According to quantum mechanics, the behavior of subatomic particles, including atoms, is described by wave functions that determine the probability distribution of finding the particle in different locations. The wave function assigns a probability amplitude to each possible location, and the square of the absolute value of the probability amplitude gives the probability of finding the particle at a specific position.
In quantum mechanics, the concept of wave function collapse occurs when a measurement is made, and the particle's position is determined. Until the measurement takes place, the particle is described by a superposition of possible states, which means it can exist in multiple locations simultaneously with different probabilities.
However, it's important to note that the probability distribution is not evenly spread across the entire universe for an atom or any other particle. The distribution is determined by various factors, such as the specific quantum state of the particle, its interactions with other particles, and the potential energy landscape it experiences.
While it is theoretically possible for the wave function to have non-zero probability amplitudes in multiple locations, the probability of finding an atom in (almost) every place in the universe simultaneously is extremely low for typical scenarios. The vastness of the universe and the constraints imposed by various physical interactions make such scenarios highly improbable.
In practical terms, the behavior of macroscopic objects, including atoms, is described by classical physics and their wave functions typically localize to specific regions determined by the dynamics and interactions of the system. Quantum effects become more pronounced at the microscopic scale and in systems involving particles with very low masses, such as electrons and photons.