Daria Kulkova/Alamy
I RECENTLY walked by a physics department office that had a sticker on it saying something like “Heisenberg may or may not have been here”. This is in part a nod to the quantum cat, which, while it is inside a box with no observer, may be dead or alive. We aren’t sure until we look at it.
This feline thought experiment is intended to help us visualise a deep conceptual difficulty in quantum mechanics: the fact that the act of observing seems to determine what state matter is in. This is due to the probabilistic nature of quantum mechanics …
