b. What is wave particle duality?
One of the most fascinating and counter-intuitive concepts of quantum mechanics is that all particles in the quantum regime exhibit both wave and particle properties.
The most popular interpretation of this fact is that as long as a quantum object does not interact with the environment it behaves like a wave, while the interaction with the environment is particle like (for specialists: collapse of the wave function). But this is a crude picture and does not contain all aspects of the wave-particle duality.
As in our everyday world particles and waves are very distinct phenomena it is convenient to describe certain experiments with the particle or wave representation. There are a few cases in which it is not possible to describe a experiment in one of those classical pictures, especially if an experiment exploits the wave-particle duality, then the whole quantum mechanical description has to be used which is in most cases counter intuitive. Normally a physicist can decide whether his experiment can be better described by the wave or the particle picture. Statistical phenomena, like they appear in quantum statistics, are easier described in the particle picture. The quasi particle of a spin wave is the magnon. The next section will treat the question
in more detail.