Schrödinger's cat is the most well-known thought experiment in quantum physics. A thought experiment is like an imagination game! It’s when you use your imagination to think about a situation, even if you can’t actually do it in real life. Schrödinger used it to illustrate the strange world of quantum physics.

Imagine to put a cat inside a box with a small bottle of poison.

The bottle of poison is very fragile and it could easily break and kill the cat.

We don’t know if the bottle has broken or if the cat is dead or alive until we open the box.

In the strange world of quantum physics, before we open the box, the cat is in a state of being both “alive and dead” at the same time. Both possibilities exist simultaneously until we look inside. This is known as the superposition principle. It suggests that a quantum object, like a tiny particle, can exist in multiple states at once, as a blend of all possible outcomes until it’s measured or observed. When we observe it, the object “chooses” a definite state.

Erwin Schrödinger originally created this thought experiment to show how bizarre it would be to apply quantum rules to larger objects, like cats. In the everyday world, things are only in one state at a time.