Schrödinger's cat

I’m not a fan of gatekeeping jargon, but if I heard the phrase Schrödinger's cat when I was in my 20s, my ears would perk up. I knew I was talking with another physics nerd.

Because this was long before the internet had become useful, this coded language was all the more effective at identifying fellow nerds, although it might be a stretch to include myself in that category. I didn’t major in physics in college, and my career paths have driven me away from formal STEM training ever since then.

Still, my childhood interest in discovering how things work has never waned, beginning with whatever books I could find at used book shops. As videos on the internet became more accessible during the early to mid 2000s, I watched all the physics lectures I could find. I stayed in the loop, taking advantage of technological leaps to stay connected, like listening to popular science books when I’m going for walks.

While Schrödinger's cat may have been on the back burner of popular culture back then, it’s pretty much front and center these days. Many people know the general premise behind the experiment.

A cat’s life hangs in the balance, as a single atom determines its fate. A Geiger counter sits in the box with the cat, waiting to detect a single particle that might or might not decay. If it decays, the Geiger counter goes off, activating a device and killing the cat.

These days, the experiment invokes the idea of multiple worlds much more readily than during Schrödinger's days. We’re talking 75 years before the Marvel Universe really took off, so there was nothing mainstream about multiverses or multiple dimensions.

No way. Back then, this was supposed to be shocking.

That was the whole point! Schrödinger wanted to pull the emergency brake to stop the train, so everyone else would come and take a look at how silly the idea itself was. He wanted the physics elite to see the silliness of superposition, so they would understand how incomplete and absurd quantum mechanics really was.

That’s not exactly what happened next. Instead, the physics community—at least some of them—took the results of this morbid thought experiment seriously. Niels Bohr, who was the champion of this idea in the first place, took up the mantle of defense immediately, doubling down on quantum superposition.

Schrödinger was trying to point out how silly the whole idea was, since the cat couldn’t be both alive and dead. Here was Bohr, seeming to suggest the absurd reality was how nature actually behaved. Bohr’s main idea was that the superposition—the multiple states—existed right up until the moment of observation.

I wrote about this brain-bender a bit here, so you might want to bookmark this for later:

Bohr’s Copenhagen interpretation became the most widely accepted view for quantum mechanics, and it was mainly uncontested until the 1950s, when another interpretation began to gain momentum and to be taken seriously.

While Bohr suggested that the states collapsed into one when you looked at them, Hugh Everett III suggested in his PhD thesis that all of these possible worlds actually happened. Each time there was more than one possible state at the same time, this new theory claimed, all of those possible outcomes really happened.

This became known as the Many Worlds Theory, contrasting with the Copenhagen interpretation in a few notable ways. As mentioned, the branches really happen in MWT, so this leads to other interesting conclusions.

First, you (the observer) don’t really matter. Looking at a system and somehow affecting its outcome seems… well, spooky, not scientific. Now, just because something seems spooky, doesn’t mean it’s not true, but MWT was certainly helped along because it satisfied at least one of the toughest things to accept with Copenhagen.

Second, MWT means the universe can be deterministic. In Copenhagen, the interpretation implies that there’s some kind of uncertainty in the outcome that isn’t predetermined, but hundreds of years of incredible scientific discovery had pointed everything in the exact opposite direction for hundreds of years.

On the other hand, no matter how you interpret what’s going on at the smallest scales, it’s going to seem very weird to us here at the macro scale. Schrödinger wanted to sound the alarm that there was some weird stuff going on, and no matter how you slice it, he was right.