What is Dirac large numbers hypothesis?

The Dirac Large Numbers Hypothesis is a speculative idea proposed by the British physicist Paul Dirac in 1937. The hypothesis suggests a relationship between the fundamental constants of nature and the scale of the universe. Specifically, Dirac noted an intriguing observation that certain large dimensionless numbers, which arise in the physics of the universe, might have a deep physical significance. One of the central points of the hypothesis is the observed ratio between the gravitational force and electrostatic force. Dirac suggested that as the universe expands, the values of physical constants might change in a way that keeps these large dimensionless numbers constant over cosmic time. For example, he proposed that the ratio of the mass of the electron to the mass of the universe might be constant. This led him to speculate that the universe's expansion and the evolution of physical constants may be fundamentally linked, implying that certain aspects of physics might vary over cosmological timescales. Dirac's Large Numbers Hypothesis was influential in prompting further investigation into the relationships between different physical phenomena and has connections to various topics in cosmology and theoretical physics, notably in discussions about the nature of forces and the physical structure of the universe. However, the hypothesis itself remains somewhat controversial and is not widely accepted in the mainstream physics community without further empirical support.