Our universe has been expanding for 13.8 billion years.

 

. It explains the universe’s large-scale structure

Starting out as a singularity, the universe has been expanding for 13.8 billion years. (

Our best theory of the universe’s origin is the Big Bang. Yet it was modified in the 1980s to include another theory called inflation. In the first trillionth of a trillionth of a trillionth of a second, the cosmos ballooned from smaller than an atom to about the size of a grapefruit. That’s a whopping 10^78 times bigger. Inflating a red blood cell by the same amount would make it larger than the entire observable universe today.

As it was initially smaller than an atom, the infant universe would have been dominated by quantum fluctuations linked to the Heisenberg uncertainty principle. Inflation caused the universe to grow rapidly before these fluctuations had a chance to fade away. This concentrated energy into some areas rather than others — something astronomers believe acted as seeds around which material could gather to form the clusters of galaxies we observe now