Cosmology and Gravitation Theories

Cosmology and gravitation theories concern the large-scale structure, composition, and history of the universe, drawing on observations of the cosmic microwave background, supernovae, and baryon acoustic oscillations to measure fundamental quantities like the Hubble constant and the density of matter and energy. General relativity provides the governing framework, but mounting evidence that roughly 70 percent of the universe's energy budget consists of a poorly understood "dark energy" driving accelerated expansion has pushed researchers to probe whether Einstein's equations need modification at cosmological scales. Two of the most pressing open questions are the precise nature of dark energy — whether it behaves as a simple cosmological constant or evolves over time — and a growing tension between different methods of measuring the universe's current expansion rate, which may signal new physics beyond the standard cosmological model. Inflation, the hypothesized period of rapid early expansion, remains a third active frontier, with ongoing efforts to detect its predicted signature in the polarization of the cosmic microwave background.

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Keywords

Cosmological ParametersDark EnergyCosmic Microwave BackgroundInflationModified GravitySupernovae