Scientists talk about things taking billions of years in space, and then in the next sentence they talk about how time is affected by what's going on in space. A year is based on how long it takes the planet Earth to get around the Sun. Other planets and stars move at different speeds, and the speed of light and great distances seem to affect time and space. When people say "billions of years" in the context of outer space, what are they talking about? I don't think anybody really knows.