Fingerprints of Other Universes

RICH, TOMO, AND I finally worked up the courage to submit our results for publication in 2005 in a paper we titled “Avatars of the Landscape.” Then we held our breath, waiting to see the reactions among our colleagues. And for a while, it was radio silence. As we waited, lines from William Blake’s poem “Auguries of Innocence” kept playing in my mind: “To see a World in a Grain of Sand / And a Heaven in a Wild Flower / Hold Infinity in the palm of your hand / And Eternity in an hour.”

Our calculations had led to several anomaly predictions. First among them was the existence of a giant void. We believed that resting in the distant sky above the Southern Hemisphere there was a primordial giant void, a hole signifying an almost empty region where the stars and galaxies are mostly “scooped out.” On CMB-temperature maps of the sky, over-dense regions full of matter appear as hot spots, while empty regions, or voids, show up as cold spots. Normally, a CMB-temperature map of the sky shows a uniform sprinkling of small hot and cold spots, based on the uniformity feature of cosmic inflation (even though the hot and cold spots are randomly scattered, when they are all compared to one another, their distribution ends up being balanced, making them uniform).

But the primordial cold spot we predicted was different—it was huge! It covered an area of ten degrees, or roughly one-tenth of our visible sky, which is at least ten times larger than any of the normal CMB hot and cold spots originating from cosmic inflation. This was a gargantuan structure, and we named it the Giant Void. We had a mathematical derivation predicting its existence that showed it to be a scar left over from our universe’s birth. We also predicted it would be about ten billion light-years away.

It was a bold claim, and naturally, we were nervous. Such a giant void clearly broke the uniformity principle of cosmic inflation. Indeed, at that time, talking about a giant hole in our sky and positing its relation to the multiverse did sound ridiculous. It seemed to be the surest way for future observations to prove us wrong.

But we expected that those observations would take awhile to be collected. We thought our telescopes and other observational technology here on Earth and even the satellites in space would not be strong enough to see into the universe with enough detail to confirm (or contradict) our predictions. As confident as we were, we were almost certain that we would not know whether our theory was right or wrong in our own lifetimes. None of us anticipated the surprises awaiting us.

Half a year after we published our first paper, “Avatars of the Landscape,” with a list of predictions for what and where the anomalous scars were in our sky, a team of radio astronomers at the University of Minnesota accidentally spotted exactly the sort of giant void that we had predicted at precisely the size and distance we had predicted. The Giant Void was observed again, two years later, in the CMB maps created by the WMAP (Wilkinson Microwave Anisotropy Probe) experiment, but the data was inconclusive. Thus, for more than a decade, the status of the Giant Void was the subject of bitter fights among scientists in the observational cosmology community.

In May 2009, while I was on sabbatical from UNC and living in England as a visiting professor at the University of Cambridge, I sat with a few dozen other scientists in a room at the Kavli Institute for Cosmology to watch the launch of the Planck satellite from the European Space Agency. The satellite’s name was chosen to honor Max Planck, one of the founding fathers of quantum theory. Aboard the satellite was a powerful telescope designed to produce the most accurate measurements of the gentle glow of light left over from the fiery birth of our universe, the CMB. When the countdown began, the room fell eerily quiet. Liftoff was met with cheers and loud applause. Planck was on its way.

In March 2013, four years into its mission, the Planck satellite released the most finely detailed measurement of the CMB ever mapped. I was again in Cambridge, this time for a conference, listening to the press reports and preparing for bad news. Perhaps Planck’s data and observations had ruled out all the anomalies in the sky that Rich, Tomo, and I had predicted in 2005 and 2006. Instead, just the opposite happened.

Planck’s map contained a bombshell: The anomalies in our sky, including the Cold Spot, could not have been caused by anything in our own universe because they violated the uniform distribution of structure expected from cosmic inflation in a single universe. They had to have come from a different, noninflationary source outside its borders.

Later that day, I was scheduled to lecture at a conference. When the conference host introduced me, he remarked casually, “I believe Laura received some good news this morning.”

