The term quantum theory of relativity is often misunderstood. It does not refer to a single established theory, but rather describes the ongoing scientific quest to unify two fundamental theories of physics: quantum mechanics, which governs the microscopic world of particles, and general relativity, which describes gravity and the macroscopic universe.
Currently, physics operates with two separate and highly successful theories. Quantum mechanics perfectly describes the behavior of atoms, subatomic particles, and forces like electromagnetism. General relativity accurately explains gravity and the motion of planets, stars, and galaxies. However, these theories become incompatible in extreme conditions such as inside black holes or during the first moments after the Big Bang, where both quantum effects and strong gravity are important.
The scientific field dedicated to finding this unified theory is called quantum gravity. Several promising candidate theories are being actively researched. String theory proposes that fundamental particles are actually tiny vibrating strings in multiple dimensions. Loop quantum gravity suggests that space-time itself has a discrete, quantum structure. Other approaches include causal sets and emergent gravity theories, each offering different perspectives on how to merge quantum mechanics with general relativity.
Unifying quantum mechanics and general relativity faces enormous challenges. The theories use different mathematical frameworks and have seemingly incompatible fundamental principles. Experimental verification is nearly impossible due to the extreme energy scales required. Currently, no complete unified theory exists, though researchers continue making progress in specific areas and gaining mathematical insights. The quest for quantum gravity remains one of physics' greatest unsolved problems.
To summarize what we have learned: The term quantum theory of relativity describes the ongoing quest to unify quantum mechanics and general relativity into a single theory called quantum gravity. While no complete unified theory exists yet, researchers continue working on promising approaches like String Theory and Loop Quantum Gravity. Success in this endeavor would revolutionize our understanding of extreme phenomena like black holes and the birth of our universe.