Eli5 Why can’t we “know” the speed and position of an electron simultaneously? Why can we only measure one of these properties at a time?

Question

This always confuses me and I’m not sure how it works. Please explain…

In: 252

Answer 1

Let’s start with quantum mechanics is *really* weird. The only way to really explain it is that it’s pure math and completely ignores human concepts of reality.

This is related to the Heisenberg Uncertainty Principle (HUP). The typical explanation of HUP relies on the analogy that to measure something we need to hit it with something like a photon, which introduces error in either speed or position.

The flaw with this explanation is that it leaves out that the electron’s position and velocity are defined by something called a wave function. This is a mathematical equation that describes how position and velocity are related. Specifically, it’s an equation that we use to describe the motion of waves, like waves on the surface of water.

The HUP is a direct result of the wave function. The wave function quite literally makes it impossible to describe both position and velocity of any quantum particle with perfect accuracy. The closer you get to perfect accuracy of one property, the less accurate you are on the other. The HUP is quite literally a fundamental property of the universe and has nothing to do with our ability to measure it. Rather the math tells us that electrons literally don’t have a fixed position and speed. The more you fix the electron in place, the less you know about the speed and vice versa.