Uncertainty+Principle


 * Heisenberg’s Uncertainty Principle **

One of the most important consequences of the probabilistic nature of the wavefunction is the concept of indeterminacy. This means that we can never know with total precision everything about a quantum system however we measure it.

The already-discussed wavefunction is called the position wavefunction. There is another quantity called a momentum wavefunction, which tells us the probability that the electron has a certain momentum or velocity at any given moment.

An electron with a localized position wavefunction, meaning its position is pretty well known, will have a spread out momentum wavefunction. An electron with a localized momentum wavefunction, meaning it has a well-known velocity, will have a spread out position wavefunction.

For example, a ball is placed into a box just slightly bigger than the ball. Assuming gravity is negligent, the box is shaken and the ball moves. Its position is pretty well-known but its velocity fluctuates a great deal. However, a small ball placed into a big box which is shaken will have a velocity which fluctuates a lot less but its position is a lot less well-known.

The uncertainty principal states that one can never know at the same time the location and velocity of an electron. The accuracy of one can only be achieved with the expense of the accuracy of the other. The act of observing interferes with the particle being observed.