Chances are that you’ve heard someone reference Schrodinger’s cat at one point or another. Perhaps you’ve been reading on Reddit about why Schrodinger’s cat appears in the Rick and Morty episode “A Rickle in Time”. Regardless, if you don’t have any idea what Schrodinger’s cat is, don’t worry, you’re not alone. While people like to throw this term around to sound smart in front of their friends, very few of us non-physicists actually understand what Schrodinger’s cat is all about.
No, there was no actual cat involved. Schrodinger’s cat refers to a thought experiment created by Austrian-Irish physicists Erwin Schrodinger to demonstrate a fundamental principle of quantum physics. The experiment basically involved an unobservable cat in a box that could be considered both dead and alive at the same time. That’s right, we’re talking about a hypothetical zombie cat.
Even when explained in the simplest terms, the conclusions drawn from the Schrodinger’s cat thought experiment seem to make absolutely no sense at all. In fact, it seems as if the principle it demonstrates is sort of a mystery to even the world’s most profound physicists. So, trying to explain this highly complicated idea to a five-year-old is no easy task; nonetheless, I will endeavor to do so with this article. But first, let’s talk about the cat’s owner, Mr. Erwin Schrodinger, and why people have been talking about his theories for decades.
Who Is Schrodinger and Why Should I Care?
Erwin Schrodinger was born in Vienna in 1887 to a family that was deeply involved in science. His mother was a Professor of Chemistry at the Technical College of Vienna. While Erwin was always an intelligent young man, he did not devote himself to physics right away. He studied chemistry, then devoted himself to learning Italian painting for years, and then moved over to botany. He was also apparently a big fan of German poetry. Many attribute Schrodinger’s ability to think abstractly, as we see with his cat-based thought experiment, to his knowledge of a wide range of disciplines.
It was only when he arrived at the University of Vienna that Erwin Schrodinger developed a profound interest in physics. However, after studying for several years under Franz Exner, his journey into the world of physics was put on pause when he was enlisted to serve as an artillery officer in the First World War.
In 1920, Erwin moved back to Germany and took up several academic positions at several universities. It was during this period that he began engaging heavily in theoretical physics. His papers during this period dealt mostly with atomic spectra, specific heats of solids, and thermodynamics. His great discovery, however, was Schrodinger’s wave equation, which would win him a Nobel Prize in 1933. Two years later, Erwin Schrodinger conceived the Schrodinger’s cat thought experiment in response to questions originally posed by Albert Einstein.
While Schrodinger never won a Nobel Prize for his Schrodinger’s cat experiment, most people today associate his name with his feline conundrum rather than his prize-winning wave equation. Now, let’s take a look at what the Schrodinger’s cat experiment is all about, and why it’s made him so famous even after his death in 1961.
Schrodinger’s Cat Explained
Alright, here’s the basic setup in this theoretical experiment:
- There’s a cat in a box.
- There is also a tiny bit of radioactive substance in the box.
- There is a Geiger counter (a tool used to measure radioactivity) in the box.
- The Geiger counter is hooked up to a hammer that is set to smash a vial of poison.
- If the Geiger counter registers any radioactivity, it will trigger the hammer, which will smash the vial, releasing the poison and killing the cat.
- The radioactive substance exists in a superposition of states, meaning that it has a 50% chance of decay and a 50% chance of not decaying.
- If the radioactive substance decays, the cat will die. If it does not decay, the cat will live.
- While the box is closed and the cat is unobservable, the cat is presumed to be both alive and dead at the same time.
If that last point really confused you, you’re not alone. How can something be both alive and dead at the same time? Surely, it has to be one or the other, right? In our day-to-day lives, this is entirely true. However, the world of quantum physics seems to play by different rules, or so thought Niels Bohr.
Niels Bohr was a Danish physicist who won a Nobel Prize in 1922 for his contributions to the understanding of atomic structure and quantum theory. One of his most famous contributions to the field of physics is what’s known as the Copenhagen Interpretation, which is largely responsible for the concept of a “superposition of states”. In this interpretation, he claimed that a quantum particle could be in two states at the same time until observed. Therefore, a particle could exist in a superposition of decay and non-decay until its state was measured, at which point it would take on one state or another.
In Schrodinger’s cat experiment, the unfortunate kitty represents a quantum particle. Since the cat is unobserved until the box is opened, the cat can be in a superposition of dead and alive until the box is opened, at which point it will either take the state of being dead or alive. If that makes no sense whatsoever to you, then you’d be in agreement with Schrodinger.
Schrodinger came up with this thought experiment precisely to refute the Copenhagen Interpretation and show that such a superposition would be completely absurd on a larger scale. This belief rests on the idea that quantum physics obeys the same set of physics that govern the larger world. By relating the idea of a quantum superposition to something as large and tangible as a cat, he attempted to prove that nothing could be in two states at once. A particle cannot be decaying and not decaying at the same time. A cat cannot be dead and alive at the same time.
While you may still think that the Copenhagen Interpretation is a load of poppycock, most modern physicists still believe it to be correct. Apparently, quantum particles follow a far different set of rules than your average cat. To boil it down, the wave function of a quantum particle is what allows it to remain in a superposition of states; however, when that particle is observed, the wave function collapses. There are also modern physicists who oppose the Copenhagen Interpretation, most notably American physicist Hugh Everett. I’m not going to try to explain this any further, just understand that the belief of the Copenhagen Interpretation is that there’s something about being observed that makes quantum particles jump to one state or another.
Things Just Got Weirder
As if all that wasn’t confusing enough, a new thought experiment has arisen that complicates things even further, and questions the very foundations of our understanding of quantum physics. The Wigner’s friend thought experiment takes it one step further, imagining a friend of his observing the Schrodinger’s cat experiment while inside a lab with the door closed. The purpose of this thought experiment is to show that Wigner’s friend would be in a superposition of having seen and not having seen the cat until Wigner opens the lab door and observes him.
Getting too meta for you? Well, the basic idea of this thought experiment is to show that things can get very weird if the observer is themself observed. Apparently, this thought experiment has had massive implications in the physics community about the role of consciousness in quantum physics and even the nature of reality itself.
Hopefully, by reading this article, you’ve gained a greater understanding of what exactly the Schrodinger’s cat experiment is and learned about some of the biggest questions in modern physics. If you’re an actual five-year-old and didn’t understand a single word of what you just read, I’m sorry, I tried my best.