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THE TRAJECTORY OF my own life was changed by a momentous historical bang: the fall of the Berlin Wall in 1989. Although Albania was not a part of the Soviet Union, the tide of transformation was impossible to ignore. Students began rallying for free speech and pluralism in 1990, but the real revolution arrived in 1991. That February, a group of university students initiated a hunger strike in their dormitories, demanding that the current ruler, Ramiz Alia, give up power.
At the time, I was an undergraduate at the University of Tirana, but I lived at home with my parents, so I didn’t know about the plans for the hunger strike until the day it happened. As it dragged on, I sat with my friends and their parents outside the dorms to keep the strikers company.
When the students’ medical conditions deteriorated, a few hundred miners walked fifty miles to Tirana, determined to free the students and overthrow the government. My family and I joined the students, parents, and miners as they marched from the dorms to the center of the city to protest. Along the way, the crowd kept swelling as many other citizens joined the demonstration. Young soldiers, only eighteen to twenty years old, looked confused as they hesitantly pointed their guns at the crowd. A touching moment that day was when the numerous elderly Albanians who were marching courageously approached and hugged the soldiers. They pressed their chests against the gun barrels, saying: “You are our blood, our kids, we are fighting for your future too. Your own family must be somewhere in the crowd. Don’t shoot at them. Drop your weapons and come and join us.”
By the time we reached Tirana’s central square, the crowd had expanded to many thousands. The army was deployed to close off the streets and stop people from joining the protests. With the streets shut, we were trapped in the square. Helicopters flew overhead, and snipers took up positions on the rooftops. People began pulling up cobblestones and ripping marble steps from stairways inside buildings to be able to defend themselves in case the army shot at them. Had the soldiers opened fire on the crowd, it would have been a massacre. But sensing that freedom was only hours away, after a fifty-year wait under the worst dictatorship in Europe, the protesters did not turn back.
At this tense moment, my younger brother disappeared into the teeming throng. My dad and I sent my mom home to wait for my brother, but as it turned out, she was wasting her time; he had taken up a position at the front line of the protesters. All around us, the crowd was chanting, “Freedom! Down with Alia. We want Albania to be a democracy; we want Albania to be like the rest of Europe,” over and over again.
Police, soldiers, and special security forces in long coats leading fierce Alsatian dogs swarmed the square, but the protesters kept chanting. Then the demonstrators began pulling down the giant bronze statue of Albania’s first Communist ruler, Enver Hoxha, which had stood for what seemed like forever in the central square.
The soldiers were poised for action, expecting to receive the order to shoot. But for some reason, as the colossus toppled, their radio communication was cut off.
Over the din, we could hear the soldiers screaming at one another, asking what the order was and why their radios had suddenly gone silent. Later, a rumor circulated that Ramiz Alia had cut the signal to keep the generals from taking matters into their own hands and giving the order to fire without his permission. Incredibly, that day, both the protest and Communism in Albania ended without a massacre. My brother later brought home chunks of marble from the pedestal of the statue of Hoxha, a small reminder of the day that Albanian democracy almost died in the womb.
The months between the first student strikes and Albania finally shedding Communism had been brutal and chaotic. Thousands of people jumped over foreign embassy walls to seek protection, including all the students at the University of Tirana—except me and one other classmate. (It is estimated that between 170,000 and 300,000 people left the country during that period; the only two who failed to get out were the ones who jumped the walls at the Cuban embassy—the guards there handed them back to the Albanian authorities.)
On the night that my classmates had picked to leave, we all gathered in Tirana’s main park at sunset to say our goodbyes. Until then, we had shared every little thing we had: pocket money, lunches, pencils, and notebooks. I tried to stop them from leaving by suggesting that they should finish their degrees (we still had a year and a half to go) and explaining that where they were headed was not like the Dynasty series we had recently been secretly watching on TV using homemade antennas. I argued that Communism was over and we had nothing to fear. They, in turn, pleaded with me to go with them, teasing me that I thought too much about everything. But I had made my decision. I couldn’t abandon my parents, and I wouldn’t be a beggar at the mercy of strangers for food and shelter. I had (clandestinely) read enough English books at the private library of the League of Writers and Artists, my mom’s workplace, to know that life was hard in the West too. After we’d talked for hours, they asked me and the other classmate who was staying behind to find their parents and tell them not to worry.
Around midnight, I walked with my friends to the German and French embassies and wished them luck, then watched them climb over the fences and disappear. The embassies would arrange to take them by plane or ship away from Albania.
