by Adam Frank
Leonard Susskind is not a member of the faithful. Susskind, the string theorist who coined the term “string landscape”, has argued strongly that the Anthropic Principle’s time has come.16 He advocates its embrace as a means of making further progress in articulating why our universe has the structure it does. By thinking in terms of pocket universes and their statistics, Susskind and others suggest that it is time to change the goal of cosmological theorizing. Instead of finding the one eternal law of nature that ordained this universe, we must look for an eternal law governing all universes. The physics of our one universe then becomes an accident of statistics. It is a radical idea, one that many scientists rail against.
If inflation is true (and there is a slim but growing body of data to support it), does eternal inflation necessarily follow? And if eternal inflation is a consequence of inflation, does a multiverse without beginning or end have to exist? If the multiverse is real, does the project of physics and cosmology with its grand dreams of a final theory become a relic of a more naive era? The questions of multiverses and eternal inflation should, ultimately, be answered by data. But how long will it take to compile that data? In the meantime, what price will we pay for pushing beyond the Big Bang? These are questions facing the entire community of physicists, astronomers and cosmologists. For some the answer lies not in multiple universes or string-theory-based cyclic models but in something altogether new and radically different.
Chapter 11
GIVING UP THE GHOST: THE END OF BEGINNINGS AND THE END OF TIME
Cosmology’s Radical Alternatives in Three Acts
THE BAVARIAN ALPS • OCTOBER 1963
It was supposed to be a simple weekend trip to the mountains. Now, as the train headed back to Munich, Julian Barbour wasn’t sure where he was headed.
Barbour and a friend had just wanted to get away, recharge their mental batteries. Things were going well with his PhD programme and soon he would start a real research project in astrophysics. At least that had been the plan. Now an inescapable question gripped him, upending his tidy future.
What is time, really?
Two days before, he had been on a train heading up to the mountains. Reading the newspaper, he found a story about Paul Dirac, one of the founders of quantum physics. The article discussed Dirac’s new thinking on time, space and relativity. It described how Dirac’s new work had led him “to doubt how fundamental the 4-D requirement is in physics.” Then Dirac asked the question that brought on this crisis: “Perhaps we should ask what is time itself.”
The next day he woke with a terrible headache and his friend had to go hike up the mountain alone. All day as he lay in the dark room, Dirac’s question haunted him. It was as if the great physicist’s speculations had given him some kind of horrible form of mental indigestion.
“Perhaps we should ask what is time itself.”
Now bleary-eyed and soul-wracked, he knew things would have to change. As the train headed back to Munich, he knew he could not spend a career writing acceptable “mainstream” scientific articles. He would have to leave academic physics and devote all his efforts to this one question. There was no other choice. He looked out of the window at the mountains receding in the distance. Now he had his own mountain to climb and he would need to husband all his time and effort for the ascent.1
THE REBELS
Julian Barbour’s encounter with Paul Dirac’s musings on time and space that day in 1963 set his life on a new path. “I knew it would take years to understand my question”, says Barbour. “There was no way I could have a normal academic career, publishing paper after paper, and really get anywhere.” With a bulldog’s determination, Barbour left his PhD programme and settled in rural England, where he supported his family translating Russian scientific texts. Thirty-six years later, he published his hard-won answer in scientific monographs and a popular book, The End of Time.2 Even though he had no academic affiliation, physicists across the world took notice of Barbour’s creative theorizing.
Barbour is a rebel physicist, a researcher convinced that moving beyond and before the Big Bang will require more than just new theories of strings, branes or inflation. Instead, Barbour is ready to challenge the fundamental assumptions that physics has stood upon for centuries. He is not alone.
Across the globe a small but determined group of scientists has taken on the rebel’s mantle as well. Each, in his or her own way, believes that progress at the frontiers of physics and cosmology has stalled. A renewed path forward will, in their eyes, require a radical departure from current methods and models. For some of these researchers, their path out of the mainstream was forced on them through work within it. Others have experienced a growing discord with the direction cosmology and fundamental physics have taken, leading them to ask deeper and more fundamental questions. For each of them, string theory and its 10500 possible solutions seem like a dead end, and the multiplication of unobservable universes in multiverse models appears more like science fiction than science. Something else, something better, something not yet imagined, must be waiting.
Each of the rebels sees a fundamental problem with physics and cosmology. In almost all cases the problem they see is time. Each is prepared to scrap the way physics describes time and begin again. Sometimes they are ready with radical solutions that, if correct, will profoundly alter the meaning of time on its own and in its role in cosmology. In other cases, the critiques lean towards metaphysics, asking what physics means, how it is carried forward and how it all begins with time. In every case, these rebels are willing to stand against the mainstream and re-examine how questions of time, physics and cosmology should be asked.
