What is Schrodinger's Cat

(And Can I Pet Him?)

What is Schrodinger's Cat and Can I Pet Him?

Don't be a silly sausage, you can't pet Schrodinger's Cat because he isn't real. He's a hypothetical cat in an 80-year-old thought experiment.

The famous cat was created by Erwin Schrodinger in an attempt to illustrate his objection to quantum uncertainty.

But the thought experiment rather backfired. Instead of discrediting quantum theory, he popularised the concept by putting it into layman's terms - more on this later.

Due to the nature of the experiment, there's a 50:50 chance the cat is about to succumb to a fatal poisoning. So rather than make him cute and pettable, I decided to make him an arsehole.

I mean, a really grumpy arsehole of a cat.

Don't believe me? Just look at him.

Schrodinger's Cat Cartoon

Here he is stealing candy from a baby.

Schrodinger's Cat Stealing Candy From a Baby

And here he is trying to convince said baby's mother that the MMR vaccine causes autism.

Schrodinger's Cat Posing as a Doctor

Like I say. Total arsehole.

Why Does a Cat = Quantum Mechanics?

Let's take in a little background.

In the year 1900, Max Planck gave glorious birth to the theoretical study of quantum theory.

Planck had some rather smashing ideas about the nature of reality at the subatomic level. Namely, that when it comes to quantum scales, the traditional laws of physics no longer apply.

This was a big problem for physicists. Not only did Planck declare that Newton's laws break down in the quantum world, but the rules that do apply are completely stupid and illogical. My words, not his.

The Double Slit Experiment

Take the Double Slit experiment. It demonstrates that quantum particles behave differently depending on whether or not they're being observed.

Here's how we reach this conclusion (which by the way completely destroys our deterministic understanding of cause-and-effect):

If a photon of light is being observed in terms of position or momentum, it behaves like a particle with a definite point in space.

Paranoid Particle

The Double Slit experiment illustrates this effect by firing single photons, one at a time, through a screen with two slits.

Consequently, the photons either pass through one slit or the other (or neither, bouncing off) and land predictably in two straight lines on the detector screen.

Double Slit Experiment Cartoon

So far, so good. This is reality as we know it.

But look what happens when you turn your back on the quantum world.

If you simply stop measuring a photon's position or momentum, he goes bonkers and behaves like a wave.

Quantum Probability Wave

Despite still being fired one at a time, the photons now leave a complex interference pattern on the detector screen.

This reflects waveform behaviour - and not particle behaviour.

Double Slit Experiment Cartoon

The Double Slit experiment suggests that each individual photon of light travels through both slits simultaneously as a wave of probabilities.

At the quantum level, many alternate realities are played out for the path of each photon. Some in which it takes the first slit, some in which it takes the second slit, and some in which it takes neither and hits the screen.

With all possibilities played out simultaneously, the photons now bounce off each other like waves in a pond. This leaves a very specific result on the detector screen, revealing an interference pattern.

Did I say stupid and illogical? No, the quantum world is downright insane.

Each photon of light exists in all possible places at once but only when no-one's looking.

And that left the world of physics in quite a pickle.

Get Heisenberg on The Case

To bring some order to this chaos, Werner Heisenberg came up with the Uncertainty Principle.

He said it's impossible to know both the position and the momentum of a quantum particle at the same time. By measuring one trait, you automatically affect the other and determine its path.

Albert Einstein famously struggled to accept the conclusion of quantum uncertainty. In fact it has long been the main reason why physicist's cry themselves to sleep at night.

Quantum Uncertainty

So quantum behaviour is a big hot mess. But what about Schrodinger's cat?

I'm getting to that, but first this story gets weirder.

Despite struggling with the dreadfully counter-intuitive nature of quantum mechanics, Einstein was still able to further the field with his theory of Quantum Entanglement.

Here, quantum particles are invisibly connected and talk to each other instantaneously, even when separated by vast distances.

Quantum Entanglement Illustration

Einstein himself said that nothing can travel faster than the speed of light. That includes the simultaneous exchange of dinner plans between entangled particles on different sides of the planet.

Einstein referred to it as "spooky action at a distance" to stress the silliness of it all, and concluded the theory of quantum mechanics must be incomplete.

But he was wrong.

