I have been reading about the history of quantum theory and how this history has shaped the different interpretations of it. ‘Helgoland’, by Carlo Rovelli, ‘Quantum’, by Manjit Kumar, and ‘What is real?’, by Adam Becker, are excellent books that discuss these issues. The weirdness of quantum physics is fascinating. And an experiment that illustrates this weirdness wonderfully is the quantum bomb experiment.

Imagine that you have several bombs that are activated—i.e., they explore—when a photon (the particle that light is made of) passes through them. You need to get a bomb for a mission, but some of the bombs do not work anymore: their photon detector is broken. The only way to check whether a bomb works is to send a photon and see what happens. Can you find a bomb that works without actually make it explode?

It turns out that using quantum physics you can. Intuitively, when the bomb works, it is a detector to observe where the photon is, so it forces the collapse of the wave function; but when it does not work, quantum superposition is maintained. Using this difference, one can construct a device that can tell you whether the bomb works even when the photon does not go through it. I am not going to explain the inner workings of this device, but I’ll leave a couple of videos that do so.

The Bomb Experiment, by Sabine Hossenfelder:

Elitzur-Vaidman Bombs, by Barton Zwiebach: