Description: Dark energy is a proposed cause for the accelerated expansion of the Universe, which has been happening for the past six billion years on the largest scales. Dark energy is often described as exhibiting a "force" opposite to gravity. The effects of dark energy are inferred through indirect observations and measurements of Type Ia supernovae, the cosmic microwave background (CMB) radiation, clusters of galaxies, gravitational lensing, and baryon acoustic oscillations, which seem to indicate that dark energy makes up just over 70% of the Universe’s composition. Despite this, there is much research and debate about the nature of dark energy, whether there are different types of dark energy, whether dark energy changes over cosmic time, and alternatives to dark energy.

Related Terms:

• Cosmic Microwave Background (CMB)
• Dark Matter
• Galaxy Cluster
• Gravitational Lens
• Supernova
• Standard Candle

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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