What Is Real- The Unfinished Quest for the Meaning of Quantum Physics
How much do I want to read more? 8/10
Another fascinating book about Quantum Physics and its paradox.
The mystery of the success of its prediction versus the void when it comes to its interpretation and meaning of the world surrounding us.
The objects in our everyday lives have an annoying inability to appear in two places at once.
Your house keys are a temporary alliance of a trillion trillion atoms, each forged in a dying star eons ago, each falling to Earth in its earliest days. They have bathed in the light of a violent young sun. They have witnessed the entire history of life on our planet. Atoms are epic.
Like most epic heroes, atoms have some problems that ordinary humans don’t. We are creatures of habit, monotonously persisting in just one location at a time. But atoms are prone to whimsy. A single atom, wandering down a path in a laboratory, encounters a fork where it can go left or right. Rather than choosing one way forward, as you or I would have to do, the atom suffers a crisis of indecision over where to be and where not to be. Ultimately, our nanometer Hamlet chooses both. The atom doesn’t split, it doesn’t take one path and then the other—it travels down both paths, simultaneously, thumbing its nose at the laws of logic. The rules that apply to you and me and Danish princes don’t apply to atoms. They live in a different world, governed by a different physics: the submicroscopic world of the quantum.
Quantum physics—the physics of atoms and other ultratiny objects, like molecules and subatomic particles—is the most successful theory in all of science. It predicts a stunning variety of phenomena to an extraordinary degree of accuracy, and its impact goes well beyond the world of the very small and into our everyday lives. The discovery of quantum physics in the early twentieth century led directly to the silicon transistors buried in your phone and the LEDs in its screen, the nuclear hearts of the most distant space probes and the lasers in the supermarket checkout scanner. Quantum physics explains why the Sun shines and how your eyes can see. It explains the entire discipline of chemistry, periodic table and all. It even explains how things stay solid, like the chair you’re sitting in or your own bones and skin. All of this comes down to very tiny objects behaving in very odd ways.
But there’s something troubling here. Quantum physics doesn’t seem to apply to humans, Yet all the mundane things in the world around us are made of atoms—including you, me. And those atoms certainly are governed by quantum physics.
The problem isn’t that quantum physics is weird. The world is a wild and wooly place, with plenty of room for weirdness. But we definitely don’t see all the strange effects of quantum physics in our daily lives. Why not?
a border beyond which quantum physics doesn’t work. In that case, where is the boundary, and how does it work?
Eighty years ago, one of the founders of quantum physics, Erwin Schrödinger, was deeply troubled by these problems. To explain his concerns to his colleagues, he devised a now-famous thought experiment: Schrödinger’s cat.
Schrödinger imagined putting a cat in a box along with a sealed glass vial of cyanide, with a small hammer hanging over the vial. The hammer, in turn, would be connected to a Geiger counter, which detects radioactivity, and that counter would be pointed at a tiny lump of slightly radioactive metal. This Rube Goldberg contraption would be set off the moment the metal emitted any radiation; once that happens, the Geiger counter would register the radiation, which would release the hammer, smashing the vial and killing the cat.
Schrödinger proposed leaving the cat in the box for a certain period of time, then opening the box to find the cat’s fate.
Schrödinger’s cat. When the metal gives off radiation, the Geiger counter will register it and drop the hammer, releasing the cyanide and killing the cat:
The radiation emitted by the lump of metal is composed of subatomic particles, breaking away from the atoms in the metal and flying off at high speeds. Like all sufficiently tiny things, those particles obey the laws of quantum physics. But, instead of reading Shakespeare, the subatomic particles in the metal have been listening to the Clash—at any particular moment, they don’t know whether they should stay or they should go. So they do both: during the time the box is closed, the indecisive lump of radioactive metal will and won’t emit radiation.
Thanks to these punk-rock particles, the Geiger counter will and won’t register radiation, which means the hammer will and won’t smash the vial of cyanide—so the cat will be both dead and alive. And this, Schrödinger pointed out, is a serious problem. Maybe an atom can travel down two paths at once, but a cat certainly can’t be both dead and alive.
Some claimed that the cat was in a state of dead-and-alive until the moment the box was opened, when the cat was somehow forced into “aliveness” or “deadness” through the action of looking inside the box.
