Quantum mechanics turned physics upside down in the early 1900s. The microscopic world didn’t follow the logical rules scientists expected; instead, it revealed a reality that seemed impossible. Enter Albert Einstein. Quantum mechanics came about in part because of his contributions. Yet he spent decades arguing against how other physicists interpreted it.
Einstein’s famous debates with Niels Bohr weren’t about math or experiments. They were about something deeper: what reality actually is, and whether science should describe an objective world or just predict what we’ll see when we measure it. Continue reading to find out why one of history’s greatest physicists rejected the revolutionary theory he helped create.
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Albert Einstein & Quantum Mechanics
As described in the book What Is Real? by Adam Becker, the story of quantum mechanics is one of science’s most profound intellectual upheavals—a revolution that forced physicists to abandon centuries of intuitive understanding about how reality works. At the turn of the 20th century, the microscopic world revealed itself to be far stranger than anyone imagined, operating by rules that defy common sense and challenge our most basic assumptions about the nature of existence. This transformation didn’t just require new experimental techniques or mathematical tools; it sparked a philosophical crisis that divided the scientific community into opposing camps.
At the heart of this divide stood Albert Einstein. Quantum mechanics, despite Einstein’s own contributions to its development, troubled him deeply—not because of its mathematical predictions, but because of what accepting those predictions might mean for the nature of reality itself. His objections would shape decades of debate about what physics should describe: Is it the objective reality of the world as it exists independent of us, or merely a powerful tool for predicting what we’ll observe when we look?
The Background of the Quantum Revolution
At the dawn of the 20th century, physicists believed they understood reality’s basic structure. But atomic experiments shattered their fundamental assumptions, forcing them to develop quantum mechanics—a new branch of physics with new mathematics. This revealed that nature’s building blocks operate according to rules so strange they seem illogical.
Before this revolution, classical physics rested on intuitive assumptions that explained the observable world. Physicists viewed atoms as tiny spheres that combined to form compounds, with specific positions, velocities, and energies governed by Newton’s laws. Later discoveries showed atoms consist mostly of empty space, with electrons orbiting a nucleus—a “planetary model” suggesting atoms obeyed the same laws as celestial bodies.
However, experiments with atoms and light revealed a radically different microscopic world where energy comes in discrete chunks, matter and light behave as both waves and particles, and electrons occupy only specific energy levels. The mathematics developed to explain these observations showed that particles can exist in multiple states simultaneously and influence each other across vast distances—contradicting everyday experience.
In his book, Adam Becker explains that quantum mechanics applies different physical laws to identical particles depending on whether they’re observed—the “measurement problem.” Physicists developed three responses:
- Albert Einstein and realists argued quantum mechanics is incomplete and particles have properties the theory misses.
- Niels Bohr and anti-realists claimed particles lack properties until measured, making questions about unmeasured reality meaningless.
- Werner Heisenberg argued particles exist as “potentialities” until measurement.
By 1927, two competing visions emerged: realists insisted physics must describe objective reality independent of observation, while anti-realists viewed quantum mechanics as a tool for organizing experimental results rather than describing reality.
Einstein’s Realist Position: Quantum Mechanics Must Be Incomplete
Einstein had contributed to quantum theory. In 1905, he proving that light itself travels in discrete, quantized packets called “photons.” But he found other physicists’ interpretations of the math unsatisfactory. Becker explains that Einstein objected to abandoning a reality that exists independently of observation. He believed science should describe the world as it really is and argued that, if quantum mechanics described situations such as Schrödinger’s cat, the theory must be incomplete.
Einstein aired this objection in a thought experiment about two particles that bounce off each other. If you measure one particle’s position and momentum after the collision, that instantly determines the other’s properties, regardless of the distance between them. However, according to quantum mechanics, the other particle can only exist as a probability wave until it’s directly observed. So, either that particle has properties (momentum and position) that quantum mechanics doesn’t describe, or nature violates the principle of locality—the idea that objects can only be influenced by their immediate surroundings. Because of this, Einstein concluded that quantum mechanics couldn’t represent the final truth about reality.
(Shortform note: Einstein’s principle of locality says that influences between distant objects must travel through space between those objects and take time to do so—like the delay between flipping a light switch and the electrical signal reaching a lamp. But quantum mechanics predicts that measuring one particle can instantly affect its distant partner, as if flipping a switch in New York could instantly turn on a light in Tokyo, without any physical connection between them. In addition to the problem Becker describes, this also troubled Einstein because it conflicted with his theory of relativity, which says nothing can travel faster than the speed of light.)
Einstein believed future developments would reveal quantum mechanics to be a statistical approximation of some deeper, more complete theory. Becker explains that, in Einstein’s mind, this deeper theory could restore both locality and objective reality while preserving quantum mechanics’ practical successes.
| Is It Possible to Find a Theory of Everything? As Becker explains, Einstein envisioned a unified theory that would resolve the conflicts between relativity and quantum mechanics. The search for a “Theory of Everything” has captivated physicists for nearly a century, but some scientists question whether it’s a realistic goal. This theory would unify the four forces that govern everything in the universe: electromagnetism (which holds atoms together), the strong nuclear force (which binds particles in atomic nuclei), the weak nuclear force (which causes radioactive decay), and gravity. Currently, quantum mechanics explains the first three forces but fails to account for gravity, which Einstein’s general relativity describes instead. Einstein spent 30 years pursuing this goal. But, in Lost in Math, physicist Sabine Hossenfelder argues the search rests on an unscientific premise: the assumption that the laws of nature should be elegant and unified just because physicists find such theories mathematically pleasing. The problem isn’t that we lack the mathematical sophistication to explain the complexity of the universe, but that we may be chasing an idealized vision of that universe that’s just an illusion. |
John Bell’s Experiments Validated & Challenged Einstein’s Beliefs
In 1964, John Bell challenged John von Neumann’s 1932 “impossibility proof” that had seemed to rule out any interpretation of quantum mechanics where particles have definite properties before measurement (hidden variables theories). Becker explains that Bell found the proof was flawed and developed a mathematical test—Bell’s inequalities—to experimentally determine whether particles have predetermined properties.
Experiments in 1972 and 1982 showed that entangled particles violate Bell’s inequalities, proving that quantum mechanics exhibits “spooky action at a distance” (nonlocality)—just as Einstein had feared. However, this also showed Einstein was wrong about quantum mechanics being incomplete; the theory wasn’t missing information, but rather reality itself is fundamentally nonlocal.
| Why Bell Thought Einstein’s Worries Were Valid For years, physicists rejected Einstein’s doubts about quantum mechanics based on von Neumann’s proof that hidden variables were impossible. However, this proof was flawed—it imposed an unrealistic requirement that combinations of quantum properties that can’t be measured together should still be measurable, which is physically nonsensical. Later experiments testing Bell’s inequalities revealed that particles do possess objective reality (supporting realism) but also confirmed that “spooky action at a distance” is real. This validated Einstein’s concerns: abandoning locality—the principle that distant locations are independent—threatens our fundamental understanding of cause and effect. Bell’s theorem ultimately proved that quantum reality is indeed as strange and troubling as Einstein suspected, showing his concerns were justified rather than overly cautious. |
Learn More Einstein’s Take on Quantum Mechanics
To understand Albert Einstein’s view of quantum mechanics in the broader context of the debate, check out Shortform’s guide to What Is Real? by Adam Becker.
