This fascination is exhilarating but sometimes also ludicrous. When my son called me irresponsible for, in some indirect way, willing the Large Hadron Collider into existence, he was not alone. The media had repeatedly advertised the idea that string theory, one of the candidate theories of quantum gravity, predicted that black holes would be formed when the Large Hadron Collider switched on. When the beams of protons actually collided, among the multitude of stuff that would spew out into the detectors would be microscopic black holes, mini portals into other dimensions. My son also knew that black holes suck up everything around them. Everyone knows that. So why on earth would I, or anyone in his or her right mind, want to produce these incredibly dangerous things? It was obviously a stupid thing to do.
One physicist of sorts, of all people, actually tried to stop the LHC from being switched on by going to court. When interviewed on the Jon Stewart show, he was asked about the probability of a catastrophe actually happening, and in a remarkable flourish of on-air reasoning he said, “Fifty percent.” He lost, the LHC was switched on, and we are still here. Unfortunately, no miniature black holes have been found.
Every time I give a public lecture about what I do, I am asked the same thing: “What was there before the Big Bang?” I resort to the various explanations. There is the “There was no before, no time, before the Big Bang” answer. Or there is my colleague Jocelyn Bell Burnell’s more Zen-like answer: “That is like asking what is north of the North Pole.” It would be so much easier if I could resort to mathematics, but I can’t because most of my audience would find that it went over their heads. And for decades, because of Stephen Hawking’s and Roger Penrose’s singularity theorems, we have believed that, indeed, there was nothing before the Big Bang. It is one of those truths, those mathematical truths, we can’t get around that came out of the Golden Age of General Relativity.
Very recently, I’ve found my answers to the Big Bang questions becoming much more diverse and much less definitive. Over the past few years, the beginning of time has been thrown wide open by developments in quantum gravity and cosmology. When you wind back the clock and make the universe denser, hotter, and messier, that is when quantum foam, strings, branes, or even the loops have a say. It is where, it seems to some, spacetime breaks down and it no longer makes sense to talk about the initial singularity.
So what happened before the Big Bang? One possibility is that our universe popped into existence out of a vacuum, a bubble of spacetime that grew and grew to become what we are today. And like ours there are many universes that just popped up out of the vacuum. Another guess comes out of ideas in string and M-theory, which posit that the universe has many more than four dimensions and that we live on a three-dimensional “brane” in this spacetime and roll with it. Our domicile, our brane, feels just like a three-dimensional universe that every now and then collides with another brane just like ours. When they collide, they heat up, and as a result our universe feels as if it has undergone a hot Big Bang. There is no singularity, just an infinite succession of hot Big Bangs, a cyclic universe that would have made the Soviet orthodox philosophers, and possibly even Fred Hoyle and his cronies, proud. The model’s creators have dubbed each new Big Bang Ekpyrosis, an ancient Greek term for the periodic destruction of the universe, inevitably followed by a rebirth.
But, of course, so much of quantum gravity seems to point to the fragmentation of spacetime if looked at under an all-seeing microscope. If we wind back the clock so that spacetime is concentrated at a point, surely we must run up against the bits and pieces that make up the fabric of space. Before any initial singularity is reached, when the chunkiness comes into play, known physics breaks down. Those who believe that loop quantum gravity is the answer say that there was a before, a time when the universe was collapsing until it reached the quantum wall and magically started expanding again. The universe underwent what has prosaically become known as a “bounce.”
It might not even be necessary to resort to that weird, dark era where quantum gravity comes into play, where so many differing opinions lead to so many different conjectures. A grander possibility is that spacetime is much vaster than we previously envisioned and our universe is only one of countless universes that together make up the multiverse. All over the multiverse, universes are breaking out into existence, growing to cosmic proportions, each one at its own pace and made up in its own particular way. If we follow back the existence of our own universe, we find that it is embedded like a pustule in a much wider spacetime that has existed for all eternity. The multiverse is a wild, immense realm of what is ultimately stasis: a steady state of creation and destruction.
