The greatest joke in the world

And what it can teach you about quantum physics

I made this. I’m not all that proud of it to be honest.

Four quantum physicists are in a car. Heisenberg is driving like he is in The Matrix. Schrödinger is in the front seat waving at the other cars. Einstein and Bohr are in the back arguing when they get pulled over. The officer asks Heisenberg, “do you know how fast you were going?”

“No, but we know exactly where we are,” Heisenberg replies.

The officer looks confused and says, “you were going 120 km/h!”

Heisenberg throws his arms up and cries, “Great! Now we’re lost!”

The officer looks over the car and asks Schrödinger if they have anything in the trunk. “A cat,” Schrödinger replies.

The officer opens the trunk and yells, “This cat is dead!”

Schrödinger angrily replies, “Well it is now.”

Bohr says, “on the bright side, a moment ago we didn’t have a position, speed, or a cat. Now we have all three!”

Fed up, the officer says, “I just want to know how many of you I need to bring back to the station!”

“Roll dice for it?” Einstein asks.

Not laughing? Read on.

Heisenberg

Heisenberg’s name is attached to probably the first conceptual hallmark of quantum physics to reach popular culture: the uncertainty principle. Colloquially, the uncertainty principle has been understood to be the incontrovertible fact that some things can never be known. This doesn’t sound so profound. In fact, it sounds a bit lame.

However, there is a sense in which you, more than anyone in history, should find that a limit on knowledge is empowering. Whereas waves and energy seem like properties of the world independent of us, uncertainty pertains to knowledge and that means we are back at the center of it. And nothing delights humans — especially 21st century humans — more than being the center of the universe.

For if there is a limit on knowledge, it must be invoked only after I choose to obtain that knowledge. So, in a sense, I invoke the laws of the universe — I create the universe. Yeah, take that 8th grade teacher that said I would never amount to anything!

In classical physics everything is predetermined and the precision in actual measurement is only limited by the amount of noise present. In quantum physics some pairs of properties cannot simultaneously be defined and attempting to measure one forces less precision in the other. Heisenberg said, paraphrasing, “the more precisely position is known, the less precisely speed is known — and vice versa.”

This is why Heisenberg says to the police officer — yeah, yeah, I’m explaining the joke — he doesn’t know how fast he was going. He can’t. He can’t because he knows exactly where he is. If the uncertainty in his position is very small, the uncertainty in his speed must be high. When the officer tells him how fast he was going, the relationship flips and Heisenberg must no longer know where he is. Funny, right?

For what it’s worth, uncertainty in quantum physics goes beyond the position-speed relationship Heisenberg identified — which is about observation and knowledge of otherwise real things. Quantum physics demonstrates that, independent of someone’s knowledge of it, the properties of a thing are not so much uncertain as they are just not definable. And if we can’t define it, is it even real? Mind. Blown.

Schrödinger

Schrödinger is probably the second most famous quantum physicist behind Einstein, and it’s all because of a cat. Schrödinger’s Cat appears in poetry, television, web comics, films, videos games, music, and adorns the t-shirts of every undergraduate physics nerd.

The origin of the cat is not a complicated story at all. It appeared as an almost parenthetical comment in a lamentation Schrödinger wrote about the interpretational issues still being argued about in quantum physics today. The excerpt was translated as follows:

One can even set up quite ridiculous cases. a cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.

The public understanding of Schrödinger’s cat more-or-less mirrors this — but without the complicated language. Basically, Schrödinger put a cat in a box and maybe it would be poisoned or maybe not. We can’t find out until the box is opened, so until then quantum physics says the cat is both dead and alive at the same time — a state known as superposition. People usually take this at face value, believing that quantum physics actually proves this fact to be true.

The joke then is that Schrödinger is keeping a quantum cat in superposition in the trunk of the car. The police officer ruins the superposition and collapses the “psi-function” by revealing a dead cat. Actually, killing animals isn’t funny. I don’t know why I’m laughing.

