What REALLY Happens When You Squeeze Light?

Video Description

What happens when you squeeze light? Why does narrowing a beam through a small gap make it spread out — and what does this have to do with quantum mechanics? In this video, we explore how one of the most iconic experiments in physics reveals the deep and beautiful consequences of the Heisenberg uncertainty principle. In the first part of the video, we investigate what happens when a laser beam passes through a narrow slit. Rather than simply producing a thinner beam, we observe a striking diffraction pattern — a clear sign that something deeper is at play. By turning down the intensity and firing one photon at a time, we reveal that the pattern emerges from quantum probability, not classical interference. In the second part, we connect this spreading out to the momentum of individual photons. Using simple geometry and the de Broglie relation, we show that squeezing light into a narrow space creates uncertainty in its momentum — and that this uncertainty grows as the slit gets smaller. Finally, we combine these ideas to derive a powerful result: a mathematical expression of the Heisenberg uncertainty principle. This familiar diffraction pattern, seen in countless classrooms, becomes a vivid and tangible demonstration of one of the most fundamental limits in all of physics. You can help support this channel via the Physics Explained Patreon account: https://www.patreon.com/physicsexplained You can follow me on instagram: https://www.instagram.com/physics_explained_ig You can follow me on X: https://twitter.com/PhysicsExplain1