THE QUESTION LIBRARY EINSTEIN CENTENNIAL
A century after his famous letter to Max Born, experiments have ruled on part of Einstein’s hope, while the question of dice itself is still argued.
Mostly, but not completely. Einstein hoped quantum physics was incomplete, and that hidden details, never faster than light, decided each result. Experiments from 1972 to the loophole-free tests of 2015, honored by the 2022 Nobel Prize, went against that local version of his hope. But he was right that entanglement is deeply strange, and the question he raised about what the theory leaves out is still unsettled. Whether nature truly “plays dice” is still debated, because some readings of quantum theory keep it fully determined.
Niels Bohr (front) and Albert Einstein, photographed by their friend Paul Ehrenfest at his home in Leiden, most likely in December 1925. Less than two years later, at a conference in Brussels, they argued over quantum physics and dice.
WHERE THE EVIDENCE STANDS
WHAT WE DON’T KNOW YET
Nobody knows whether quantum outcomes are truly random or follow a deeper order, such as hidden particle positions, branching worlds, or a shared cause in the distant past. Nobody knows yet which reading of quantum theory, if any, is right.
WHAT WOULD CHANGE THIS ANSWER
A deeper theory that matches every quantum result and makes a new prediction that passes a test could revive part of Einstein’s hope. Strong evidence for superdeterminism would also reopen the case.
Mostly, but not completely. Einstein hoped that quantum physics, the theory of atoms and light, was missing something. He suspected that hidden details, carried by each particle and never faster than light, decided every result. Experiments over fifty years went against that version of his hope. But the deeper question he cared about, whether chance really sits at the bottom of nature, is still argued today.
The famous line comes from a letter. On December 4, 1926, Einstein wrote to his friend, the physicist Max Born. In the English translation published by Physics Today, he says an inner voice tells him the new theory “is not yet the real thing.” Then he writes: “I, at any rate, am convinced that He is not playing at dice.” “He” is “the Old One,” Einstein’s name here for God. It was a figure of speech. He meant that nature’s deepest laws should be exact, not a game of chance. Born called Einstein’s verdict “a hard blow.”
People ask this question for different reasons. Some want to know whether Einstein, of all people, was wrong. Some hope, or fear, that chance leaves room for God. The answer has a birthday, too: the letter turns 100 on December 4, 2026.
Here is the short scorecard. In 1935, Einstein and two colleagues argued that quantum theory must be incomplete. In 1964, John Bell turned that argument into a test. Experiments starting in 1972 broke Bell’s limit, and in 2015 three teams closed the main loopholes. In 2022, Alain Aspect, John Clauser and Anton Zeilinger shared the Nobel Prize in Physics for this work.
So Einstein lost on the testable part: hidden, local instructions are out. He was right that entanglement is deeply strange. And some readings of quantum theory still have no dice at all. That is why we label the verdict Supported, still debated.
Free long answer 1 of 3 this month.
Einstein’s main opponent was the physicist Niels Bohr. The two men agreed that quantum theory predicts experiments very well. They argued about what it says is real. Our story Einstein vs. Bohr: The Debate tells it in full.
They met at the Fifth Solvay Conference in Brussels in October 1927. In the part of his 1949 essay that covers that meeting, Bohr recalled that Einstein “mockingly” asked whether they could really believe that “the providential authorities took recourse to dice-playing.” Bohr also gives Einstein’s German words, which mean “whether dear God plays dice.” Bohr said he replied by pointing to the “great caution” needed in describing Providence in everyday words. Bohr also stressed that a humorous spirit filled their talks.
At the 1930 Solvay Conference, Einstein tried a sharper challenge. He imagined a box holding some light, with a shutter run by a clock. Open it briefly, weigh the box before and after, and you could know both the exact time a single photon left and its exact energy. Quantum theory says you can’t. Bohr recalled that the argument “amounted to a serious challenge.” His answer used Einstein’s own theory of gravity: a clock runs at a different rate depending on where it sits in a gravitational field. The argument could not be upheld.
In 1935, Einstein, Boris Podolsky and Nathan Rosen published “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?” Their answer was no. The paper, known as EPR, used two particles that had interacted and then moved apart. Measure one, and you can predict a result for the other without touching it. EPR argued that such a predictable value must be real, so quantum theory, which does not include it, must be incomplete. Einstein later complained that Podolsky’s write-up had “smothered” his main point in formalism. Bohr replied that the phrase “without in any way disturbing a system” was ambiguous, because the choice of measurement still shapes what can be predicted. Today we call this link between particles entanglement. Our story What Is Quantum Entanglement? explains it.
The Stanford Encyclopedia of Philosophy notes that Einstein had two worries, not one. The theory seemed silent about what is real when no one looks. And its odds seemed basic, not a sign of missing details. The dice line points to the second worry.
