>>116790199In 1922 physicist Alexander Friedmann extensively examined the work of numerous historical astronomers and the wavelengths of the galaxies they'd studied. What he found was that the galaxies were getting further away from us.
Not in only one direction as we'd expect. All galaxies at all times are constantly moving further away from us.
This lead him to discover the evidence, using Eistein's equations, that the universe is constantly expanding. A few years later, Georges Lemaître published work that he had done independently that came to the exact same conclusion. Two separate brilliant physicists coming to the same conclusion, because that's how science works: When you're observing the natural world, you'll always come to one true answer.
Not long after he also provided observational evidence of galaxies moving apart, and famous astronomer Edwin Hubble also confiemed the findings in his own observations.
This view is based on a massive amount of evidence gathered over hundreds of years from the world's greatest experts in the fields of astronomy, cosmology and physics. It is an undeniable fact that the universe is expanding.
Once you have these equations and understand the expansion of the universe, you're able to track it backwards in time. You can reverse the equations to figure out, how big was the universe n billion years ago? If you follow this to it's ultimate conclusion, the universe was at one point smaller than the head of a pin. In fact this is how we know how big the univers is (13.8bn years): We know how fast it's expanding right now, and can extrapolate backwards to find out at which point it was infintesmally small.
