Heisenberg's Uncertainty Principle states that it is impossible to determine simultaneously the exact position and exact momentum (or velocity) of a subatomic particle like an electron. Mathematically: $\Delta x\cdot \Delta p\ge \frac{h}{4\pi }$

• This is not due to instrumental limitations but is a fundamental property of matter waves.
• If uncertainty in position ($\Delta x$) is zero, then uncertainty in momentum ($\Delta p$) must be infinite, and vice versa.