Do you know how the Universe began? Many scientists believe it has to do with a theory called the “Big Bang.”
The Universe didn’t exist until 13.7 billion years ago. Astronomers and scientists believe the Universe was in a bubble in space that was as small as a single atom. The bubble was hotter and denser than we can understand. All of a sudden, in less than a second, it exploded and grew. This explanation is known as the Big Bang.
According to their theory, right after the Big Bang explosion, the Universe cooled down and expanded. After this, protons and neutrons began to form. The temperatures dropped to one billion degrees Celsius, which is low enough that protons and neutrons came together to form hydrogen and helium nuclei. Then, 300,000 years later, the Universe cooled down to 3,000 degrees Celsius—enough for it to fill with clouds of helium and hydrogen. Shortly after, gravity drew matter together, thus creating the first star.
Since then, many other stars, galaxies, and even planets have formed. To this day, the Universe is still expanding. Who knows what the Universe might look like or include in another 13.7 billion years!
[Sources: Factmonster.com; Dorling Kindersley; European Space Agenay]