THE DISCOVERY OF the string-theory landscape serendipitously came to light just as I started researching the creation of the universe full-time. When I arrived at the University of North Carolina at Chapel Hill in January 2004, I was convinced that to meaningfully inquire about the origins of our universe, I needed a pool of infant universes from which to choose. However, I had no preconceived notion of what the ultimate theory of the universe should look like, so I began my investigation of the universe’s origins with no idea of where it would lead.
I did, however, have a sense of where it would probably not lead—to an increase of my chances of tenure. Under the pressure of tenure decisions, assistant professors work long hours, and most decide to join established fields of research, such as, in my field, post-inflationary cosmology. With my best interests at heart, my mentors had advised me to follow this path and avoid working on high-risk challenging problems like the creation of the universe, at least until I had achieved tenure. They recommended that I work on more conventional topics and join large research groups led by well-known authorities.
Given that only about 30 percent of PhD graduates are able to secure jobs in academia and fewer still are able to advance on the tenure track, this advice was intended to help me thrive in my new profession and make sure I stayed in it. Some of my peers in the broader physics community were clearly following similar advice; they spoke of being careful to map their career paths long in advance by joining the “right” camp while not upsetting anyone in the “rival” camp. I heard tales of the consequences of going against the trend, but even so, I could not fully comprehend the concern that openly debating ideas with other scientists could be considered personal attacks against them—and indeed, once I found my niche within the world of physics, this proved not to be the case.
To be sure, I was fully aware that working on risky, envelope-pushing subjects was unwise from a professional standpoint; I only had to look at the sad example of Hugh Everett to understand that. But I had become a theoretical physicist precisely because I was fascinated by problems such as the beginning and the end of the universe, and I had already devoted all my spare time to these subjects before arriving at UNC. I found it very hard to resist the attraction of what had gotten me interested in science in the first place.
When in doubt on a major decision, I have always picked the choice I won’t regret later. And by the time I arrived at UNC Chapel Hill, I knew that if I didn’t work on the universe’s origins, I might regret it for the rest of my life. So that is the field of research that I picked.
Rationalizing my very impractical selection, I told myself that if I had been a practical person, I would have chosen to work in a more lucrative profession to begin with; I would never have picked the path of a physics professor. Then, too, in light of my childhood experiences in Albania, the decision to research the creation of the universe didn’t feel like a particularly courageous act. As far as I knew, in modern times in the West, no heads rolled for proposing new ideas, and everyone was free to speak his or her mind—even if doing so ruffled some other people’s feathers.
In large part because of my background, I felt protective of the freedom to think for myself. This freedom also seemed like a cornerstone of science; looked at in certain lights, after all, the whole history of science is one continuous, never-ending battle of challenging and improving on ideas that previously were worshipped as “conventional wisdom” or the “final truth” on a subject. And, just like the magic that animates Beethoven’s music even hundreds of years after he composed it, good, original scientific ideas (which are few and far between) in the end survive the most challenging test of all: the test of time.
I had prepared myself for the likelihood that I would fail. In fact, the entire field of theoretical physics prepares you to cope with disappointments and failure. For theoretical physicists, a best-case scenario is one where only nine out of ten of your ideas are wrong—and even then, most of us never know that we were correct one-tenth of the time, because opportunities for theoretical physicists to test their new ideas observationally are rare.
But where observations fail, the scrutiny of peers comes to the rescue. The theoretical physics community operates like an extended family. The bond among its members is based not on blood but on a deep respect for one another’s views. Of course, as in any family, respect has to be earned the hard way—in our case, by contributing to groundbreaking ideas and advancing knowledge. To that end, we scrutinize, criticize, and work hard to pinpoint logical flaws in the ideas of our colleagues as well as in our own. Even if we rip apart each other’s reasoning, we remain united by our shared pursuit of the same goal: to learn the true answer to the mysteries of nature.
As I got to know the culture of my new academic family, I came to realize that, to pursue my investigation of the universe’s origins thoroughly, I had to first give serious, sustained consideration to the single-universe view and fully understand the reasons why the scientific community had largely rejected the idea of the multiverse.
I kept revisiting the arguments for a single universe, sometimes during walks on the baking-hot trails and streets of Chapel Hill, North Carolina, accompanied by snakes, deer, beautiful birds, and exotic creepy-crawlies that, before arriving at UNC, I had seen only in the movies. (I was one of the very few people walking to and from work. Locals would often stop their cars and kindly offer me a ride. They must have thought it strange that I was determined to walk to the university, regardless of the weather. But once they learned I was a physicist, they seemed to accept these walks as “normal” behavior.)
As I already knew, and as we have seen, the deeply held belief in a single universe ruled by a single theory was powerfully embedded in tradition. But there was more to its appeal than that. The single-universe view dominated contemporary thinking and a unified theory was the holy grail of physics because scientists, including me, wanted simplicity and testability in the theories that we constructed to explain the universe.
