The evidence for dark energy is derived from several independent observations and experiments in the field of cosmology. While our understanding of dark energy is not yet complete, the existing evidence strongly suggests its existence. Here are some key pieces of evidence:
Supernovae observations: In the late 1990s, astronomers studying the brightness of distant supernovae made a surprising discovery. They found that the observed brightness was lower than expected, indicating that the expansion of the universe was accelerating rather than slowing down. This observation, for which Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess were awarded the Nobel Prize in Physics in 2011, provides strong evidence for the existence of dark energy.
Cosmic Microwave Background (CMB): The CMB is the afterglow of the Big Bang and provides valuable information about the early universe. Precise measurements of the CMB, such as those made by the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck satellite, have been used to determine the composition of the universe. These measurements support the presence of dark energy, which is necessary to explain the observed patterns in the CMB.
Large-scale structure of the universe: The distribution of galaxies on large scales can also provide insights into the nature of dark energy. Experiments like the Sloan Digital Sky Survey (SDSS) have mapped the distribution of galaxies in the universe. These observations indicate that the large-scale structure is consistent with the presence of dark energy.
Baryon Acoustic Oscillations (BAO): BAO refers to periodic fluctuations in the distribution of matter in the early universe. Measurements of BAO by surveys like the BOSS (Baryon Oscillation Spectroscopic Survey) have provided additional evidence for the existence of dark energy.
While these lines of evidence strongly support the existence of dark energy, its precise nature remains unknown. Dark energy is often attributed to a property of space itself, known as the cosmological constant, but alternative theories such as modified gravity or dynamical dark energy models are also being explored. Ongoing and future observations, as well as theoretical developments, aim to further refine our understanding of dark energy.