In quantum field theory, particles are indeed considered excitations or disturbances in their respective fields. Each type of particle, such as electrons, quarks, or photons, corresponds to a specific field in the Standard Model of particle physics. These fields permeate all of space and interact with each other.
While particles are described as waves in these fields, their localization is a result of a phenomenon known as wavefunction collapse or particle detection. When a particle is measured or observed, its wavefunction collapses to a specific state or location. This collapse is a probabilistic process, governed by the rules of quantum mechanics.
Prior to measurement, a particle's wavefunction is typically described by a superposition of various possible states or locations, meaning it exists in multiple states simultaneously. However, upon interaction with a measuring device or through an observation, the wavefunction collapses, and the particle is found in a particular state or location corresponding to the measurement outcome.
The process of measurement or observation is still an area of ongoing research and interpretation within quantum mechanics. There are different interpretations, such as the Copenhagen interpretation or the Many-Worlds interpretation, which offer different perspectives on the nature of wavefunction collapse and the resulting particle localization.
It's important to note that the concept of particle localization is a manifestation of the probabilistic nature of quantum mechanics. The exact position of a particle is not determined until it is measured, and prior to measurement, it is described by a probability distribution or a wavefunction that extends over space.