- Big Bang took place 13 billion years ago.
- Space, time, radiation were made in the big bang. At first, the Universe was a hot glowing ball of radiation and matter. As it expanded, temperature fell. Now the universe is cold and dark except for hot spots (Stars)
- Timeline for the Universe : Quarks and electrons form from radiation
- - Neutrons and protons form after 100 s
- - Hydrogen and helium atoms form after 100,000 years
- - First galaxies and stars form after a few billion years.
- The stars we see in the night sky are all in the Milky Way galaxy, our home galaxy. The sun is one of the billion of stars in the galaxy. Using telescopes, we can see many more stars in our and other galaxies.
- We know there are billions of galaxies in the universe with a big empty space between them. Light from the furthest galaxies we can see has taken billions of years to reach us.
The Dark Age of the Universe
- As the Universe expanded, it became transparent as radiation passed through the empty space between the atoms.
- The background radiation that causes the spots on an untuned TV was released at this stage.
- The Dark Age had then begun.
- For the next few billion years, the Universe was dark, patchy, expanding cloud of Hydrogen and helium. Then the stars and galaxies form and fill up the universe.
The force of gravity takes over
- Uncharged atoms don't repel each other. But they can attract each other.
- During the dark ages, the force of gravitational attraction was at work without any opposition from repulsive forces.
- As the universe kept expanding, it became more patchy as the denser parts attracted nearby matter.
- Gravity pulled more matter into denser parts and turned them into gigantic clusters.
- Eventually, the force of gravity turns the clumps into galaxies and stars.
- A few billion years late, the dark age came to an end and the stars lit up the universe.
The life history of a star
- Stars form out of clouds of dust and gas.
- The particles in the clouds gather together under their own gravity. The clouds merge and become more concentrated to make a protostar.
- As the protostar becomes denser, it gets hotter. If it becomes hot enough, the nuclei of hydrogen atoms and other light elements fuse together.