Few Understand Why Quantum Physics Feels Impossible — Are You Ready to Join Them?

A 3-step quantum experiment that defies intuition

Quantum physics is weird. That’s what you’re supposed to think, anyway. But, also, it’s over one hundred years old and is the most accurate scientific theory ever created. It provides the basis for all modern technology. Surely, then, someone understands what’s going on, right? …right?

I’ll let you decide for yourself. I’m going to show you the simplest set of experimental facts about quantum physics, which display the problem of its interpretation. Fair warning, though: there will be no answers that will satisfy you here.

If nothing else, quantum physics shows us that Nature is much richer than the world constructed by our senses.

Step 1: light is a wave

If you shine a laser in the following arrangement of mirrors and beam splitters — called a Mach-Zehnder interferometer — here is what will happen.

Because laser light — in fact, all light — is an electromagnetic wave, it can experience constructive and destructive interference. Depending on which way the laser light passes through the beam splitter, it may flip its orientation or not.

For the top observer, the light taking the top path has reflected off the “back” of the beam splitter twice, while the light from the bottom path has not reflected off any beam splitter, passing through both. The two reflections in the top path cancel, and the light “adds up” — that’s constructive interference.

For the bottom observer, the opposite is true. The light taking the top path reflects off the back of the first beam splitter but passes through the second — only one inversion. The light in the bottom path reflects off the second beam splitter, but it hits the “front” and does not invert. So, for the bottom observer, one path has inverted light, and the other does not, forcing the light to “cancel out” — destructive interference.