The Heisenberg uncertainty principle is a statement about the way quantum objects, such as atoms and the smaller particles inside atoms, behave. It was developed in i927 by Werner Heisenberg, and so bears his name. The principle states that we can never know exactly where an electron, say, is located, while at the same time knowing exactly how fast it is moving. Either property-its speed or position -can be measured to infinite accuracy in principle, provided we sacrifice any knowledge of the other. This is not a shortcoming of our understanding of the workings of nature, nor is it due to the sheer minuteness of an electron, but is simply the way electrons are. In fact, it has nothing really to do with us at all. The electron itself does not have a well-determined position and speed. The best we can do is to identify a region in which the electron is likely to be moving.Another way of stating the uncertainty principle is in terms of energy and time. We can measure the exact energy of a particle, provided we do not care about when it has this energy. Conversely, if we fix the time of measurement exactly, then we give up any hope of finding out how much energy it has.
by Jim Al-Khalili, 30 Second Theory