In quantum physics, particles can exhibit a phenomenon called wave-particle duality, which means that they can exhibit both particle-like and wave-like properties. This duality is described by a mathematical framework known as quantum mechanics.
According to quantum mechanics, the state of a particle is described by a mathematical object called a wave function. The wave function contains information about the probabilities of different outcomes when the particle is measured. Importantly, the wave function can spread out over space, which allows for the possibility of a particle existing in multiple places simultaneously.
This spreading out of the wave function is referred to as superposition. It means that the particle is in a combination or superposition of different states or locations. However, when the particle is measured or observed, its wave function collapses into a single definite state, and it appears as if the particle is localized at a specific position.
The famous example often used to illustrate this concept is the double-slit experiment. In this experiment, particles such as electrons or photons are fired at a barrier with two small slits. If the particles are fired one by one, they can exhibit an interference pattern on a screen behind the barrier, suggesting that they behave as waves that interfere with each other. However, when a measurement is made to determine which slit the particle passes through, the interference pattern disappears, and the particles behave as particles with definite positions.
The idea that particles can exist in multiple places simultaneously is a consequence of the mathematical formalism of quantum mechanics. It is important to note that the concept of "being in two places at once" is not the same as physically splitting the particle into two separate entities. Rather, it describes the probabilistic nature of the particle's behavior and the superposition of different states allowed by the mathematics of quantum mechanics.