To appreciate the sway that these values hold, consider cosmic inflation. Relying on only one assumption, the inflaton potential energy, cosmic inflation elegantly accounted for the main features observed in our universe; equally important, its predictions about flatness, homogeneity, and uniformity of structures in the universe are testable.
By contrast, the study of the multiverse had remained almost taboo because scientists were convinced that the multiverse could not be tested or independently observed. Einstein’s theory of gravitation was based on the postulate that nothing, absolutely nothing, could travel faster than light in the universe. We observe objects—for example, stars—by sending and receiving light signals. The horizon of our universe, which is only about 10^(27) centimeters from Earth (10 with 27 zeros behind it), is defined as the farthest distance that light in the universe can travel and still return to us. The speed-of-light limit will not permit us to exchange light signals outside the horizon of our universe into the multiverse to observe what lies beyond its “edge.” If the existence of the multiverse could not be tested or observed, scientists believed, then it could not be a scientific theory. This, I fully appreciated. However, the single-universe scenario suffered from its own share of unsurmountable problems, many of them related to the second of law of thermodynamics, as I described in earlier chapters.
Consequently, I was among the very few physicists to be delighted when, in 2004, around the time of my arrival at UNC Chapel Hill, the discovery of the landscape of string theory took off. In contrast to string theorists, who were working to mathematically reduce or compactify the extra dimensions in order to produce a single universe, I was approaching this problem as a cosmologist. In searching for an answer to two very specific questions—what jump-started the universe, and what was there at a time before our time?—I had convinced myself through various thought experiments that this mystery would make sense only if we had a pool of possible origins from which to choose, along with the initial energies with which to inflate them. This pool of possible origins is known in cosmology as “the space of initial states for the universe,” and until the discovery of the string-theory landscape, it had been an abstract hypothetical space of possibilities.
Up until that moment, the pool of energies that I was using was merely an abstract possibility. Serendipitously, the discovery of the string-theory landscape offered exactly the pool of initial states of the universe that I needed: a collection of actual energies derived by an underlying theory.
In my view, the landscape discovery was not a disaster; far from it. I thought it was the best possible news for any theory that attempted to explain the origin of our universe and what was there before. With this breakthrough, I could now calculate the probability of our origins using the landscape of string theory as the physical space of potential initial states for our universe. And this derivation of an answer led me to a multiverse.
The discovery of the string-theory landscape had opened up new intellectual horizons for me. But a formidable challenge remained: How could I relate a physical object—a thing that exists in real space-time, like our universe—to the string-theory landscape, an abstract space of energies obtained from an eleven-dimensional world? At first glance, the two seemed incompatible. But I suspected that the underlying connection between our universe and the landscape resided somewhere in the intersection between string theory and quantum theory.
Then, one day, the pieces of the puzzle began to fit together.
When the idea came to me, I was sitting in a Chapel Hill coffee shop. I like working in cafés; like my long walks, sitting in coffee shops gives me the many hours of unencumbered concentration and the thinking time I need to detach from my surroundings and be fully absorbed with the problem in my head. Wherever I live, baristas soon get to know my habits and my love of long espressos, and the anonymous collective buzz of a café is less of a distraction to me than a silent office with frequent knocks on the door from colleagues and students.
I was staring out the window, going through the arguments in my head, when a notion crept in: quantum mechanics on the landscape of string theory.
Yes, of course! I thought. Put the two truths together to produce a single, greater prospect.
I started with the idea of our infant universe as a tiny, particle-type object. This meant that I could apply quantum mechanics to it. As I hinted before, thanks to the wave-particle duality of quantum mechanics (which we saw in detail in chapter 3), I could think of our infant universe not only as a quantum particle but also as a bundle of waves tightly packed together into a wave packet to resemble a particle. These wave packets are the branches of the wave function of the universe we came across previously.
At this stage, the connection between what appeared to be two incompatible subjects—a physical universe existing in a real space and time, and a pool of energies existing in a string-theory landscape—became clear. Let this wave function of the universe pass through the chain of landscape energies, I thought. Find out how and where these wave-universes (1) take their energy from the landscape, (2) go through their individual Big Bangs, and thus (3) transition to growing physical universes in space-time.
It was a simple idea: By expressing the infant universe as a wave packet that travels through the landscape of string theory, I could use quantum equations to find out which energy site it would settle into in the midst of that vastness. Furthermore, the family of solutions, derived from the Schrödinger-like equation, for all the branches of the wave function of the universe provided direct information on their probability of existence. In quantum mechanics, the probability of each wave packet (or branch) solution of the wave function is directly proportional to the square of the respective solution. It was essentially a mathematical “experiment,” just as one might set up an experiment to find out what happens to a handful of marbles if we let them roll down mountainous terrain. The energy site that I was seeking was the valley where my quantum-particle marble would end up. Ultimately these solutions to the wave function of the universe and the vacuum energies into which its branches settled would allow me to calculate the probability that the wave function of the universe has to select an initial energy like the one that started our universe.
