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Dead or alive – or both? The fate of Schrödinger’s Cat has challenged the premises of quantum physics - Catholic Herald
Police were recently called to disperse some animal rights protesters from the Cavendish Laboratory in Cambridge after they got wind of news that a group of physicists were attempting to replicate the results of the Schrodinger’s Cat experiment.
OK, well, this didn’t actually happen, but it’s the sort of story that could conceivably be reported on the first day of April. Nevertheless, since Erwin Schrödinger suggested his thought experiment in 1935, more ink has been spilt over it than many experiments that really have been performed.
Originally, Schrödinger proposed his thought experiment in order to argue that something was wrong with quantum physics. Quantum physics is a very powerful theory that describes many phenomena. This theory emerged at the beginning of the 20th century with Max Planck’s discovery that if energy came in little packets called quanta, then this could account for the range of frequencies of radiation emitted from warm bodies. It is from these quanta that the science of quantum physics takes its name.
In the decades that followed, many other discoveries were made in quantum physics. One of the most significant was that of Werner Heisenberg who in 1927 formulated his uncertainty principle. Heisenberg’s uncertainty principle implies that it is impossible to perform an exact measurement of both a particle’s position and momentum. Naively, we might suppose this means that there is an exact description of the particle which we will never know. However, this is not the view adopted by many physicists.
Instead, they suppose that the particle itself doesn’t have a definite position and momentum. It is as though physical reality is fuzzy at the microscopic level. The reason we don’t notice this fuzziness at the macroscopic level is that all the indeterminacies at the microscopic level average each other out. Because of this averaging out, we can therefore make objective truth claims about the physical states of the macroscopic objects around us.
But Schrödinger wasn’t happy with this explanation. He worried that if quantum physics provided a complete description of physical reality, then it wouldn’t be possible to limit the domain of indeterminacy to the microscopic realm; rather these indeterminacies would propagate up to macroscopic objects. This worry provided the motivation for the Schrödinger’s Cat thought experiment.
In this thought experiment, Schrödinger places his cat in a steel chamber together with a tiny bit of radioactive substance, a flask of poison, a hammer contraption, and a Geiger counter. The Geiger counter is hooked up to the hammer contraption so that if the Geiger counter detects that one of the radioactive atoms has decayed, then it will cause the hammer contraption to smash the flask of poison, thus killing the cat. But according to quantum physics, the radioactive atom is not in a definite state of either having decayed or not decayed.
Rather, the radioactive atom is in an indeterminate state of being decayed and non-decayed. This means the poison flask will be in an indeterminate state of being smashed and not smashed, from which it follows that the cat will be in an indeterminate state of being dead and alive. Until the steel chamber is opened and the state of the cat is observed, there will be no fact of the matter about what state the cat is in.
Given this reductio ad absurdum, the reasonable thing to do would be to question the premises of quantum physics that lead to it. However, in recent decades, it has become increasingly common for philosophers of physics to accept all the premises of quantum physics and to embrace the absurdity. In doing so, they suppose that Schrödinger himself is also a quantum system, and that when he opens the steel chamber, Schrödinger also enters into an indeterminate state of seeing the cat alive and seeing it dead.
Although there is much mathematical elegance to this interpretation of quantum physics, there’s a high price to pay. For in supposing that quantum physics is a complete scientific theory, one ends up doubting the reality of all the scientific observations on which this theory is based. The only reasonable conclusion to draw is that quantum physics is not a complete description of reality.
Given the lack of consensus among physicists on how to interpret quantum physics, it is surprising that so many people think that physics can do what was once the job of metaphysics, namely, explaining the ultimate cause of everything. Physicists will no doubt continue to put forward their interpretations of quantum physics, but if a consensus is to be achieved, the interpretation must help us to understand physical reality as something intelligible. What it mustn’t do is sound like a theory that’s based on an April Fool’s joke.
This article originally appeared in the April 2024 issue of the Catholic Herald. To subscribe to our award-winning, thought-provoking magazine and have independent and high-calibre counter-cultural Catholic journalism delivered to your door anywhere in the world clickhere.
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