Is the Universe Truly Random?

The honest answer is that nobody knows yet. Most of the randomness in daily life, like dice, coin flips and weather, is not built into nature. It comes from tiny details we cannot measure or control. Quantum events are different. Experiments show that their outcomes cannot be explained by hidden instructions stored inside each particle. But whether those outcomes are truly random, or follow some deeper hidden or branching order, depends on how we interpret quantum theory. That question is still open.

So it helps to separate two kinds of “random.” One is randomness from ignorance: the outcome is fixed, but we cannot know it. The other is fundamental randomness: nothing in the universe fixes the outcome until it happens.

Is a rolled die really random?

Not in the deepest sense. A die follows the ordinary laws of motion. Its final face depends on how hard you throw it, how it spins, the air and the table. We call it random because we cannot track those details closely enough. The Stanford Encyclopedia of Philosophy notes that studies of coin flipping found that when starting conditions are precisely controlled, the coin behaves the same way every time.

A Galton board, like the one shown with this article, makes the same point. Beads drop through rows of pins, and each bead’s bounces are very hard to predict. Yet many beads together pile up into a smooth, predictable curve. Unpredictable does not have to mean lawless.

What about weather and chaos?

Weather adds a twist called chaos. A chaotic system follows fixed rules, but tiny differences in its starting point grow very fast. In 1963, the scientist Edward Lorenz showed that a simplified weather model was extremely sensitive to small changes in its starting conditions. This sensitivity is popularly called the “butterfly effect.”

Chaos teaches an important lesson. A world can be completely determined and still be impossible to predict in practice. So “we can’t predict it” is not proof that “nothing decides it.”

Why is quantum randomness different?

Quantum theory often gives only probabilities. It can say how likely a radioactive atom is to decay in the next hour, but not when a particular atom will decay. Einstein believed this meant the theory was missing something. In a December 1926 letter to the physicist Max Born, he wrote: “Jedenfalls bin ich überzeugt, daß der nicht würfelt.” In our translation: “At any rate, I am convinced that He does not throw dice.” Einstein’s “He” is “the Old One,” a name he used for God. What he meant by God is its own question, which we explore in What Did Einstein Mean When He Said God Does Not Play Dice? and the dice letter at 100.

Later experiments called Bell tests checked Einstein’s hope directly. They showed that quantum results cannot come from pre-set instructions inside each particle, as long as no influence travels faster than light and the experimenters’ choices are truly free. The full story is in How Scientists Tested Einstein’s Hunch. NIST and the University of Colorado Boulder now use such a test to run a public random-number service called CURBy, described in the journal Nature in 2025.

Here is the fine print. The randomness is “certified” only if some basic assumptions hold, such as that no signal travels faster than light. Bell tests rule out Einstein’s local kind of determinism. They do not rule out every kind.

What do the main interpretations say?

Physicists agree on the math of quantum theory. They disagree about what it describes. Here are five serious options, presented as competing ideas, not settled facts.

• Copenhagen-style views. Linked to Niels Bohr, Werner Heisenberg and Max Born, this family of views treats quantum chance as real. The theory gives probabilities, and asking for more may go beyond what physics can answer. On this view, the universe really does roll dice.
• Many-worlds. The quantum state never “collapses” to one result. Every possible outcome happens, each in its own branch of reality. According to the Stanford Encyclopedia, this removes fundamental randomness from physics. Chance becomes what it feels like to be inside one branch. A hard question remains: what does probability even mean if everything happens?
• Pilot-wave (Bohmian) theory. First proposed by Louis de Broglie in 1927 and rediscovered by David Bohm in 1952, it says particles always have definite positions, steered by a guiding wave. It is fully deterministic, but the steering links distant particles. Randomness is ignorance again, like dice. Extending it to all of modern particle physics is still unfinished work.
• Objective collapse. Collapse theories, such as one proposed by Ghirardi, Rimini and Weber in 1986, change the equations so that quantum states collapse on their own, at random moments. Here randomness is written into the laws of nature. Because the math changes, these theories make new predictions that can be tested.
• QBism. Short for quantum Bayesianism, this view says a quantum state is not a picture of the world. It is a user’s own degrees of belief about what they will experience next. Quantum probabilities are then personal, like a well-informed bet.

Can experiments decide, and what don’t we know?

For now, mostly not. Copenhagen-style views, many-worlds, pilot-wave theory and QBism make the same predictions for every experiment done so far. Choosing among them rests on things like simplicity and taste, which is partly philosophy.

Collapse theories are the exception, because they predict tiny new effects. In a study published in 2020, researchers working deep under Italy’s Gran Sasso mountain looked for faint radiation that one gravity-related collapse model predicts. They did not find it, which ruled out the simplest version of that model. Other versions remain open. Testing many-worlds directly would require interference between large, everyday objects, far beyond today’s technology.

There is also a question science alone cannot settle: what randomness means for purpose. A thoughtful believer may see fundamental chance as room for freedom, or as a way a Creator could work through probabilities. A thoughtful skeptic may see it as a sign that no guiding hand is needed. Both are perspectives, not findings, and both go beyond what physics can test. We look at that boundary in Can Science Decide Whether God Exists?

What would change the answer?

Several findings would shift the balance. Spotting a real collapse effect would strongly support randomness built into nature. Showing large objects in two states at once, without collapse, would put pressure on collapse theories. And if anyone found that the “random” choices in Bell tests were secretly linked to the particles, determinism would be back on the table in a new form.

Einstein wrote his dice letter in December 1926, and his question is still alive a century later. Perhaps that is fitting. What kind of universe would you expect: one that decides everything in advance, or one that leaves some of the story unwritten?