Today, the Universe is a patchwork of galaxies separated by large swaths of empty space, but it wasn’t always that way. Back in its early days, before galaxies came into being, matter was more evenly spread across the Universe, shrouding it as a blanket does a newly made bed.
But this matter blanket, like even the most meticulously laid out duvet, had tiny wrinkles in the form of density fluctuations. Over time these wrinkles got amplified as gravity attracted more and more matter to the slightly denser regions. Researchers can observationally measure the pattern of initial wrinkles from something called the cosmic microwave background (CMB), and they can see the outcome by observing the Universe today, but what exactly happened in between remains somewhat of a mystery. Now Sebastian von Hausegger of the University of Oxford, UK, and colleagues have developed a method for predicting an earlier matter distribution from a later one [1]. The method could give astrophysicists the power to rewind the clock to any point in the Universe’s history, allowing them to better understand how galaxies evolved.
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