It was good news indeed. As we had thought, the truth was sitting right there in our sky, waiting for us. It turned out that entanglement did actually leave imprints on our own sky, and these imprints are indeed strong enough to be detected by the technology we have today. Our universe, it seemed, was not alone. Nor was it such a fluke after all.

In addition to the Cold Spot, Rich, Tomo, and I predicted six other anomalies. Most of these anomalies, we calculated, would be strongest near the edge of our universe because that is where the net effect of entanglement remains the largest and purest. At smaller distances, we predicted, the violent, nonlinear processes of star and galaxy formation, such as swirling clouds of gas and the turbulence of collapsing matter, explosions, and ejections of material from exploding stars, were so powerful that they would wash out any signs of the weak signal from the entanglement contributions.

At the largest scales, we predicted another giant void, this time the size of one of our hemispheres as viewed from our location on Earth. Although it has the same origins as the first Giant Void, this one is larger in size but much weaker in strength. This second gargantuan void covers half the sky and creates small differences in the matter content between the two hemispheres. We anticipated it would show up on observed temperature maps of the sky as a slight difference, an asymmetry (or lopsidedness) between the average matter contents of the northern and southern hemispheres. And we predicted it could be found by studying the CMB.

CMB radiation waves are named after musical harmonics and are called multipoles. The largest CMB wave, the monopole, with a wavelength of about twice the size of the whole universe, would be equivalent to the fundamental or first harmonic; the CMB dipole would be equivalent to the second harmonic; the CMB quadrupole, roughly a fourth of the universe’s size, would correspond to the fourth harmonic, and so on. A CMB wave with a wavelength about the size of the universe, the dipole distance, is what divides our sky into two hemispheres.

The effect of entanglement on our universe’s gravitational potential is to (gently) deplete the long-wavelength CMB harmonics. This depletion manifests itself as a suppression of the CMB spectrum at the lowest harmonics, in addition to the slight hemispheric differences in the amount of matter content in the universe, and that is how we encountered the second giant, hemisphere-size void.

To understand why entanglement would deplete these CMB harmonics rather than amplify them, it is useful to go back to the analogy of Newton’s apple. Like the moon, the planets, and all the stars in the universe pulling on the apple, the surviving infant universes on the quantum landscape multiverse pull on our universe. This pull, however weak, would still be significant and noticeable at the largest scales (the first few lowest harmonics), which is why the giant voids and other anomalies are found at those greater distances.

The hemispheric asymmetry in the CMB that we predicted was confirmed observationally by the Planck satellite in 2013 and 2015, two years after it found the first Cold Spot.*


Figure 13. The CMB map observed by the European Space Agency Planck satellite indicating the Cold Spot (circled) and the asymmetry of matter between the two hemispheres (separated by the curving line). When the map was released in 2013, its surprising anomalies were in complete agreement with our predictions about the scars of the universe’s birth that should be visible in our own sky.

Based on the fact that the remnants of entanglement are stronger and more easily observed at the largest distances, we made an additional prediction that the overall CMB temperature would be lower at those distances. Again, observational findings, including by the Planck satellite, show that the CMB temperature at the lowest harmonic scales (the size of the universe to its edges) is less than expected. And it’s not just the temperature that is lower; the net effect of entanglement, at all the scales we estimated, is to decrease the overall strength (amplitude) of the inflationary CMB radiation (known as sigma 8) by around 20 percent. The combined observations of the CMB, including the Planck data, have also confirmed this prediction.

One of our other predicted signatures of the multiverse relates to the standard model of particles. The standard model of particles explains the origin of all known elementary particles in nature, from quarks to photons. Elementary particles are the offspring of a single fundamental particle—the Higgs particle, sometimes referred to as “the God particle.” The Higgs particle was predicted in 1964 by Peter Higgs at UNC Chapel Hill, where he had been invited as a visiting scholar by Bryce DeWitt. The Higgs particle exists at energies of the order of a quarter of a trillion electron-volt, or tera-electron-volt (TeV). The particle was discovered in 2012 at the Large Hadron Collider (LHC) in Switzerland. The LHC is the world’s largest machine; it is located in a circular underground tunnel with a circumference of twenty-seven kilometers. Beams of protons circle around the tunnel many times over before they collide, head-on at full speed, with each other. The energy of their collisions, which is a few TeV, is the highest energy we have produced on Earth.

