The Wavey Reality Behind the Uncertainty Principle

It’s turns out that you don’t need a high-powered quantum experiment to observe Heisenberg’s uncertainty Principle. You just need to go the beach.

Heisenberg’s famous principle tells us that the more precisely we try to measure the position of a subatomic particle, the less we know about its momentum, and vice versa. While the roots of this principle lay in a fundamental mathematical property of quantum mechanics, it’s easy enough to see this play out in a completely different context.

The next time you’re at a beach, check out the waves rolling onto shore. If you happen to see a perfectly even line of wave crests following one after another, you are looking at something called a plane wave. Plane waves have extremely easy to measure wavelengths. You simply break out a ruler and measure the distance from wave crest to wave crest.

But if I were to ask you to pinpoint the location of the wave, you wouldn’t be able to be that precise. You would just look out over the ocean, seeing all those beautiful waves lined up right against each other, and just wave your hand and say that the wave is just kind of all over the place.

So when it comes to plane waves, you can accurately measure their wavelength, but not their position.

Now let’s say that a tsunami wave is coming in. This kind of wave looks more like a pulse. If I asked you where the tsunami wave was, you would be able to point right to it and say it’s right there – it’s highly localized in space.

But what about its wavelength? Well, there’s no successive lines of wave crests to measure. At first there’s nothing, then there’s the big wave, and then there’s nothing again. So how do you define the wavelength of something like that?

It turns out that in order to describe a pulse, you need to combine lots of waves with all sorts of different wavelengths. They all work together to make the pulse happen, canceling each other out at the edges of the pulse in reinforcing each other at the center. So when it comes to a pulse, you know it’s position very well, but you are much less certain about its wavelength.

This relationship holds for all kinds of waves in the universe. And in the early 20^th century, we realized that all particles had waves associated with them. These waves are very strange, they are waves of probability that describe where we are likely to see a particle the next time we go looking for it, but it’s still a wave. And as a wave, there is a trade-off we must make when trying to accurately measure one property versus another.

It means, fundamentally, that the precision of our knowledge of the subatomic world is limited. And there’s absolutely nothing we can do about it. It’s not a matter of technology or cleverness – it’s simply the way that nature plays the game.