Ontario Grade 9 Science Class Practice Exam

Big Bang Theory describes the origin of the universe as starting from a hot, dense state and expanding over time. The best description among the options is that the universe began about 13.8 billion years ago from a very small, extremely dense amount of matter and energy and has been expanding ever since. This matches what we observe: galaxies moving away from us (redshift), the afterglow of the early universe (the cosmic microwave background), and the amounts of light elements like hydrogen and helium.

The idea that the universe is infinite isn’t what the Big Bang asserts, and the theory doesn’t claim the universe stopped expanding. The notion of a future collision of galaxies describes a future event, not the origin of the universe. The phrase about an explosion is a common, simplified way to describe rapid expansion from a dense state, not a literal explosion into preexisting space.