You will have most likely heard it being referenced to at some point in your life. TV shows like the Big Bang Theory and Futurama, and films like The Prestige have all mentioned one of the most famous thought experiments there has been in the past hundred years. Hell, even I have referred to it in the very first post I wrote for Sincy Science, albeit in a very poor joke/pun!
I am of course talking about Schrodinger’s Cat.
Now you may have heard of this feline before, but what you may not know is what the cat represents and how it came into existence. This is what I am hoping to explain.
Let us start with the scientist in question, Edwin Schrodinger. Born on the 12th August 1887, Schrodinger was a Nobel Prize winning Austrian physicist who did a lot of work in wave mechanics. He was involved in the First World War as a commissioned officer of the Austrian fortress artillery which served on the Italian front, but after the war finished he became a professor in Breslau, Poland. Later that year, he moved to the University of Zurich before eventually ending up in Berlin in 1927. However, he left Germany in 1934 due to the rise of Nazism, and spent a brief period as a fellow of Oxford University. At this point he received his Nobel Prize, shared with Paul Dirac for the publication of the wave function equations. He didn’t like Oxford though, and almost moved to Edinburgh University but for visa issues, before heading back to Austria at the University of Graz in 1936. He eventually had to leave Austria in 1938 as a result of the Anschluss with Nazi Germany, which is kind of ironic when you think about it!
Now by this point something called The Copenhagen interpretation of quantum mechanics had been around for about 9 years. This stated than quantum systems exist as a cloud of probability until an observer flicks the switch and selects one outcome for their experiment. Before being observed, the system takes on all possibilities. For example, light can be viewed as both a wave and a particle until we decide which form we want to measure, then it will adopt that form.
Schrodinger thought this interpretation was ridiculous, and this is the birth of Schrodinger’s Cat. (Please note he didn’t actually give birth to a cat, he just thought up an experiment!)
The Copenhagen interpretation seemed plausible for small quantities like photons and light waves, but Schrodinger wanted to show how daft the interpretation was by proposing something a lot bigger – a cat.
This is what he proposed……
“A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against any 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 one 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 which 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.”
So Schrodinger argued that according the Copenhagen interpretation, the cat would have to be viewed as a fuzzy blend of states, being both alive and dead at the same time whilst the box was closed, which he found ridiculous. Amongst others, Albert Einstein agreed and even proposed other questions to ridicule the interpretation further, including ‘As an animal, was the cat able to observe itself, and so collapse its own wave function?’ and’ How about bacterium?’
The initial problem was always about how observations resolve outcomes, and another theory was suggested by Hugh Everett in 1957. He hypothesised that every time an observation is made, and a specific outcome noted, then a new universe splits off – the many worlds hypothesis. In the case of Schrodinger’s cat, when the box is opened then the cat is no longer in all possible states. Instead it is either alive in one universe, or dead in another parallel universe. In one universe the poison is released, in the other it is not.
Ultimately Schrodinger’s cat is all about interpretation, for which you can see there has been and still is plenty of debate. You may be wondering if Schrodinger did indeed own a cat, and if he carried out his thought experiment in real life. Well he did have a cat named Milton, and no he did not carry out his thought experiment on it because that would be animal cruelty, you monster!