einstein

An additional step was taken by another unlikely player, Erwin Schrödinger, an Austrian theoretical physicist who despaired of discovering
anything significant and thus decided to concentrate on being a philosopher instead. But the world apparently already had enough Austrian
philosophers, and he couldn’t find work in that field. So he stuck with physics and, inspired by Einstein’s praise of de Broglie, came up with a theory
called “wave mechanics.” It led to a set of equations that governed de Broglie’s wavelike behavior of electrons, which Schrödinger (giving half
credit where he thought it was due) called “Einstein–de Broglie waves.” 54
Einstein expressed enthusiasm at first, but he soon became troubled by some of the ramifications of Schrödinger’s waves, most notably that
over time they can spread over an enormous area. An electron could not, in reality, be waving thus, Einstein thought. So what, in the real world, did
the wave equation really represent?
The person who helped answer that question was Max Born, Einstein’s close friend and (along with his wife, Hedwig) frequent correspondent,
who was then teaching at Göttingen. Born proposed that the wave did not describe the behavior of the particle. Instead, he said that it described
the probability of its location at any moment. 55 It was an approach that revealed quantum mechanics as being, even more than previously thought,
fundamentally based on chance rather than causal certainties, and it made Einstein even more squeamish. 56
Meanwhile, another approach to quantum mechanics had been developed in the summer of 1925 by a bright-faced 23-year-old hiking
enthusiast, Werner Heisenberg, who was a student of Niels Bohr in Copenhagen and then of Max Born in Göttingen. As Einstein had done in his
more radical youth, Heisenberg started by embracing Ernst Mach’s dictum that theories should avoid any concepts that cannot be observed,
measured, or verified. For Heisenberg this meant avoiding the concept of electron orbits, which could not be observed.
He relied instead on a mathematical approach that would account for something that could be observed: the wavelengths of the spectral lines of
the radiation from these electrons as they lost energy. The result was so complex that Heisenberg gave his paper to Born and left on a camping trip
with fellow members of his youth group, hoping that his mentor could figure it out. Born did. The math involved what are known as matrices, and
Born sorted it all out and got the paper published. 57 In collaboration with Born and others in Göttingen, Heisenberg went on to perfect a matrix
mechanics that was later shown to be equivalent to Schrödinger’s wave mechanics.
Einstein politely wrote Born’s wife, Hedwig, “The Heisenberg-Born concepts leave us breathless.” Those carefully couched words can be read in
a variety of ways. Writing to Ehrenfest in Leiden, Einstein was more blunt. “Heisenberg has laid a big quantum egg,” he wrote. “In Göttingen they
believe in it. I don’t.” 58
Heisenberg’s more famous and disruptive contribution came two years later, in 1927. It is, to the general public, one of the best known and most
baffling aspects of quantum physics: the uncertainty principle.
It is impossible to know, Heisenberg declared, the precise position of a particle, such as a moving electron, and its precise momentum (its
velocity times its mass) at the same instant. The more precisely the position of the particle is measured, the less precisely it is possible to measure
its momentum. And the formula that describes the trade-off involves (no surprise) Planck’s constant.
The very act of observing something—of allowing photons or electrons or any other particles or waves of energy to strike the object—affects the
observation. But Heisenberg’s theory went beyond that. An electron does not have a definite position or path until we observe it. This is a feature of
our universe, he said, not merely some defect in our observing or measuring abilities.
The uncertainty principle, so simple and yet so startling, was a stake in the heart of classical physics. It asserts that there is no objective reality—
not even an objective position of a particle—outside of our observations. In addition, Heisenberg’s principle and other aspects of quantum
mechanics undermine the notion that the universe obeys strict causal laws. Chance, indeterminacy, and probability took the place of certainty.
When Einstein wrote him a note objecting to these features, Heisenberg replied bluntly, “I believe that indeterminism, that is, the nonvalidity of
rigorous causality, is necessary.” 59
When Heisenberg came to give a lecture in Berlin in 1926, he met Einstein for the first time. Einstein invited him over to his house one evening,
and there they engaged in a friendly argument. It was the mirror of the type of argument Einstein might have had in 1905 with conservatives who
resisted his dismissal of the ether.
“We cannot observe electron orbits inside the atom,” Heisenberg said.“A good theory must be based on directly observable magnitudes.”
“But you don’t seriously believe,” Einstein protested, “that none but observable magnitudes must go into a physical theory?”
“Isn’t that precisely what you have done with relativity?” Heisenberg asked with some surprise.
“Possibly I did use this kind of reasoning,” Einstein admitted, “but it is nonsense all the same.” 60
In other words, Einstein’s approach had evolved.
Einstein had a similar conversation with his friend in Prague, Philipp Frank. “A new fashion has arisen in physics,” Einstein complained, which
declares that certain things cannot be observed and therefore should not be ascribed reality.
“But the fashion you speak of,” Frank protested, “was invented by you in 1905!”
Replied Einstein: “A good joke should not be repeated too often.” 61
The theoretical advances that occurred in the mid-1920s were shaped by Niels Bohr and his colleagues, including Heisenberg, into what
became known as the Copenhagen interpretation of quantum mechanics. A property of an object can be discussed only in the context of how that
property is observed or measured, and these observations are not simply aspects of a single picture but are complementary to one another.
In other words, there is no single underlying reality that is independent of our observations. “It is wrong to think that the task of physics is to find
out how nature is,” Bohr declared. “Physics concerns what we can say about nature.” 62
This inability to know a so-called “underlying reality” meant that there was no strict determinism in the classical sense. “When one wishes to
calculate ‘the future’ from ‘the present’ one can only get statistical results,” Heisenberg said, “since one can never discover every detail of the
present.” 63
As this revolution climaxed in the spring of 1927, Einstein used the 200th anniversary of Newton’s death to defend the classical system of
mechanics based on causality and certainty. Two decades earlier, Einstein had, with youthful insouciance, toppled many of the pillars of Newton’s
universe, including absolute space and time. But now he was a defender of the established order, and of Newton.
In the new quantum mechanics, he said, strict causality seemed to disappear. “But the last word has not been said,” Einstein argued. “May the
spirit of Newton’s method give us the power to restore union between physical reality and the profoundest characteristic of Newton’s teaching—
strict causality.” 64
Einstein never fully came around, even as experiments repeatedly showed quantum mechanics to be valid. He remained a realist, one who made
it his creed to believe in an objective reality, rooted in certainty, that existed whether or not we could observe it.
“He does not play dice”