How the universe will end?

Answer 1

The Universe, as unimaginably vast as it is, will eventually cease to exist, at least as we currently know it. Whether it will truly "end" and exactly what will happen to it, scientists still aren't sure. The Universe's fate will come billions, maybe even trillions of years from now, and the human race will not be around to witness it. There are currently three main competing hypotheses regarding the ultimate fate of the universe. As we gather more evidence, we will begin to see which event is most likely to occur.

1) The Big Freeze, also known as Heat Death, is a scenario under which the universe continues to expand indefinitely at an ever increasing rate, as matter move away from each other and the gravitational attraction between them is weakened by the increasing distance. The expansion causes heat to disperse and the Universe will continue to get colder until it reaches absolute zero. Stars and galaxies will slowly die and the Universe will go dark. After that it is not known what will happen to space and time itself. The Big freese could occur under a flat or hyperbolic geometry, because such geometries are a necessary condition for a universe that expands forever. Of course, there is no "end" to the universe anymore should this scenario occur, in the usual sense, but nonetheless it could be considered as some ultimate fate to which the current universe may be susceptible.

2) The Big Rip will only occur if the energy density of dark energy increases without limit over time. The Universe will expand so rapidly that everything will be "ripped" apart, from galaxies to stars to atoms. At one point the expansion rate of the Universe will reach infinity, and everything in the entire Universe, even space and time itself, will be completely destroyed. With the discovery that the Universe is actually expanding faster, the Big Rip is a probable scenario.

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3) The Big Crunch model is a symmetric view of the ultimate fate of the universe. Just as the Big Bang started a cosmological expansion, this theory postulates that the average density of the universe is enough to stop its expansion and begin to contract. The end result is unknown; a simple extrapolation would have all the matter and space-time in the universe collapse into a dimensionless singularity of unimaginable density. In a closed Universe this scenario could occur. But according to the most recent findings, scientists have determined that the Big Crunch is unlikely to happen.

The Big Bounce, Oscillating Universe, or Cyclic Universe model is an extension of the Big Crunch hypothesis and says that the Universe undergoes an infinite series of Big Bangs and Big Crunches. This scenario allows the Big Bang to have been immediately preceded by the Big Crunch of a preceding universe. If this occurs repeatedly, we have what might be said to be a cyclic universe, and the Universe has existed for infinity. However, there are problems with this hypothesis regarding entropy and thermodynamics, and it has also been deemed unlikely.

It should be noted that these theories are not mere idle speculation. Theoretical scientific exploration on this topic was made possible by General Relativity, which could be employed to describe the universe on the largest possible scale. Mathematically there are many solutions to the field equations of General Relativity, depending on how much matter there is in the universe, each implying a possible ultimate fate of it. Experimental evidence surrounding the expansion of the universe from Hubble and co. were also very helpful.

See the links below for more details on each hypothesis

Answer 2

That is still one of the great unanswered questions. At the moment we do not know, though research is currently underway to get a better idea - even then we may never know.

Current thoughts are:

• Big freeze: The Universe continues to expand forever.
• Big Crunch: The Universe slows it's expansion and then starts to contract.
• Big Rip: All matter will be reduced to particles.
• Big Slow: The universe will slow it's expansion and then stop.

Of course if you are religious, your top man or book (Whatever the flavour) will have the answer.