Quantum mechanics presents a strange puzzle: particles seem to follow different rules depending on whether we’re watching them or not. When physicist Niels Bohr tackled this “measurement problem,” his answer was radical—he argued that particles simply don’t have properties until we measure them.
This view reshaped physics, but not necessarily because it was the most convincing solution. As Adam Becker explains in What Is Real?, a combination of historical events and professional pressure led physicists to accept Niels Bohr’s quantum mechanics interpretation while silencing alternative perspectives. Read on to discover how the approach worked and why it became the dominant view in quantum mechanics.
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Niels Bohr on Quantum Mechanics
In his book What Is Real?, Adam Becker describes the “measurement problem” in quantum mechanics—the puzzle that particles seem to follow different physical laws depending on whether or not they’re being observed. This raises the question of when and how the transition between these rule sets occurs. One physicist that responded to the question was Niels Bohr. Quantum mechanics, he believed, required that particles have no properties until measured, making questions about unmeasured reality meaningless.
Bohr’s response was to abandon the goal of making physics describe objective reality. As Becker explains, Bohr’s principle of complementarity held that certain pairs of properties can’t be observed at the same time, and that physicists needed both wave and particle descriptions to fully explain the world: Different experiments would reveal that light and matter have both of these “complementary” aspects, but they never apply at the same time. Further, Bohr argued that particles don’t have definite properties independent of measurement, so asking about where they are or what they’re doing when nobody is measuring them is meaningless. In sum, he concluded that quantum phenomena aren’t independently real.
(Shortform note: Bohr’s interpretation means that every object in the universe has both wave and particle properties. If so, then even a human has a measurable wavelength, though it’s too tiny to detect, and particles have wavelengths and create interference patterns just like light waves. But what actually causes this wave behavior to show up in physicists’ experiments? Bohr’s answer is that there’s nothing physically causing the wave behavior: What’s waving is a probability rather than a physical reality. For example, in the double-slit experiment, the electron exists in a wave of uncertainty representing all the places it could be, and this probability wave interferes with itself until the electron “decides” where to land.)
Becker points out that Bohr’s interpretation created a divide in the anti-realist view of the world: There was a classical realm of real measurement devices and concrete experimental outcomes, and a quantum realm existing only as a mathematical formalism, not an independent reality. Bohr dismissed questions about what happens in the absence of observation, arguing that physics should focus on experimental results, not speculate about what’s unobservable. This let physicists use quantum mechanics without confronting its interpretive puzzles. Rather than asking what the mathematics meant about reality, they could just use it to predict experimental outcomes and leave philosophical questions aside.
(Shortform note: Physicist Katie Mack, author of The End of Everything (Astrophysically Speaking), explains that physics has only ever created mathematical models to accurately predict observations; it doesn’t necessarily reveal the truth about reality. For example, Newton’s equations predict planetary motion, but they don’t tell us what gravity really is—they just make calculations possible. Focusing on what works rather than what it means, as Bohr did, has allowed physics to move forward and inspired advances in abstract math. Mack argues that abstraction is “the whole point” of physics: creating models that explain what we observe, whether or not they describe the universe as it really is.)
Why Bohr’s Anti-Realism Prevailed
While Bohr and other anti-realists argued that particles don’t have properties until they’re measured (taking away any meaning of unmeasured reality), other scientists had different responses to the measurement problem. Werner Heisenberg (also an anti-realist) proposed that particles exist as “potentialities” that become actual through measurement. Albert Einstein and realists believed that quantum mechanics was incomplete and that particles possess definite properties the theory doesn’t capture.
Becker contends that the measurement problem should have started a debate that didn’t stop until answers emerged. Instead, physicists accepted Bohr’s anti-realism—not because it offered a compelling solution to the problems posed by quantum mechanics, but because world events and institutional forces made pursuing answers professionally dangerous. The textbook story is that physicists agreed on a new interpretation of quantum mechanics at the 1927 Solvay Conference. But Becker argues this story is false. The debate revealed no unified position among Bohr’s supporters, just an alliance of opposition to Einstein’s realism. Only decades later would this collection of anti-realist views be labeled the “Copenhagen interpretation.”
There were two other reasons that anti-realism prevailed. First, physics evolved from a philosophical discipline into a massive military enterprise. During World War II, thousands of physicists worked on the Manhattan Project, the US’s program to build atomic bombs. After the war, military funding continued pouring into physics to develop weapons, radar systems, and other technologies. This meant physicists spent their time completing practical calculations rather than solving the theoretical puzzles that Einstein and Bohr’s generation debated.
Second, physicists who attempted to develop realistic alternatives to the Copenhagen interpretation faced career destruction. Becker reports that those who proposed viable interpretations were dismissed without serious scientific engagement and often lost their chances of finding academic employment because they didn’t “toe the line.” By the 1960s, the physics community had stopped asking hard questions about the meaning of quantum mechanics, treating this abandonment of foundational inquiry as scientific maturity rather than intellectual failure.
Exercise: Reflect on What Happened
Becker argues that Bohr’s interpretation won through politics and institutional pressure, not logical superiority. Does this make you question how scientific “truth” is established, or do you think good ideas eventually win regardless of how they initially gain acceptance?
Learn More
To better understand Niels Bohr’s quantum mechanics contributions and perspectives in their broader context, take a look at Shortform’s guide to the book What Is Real? by Adam Becker.
