Quantum+Unpredictability


 * Quantum Unpredictability **

Down in the quantum domain, we find a very serious kind of unpredictability that cannot be blamed on our ignorance of details of the system being studied. Instead, it turns out to be a fundamental feature of nature. In essence, we cannot predict with certainty what will happen next in the quantum world. If I were to be shrunk to the size of an electron, I could be either here or there, both places at the same time, or everywhere. The concept of time breaks down as well. This is certainly not everyday experience.

It turns out that the best we can do is to calculate probabilities. However, they cannot be calculated like we calculate those of flipping coins and throwing die. Quantum probabilities cannot be changed and are built into the theory itself.

The radioactive decay of atomic nuclei is a good example of this. Quantum mechanics have taught us that a radioactive nucleus does not have a built-in timer telling it exactly when to decay. The process of radioactive decay is subject to the probability rules of quantum mechanics. While this means that we can never predict when an individual nucleus decays, we can say something about a statistically large sample of nuclei and assign to it a half-life.