The Cosmic Perspective: an Overview of the Universe

What is the universe?
According to the Merriam Webster Dictionary it is "all of time and space and everything in it.".But that is a very vague definition, for we don't really know how big, or how many things there are. When a cosmologist, or astronomer refers to the universe, they mean the Observable Universe, all the light we can see.
So how big is it? Even though the universe is 13.8 billion years old, the furthest thing we see is actually 46 billion light-years away, due to the expansion of the universe. This point is called the particle horizon and is the known edge of the universe. The Observable Universe has a diameter of 93 billion light years.
But a really interesting thing happens when you look at stars and galaxies. The further away you look, the further you are looking back in time. For example, the galaxy  GN-z11 is 13.4 billion light-years away. That means that we are seeing how it was 13.4 billion yeas ago, only about 400 million years after the Big Bang. For all we know, that galaxy could not exist anymore! This allows scientists to study the earliest stages of the universe.

From the Big Bang to Heat Death: a "brief" timeline of the universe.
You have probably all heard of the Big Bang, but, what is it? The Big Bang Theory is a widely accepted cosmological model first proposed by the catholic priest and physicist George Lemaître that describes how the universe came to be as big as it is now.
Before, it was thought that the universe was static, and that time and space had no beginning. However, in 1929, astronomer Edwin Hubble made a revolutionary discovery. When he looked through his telescope, he saw that galaxies where getting away from us. The universe was expanding. Reverse the laws of physics, and you get that things should have been much closer together, in a tiny infinitely dense point called a singularity containing space-time itself and everything in it. This dot then expanded in a burst of light to about 1026 times its size in less than a billionth of a second in a process called inflation. After that, everything was too hot for anything to exist, and matter existed in a plasma state. It was about 400,000 thousand years later that it cooled down enough for the first photons to travel freely through the universe. Today, this "glow" is called the Cosmic Microwave Background (CMB), the "baby picture" of the universe. Later, each one of those dots came to be the stars and galaxies we know today.
But the story is far from over. In fact, right know, the universe is not only expanding, but does it at an accelerated rate. A mysterious force, which scientists call Dark Energy that makes up about 70% of the universe is pushing the expansion. Many think, this energy comes from space itself. So, the more space there is, the more Dark Energy and the more it expands.
Thence, the fate of the universe is in the hands of this energy, and the end is a big battle between gravity vs Dark Energy. Unfortunately for gravity, there are not enough things, about a quarter of the necessary, in the universe to stop the expansion. The most likely outcome is that the universe will expand forever, so much that stars will not be able to form and the universe will adapt the lowest possible energy state. This is called "Heat Death".

But, what is humanity's place in the vastness of the cosmos? Are we alone? What is beyond the known boundaries of the universe? The truth is, the more we know about the cosmos, the larger it seems to get, while we become smaller and smaller. When our ancestors looked at the sky, they saw hidden messages from their gods. They thought the Earth was at the center of everything, that they, we, were special. Then, we discovered that the Earth was one of 8 planets orbiting a star. And that the sun wasn't special at all, for there are hundreds of millions of stars only in the Milky Way, our home galaxy. Then, we raised our telescopes and saw hundreds of billions of more galaxies around us, with hundreds of billions of more stars. Possibly, we are wrong to think that this universe is unique, putting the idea of the multiverse on the table. I mean, we've been wrong before, right?
You may argue that life is what makes us, this planet, special. But, for how long can you hold on to those thoughts? Even within our solar system, there are other possible habitable worlds, such as Europa or Titan. However, this idea poses a big question, known as the Fermi paradox. If life is so common, then where are all the aliens? Maybe they're hiding, or they haven't found us, or they don't want to. Perhaps intelligent life is rare, or distances are too vast. Anyway, personally, I think it is unreasonable to think that we are alone knowing the true vastness, or possibly not really knowing the real extent, of the cosmos. Even if it is rare, it must've happened elsewhere in the universe.
Yet, for me, this view is far from scary or depressing, but it opens my eyes to a beautiful perspective: I am glad to be alive to see it. As Carl Sagan once said:

"We are a way for the cosmos to know itself."