After Einstein's death, quantum theory was proven experimentally by John Stewart Bell. Its absurd conclusions and implications are very much real.

Further experiments went on to measure entangled particles communicating within 0.01% of the travel time of light between them.

How can we get to grips with this absurd carry-on?

The truth is we still don't have a definitive answer, but there are two theories which hold a lot of ground today.

The Copenhagen Interpretation

Niels Bohr said that quantum particles simply don't exist in any fixed location until we measure or observe them.

They exist only in hypothetical states of quantum superposition, across all the possible states at the same time, like overlapping waves.

Einstein agreed with Bohr's maths on quantum superposition but refused to accept the conclusion. Since everything is made up of quantum particles, it means that nothing is real until we measure it.

I like to think the moon is there, even if I am not looking at it. Albert Einstein

Despite this scathing indictment, the Copenhagen Interpretation remains one of the most commonly taught explanations of quantum mechanics today.

Einstein vs The Moon

The Many Worlds Interpretation

As disturbing as Bohr's non-reality may sound, the alternative is really no better.

Proposed by Hugh Everett, the Many Worlds Interpretation claims the complete opposite of Copenhagen. Here, every possible outcome of every possible event already exists in an infinite number of alternate universes.

Kanye West as a Proctologist Cartoon

The Many Worlds theory states that you die horribly an infinite number of times before breakfast. Frankly that doesn't sit well with me.

Still, this extraordinary theory has been favoured by Stephen Hawking and Richard Feynman and whoever created the cutest science fiction show ever.

Schrodinger's Cat Explained

Now, having heard the elevator pitch of quantum mechanics, Schrodinger's cat will make a lot more sense.

Amid the quantum hullabaloo of the 1930s, Erwin Schrodinger came up with a thought experiment to illustrate the problem with quantum uncertainty.

He imagined a cat inside a lead box. A real arsehole of a cat, if you recall.

Beside him there's a hammer, suspended over a glass vial of poison. Triggering the hammer to fall is a Geiger counter, and a single atom of radioactive material that has a 50:50 chance of decaying in the next hour.

That may sound like a convoluted set-up, but being a man of scientific rigour, Schrodinger's idea was to create a set of circumstances in which the cat has a completely random and unknowable chance of being dead or alive.

Schrodingers Cat Cartoon is Alive

If the atom doesn't decay, the Geiger counter doesn't detect any radiation, nor trigger the hammer to fall, nor smash the vial. Schrodinger's cat lives.

If the atom does decay, the Geiger counter detects radiation, triggers the hammer to fall, and smashes the vial. The poison escapes and Schrodinger's cat dies. Sad face.

Schrodingers Cat Cartoon is Dead and Alive

If you're an animal lover, which you should be, why not consider an alternative victim in our quantum murder fantasy? Someone who actually deserves to be put in the box, like a racist, narcissistic megalomaniac?

Schrodinger's Trump Cartoon

That's the spirit.

Now according to Bohr's theory, the victim is in a superposition of two states. He's both dead and alive in a ghostly but also literal sort of way.

It's only when we look inside the box (or shake it, according to Gisby's attempt to circumvent quantum law) that we break the superposition and the cat becomes dead or alive.

We all know it's incorrect to declare that something "becomes dead". It's just bad grammar. But that's the whole problem with quantum superposition, isn't it? It breaks all our comfortable rules.

Schrodinger thought so too. He insisted that it was impossible for a living organism as large as a cat to be both dead and alive in the same universe.

And that is what Schrodinger's cat is really all about. He took a familiar object and stuck it in a scientifically controlled setting and then called up quantum law.

"This is bullshit," Schrodinger pointed out. Except he was Austrian so he would really have said, "Das ist Kuhscheiße".

Most people assume Schrodinger's cat was created in support of Bohr's Copenhagen Interpretation as a way to better visualise it.

I bet he hated that.

Unfortunately for Schrodinger, experimental data continue to show that quantum superposition does actually exist, rendering the whole cat scenario moot.

And you didn't even get to pet him.

What is Schrodinger's Cat and Can I Pet Him?
Rebecca Turner Bio

ABOUT THE AUTHOR: Rebecca Turner is the founder of Science Me, a biology student and a nurturer of tiny people. Read more about her story here.