Schrödinger’s cat, and all that

On my daily “Let’s see what’s up on Twitter” check, I glanced at yet another mention of the paradox involving Schrödinger’s cat and instinctively thought about skipping it – mostly by fear of disagreeing with the context in which the famous thought experiment was discussed.

See, I have no problem with Schrödinger’s cat. But as a physics student who took a few courses on quantum mechanics and whose PhD studies focussed on quantum optics – optics being a great platform for testing the theory of quantum mechanics – I am still surprised when I realise how often this paradox seems to appear in popular science (and not only). In fact, let’s try to roughly quantify the latter statement: a Google search for “Schrodinger’s cat” (without the Umlaut) outputs 668000 results.

On a positive note, I clicked on a few links that appeared among the results of this quick online search and found that the core idea of the thought experiment starring the famous cat was presented in a correct (albeit not necessarily clear) manner. Indeed, my problem with Schrödinger’s cat arises whenever it is hailed as the prime example for illustrating the weirdness of quantum mechanics – which simply isn’t true.

I also find it amusing that I did not encounter Schrödinger’s cat at all when  I was a physics student; in fact, the first time I heard of it was probably through some science magazine. A while later, having familiarised with the paradox and its origin, I had a conversation about this topic with a postdoc in the group where I was a PhD student. He remarked that a crucial point about Schrödinger’s hypothetical experiment is to show that physical systems exist at different scales. In this sense, if you apply quantum mechanics – a theory developed to understand the microscopic world – to macroscopic objects… you end up with a logical paradox, that is, a macroscopic system (the cat) that exists in a superposition of two logically exclusive states (alive and dead). This point is explained quite well in this post by Philip Ball (which was written precisely as a comment on the infographic published by New Scientist).

Thinking about what I read on Twitter earlier today, I have to say that most constructive effect was to encourage me once again to read a bit more about the many interpretations of quantum mechanics, which I don’t know much about! Ah, science – always something to learn.


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