It seriously makes my mind hurt.
Can the double split experiment be explained in an eli5 way or is it just too complex for the layman with an average IQ to understand?
How does observing a photon crate a wave pattern *AND* change events that have already happened?
In: 5
Let’s start with the classical double slit experiment.
Light is a wave. It goes up and down with a certain frequency and wavelength. If two waves overlap such that they peak and fall in the same places, we get constructive interference, so it looks like we just have one big wave. If the peaks of one line up with the falls of another, we get destructive interference, and it looks like there’s no wave there.
When we send light through the double slits, it’s like we have two light sources. When they hit the screen,the light has to travel some distance from each slit. If the difference between those two distances is a multiple of the wavelength of the light, then the peaks line up, and we get a bright spot on the screen. If the difference in distance is a multiple of the wavelength, plus an additional half wavelength, then a peak and fall will line up with each other, causing destructive interference and a dark spot.
Now, once we do the single photon double slit experiment, we need to know that a photon is both a particle and a wave. When the photon acts as a wave, we describe its location as a probability curve. When it passes through the slit, we don’t know which one it goes through, so we have two different probability curves that we have to add together to describe the photon’s position. This is essentially schrodinger’s cat, we don’t know if it’s alive or dead, so it’s in a superposition of both states until we observe it, and it must collapse into one of the valid states. While the photon is traveling to the screen, it’s in this superposition, the two halves of the probability curve (left slit and right slit) are interfering with each other. This makes the probability curve look just like the diffraction pattern we saw in the classical double slit experiment, and once the photon hits the screen, it collapses that probability function into a single point. We still don’t know which slit the photon went through, but we do know where it is now.
If you were to put something that could detect a photon passing through it on just one of the slits, you would no longer get the diffraction pattern. Instead, you would just get two images of the slits on your screen. That’s because that superposition is no longer occurring because you will always know which slit the photon went through depending on whether or not it set off the detector. No interference occurs.
Finding a photon in the dark spot of the single photon double slit experiment would be like doing Schrodingher’s cat, but once you open the box at the end, you find an eggplant rather than a cat.
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