This sure is a nice planet we have here — but we shouldn't get to attached to it. Nothing lasts forever: Not our planet, not our solar system, not even the entire universe. But how will our world and everything else meet their fates?
Check out the ultimate spoilers, below.
Technically, life on Earth might have ended already, if it weren't for the copious atmosphere that it has shrouded itself with. The sun has been slowly getting brighter, and it would have cooked a less cloud-covered planet, and probably will cook life off of the planet within a billion years. But the sun has also been getting smaller. Remember that lost light is lost mass — since that light was generated by fusion, during which atoms fuse to form a less-massive combined particle, with some of its extra mass being given off as energy. Some scientists once believed that eventually the sun would drop so much mass that the Earth would go sailing off into space.
Now it looks more like the Earth, over the next 7.6 billion years, will be engulfed by the sun. Exactly how it'll be engulfed is a matter of debate. Some say the sun will expand enough to swallow the Earth. During its red giant phase, when inner fusion blows its outer layers farther and farther out, the Earth might fall within that territory. Alternately, the outer layers of the sun could be pulled around by the Earth, the way the tides on Earth are pulled by the Moon. This pull forward on the sun's tides would pull backwards on the Earth, slowing it in its orbit until it falls into the sun.
Some scientists think that, if intelligent life survives that long, civilizations might be able to move the Earth, slipping it out of the range of the sun. Even if that happened, though, the sun will eventually collapse until it's the size of the Earth, and simply sit there, cooling. At that point, any survivors on the boiled, baked, and barren remains of the Earth they salvaged would simply freeze to death.
Not all parts of the solar system will end the same way. As mentioned before, the sun will expand into a huge Red Giant. Earth may be able to slip away from its grasp, if the people(?) on it play the situation right. Mercury and Venus, however, will not be able to get away - unless people(?) put in the same effort to save them. The innermost planets will be gobbled up by the sun and vaporized. Maybe.
Any new gravitational force will play hell with the things around it. There is one theory that, as the sun expands, Mercury's orbit will get erratic. That orbit could make it collide with Venus or the Earth, but that's unlikely. What is certain is that a new orbit to Mercury will exert gravitational forces that, in turn, will pull enough to change the Earth's orbit. Planets gravitationally tug each other all the time, and eccentricities in planetary orbits clue astronomers in to other planets nearby. Start one planet careening about the solar system, and others could follow. In some simulations, Mercury falls into the sun. In others, Mercury hits Venus. In still other's it simply flies out of the solar system. Whatever happens, it will affect the other planets, possibly starting a domino effect.
As for the rest of the planets? The sun will end its days as a white dwarf. Astronomers have seen an asteroid sucked into a white dwarf system in a way that can only mean there are planets orbiting the cooling star. While the inner planets are doomed, the outer planets could still be orbiting the star forever. They could, on the other hand, break free of the star's gravitational pull just as astronomers thought Earth might, and wander around the rest of the universe. Either way, it's going to be cold.
How the Milky Way Galaxy Ends
Our tiny little world and our insignificant sun don't mean anything to the larger galaxy. The Milky Way will do fine without us. If anything, a few flaring red giants and white dwarf, decorated with flaming planets, might make it prettier. But there's something heading towards the Milky Way. About five billion years from now, when the Earth is an ocean-less hunk of rock, baking in the giant red sun's heat, this galaxy will collide with the Andromeda galaxy.
This isn't as violent an event as it might seem. Although galaxies look like dense clusters of stars, but they're just dense clusters of light. The actual stars that make up galaxies are so far apart that galaxies can move right through each other without stars colliding. This galaxy, however, won't finish moving through Andromeda. Over hundreds of millions of years, it will be tugged out of shape by the gravity of Andromeda, and tug Andromeda out of shape in its turn. In the end, the two galaxies will become one, larger, and more diffuse and shapeless group of stars.
So at least, there's some hope for the Milky Way. It is going to end by evolving into something else, not just being destroyed. At least, it will for a while.
How the Universe Ends
Of course 'end' is a relative term. The real end, it looks like, will be the same for everything. And it's caused by the villain of the piece, dark energy. We don't know what dark energy is, but we do know that it is a strange, repulsive force that causes the universe to push away from itself. Like most good villains, it's a three-dimensional, complicated character. At first it seemed like the best way to keep the universe from falling in on itself, and it kept creating 'more' universe to explore. Then reality sunk in.
The universe, famous for its size already, is getting bigger on a problematic scale. First galaxies will recede beyond view. Eventually, that lovely galaxy that Andromeda and the Milky Way made will be expanded so far that anything living on Earth — or any other planet — won't see the stars anymore. Most stars, we think, will be sucked up by their galactic central black holes. The black holes themselves will evaporate, emitting energy faster and faster as they shrink. Eventually, the universe will simply dissolve, like tissue paper in a bath over the next ten to the one hundredth years.
Of course, there is another theory, which states that dark energy will just get stronger, and rip the universe to pieces over the course of about a half of an hour about twenty billion years from now. On the grounds that that would be a spectacular show, I think that it would be a good idea to try to survive until then — so lets start looking at ways to move the Earth.
Top Image: NASA
Earth Image: NASA
Planets Image: NASA
Milky Way Image: ESO
Black Hole Image: NASA