Future of an expanding universe
[1][2] If dark energy—represented by the cosmological constant, a constant energy density filling space homogeneously,[3] or scalar fields, such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space—accelerates the expansion of the universe, then the space between clusters of galaxies will grow at an increasing rate.
Redshift will stretch ancient ambient photons (including gamma rays) to undetectably long wavelengths and low energies.
As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker.
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.
[citation needed] In the 1970s, the future of an expanding universe was studied by the astrophysicist Jamal Islam[12] and the physicist Freeman Dyson.
Finally, in the Dark Era, even black holes have disappeared, leaving only a dilute gas of photons and leptons.
Since then, stars have formed by the collapse of small, dense core regions in large, cold molecular clouds of hydrogen gas.
After the protostar contracts for a while, its core could become hot enough to fuse hydrogen, if it exceeds critical mass, a process called 'stellar ignition' occurs, and its lifetime as a star will properly begin.
22 billion years in the future is the earliest possible end of the Universe in the Big Rip scenario, assuming a model of dark energy with w = −1.5.
It is expected that between 1011 (100 billion) and 1012 (1 trillion) years from now, their orbits will decay and the entire Local Group will merge into one large galaxy.
[5] Assuming that dark energy continues to make the universe expand at an accelerating rate, in about 150 billion years all galaxies outside the Local Supercluster will pass behind the cosmological horizon.
Technically, it will take an infinitely long time for all causal interaction between the Local Supercluster and this light to cease.
[26] 2×1012 (2 trillion) years from now, all galaxies outside the Local Supercluster will be redshifted to such an extent that even gamma rays they emit will have wavelengths longer than the size of the observable universe of the time.
[4] By 1014 (100 trillion) years from now, star formation will end,[5] leaving all stellar objects in the form of degenerate remnants.
[5] Once star formation ends and the least-massive red dwarfs exhaust their fuel, nuclear fusion will cease.
The resulting object will then undergo runaway thermonuclear fusion, producing a Type Ia supernova and dispelling the darkness of the Degenerate Era for a few weeks.
Neutron stars could also collide, forming even brighter supernovae and dispelling up to 6 solar masses of degenerate gas into the interstellar medium.
When this happens, the trajectories of the objects involved in the close encounter change slightly, in such a way that their kinetic energies are more nearly equal than before.
The result is that most objects (90% to 99%) are ejected from the galaxy, leaving a small fraction (maybe 1% to 10%) which fall into the central supermassive black hole.
[38][39] Recent research showing proton lifetime (if unstable) at or exceeding 1036–1037 year range rules out simpler GUTs and most non-supersymmetry models.
Planets (substellar objects) would decay in a simple cascade process from heavier elements to hydrogen and finally to photons and leptons while radiating energy.
This means that there will be roughly 0.51,000 (approximately 10−301) as many nucleons; as there are an estimated 1080 protons currently in the universe,[41] none will remain at the end of the Degenerate Age.
On a time scale of 1065 years solid matter is theorized to potentially rearrange its atoms and molecules via quantum tunneling, and may behave as liquid and become smooth spheres due to diffusion and gravity.
[13] Degenerate stellar objects can potentially still experience proton decay, for example via processes involving the Adler–Bell–Jackiw anomaly, virtual black holes, or higher-dimension supersymmetry possibly with a half-life of under 10220 years.
[5] 2018 estimate of Standard Model lifetime before collapse of a false vacuum; 95% confidence interval is 1065 to 10725 years due in part to uncertainty about the top quark mass.
During most of a black hole's lifetime, the radiation has a low temperature and is mainly in the form of massless particles such as photons and hypothetical gravitons.
2018 estimate of Standard Model lifetime before collapse of a false vacuum; 95% confidence interval is 1065 to 101383 years due in part to uncertainty about the top quark mass.
[13] Before this happens, however, in some black dwarfs the process is expected to lower their Chandrasekhar limit resulting in a supernova in 101100 years.
[49] Quantum tunneling should also turn large objects into black holes, which (on these timescales) will instantaneously evaporate into subatomic particles.
[13] With black holes having evaporated, nearly all baryonic matter will have now decayed into subatomic particles (electrons, neutrons, protons, and quarks).
