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What Was It Like When Dark Energy First Took Over The Universe?

27 Feb 2019, 15:01 UTC
What Was It Like When Dark Energy First Took Over The Universe?
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As we look to greater and greater distances, we find that objects are not only receding away from us at greater and greater apparent speeds, but that any individual, distant galaxy began accelerating, from our perspective, some 6 billion years ago. Two of the most distant quasars, shown inset, support this picture as well. (ILLUSTRATION: NASA/CXC/M.WEISS; X-RAY: NASA/CXC/UNIV. OF FLORENCE/G.RISALITI & E.LUSSO)For billions of years, dark energy couldn’t have been detected. Now, it’s everywhere we look.When we look out at the ultra-distant Universe, billion of light-years away, we’re seeing it as it was in the distant past as well. At those earlier times, the Universe was hotter, denser, and filled with smaller, younger, less-evolved galaxies. The light we see from way back in our Universe’s history only arrives at our eyes after journeying across these vast cosmic distances, where it’s stretched by the expanding fabric of space.It’s these early signals, and how that light gets stretched to longer wavelengths — i.e., redshifted — as a function of distance, that enable us to infer how the Universe expanded throughout its history. That’s how we discovered that the Universe wasn’t just expanding, but accelerating. That’s how we discovered dark energy and measured ...

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