Changes

[[Image:56200main dark expansion-lg.jpg|300px|right]]'''Dark energy''' is one of two concepts (the other is [[dark matter]]) that [[Big Bang]] [[cosmology|cosmologists]] and [[astrophysicists]] have invented to explain the most serious differences to date between [[astronomy|astronomical]] observations of an [[expanding universe]] and their own expectations. It is "the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate";<ref>[http://www.encyclopediaproject.net/wiki/Dark_energy New World Encyclopedia]</ref> Astronomers and cosmologists have been speculating on the nature of this dark energy for ten years.  

[[Image:56200main dark expansion-lg.jpg|300px|right]]The '''dark energy''' hypothesis is one of two concepts that [[Big Bang]] [[cosmology|cosmologists]] and [[astrophysicists]] to support the [[expanding universe]] theory. Along with [[dark matter]], it was invented to explain the most serious differences to date between [[astronomy|astronomical]] observations of an [[expanding universe]] and their own expectations. It is "the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate";<ref>[http://www.encyclopediaproject.net/wiki/Dark_energy New World Encyclopedia]</ref> Astronomers and cosmologists have been speculating on the nature of this dark energy for {{years ago|1998} years.  

== The problem ==

== The problem ==