Many Worlds

Schrödinger’s Cat

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I’m sure you’ve heard some version of this famous thought experiment regarding a hypothetical paradox involving a cat that has perplexed and annoyed physics geeks for years. It was designed by physicist and theoretical biologist Erwin Schrödinger to illustrate the quantum mechanical concept of superposition, or the ability of a sub-microscopic object to exist in many different states, or occupy many different places, all at once. This is how the thought experiment went. You put a cat in a bunker with some unstable gunpowder that has a 50% chance of blowing up in the next minute, and 50% chance of doing nothing. The gunpowder is Einstein’s version, Schrödinger preferred poisonous gas. So until we look into the bunker, we don’t know whether the cat is dead or alive. And when we do look, it is either dead or alive. So if we repeat the experiment enough times with enough cats and bunkers and gunpowder, we’ll see that half the time kitty survives, and half the time kitty goes bye-bye.

Dead or alive?

 The quantum mechanical interpretation is that before we look, the cat is in a superposition - it’s both dead and alive, and our act of looking forces nature’s decision. So our curiosity kills the cat. But what about the cat’s perspective? Well, the cat either sees the gunpowder explode or not – so inside the bunker we actually have these two possibilities: the powder explodes and the cat sees it explode or the powder doesn’t explode and the cat doesn’t see it explode. There’s no option that the powder explodes and the cat doesn’t see it explode. So the cat’s reality becomes entangled with the outcome of the experiment. And it’s our observation of the experiment that forces nature to collapse to one option or the other. But we’re like the cat too – either the cat dies and we see it dead, or the cat lives and we see it alive. So who’s observing us to force nature to collapse to one reality? Or do both possibilities happen in parallel within a larger multiverse? This collapsing to one reality problem is one of the biggest unanswered questions in quantum physics.

Who is observing us?