Dark Energy Expansion

Dark energy — a hypothetical form of energy permeating all space, responsible for the accelerating expansion of the universe — was discovered in 1998 when two teams studying Type Ia supernovae (which serve as 'standard candles' of known brightness) found they were dimmer than expected: the universe wasn't just expanding but expanding faster and faster. This won the 2011 Nobel Prize in Physics. Dark energy appears to comprise approximately 68% of the total energy of the observable universe. The nature of dark energy is completely unknown — the greatest mystery in physics and cosmology. The leading candidate is the cosmological constant (Λ) — Einstein's 'greatest blunder' that he introduced to make a static universe and then removed, which turned out to be right for the wrong reason. Other candidates: quintessence (a scalar field that varies in space and time); phantom energy (which would lead to a 'Big Rip' in which the universe tears itself apart in 22 billion years); or a sign that general relativity breaks down at cosmological scales. The DESI (Dark Energy Spectroscopic Instrument) survey (2024) found hints that dark energy may not be constant — potentially the biggest physics discovery in decades.