Big Crunch Theory
The Big Crunch theorises that gravity will pull the universe back into itself in a way similar to the air being let out of an inflated balloon, and that the end of the universe will be a big fireball as all that matter collapses onto itself.
The universe has its own momentum, its own energy, and it is moving outward. But in the Big Crunch Theory there will be a point where the universe will stop its outward movement and collapse under the force of its own gravity. In this scenario, the universe returns to its original state just before the Big Bang, setting the stage for a perpetual seesaw of creation and destruction.
Cosmologists have calculated that there is some form of energy that keeps the universe from collapsing, and may prevent the Big Crunch from happening. The existence of such a force leads to new theories about what the universe is made of and how it might end.
Big Chill Theory
The Big Chill Theory hypothesises that the universe will expand until the nuclear furnaces that power all the stars burn out, and the universe grows cold and dies. The universe continues to expand forever and grows into an increasingly cold and lonely place as the expansion removes our nearest neighbours from us and we end up a single isolated community.
In the Big Chill scenario, Earth becomes a lonely cold planet as the universe expands. Distances between stars grow so vast that they nearly disappear from view, burning out over time and, eventually, the entire universe ends in a frozen state.
According to the Big Chill Theory, from Earth’s perspective the first thing to go is sunlight. The sun dims as it exhausts its last bits of nuclear fuel. Earth freezes and becomes lifeless. And billions of years after humans are gone, the cosmos expands out of view. A few newer stars remain, but most have long moved away. The furnace powering the universe burns out. The darkened universe continues to expand. A frozen and lifeless remnant of its once vibrant existence.
Big Rip Theory
Einstein believed that there is more mass in the universe than we can actually see, claiming that there are patches of invisible supergravity from which not even light can escape. The forces outlined in this prediction might just be responsible for a crushing end of the cosmos.
When certain stars run out of fuel they collapse in on themselves into a smaller and far denser mass that attracts more and more matter, just like the Big Crunch. The gravitational pull of these “black holes” is so powerful that anything that falls near them will be forever trapped – not even light can escape.
Clearer pictures of the universe that have only been possible in recent years have led many cosmologists to conclude that not only is the universe expanding, it is speeding up. This suggests that there is an invisible force that exists in the universe – named Dark Energy – that is working against gravity, and could eventually lead to the end of the universe.
The battle between dark matter, the force that holds the universe together, and dark energy, the force seeking to tear it apart, has set the universe on a path of destruction. If dark energy rules the cosmos, the universe could rip to shreds atom-by-atom.
If the universe is continually accelerating, the Big Rip Theory proposes, then 50 billion years from now the universe will tear itself apart. All the distant stars and galaxies will be pulled away from each other. Stars are ripped apart, planets are ripped apart, and even atoms are torn apart before the universe ends.