Ultimate fate of the universe
The ultimate fate of the universe is a valid question because according to all models on the universe, the universe is finite, and will end. The only question logically, is what will happen at the end of the universe. There are many different scientific scenarios, and religious scenarios as well. When the Big Bang theory became the foremost explanation for the current state of the universe, the fate of the universe became a valid question.
The universe is currently expanding at a rate of 73.8 ± 2.4 kilometers per second per Megaparsecs. (A megaparsec is 3.08x1019 kilometers) Under the big bang model, expansion is currently accelerating. When catholic priest George Lemaitre proposed that the universe was born from a singularity, which was expounded on by Edwin Hubble, using the theory of relativity, it became clear that all theories implied an ultimate fate to the universe.
There are three commonly accepted theories on how the universe will end. They are the Big crunch, where the universe collapses on itself, the Big Rip scenario, where acceleration destroys the bonding of atoms, and all matter decays, and the Heat death, where the universe reaches a maximum state of entropy.
The Big Crunch theory is a symmetric view of the ultimate fate of the Universe. Just as the Big Bang started a cosmological expansion, this theory assumes that the average density of the universe is enough to stop its expansion and begin contracting. The end result is unknown; a simple estimation would have all the matter and space-time in the universe collapse into a dimensionless singularity, but at these scales unknown quantum effects need to be considered. This scenario allows the Big Bang to be immediately after the Big Crunch of a preceding universe. If this occurs repeatedly, we have a cyclic model which is also known as a oscillatory universe. The universe could then consist of an infinite sequence of finite universes, each finite universe ending with a Big Crunch that is also the Big Bang of the next universe. Theoretically, the cyclic universe could not be reconciled with the second law of thermodynamics: entropy would build up from oscillation to oscillation and cause heat death. Other measurements suggested the universe is not closed. These arguments caused cosmologists to abandon the oscillating universe model. A somewhat similar idea is embraced by the cyclic model, but this idea evades heat death, because of an expansion of the branes that dilutes entropy accumulated in the previous cycle. In the big crunch, the universe will end approximately 30 billion years from now.
In the special case of phantom dark energy, which has even more negative pressure than a simple cosmological constant, the density of dark energy increases with time, causing the rate of acceleration to increase, leading to a steady increase in the Hubble constant. As a result, all material objects in the universe, starting with galaxies and eventually, all forms, no matter how small, will disintegrate into unbound elementary particles and radiation, ripped apart by the phantom energy force and shooting apart from each other. The end state of the universe is a singularity, as the dark energy density and expansion rate becomes infinite. For a possible timeline based on current physical theories, see 1 E19 s and more. This universe will end approximately 100 billion years from now.
After the Stelliferous Epoch, all hydrogen in the universe will be exhausted. Then, only remnants remain. After 1017 billion years from now, protons will decay into a positron, and a pion. All particles will decay, leaving behind nothing but simple particles. The rate of entropy will be at a maximum, and nothing will interact ever again.
Most organized religions have a prophecy regarding the end of the universe, and of time itself. The 3 Abrahamic religions predict a "judgement day", while Buddhism follows a more "heat death" scenario. Others believe in an infinite "flat" universe, where everything is static
The Abrahamic religions teach a judgement day, where the righteous will enter heaven, and the wicked, shall either be destroyed, or suffer for all eternity in hell. Regarding the universe, the three religions agree that the universe will be destroyed, and replaced with a new earth, universe, and God will reign forever and ever.
Buddhism and Hinduism teach that the universe will one day be devoid of life, and action. This is because the people will have escaped the cycle of life and death, desire, and suffering, and enter a state of nirvana. The wicked will suffer in naraka, for unimaginably long periods of time, but not forever.
Atheism and agnosticism and the fate of the universe
|“|| That man is the product of causes that had no prevision of the end they were achieving; that his origin, his growth, his hopes and fears, his loves and his beliefs, are but the outcome of accidental collocations of atoms; that no fire, no heroism, no intensity of thought and feeling, can preserve individual life beyond the grave; that all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and that the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins- all these things, if not quite beyond dispute, are yet so nearly certain that no philosophy which rejects them can hope to stand.
"Only within the scaffolding of these truths, only on the firm foundation of unyielding dispair, can the soul's habitation henceforth be safely built." 
In a letter to Lowes Dickinson, Bertrand Russell wrote:
|“||We stand on the shores of an ocean, crying to the night and the emptiness; sometimes a voice answers out of the darkness. But it is a voice of one drowning; and in a moment the silence returns” (Bertrand Russell, Autobiography, p. 287 as quoted by Leroy Koopman, “Famous Atheists Give Their Testimonies,” Moody Monthly, Nov. 1975, p. 124.) ||”|
Certain fringe groups, such as Scientology, hold that the universe is static, and will never change. Specifically, it states that all consciousness will follow the same pattern of birth and rebirth, forever.
- When he opened the sixth seal, I looked, and behold, there was a great earthquake, and the sun became black as sackcloth, the full moon became like blood, and the stars of the sky fell to the earth as the fig tree sheds its winter fruit when shaken by a gale. The sky vanished like a scroll that is being rolled up, and every mountain and island was removed from its place. (Revelation 6:12–14)
- ^ a b Lemaître, Georges (1927). "Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques". Annales de la Société Scientifique de Bruxelles A47: 49–56. Bibcode 1927ASSB...47...49L translated by A. S. Eddington: Lemaître, Georges (1931). "Expansion of the universe, A homogeneous universe of constant mass and increasing radius accounting for the radial velocity of extra-galactic nebulæ". Monthly Notices of the Royal Astronomical Society 91: 483–490. Bibcode 1931MNRAS..91..483L
- Thomson, William. (1851). "On the Dynamical Theory of Heat, with numerical results deduced from Mr Joule’s equivalent of a Thermal Unit, and M. Regnault’s Observations on Steam." Excerpts. [§§1–14 & §§99–100], Transactions of the Royal Society of Edinburgh, March, 1851; and Philosophical Magazine IV. 1852, [from Mathematical and Physical Papers, vol. i, art. XLVIII, pp. 174]
- M. Stone (1976). "Lifetime and decay of excited vacuum states". Phys. Rev. D 14 (12): 3568–3573. Bibcode 1976PhRvD..14.3568S. doi:10.1103/PhysRevD.14.3568.
- Jātaka 20:12-1 And the all will fall quiet, forever; all will reach nirvana, or perish in "naraka"
- Dianetics: The Modern Science of Mental Health, Hubbard, Ron, L accessed 11/21/11
- Revelations 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death
- Russell, Bertrand (1947) "Am I An Atheist Or An Agnostic?" Most online sources say "by which one prove," probably a mistake.
- Entropy and heat death
- Atheism and the despair of hope