Others believed that talking about what was going on inside the box before it was opened was meaningless, because the interior of the unopened box was unobservable by definition, and only observable, measurable things have meaning.
Schrödinger’s concerns about his cat weren’t allayed by these arguments. He thought that his colleagues had missed the point: quantum physics lacked an important component, a story about how it lined up with the things in the world. How does a phenomenal number of atoms, governed by quantum physics, give rise to the world we see around us? What is real, at the most fundamental level, and how does it work? Yet Schrödinger’s opponents carried the day, and his concerns about what was actually happening in the quantum world were dismissed.
Schrödinger was in a minority, but he wasn’t alone. Albert Einstein also wanted to understand what was really happening in the quantum world. He debated Niels Bohr, the great Danish physicist, over the nature of quantum physics and reality. The Einstein-Bohr debates have entered into the lore of physics itself, and the usual conclusion is that Bohr won, that Einstein’s and Schrödinger’s concerns were shown to be baseless, that there is no problem with reality in quantum physics because there is no need to think about reality in the first place.
There are also instantaneous long-distance connections between objects: subtle, useless for direct communication, but surprisingly useful for computation and encryption.
a bitter debate has raged over its meaning for the past ninety years.
Many physicists are driven to enter the field out of a desire to understand the most basic properties of nature, to see how the puzzle fits together. Yet, when it comes to quantum physics, the majority of physicists are perfectly willing to abandon this quest and instead merely “shut up and calculate,”
Thus, nearly a century after quantum theory was first developed—after it has thoroughly altered the world and the lives of every single human in it, both for better and worse—we still don’t know what it’s telling us about the nature of reality. This thoroughly strange story is the subject of this book.
After all, quantum physics certainly works. For that matter, why should physicists care? Their mathematics makes accurate predictions; isn’t that enough?
But science is about more than mathematics and predictions—it’s about building a picture of the way nature works.
The stories told by the best scientific theories determine the experiments that scientists choose to perform and influence the way that the outcomes of those experiments are interpreted. As Einstein pointed out, “The theory decides what we can observe.”
Galileo didn’t invent the telescope—but he was the first to think of pointing a good one at Jupiter.
After that, telescopes were used regularly to look at everything from comets to nebulae to star clusters.
But nobody bothered to use a telescope to find out whether the Sun’s gravity bent starlight during a solar eclipse—not until Einstein’s theory of general relativity predicted just such an effect, over three centuries after Galileo’s discovery.
The practice of science itself depends on the total content of our best scientific theories—not just the math but the story of the world that goes along with the math. That story is a crucial part of the science, and of going beyond the existing science to find the next theory.
The discovery that the Earth was not at the center of the universe, Darwin’s theory of evolution, the Big Bang and an expanding universe nearly 14 billion years old, containing hundreds of billions of galaxies, each containing hundreds of billions of stars—these ideas have radically altered humanity’s conception of itself.
Quantum physics works, but ignoring what it tells us about reality means papering over a hole in our understanding of the world.
Prologue - The Impossible Done
“I hesitated to think it was wrong,” said Bell, “but I knew it was rotten.”
The godfather of quantum physics, Niels Bohr, talked about a division between the world of big objects, where classical Newtonian physics ruled, and small objects, where quantum physics reigned. But Bohr was maddeningly unclear about the location of the boundary between the worlds.
And Werner Heisenberg, the first person to discover the full mathematical form of quantum physics, was no better.
Shortly before Bell graduated from university in 1949, he stumbled upon a book by Max Born, another architect of quantum physics. Born’s book, Natural Philosophy of Cause and Chance, made quite an impression on Bell—especially the discussion of a proof by the great mathematician and physicist John von Neumann. According to Born, von Neumann had proven that the Copenhagen interpretation was the only possible way of understanding quantum physics. So either the Copenhagen interpretation was correct or quantum physics was wrong.
Bell couldn’t read von Neumann’s original proof himself—it had been published only in German, which Bell didn’t speak.
He went to work on Britain’s nuclear energy program and put his doubts about quantum physics aside. But, in 1952, Bell “saw the impossible done.” A new paper shattered his short-lived complacency about the problems of the Copenhagen interpretation.
