Measuring Uncertainty

Probability assigns a number between 0 and 1 to how likely an event is. Zero means impossible; one means certain. Everything interesting lives between. But probability is not a property of the event itself — it reflects your state of knowledge about the situation.

Flip a coin. Most say the probability of heads is 50%. But if a physicist knew the exact force, angle, and air resistance, they could predict the outcome with near certainty. The 50% reflects our ignorance, not some fundamental randomness baked into the coin.

Pierre-Simon Laplace formalized this view in the 1700s, arguing that a sufficiently powerful intellect could predict everything from initial conditions alone.