The scoop on the uncertainty principle
Heisenberg's Uncertainty Principle (using capital letters to begin the words emphasizes that this is Important, as opposed to merely important) states, briefly summarized, that it is not possible to know with complete accuracy the position and the momentum of an electron at the same time. When the position is determined with increasing accuracy, knowledge of the momentum becomes fuzzier, and vice versa. This simple proposition caused profound rumbling in the world of physicists, and eventually among other scientists as well. Scientists have always believed that the accuracy of information we can collect depends entirely on our ability to create ingenious measuring devices.
The uncertainty principle was revolutionary because it stated that some forms of knowledge are not merely unknown, they are unknowable. This was a radical turn for scientists who had always believed they could know the outcome of any event with great precision if they only had enough information about the preceding events and instruments that were sufficiently accurate. The way modern quantum physicists look at things is even more radical. The idea is that a quantum entity does not have a specific location until the measurement is made. Richard Feynman came up with the concept of a sum over histories to define the current position and state of a quantum entity. It is not at a precise place moving at a precise velocity. It is everywhere it can possibly be at the same time and all we can do is examine the probabilities and determine the most likely result.
Niels Bohr would appreciate this theory. When asked about the underlying reality beneath the statistical determination of quantum events, his contention was that there is no underlying reality. The world at the quantum level not only looks like a vague and fuzzy place, it is vague and fuzzy. When Einstein asserted that God does not play dice with the world, Bohr retorted, "Stop telling God what to do."
Even the daily events we see in the macroscopic world are asserted by some physicists to be quantum events. Their point of view is that the outcome of some events has such a strong probability of occurring in the "normal" way that we could observe the same vent every day from the beginning of the universe to its end and never see a different outcome. For example, place a pan of cold water on the burner and turn it on. It is possible that the cold water will actually lose heat and become colder, with the heat from the water being transferred to something else (the air around it, the burner itself, etc.). Have you ever seen that happen? Neither have I. Nor is it likely either of us ever will see it. The probability of the cold water becoming colder when heat is applied is so low that the world at a macro level appears to operate in a deterministic manner, whether it "really" (whatever that means) does so or not.
I will finish this with a joke that only those who understand the uncertainty principle will get:
Why do quantum physicists make lousy lovers?
When they have the momentum, they cannot find the position. When they get the position, they cannot get the momentum.