... like I'm 5 years old
Schrödinger's cat is a thought experiment, or a hypothetical situation, proposed by physicist Erwin Schrödinger in 1935. It was used to illustrate a strange concept in quantum mechanics. Here's a simplified version of the scenario:
Imagine you have a cat inside a sealed box. Also inside the box is a tiny bit of radioactive substance, a Geiger counter (a device that detects radiation), a vial of poison, and a hammer. If the radioactive substance decays, it will trigger the Geiger counter, which then releases the hammer to break the vial of poison, killing the cat. If the radioactive substance does not decay, the Geiger counter won't trigger, the hammer won't break the vial, and the cat remains alive. Now, until we open the box to check, we don't know whether the cat is alive or dead.
According to quantum mechanics, the cat is in a state of superposition, meaning it's both alive and dead at the same time, until we observe it. Only when we open the box does the cat become one or the other. This is the essence of Schrödinger's cat.
Imagine you're baking a cake, but you don't know what kind it will be until you open the oven. Until then, it's both a chocolate cake and a vanilla cake at the same time.
... like I'm in College
Schrödinger's cat further explores the concept of superposition in quantum mechanics. Superposition is the idea that any two (or more) quantum states can be added together, or "superposed," and the result will be another valid quantum state; and, conversely, that every quantum state can be represented as a sum of two or more other distinct states.
In the thought experiment, the quantum system is the radioactive substance that may or may not decay. The macroscopic system, which is typically assumed to have definite states, is the cat that is either dead or alive. The paradox lies in the fact that a macroscopic object (the cat) is coupled to a quantum system (the radioactive substance) and is thus forced to be in a superposition of states.
Imagine you have a box of Lego bricks. Some bricks are red (representing the cat being alive) and some are blue (representing the cat being dead). You reach into the box without looking and grab one brick. While it's in your hand and you haven't looked at it, it's as if you're holding both a red brick and a blue brick at the same time. This is the superposition.
It's only when you open your hand and look at it that you see the color of the brick. The act of observing the brick "collapses" it from being both red and blue to being one or the other. Similarly, in Schrödinger's cat experiment, the cat is both dead and alive until observed, at which point it becomes either dead or alive.
... like I'm an expert
Schrödinger's cat was a critique of what's known as the Copenhagen interpretation of quantum mechanics. The Copenhagen interpretation posits that a quantum particle exists in all states at once until observed or measured, at which point, the particle's wave function collapses to a single state.
Schrödinger proposed his cat thought experiment to illustrate the absurdity of this interpretation when applied to everyday objects. The cat, he argued, is both dead and alive until someone observes it, at which point the "wave function collapses" to either a live cat or a dead one. This challenges the notion of classical reality and raises questions about the nature of the observer and the role of consciousness in the determination of quantum states.