How Beach Waves Illustrate Heisenberg’s Uncertainty Principle

By Paul M. Sutter, Universe Today January 19, 2025

Collected at: https://scitechdaily.com/how-beach-waves-illustrate-heisenbergs-uncertainty-principle/

Discover the practical illustration of Heisenberg’s Uncertainty Principle at the beach, where observing the behavior of waves can reveal the fundamental trade-offs in measuring physical properties like position and momentum.

This principle, which underpins quantum mechanics, shows that precision in one measurement can obscure clarity in another, akin to distinguishing individual waves versus measuring their spread along the beach.

Exploring Heisenberg’s Uncertainty Principle

You don’t need a high-tech quantum lab to witness Heisenberg’s Uncertainty Principle in action. A simple trip to the beach will do.

Heisenberg’s principle reveals a fundamental truth about the quantum world: the more precisely we measure the position of a subatomic particle, the less we can know about its momentum — and vice versa. While this principle originates from the mathematics of quantum mechanics, it can also be observed in a much more relatable setting.

Observing Wave Behavior

Next time you’re at the beach, watch the waves rolling toward the shore. If you see a series of perfectly even wave crests aligned one after another, you’re looking at what’s known as a plane wave. Measuring the wavelength of a plane wave is straightforward — just take a ruler and measure the distance from one wave crest to the next. It’s that simple.

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.

The Complexity of Pulse Waves

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 are 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 its position very well, but you are much less certain about its wavelength.

Understanding Particle-Wave Duality

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.