I wrote the words QM on the landscape on a slip of paper as a reminder—not that there was any danger I might forget. Then I decided to call it a day. Putting a set of scribbled ideas away for a while helped me detach myself from them. I would return to them later with fresh eyes and a fresh mind and be better able to spot any blunders or flaws in my logic or calculations.
Before I packed up my notes and headed home, I went outside for a cigarette. During periods of intense concentration, in moments of frustration or anticipation, when I am close to solving a problem but am not there yet, I take short breaks in the fresh air. They help me to be cautious and curb the excitement that comes with a new idea, allowing me to clear my head and put the pieces of an idea together in a meaningful way. Cigarettes, ironically, were my excuse to get some fresh air. I had started smoking years before—the night in Tirana, in fact, when I watched my classmates and friends scale foreign embassy walls to escape Albania. I never saw or heard from them again. Nor did I manage to quit smoking until quite recently. In Chapel Hill, cigarettes and classical music were for many years my daily companions.
As I stood outside trying to visualize the idea, my internal monologue kept going nonstop. This is all so beautiful, I thought, and so simple. What took me so long to see it?
No—it can’t be this straightforward! What am I missing?
Figure 11. A visualization of the transition from wave-universes settling on the energy vacua of the landscape to inflating physical universes that exist in real space-time.
It seems so obvious. Other people must surely have thought of it and decided it doesn’t work.
It must be wrong . . . or dumb . . . or both. But why can’t I see what’s wrong with it?
These were the thoughts that raced through my mind as I stood in front of that coffee shop.
When I went back inside and packed up my notebooks, I couldn’t resist taking another peek at the notes I’d written on the scrap of paper. All the equations suddenly started to flow. I could now see how this idea would take me to the answer to the mystery of the universe’s birth. It would allow me to derive the probability of the origin of our universe and thus evade the swamp to which Penrose had banished our chance of existence.
The landscape was exactly the starting point that I needed. And by using quantum rules to calculate the answer instead of just postulating it, I finally had a way to connect the landscape of string theory to our universe’s origin.
Importantly, the conceptual step of a wave function of the universe on the landscape energies meant I could merge the two parallel tracks of quantum theory with gravitational theory, since our universe was a quantum wave filled with energy until 13.8 billion years ago, when it exploded into a physical universe governed by this energy’s powerful gravitational forces.
Tired and excited, I left for home. It was late, but I had to tell someone what I had found. So I phoned my two biggest fans: my husband (he worked overseas and we were in different time zones) and then my dad. Both knew what I was working on, and I knew they would not mind listening to this new development no matter what time it was.
I explained my idea animatedly to my husband first. And then I called my parents. “Dad,” I said when he picked up, “do you remember when we would stay up at night and listen to classical music on Radio Tirana?”
“Yes, of course I remember,” he said.
“Dad, I think I may have cracked the problem.”
“How?” my dad replied. I could hear Mom protesting on the other end of the line: “I want to talk to my daughter. She’s my daughter too.” My dad said, “Talk to your mom first,” and I knew he was right. My mother had been diagnosed with cancer a year before and had just finished chemotherapy, which had successfully arrested the cancer. But our whole family was extra-gentle around her. She managed to retrieve the phone from my father. “Hello, how are you, darling?” But before she could continue, I said, “Mom, I’m so sorry, but please, this is important, and I haven’t finished. Can you put Dad back on the phone?”
I blurted the whole thing out in a few minutes without taking a breath. My dad said, “Hmm,” which I knew meant he had concentrated on every word and was thinking. Then he said, “Talk to your mom. She has missed you.” This time, desperate, I protested. “But Dad, first tell me, what do you think? Do you think it is total nonsense?”
“No . . . beautiful,” he said. Then both of them said in unison: “When are you coming to visit?” The longing in their voices lingered in my head until I reached home.
I entered the house and headed straight for the bedroom, and I was switching the lights on when I heard knocking at the front door.
I was not expecting anyone. The knocking intensified, and I got a bit scared. A colleague at work had been harassing and threatening me daily—something that is, unfortunately, a routine experience for women who have chosen a career in the hard sciences. I had ignored all his threats and advances, writing them off as a nuisance, which had led this character to nickname me “Her Majesty.”
The knocking at the door became more persistent and would not stop. Then I saw a silhouette on the veranda and heard still louder knocks on the veranda’s glass door.
I dialed 911. A few minutes later, the police arrived, and I opened the door.
The officer stood there holding a beautiful big bouquet of exotic flowers. “These are for you,” he said. “The man knocking on your door and windows was trying to finish his last flower delivery of the day.” I thanked him and apologized, and he told me, “Better safe than sorry—you did the right thing.”
The flowers were from my husband. I started laughing. Somehow, I had managed to involve the local Chapel Hill police in a weighty academic problem.