Physics 3 - Stars and Space - Galaxies

The Big Bang that created the Universe was about 13 billion years ago. Space, Time and Radiation were created in the Big Bang. At first, the Universe was a hot glowing ball of radiation and matter. As it expanded, its temperature fell. Now the Universe is cold and dark, expect for hotspots we call stars.

- Quarks and Electrons formed from radiation after 0.1s

- Neutrons and Protons formed after 100s

- Hydrogen and Helium atoms formed after 100,000 years

- First Galaxies and Stars formed 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 just one of the billions of stars in the Milky Way Galaxy. Using powerful telescopes, we can see many more stars in the Milky Way Galaxy and individual stars in other Galaxies.

We now know there are billions of Galaxies in the Universe with vast 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 throught the empty space between its atoms. The background microwave radiation that causes the spots on an untuned TV was released at this stage. The Dark Age of the Universe had begun!

For the next few billion years, the Universe would have been a dark, patchy, expanding cloud of Hydrogen and Helium. Then the Stars and Galaxies formed and lit up the Universe

Uncharged atoms don't repel each other. But they can attract each other. During the Dark Age of the Universe, the force of Gravitational Attraction was at work without any opposition from repulsive forces.

As the Universe continued to expand, it became more patchy as the denser parts attracted nearby matter. Gravity pulled more matter into the denser parts and turned them into gigantic clumps.

Eventually, the force of gravity turned the clumps into Galaxies and Stars. A few billion years after the Big Bang, the Dark Age came to an end as the stars lit up the Universe.