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Astronomy Fun Fact #94

The universe is expanding, and that expansion is speeding up.


But even though the universe is getting bigger, it's not creating any new mass. No, the universe has the same mass now that it did when it first formed. What is that mass?


Obviously astronomers can't take out a giant scale and directly measure the observable universe's mass, but we can estimate its density and size.


The average density of the observable universe is 3x10^-30 grams per cubic centimeter, and the observable universe is about 13.5 billion light years across. If you combine those values, you find that the mass of the observable universe is about 10^55 kg, which is 25 BILLION times more massive than the Milky Way Galaxy.





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