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DARK ENERGY
Dark energy - the most abundant and the most mysterious stuff in the Universe. Is it even "stuff"? Perhaps it is a strange property of empty space or rather space as empty as it can possibly be. When Albert Einstein developed his theory that gravity is curved spacetime, General Relativity, he applied it to the whole Universe - as he knew it. His equations told him that the Universe should be expanding or contracting. However, he thought it to be neither. Then he made what he later called his "greatest blunder." He added a term to his equation called the "cosmological constant" to keep it static. Is it just a term in an equation or a fundamental property of the vacuum?
Later we discovered that the Milky Way is only one of many galaxies. Hubble discovered that they are rushing away - the whole Universe is expanding! Einstein could have predicted that to add to his many revolutionary discoveries. Cosmologists debated: Will the expansion never stop, just slowing down by the gravitational attraction between the galaxies, time being eternal? Perhaps gravity will win, taking over, the Universe collapsing to end in a Big Crunch, the end of time.
Then in 1998, the shocking discovery was made that the expansion was happening faster and faster. Accelerating! Was this due to Einstein's cosmological constant after all? If that happens forever, will the Universe become emptier and emptier until there is not one atom in a cubic light year? Today about 2/3 of the total energy content of the Universe is dark energy. Does it have the same tiny value everywhere throughout the Universe, not changing even as the Universe expands while the matter density decreases? Astronomers are studying the most distant galaxies to try to answer these questions. The future of the Universe depends on it! |