cosmologists, believe that a mysterious force known as "dark energy" is behind the reason why the universe is expanding at a faster rate. now, scientists are comparing seemingly unrelated astronomical observations to study the mysterious energy.
american scientists Eric Linder of Berkeley Lab and Robert Caldwell of Dartmouth in the United States are working to discover how dark energy interacts with the universe. in their paper, to be published in Physical Review Letters, Linder and Caldwell described two scenarios that could be used to rule out Einstein's cosmological constant and explain the nature of dark energy. the cosmological constant is a vacuum energy-the energy of empty space-that keeps gravity from pulling the universe into itself.
Linder and Caldwell call the two scenarios as "thawing" and "freezing." these scenarios are models that point toward distinctly different fates for a permanently expanding universe. in the thawing scenario, the acceleration of the expansion will gradually decrease and eventually come to a stop. expansion may continue more slowly, or the universe may even collapse. on the other hand, under the freezing scenario, acceleration continues indefinitely.
both of these scenarios rule out Einstein's cosmological constant.
"a problem with the cosmological constant is that it has the same energy density and pressure over time. dark energy, however, had to be negligible in the universe's earliest stages; otherwise the galaxies and all their stars would never have formed," said Linder.
Linder added that dark energy will govern the expansion of the universe and ultimately, its fate, because "dark energy makes up about 70% of the content of the universe, so it dominates over the matter content."
(the search for dark matter and dark energy, physicists propose search for dark energy)
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