The Big Bang

Last time, we discussed the evolution of the universe and the prevailing theories put forth in the early part of the 20th century. Here, we will focus only on one: the Big Bang Theory (and not the TV show), since evidence supports the Big Bang Theory rather than the Steady State Model of the Universe.


The Big Bang Theory, as mentioned in the last post, is the accepted theory of how the universe began. It is best described as a sudden explosion of matter, energy, and space into nothing. Before the Big Bang occurred, we really don't know what there was since we cannot look at the universe before the Big Bang took place. The Big Bang started out as a singularity, that was very dense (denser than any black hole since it contained all the matter and energy that ever existed and will ever exist) and very hot. Right after the Big Bang (henceforth, ABB), space itself began to expand, carrying the mass and energy of the universe along with it. It also immediately began to cool off.


At about 10e-36 seconds ABB, the universe went under an inflationary period. Up until that time (which is a really tiny number, and may be hard to comprehend), the universe expanded at a constant rate. When inflation began, the universe suddenly accelerated its expansion until about 10e-33 or 10e-32 seconds ABB. We will discuss more about inflation later.

At the beginning, until around 380,000 years ABB, the universe was just a soup of electrons and prtons, mixed in with photons. The universe was so dense, that photons scattered easily and the universe was opaque. At around 380,000 years ABB, the universe was cool enough that recombination occurred (which really is a misnomer since protons and electrons didn't begin to combine until the temperature of the early universe was cool enough) and atoms began to form. These atoms were primarily hydrogen (75%) and helium (25%) which is still the relative proportions today.


The time at the 380,000 ABB is called the surface of last scattering since this is where the universe became transparent to electro-magnetic radiation and photons were free to travel without being easily scattered by the dense soup of electrons and protons. These photons are still detected today and are called the Cosmic Background Radiation. We will talk more about the CBR later.