By figuring out how fast the universe is expanding, scientists can calculate when the Big Bang occurred.
The universe was created from a super dense spect of pure energy, the size of a single atom. In a fraction of a second, the size of the universe grew from the size of an atom to the size of a baseball. In another fraction of a second, it grew to the size of the Earth.
When our universe was only 380,000 years old, it was trillions and trillions of miles across. It would take another 200 million years before the first stars were created. One billion years after the Big Bang, the first galaxies formed. Nine billion years after the Big Bang, our solar system comes into being.
Our universe had a beginning, and at some point, it will come to an end.