# A signature

The simplest grating you can imagine has just two slits: everywhere else is black. So a photon gets to explore only two paths.

### One plus one, more or less

Almost everything weird about the quantum scale comes together in this famous two-slit experiment.

There has been mu

TeacherOne{Did the photon go through one slit or the other?}

But as you now know, photons are not like everyday large scale things.

TeacherTwo{Photons don't do either-or, they do both.}

TeacherThree{Every photon explores both paths, so the whole space, which includes both slits.}

TeacherThree{It's just like SchrÃ¶dinger's cat.}

### Again, with triplets

Curling up and lining up works here as well, giving you a better sense of how these restricted paths predict this new phenomenon.

This phenomenon is called interference, another successful prediction as it happens.