VERY 1337 SHIT
Quantum mechanics, the best theory we have for describing the atomic and subatomic world, comes up with some extraordinary portraits of nature. One example is the uncertainty principle, which says that the position and velocity of a particle (its state, as a physicist would say) can’t both be measured with unlimited accuracy. A related idea is that the state of a particle cannot be known precisely until the particle is observed; in other words, each and every particle has a probability of being in any state. It does not exist in a particular state until an experimenter observes it.
The Austrian physicist Erwin Schrödinger, one of the founders of quantum mechanics, thought of a paradox to show that quantum mechanics doesn’t apply to larger, tangible things. He envisioned a cat locked in a steel chamber with a tiny amount of radioactive material, a Geiger counter, and a diabolical device designed so that if the Geiger counter detects a radioactive decay, it activates a hammer that breaks a flask of acid and poisons the cat. It takes only one decaying atom to kill the cat, but whether an atom decays or not is governed by probability. Applying the rules of quantum mechanics to this system would mean that the cat is neither alive nor dead until a human observer actually looks in the chamber. Schrödinger argued that this was nonsense and merely an example of applying quantum mechanics to situations in which it doesn’t apply. Still, a few physicists defend the idea that the cat doesn’t take on an existence (or lack thereof!) until it’s observed.