For Dummies: Schrödinger’s Cat Paradox explained

Have you heard about the Schrödinger’s cat paradox but haven’t understood a single thing? Here we explain it to you in a nutshell.

Many of us have heard about Schrödinger’s cat, but let’s be honest, either we don’t even know what it is or we know about the theory but we don’t understand anything. Certainly, quantum mechanics is not exactly a piece of cake, so in order for you to have something to talk about at the next party, we leave you with a for dummies so you know it and can show it off to your friends.

What is Schrödinger’s cat?

We are sorry to tell you this cat never actually existed. Although it’s already part of popular culture (yes, they even talked about this cat in an episode of The Big Bang Theory), the Schrödinger’s cat paradox is a thought experiment devised by Austrian physicist Erwin Schrödinger - one of the founders of quantum mechanics - back in 1935.


And what was this mad scientist trying to do? Well, he was trying to talk about a basic principle of quantum mechanics, that branch of physics that some people find exciting, while others flatly hate it. And believe it or not, this is how Erwin felt about quantum physics: he found it so philosophically disturbing that he decided to send it to hell and dedicate himself to biology.

So, what’s the experiment all about?

Now comes the good stuff, so sit up and pay attention to expand the horizons of your intellect (or have your brain explode).


The experiment Erwin devised goes like this: you have to put a cat inside a sealed box. Inside, next to the cat, is a container with hydrogen cyanide (a poisonous gas) threatened by a hammer connected to a radioactive container.

There is a 50% chance that after a period of time (say, one hour) radioactive decay of some atom inside the container will occur which would activate the hammer and break the cyanide container, releasing the poison that would kill the cat.


The other 50% of possibility tells us that this will not happen and therefore the cat is still alive.

Well, Schrödinger’s paradox tells us that we as spectators, on the outside, do not know if inside the box the cat is alive or dead, therefore, without verification, it is alive and dead at the same time.



Yes, think about it, it’s like those times when you are asked if a tree falls in the middle of a forest but no one hears it, does the tree actually sound the thump of the falling tree? And the fact is that the spectator, not seeing inside the box, does not know the result, so the cat is alive and dead, and only the observation is what would change the result.

And this, my friends, is precisely quantum physics, which says that quantum objects can be in two states at the same time.


Two states at once? You don’t say...

This is not just a matter of the cat but is a metaphor to describe the state within this type of mechanics. According to quantum laws, the atom is in an intact and disintegrated state at the same time, which is called quantum superposition*. Only when we look at the particle can we know what state it is in at the moment (like the cat, remember?).

*Quantum superposition: a quantum phenomenon that is a consequence of the dual particle and wave nature of everything.


This action of looking to determine the state (of the atom or the cat, it doesn’t matter, the cat was just an example) is called collapse, and it is that we practically screw up the quantum property it has and it will only be able to materialize in one state (like looking in the box and knowing if it is alive or dead).

But it doesn’t make sense

No, maybe our logic tells us that the cat is going to be alive or dead (there is no other way!) but in the atomic world, the properties of things are governed by laws that are not simple and that is where probability comes in.


For example light. Light, like electrons, has a wave nature, but it also has particle characteristics. But you can’t pick up light with your hands, can you? It stays in two simultaneous states.

Let’s go back to the superposition

The fact of two states at the same time responds to the fact that for an object to have a wavelength, it must extend over some region of space, i.e... it occupies many positions at the same time. omg!


This can lead to other theories such as those of the quantum multiverse. Let’s think: if the cat can be alive or dead but it depends on observation, isn’t it feasible that both possibilities are in fact occurring in parallel but within a multiverse?

More than a cat

Although Schrödinger got fed up with quantum physics and decided it was not worth it, beyond the cat, the physicist formulated one of the most important equations in history: the Schrödinger equation (he was not so original when it came to names).


Here we leave the formula for you to calculate it (Photo: YouTube).

This formula, something like Newton’s second law but for quantum mechanics, contains all the properties and information of any particle. This simple formula is a wave function capable of describing the state of a particle such as energy or position. Because let’s review: if the particle is in two states at the same time, how do you determine anything about it? Unfortunately one of the problems with the equation is that it cannot measure all values simultaneously.

Well, now you know about Schrödinger’s cat and the next time it comes up in the conversation of your educated friends you will be able to explain clearly (or not?) why this cat lives in the collective mind of the whole world.


Story originally published in Cultura Colectiva in Spanish

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