How It All Began…

Chapter 1: The Big Bang Chapter 2: The Galaxies Chapter 3: The Fate of the Universe

Chapter 1: The Big Bang 13,700 million years ago our universe began as a very small, very dense mass. It “exploded” at that point creating all time and space.

As with stars, “explosion” may not be an accurate term. The universe expanded outward VERY QUICKLY instead.

Within 1 second of the Big Bang, the four forces in the universe formed: gravity, strong force (keeps nuclei of atoms together), weak force (allows for radioactive decay), and electromagnetic force (keeps atoms together).

Within 3 minutes of the Big Bang, simple elements had formed (H, He).

It took 1,000,000,000 years after the Big Bang for stars and galaxies to start to form.

(Our sun did not form until 5,000,000,000 years after the Big Bang.)

Chapter 2: The Galaxies There are billions of galaxies in the universe. Each is a collection of stars, planets, black holes, moon, comets, asteroids,….

We now think that galaxies form around supermassive black holes.

Edwin Hubble classified the galaxies into four different categories in the early 1900s: elliptical, spiral, barred spiral, and irregular.

Hubble thought that galaxies began as either irregular or elliptical and ended as one of the spirals. His evolution of galaxies diagram is called the Hubble Tuning Fork Diagram.

Irregular Galaxies

Elliptical Galaxies

Spiral Galaxies

We now know that Hubble’s Tuning Fork diagram does not really show how galaxies evolve, but it is still useful for classification purposes.

Our galaxy, the Milky Way, is a spiral galaxy.

Chapter 3: The Fate of the Universe There are four ways astronomers feel that our universe could “end”.

The Big Crunch –Gravity could eventually pull the universe back to the state it was in when the Big Bang happened.

Coasting –The universe could continue to expand forever. All stars would eventually die out leaving nothing but giant black holes.

“Critical” Expansion (Steady State) –The universe could expand for some time and then just grind to a halt.

Accelerating –The universe could continue to expand ever faster and faster.