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" Imagine a cat, a vial of poison, and a radioactive source in a sealed box. If an internal sensor registers radioactivity, like an atom decaying, the vial is broken, releasing a poison that kills the cat. The atom has an equal chance of decaying or not decaying. It’s an ingenious way of linking an outcome in the classical world, our world, to a quantum-level event. The Copenhagen interpretation of quantum mechanics suggests a crazy thing: before the box is opened, before observation occurs, the atom exists in superposition—an undetermined state of both decaying and not decaying. Which means, in turn, that the cat is both alive and dead. And only when the box is opened, and an observation made, does the wave function collapse into one of two states. In other words, we only see one of the possible outcomes. For instance, a dead cat. And that becomes our reality. But then things get really weird. Is there another world, just as real as the one we know, where we opened the box and found a purring, living cat instead? The Many-Worlds interpretation of quantum mechanics says yes. That when we open the box, there’s a branch. One universe where we discover a dead cat. One where we discover a live one. And it’s the act of our observing the cat that kills it—or lets it live. And then it gets mind-fuckingly weird. Because those kinds of observations happen all the time. So if the world really splits whenever something is observed, that means there’s an unimaginably massive, infinite number of universes—a multiverse—where everything that can happen will happen. "
― Blake Crouch , Dark Matter
