The End of The Universe
The universe was really small and dense at one point, and then all of a sudden it wasn't. But whoa, whoa, wait a minute! Let's rewind and figure out what happened right here. This is because of two things: entropy and dark energy.
Put it simply, entropy is the measure of order in the universe. It's a measure of uncertainty or randomness. The higher the entropy, the more disorderly the universe's state. It's like your bedroom: a messy room is a high entropy state because it's much harder for you to be certain of where any specific object could be, for example, that sock you lost last week. But once you clean everything up and make it an orderly space, it's much easier to be certain about where an object will be. This is entropy in a simple nutshell.
Why is it important? Simply put, it could be what causes the end of our universe. Before we get to the end of the universe, we need to discuss what events will occur between now and then. This video is much like a sequel to a video I made recently called "What Will Happen in 1 Billion Years." If you haven't seen it, I suggest you watch it. If you do, this video will make more sense.
Anyway, right now the Milky Way galaxy and the Andromeda galaxy, the closest galaxies to our own, are racing towards each other at a speed of about 110 kilometers per second. But in 4 billion years, the night sky will look the most beautiful than it has ever been. The collision of galaxies sounds like a really big threat, but actually, our solar system will most likely remain intact due to the huge sizes of our galaxies.
This most likely won't affect anything inside our immediate neighborhood. Andromeda is 260 thousand light years across, while the Milky Way is only about a hundred thousand light years. And I say only a hundred thousand light years like it's nothing! But at our highest estimate, our solar system is only about four light years in diameter. When our galaxy collides with Andromeda, the night sky will be filled with gas clouds and nebulas forming new stars.
Assuming there's still life on Earth or in our solar system at this point—because galaxies are mostly empty space—we only need to be worried about avoiding any object within my ears. Oh, it may be our own Sun!
In about five billion years, the hydrogen in the Sun's core will be completely exhausted and we'll leave what is called the main sequence—a place where dwarf stars who aren't quite giants live. This is when the Sun will begin to expand, which isn't exactly good for any life on Earth. The Earth, Moon, and, according to many scientists, maybe even Mars will be swallowed whole by what is now the red giant Sun.
But there’s an upside! This destruction may cause Titan, one of Saturn's moons, to have conditions extremely similar to what Earth’s are today, meaning that we could possibly have living conditions on Titan. But even then, things aren't too safe because in the year 22 billion, the first universe-ending scenario comes into play: the big rip.
Low entropy states require work to achieve, so naturally, everything, even on the scale of the universe, seems to tend towards disorder. You can tie this in with the Big Bang: the universe was in an extremely low entropy state in the beginning. All the matter and energy in the entire universe today is compacted down into one minuscule point.
Since then, the universe has been expanding and cooling down into a higher entropy state—a more disorderly state. You would think that over the billions of years since the universe's beginning, the universe's expansion would slow down, but actually, it's doing quite the opposite; it's speeding up. This is due to dark energy.
We have known that the universe's expansion has been speeding up for decades, but the reason why remained unknown, so we call it dark energy. Right now, the idea is that dark energy will continue expanding the space between galaxies and that large structures in the universe—like galaxies, stars, planets, and even molecular bonds—will be strong enough to stay held together.
This is due to forces such as gravity and the weak and strong nuclear forces. If this is true, then dark energy will never be able to become strong enough to pull...