One theory is the one of the expansive universe; according to which this last one, will expand until it cools off and it stops.
The other version is more fascinating and speaks of a universe that will reach a zone of Maxima expansion and soon it will begin to be contracted until finalizing in a Big Crunch.
Which of the two theories is the real one, it certain depends on how many dark matter there is in the universe, since if the mass of the dark matter is sufficient like to invert the expansion, a moment will arrive at which the universe will begin to be contracted.
Now, from this second hypothesis, I want to make clear that the time is not a separated part of the space but it is an intrinsic part of; and an inherent part to him.
So that if we travel towards the Big-Bang, we would travel towards the past and if we travel towards the Big- Crunch, we would travel towards the future.
But not only; there is a question that troubles me; to where it is going to go all the matter and energy that enters by the black holes? ; if the matter-energy is not destroyed, where is the white holes by which it leaves all that matter-energy absorbed by the black holes? ; and let be clearly understood that in the center of all the galaxies, there is a massive super black hole, apart from those that there are watered in all cosmos, product of the compression of stars.
Until now, nobody has seen a white hole that it expels energy, as if outside Small-Bangs aside of the big one that gave origin itself to the same universe we are talking about.
Therefore, I have imagined the Universe as a multidimensional spheroid (I call it this way because I would not know how to call it, since my brain still thinks three-dimensionaly), that in addition it is hollow in its interior, like a fountain, so that all the energy that enters the center of the universal hollowness through the black holes and the Big-Crunch, leaves again by Big-Bang.
According to this model, the Universe did not have a beginning nor will have an end, but it recycles to itself, eternally, detached to the time contained in it; then also the time, that is part of the space-time continuum would be recycled until being absorbed under the form of stars, nebulas and galaxies, by the different black holes; including a the Big-Crunch.
And yes, I am speaking of a cyclical Universe!
The white hole always was there; it is the Big-Bang, that would happen to be the North Pole of this multidimensional spheroid, while the Big-Crunch would be its South Pole, and the zone of Maxima expansion and minimum contraction would be its Ecuador.
We do not have to try to understand the Universe in terms of linear time, because the time is one of its characteristics; it is part of its constitution.
The matter-energy neither is created nor destroyed, it becomes moved, it changes, that yes, but it is not destroyed.