Quick Answer: Quantum mechanics provides what is believed to be the only source of genuinely irreducible randomness in nature. Quantum events (like radioactive decay and photon path measurement) are not deterministic — even with perfect knowledge of the past, the future outcome cannot be predicted. This makes quantum randomness physically different from algorithmic randomness.
Determinism vs Quantum Indeterminacy
Classical physics is fundamentally deterministic: if you know the exact state of a system, you can predict its future evolution perfectly. This challenges the philosophical notion of true randomness — perhaps all "random" events are just deterministic events we cannot predict due to incomplete knowledge. Quantum mechanics breaks this view: at the quantum scale, physical outcomes are inherently probabilistic, not merely unpredictable due to ignorance.
Quantum Events Used for Randomness
- Radioactive decay: The moment a specific atom decays is fundamentally unpredictable — not just practically unpredictable, but theoretically impossible to predict
- Photon path: A photon hitting a half-silvered mirror has a 50% quantum probability of passing through or reflecting — neither outcome is determined until measurement
- Vacuum fluctuations: The quantum vacuum has measurable energy fluctuations that serve as random seeds for hardware RNGs
- Electron spin: Measuring the spin of an unprepared electron gives a completely random result (up or down)
Quantum Random Number Generators (QRNG)
Commercial quantum random number generators are available that use photonic quantum events to produce certified truly random bit streams. They are used in high-security applications, scientific simulations, and cryptographic key generation. However, for practical everyday use, CSPRNG (using hardware entropy) is indistinguishable from quantum randomness for any real application.
Is CSPRNG Good Enough?
For all practical purposes — including cryptography, privacy tools, and fair selection — CSPRNG based on hardware entropy is sufficient. The computational security guarantee of CSPRNG (indistinguishable from true randomness without the internal state) provides the same security properties as quantum randomness for every known application.