Future of an expanding universe
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Articles Which Contain Graphical Timelines
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- Cosmology
- Future history
- Timeline
- The Stelliferous Era
- Milky Way Galaxy and the..
- Coalescence of Local Gro..
- Luminosities of galaxies..
- Galaxies outside the Loc..
- Degenerate Era
- Future with proton decay
- Nucleons start to decay
- All nucleons decay
- If protons decay on high..
- Black Hole Era
- Dark Era and Photon Age
- Future without proton de..
- Beyond
- Graphical timelines
- See also
- Notes
- References
- External links
Current observations suggest that the expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario popularly called "Heat Death" is also known as the "Big Chill" or "Big Freeze". Some of the other popular theories include the Big Rip, Big Crunch, and the Big Bounce.
If dark energy—represented by the cosmological constant, a constant energy density filling space homogeneously, 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. are expected to form normally for 1012 to 1014 (1–100 trillion) 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.Adams & Laughlin (1997), §IIE. According to theories that predict proton decay, the compact star left behind will disappear, leaving behind only , which themselves eventually disappear as they emit Hawking radiation.Adams & Laughlin (1997), §IV. Ultimately, if the universe reaches thermodynamic equilibrium, 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.Adams & Laughlin (1997), §VID.
Cosmology
Observations of the Cosmic microwave background by the Wilkinson Microwave Anisotropy Probe and the Planck mission suggest that the universe is spatially flat and has a significant amount of dark energy. In this case, the universe might continue to expand at an accelerating rate. The acceleration of the universe's expansion has also been confirmed by observations of distant supernovae. If, as in the Lambda-CDM model of physical cosmology (Lambda-cold dark matter or ΛCDM), dark energy is in the form of a cosmological constant, the expansion will eventually become exponential, with the size of the universe doubling at a constant rate.
If the theory of inflation is correct, the universe went through an episode dominated by a different form of dark energy in the first moments of the Big Bang; but inflation ended, indicating an equation of state much more complicated than those assumed so far for present-day dark energy. 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.
Future history
This future history and the timeline below assume the continued expansion of the universe. If space in the universe begins to contract, subsequent events in the timeline may not occur because the Big Crunch, the collapse of the universe into a hot, dense state similar to that after the Big Bang, will prevail.Adams & Laughlin (1997), §VA.
Timeline
The Stelliferous Era
- From the present to about (100 trillion) years after the Big Bang
Stars of very low mass will eventually exhaust all their fusible hydrogen and then become helium . Stars of low to medium mass, such as our own sun, will expel some of their mass as a planetary nebula and eventually become white dwarfs; more massive stars will explode in a core-collapse supernova, leaving behind or black holes. In any case, although some of the star's matter may be returned to the interstellar medium, a compact star will be left behind whose mass is not returned to the interstellar medium. Therefore, the supply of gas available for star formation is steadily being exhausted.
Milky Way Galaxy and the Andromeda Galaxy merge into one
- 4–8 billion years from now (17.8–21.8 billion years after the Big Bang)
The Andromeda Galaxy is approximately 2.5 million light years away from our galaxy, the Milky Way galaxy, and they are moving towards each other at approximately 300 kilometres (186 miles) per second. Approximately five billion years from now, or 19 billion years after the Big Bang, the Milky Way and the Andromeda galaxy will collide with one another and merge into one large galaxy based on current evidence. Up until 2012, there was no way to confirm whether the possible collision was going to happen. In 2012, researchers came to the conclusion that the collision is definite after using the Hubble Space Telescope between 2002 and 2010 to track the motion of Andromeda. This results in the formation of Milkdromeda (also known as Milkomeda).
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 = −1.5.
False vacuum decay may occur in 20 to 30 billion years if the Higgs boson is metastable.
Coalescence of Local Group and galaxies outside the Local Supercluster are no longer accessible
- (100 billion) to (1 trillion) years
The galaxies in the Local Group, the cluster of galaxies which includes the Milky Way and the Andromeda Galaxy, are gravitationally bound to each other. It is expected that between (100 billion) and (1 trillion) years from now, their orbits will decay and the entire Local Group will merge into one large galaxy.
