Yes, as far as our best physics can tell, some things in nature are genuinely, irreducibly random. Quantum mechanics describes events at the subatomic level that have no hidden cause, no deeper explanation, and no way to predict them even with perfect information. But the question has more layers than a simple yes, and the answer depends on what kind of “random” you mean.
What Quantum Mechanics Says
When a radioactive atom decays, or a photon passes through a beam splitter, the outcome is not determined by anything we can measure or know. This isn’t a gap in our knowledge. According to the standard interpretation of quantum mechanics, the outcome literally does not exist until the moment it happens. Properties of quantum particles remain objectively indefinite until measurement forces them into a definite state.
The strongest evidence for this comes from experiments testing something called Bell’s inequality. In the 1960s, physicist John Bell devised a mathematical test that could distinguish between two possibilities: either quantum events are truly random, or there are hidden variables, some deeper layer of reality secretly determining outcomes in advance. If hidden variables exist, measurements on pairs of entangled particles would obey certain statistical limits. Quantum mechanics predicts those limits get violated. Dozens of experiments since then have confirmed the violation, ruling out the most natural versions of hidden-variable theories. Some technical loopholes remained in earlier experiments, but increasingly precise tests have continued to side with quantum mechanics.
The practical upshot: if you measure the spin of an electron that’s in a quantum superposition, no amount of information about the universe could have told you the result beforehand. The randomness isn’t a shortcut for “we don’t know yet.” It appears to be woven into the fabric of reality.
The Case Against: Superdeterminism
Not everyone accepts this conclusion. A minority view called superdeterminism, first outlined by John Bell himself, argues that the universe is entirely deterministic, and we only think quantum events are random because we’re missing hidden information. In this picture, even the choices experimenters make about how to set up their equipment were predetermined at the beginning of time. The reason quantum measurements look random is that we can never access the variables controlling them, not that those variables don’t exist.
Physicist Sabine Hossenfelder has argued that superdeterminism neatly resolves several quantum puzzles at once. If hidden variables determine everything in advance, quantum randomness, the measurement problem, and the strange phenomenon of nonlocality all disappear. The catch is that superdeterminism doesn’t specify what these hidden variables are. It simply insists they must exist. Most physicists find the idea too extreme, since it implies that every particle in the universe has been conspiring since the Big Bang to make experiments come out a certain way, including your decision to read this sentence. It remains a logical possibility, but one without direct experimental support.
Chaos Is Not Randomness
Much of what feels random in everyday life isn’t random at all. Weather, turbulence, a coin toss, the path of a leaf falling from a tree: these are chaotic systems, not truly random ones. The distinction matters. A chaotic system is fully deterministic. If you knew its starting conditions with perfect precision, you could predict its future exactly. The problem is that any tiny imprecision in your starting measurement grows exponentially over time, making long-term prediction impossible in practice.
Randomness is different. A truly random process can’t be predicted even with perfect knowledge of every relevant detail. Chaos fools us because its practical unpredictability feels identical to randomness. But the unpredictability of a coin flip comes from your ignorance of the flipping force, air resistance, and landing surface. The unpredictability of a quantum event comes from the event itself having no predetermined answer.
Randomness Inside Your Body
Biology is full of processes that behave randomly at the molecular level, and many of them turn out to be useful rather than just noisy. One striking example is how your brain’s neurons communicate. When an electrical signal reaches the junction between two neurons, small packets of chemical messenger molecules are released to carry the signal forward. This release is surprisingly unreliable. Each packet that’s ready to go has only about a 10% chance of actually being released when a signal arrives.
Research published in the Proceedings of the National Academy of Sciences found that this low probability isn’t a flaw. It’s a feature. That built-in randomness actually reduces errors in how signals are reconstructed on the receiving end, improving information transfer rather than degrading it. Randomness appears at nearly every level of the nervous system, from the opening and closing of individual ion channels in nerve cells to the timing of electrical impulses. Your brain doesn’t work in spite of this noise. It works partly because of it.
Genetic mutations follow a similar pattern. When DNA copies itself, errors occur at random positions. Environmental factors like radiation or toxic chemicals can increase the overall rate of mutations, but they don’t direct where those mutations land. A bacterium exposed to an antibiotic doesn’t generate mutations specifically designed to resist that antibiotic. Classic experiments by Esther and Joshua Lederberg showed that resistant bacteria already existed in populations before any antibiotic exposure. The mutations were random with respect to their usefulness. Natural selection then filters which random changes get passed on.
How We Harvest Randomness
If true randomness exists, it should be possible to capture it, and that’s exactly what engineers do. Most “random” numbers generated by computers are actually pseudorandom: produced by mathematical formulas that look random but are completely deterministic. Give the formula the same starting seed, and you get the same sequence every time. For most purposes, like shuffling a playlist, this is fine. For encryption protecting financial transactions, military communications, or personal data, it’s a vulnerability. An attacker who figures out the formula can predict every “random” number it produces.
True random number generators pull their randomness from physical processes. The thermal noise inside electronic components, caused by electrons randomly colliding with heat-excited atoms, is one common source. Shot noise, the statistical fluctuation of electrical current as individual electrons cross a gap, is another. These are analog, physical phenomena whose unpredictability traces back to the quantum behavior of particles.
Quantum random number generators go a step further, deliberately exploiting quantum events like photon detection to produce streams of numbers that are certifiably unpredictable. Argonne National Laboratory has supported development of these devices for cybersecurity, and prototype quantum random number generators are being designed for use in communications systems and even the processors of autonomous vehicles. The logic is straightforward: if quantum mechanics is right that these events have no hidden cause, then no adversary, no matter how powerful, can predict the output.
So What’s the Answer?
The honest answer is that our best-tested theory of physics, quantum mechanics, says yes: some events are fundamentally random, with no cause, no pattern, and no way to predict them. Every experiment designed to prove otherwise has instead confirmed quantum predictions. The only way to rescue a fully deterministic universe is superdeterminism, which requires accepting that every measurement choice and experimental outcome has been locked in since the origin of the cosmos, a position that remains speculative and untestable.
Meanwhile, the randomness we encounter in daily life, weather, dice, stock markets, is almost certainly not true randomness. It’s chaos and complexity masquerading as unpredictability. The genuinely random stuff happens at scales too small to see: inside atoms, at synapses in your brain, in the molecular machinery copying your DNA. True randomness, as far as science can currently determine, is real. It’s just not where most people expect to find it.