The two most common beliefs of the formation of the Universe and Solar Systemare The Expanding Universe Theory and The Big Bang. There are some comparisonsbetween the two and some contrasts.
Almost all astronomers believe that theuniverse is expanding although they may have different theories on how this ishappening. The Expanding Universe Theory is based on the Doppler Effect, theredshift of different galaxies and the assumption of the Hubble Law. The Dopplereffect occurs when a wave-emmitting object moves toward or away from an observerand the sound has a change in pitch as the object continues to move. For examplethe sound a police car siren when it comes from behind and passes you. Theredshift of different galaxies is the change or shift in the light radiated byan object such as a star of galaxy that indicates the objects motion. Scientistshave used redshifts to measure the speed and direction of distant galaxies.
TheHubble law showed that the further away the galaxies were the higher theredshift was, that means the more distant galaxies were moving away at a muchfaster velocity than those closer to us. The Expanding Universe theory is merelyan assumption by astronomers that all the galaxies in the universe are movingaway from the earth. The more distant the galaxy the faster its moving awayfrom us.
According to the Big Bang theory a gigantic explosion created theuniverse billions of years ago. It appeared that the universe we now see couldbe the remnants of an enormous explosion of the distant past.