Night after night, Tirana was alive with young people planning their escape and parents who had come from all over the country searching frantically for them in the dark, first in the center of the city, then in the gardens along Embassy Road. The city sounded as if it were in mourning, filled with rushing footsteps, whispering silhouettes, and crying and sobbing.
I remember one man approaching me as I headed home one night. He was weeping quietly and cradling a pillow next to his face. He told me he had heard a rumor that his son wanted to leave, and he had traveled for four hours to reach Tirana to try to stop him. He had gone to his son’s dormitory and found his bed untouched. He described his son and asked if I had seen him; I hadn’t. He sniffed the pillow, showed it to me, and said, “This is all I have left of my son—this has his smell.”
When I left for the United States two years later, I carried the marble pedestal fragments that my brother had given me as a reminder of my new freedom and the lack of it in my previous life. I still keep them, and not merely as mementos. The lessons they contain about intellectual courage and the need to confront orthodoxy remain as relevant to me today as when I left Albania. And during my graduate studies at the University of Maryland, these lessons were foremost in my mind as I dug deeper and deeper into the questions unleashed by Penrose’s paper.
The more that I learned about my new field of study, the more uncertain I became about the validity of its dominant arguments concerning the big questions about our universe. The biggest question was, of course, how our universe was created and what had been there before. And the prevailing answer to this question did not satisfy me at all.
In 1997, after I earned my master’s degree at the University of Maryland, I began studying for my PhD at the University of Wisconsin–Milwaukee. I wanted to focus on the quantum aspects of the early universe, and I chose UWM because it has one of the strongest theoretical physics groups, especially in quantum physics, in the United States. In particular, I wanted to work with Leonard Parker, a world-renowned theoretical physicist and one of the founders of a new discipline called quantum field theory in curved space-time.* Parker’s work demonstrates that as the universe expands and changes curvature (shape), the corresponding change in its gravitational field is converted into an energy that produces particles that populate the universe. This field is one of the most groundbreaking areas of scientific study today.
Professor Parker was among the kindest and most modest people I ever met. He welcomed me as his student, and he and his wife treated me as if I were one of their own children. I spent three graduate-school years in a cold, windy, and snowy city with beautiful architecture influenced by Frank Lloyd Wright, but I never noticed the cold because of the warmth of the physics group and the people of Milwaukee.
During my years in Milwaukee, I came to understand more completely why cosmic inflation, despite Penrose’s argument that it had a near zero chance of igniting a universe, had nevertheless earned its central place as the theory of the universe, commonly known as the standard model of cosmology. In fact, in my doctoral dissertation, I investigated the alternative theories to cosmic inflation (the gargantuan explosion of an infant universe filled with high energies to produce a big universe like ours) that had been proposed by the theory’s opponents. Those opponents included Hawking and Penrose. The investigations of scientists who came up with alternative models for the creation of our universe were very important in scrutinizing cosmic inflation. Such alternative models included tunneling of an infant universe through a gravitational field and a group of scenarios of possible phase transitions that could have potentially produced a universe like ours.*
The more I scrutinized cosmic inflation’s foundations, the more convinced I became that despite the problem of the unlikeliness of our universe coming into existence, the theory still offered by far the most logical and elegant explanation for the fundamental properties of our universe. This is in part because it preserves the integrity of major theories such as Einstein’s theory of general relativity and the assortment of models collectively known as Big Bang theory—theories that otherwise struggle to account for how to obtain our present universe from the strange conditions that existed at the dawn of the universe as we have come to understand them.
Cosmic inflation uses Einstein’s theory of general relativity to link the universe’s matter and energy to its curvature—that is, its shape—and its expansion. Einstein produced this theory in 1915 while standing on the shoulders of mathematical giants.* He came to regret the name general relativity because it seemed to contradict his belief that the world existed independently of human observation. According to Einstein, what happens in the universe is definitely not relative to who is observing it or how the observer is moving; reality, he felt, must be objective.
To make his theory hang together, Einstein relied on two postulates. The first one is that the speed of light is the absolute limit of speed that any object in the universe can travel. With his second postulate, Einstein united three-dimensional space (height, width, and length) and one-dimensional time into a single entity, which he called space-time. Our universe, Einstein asserted, exists in a four-dimensional space-time.
Einstein’s second postulate is the amazing insight that we can essentially trade the force of gravity for the shape of space. The way that Einstein achieved this trade-off in his theory of general relativity is beautifully simple: According to him, the gravitational force of matter and energy in the universe tells space-time how to curve, and curved space forces objects and light to move along certain paths that follow the curvature of space. His theory replaces the gravitational force exerted on any object produced by all the matter and energy in the universe with the curvature of space-time shaping the paths along which that object moves. Gravity is curvature.
