The classic demonstration of superposition is the double-slit experiment [0], where an experimenter shines a (coherent) light through a pair of slits at a scree

The classic demonstration of superposition is the double-slit experiment [0], where an experimenter shines a (coherent) light through a pair of slits at a screen (or fires a stream of electrons through a pair of slits, or small particles- it works with anything.) Because light is waves [1], light coming through one slit will interfere with light coming through the other slit, producing an interference pattern. But weirdly, this still happens if you turn the light source down so low that it emits only one photon at a time. In that case, the photon is in a superposition that travels through both slits, and the interference is between "the part of the superposition going through the right slit" and "the part of the superposition going through the left slit." So it's not a matter of our being unable to make detailed enough measurements; we can actually observe phenomena that directly indicate superposition happens. [0] https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment [1] And so are electrons, particles, humans, etc.