What is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

All of this comes down to very tiny objects behaving in very odd ways.

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,” in the words of physicist David Mermin.

The story that comes along with a scientific theory influences the experiments that scientists choose to perform, the way new evidence is evaluated, and ultimately guides the search for new theories as well.

What if we treat you the same way we treated everything in the box? Well, in that case, when you look in the box, you’re interacting with it—which means you get entangled with the shared wave function of the box and everything in it. So now we have an even bigger wave function, still with two parts: one where you see a dead cat and a smashed vial of poison, and one where you see a happy cat and an intact vial. Which part of the wave function is real? Everett, remembering Wheeler’s advice to take the consequences of physical laws seriously, answered that both are real. There’s no way to pick one as more real than the other; the Schrödinger equation treats them equally. So when you perform this experiment, Everett said, both outcomes occur—and you split in two.

“I can testify to this from personal introspection, as can you. I simply do not branch

Now in your letter you say, “… I simply do not branch.” I can’t resist asking: Do you feel the motion of the earth

So Bell’s theorem does suggest that the strangest piece of Everett’s scheme could be a necessary feature of the world if we don’t want to abandon locality.

In short, Bell’s theorem really leaves only three unequivocal possibilities: either nature is nonlocal in some way, or we live in branching multiple worlds despite appearances to the contrary, or quantum physics gives incorrect predictions about certain experimental setups. No matter the outcome, Bell’s work presents a threat to the Copenhagen interpretation.

“Nonlocality, I think, was [Bell’s] great discovery,” said Bertlmann. “I think it [is] one of the greatest discoveries in the last century, that there is nonlocality in nature.”

“The fact that an adequate philosophical presentation [of quantum physics] has been so long delayed is no doubt caused by the fact that Niels Bohr brainwashed a whole generation of theorists

Despite the challenge that probability poses to the many-worlds interpretation and other multiverse theories, the most frequent objection to the idea of a multiverse (be it quantum, cosmological, or stringy) is simply its profusion of worlds. “It is hard to imagine a more radical violation of Occam’s razor, the law of parsimony which urges scientists to keep entities to a minimum,”

If shutting up is the price of doing these calculations, then pass the ball gag and break out the graph paper.

The history of quantum foundations is soaked in personalities. If David Bohm had held more palatable political convictions, if Hugh Everett hadn’t hated public speaking, if Einstein had had Bohr’s charisma, the story told in this book likely would have been dramatically different. So many of the key events were driven by political or social or interpersonal interactions, not by scientific considerations.

And, indeed, this isn’t limited to quantum foundations: all of science is vulnerable to human biases and to influences from all the other spheres of human endeavor—politics, history, culture, economics, art—that some of those biases spring from.

Richard Feynman pointed out that although there’s no experimental way to tell the difference between two mathematically equivalent theories (i.e., two different interpretations of the same math), subscribing to one theory or the other makes a huge difference in how you think about the world. That difference, in turn, affects the new ideas and new theories we develop.

Stating that the conclusions of the Copenhagen interpretation are “inevitable” or “forced upon us by the mathematics of the theory” is simply wrong. It is not true that it’s meaningless to talk about reality existing independently of our perceptions, that we must think of the world solely as the subject of our observations. Solipsism and idealism are not the messages of quantum physics.