A. How did our present universe come to be?  

Using cepheid variables, Hubble pioneered the work that demonstrated that spiral nebulae were actually galaxies located 'way beyond the Milky Way. In the first quarter of this century, Slipher showed that the light of these spiral nebulae was red-shifted almost without exception. The only exception to this pattern were some galaxies in our own local cluster. In 1929 Hubble had shown that these spiral nebulae were actually at great distances outside the Milky Way and were galaxies in their own right. By 1930 he had further shown that the amount of red shift was proportional to their distance from earth. The farther galaxies show a greater red shift, indicating that the further away they are, the greater their recessional velocity (the faster they move away from us). This relationship between recessional velocity and distance is known as Hubble’s Law. 

This Cosmological (universal) red shift is the basic evidence that shows that all objects within the universe are moving farther and farther away from us, and from each other. Given this universal red shift, where every galaxy in this universe is moving away from every other galaxy, the universe is expanding. But how did this actually come about? In order to answer this question astronomers evolved two models, the Big Bang and Steady State.