The macroscopic (aka, observable) world we live in is physical. We use our senses to observe things around us and those things happen in an ordered, cause-and-effect fashion. This is because things in our world take on discrete properties. A ball is a round. A pancake is soft (you hope!). A brick is heavy. You get the picture.
But in the quantum world, properties aren’t discrete. Rather, there is only a likelihood of a given property existing and all potential properties exist simultaneously. A ball is round. And oval. And egg-shaped. And maybe not even a ball. You get the picture (again). It’s only once something becomes part of our macroscopic world does it take on a discrete property.
Consider one of the most famous quantum world figures, Schrödinger’s Cat. To illustrate this feature of the quantum world (called “superposition”), physicist Erwin Schrödinger devised a famous thought experiment while in conversation with Albert Einstein in 1935. (The two were actually critiquing superposition and the thought experiment was supposed to illustrate how preposterous it was. Even Einstein missed the impossible from time to time!)
Imagine a cat in box, and in that box is a toxic poison that slowly kills the cat. Until someone observes the cat by opening the box, the cat exists simultaneously in two states: alive and dead. It’s the act of bringing the cat into the observable world that forces it to be one (alive) or the other (dead).
This kind of conundrum makes most scientists’ brains break. Forget about alive and dead cats! The idea that something occurs because it’s been observed basically throws objective science out the window. Yet, Schrödinger’s Cat fits with the math that describes the quantum world, math that Schrödinger himself figured out.