In quantum mechanics, the behavior of particles is described by wave functions, which are mathematical functions that represent the probability distribution of finding a particle at different positions in space. According to the principles of quantum mechanics, particles do not have a definite position until they are observed or measured. Instead, they exist in a superposition of states, where they can be found in multiple locations simultaneously.
However, when a measurement is made on a quantum system, the wave function "collapses" to a specific state corresponding to one of the possible measurement outcomes. This collapse is known as the measurement problem, and it remains a subject of philosophical and interpretational debate in quantum mechanics.
In everyday macroscopic objects, such as tables, chairs, or any object we commonly observe, the behavior of individual particles is governed by quantum mechanics, but their collective properties average out and exhibit classical behavior. This phenomenon is known as quantum decoherence. The interaction of a macroscopic object with its environment leads to a loss of quantum coherence, causing the system to behave classically and giving the appearance of a definite position in space.
In other words, the superposition of quantum states becomes negligible at macroscopic scales due to the continuous interactions and entanglement with the surrounding environment. As a result, objects in our everyday experience appear to have well-defined positions and exhibit classical behavior, even though their underlying constituents follow the probabilistic rules of quantum mechanics.