According to the principles of quantum mechanics, particles can exist in a superposition of states, which means they can be in multiple states or locations simultaneously. This phenomenon is known as wave-particle duality.
In quantum mechanics, particles are described by wavefunctions, which are mathematical functions that evolve over time. The wavefunction contains information about the probabilities of different outcomes when a measurement is made. Before a measurement is made, the particle can be in a superposition of multiple states, meaning it has a certain probability of being in each of those states.
For example, in the famous double-slit experiment, if you send individual particles, such as electrons or photons, through two slits, they can exhibit wave-like behavior and create an interference pattern on a screen behind the slits. This suggests that the particle simultaneously passes through both slits and interferes with itself.
However, when a measurement is made to determine the particle's position, the wavefunction "collapses" into a single state corresponding to a specific location. This collapse is a probabilistic process, with the outcome determined by the probabilities encoded in the wavefunction.
It's important to note that the concept of being in multiple places simultaneously does not imply that particles have a physical extent spread across those locations. The wavefunction describes the probabilities associated with different measurement outcomes, but it does not represent a physical distribution of the particle in space. When a measurement is made, the particle is found at a specific location consistent with the probabilities dictated by the wavefunction.
The phenomenon of particles existing in superpositions and exhibiting wave-particle duality is a fundamental aspect of quantum mechanics. It has been extensively verified through experiments and is considered one of the most remarkable and puzzling features of the quantum world.