Einstein’s profound insight is not hard to visualize. Imagine you have set up a perfectly flat hammock in your garden. The fabric of the hammock is the space-time in this example. Now, if a person sits or lies down on the hammock, it will bulge downward—that is, it will curve according to the person’s position and weight. In our metaphor, the person is the matter-energy content, and his or her body weight and size determine how the shape of the hammock—the space-time—curves. Thus, as the physicist’s adage goes, “matter tells space how to curve.” Importantly, the shape of the hammock—the curvature of space-time—indicates how much matter-energy it contains. If you sat below the hammock, you would be able to judge the size and weight of the person in the hammock above simply by evaluating the curvature of the fabric.
If the hammock represents the curvature of space-time of the whole universe, and the person’s weight on it represents the energy of the universe at the time of cosmic inflation, then, according to Einstein’s theory, the energy of inflation determines how fast the universe can expand and what shape it will take. In this way, Einstein’s general relativity laid the foundations for the theory of cosmic inflation, which would in turn use Einstein’s general relativity to explain the strange circumstances that existed at the dawn of our universe.
Since Einstein’s day, scientists have taken precise measurements of the shape of the universe and all that’s inside it; this has allowed us to reconstruct its history at various epochs all the way back to its birth. Using Einstein’s equations, we can reverse-engineer what the universe looked like and how fast it expanded at every moment in its past. In the far past, the universe became microscopic as it approached the creation moment. Alas, at that point, Einstein’s equations break down.
This is the major downside of Einstein’s theory of relativity: it becomes invalid under conditions of very high energy densities—the type of energy density that one might find at the center of a black hole, for instance, or that existed at the first instant in the life of our universe. In fact, using Einstein’s equations to find the shape of the universe as a function of the energy contained within it at the universe’s earliest moment, just before cosmic inflation flicks on, generates a disappointing answer: it predicts that the universe started off as a pinpoint, a singularity that pinches off the very fabric of space-time.
This breakdown of Einstein’s equations at the birth of the universe is known as the Hawking-Penrose singularity, after the two iconic physicists who generated the theorem (a scientific milestone alluded to in chapter 1). Time stops at this singularity—there is no “before”; clocks freeze. Space stops there—there is no beyond. According to Hawking and Penrose, nature forbids scientists to explore the moment of creation, let alone look past it, because nothing, absolutely nothing, existed before creation.
There is a century-long history of surprises that scientists came across whenever they tried to obtain solutions to Einstein’s equations at the earliest moments in the life of our universe. In 1922, Alexander Friedmann, a Russian theoretical physicist and mathematician, used Einstein’s equations to demonstrate that they produced an expanding rather than a static, unchanging universe. He wrote to Einstein sharing his calculations, but Einstein was unconvinced.
Five years later, Georges Lemaître, a Belgian astronomer and Catholic priest, independently proposed the first model of an “exploding” universe that started small and grew exponentially. Observing that galaxies were moving away from one another, he conjectured that our universe must have been born from a “cosmic egg.” Lemaître’s finding was verified by Edwin Hubble (of subsequent telescope fame) two years later; he also proved that galaxies outside of our Milky Way were constantly moving away, or receding, from one another.
In the 1940s, Lemaître’s version of the exploding universe was developed into a model by George Gamow, a Russian-born nuclear physicist and a celebrated author of popular science books who had defected from the USSR and eventually ended up at the University of Colorado Boulder. (Gamow’s doctoral adviser, not coincidentally, had been Alexander Friedmann.) Like Lemaître and Friedmann, Gamow used Einstein’s theory of general relativity to link the matter-energy content of the universe to its curvature and expansion. The result was something that we now know as the “Hot Big Bang.”
Gamow’s theory of the universe’s creation was both elegant and attention-grabbing. Relying on Einstein’s equations, he envisioned the universe in its infancy as a tiny vessel, roughly the size of an atom, filled with a “hot primordial soup of radiation” that “banged” into being and grew large over time. He went so far as to predict the existence of radiation relics in our sky left over from the time of this Hot Big Bang.
Gamow’s Hot Big Bang marked the emergence of a new field in physics: cosmology. But his model and the other Big Bang models that followed, all of which depended on hot radiation to make the universe expand, had severe shortcomings. Specifically, these models failed to explain three crucial features of our universe: its flatness, its homogeneity, and the uniform distribution of all the matter in it. This is the failure that cosmic inflation was intended to compensate for.