In 1935, when Schrödinger wrote the above (in a single German word of course), one popular interpretation of the indeterminism of the world prescribed by quantum physics was that reality was blurred. Perhaps you recall from highschool chemistry your electron orbitals — blurry spheres and dumbbells and such. Schrödinger was basically poking fun at this interpretation, saying that if electrons are really blurred objects, then so too must be cats — obviously nonsense!

Electrons or maybe baby toys. Credit: haade on Wikipedia.

I’d love to tell you that since 1935 we’ve figured out the resolution to Schrödinger’s cat paradox. But, physicists are still arguing about it today. To be fair, we know a lot more than we did. However, it may be that we’ve only created more paradoxes! What has always been clear, though, is the experiment could never be performed. To create such a cat superposition would require perfect isolation from any environment — including air. The cat, sadly, would surely be dead.

Now I know that having to explain a joke more or less ruins it, but not this one. The parts containing Heisenberg and Schrödinger are well known. I couldn’t find the original source. Some additions have Ohm “resisting” arrest. Some have Chomsky in there doing linguistic stuff, or whatever. But, I wanted a purely quantum joke! And, damn, I collapse every time I read it!

Bohr

Neils Bohr is the most famous quantum physicist no one has heard about. To be fair, his writing was a bit Bohring. Ba dum tiss. But, seriously, he is famous in physics for two things: being the “father of quantum physics” and writing cryptic philosophy about science. Part of his writing included public debates about quantum physics with Einstein. These were legendary.

Bohr and Einstein arguing about what to order on Uber Eats for lunch. Credit: Public domain image by Paul Ehrenfest.

Most scientists believe even things they can’t directly perceive are real. Electrons, for example, can be inferred based on their influence on other things, but are they themselves real things? Not unless you directly observe them, according to Bohr. Bohr said that the very act of observation caused the existence of the thing in question. An electron, for example, has no independent reality in the ordinary sense. We are more like children that haven’t grasped object permanence yet. Or, maybe babies are actually smarter than us and objects don’t really exis… PEEKABOO!

Anyway, as Schrödinger showed us with the cat, the quantum nature of things need not be restricted to the microscopic realm. So Bohr would have to say that, until the police officer measured it, their speed did not exist — and neither did the cat for that matter.

Einstein wasn’t a fan of this point of view and famously asked another physicist if he really believed that the moon exists only when he was looking at it. I’m not sure a consensus has been reached yet on that question.

Einstein

Albert Einstein is surely the most famous physicist to have lived. His name is synonymous with “genius” and his dishevelled look epitomises the kooky theorising scientist. For most of his life, his theories were obscurities, known only to other physicists. However, he was certainly a journalist’s favorite among physicists, especially for his personability and ever-so-quotable quips.

By far his most famous line was “god does not play dice with the universe”, which he paraphrased many times. Many will know that the subject of this quote was quantum physics. Thus, it is often assumed that Einstein was religious and believed that god would not approve of quantum physics, or even that quantum physics was inconsistent with whatever religion Einstein held — presumably Judaism.

But, Einstein himself later wrote:

I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it.

Independent of the religious aspect, the sentiment of the quote is obvious — displeasure. Einstein did not like quantum mechanics. It’s not that he didn’t believe it was an accurate account of the evidence — after all, he did win a Nobel Prize for one of the key developments of quantum physics. He didn’t not like it on aesthetic grounds. At the time he was searching for deterministic laws of the universe, and not the unexplained randomness — not to mention zombie cats — that quantum physics was demanding.

Einstein wanted a deeper theory and spent his latter years searching for it. The kind of theory Einstein would have liked is impossible — a fact proven many years after his death. The key insights came from a richer understanding of entanglement, a kind of correlation only possible in quantum theory. Entanglement annoyed Einstein. But today we see it as a resource to enable a new generation of quantum technology. And that’s no joke.

Quantum theorist by day, father by night. Occasionally moonlights as a children’s book author. www.csferrie.com @csferrie

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