Glossary · Thiên văn học
Dark energy
The name astronomers give to the unknown cause of the universe's accelerating expansion. The acceleration is inferred from observations, but what dark energy actually is remains unknown.
In 1998, two teams of astronomers observing very distant Type Ia supernovae found them dimmer than expected for their redshift, meaning they were farther away than expected. They concluded that the expansion of the universe is speeding up.
NASA puts dark energy at roughly 68.3–70% of the universe; CERN gives about 68%. CERN describes it as spread evenly through the universe, apparently associated with the vacuum of space, and producing a repulsive effect that accelerates the expansion.
What dark energy is remains an open question. Results released by the DESI project in 2025, combined with other data sets, hint that dark energy may change over time, but the evidence has not reached the "5 sigma" level physicists require to claim a discovery.