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How does general relativity help scientists study the evolution of the universe?

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Brian Greene sits in a living room, holding a pen, with handwritten equations m = E/c^2 and E = mc^2 on a whiteboard beside him, highlighting c^2 as the speed of light. — relativity Brian Greene kicking off his *Your Daily Equation* video series with Albert Einstein's famous equation E = mc².

General relativity provides the fundamental mathematical framework for cosmology, the study of the universe's origin and structure. By treating gravity as a geometric property of space-time, Einstein’s field equations allow scientists to model the universe's large-scale evolution based on its matter-energy content.12

Key ways general relativity aids this study include:

Predicting Dynamics: Early solutions by Aleksandr Friedmann demonstrated that the universe is not static but dynamic, capable of expansion or contraction. This provided the theoretical basis for the big-bang model.342
Defining Fate: The theory links the universe's expansion rate—measured by Hubble’s constant—and its density to its ultimate fate, such as whether it will expand indefinitely or eventually collapse.2
Accounting for Dark Energy: General relativity incorporates dark energy as a component of the stress-energy tensor. This repulsive force, which acts against gravity, explains the observed acceleration of the universe's expansion.5

By relating the distribution of matter and energy to the curvature of space-time, general relativity remains the essential tool for interpreting observational data about the history and structure of the cosmos.512