How the Universe Works: Quantum Superposition


Amanda Austin, Reporter

Superposition. Something that seems completely impossible, confined only to the realm of science fiction, a state in with normal matter can be in two completely different positions at once. It is so strange, it almost seems like a fantasy, impossible in our world today. And yet… Quantum mechanics, although looking to be the stuff of imagination, is the necessary fundamental process that makes the world as we know it… work. But how do you imagine something like this? We’ll begin with the “simple”: quantum superposition.

A famous example of this is a thought experiment known as “Schrödinger’s cat.” In this experiment, imagine a cat, whatever breed you wish. Now put that cat in a completely sealed box (pretending it can breathe). Also in the box is a small radioactive source, which has an equal chance of decaying or not decaying, a Geiger counter, and a flask of poison. If the counter detects radioactivity, the flask will break and the cat will unfortunately die. Now, the flask as an equal chance of breaking or not breaking, and the cat an equal opportunity of living or not (although we can hope it will live).

According to a particular interpretation of the math around quantum mechanics, this cat, while sitting in the box, is in a state of superposition, both alive and dead. However, when someone opens the box, they do not see a zombie cat. They see either one or the other. The question Schrödinger struggled with is: When does this superposition end and reality collapse into either one possibility or the other? And does this only exist in the math, or, when something is not being observed directly, does reality itself not solidly exist?

In the quantum world, all we understand seems to break down. If the cat is too confusing to follow, think about this: Tiny particles can exist as different states, be in different positions, or be moving at different speeds. Because that’s not already hard to grasp, particles aren’t like physical objects we see in our world. They exist across all possible states at the same time: Superposition. However, when a particle is measured for any of these factors, one state, one position, and one speed seems to emerge. It is as though the act of measuring, of observing, forces the particle to make up its mind, and to choose one specific location.

As impossible as this may sound, this theory withstands tests again and again. The truth is, it’s our world, and as we move up in scale from these particles, things seem to become more and more definite. But down at the subatomic level, things get a little weird.

What’s more astounding is that it is believed that every little difference, every choice has happened, and will happen again. Somewhere, that cat sadly didn’t make it, while in another universe, it waltzed out of that box purring. In a different world, New York was chosen to become the capital instead of Washington D.C., or the Chinese intervened and won the Civil War. And somewhere, the particles came just right, and there’s another identical copy of you, me, and all of us. After all, who’s to say the Big Bang was an isolated event? Why couldn’t it happen again?

We don’t know if this, or any of what we think we know, is possible. Perhaps superposition and all of the craziness of quantum mechanics only exists in the math, and not in the real world. But then again… Maybe it is real. Perhaps all that we know about our world, about time, about everything we thought to be so fundamental and straightforward is just plain wrong. And maybe, just maybe, we’ll someday understand it.