You Wut Mate? Explaining The Schrödinger's Cat Thought Experiment.

Quantum mechanics is weird, as in really weird.

It is said that if you think that you understand quantum mechanics then you really don't understand quantum mechanics (reference).

It is also said that the entire mystery of quantum mechanics is contained in the double slit experiment. So let's talk about the double slit experiment for a while before getting on to the famous cat.

The Double Slit Experiment

When you pass a wave through two openings in a barrier new waves will propagate through those two openings in circular patterns on the other side. These two new openings will basically act as new sources for two new wave systems.

The waves from one opening will eventually meet up with the waves from its neighbouring opening and they will interfere with each other.

As with all waves, when two crests meet the wave will become doubled in height, when two troughs meet the wave will become doubled in depth and when a crest and a trough meet they will cancel each other out (i.e. you get a flat spot). The end result will be an interference pattern which usually manifests as bands of brightness and darkness arranged across the detection grid.

Interestingly matter can also be described using wave equations but in the case of matter waves the end result is the probability of a particle being detectable at any given location.

You can thus send an electron beam through two slits and the electrons will emerge out the other side through these two slits and interfere with each other and form an interference pattern. This is weird enough but it gets even weirder.

Turn down the emission rate on the electron beam until it emits only one electron at a time and send those single electrons through the double slit. Each electron will go through this apparatus, apparently interact with itself and an interference pattern is still formed.

You Wut Mate?

The double slit experiment is a nice illustration of the truly bizarre world of quantum superposition and it demonstrates, very much like waves in classical physics, that quantum states can be added and subtracted from each other and the result will be another quantum wave.

In addition you also cannot know what the state of that quantum wave is until you make an effort to observe it at which point is is said to have 'collapsed' and becomes one of its allowable possibilities.

For example where is an electron in an atom? We know that it is somewhere within a cloud of possible locations (called an 'orbital') but it has no definite location until you shoot another electron into the cloud and measure the results of the collision.

This all makes no sense, it is ludicrous and definitely cannot possibly be true. Right?

If you think that way then you would be in good company because Einstein did as well. Just like Einstein though, you would be wrong.

In 1935 Erwin Schrödinger devised a thought experiment that is now famously called Schrödinger's cat.

In this experiment there is a cat (the classical system) in a closed box along with a radioactive source (the quantum system). There is also a radiation detector which is hooked up to a circuit that will open a vial of poison when it detects a decay event. If a decay event occurs, it will be detected, the vial will open and the cat will die.

The cat is alive when you put it into the box. When you close this box you cannot see, or hear, or detect in any way whether the cat is alive or dead. Since the fate of this cat is now tied to a quantum system (the radioactive particle) it is said to be in both states, dead and alive, at the same time.

This thought experiment was designed to poke fun at quantum mechanics and to point out how ludicrous the interpretations of quantum mechanics were becoming. It is obvious that the cat will definitely be alive or definitely be dead and it cannot be both at the same time.

Or can it?

Quantum Tests Of Large Systems

The double slit experiment has been performed with many objects, starting from photons (easy) and then with electrons (harder). It has been done with small molecules that also showed the interference pattern and it even has been successfully performed with large molecules such as buckeyballs which are made up of 60 carbon atoms (reference),(reference).

Most recently, this experiment has been performed with a molecule assemblage massing up to 10,000 amu and self-interference superposition states were apparently successfully observed. That is getting seriously large.

Closing Words

So the Schrödinger's cat thought experiment was devised to poke holes in the interpretations of quantum mechanics but tests through the years are successfully showing that the principles of this theory are holding true for larger and larger systems.

There is even a test proposed to see if superposition of flu viruses can be successfully performed.

Looking at the track record of the previous tests, I would not bet against this experiment.

There is no way though that we will ever create a cat gun to see if we can get whole cats to exist in a quantum superposition state (or would we?).

Sometimes I think the way my cat can just magically appear in the same room as me tells me that they have somehow already mastered this technology.

Thank you for reading my post.

Post Sources

[1] Double Slit Experiment.
[2] Schrödinger's cat
[3] The Physics Behind Schrödinger's Cat Paradox
[4] Quantum superposition.
[5] Bucky balls.
[6] Molecular interferometry of C60 molecules.
[7] Molecular interferometry of molecules exceeding 10,000 amu.
[8] U WOT M8 - Know Your Memes