According to quantum mechanics, the position of a particle, such as an atom, is described by a probability distribution rather than a definite location. This is encapsulated by the wave function, which gives the probability amplitude for finding the particle in different regions of space.
In quantum mechanics, the wave function can be spread out over space, meaning that there is a non-zero probability of finding a particle in different locations. This phenomenon is often referred to as wave function "spreading" or "delocalization."
However, it's important to note that the probability of finding an atom in a particular region of space decreases rapidly as you move away from its most probable location. The shape of the probability distribution depends on various factors, such as the atom's energy state and the potential it is subject to.
For a typical atom in its ground state, the probability distribution will be localized around the atom's nucleus, forming an electron cloud or an orbital. While the electron cloud may extend beyond the boundaries of the atom, the probability of finding the atom in regions far away from its nucleus becomes extremely small.
In the context of the entire universe, the probability of finding a particular atom in any given location outside of its immediate vicinity is vanishingly small. Quantum mechanical effects are typically only noticeable on atomic and subatomic scales, and macroscopic objects like atoms are subject to classical physics principles on larger scales.
Therefore, while there is a non-zero probability for an atom to be found in various regions of space according to quantum mechanics, the probability rapidly diminishes as you move away from its most probable location, making it extremely unlikely for an atom to be found in (almost) every place in the universe.