system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do things moving fast (ex. fan blades) seem to disappear when they move very fast?
gpt
It's mostly because of how our eyes work. After we capture light, our photoreceptors have some down time before they can do it again. That means that our eyes have a refresh rate. But each cell is on its own timing, so one receptor will capture the image of the fan blade, while the one next to it will capture an image a fraction of a second later, when the blade is gone from that specific spot. So our brain averages these conflicting patterns out to a semi-transparent blade.