How can a cat be alive and dead at the same time?

 

Schrödinger's Cat: The Idea

Physicist Erwin Schrödinger proposed the thought experiment in 1935 to illustrate the weirdness of quantum mechanics:
A cat is placed in a sealed box with:
A radioactive atom (which may or may not decay),
A Geiger counter to detect the decay,
A vial of poison that breaks if decay is detected.
If the atom decays → poison is released → cat dies.
If the atom doesn’t decay → poison is not released → cat lives.
Quantum mechanics says that until we observe the atom, it exists in a superposition — both decayed and not decayed.
Therefore, before the box is opened, the cat is both alive and dead at the same time — in a quantum superposition.