dark energy, repulsive force that opposes the self-attraction of matter (see gravitation) and causes the expansion of the universe to accelerate. The search for dark energy was triggered by the discovery (1998) in images from the Hubble Space Telescope of a distant supernova that implied an accelerating, expanding universe, which in turn required a new cosmological model (see cosmology). Although dark energy is predicted in particle physics, it has never been directly observed. It is generally agreed, however, that dark energy dominates the universe, which is projected to have a composition of about 68% dark energy, 27% dark matter, and 5% normal visible matter such as stars. By 2006, astronomers using the space telescope to examine more distant supernovas had found evidence of the effects of dark energy dating to 9 billion years ago. Observations with the Chandra X-ray Observatory, published in 2008, indicate that dark energy is also retarding the growth of distant galaxy clusters.
The concept of dark energy was first proposed, and then discarded, by Albert Einstein early in the 20th cent. His theory of general relativity implied that the pull of gravity would make the universe collapse, but, like many scientists of his time, he assumed the universe to be static and unchanging. To make his equations fit these assumptions, Einstein added a "cosmological constant" whose effect was repulsive. When American astronomer Edwin Hubble discovered that the universe was expanding, it was assumed that the universe must be slowing down because of gravity and might even come to a halt. This led Einstein to remove the cosmological constant from his equations and to say that it had been the biggest blunder of his career.
"dark energy." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (August 17, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/dark-energy
"dark energy." The Columbia Encyclopedia, 6th ed.. . Retrieved August 17, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/dark-energy
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.