ACT I: THE END OF TIME
Julian Barbour’s solution to the problem of time in physics and cosmology is as simply stated as it is radical: there is no such thing as time.3
“If you try to get your hands on time, it’s always slipping through your fingers”, says Barbour. “People are sure time is there, but they can’t get hold of it. My feeling is that they can’t get hold of it because it isn’t there at all.” Barbour speaks with a disarming English charm that belies an iron resolve and confidence in his science. His extreme perspective comes from years of looking into the heart of both classical and quantum physics. Isaac Newton thought of time as a river flowing at the same rate everywhere. Einstein changed this picture by unifying space and time into a single 4-D entity. But even Einstein failed to challenge the concept of time as a measure of change. In Barbour’s view, the question must be turned on its head. It is change that provides the illusion of time. Channelling the ghost of Parmenides, Barbour sees each individual moment as a whole, complete and existing in its own right. He calls these moments “Nows”.
“As we live, we seem to move through a succession of Nows”, says Barbour, “and the question is, what are they?” For Barbour each Now is an arrangement of everything in the universe. “We have the strong impression that things have definite positions relative to each other. I aim to abstract away everything we cannot see (directly or indirectly) and simply keep this idea of many different things coexisting at once. There are simply the Nows, nothing more, nothing less.”
Barbour’s Nows can be imagined as pages of a novel ripped from the book’s spine and tossed randomly onto the floor. Each page is a separate entity existing without time, existing outside of time. Arranging the pages in some special order and moving through them in a step-by-step fashion makes a story unfold. Still, no matter how we arrange the sheets, each page is complete and independent. As Barbour says, “The cat that jumps is not the same cat that lands.” The physics of reality for Barbour is the physics of these Nows taken together as a whole. There is no past moment that flows into a future moment. Instead all the different possible configurations of the universe, every possible location of every atom throughout all of creation, exist simultaneously. Barbour’s Nows all exist at once in a vast Platonic realm that stands completely and absolutely without time.4
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��What really intrigues me”, says Barbour, “is that the totality of all possible Nows has a very special structure. You can think of it as a landscape or country. Each point in this country is a Now and I call the country Platonia, because it is timeless and created by perfect mathematical rules.” The question of “before” the Big Bang never arises for Barbour because his cosmology has no time. All that exists is a landscape of configurations, the landscape of Nows. “Platonia is the true arena of the universe”, he says, “and its structure has a deep influence on whatever physics, classical or quantum, is played out in it.” For Barbour, the Big Bang is not an explosion in the distant past. It’s just a special place in Platonia, his terrain of independent Nows.
Our illusion of the past arises because each Now in Platonia contains objects that appear as “records” in Barbour’s language. “The only evidence you have of last week is your memory. But memory comes from a stable structure of neurons in your brain now. The only evidence we have of the Earth’s past is rocks and fossils. But these are just stable structures in the form of an arrangement of minerals we examine in the present. The point is, all we have are these records and you only have them in this Now.” Barbour’s theory explains the existence of these records through relationships between the Nows in Platonia. Some Nows are linked to others in Platonia’s landscape even though they all exist simultaneously. Those links give the appearance of records lining up in sequence from past to future. In spite of that appearance, the actual flow of time from one Now to another is nowhere to be found.
FIGURE 11.1. A world without time. In Julian Barbour’s theory the true space of cosmological physics is “Platonia”, which physicists call a “configuration space”. Every instant is a distinct “Now” representing an arrangement of all the universe’s matter and energy. Time does not flow from one Now to another. The Nows exist eternally but do have an arrangement determined by physics in the abstract space of Platonia. Thus some Nows are linked which gives the illusion of time’s flow.
“Think of the integers”, he explains. “Every integer exists simultaneously. But some of the integers are linked in structures, like the set of all primes or the numbers you get from the Fibonacci series.” The number 3 does not occur in the past of the number 5, just as the Now of the cat jumping off the table does not occur in the past of the Now wherein the cat lands on the floor.5
Past and future, beginning and end have simply disappeared in Barbour’s physics. And make no mistake about it, Barbour is doing physics. “I know the idea is shocking”, he says, “but we can use it to make predictions and describe the world.” With his collaborators, Barbour has published a series of papers demonstrating how relativity and quantum mechanics naturally emerge from the physics of Platonia.
Barbour’s perfect timeless arrangement of Nows into the landscape of Platonia is the most radical of all solutions to the conundrum of Before. But his audacity reveals an alternative route from this strange moment in science’s history. In an era in which the search for quantum gravity has multiplied dimensions and the discovery of dark energy has sent cosmologists back to their blackboards, all the fundamentals seem up for grabs. Barbour is willing to step back even further and offer “no time” as a more basic answer to the question “What is time?”
Barbour’s status as a radical was freely chosen, and it led him out of an academic career and straight into his small cottage in Oxfordshire. For other rebels, the path of apostasy was not chosen but thrust upon them.
