What exactly is a particle -- in particular in constrast to a wave My first thread on this topic went soon downhill after two participants could not agree and someone locked the thread. But I have questions left. The post went like this: One of the biggest conundrums is the wave/particle duality of quantum systems as it is observed in two-slit experiments. The interference pattern seen in a two-slit experiment suggests that the quantum system is a wave. But what exactly makes us say that the quantum system also behaves like a particle? My partial answer is: 1. On the screen behind the two slits we see individual, point-like marks very much like we would expect from a particle (imagine a little ball) hitting the screen, and certainly not from a wave front hitting the screen. 2. With sufficiently capable detectors it can be shown that the energy transmitted/released while creating the mark is quantized, i.e. it cannot continuously made arbitrarily small, like could be expected from a wave amplitude. My question: Are there other points worth noting that suggest to say that the quantum system behaves like a particle? Is it correct to say that we don't know that it is a particle, we only make observations and interpret them? The question would then be: apart from the two observations above, are there other, different observations suggesting particle? Among others, the following answer was quite helpful: My followup question would be: is this absence of the multi-location property what distinguishes the "particle" from a "wave", meaning that we can detect every wave in more than one location at the same time. (If it does not work for every wave, it is not clearly distinguishing). To be honest: what I am after is a hard argument why we cannot dismiss the particle idea altogether. What is it that a particle can do that we cannot attribute to a wave plus its collapse?