If you look at the sky through a telescope lens, you will see the same distribution of matter and light no matter where you swivel the telescope. But this phenomenon isn’t new; it’s existed for the universe’s entire history. I like to picture our skies at each moment in time as a canvas that has been sprayed randomly with paint composed of light rays and particles. The distribution of the paint blobs and the blank areas of the canvas is more or less the same everywhere, on the left, on the right, in the center, at the top, and at the bottom.
Yet no matter how many tweaks were introduced to Gamow’s Hot Big Bang theory, it could not generate the same uniform and homogeneous universe that we see in our skies. The primary reason for this discrepancy was the type of energy that Gamow had chosen to bring his universe into existence. A primordial universe filled with hot radiation could not grow fast enough to reach the size of our present-day, very large universe. The only way Gamow’s Hot Big Bang could work was if it started with a huge (in relative terms) primordial universe, one roughly the size of a helium atom.
This initial size is what presented the insurmountable problem that, decades later, cosmic inflation so elegantly solved. It is one of the reasons why, despite Penrose’s argument on the unlikeliness of our universe coming into existence, cosmic inflation continues to be the foundation of cosmology.
In Gamow’s time, the trouble was that the hypothetical primordial universe was too large. During the brief instant of the Hot Big Bang explosion, light and particles would not have sufficient time to traverse the helium-atom-size universe. They would be able to travel only a short distance, a minuscule fraction of this universe, and that means that they could never become uniform or homogeneous.
Imagine a scenario where the primordial universe is comparable to the size of the United States (3.79 million square miles). In this universe, the maximum travel speed is ten miles per hour, and the Hot Big Bang lasts for an hour. During that hour, light and particles can travel only ten miles from their location to connect to other objects. Anything beyond ten miles is outside their reach. This means that, in our scenario, New York and California would not be able to exchange any information, nor would they know of each other’s existence. In this example, millions of different regions in the United States would be completely disconnected and would evolve independently of one another. The end result would be that, when we looked up at the sky, rather than seeing one large uniform universe, we would see a mosaic made up of many, completely independent skies, each with potentially radically different distributions of stars and planets. The many disconnected regions of the Hot Big Bang primordial universe would be entirely independent of one another, and so would their temperatures. Fast-forwarding to the present day, scientists would expect our skies to be a patchwork of different temperatures and matter distributions, literally trillions of different skies in one. But that is clearly not the case with our universe; everything that we can see is arranged uniformly and homogeneously.
As it turns out, the initial size of the universe required by Gamow’s Hot Big Bang theory is only part of the problem with that model of creation. By the 1960s, for reasons I will explain in a later chapter, scientists knew that the shape of space in our universe is flat. This discovery relied on basic geometry and the fact that whenever we look far away at distant stars, we are looking back in time—we are looking at the moment when the star emitted its light, and that might have been billions of years ago.
To understand how something three-dimensional, like our universe, can be described as flat, try this simple thought experiment. Pick three bright stars and use them to draw an imaginary triangle in the sky. (This triangle will actually be three-dimensional, because, although our sky may look two-dimensional from the ground, it is not; each star is located not only in space but also in space-time, so the starlight is, in fact, an incredibly complex layering of time and space, converging in the twinkling lights that we can see with the naked eye.) Now consider the angles in the triangle you’ve created. If our universe were spatially curved like a sphere, then the angles in your triangle would add up to more than 180 degrees, as shown in the top panel of figure 1. This is an example of a “closed” universe. If our universe were curved in space like a saddle, it would be an “open” universe, and the angles of a triangle drawn on that space would add up to less than 180 degrees, as in the bottom panel of figure 1. But our universe is neither open nor closed. We live in a spatially flat universe (with zero curvature) where the angles of a triangle drawn on its sky add up to exactly 180 degrees, as in the middle panel.
The revelation of a flat universe posed a thorny problem for Gamow’s elegant theory of creation. If the universe had started with a Hot Big Bang, obtaining a flat universe out of it using Einstein’s equations was hard. It required a lot of unjustified complications and contrivances that were not naturally motivated by basic physics. Such a model would not be considered plausible or attractive.
Figure 1. From top to bottom, a spatially closed, flat, and open universe.
Given what was at stake, the failure of Big Bang models to explain the three key features of our universe—its flatness, homogeneity, and uniformity—was a big deal. Was the Hot Big Bang wrong? Gamow’s theory seemed to be imploding—until a new theory swooped in to save it.