The multiverse, along with something called the anthropic principle, has emerged as the favorite solution for the cosmological constant problem. With the great successes of observational cosmology, many believe that the cosmological constant actually exists in the real universe, even though quantum theory predicts an obscenely large value for it, much larger than what we observe. String theorists now apply the lack of predictivity in string theory to posit a landscape of different possible universes, each one with its own symmetries, energy scales, types of particles and fields, and, most crucially, its own cosmological constant. Any of these universes is possible, even ones with a very small cosmological constant. The anthropic principle, first proposed by Robert Dicke and further developed by Brandon Carter, argues that the universe is the way it is because if it were any other way, we wouldn’t be around to see it. We exist and are sentient because the universe has exactly the right set of constants, particles, and energy scales—including the cosmological constant—that allow for our existence. There are countless possible universes, but only the ones with the right values for physical constants, including the cosmological constant, allow us to exist. Given that such a universe is possible, it is natural that it will be the one, of all the universes in the multiverse, that we observe.
Some argue that cosmology has become so rich and complex that we may be at the frontier of what should be called science. George Ellis is one skeptic who thinks this approach goes too far. A relativist who, with Hawking and Penrose, cemented the existence of singularities in the cosmos in the late 1960s, Ellis has been at the forefront of using the whole of the universe as an immense laboratory and testing ground for Einstein’s theory. “I do not believe the existence of those other universes has been proven—or could ever be,” he says. “The multiverse argument is a well-founded philosophical proposal but, as it cannot be tested, it does not belong fully in the scientific fold.” On this landscape of possibilities anything can be predicted somewhere. Even among the string theorists there is a sense that things have gone too far. The new approach abandons the ultimate goal of modern physics to find a unique and simple unified explanation for all the fundamental forces, including gravity. Accepting the multiverse is tantamount to giving up. Even Edward Witten, the pope of modern string theory, is unhappy with how things are turning out and says, “I hope the current discussion of the string theory isn’t on the right track.”
Yet the multiverse’s following is growing. It solves some of the great unsolved problems, such as why there is a cosmological constant and why the constants of nature are tuned to be exactly what we measure them to be. On a regular basis, there are press releases and media reports on parallel universes and evidence for the immensity and plurality of spacetime. It is, of course, a wonderful setting for speculation, a vast blank canvas for storytelling. But, to Ellis, it simply isn’t science.
In 2009 I visited Príncipe, a small, lush speck of greenery in the armpit of Africa. It was from there that, ninety years before, Arthur Eddington had telegraphed a message to Frank Dyson, then the president of the Royal Astronomical Society, saying simply, “Through cloud. Hopeful.” Eddington’s measurements of starlight during a solar eclipse had established Einstein’s general theory of relativity as the modern theory. The eclipse expedition established Eddington and Einstein as international superstars.
I traveled to the small island nation of São Tomé and Príncipe with a motley collection of Brits, Portuguese, Brazilians, and Germans to lay a plaque donated by the Royal Astronomical Society and the International Astronomical Union at the site where Eddington and Cottingham had made their measurements.
São Tomé and Príncipe had emerged from centuries of colonial rule to become, for a while, yet another African socialist state. It joined the world of free markets, and its jumbled collection of shiny new houses for affluent Angolan holidaymakers contrasted with grand, decrepit colonial farmhouses.
The main house at Roça Sundy, where Eddington made his measurements, was in better shape than most of the abandoned colonial homes scattered throughout the green countryside. The regional president of Príncipe, a tiny island of not more than five thousand people, had taken it as his holiday home. This turned out to be wishful thinking—it was still ramshackle, rusty, and uninhabitable.
I found that perfect little corner of the world deeply moving. My grandmother was born in São Tomé and Príncipe in the early twentieth century, and I had heard much about the place from her. But more important, I felt that I was witnessing a turning point in history. This is where Einstein’s theory was proved right, insofar as any scientific theory can be proved right. This is where general relativity became fact.