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. It will then be impossible for events in the Local Supercluster to affect other galaxies. Similarly, it will be impossible for events after 150 billion years, as seen by observers in distant galaxies, to affect events in the Local Supercluster. However, an observer in the Local Supercluster will continue to see distant galaxies, but events they observe will become exponentially more redshifted as the galaxy approaches the horizon until time in the distant galaxy seems to stop. The observer in the Local Supercluster never observes events after 150 billion years in their local time, and eventually all light and background radiation lying outside the Local Supercluster will appear to blink out as light becomes so redshifted that its wavelength has become longer than the physical diameter of the horizon.
Technically, it will take an infinitely long time for all causal interaction between the Local Supercluster and this light to cease. However, due to the redshifting explained above, the light will not necessarily be observed for an infinite amount of time, and after 150 billion years, no new causal interaction will be observed.
Therefore, after 150 billion years, intergalactic transportation and communication beyond the Local Supercluster becomes causally impossible.
Luminosities of galaxies begin to diminish
- (800 billion) years
(800 billion) years from now, the luminosities of the different galaxies, approximately similar until then to the current ones thanks to the increasing luminosity of the remaining stars as they age, will start to decrease, as the less massive [[red dwarf]] stars begin to die as [[white dwarf]]s. See Fig. 3.
Galaxies outside the Local Supercluster are no longer detectable
- (2 trillion) years
2 (2 trillion) years from now, all galaxies outside the Local Supercluster will be redshifted to such an extent that even they emit will have wavelengths longer than the size of the observable universe of the time. Therefore, these galaxies will no longer be detectable in any way.
Degenerate Era
- From (100 trillion) to (10 duodecillion) years
By (100 trillion) years from now, star formation will end, leaving all stellar objects in the form of compact star. If proton decay, stellar-mass objects will disappear more slowly, making this era last longer.
Star formation ceases
- (1–100 trillion) years
By (100 trillion) years from now, star formation will end. This period, known as the "Degenerate Era", will last until the degenerate remnants finally decay.Adams & Laughlin (1997), § III–IV. The least-massive stars take the longest to exhaust their hydrogen fuel (see stellar evolution). Thus, the longest living stars in the universe are low-mass , with a mass of about 0.08 (), which have a lifetime of over (10 trillion) years.Adams & Laughlin (1997), §IIA and Figure 1. Coincidentally, this is comparable to the length of time over which star formation takes place. Once star formation ends and the least-massive red dwarfs exhaust their fuel, nuclear fusion will cease. The low-mass red dwarfs will cool and become . The only objects remaining with more than planemo will be (with mass less than ), and compact star: , produced by stars with initial masses between about 0.08 and 8 solar masses, and and black holes, produced by stars with initial masses over . Most of the mass of this collection, approximately 90%, will be in the form of white dwarfs. In the absence of any energy source, all of these formerly luminous bodies will cool and become faint.
The universe will become extremely dark after the last stars burn out. Even so, there can still be occasional light in the universe. One of the ways the universe can be illuminated is if two carbon–oxygen white dwarfs with a combined mass of more than the Chandrasekhar limit of about 1.4 solar masses happen to merge. 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. could also collide, forming even brighter supernovae and dispelling up to 6 solar masses of degenerate gas into the interstellar medium. The resulting matter from these supernovae could potentially create new stars.Adams & Laughlin (1997), §IIIC. If the combined mass is not above the Chandrasekhar limit but is larger than the minimum mass to nuclear fusion carbon (about ), a carbon star could be produced, with a lifetime of around (1 million) years. Also, if two helium white dwarfs with a combined mass of at least collide, a helium star may be produced, with a lifetime of a few hundred million years. Finally, brown dwarfs could form new stars by colliding with each other to form red dwarf stars, which can survive for (10 trillion) years, or by accreting gas at very slow rates from the remaining interstellar medium until they have enough mass to start hydrogen burning as red dwarfs. This process, at least on white dwarfs, could induce Type Ia supernovae.
Because of dynamical relaxation, some objects will gain just enough energy to reach galactic escape velocity and depart the galaxy, leaving behind a smaller, denser galaxy. Since encounters are more frequent in this denser galaxy, the process then accelerates. 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. It has been suggested that the matter of the fallen remnants will form an accretion disk around it that will create a quasar, as long as enough matter is present there.
In an expanding universe with decreasing density and non-zero cosmological constant, matter density would reach zero, resulting in most matter except , , , and ionizing and dissipating at thermal equilibrium.