Theoretically, the Higgs particle has a problem: its energy can grow in an uncontrolled manner and can destabilize the whole universe. In the 1970s, particle physicists postulated the existence of an underlying hidden symmetry of nature, known as supersymmetry, that would force the Higgs particle to remain stable. Once supersymmetry had done its job of protecting the Higgs particle at higher energies, it needed to be broken down at lower energies and ultimately disappear in order to allow the Higgs particle to decay into quarks and other particles. Protecting the Higgs particle with supersymmetry was an appealing theory, and the LHC was designed to test its existence.

In our quantum landscape multiverse theory, each wave-universe has its own individual, supersymmetry-breaking energy. This is because different wave-universes localize in different landscape energy sites and therefore start their Big Bang inflationary energies at different scales. But as we discovered, these wave-universes prefer to settle on high-energy sites of the landscape, which led us to conclude that if supersymmetry existed and its breaking was responsible for producing these high-energy landscape vacua, it would be bound to energies much higher than the anticipated Higgs energy. Therefore, we predicted that this supersymmetry breaking energy would not be discovered at the energy level of the Higgs particle when it was reproduced by the collider but rather at a billion or more times higher. And indeed, the Large Hadron Collider did not find supersymmetry at the Higgs energy level.

In less than a decade, six of our seven predictions had significant if not definitive proof to support them. Our seventh prediction, which involves the motion of galaxies relative to the expansion of the universe (known as “dark flow”), remains an open question. Observational results from two different teams were inconclusive, and a NASA-led team of astrophysicists that observed dark flow has not yet finished their project due to funding cuts. I hope they will be able to resume their work someday.

Far beyond what we hoped for when we started, our predictions of entanglement anomalies had been tested and observed. What’s more, the Cold Spot observation was accurate at a sufficiently high confidence level to be considered a discovery. (In physics, the difference between an observational finding and a discovery is related to a statistical estimate of confidence level in the finding, called sigma. A sigma value higher than 4 or so indicates discovery because it means that the error in that particular observation is extremely low, and therefore the confidence level in the result is very high—what in daily parlance would be considered “beyond a shadow of a doubt.” The Cold Spot observation had a sigma value of nearly 5.)

But does this mean we have complete proof for the origin of our universe from a quantum multiverse? No. Nature guards her secrets carefully!

One of the obstacles to moving from evidence to proof of the multiverse is not the squabbles over our models or the technology; it’s a statistical problem known as cosmic variance.

Statistically, the more samples we have to measure, the more reliable our conclusions are. For example, if we measure a property of a galaxy—let’s say its temperature—then the more (and similar) galaxies we can perform our measurement on, the more reliable our findings become. Suppose astrophysicists have a theory of galaxy formation that predicts their temperature should be about half a million degrees. If they have only one galaxy available to measure, and they discover that their prediction is correct and indeed the temperature is half a million degrees, then they are happy, but they are also aware that their finding could be a fluke. Statistically, if they have only one sample, their chance of being right is only about 50 percent. Who can say that if they had measured a second galaxy, they would find the same temperature? However, if they measure a trillion galaxies and find that most of their temperatures hover around half a million degrees, then the chances of error are pretty small—in fact, they are as low as one in a million. That error rate is so low that their finding can be considered conclusive; it becomes a discovery.

The trouble with cosmology is that, when it comes to searching for signatures that lie near the horizon of the universe, such as the lowest CMB harmonics, we have only one sample, one universe on which to make this measurement: ours. We cannot repeat our measurements in a trillion other universes. Despite sophisticated technology, we will always have a large statistical error rate at the largest distances because we can measure only one universe. This is cosmic variance. Therefore, although all the CMB experiments found these large-scale anomalies, this detection carries an inherently large statistical error. We cannot overcome the problem of cosmic variance by improving our technology; it is a statistical problem, one that will always be present because we have only one universe that we can measure.