ACT II: THE END OF CLOCKS
“I was not metaphysically predisposed to give up on the idea of immutable laws”, says Andreas Albrecht, a physicist at the University of California at Davis. “I just stumbled on a problem and had to deal with it.”6 In fact, Albrecht, a highly respected cosmologist, was one of the first physicists to pick up on Guth’s inflationary cosmology. It was Albrecht, working as a PhD student with Paul Steinhardt, who elaborated many of the key details of the theory.7
Andreas Albrecht’s fascination with physics began early, especially his fire for its description of nature’s laws. “I remember learning about atoms in my high school physics textbook”, he says. “I got enthralled by the appendix on quantum physics. I just loved the idea that there were deeper laws behind what we see. After all these years it still keeps me going.”
The deeper laws inspiring Albrecht are the same siren song heard by Pythagoras and Plato. From the Greeks to Kepler to Newton to Einstein, the idea of laws, eternal and immutable rules of physics cast in the eternal and immutable language of mathematics, propels young men and women to lives in physics. It’s the Platonic laws of physics that catch their imaginations and fill them with awe. This was the inspiration that propelled Albrecht to a highly successful career as a quantum cosmologist. Ironically, it was also his work in this field that drove him to question the very fundamentals of his profession—the core idea of the eternal laws of physics.
In quantum physics, objects such as electrons have the strange property of not having any definite properties. In quantum mechanics, an electron can be in many places at the same time, existing in a kind of potential state until an observation nails it to a single location. In the language of the field, the electron is represented by a wave function, which is quantum physics’ mathematical description of the electron and its properties. In classical physics, the description of the electron allowed it to exist at only one location at a time. The wave function is different and describes the electron as having many simultaneous and different locations. “Quantum physics inherently gives us multiple coexisting possibilities”, explains Albrecht. “All those different coexisting possibilities are just an inescapable part of the theory.”
Quantum cosmology is the attempt to explain the entire universe as a quantum object. Beginning in the 1960s, physicists such as Bryce De-Witt, Jim Hartle and Stephen Hawking began exploring quantum cosmological models designed to embrace the entire cosmos.8 They were, essentially, looking for the wave function of the universe. Hawking’s own pioneering studies of quantum cosmology (and the universe’s wave function) had led him to propose “no-boundary” models of the universe, in which no origin of time ever appears (the subject of his famous book A Brief History of Time).9
Of course, without a full theory of quantum gravity, quantum cosmology can only sketch the possibilities. Researchers must explore the terrain in bits and pieces, and in hunting at the edges this way, they uncovered new and unexpected details that linked quantum physics and cosmology. It was in his exploration of those interstitial zones that Andy Albrecht stumbled on his “clock ambiguity” and the end, for him, of immutable laws.
FIGURE 11.2. Quantum physics and the wave function. In classical physics every object has definite properties such as location. Thus a classical electron placed in a two-chambered box must exist in one side or the other. In quantum mechanics multiple possibilities exist at the same time. Thus before the box is opened, the electron exists in both sides of the box.
“I started doing quantum cosmology in the 1980s”, says Albrecht. “It was a very new, very hot topic then.” Thanks to Stephen Hawking and other physicists, the broad outlines for thinking about quantum mechanics, general relativity and the universe as a whole had developed. This was possible even without a full theory of quantum gravity. Doing physics in this “half-sighted” mode is not new. As Albrecht explains, “When I was in high school we learned a lot about the atom even though we had not studied quantum physics yet. We could still do things using the incomplete tools we had learned already. When I study quantum cosmology I am doing the same thing.” Inflationary cosmology is considered one form of quantum cosmology, and clearly it has proven its usefulness.
Albrecht works with simple “toy” quantum cosmology models that capture essentials from general relativity such as the expansion of space-time and essentials from quantum physics such as multiple, coexisting possibilities for the universe. “My goal has been to understand how quantum descriptions for the universe must be
have in general”, he explains. “That was how I found this strange property relating to the laws of physics.” Deep in quantum cosmology’s basic equations, Albrecht found an ambiguity that left his faith shattered.10
“The problem relates to time and what you decide to call a clock”, says Albrecht. In normal life, we measure time by picking some object and letting it act as a measuring standard—a “clock”. A clock can be water dripping from a faucet, the swing of a pendulum or the oscillations of a quartz crystal. In each case, physicists separate out some part of the world, some subsystem, and use it as a timekeeper. Albrecht found that in quantum cosmology, this separation was anything but straightforward.
“What does it mean to measure ‘time’?” asks Albrecht. “You have to divide the world into the part you want to study and the part you call a clock. When I tried to implement this in my quantum cosmology equations I ran into a big problem.”
The way time appears in the day-to-day way of doing physics (to a student in a laboratory, for instance) and the way it appears in quantum cosmology are profoundly different. If you try to calculate the motion of a billiard ball in normal physics, you just plug time into Newton’s equations of motion and let the forces acting on the ball move it around. But when you try to explain the fundamental history of the universe, you can’t just assume time—you have to figure out where it lives in the quantum cosmology equations. You have to figure out what part of your mathematical description represents time. The problem, Albrecht found, is that no unique formula tells physicists how to do this. There is no unique rule explaining how the universe evolved because there is no unique way to pull time apart from other pieces of the equation.
