Last week we talked about quantum computing, which got me thinking about quantum mechanics. Now, I am not a physicist and I don’t claim to have a deep understanding of physics and the math behind it, I’m just a coder who enjoys reading about paradoxical and interesting concepts. So, that being said, today let’s talk about the double slit experiment.

The double slit experiment is a famous experiment that shows the dual nature of particles. What does that mean?

Pretend there is a box and on one side of the box, we cut two rectangular slits or holes on top of each other. On the other side of the box on the inside, across from these slits, there is a sticky screen that can capture what comes through the slits.

Now think about if we shot a bunch of tiny marbles through the slits. What we would expect is that the marbles on the screen would form two bands as some of the marbles go through the top slit while others go through the bottom slit.

Now let’s say we have a gun that can shoot light particles, and we fire a bunch of them at the slits. What will the inside of the box look like? Because light is a wave, alternating light and dark bands from the top to bottom of the screen form; the whole screen would look like an Excel spreadsheet where each row would be light, dark, light dark, etc. This is because as the waves go through the slits, they spread out, think of it like a radio wave, some spots cancel each other out as the wave expands and you end up with an interference pattern, what looks like a stripe pattern up and down the screen.

Now let’s go back and do this with the marbles, or particles. Here’s where things get a little strange. We don’t end up with two bands on the screen. We end up with the same stripe or interference pattern that we got with the light particles. Even if we shoot the marbles in one at a time, they will eventually arrange themselves in this stripe pattern, not the two-band pattern we would expect. This suggests that the particles go through both slits at the same time, like a wave. But how can this be?

To find out why, we cut a tiny hole in the box so we could peek in and see what was happening during the experiment. This is where things get very strange. When we ran the experiment while observing, the particles, (our marbles), ended up on the screen in the two-band pattern, the pattern we would have originally expected. Essentially, when we watch them, the particles behave differently.

If we close the spy hole and run the experiment again, we will see that the marbles will go back to the multi-striped interference pattern where they are behaving again like waves.

The double slit experiment shows that particles like electrons and photons (light particles) have properties of both waves and particles, depending on how you measure or observe them. This dual nature is one of the core concepts in quantum mechanics, illustrating that at a fundamental level, nature doesn't always behave in ways that align with our everyday intuition.

In conclusion, in classical physics, we understand particles and waves like we would a baseball versus a sound wave. But when we go down to the quantum level, this understanding of the world breaks down, and particles start to play by a different set of rules altogether. It wouldn’t even be correct to describe them as particles and waves at this level, and they seem to change based on how they are being measured. Nobody understands why this behavior occurs. It’s all very confusing and fascinating at the same time.

## #15 The Double Slit Experiment