Dark energy
Dark energy is the dominant component of the universe’s energy budget and the driver of its accelerated expansion, inferred from astronomical observations in the late 1990s. In the standard ΛCDM cosmological model it contributes roughly 68–70% of the total cosmic energy density and behaves like a component with negative pressure, closely approximated by a cosmological constant with equation-of-state parameter w ≈ −1. Despite extensive observational constraints, its physical nature remains unknown.