Somehow, despite von Neumann’s proof, a physicist named David Bohm had found another way to understand quantum physics. How? Where had the mighty von Neumann gone wrong, and why hadn’t anyone seen it before Bohm? Bell couldn’t answer these questions without reading von Neumann’s proof. And by the time von Neumann’s book was published in English three years later, life had intervened: Bell had gotten married and gone off to Birmingham to get his PhD in quantum physics. But Bohm’s paper “was never completely out of my mind,” Bell said. “I always knew that it was waiting for me.” Over a decade later, Bell finally returned to it—and made the most profound discovery about the nature of reality since Einstein.
Part I - A Tranquilizing Philosophy
The people of Tlön are taught that the act of counting modifies the amount counted, turning indefinites into definites. The fact that several persons counting the same quantity come to the same result is for the psychologists of Tlön an example of the association of ideas or of memorization.
—- Jorge Luis Borges, “Tlön, Uqbar, Orbus Tertius”
This epistemology-soaked orgy ought to come to an end.
—- Albert Einstein, letter to Erwin Schrödinger, 1935
1 - The Measure of All Things
Two great theories shook the world and shattered the earth in the first quarter of the twentieth century, scattering the remains of the physics that had come before and forever altering our understanding of reality. One of these theories, relativity, was developed in true science-fiction fashion, by a lone genius working in splendid isolation, who had left the academy only to return triumphant with profound truth in his hand—this was, of course, Albert Einstein.
The other theory, quantum physics, had a more difficult birth. It was a collaborative effort involving dozens of physicists working over the course of nearly thirty years. Einstein was among them, but he was not their leader; the closest thing this disorganized and unruly band of revolutionaries had was Niels Bohr, the great Danish physicist.
The physicists who worked there made profound discoveries across nearly every field of science: they developed the first genuine theory of quantum physics, found the underlying logic of the periodic table of the elements, and used the power of radioactivity to reveal the basic workings of living cells. And it was Bohr, along with a group of his most talented students and colleagues—Werner Heisenberg, Wolfgang Pauli, Max Born, Pascual Jordan, and others—who developed and championed the “Copenhagen interpretation,” which rapidly became the standard interpretation of the mathematics of quantum physics.
What does quantum physics tell us about the world? According to the Copenhagen interpretation, this question has a very simple answer: quantum physics tells us nothing whatsoever about the world.
Rather than telling us a story about the quantum world that atoms and subatomic particles inhabit, the Copenhagen interpretation states that quantum physics is merely a tool for calculating the probabilities of various outcomes of experiments.
According to Bohr, there isn’t a story about the quantum world because “there is no quantum world. There is only an abstract quantum physical description.” That description doesn’t allow us to do more than predict probabilities for quantum events, because quantum objects don’t exist in the same way as the everyday world around us.
As Heisenberg put it, “The idea of an objective real world whose smallest parts exist objectively in the same sense as stones or trees exist, independently of whether or not we observe them, is impossible.” But the results of our experiments are very real, because we create them in the process of measuring them. Jordan said when measuring the position of a subatomic particle such as an electron, “the electron is forced to a decision. We compel it to assume a definite position; previously, it was, in general, neither here nor there.… We ourselves produce the results of measurement.”
Despite his crucial role in the development of quantum physics, Einstein couldn’t stand the Copenhagen interpretation. He called it a “tranquilizing philosophy—or religion” that provides a “soft pillow to the true believer… [but it] has so damned little effect on me.” Einstein demanded an interpretation of quantum physics that told a coherent story about the world, one that allowed answers to questions even when no measurement was taking place. He was exasperated with the Copenhagen interpretation’s refusal to answer such questions, calling it an “epistemology-soaked orgy.”
Yet Einstein’s pleas for a more complete theory went unheard, in part because of John von Neumann’s proof that no such theory was possible. Von Neumann was arguably the greatest mathematical genius alive. He had taught himself calculus by the age of eight, published his first paper on advanced mathematics at nineteen, and earned a PhD when he was twenty-two. He played a crucial role in building the atomic bomb, and he was one of the founding fathers of computer science. He was also fluent in seven languages. His colleagues at Princeton said, only half-joking, that von Neumann could prove anything—and anything he proved was correct.
Einstein was painted as an old man out of touch with the rest of the world, and questioning the Copenhagen interpretation became tantamount to questioning the massive success of quantum physics itself. And so quantum physics continued for the next twenty years, piling success upon success, without any further questions about the hole at its heart.