If dark energy is in the form of a cosmological constant, the expansion will eventually become exponential. Stars are expected to form normally for 1012 to 1014 years, but eventually the supply of gas needed for star formation will be exhausted. As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker. Ultimately, if the universe reaches a state in which the temperature approaches a uniform value, no further work will be possible.
About Future of an expanding universe in brief
If dark energy is in the form of a cosmological constant, the expansion will eventually become exponential. Stars are expected to form normally for 1012 to 1014 years, but eventually the supply of gas needed for star formation will be exhausted. As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker. Ultimately, if the universe reaches a state in which the temperature approaches a uniform value, no further work will be possible, resulting in a final heat death of the universe. It is possible that the dark energy equation of state could change again resulting in an event that would have consequences which are extremely difficult to parametrize or predict. If space in the universe begins to contract, subsequent events in the timeline may not occur because the Big Crunch, the collapse of the world into a hot, dense state similar to that after the Big Bang, will supervene. The observable universe is currently 38×1010 years old. Since then, the first star formed, stars have formed the core of small, cold molecular clouds of hydrogen gas. At first, this produces a large, protostar, which is hot and bright because of gravitational contraction. Stars of low mass will eventually exhaust their mass and become white dwarfs and then helium fusus. After some time, they will expel some of their mass as a planetary nebula and become more massive. After a lifetime as a very low mass, a star will become hot enough to fuse its hydrogen and fuse its center to become a very massive white dwarf.
This is the time during which stars form from collapsing clouds of gas. In the subsequent Degenerate Era, the stars will have burnt out, leaving all stellar-mass objects as stellar remnants—white dwarfs, neutron stars, and black holes. Finally, in the Dark Era, even black holes have disappeared, leaving only a dilute gas of photons and leptons. This future history and the timeline below assume the continued expansion of the universes. If the universe is spatially flat and has a significant amount of dark energy, it should continue to expand at an accelerating rate. If it is open, flat, or closed, although if it is closed, sufficient dark energy must be present to counteract the gravitational forces or else the universe would end in a Big Crunch. The acceleration of universe’s expansion has also been confirmed by observations of distant supernovae. The universe went through an episode dominated by a different form of darkEnergy in the first moments of the Big bang; but inflation ended, indicating an equation ofState much more complicated than those assumed so far for present-day dark energy. If this is true, then the universe wentthrough an episode of inflation in the early universe. The Big Crunch may not have happened as predicted by the theory of inflation, but rather a period of time when the universe was expanding at a constant rate. This time period is about 155 million years after the First Big Bang.
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This page is based on the article Future of an expanding universe published in Wikipedia (as of Dec. 08, 2020) and was automatically summarized using artificial intelligence.
