Beyond Certainty: Young's Experiment and the Weirdness of Quanta

Beyond Certainty: Young's Experiment and the Weirdness of Quanta

Introduction:

Throughout human history, we human beings, some meat wrapped around a central pipe with blood pumping through us, have been asking a lot of questions. So many that we had to give this feeling of wanting to know a special word, "Curiosity!" Curiosity has led to so many discoveries and inventions. One such very interesting question was asked by Thomas Young in 1801. "What is even special about shining some light through two slits?" This question in my opinion has led to the most important slippery slope in the history of science.

Abstract:

 

Young's double slit experiment has proven itself to be the cornerstone of Quantum mechanics.
It demonstrates the particle-wave duality of light, which in itself is the most purest form of the study of quantum mechanics. In this blog we will go over the physical experiment and also derive and have fun with some equations!

The experiment:

Imagine a very thin sheet of metal, with two closely spaced, thin, parallel slits. Now, let's take a laser and fire light towards the piece of metal. We will expect two long lines of light, but in fact we get the infamous interference pattern; a wave like structure!

You might be asking yourself a very important question, "Why?" Why in the world will we get a wave pattern. This is because of the wave nature of light! Imagine two ripples in water, sometimes they interact and cancel each other out, exactly like this the waves of light are interacting with each other and showing us this interference pattern.

Scientists were curious and started to track each individual photon by putting a special detector next to each of the slits, after doing this they saw a completely different type of pattern! They were two big slits where the photons landed, this suggests that the photons existed in both of the slits simultaneously and also interacted with themselves!

This "observed effect" further makes the particle-wave duality of light more complex. Researchers also found this type of behavior in several other particles.

The principal of superposition:

Superposition is a mind bending concept in quantum mechanics, it is when a single particle exists in multiple states simultaneously. So, when a photon travels through one of the slit it is actually traveling through both of the slits simultaneously.  

The specific locations of these bright and dark spots depend on the separation between the slits denoted by: d and the wavelength of the light denoted by: λ. 

Imagine a point on the screen that's slightly off-center. If the difference in the path lengths for the two waves reaching that point is a whole number of wavelengths, the waves will be in sync and create a bright spot. However, if the path difference (Δd=±mλ for constructive interference and Δd=±(m+1/2)λ for destructive interference) (Destructive interference is when two waves traveling in the same direction are aligned at the crest of one wave and the trough of the other. The waves cancel out. Constructive interference is when two waves traveling in the same direction overlap, and their crests combine to produce a larger wave.) is a half-wavelength or any odd multiple of a half-wavelength, the waves will be out of sync and create a dark spot.

The equations provided is d sin(θ) = mλ and d sin(θ) = (m + 1/2)λ mathematically predict when these constructive and destructive interferences occur, based on the angle θ at which we observe the point on the screen and the order m of the bright or dark band with   m = 0 being the central bright spot.

Conclusion:

Physicists are still investigating the experiment's ramifications today. It opens the door for developments in areas like quantum computing and encryption and provides a basis for comprehending a variety of quantum phenomena. The Young double-slit experiment continues to be a potent reminder of the weird and amazing character of the cosmos as we explore farther into the quantum realm.

-Ruhan