Dark Energy theory reverses

Contrary to all expectations, the mysterious dark energy that is pushing the Universe apart may be changing with time.

In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. According to the theory of relativity, the effect of such a negative pressure is qualitatively similar to a force acting in opposition to gravity at large scales. Invoking such an effect is currently the most popular method for explaining recent observations that the universe is expanding at an accelerating rate, as well as accounting for a significant portion of the missing mass in the universe.

During the late 1990s, observations of type Ia supernovae ("one a") suggested that the expansion of the universe is accelerating. These observations have been corroborated by several independent sources since then: the cosmic microwave background, gravitational lensing, large scale structure as well as improved measurements of the supernovae. All these elements are consistent with the concordance Lambda-CDM model.

By observing distant, powerful bursts of gamma rays (-rays), Brad Schaefer says he has preliminary evidence that the strength of dark energy is different today from when the Universe was very young. Schaefer, an astronomer at Louisiana State University in Baton Rouge, presented his results at an American Astronomical Society meeting in Washington DC.

Just minutes after the data were presented in a late afternoon session, some astronomers were already calling the bold claim into question.

An idea that arose in the late 90s, dark energy seems to act over very large distances, pushing the Universe apart at an ever increasing speed. At the moment, many researchers believe that dark energy may be a foam of quantum particles that exists throughout the vacuum of space. Under that scenario, dark energy would be a constant and unchanging force, according to Michael Turner, a cosmologist from the University of Chicago, Illinois.

Schaefer's findings, if they are true, would turn that idea on its head.