The Big Bang (Overview)

How did it all begin? Was there even a beginning at all, or has reality existed since forever? Was there a time where time itself didn't exist? All of these questions have been asked since the dawn of humanity, and we are now closer than ever to understanding what really is going on. The Big Bang theory is the current prevailing theory about the creation of our universe. It was first put forth in the 1920s by a Belgian priest by the name of Georges Lemaître, who postulated that the universe originated from a single primordial atom. Then came Edwin Hubble, who noticed that most galaxies are actually 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. This is why Hubble's observations supported the Big Bang theory perfectly. Now, let's talk about what the Big Bang theory actually proposes. At first, the universe was unimaginably dense, calculated to be less than a million billion billionth the size of an atom. Imagine the amount of energy that was in this single point of energy. In this state, the four forces of the universe (gravity, electromagnetism, and weak and strong nuclear forces) were originally merged into a single force. We currently don't know how this force would work, and we would have to understand gravity at the quantum level to do so, which as of right now, we simply don't. Surprisingly, all of this happened during the first 10^-43 seconds of the universe's existence, and at these conditions, the first particles mixed and settled at the same temperature. At this moment is when the event known as "inflation" happened. In less than a fraction of a second, matter and energy expanded mostly evenly. This is how the universe was created. It expanded from an unimaginably tiny space into an unimaginably vast space, although inflation didn't cause it to expand to what we see today. After inflation, the universe actually kept expanding, just at a slower rate than during inflation, and as of today, it in fact keeps on expanding. There are still plenty of unknowns. For example, scientists aren't sure what exactly caused inflation itself, and you can argue, then what created that tiny space with all that energy that expanded into what we see today? So yes, although the Big Bang theory has plenty of evidence that supports it, that doesn't mean we understand everything about it.

What Happened After Inflation?

After cosmic inflation, the universe was born, and as soon as it 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 at this point that whenever photons collided with each other, they created pairs of particles of matter and anti-matter. 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 lots of the other pairs started annihilating themselves (since when matter interacts with anti-matter, they destroy themselves). For some unknown reason, more matter was left than anti-matter, and everything else in the universe is now made up from this matter.

The First Element

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 after roughly three minutes of inflation. 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 an afterglow of this event known as the cosmic microwave background.

The First Stars

After roughly 180 million years, there was enough hydrogen gathered by gravity for the first stars to be born. This process kept going. More and more stars were born, and after 400 million years, galaxies began to form out of all of these stars. After 13.8 billion years, there are now trillions of galaxies in the universe, each containing millions or billions of stars, including the Milky Way Galaxy, our solar system, and Earth, which leads to life forms such as humans that can question creation itself.