The theories of how the universe may end

There are many ways in the universe could end, here are a couple of the theories and their explanations.

There was a time that it was thought impossible to destroy a city however then the atomic bomb was created, and thus the intelligence of destruction grew. One theory suggests that our knowledge of destruction will increase to its peak, aka we'll invent a device that will destroy the universe.

The universe is very vast, and it keeps expanding. But what to say a collision with another universe will not occur? Scientists believe that this is a reasonable theory, that outside our universe, others exist, perhaps they even parallel ours. The hypothetical force that would be caused by such a collision with these universe would destroy our universe.

Another theory is that due to the nature of how our universe was created, the big bang theory, our universe will likely be destroyed by the reciprocating force of our creation, little ironic isn't it? This theory is called the Big Crunch. You have to envisage the big bang as a ripple of waves, once the waves have reached their ultimate length (like the waves on a beach) they will retreat back to the centre (or a single point). In terms of the universe, this would mean our universe expanding to such an extent that it collapses in on itself.

 Another theory similar to the Big Crunch is the Big Bounce. It follows the same guidelines as the Big Crunch, our universe expanding to such an extent that it'll reach a point where it cannot extend any more, and therefore will retract back to a singular point. However the difference is once retracted back to this point, the force and energy created will be so powerful that Big Bang Theory 2 will occur. So instead of our universe being crushed, it's just 'recycled'.

 The Big Rip theory suggests that our universe will expand to such a point and to such an extent that like a piece of fabric, it will tear itself apart into nothingness. A rather abrupt theory I think most would agree.

The End Of Time. This theory suggests that there is a possibility that the universe will end due to the end of time. Now, this might be inconceivable to think of, as time is constant. However, scientists have concluded that at some point time, like all things must stop.  The question is, will it be the culprit of our demise?

 The Heat Death theory or the Big Freeze suggests (opposite to the Big Crunch) the universe will keep on expanding and will not stop. And therefore will get to a stage where all matter is evenly dispersed, this will eventually lead to stars burning out. Particles will be left to bounce off each other but with not enough energy to make anything happen. They would exist in this expanding void.

But of course, there is always optimism:

The Eternal Universe theory. Some scientists believe that the universe has always been and still will be. Now, this isn't a far-fetched idea as the universe so far has existed for as long as we've known. But due to the stories of our suns expiration date and these other theories that may occur millions of years from now, this theory can be a little too optimistic.