vity suggested an expanded universe. He introduced a cosomological constant to the theory to make the universe seem static, or unchanging. This theory introduced a small change; a constant term that created an anti-gravity force that existed in equations. There was no explanation for it and no known source. In other words, he pulled this term out of nowhere. Einstein later called this his greatest mistake after Hubbles discovery that proved the universe is constantly expanding. In 1922, seven years before Hubbles discovery of the red shift, a Russian mathematician, Alexander Friedmann, based the model of the universe on Einstein's General Theory of Relativity without the cosmological constant. In 1935, Friedmann's three models of the universe were introduced. The first assumption was which ever way one may look, everything at any point in the universe will appear to be identical. Hubble's law proved this seven years later. The universe is not totally uniform, but on an average is considered to be uniform. On a large scale (multiple galaxies) this theory works. Friedmann envisioned the universe to be like the surface of a balloon, and galaxies could be treated like spots on the balloon. Spots will move farther away from each other when you blow it up and it increases. No single spot is the center of expansion. The further apart the dots are, the faster they move away from each other. Friedmann's law predicted exactly what hubble's law proved. Friedmann's model of the universe is not infinite. Gravity is so stron inthis model that it pulls the universe in upon itself. The universe is finite and has no boundaries, and at some point in time it will stop expanding and become a singularity. The second model says space is curved outward instead of inward like the first model. It is comparable to a saddle. This makes the universe an open model, or infinite. The third model says space becomes flat. The universe expands, ...
