Quantum physics is fundamental in understanding which two major physical theories?

Quantum physics plays a critical role in the development and understanding of both quantum mechanics and relativity. These two theories represent foundational aspects of modern physics that explain phenomena occurring at very small scales (quantum mechanics) and at very high speeds or under strong gravitational fields (the theory of relativity).

Quantum mechanics describes the behavior of particles at atomic and subatomic levels, addressing the probabilistic nature of particles, wave-particle duality, and the concept of superposition. It provides a framework for understanding the interactions of fundamental particles, which is essential for developing technologies like semiconductors and lasers.

Relativity, particularly Einstein's theory of special relativity, complements quantum mechanics by describing the effects of high-velocity motion and the influence of gravity on time and space. The interactions between these two theories are particularly significant in areas like quantum field theory and the search for a unified theory of gravitation that incorporates quantum mechanics.

In contrast, the other choices either focus on classical theories that don’t integrate quantum concepts or represent fields of study that don’t have a direct foundational relationship with quantum physics. Thus, the correct link between quantum physics and the major physical theories is best represented by the combination of quantum mechanics and relativity.