How and when the universe may end.

The universe will not exist forever. It could end at any time. It is as if the dice are constantly being rolled and when the end number comes up the universe ceases to exist. Due to the low probability of this, the end will most likely come after heat death has already occurred. Left to its own devices the universe will eventually run down. All motion will stop and nothing will appear to be happening. (except at the quantum level of the very small)

If there were enough mass Gravity would eventually overcome the expansion of the universe causing it all to pull together in a Big Crunch. This would end in a Big Bang perhaps starting a new universe. The idea of a continuing Big Bang/Big Crunch cycle is very compelling. However current explorations find that there is insufficient mass and therefore insufficient gravity for this to come about.

And so we look forward to everything just running down. However the stillness will not last forever.Beneath the stillness random quantum events continue to occur. The dice continue to roll.

The creation of the universe was an improbable quantum fluctuation.It was improbable but not impossible, with only the near infinite number of trials allowing it to occur. The spontaneous end of the universe is also improbable. The large number of trials (dice rolls) likely to bring it about will most likely delay its happening until after all motion stops and our story has long ended.

There is however no reason why a new improbable event will not give rise to another universe and perhaps all possible universes with all possible endings.