The Hidden Reality_ Parallel Universes and the Deep Laws of the Cosmos - Brian Greene [3]
Some of the earliest scientific forays into parallel worlds were initiated in the 1950s by researchers puzzling over aspects of quantum mechanics, a theory developed to explain phenomena taking place in the microscopic realm of atoms and subatomic particles. Quantum mechanics broke the mold of the previous framework, classical mechanics, by establishing that the predictions of science are necessarily probabilistic. We can predict the odds of attaining one outcome, we can predict the odds of another, but we generally can’t predict which will actually happen. This well-known departure from hundreds of years of scientific thought is surprising enough. But there’s a more confounding aspect of quantum theory that receives less attention. After decades of closely studying quantum mechanics, and after having accumulated a wealth of data confirming its probabilistic predictions, no one has been able to explain why only one of the many possible outcomes in any given situation actually happens. When we do experiments, when we examine the world, we all agree that we encounter a single definite reality. Yet, more than a century after the quantum revolution began, there is no consensus among the world’s physicists as to how this basic fact is compatible with the theory’s mathematical expression.
Over the years, this substantial gap in understanding has inspired many creative proposals, but the most startling was among the first. Maybe, that early suggestion went, the familiar notion that any given experiment has one and only one outcome is flawed. The mathematics underlying quantum mechanics—or at least, one perspective on the math—suggests that all possible outcomes happen, each inhabiting its own separate universe. If a quantum calculation predicts that a particle might be here, or it might be there, then in one universe it is here, and in another it is there. And in each such universe, there’s a copy of you witnessing one or the other outcome, thinking—incorrectly—that your reality is the only reality. When you realize that quantum mechanics underlies all physical processes, from the fusing of atoms in the sun to the neural firings that constitutes the stuff of thought, the far-reaching implications of the proposal become apparent. It says that there’s no such thing as a road untraveled. Yet each such road—each reality—is hidden from all others.
This tantalizing Many Worlds approach to quantum mechanics has attracted much interest in recent decades. But investigations have shown that it’s a subtle and thorny framework (as we will discuss in Chapter 8); so, even today, after more than half a century of vetting, the proposal remains controversial. Some quantum practitioners argue that it has already been proved correct, while others claim just as assuredly that the mathematical underpinnings don’t hold together.
Such scientific uncertainty notwithstanding, this early version of parallel universes resonated with themes of separate lands or alternative histories that were being explored in literature, television, and film, creative forays that continue today. (My favorites since childhood include The Wizard of Oz, It’s a Wonderful Life, the Star Trek episode “The City on the Edge of Forever,” the Borges story “The Garden of Forking Paths,” and, more recently, Sliding Doors and Run Lola Run.) Collectively, these and many other works of popular culture have helped integrate the concept of parallel realities into the zeitgeist and are responsible for fueling much public fascination with the topic. But quantum mechanics is only one of numerous ways that a conception of parallel universes emerges from modern physics. In fact, it won’t be the first I’ll discuss.
In Chapter 2, I’ll begin with a different route to parallel universes, perhaps the simplest route of all.