However, the observational evidence in support of our six predictions establishes overwhelmingly that we are part of a multiverse. First, although it is possible to construct a model to explain one of these anomalies after it has been observed, constructing a model that not only explains but also predicts all six of them retroactively and simultaneously under one theory is nearly impossible. Even more important, making accurate predictions before observational results are known—rather than explaining the anomalies after they have been observed—should be both powerful and persuasive.

Second, recall that two overriding predictions of Big Bang inflation are uniformity and homogeneity. The significance of our observed anomalies is that they break this uniformity principle; they cannot be explained by a single, inflationary universe produced solely through cosmic inflation. They require a second source that additionally affected the formation of the CMB and all the structures in our universe—a presence that my collaborators and I argue, persuasively, I hope, is a quantum multiverse.

There are limits set by nature in our pursuit of proof and evidence for the multiverse. Owing to the speed-of-light limit, we cannot directly observe structures beyond the horizon of our universe, and we are also constrained by cosmic variance when measuring at distances near the horizon of the universe. Does this mean we should give up hope of ever deducing information about the multiverse? I don’t think so. Consider this example: If you look at your arm, you can see neither the atoms in it nor the protons, neutrons, and electrons inside those atoms. If you are looking at yourself in the mirror, you can’t see electrons flying around in your head as your neurons fire. However, your conscious thinking tells you not to doubt for a minute that you are made up of atoms. You don’t question the truth of atoms in your body because you know the theory that has been tested in labs and in the sky: the standard model of cosmology in tandem with the standard model of particles. You know it provides a coherent answer for the whole chain of events that led to us. You wouldn’t need to test the standard model of particles or cosmology on your body to know that it is correct.

Likewise, our theory of our universe being part of the quantum multiverse provides a consistent and coherent story of both our existence and what lies beyond, and it offers a series of predictions that are supported by all our observations. Our theory demonstrated that the answer to our origins can be derived, and using quantum entanglement, it proposed how to scientifically test the existence of the multiverse. And these reasons are sufficient to make me believe in the existence of a vaster, more complex, and more beautiful cosmos of which our universe is just a small part.

By demonstrating mathematically that the most likely way to start a universe is from high energies in a landscape of possibilities and by showing how to test its origins from a quantum multiverse, my work with Tomo and Rich stands in sharp contrast to previous estimates that gave our universe a nearly zero chance of existence. Instead, we could demonstrate that our universe is not at all special! I argued earlier in the book that cosmic inflation was an incomplete story of our universe because it could not explain its own origin. Our theory offers a completion of the standard model of cosmology by extending the cosmic story to the time before the Big Bang and to realms beyond our universe. It gives a coherent story that can be tracked step by step in the evolution of our universe, from its beginning as a quantum wave packet settled on some vacua on the landscape through its Big Bang inflationary explosion and growth into a large classical universe bearing the scars of its origin from the quantum multiverse on its skies.

As the multiverse moved into the realm of scientific study, researchers became increasingly aware that a single-universe scenario was deeply problematic. Hints of the multiverse had been there all along, but they went unnoticed because of prejudice and focus on the theory of everything.

Today, this state of affairs seems to be changing. While I was writing this book, many scientists who once worked toward a theory of a single universe switched camps and are now working on models of the multiverse in an understanding of our origins as being simply a single chapter in a larger cosmic story. What was for years, indeed millennia, considered a radical idea is now mainstream. And despite the late Stephen Hawking’s prediction that the theory of everything for a single universe would be discovered before the year 2000, he himself, like many of his peers, started working toward a multiverse theory in the twenty-first century.

Science is crossing the knowledge threshold to the moment of creation and the time before, and what we are finding is poised to upend centuries of cherished theories. We are at an unprecedented moment in scientific history because for the first time, the rules of nature and the origin of the cosmos are not simply a theoretical construct—they can be tested and proven. Indeed, this paradigm shift from a single universe to many moves science from the quest for a mega-theory to that of a multiverse; it extends the Copernican principle to the whole universe. If it passes all the tests, it will be one of the most important discoveries in the history of humanity.

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