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

by Adam Becker

pervasive in quantum physics.

nearly any interaction between any particles would cause them to become entangled,

sharing a single wave function in the same way as the particles in the EPR thought experiment.

challenge the EPR paper

deeply embedded in the fundamental structure of the theory.

Einstein’s concerns had little, if anything, to do with determinism—

they were about the importance of locality and a physical reality that exists independently of anyone observing it.

Einstein, “avoids reality a...

described Bohr as a “talmudic philosopher [who] doesn’t give a hoot for ‘reality,’ which he regards as a hobgoblin of the naive.”

of most contemporary physicists, Einstein’s concerns were irrelevant at best and misguided at worst.

The new theory allowed physicists to calculate and predict an enormous variety of phenomena with unprecedented accuracy, most of which had little if anything to do with the mysteries of entanglement.

mysteries, more amenable to experimental exploration, beckoned—particularly the dark and powerful ones that lay in the atomic nucleus.

“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,” Heisenberg said, “is impossible.”

“The transition from the ‘possible’ to the ‘actual’ takes place during the act of observation,”

what constituted a “measuring device”

Heisenberg was infuriatingly unclear.

Heisenberg depicted the Copenhagen interpretation as a unified body of work that was developed by Bohr, himself, and a handful of others in 1927—and in both essay and lecture, Heisenberg took it upon himself to defend the Copenhagen interpretation against its enemies.

crucible of war had also radically reshaped physics

dizzying changes had made physicists much more receptive to the Copenhagen interpretation.

On May 16, 1933, Max Planck, the physicist whose black-body radiation law had set off the quantum revolution, met with Adolf Hitler.

Jews no longer had a place in German science, and there was nothing Planck could do about it.

1,600 scholars were out of a job. The burden fell disproportionately on the sciences:

With a single act, physics in Germany had been destroyed.

Einstein’s stepdaughter managed to smuggle his papers safely out of his Berlin apartment before the Nazis could destroy them;

Jewish heritage fled Nazi Germany after the Civil Service Act.

many of the great Jewish intellectuals of Viennese culture had already left: Ludwig Wittgenstein was teaching in Cambridge, Karl Popper was a lecturer at the University of New Zealand, and Billy Wilder was writing lines for Greta Garbo in Hollywood.

Schrödinger, wasn’t Jewish, but his wife was. Schrödinger had been at the University of Berlin in 1933 but had quit in protest when Hitler came to power. After Hitler invaded Austria, Schrödinger publicly

Schrödinger fled to Ireland

After Stockholm, the Fermis went to Copenhagen to visit Bohr, and, finding the wheels of American immigration greased by the words “Nobel Prize winner,” they set sail for Manhattan just before Christmas, arriving on January 2, 1939.

the lives of students and younger researchers were far more thoroughly disrupted.

September 1, 1939, more than a hundred physicists had emigrated from the European continent to the United States and the UK—

John von Neumann,

made it out of Germany early.

and fellow Hungarian Eugene Wigner were both offered positions a...

Von Neumann immediately took to the States,

Wigner was more reluctant to leave Europe behind.

Wigner and von Neumann simply didn’t return to Berlin—

Von Neumann in particular seemed almost inhuman in his brilliance.

he had made a thorough, detailed study of human beings and could imitate them perfectly.”

Neumann completed a textbook on quantum physics that became an instant classic.

von Neumann breezily dismissed the best known and most technically sophisticated of them in the introduction to his own,

wave functions normally obey the Schrödinger equation but collapse on measurement.

But, once a measurement is made, the smooth regularity of the Schrödinger equation goes out the window. “The arbitrary changes by measurements,” said von Neumann, are “discontinuous, non-causal, and instantaneously acting.”

this lack of clarity was unacceptable to von Neumann in his quest to make quantum physics more

mathematically rigorous.

Quantum physics, in von Neumann’s view, was a theory o...

measurement problem far m...

bizarre situation known as a superposition—and because their wave function never collapsed, they ultimately forced Schrödinger’s cat to be in a superposition as well, somehow both dead and alive.

still left the problem of how and why that collapse occurred.

“We must always divide the world into two parts, the one being the observed system, the other the observer,”