Eli5: Does a photon really act different by looking at it? How does it know it’s being observed?
In: 11
Yes, the act of “observing” a photon does change its behavior. We discovered this by way of an experiment known as the “double slit experiment.”
It’s a bit difficult to explain without visual aids, but I’ll try and will also include a video detailing it at the end.
So you take a barrier and put two parallel slits in it, wide enough to allow something to pass through. Depending on what this something is (particle or wave), you will end up with two different patterns on the other side of the barrier. For a particle, you will have two lines of particles which neatly correspond to the slit locations with little to nothing beyond where the slits are. However if you have waves (like water, for instance) you end up with the one wave being split in half and then interfering with itself, giving you a wide pattern that repeats beyond the “boundaries” of the original slits. This is an interference pattern, and is the hallmark of waves interacting with one another.
So as an experiment, scientists fired photons at the two slits. Believing photons to be particles, they were surprised to find an interference pattern on the other side. That makes light a wave. But photons are particles, right? So how did it produce a wave pattern? So they set up equipment to record the path of the photons to see how the wave pattern was produced by particles. And in watching it happen, the pattern on the other side was changed to a particle pattern as each photon was observed passing through each slit individually.
Like I said, difficult to explain without visual aid, so [here’s a link for you.](https://youtu.be/Iuv6hY6zsd0)
For what it’s worth, I have not actually watched this video in particular. However, I like Veritasium and know he’s very good at explaining things in an easy-to-digest manner. I hope this helped!
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