The behavior of particles as both waves and particles, and the ability to exist in multiple places simultaneously, is a fundamental aspect of quantum mechanics known as wave-particle duality and superposition.
In quantum mechanics, particles are described by wave functions, which are mathematical descriptions that encode the probabilities of different outcomes when measuring properties of the particles. The wave function evolves over time according to the Schrödinger equation, which governs the behavior of quantum systems.
When a particle is not being measured or observed, its wave function can spread out and exhibit wave-like behavior, creating interference patterns and exhibiting properties such as diffraction. This is similar to how waves behave when they pass through slits or interfere with each other.
On the other hand, when a particle is measured or observed, its wave function collapses to a specific state or position, and it behaves like a localized particle with definite properties. This collapse of the wave function is described by the process of wave function collapse or quantum measurement, and it results in the particle being detected at a specific position or having a specific property.
The ability of particles to exist in multiple places simultaneously is related to the concept of superposition. A superposition occurs when a particle's wave function combines multiple possible states or positions. For example, an electron can be in a superposition of being in two different locations at the same time, meaning that it has a certain probability of being found in either location when measured. This superposition is maintained until a measurement is made, which causes the wave function to collapse to a single outcome.
The phenomenon of wave-particle duality and superposition has been extensively confirmed by experiments in quantum mechanics, such as the famous double-slit experiment, where particles exhibit interference patterns suggesting wave-like behavior. Other experiments, such as the Stern-Gerlach experiment and the delayed-choice quantum eraser, also demonstrate the ability of particles to exhibit both wave-like and particle-like behavior.
It's important to note that the wave-particle duality and the ability to exist in multiple states simultaneously are unique to the quantum realm and do not have direct analogs in our everyday macroscopic world. They are fundamental features of the quantum mechanical description of particles and are essential for understanding and predicting the behavior of systems at the microscopic scale.