Two possibilities for the possible end of the universe exist.
The first one is the “Big Crunch”.
The Big Crunch is a theory according to which the universe will start in the future to contract itself, due to gravitational attraction, until entering exactly in collapse on itself.
Some questions of the cosmologists are: E later? It will be that the universe really goes to finish? Or it will be that it will continue to become enlarged itself forever until cooling itself total and if to become a Universe of blackout? Or it will be that still it would continue in a perpetual cycle of Big Bangs and Big Crunchs?
The beginning of the gravitational elasticity.
Up to 1998 one thought that the speed with which the galaxies if move away would have to diminish with the time due to gravitational atracção between them. To this principle some astrophysical ones call “universal elastic memory”.
More recent research (1998), based in new comments of extremely distant, had proven that the acceleration of the expansion of the universe is positive, what means that the speed with which the galaxies if move away ones from the others is increasing, and not diminishing as it would be of if waiting for the gravitational attraction. This means that the Universe is if expanding each time more quickly, speeding up, and the cosmologists do not see as this situation could be reverted. To explain this fact, new gravitational theories are being formulated, implying slight knowledge as black substance and black energy. The evidence of the acceleration of the expansion of the universe is considered as conclusive by the majority of the cosmologists since 2002, and with this discovery the hypothesis of the Big Crunch suffered great revés.
The second possibility is big-freeze.
In this second hypothesis the universe would continue if to expand forever. Everything would go to disappear and the temperature of the universe would fall for the absolute zero. (0 K, -273,15°C, -459,688 °F). This would be inverse the situation of big crunch. The universe would not have substance enough to contain the expansion speed.
A geometry lesson.
The future of the universe lately depends on its global geometry: Plan, spherical or hyperbolic. (It does not interpret in literal way the examples that if follows). The three examples if follow below:
The geometry of the universe is determined by everything what the mass function exists in it -.
A magical number called critical density represented by PC exists, that determines which destination the universe will have.
Big crunch will happen if the universe to possess a " spherical geometry ". Spherical geometry is not an abstract idea: Not truth, says respect to the fact of that we would see the universe thus if we could observe it “of it are.”
In this in case that, the universe contains mass sufficiently - and it would be above of the critical density - that the expansion would stop. A time stopping the expansion, would start if to contract. It would start to devagar, and later it would go fast, and each faster time. The universe would go to contract itself and the next galaxies would be each time. Eventually, everything will go to merge itself, and the universe already will not be greater the sufficient to separate to galaxies or stars. Everything will follow if shrinking and the universe it will be heated to an immense temperature. Then, everything will be compact in a black hole. Finally the universe will come back to be as it started. - infinitely small, infinitely dense and an infinitely hot microscopical point. Nobody knows to the certainty what it can happen after this.
An easy way of if thinking about this, are playing a ball. Launch you it in air, and its acceleration is as the big-bang. After the launching, it diminishes its ascenção, because the land has gravity enough to delay its ascent and to pull it in return. This is as the mass of the universe to be enough to stop its expansion. When the ball reaches its maximum height, it so that it is the same that the universe goes to make to reach its critical density. Then, very slowly the ball will start to fall, increasing its speed each time more during the fall, until it reaches the soil again. This is the same that it occurs in the end of the universe with the “Big Crunch”.