Einstein died on April 18, 1955. Nine years later, John Bell, a Northern Irish physicist at CERN, published “On the Einstein Podolsky Rosen paradox.” He showed that if particles carry pre-set instructions, and no influence travels faster than light, then measurements on linked pairs must stay under a fixed limit. Physicists call such instructions local hidden variables. Quantum theory predicts the limit can be broken.
In 1972, John Clauser and Stuart Freedman broke it with pairs of photons, particles of light. Some gaps remained. In 1982, Alain Aspect’s team switched the measurement settings while the photons were in flight, so the settings could not have shaped the photons at their source. In 2015, teams in Delft, Vienna and Boulder each closed the two main loopholes at the same time. The Delft team placed its measuring stations 1.3 kilometres apart. The U.S. National Institute of Standards and Technology (NIST) team in Boulder estimated that the chance of local realism producing its results was at most about 1 in 170 million.
In 2022, Aspect, Clauser and Zeilinger shared the Nobel Prize in Physics “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.” Our story How Scientists Tested Einstein’s Hunch walks through each test.
The strongest objection is that this scorecard is too kind to Einstein. NIST’s own 2025 announcement says scientists have “proved that Einstein was wrong.” NobelPrize.org’s plain-language guide says Aspect’s result showed that “quantum mechanics is correct and there are no hidden variables.” On this view, the case is closed.
Careful sources draw a narrower line: the tests rule out local hidden variables, not every hidden variable. The Stanford Encyclopedia’s entry on Bell’s theorem says that if we accept the results, one of the assumptions behind Bell’s limit must go, but it lists several ways to choose. Bohmian mechanics keeps a fully determined world, with no dice, but its particles depend on distant partners. The many-worlds reading, says its Stanford Encyclopedia entry, “allows Nature to avoid ‘playing dice’,” because every outcome happens in its own branch. Superdeterminism says a shared cause set up both the particles and the experimenters’ choices; critics call it “conspiratorial.”
Notice what these options share. Each gives up something Einstein’s picture took for granted: a single world, influences that stay local, or free choice of what to measure. The Stanford Encyclopedia says the tests leave local hidden instructions only one way out, superdeterminism, and that option has critics. So the exact picture Einstein hoped for is in deep trouble. The question of dice is not settled. Our answer Is anything truly random? looks at what that means for chance itself.
“It was a statement about religion.” The letter was about physics. “The Old One” was Einstein’s figure of speech for nature’s laws. Our answer What did Einstein actually believe about God? covers his real views.
“Bohr told him to stop telling God what to do.” In Bohr’s own 1949 account, he pointed to the “great caution” needed in describing Providence in everyday words. The snappy version does not appear there.
“Einstein didn’t understand quantum theory.” He helped found it. His objections were sharp enough that his opponents took decades to test them.
“Entanglement lets you send messages faster than light.” It does not. The Stanford Encyclopedia notes that even Bohmian mechanics, with its distant links, does not allow faster-than-light signals.
After all this detail, the verdict stands. Einstein lost the testable part of his hope, won lasting credit for the puzzle, and left the dice question open.
THREE THINGS TO REMEMBER
WHERE THE AUTHOR’S RESEARCH TOUCHES THIS
Author’s hypothesis. The book GOD PLAYS DICE takes its title as a reply to Einstein’s famous remark. In the Introduction, Ricardo Maldonado, author of GOD PLAYS DICE, calls the title “a playful act of rebellion, not a religious claim.” In the book, God is shorthand for the deep laws of nature, and dice are shorthand for quantum events that are random but follow precise rules. The Introduction also notes that physicists still debate what quantum chance means at the deepest level.
The book then carries the dice image further. It asks whether some of the “dice rolls” that shaped our universe happened in a space with more dimensions than we can see. Ricardo’s idea, HD-Blast, asks whether the hot, dense start of our universe was the local aftermath of a short burst of energy in such a space. No one has observed such an event. It is an Author’s hypothesis, not a finding: the research page lists its benchmark curve for a slow hum of gravitational waves as frozen and waiting for later, independent pulsar-timing data. No test of that curve against such data has been published. The test ledger tracks where it stands.
Nobody knows yet.
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
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CONTINUE THE THREAD
Einstein CentennialExplainer
Einstein and Bohr agreed that quantum mechanics works, but they spent decades arguing about what it tells us is real, and the argument still echoes today.
Einstein CentennialExplainer
Einstein suspected quantum physics was hiding something. John Bell found a way to check, and decades of experiments gave a clear answer, with limits.
Einstein CentennialFeature
A century ago, Einstein told Max Born that "the Old One" does not throw dice, starting an argument that reshaped physics and is still not finished.
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