What is decoherence?

Decoherence is when things that are acting like they're connected start to behave like they’re not, kind of like how your toy train tracks stop working if you knock them over.

Imagine you have a special kind of toy car that can be in two places at once, like it’s ghosting between the red track and the blue track. This is superposition, it's being in more than one place all at once. Now, imagine your toy car is playing hide-and-seek with its friends on both tracks at the same time.

But then a little brother comes along and accidentally knocks over the track. The toy car can’t be in two places anymore, it picks one path and keeps going. This is decoherence, it’s when things that were acting like they’re connected suddenly stop being connected because something else happens around them.

It’s like how your favorite ice cream cone melts when you leave it outside on a hot day, the cool, neat shape becomes messy and runny, just like how connected things become unconnected.