In the late 1970s and early 1980s, two young scientists, Alan Guth, then a postdoctoral fellow at Cornell University, and Andrei Linde, working behind the Iron Curtain in Moscow, independently came up with a clever idea to fix the problems that dogged Gamow’s Hot Big Bang theory. Their solution was dubbed the “inflationary universe,” or “cosmic inflation” for short, and it is considered a masterpiece of twentieth-century physics.
Guth and Linde’s cosmic inflation solves the original Hot Big Bang problems very simply: it replaces the primordial hot soup of radiation that Gamow thought had banged the universe into creation with a hot soup of energy. Specifically, Guth and Linde postulated the existence of a slowly rolling primordial particle at the Big Bang moment that they dubbed the “inflaton.”* Starting a universe with a hot soup of energy from the slowly rolling inflaton seems to make all the problems vanish.
Central to the power of Guth and Linde’s theory of cosmic inflation is the nature of the inflaton energy that drives the expansion of the universe. It is a special kind of energy, sometimes referred to as “vacuum energy.” Guth and Linde’s solution to all the problems that the Hot Big Bang models faced relies on a crucial property of vacuum energy: negative pressure, a repulsive gravitational force that tends to blow things up—that is, inflate them. Thus, a primordial universe filled with vacuum energy explodes and grows much faster than one filled with the regular radiation posited in the old Big Bang models.
In fact, according to cosmic inflation, our infant universe grew so quickly that within an instant—10^(-45) seconds, to be exact—the size of the original universe, whatever it was, increased by about twenty orders of magnitude. That is, its original size multiplied by 10 with 20 zeros. To get an idea of the scale involved, first imagine the very thin wall of a soap bubble (only a few nanometers thick). Next, picture the distance from the Earth to the sun (roughly 146 million kilometers, or twenty orders of magnitude bigger than the thickness of our soap bubble). With cosmic inflation, the wall of the soap bubble expands the distance of the Earth to the sun in a minuscule fraction of a second.
So, unlike the original Big Bang models in which the primordial universe had to be, in our analogy, the size of the United States in order to evolve billions of years later into the presently observed size of our large universe, a cosmic-inflation universe needed to be only the size of Manhattan to achieve the same expansion. It blows up so quickly that, within a fraction of a second, Manhattan becomes as large as the entire United States.
All the stuff contained inside this primordial universe, whether waves of light or particles, stretches with the universe’s accelerated growth. And during inflation, these elements remain in communication with one another across the span of the universe, continually equalizing their temperature and spreading homogeneously everywhere inside. Particles being able to maintain communications throughout the universe implies that the chain of cause and effect, that sacred principle of nature known as causality, is preserved.
Next, as the universe inflates to trillions of times beyond its infant size, it stretches itself to flatness.
Thus, in contrast to Hot Big Bang models, the cosmic-inflation model achieved flatness, homogeneity, and uniformity all in one, in the most natural way.
Guth and Linde’s explanation for cosmic inflation relied heavily on a new area of physics that arose in the twentieth century, quantum theory, which I will write more about in the next chapter. Both the energy field they postulated for cosmic inflation and the microscopic universe that existed in the first moments are quantum in nature. It turns out that the quantum energy of cosmic inflation that started the universe also has an extremely low entropy, which, according to Boltzmann’s formula—as Penrose pointed out—implies a very small probability of existence. Therefore, the very conditions that they had declared were present at the creation of the universe were the same ones that made the universe’s creation incredibly unlikely.
As this connection between the energy of cosmic inflation and the fact that inflationary energies will always have a very low entropy clicked, it triggered a new picture in my mind.
Cosmic inflation is amazing, it’s brilliant, it is probably the finest origin story of our universe so far—of that I have no doubt. It offers the most logical explanation for the fundamental properties of our universe in what seems to be the most natural way; astrophysical observations agree exquisitely well with its predictions. It is correct.
But my personal belief is that, although correct, cosmic inflation is an incomplete theory. It requires us to accept an impossibly unnatural assumption: that our universe began in the most special way possible, with a perfect inflaton in a perfect hot soup of energy in a smooth space that was the smallest possible size it could be without Einstein’s theory of gravity breaking down (something physicists call a Planck length). So, while cosmic inflation, based on one assumption (the existence of an inflaton energy in the first instant of the life of the universe), provides the perfect explanation of how a tiny universe evolved to its present state, the entire story hung on one mystery: What gave that inflaton the energy that jump-started the inflationary process?
I was still only a graduate student gathering information step by step. But here, sitting before me, was an increasingly intriguing mystery—one that I found hard to resist.