Heisenberg Uncertainty Principle

Imagine that you take a picture of a moving car. Depending on the kind of camera you have, your pictures will develop in one of two ways. First, it is possible that your camera has a really slow shutter and that the car is blurry. If you knew the shutter speed of your camera, you could make a pretty good guess at how fast the car was going by studying the size of the blur. Even then, however you wouldn't be exact. The only problem would be to describe exactly where the car was at the moment you took the shot. In fact, you couldn't say that it was anywhere precisely at the time you took the picture. All you could do with any degree of certainty is decide that the car was between two definite points (the beginning and end of the blur) during the entire second that you took the picture.

The other kind of shot would have been taken with a camera that had a very, very fast shutter speed. The picture would turn out crisp, with almost no blurs at all. Finally, we know exactly where the car was at the instant the picture was taken. Unfortunately, by gaining this information, we've lost information that we could have known. Now, looking at the picture, we have no way of saying how fast the car was moving. For all we know, it could be standing still.

In either case, the picture cannot ever tell us everything we want to know about the car. We get one side or the other. And it has nothing to do at all with the quality of the camera. Even if we were using the best camera in the world, a slow shutter would tell us lots about velocity and a fast shutter would give us a good idea of position. This conundrum is the basic idea of the Heisenberg Uncertainty Principle.

Before the advent of quantum physics, it was believed that if we knew the exact position and velocity of a particle then we could determine exactly where it would be at any point in the future. I suppose we could still think of that as being true. The problem is trying to measure both of those quantities simultaneously. We encounter the same problems as we did with the camera. We can only simultaneously determine momentum and position to a certain degree of accuracy.

It's important to realize that the illustration that I gave above with the car is only a metaphor to help us describe the real Uncertainty Principle. In actuality, that "certain degree of accuracy" is an extremely small number (≈10^-34) and is thus only really an issue when we are talking about very small things like electrons.

The issue is not, however, as trivial as the particles are small. What are the implications of the Uncertainty Principle? First, we learn that it is impossible, regardless of the quality of the instrument, to learn everything about everything. The information provided to us on the sub-atomic scale is finitely limited. But, that's not necessarily a bad thing. Sometimes it is useful to know in precise terms that which we do not know. Such limits imposed on us by the universe have helped us to understand the shape, size, and configuration of an atom, and thus to describe more completely atomic interactions.

Further, the very idea that we cannot be exactly precise in our measurements caused a paradigm shift that defines the way we think about science today. Before this principle (and others such as de Broglie's wave mechanics and wave-particle duality), people were generally under the impression that the universe was deterministic—that every future event could theoretically be predicted. Now, we view the universe as being probabilistic instead—that we can only know the probability of a future event to happen. The probabilistic ideology, though seemingly less "correct" was something of a step away from perfect—though ultimately incorrect—answers and a step toward the best philosophy of understanding at which we can arrive.