According to the principles of quantum mechanics, the state of a particle is described by a wave function, which evolves over time according to a mathematical equation known as the Schrödinger equation. The wave function provides a probabilistic description of the possible outcomes of measurements that can be made on the particle.
In the framework of quantum mechanics, it is generally understood that a particle does not possess definite properties, such as position or momentum, until it is observed or measured. Instead, the particle exists in a superposition of multiple states, where each state corresponds to a different possible outcome. This is often referred to as the principle of superposition.
When a measurement is made on the particle, the wave function "collapses" into one of the possible states, and the corresponding property of the particle becomes definite. This collapse is described by a process called wave function collapse or quantum measurement. The specific outcome of the measurement is probabilistic and governed by the probabilities encoded in the wave function.
The interpretation of quantum mechanics is a topic of ongoing debate among physicists, and there are different interpretations that offer various explanations for the nature of wave function collapse and the role of observation. These interpretations include the Copenhagen interpretation, the many-worlds interpretation, and the pilot-wave theory, among others. Each interpretation provides a different perspective on the question of whether a particle exists before it is observed.
In the Copenhagen interpretation, which is one of the most commonly used interpretations, the act of observation is considered essential for the collapse of the wave function and the emergence of definite properties. In this view, the particle's properties are not considered to exist objectively prior to measurement. Other interpretations, such as the many-worlds interpretation, propose that all possible outcomes of a measurement exist simultaneously in different branches of a "multiverse," and observation merely selects one of those branches.
It's important to note that the precise nature of wave function collapse and the interpretation of quantum mechanics are still subjects of active research and philosophical investigation. While quantum mechanics has been remarkably successful in describing and predicting the behavior of particles at the microscopic scale, the philosophical implications and the exact underlying mechanisms are still being explored.