Which scientific theory explains that the universe originated from a small, country densely packed space?

Explanation:

The Big Bang theory explains that billions of years ago, before the current universe was born, matter was concentrated in an infinitely small and highly dense point. Then, a large explosion caused this matter to expand in all directions, creating the universe we now know (including space and time).

In addition, this theory explains that our universe still continues its expansion process.

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.