The observable Universe is made up of amazing stuff. We more formally call this stuff matter. Humans have always been curious about the nature of matter: where did matter come from? what is it made out of? why does it behave the way it does?

"As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled and stable atoms could form, they eventually could no longer absorb the thermal radiation and the universe became transparent instead of being an opaque fog. The photons from that time have been propagating ever since, growing fainter and less energetic."

expanded and then rapidly stopped expanding

expanded and has not stopped expanding since

rapidly expanded and then shrunk back to its original size

expanded and then began shrinking over time

learn what triggered the big bang and how atoms first originated.

What Triggered The Big Bang?