The big bang theory: the big bang theory is an effort to explain exactly what happened at the very beginning of the universe (cid:498)three pillars of proof(cid:499, (ubble(cid:495)s law: recession of stars and galaxies, doppler effect. The observed abundance of all the different atoms of those elements can be explained only if they originated from one single ratio of the first subatomic particles of matter that can be formed from a super- hot environment. The only way to get that one critical ratio is through a unique event like a big bang. September 10th/2017 energy of the big bang expansion, we are at the (cid:494)critical(cid:495) value of 1 for a density parameter. Age of the universe- several ways we can determine the age of the universe. Determining the age using hubble"s expansion constant 13 14 billion years. Determining the age using cosmic microwave background radiation signals.