Scattered around were relics of the bygone era when Eddington passed through. There was the tennis court, cracked concrete fighting a losing battle with the inexorable vegetation seeping up from the ground. Everywhere I looked was lush, overwhelming green. It was a far cry from the bleak, manicured landscape of the fens where Eddington had spent almost all his life. Now, with our visit, there was a shiny plaque marking Eddington’s achievement and, we hoped, explaining to any passerby of this remote location how stupendous the event had been.
Looking back to 1919, it is amazing how Einstein’s and Eddington’s ideas developed. The simple idea that light would be deflected by warped spacetime, the key to testing Einstein’s theory, was now, ninety years later, one of the most powerful tools in astronomy. Over the past twenty years it has become the norm to look at how light is deflected by spacetime to learn about the universe. By looking at stars in nearby galaxies and waiting to see if their light is suddenly focused due to the passage of a dark heavy object in front of them, it has been possible to look for dark matter in our galaxy. The nuggets of dark matter, if they exist, will play the role of the sun in Eddington’s experiment, bending starlight, lensing it, as the effect has become known. On a grander scale, we now use lensing to look at clusters, swarms of tens to hundreds of galaxies. These behemoths sink into spacetime, creating gigantic warps that scatter and align the light from distant galaxies. Astronomers now use the distortions and shifts in the light of these distant galaxies to weigh the clusters.
Why stop there? With typical hubris, astronomers, cosmologists, and relativists have now set their sights on mapping the distortions of spacetime all the way out, as far as can possibly be observed. By observing slices of the universe and seeing how the light of those galaxies is affected by intervening spacetime, it should be possible to build up a detailed description of what spacetime actually looks like all around us. Taking Einstein’s and Eddington’s ideas to a new level, we harness the universe, learning what it is made of and whether our current laws for the way spacetime behaves are correct.
Throughout the day, as festivities continued in Príncipe, Einstein’s and Eddington’s names were on everyone’s lips. In this lost corner of a minuscule island, it was too much to ask that anyone would actually know what we were talking about. Ponderous nods from the local and visiting dignitaries didn’t mean much, and a shoal of children and teenagers ran around during the ceremony. They didn’t know what it was about, true, but they had of course heard of Einstein. And some even knew about the famous Englishman Eddington who had come to visit many years ago. They all agreed that it was a good thing—that small island’s claim to fame.
As I watched the crowd joining in this odd, esoteric celebration, I saw it as yet another quirky sign of how universal and democratic Einstein’s theory has become. While tortuous and often intractable, Einstein’s theory has been at the same time democratic, easily encapsulated in a few pages of condensed equations. The history of general relativity spans many continents, with a full cast of characters that is truly international and varied. British astronomers, a Russian meteorologist, a Belgian priest, a New Zealander mathematician, a German soldier, an Indian child prodigy, an American expert on the atom bomb, a South African Quaker, and so many more have been brought together by the elegance and power of Einstein’s theory.
That night, we handed out telescopes to the crowd and looked up at the stars. The sky was breathtaking, ready to offer up much more that would help us delve deeper into Einstein’s theory. I thought of how, even now, Einstein’s theory was driving us to look out into the cosmos on a grander scale. The new Príncipe might now be in the south of Africa or in the Australian desert, and the new telescope would use the latest, most powerful technologies of the twenty-first century.
