What is the Big & how does it factor in?

       

      The Big Bang Theory is an idea about how the universe came into existence.  It is an explanation of what happened during and before the universe became existence.  According to the Big Bang theory, 10 to 20 billion years ago, a sudden explosion created the Universe. Ever since this instant, the Universe has been expanding and cooling from the infinite temperatures in which it began.

            Why do we speak of the Big Bang so often when we talk about the cosmic microwave background? For the simple reason that discovery of the CMB’s existence has served as possibly the strongest evidence for the Big Bang Theory; the CMB provides the nearest “look” back to the creation of the Universe!

   Photons from the Big Bang moved throughout the Universe and became the radiation we know as the cosmic microwave background. As you’ll recall, observations show the cosmic microwave background to be a nearly perfect blackbody with a temperature of approximately 2.72 K. Well, this measurement matches predictions of the Big Bang theory very well. Though, this alone does not support the theory. The fluctuations in the CMB that make it nearly, but not perfectly, uniform need to be taken into consideration.

Sources:

http://lambda.gsfc.nasa.gov/product/cobe/

http://www.astro.ubc.ca/people/scott/cmb_intro.html