The space between the quantum scale of existence and the stellar/macro scale of existence is occupied by the realm of classical physics. Classical physics, which encompasses the theories of motion, electromagnetism, and thermodynamics, deals with phenomena that occur on a macroscopic scale, such as the motion of planets, the behavior of fluids, and the propagation of light.
At the quantum scale, the behavior of particles is described by quantum mechanics, which introduces concepts such as wave-particle duality, superposition, and quantum entanglement. Quantum mechanics provides a highly accurate description of the microscopic world, but its predictions deviate from classical physics when dealing with extremely small particles and short distances.
The transition from the quantum to the classical realm occurs due to a phenomenon called decoherence. Decoherence is the process by which a quantum system interacts with its environment, causing it to lose its quantum properties and behave classically. As the number of particles involved in a system increases, their interactions with the environment become more significant, leading to a classical description of the system's behavior.
In summary, the space between the quantum and macro scales is occupied by classical physics, which provides a framework for understanding the behavior of macroscopic objects. While quantum mechanics accurately describes the behavior of particles at the microscopic level, classical physics offers a reliable approximation for most everyday phenomena and the behavior of large-scale objects such as stars and galaxies.