While Eddington had used an optical telescope, something with a lens, an eyepiece, and a photographic plate, this new phase will rely on radio antennas and dishes. Radio has already given so much to general relativity, but this time it will go much further than has ever been envisaged. The idea is to build a collection of tens of thousands of radio antennas scattered across hundreds and thousands of kilometers. Known as the Square Kilometer Array, or SKA, because the total collecting area of all the antennas should add up to a square kilometer, it will take one, possibly two continents to support it. Some of the telescopes will lie out in the vastness of the Australian west, and others will be strewn throughout southern Africa. The core of the beast will be laid out in the Karoo Desert, but a number of these dishes will be scattered throughout the continent in places like Namibia, Mozambique, Ghana, Kenya, and Madagascar. It will be a truly continental, African endeavor. And, in the same way that Eddington used Príncipe to establish general relativity, the SKA would be the beast that could test Einstein’s theory on cosmological scales with unprecedented precision. The SKA would detect if there were, indeed, any cracks in Einstein’s grand idea. It would be able to detect the elusive gravitational waves that are still out there, waiting to be discovered. It might even reveal the nature of the infamous dark energy that seems to have cemented itself into the current model of the universe.
That night as we celebrated Eddington’s and Einstein’s colossal achievements, I thought about how we are only at the beginning of what the theory of spacetime is going to tell us about the universe. The twenty-first century is surely going to be the century of Einstein’s general theory of relativity, and I feel fortunate to be living at a time when so many new things are waiting to be discovered. Almost a hundred years after Einstein finally came up with his theory, something fantastic is going to happen.
Acknowledgments
Two people made this book happen. Patrick Walsh convinced me, and gave me the opportunity, to write about this obsession of mine. Courtney Young took my manuscript and, with remarkable grace and firmness, made it into something I would want to read.
I have relied on testimony, advice, and criticism from a long list of colleagues, friends, family, readers, and writers over many years. Here is an attempt at a (quite possibly incomplete) list: Andy Albrecht, Arlen Anderson, Tessa Baker, Max Bañados, Julian Barbour, John Barrow, Adrian Beecroft, Jacob Bekenstein, Jocelyn Bell Burnell, Orfeu Bertolami, Steve Biller, Michael Brooks, Harvey Brown, Phil Bull, Alex Butterworth, Philip Candelas, Rebecca Carter, Chris Clarkson, Tim Clifton, Frank Close, Peter Coles, Amanda Cook, Marc Davis, Xenia de la Ossa, Cécile DeWitt-Morette, Mike Duff, Jo Dunkley, Ruth Durrer, George Efstathiou, George Ellis, Graeme Farmelo, Hugo and Karin Gil Ferreira, Andrew Hodges, Chris Isham, Andrew Jaffe, David Kaiser, Janna Levin, Roy Maartens, Ed Macaulay, João Magueijo, David Marsh, John Miller, Lance Miller, Jos
é Mourão, Samaya Nissanke, Tim Palmer, John Peacock, Jim Peebles, Roger Penrose, João Pimentel, Andrew Pontzen, Frans Pretorius, Dimitrios Psaltis, Martin Rees, Bernard Schutz, Joe Silk, Constantinos Skordis, Lee Smolin, George Smoot, Andrei Starinets, Kelly Stelle, Francesco Sylos-Labini, Kip Thorne, Neil Turok, Tony Tyson, Gisa Weszkalnys, John Wheater, Adam Wishart, Lukas Wilowski, Andrea Wulf, and Tom Zlosnik. While their contributions have been invaluable, any errors or misconceptions in the final text are my own.
The team at Conville and Walsh have been incredibly supportive in seeing this book through, and my colleagues at the University of Oxford have been enthusiastic and helpful. It is a real privilege working with them all.
Notes
One of the joys of writing this book has been reading many of the original papers and articles on general relativity as well as histories, biographies, and memoirs. I hope the specific sources that follow will be taken as encouragement for further reading in the subject. It is definitely worth the effort. Full references for the publications cited in this section can be found in the bibliography.
I highly recommend plowing through some of the scientific literature, even if you don’t have the background to understand much of what is being done. It will give you a real flavor of what science is about, how things are presented, explained, and promoted, and how the vast cast of characters interact with each other through the scientific journals. Unfortunately, many of the journals are behind “paywalls,” and some of the articles I refer to here cannot be accessed if you are not in an academic institution. A surprising number of them can, however, and I suggest you look for them. I recommend using one of the following search engines:
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