The universe why would swell? This makes Einstein very“troubles”you!

　　 China's ancient ancestors are very wise, in the Han Dynasty, Liu An's ancient book "Huainanzi - Qi custom", mentioned "four sides up and down is called the Yu, to the solid to the present is called the Zeus", simply put Yu is space, Zeus is time, so theUniverseLearning is the study of time and space.

　　In the universe, time and space are basically the same thing. Because when you see into the depths of the universe, you see into the past. The cosmological unit of length that we usually refer to: the light year, which looks kind of strange, like a unit of time, is actually a unit of length, representing the distance that it takes light to travel a year.

　　How far is the distance traveled in one year by light? It's not very far, it's about 946 billion kilometers. And how big is the Milky Way? More than 100,000 light-years in diameter, which means that it takes light 100,000 years to travel from one end of the galaxy to the other.