The term "quantum realm" is often used in popular culture to refer to the microscopic world governed by quantum mechanics. However, it's important to clarify that the size of the quantum realm is not strictly defined or limited to a specific scale.
Quantum mechanics describes the behavior of particles at the atomic and subatomic level, including electrons, protons, and neutrons. These particles are typically on the scale of femtometers (10^-15 meters) or smaller. At this scale, quantum effects become significant, and the classical laws of physics break down.
While the quantum realm encompasses the behavior of particles within atoms, it doesn't have a precise boundary or limitation in terms of size. The principles of quantum mechanics can be applied to larger systems as well, including molecules, nanoparticles, and even macroscopic objects under certain conditions.
Therefore, rather than thinking of the quantum realm as being strictly smaller than an atom, it's more accurate to view it as a framework that describes the behavior of particles at the atomic and subatomic level, regardless of their specific size.