Everyday Quantum Reality

6. Everyday Superposition

77 In his modern physics lecture course, Paul Dirac, one of the architects of quantum mechanics, would break a piece of chalk while trying to explain the concept of superposition.1 That was the only way he could put the chalk in two distinct places—by breaking the original piece and moving the two halves away from each other. This wasn’t an illustration of superposition; this was just what happens when we break one thing into parts and then spread the parts out. Superposition, by contrast, occurs as one thing occupies many space-time locations, all mutually exclusive from the perspective of common sense, without being broken apart. Electrons can do this, said Dirac, but not relatively large objects like pieces of chalk. For some thinkers, notably Einstein and Erwin Schrödinger, superposition was merely an index of our uncertainty about the Everyday Superposition It took me no time at all to notice that this nothing, this hole, where a head should have been, was no ordinary vacancy, no mere nothing. On the contrary, it was very much occupied. It was a vast emptiness vastly filled, a nothing that found room for everything—room for grass, trees, shadowy distant hills, and far above them snow-peaks like a row of angular clouds riding the blue sky. I had lost a head and gained a world. Douglas E. Harding 6 78 Everyday Quantum Reality electron’s position prior to measurement. The electron, they said, is always precisely located; it’s just that, until we measure it, we have only probabilistic knowledge of where it’s at. If I close my eyes and toss a nickel, I will be in a state of uncertainty regarding the outcome of the toss; all I can say is that there is 50 percent probability that it landed heads or tails. My uncertainty regarding the outcome of the coin toss leaves me probabilistically suspended or superposed between two possibilities (heads or tails), and until I open my eyes and look at the nickel, I don’t know which possibility is real. Similarly , said Einstein and Schrödinger, the electron is somewhere—at one distinct place—but until someone looks at it (measures it), he or she is probabilistically suspended among different possibilities, even though, like the nickel, the electron realizes just one possibility . For those following Einstein and Schrödinger, then, superposition is nothing more than a reflection of our probabilistic (imprecise ) knowledge regarding the electron’s non-probabilistic (precise) location. Though eminently commonsensical, this outlook has lost ground to the radical alternative view that unmeasured electrons exist in states of superposition, at least with respect to their location or position. Our probabilistic knowledge of their position, therefore , perfectly coincides with fact or reality. We know as much as we can know, because prior to measurement, electrons are schizophrenically smeared across regions of space-time in a manner fully coincidental with our probabilistic understanding of their position . It is as if the unobserved nickel lands both heads and tails in some sort of schizophrenic way; then, when we look at it, one outcome instantaneously materializes while the other collapses to zero probability. If this radical outlook is right, it would seem to count against my argument that quantum physics reenacts everyday experience. After all, as Dirac noted, pieces of chalk can’t exist in superposition states, whereas electrons can. This dissimilarity between everyday objects and quantum objects seems unbridgeable, and yet there is something about our everyday experience that aligns with superposition states. It doesn’t concern material objects as we normally understand them. It concerns the knowing of those objects and, speaking more broadly, our consciousness of reality. 79 Everyday Superposition Superposed Minds Among other things, quantum physics narrows the Cartesian divide between mind and matter. For some thinkers, it has eliminated that divide. In his 1930 review of modern cosmology and physics, Sir James Jeans wrote: Thirty years ago, we thought, or assumed, that we were heading towards an ultimate reality of a mechanical kind. It seemed to consist of a fortuitous jumble of atoms, which was destined to perform meaningless dances for a time under the action of blind purposeless forces, and then fall back to form a dead world. . . . To-day there is a wide measure of agreement, which on the physical side of science approaches almost to unanimity, that the stream of knowledge is heading toward a non...