1. oscillating universe theory the universe is a never-ending cycle of big bangs and big crunches. 2. inflation theory a very, very fast expansion and acceleration of the universe happened milliseconds after the big bang. 3. big bang theory the universe has always been and continues to be the same. 4. steady state theory the universe came from a very dense, very hot "fireball" that exploded and expanded into existence.

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.