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Ask Ethan: Why Was The Universe Dark For So Long?

11 Nov 2017, 15:01 UTC
Ask Ethan: Why Was The Universe Dark For So Long?
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The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. Once neutral atoms form, however, it takes roughly 550 million years for the ‘dark ages’ to end. Image credit: C. Faucher-Giguère, A. Lidz, and L. Hernquist, Science 319, 5859 (47).The first stars formed almost half a billion years before we could see their light. Here’s why.At the moment of the Big Bang, the Universe was full of matter and radiation, but there were no stars. As it expanded and cooled, you formed protons and neutrons in the first fraction of a second, atomic nuclei in the first 3–4 minutes, and neutral atoms after about 380,000 years. After another 50–100 million years, you form the very first stars. But the Universe remains dark, and observers within it are unable to see that starlight, until 550 million years after the Big Bang. Why so long? Iustin Pop wants to know:One thing I wonder though is why did the dark ages last hundreds of millions of years? I would have expected an order of magnitude smaller, or more.Forming stars and galaxies is a huge step in the creation of light, but ...

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