One property that astronomers have tried to use to help them do this, however, is a number known as the Hubble Constant. “It’s a measure of how fast the universe is expanding at the current time,” says Wendy Freedman, an astrophysicist at the University of Chicago who has spent her career measuring it. “The Hubble Constant sets the scale of the Universe, both its size and its age.” It helps to think about the Universe like a balloon being blown up. As the stars and galaxies, like dots on a balloon’s surface, move apart from each other more quickly, the greater the distance is between them. From our perspective, what this means is the further away a galaxy is from us, the faster it is receding. Unfortunately, the more astronomers measure this number, the more it seems to defy predictions built on our understanding of the Universe. One method of measuring it directly gives us a certain value while another measurement, which relies on our understanding of other parameters about the ...
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