Reconciling quantum mechanics and gravity is a major challenge in theoretical physics, and it arises due to fundamental differences between the two theories. Here are a few reasons why it is difficult to merge quantum mechanics and gravity:
Different scales: Quantum mechanics describes the behavior of particles and fields on very small scales, such as atoms and subatomic particles. On the other hand, gravity is a theory that explains the dynamics of spacetime and massive objects on cosmological scales. The stark contrast in the scales at which these theories operate makes it challenging to reconcile them mathematically.
Incompatibility of principles: Quantum mechanics is based on principles such as superposition and uncertainty, where particles can exist in multiple states simultaneously and measurements have inherent limitations. Gravity, as described by Einstein's general theory of relativity, is based on the curvature of spacetime due to the presence of matter and energy. These principles are very different from those of quantum mechanics, making it difficult to find a common framework that encompasses both.
Renormalization problem: In quantum field theory, which is the framework for combining quantum mechanics and special relativity, a phenomenon called "renormalization" arises. It involves the need to cancel out infinite values that appear in certain calculations. While renormalization has been successful in the quantum field theories of other fundamental forces, it becomes problematic when gravity is included. The infinities encountered in gravity calculations cannot be easily renormalized, suggesting a fundamental incompatibility between quantum mechanics and gravity.
No established theory of quantum gravity: Despite numerous attempts, a complete and widely accepted theory of quantum gravity has not yet been developed. Various approaches, such as string theory, loop quantum gravity, and others, offer different perspectives on how to unify the two theories. However, these approaches are still under active research and do not have experimental confirmation.
Researchers continue to explore possible frameworks and solutions to reconcile quantum mechanics and gravity. The quest for a theory of quantum gravity is an active area of research, and it is hoped that future breakthroughs will shed light on this fundamental puzzle of theoretical physics.