaning' that would summarize, and be built on, the findings of all the ‘observer-participators' that I have been concerned about for so long,” Wheeler wrote in one of the journals. “I now cite [Walter Lippman] (which make[s] me think it is conceivable we must give up any ‘one-world' view of physics): ‘Man is no Aristotelian god contemplating all existence at one glance.' ”

Is “ ‘this world' a misleading simplification for ‘all our worlds'?” he wondered. “What these separate worlds are and how they fit together the central problem? … 
Lots
of recognition circuits, not a universal one? That's honesty. And that raises the issue of linkage,
how
to link, fascinating in its own right. ‘Big buzzing confusion' indeed!” A few days later he wrote, “Idea, surely not new, that there is
not
‘one world,' but as many worlds as observers, and that ‘meaning' comes in the reconciliation of them, but how much reconciliation?”

“He's starting to question whether the universe itself is invariant,” I whispered to my father. My father looked up from the journal he was reading and leaned over to see the passage to which I was pointing: “I'm prepared to question the very term ‘universe.' ”

But reading on, I saw that solipsism made Wheeler profoundly uncomfortable, and he inevitably swung back toward a more communal view. “I can't make something out of nothing,” he wrote, “and you can't, but altogether we can.”

I thought back to Wheeler's book
At Home in the Universe
, where he had argued explicitly that you
need
multiple observers in order to build reality. No single observer, he had said, was capable of making enough measurements to bring into being all the bits you'd need to build the whole universe.
“Mice and men and all on Earth who may ever come to rank as intercommunicating meaning-establishing observer-participants will never mount a bit count sufficient to bear so great a burden,” he wrote.

Wheeler was stuck. The only way to have multiple observers living in the same universe without having to give up the observer's ability to create reality was to afford some special role for consciousness, however reluctant he was do it. That opened up a host of bizarre but unavoidable
questions, like “What level of consciousness?” “Does a worm qualify?” “What about household appliances?”

“For computer, is there a brain? For hard-wired worm, what difference from any gadget—such as electric dishwasher—with built-in responses to a few standard pokes? For higher brain, learning possible: strengthen favorable responses, weaken unfavorable ones. For still higher, learn from others, especially learn language, invent words like meaning, then puzzle what they mean!” At one point he even pasted in an article by E. O. Wilson on animal communication.

“Where then is the role of consciousness in giving meaning?” Wheeler wrote. “And how does one see the necessity of the quantum principle in the construction of the world? I keep going around and around the same circuit of questions, trying to find a way in to the center of the mystery.”

There we were going around and around with him. I had to wonder whether we were getting anywhere, or just circling the drain.

“I can't stop thinking about the problem of the second observer,” I told my father over lunch. We had been going to the same restaurant every day and the waitstaff had gotten to know us.

“Are you doing some kind of work nearby?” our waiter asked us, having witnessed several of our lunches spent poring over our notes.

“We're doing research at the American Philosophical Society library around the corner,” my father told him.

“Oh, cool!” he said. “What kind of research?”

“Physics,” I answered.

“Very cool,” he said. “I studied philosophy of physics.”

My dad gave me a smile that seemed to say,
Congratulations! Behold your future.

“Wow,” I said, nodding. “Wow.”

The waiter smiled. “I'll be right back with your food.”

“The second observer?” my father asked.

“Yeah, the idea that one observer can collapse a wavefunction, while a second observer sees him in a superposition correlated with the thing he's measuring. Wavefunction collapse is supposed to be,
like, the thing that
creates reality
, and yet it seems to occur at different times for different observers.”

“Like reality is observer-dependent?” my father asked.

“I guess. It's just another way of stating the inside/outside problem,” I said. “Because according to the first observer, he's outside the system he's measuring. But then the second observer comes along and measures the first observer, which means the first observer is now
inside
the system, and the second observer is outside. And then you could have a third observer—”

“There's always some perspective where the observer becomes the observed.”

“Right. And that implies that there's nothing ontologically special about observers; they're just part of the universe, on the inside. But then you can't explain the universe as a self-excited circuit, because how do observers have some special power to create the universe? Like, what counts as an observer? Wheeler thinks consciousness could be the criterion for an observer, but that's obviously bullshit. I mean, consciousness is just a physical process in the brain. It's not magic.”

My father nodded. “The consciousness talk made him sound a little like a crackpot.”

“Right,” I said. “But you can tell he's, like, forced into it. He's backed into a corner. He can't take the Everett view without giving up the ability to explain existence, and he can't take the solipsistic view and say there's just one observer.”

“Why not?”

“Because he doesn't think one observer is enough to create all the bits you need to make a universe. He said that the total number of bits in the universe has to be finite and that you have to count the contributions of all observers who had ever and would ever live.”

The waiter arrived with plates of steaming food.

“You know, the holographic principle has taken care of that first part,” I said. “It says that the amount of information in any region of spacetime has to be finite. But I think it makes the second part more difficult.”

“The part about counting up the measurements of multiple observers?”

“Yeah, because Susskind's horizon complementarity shows that you'd end up vastly overcounting. You'd clone information, violate quantum mechanics.” You couldn't count Safe's and Screwed's observations together or you'd get the wrong number of bits—not to mention elephants. “When you think about it that way, solipsism seems the most likely.”

“So you're talking to yourself right now?” my father said with a laugh.

“Yup!” I said. “And it looks like I don't have to share these noodles!”

Back in the reading room, I thought more about the holographic principle. It was a shame Wheeler hadn't had a chance to appreciate its discovery. Maldacena had given a talk about AdS/CFT at the Princeton symposium, but Wheeler was ninety then and most likely couldn't hear it. Still, it was strange that there wasn't more mention of Hawking radiation and event horizons in the journals, given their radical blow to our conception of reality. Not only had Wheeler been around for those discoveries, he had been at the center of them. After all, it was because of Wheeler's riddling that Bekenstein discovered that horizons have entropy. In fact, it now occurred to me that the drawing featured on our Science and Ultimate Reality press badges—the sphere tiled with 0s and 1s—was a drawing of the entropy on a black hole horizon. Wheeler had obviously thought it was important. It showed that the universe was built of binary bits. Of information. But why hadn't he focused more on the fact that horizons rendered particles and the vacuum observer-dependent? Given how badly he wanted to show observers creating reality, you'd think he would have been psyched.

In a 1974 journal entry, Wheeler had commented on Hawking's original paper “Black Hole Explosions?,” which had just been published in
Nature.
“Amazing result,” Wheeler had scrawled. “Viewpoints. Conservative.”