The Big Bang Theory

• The Big Bang is our current theory about the creation of the universe.

• Edwin Hubble noticed that most galaxies are moving away from us in all directions. This meant that galaxies had to be closer before, so close that they were all joined together at a single point in space.

What exactly does the Big Bang propose?

• At first, the universe was unimaginably dense, less than a million billion billionth the size of an atom.

• In this state, the universe's four forces (gravity, electromagnetism, and the weak and strong nuclear forces) were originally merged into a single force.

• The universe at these conditions was incredibly energetic, and the first particles mixed and settled at the same temperature.

  • All of this happened during the first 10^-43 seconds of the universe’s existence

• This is where the event known as ‘inflation’ happened. Matter and energy expanded mostly evenly in less than a fraction of a second.

• After inflation, the universe kept expanding, just at a slower rate than during inflation, and as of today, it in fact keeps on expanding.

After Inflation

• As soon as the universe was a billionth of a second old, the universe cooled down enough so that the four forces separated into what we know today.

• More particles started to form as well, which led to the creation of the fundamental particles of the universe.

• At this time, the universe was like a soup of particles called the primordial soup (quark-gluon plasma).

• This soup began to cool down as the universe kept expanding, and radiation was so intense that when photons collided with each other, they created pairs of matter and anti-matter.

First Atoms

• At this moment the universe had equal amounts of matter and anti-matter, but later as it cooled down, photons didn’t have enough energy to create more of these pairs, and many of the other pairs started annihilating themselves (this happens because when matter and anti-matter interact, they destroy themselves).

• After the first second of the universe’s existence, the first atoms started to form out of matter.

  • Hydrogen and helium were the first elements that formed roughly three minutes after inflation (hydrogen and helium are the simplest elements).

First Stars

• At this time, atoms weren’t stable yet, and photons couldn’t move uninterrupted. It was only after around 380,000 years that it cooled down enough for atoms to become stable and the universe to become clear for the first time.

• This allowed photons to move freely, and we can still see the afterglow of this event known as the cosmic microwave background.

• After roughly 180 million years, there was enough hydrogen gathered by gravity for the first stars to be born.

• This process kept going and more and more stars were born. After 400 million years, galaxies began to form out of all these stars, and eventually, the Milky Way galaxy where our solar system is.

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