Dark Energy: the Cosmological Challenge of the Millennium

TL;DR

This paper reviews the observational evidence for dark energy, discusses conceptual issues related to its modeling—particularly the cosmological constant—and explores its geometrical implications in the universe's accelerated expansion.

Contribution

It provides a comprehensive review of dark energy's nature, focusing on the cosmological constant and its role in cosmic acceleration, highlighting unresolved conceptual challenges.

Findings

Dark energy constitutes about 70% of the universe's energy density.

The cosmological constant is a leading candidate for dark energy.

Universe with a cosmological constant exhibits unique geometrical features.

Abstract

Recent cosmological observations suggest that nearly seventy per cent of the energy density in the universe is unclustered and has negative pressure. Several conceptual issues related to the modeling of this component (`dark energy'), which is driving an accelerated expansion of the universe, are discussed with special emphasis on the cosmological constant as the possible choice for the dark energy. Some curious geometrical features of a universe with a cosmological constant are described and a few attempts to understand the nature of the cosmological constant are reviewed.