The subsequent evolution of the universe depends on the possibility and rate of proton decay. Experimental evidence shows that if the proton is unstable, it has a half-life of at least years. Some of the Grand Unified theories (GUTs) predict long-term proton instability between and years, with the upper bound on standard (non-supersymmetry) proton decay at 1.4 years and an overall upper limit maximum for any proton decay (including supersymmetry models) at 6 years. Recent research showing proton lifetime (if unstable) at or exceeding – year range rules out simpler GUTs and most non-supersymmetry models.
If the proton does not decay at all, then stellar objects would still disappear, but more slowly. See below.
Shorter or longer proton half-lives will accelerate or decelerate the process. This means that after years (the maximum proton half-life used by Adams & Laughlin (1997)), one-half of all baryonic matter will have been converted into gamma ray and leptons through proton decay.
Given our assumed half-life of the proton, (protons and bound neutrons) will have undergone roughly 1,000 half-lives by the time the universe is years old. This means that there will be roughly 0.51,000 (approximately ) as many nucleons; as there are an estimated protons currently in the universe,
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.
Although protons are stable in standard model physics, a chiral anomaly may exist on the electroweak level, which can cause groups of baryons (protons and neutrons) to annihilate into antileptons via the sphaleron transition. Such baryon number have a number of 3 and can only occur in multiples or groups of three baryons, which can restrict or prohibit such events. No experimental evidence of sphalerons has yet been observed at low energy levels, though they are believed to occur regularly at high energies and temperatures.
After years, black holes will dominate the universe. They will slowly evaporate via Hawking radiation. A black hole with a mass of around will vanish in around 2 years. As the lifetime of a black hole is proportional to the cube of its mass, more massive black holes take longer to decay. A supermassive black hole with a mass of (100 billion) will evaporate in around 2 years.. See in particular equation (27).
The largest in the universe are predicted to continue to grow. Larger black holes of up to (100 trillion) may form during the collapse of superclusters of galaxies. Even these would evaporate over a timescale of See page 596: table 1 and section "black hole decay" and previous sentence on that page
to years.
Hawking radiation has a thermal spectrum. 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 and hypothetical . As the black hole's mass decreases, its temperature increases, becoming comparable to the Sun's by the time the black hole mass has decreased to kilograms. The hole then provides a temporary source of light during the general darkness of the Black Hole Era. During the last stages of its evaporation, a black hole will emit not only massless particles, but also heavier particles, such as , , , and .
After all the black holes have evaporated (and after all the ordinary matter made of protons has disintegrated, if protons are unstable), the universe will be nearly empty. , , , , , and will fly from place to place, hardly ever encountering each other. Gravity, the universe will be dominated by dark matter, , and (not ).Adams & Laughlin (1997), §VD.
By this era, with only very diffuse matter remaining, activity in the universe will eventually tail off dramatically (compared with previous eras), with very low energy levels and very large time scales, with events taking a very long time to happen if they ever happen at all. Electrons and positrons drifting through space will encounter one another and occasionally form positronium atoms. These structures are unstable, however, and their constituent particles must eventually annihilate. However, most electrons and positrons will remain unbound.Adams & Laughlin (1997), §VF3. Other low-level annihilation events will also take place, albeit extremely slowly. The universe now gradually tends towards its lowest energy state.
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.
Quantum tunneling should also turn large objects into , which (on these timescales) will instantaneously evaporate into subatomic particles. Depending on the assumptions made, the time this takes to happen can be calculated as from years to years. Quantum tunneling may also make iron stars collapse into in around years.
With black holes having evaporated, nearly all baryonic matter will have decayed into subatomic particles (electrons, neutrons, protons, and quarks). The universe is now an almost pure vacuum (possibly accompanied with the presence of a false vacuum). The expansion of the universe slowly causes itself to cool down to absolute zero. The universe now reaches an even lower energy state than the earlier one mentioned.
Whatever event happens beyond this era is highly speculative. It is possible that a Big Rip event may occur far off into the future. This singularity would take place at a finite scale factor.
If the current vacuum state is a false vacuum, the vacuum may decay into an even lower-energy state.Adams & Laughlin (1997), §VE.
Presumably, extreme low-Energy level imply that localized quantum events become major macroscopic phenomena rather than negligible microscopic events because even the smallest perturbations make the biggest difference in this era, so there is no telling what will or might happen to space or time. It is perceived that the laws of "macro-physics" will break down, and the laws of quantum physics will prevail.
