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ShivaniMemberJuly 2, 2021 at 10:03 am::
WE KNOW the size of the Earth from the time of the ancient Greeks. The sun, the solar system, and the Milky Way? No problem. But when it comes to the size of the universe, we have not yet found a clue.
“It’s weird: the size of the visible universe is one of the most well-known astronomical phenomena, but the size of the universe is one of the most obscure,” said Scott Dodelson, an astronomer at Fermilab in Batavia, Illinois.
One way to think about the size of the visible universe is to consider how far the light emitted by the big bang would travel. According to our best models of nature, that distance is estimated at 46 billion light-years. This is the “horizon” of the universe, a type of three-dimensional 2D-horizon we see on Earth.
“That’s our vision and how big, physically, we can see the whole world,” said Adam Riess of Johns Hopkins University in Baltimore, Maryland, who shared the 2011 Nobel Prize for finding the expansion of the universe. “Of course we’re sure it’s going to go a long way.”
Why? Because the universe looks very similar no matter what it looks like. Take the background of the cosmic microwave (CMB), the rays left behind by the big bang. It’s very similar in the sky, and we have no reason to think that that will change beyond the horizon.