The contradictions between general relativity (GR) and quantum physics arise primarily due to the fundamental differences in their underlying principles and mathematical formulations. While GR describes the behavior of gravity and the large-scale structure of the universe, quantum physics deals with the behavior of particles and their interactions on a small scale.
Here are some of the key contradictions between GR and quantum physics:
Scale: GR is successful in describing the behavior of gravity on cosmological scales and the curvature of spacetime, while quantum physics is applicable at the microscopic level, describing the behavior of particles and their interactions. These two frameworks have not been fully reconciled to provide a comprehensive theory that applies to all scales.
Nature of Spacetime: In GR, spacetime is described as a smooth, continuous, and curved entity. Quantum physics, on the other hand, involves discrete entities and quantized quantities. Combining the smooth nature of spacetime in GR with the discrete nature of quantum physics poses a challenge in their unification.
Singularities: GR predicts the existence of singularities, such as those found at the centers of black holes or the Big Bang. These singularities represent points of infinite curvature and density, where our understanding of physics breaks down. Quantum physics, on the other hand, aims to resolve such singularities and provide a consistent description of physical phenomena.
Renormalization: In quantum field theories, including the Standard Model, the calculations often involve infinities that arise due to the self-interactions of particles. These infinities are removed through a process called renormalization, which allows for finite and meaningful predictions. However, when trying to apply renormalization techniques to the gravitational field in the context of GR, the calculations encounter severe difficulties and inconsistencies.
Information Loss: The "information loss paradox" arises when trying to reconcile quantum mechanics with black hole evaporation, as predicted by Hawking radiation. According to quantum mechanics, information is always conserved, but if a black hole evaporates completely, it appears that information is lost. Resolving this paradox requires a deeper understanding of the interplay between quantum physics and gravity.
These contradictions highlight the need for a more complete theory, often referred to as a theory of quantum gravity, that successfully merges the principles of GR and quantum physics. Researchers are actively exploring various approaches, such as string theory, loop quantum gravity, and other quantum gravity frameworks, in an attempt to achieve this unification.