My favorite explanation comes from Greg Egan[0]: "The uncertainty principle is the inability of a quantum system to possess sharply defined values of certain p

My favorite explanation comes from Greg Egan[0]: "The uncertainty principle is the inability of a quantum system to possess sharply defined values of certain pairs of variables, such as position and momentum. Unfortunately, this simple fact is sometimes shrouded in confusion, some of which probably dates back to a famous thought experiment of Heisenberg’s in the 1920s. Heisenberg pointed out that, because light comes in quanta with a minimum amount of energy and momentum for any given wavelength, even if an electron was a point particle straight out of classical physics, we could never illuminate one in order to see where it was without disturbing it to some degree in the process. This is a perfectly true statement — but it’s a true statement about a hypothetical alternative universe, because electrons aren’t classical point particles. A correct description of an electron, whether as a wave function in ordinary space or a state vector in a Hilbert space, shows that it doesn’t need to be “disturbed” by anything in order to be subject to the uncertainty principle. It simply can’t possess an exact momentum and an exact position at the same time, any more than a musical note can be a perfect middle C, giving it a well-defined frequency, while lasting for a billionth of a second, giving it a well-defined location in time." [0] http://gregegan.customer.netspace.net.au/FOUNDATIONS/04/found04.html#s5 http://gregegan.customer.netspace.net.au/FOUNDATIONS/04/foun...