The interplay between general relativity, quantum mechanics, and string theory is a complex and ongoing area of research in theoretical physics. Currently, there is no universally accepted theory that seamlessly combines all three theories into a single, comprehensive framework. However, in different physical regimes, one theory may be more applicable than the others.
General relativity is the theory of gravity and provides a description of the force that governs the large-scale behavior of objects in the universe. It successfully explains phenomena like the motion of planets, the bending of light around massive objects, and the expansion of the universe. General relativity is primarily relevant when dealing with macroscopic objects and cosmological scales.
Quantum mechanics, on the other hand, describes the behavior of particles on a microscopic scale, such as atoms and subatomic particles. It is incredibly successful in explaining phenomena like particle interactions, energy quantization, and wave-particle duality. Quantum mechanics is essential in many areas of physics, including quantum field theory, particle physics, and condensed matter physics.
String theory is a theoretical framework that attempts to unify general relativity and quantum mechanics by postulating that fundamental particles are not point-like but instead tiny, vibrating strings. It is a quantum theory of gravity and is expected to incorporate both general relativity and quantum mechanics. However, string theory is still a subject of active research and does not yet have definitive experimental support.
In current physics research, these three theories are typically used independently in different contexts. General relativity is used to study gravitational phenomena at macroscopic scales, such as black holes and the early universe. Quantum mechanics is employed to describe the behavior of particles and their interactions at microscopic scales. String theory is explored in attempts to find a unified theory that encompasses both gravity and quantum mechanics.
While there have been attempts to merge these theories, such as certain approaches in string theory, a complete and widely accepted synthesis remains elusive. Researchers continue to investigate the nature of the fundamental laws of physics, striving for a comprehensive theory that incorporates all the phenomena described by general relativity, quantum mechanics, and potentially string theory.