It has been hypothesized that the universe could possibly avoid an eternal heat death through random quantum tunneling and quantum fluctuations, given the non-zero probability of producing a new Big Bang creating a new universe in roughly years, according to physicists Sean M. Carroll and Jennifer Chen.
Over an infinite amount of time, there could also possibly be a spontaneous entropy decrease, by a Poincaré recurrence or through thermal fluctuations (see also fluctuation theorem).
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Planets fall or are flung from orbits by a close encounter with another star
Over time, the of planets will decay due to gravitational radiation, or planets will be rogue planet from their local systems by gravitational perturbations caused by encounters with another compact star.Adams & Laughlin (1997), §IIIF, Table I.
Stellar remnants escape galaxies or fall into black holes
Over time, objects in a galaxy exchange kinetic energy in a process called dynamical relaxation, making their velocity distribution approach the Maxwell–Boltzmann distribution.p. 428, A deep focus on NGC 1883, A. L. Tadross, Bulletin of the Astronomical Society of India 33, No. 4 (December 2005), pp. 421–431, . Dynamical relaxation can proceed either by close encounters of two stars or by less violent but more frequent distant encounters. Reading notes , Liliya L. R. Williams, Astrophysics II: Galactic and Extragalactic Astronomy, University of Minnesota. Retrieved 20 July 2008. In the case of a close encounter, two brown dwarfs or compact star will pass close to each other. When this happens, the trajectories of the objects involved in the close encounter change slightly, in such a way that their kinetic energy are more nearly equal than before. After a large number of encounters, then, lighter objects tend to gain speed while the heavier objects lose it.Fred Adams and Greg Laughlin, The Five Ages of the Universe, New York: The Free Press, 1999, .
Possible ionization of matter
Future with proton decay
Nucleons start to decay
All nucleons decay
If protons decay on higher-order nuclear processes
If the proton does not decay according to the theories described above, then the Degenerate Era will last longer, and will overlap or surpass the Black Hole Era. On a time scale of years solid matter is theorized to potentially rearrange its and via quantum tunneling, and may behave as liquid and become smooth due to diffusion and gravity. Degenerate stellar objects can potentially still experience proton decay, for example via processes involving the Chiral anomaly, virtual black holes, or higher-dimension supersymmetry possibly with a half-life of under years.
Black Hole Era
Dark Era and Photon Age
Future without proton decay
/ref>
Degenerate Era
Matter decays into iron
In years, pycnonuclear fusion occurring via quantum tunnelling should make the light atomic nucleus in stellar-mass objects fuse into iron-56 nuclei (see isotopes of iron). Nuclear fission and alpha particle emission should make heavy nuclei also decay to iron, leaving stellar-mass objects as cold spheres of iron, called . Before this happens, however, in some the process is expected to lower their Chandrasekhar limit resulting in a supernova in years. Non-degenerate silicon has been calculated to tunnel to iron in approximately years.
Black Hole Era
Collapse of iron stars to black holes
Dark Era (without proton decay)
Beyond
Graphical timelines
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from:8 till:14 shift:(0,15) color:era2 text:"Stelliferous Era"
from:14 till:40 shift:(0,-5) color:era1 text:"Degenerate Era"
from:40 till:100 shift:(0,-25) color:era2 text:"Black Hole Era"
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at:14 shift:(0,-25) text:"The last star has died"
at:40 shift:(0,-35) text:"The last proton has decayed"
at:100 shift:(0,-45) text:"The last supermassive black holes have evaporated"
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from:90 till:115 shift:(0,15) color:era2 text:"Stelliferous Era"
from:115 till:317 shift:(0,-5) color:era1 text:"Degenerate Era"
from:317 till:5000 shift:(0,-25) color:era2 text:"Ferostelliferous Era"
from:5000 till:5500 shift:(0,-45) color:era1 text:"Dark Era"
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at:90 shift:(-2,15) text:"First star began to shine"
at:101 shift:(-2,-5) text:"13.8 billion years, the present day"
at:115 shift:(0,-25) text:"The last star has died"
at:200 shift:(0,-45) text:"The last supermassive black holes have evaporated"
at:317 shift:(0,40) text:"The first iron stars form"
at:5000 shift:(0,0) text:"The last iron stars collapse into black holes"
See also
Notes
External links
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