Future of an expanding universe
Encyclopedia
Observations suggest that the expansion of the universe
will continue forever. If so, the universe will cool as it expands, eventually becoming too cold to sustain life
. For this reason, this future scenario is popularly called the Big Freeze.
The future of an expanding universe is bleak. If a cosmological constant
accelerates the expansion of the universe, the space between clusters of galaxies will grow at an increasing rate. Redshift will have stretched ancient, incoming photons (even gamma rays) to undetectably long wavelengths and low energies. Star
s are expected to form normally for 1 to 1 years, but eventually the supply of gas needed for star formation
will be exhausted. Once the last star has exhausted its fuel, stars will cease to shine., §IID, IIE. According to theories that predict proton decay
, the stellar remnants
left behind would disappear, leaving behind only black holes which themselves eventually disappear as they emit Hawking radiation
., §IV. 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
., §VID.
of the universe. It can be open (with negative spatial curvature), flat, or closed (positive spatial curvature), although if it is closed, sufficient dark energy
must be present to counteract the gravitational attraction of matter and other forces tending to contract the universe. Open and flat universes will expand forever even in the absence of dark energy.
Observations of the cosmic background radiation by the Wilkinson Microwave Anisotropy Probe
suggest that the universe is spatially flat and has a significant amount of dark energy
. In this case, the universe should 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 concordance model
of physical cosmology
(Lambda-cold dark matter or ΛCDM), the 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 true, 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.
and the physicist Freeman Dyson
.
More recently, the astrophysicists Fred Adams
and Gregory Laughlin have divided the past and future history of an expanding universe into five eras. The first, the Primordial Era, is the time in the past just after the Big Bang
when star
s had not yet formed. The second, the Stelliferous Era, includes the present day and all of the stars and galaxies we see. It 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 dwarf
s, neutron stars, and black hole
s. In the Black Hole Era, white dwarfs, neutron stars, and other smaller astronomical objects have been destroyed by proton decay
, leaving only black holes. Finally, in the Dark Era, even black holes have disappeared, leaving only a dilute gas of photons and leptons., pp. xxiv–xxviii.
This future history and the timeline below assume the continued expansion of the universe. If the universe begins to recontract, subsequent events in the timeline may not occur because the Big Crunch
, the recontraction of the universe
into a hot, dense state similar to that after the Big Bang, will supervene., pp. 190–192;, §VA
The universe is currently 1.37×1010 (13.7 billion) years old. This time is in the Stelliferous Era. About 155 million years after the Big Bang, the first star formed. Since then, stars have formed by the collapse of small, dense core regions in large, cold molecular cloud
s of hydrogen
gas. At first, this produces a protostar
, which is hot and bright because of energy generated by gravitational contraction. After the protostar contracts for a while, its center will become hot enough to fuse
hydrogen and its lifetime as a star will properly begin., pp. 35–39.
Stars whose mass is very low will eventually exhaust all their fusible hydrogen
and then become helium
white dwarf
s. Stars of low to medium mass will expel some of their mass as a planetary nebula
and eventually become a white dwarf
; more massive stars will explode in a core-collapse supernova, leaving behind neutron star
s or black holes. In any case, although some of the star's matter may be returned to the interstellar medium
, a degenerate remnant
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.
The Andromeda Galaxy
is currently approximately 2.5 million light years away from our galaxy, the Milky Way Galaxy, and the galaxies are moving towards each other at approximately 120 kilometers per second. Approximately three billion years from now, or 17 billion years after the Big Bang, the Milky Way and the Andromeda Galaxy may collide with one another and merge into one large galaxy. Because it is not known precisely how fast the Andromeda Galaxy is moving transverse to us, it is not certain that the collision will happen.
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 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., §IIIA.
Assuming that dark energy
continues to make the universe expand at an accelerating rate, 2×1012 (2 trillion) years from now, all galaxies outside the Local Supercluster will be red-shifted to such an extent that even gamma ray
s 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.
By 1014 (100 trillion) years from now, star formation will end, leaving all stellar objects in the form of degenerate remnants
. This period, known as the Degenerate Era, will last until the degenerate remnants finally decay., § III–IV.
It is estimated that in 1014 (100 trillion) years or less, star formation will end., §IID. 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 red dwarf
s, with a mass of about 0.08 solar mass
es, which have a lifetime of order 1013 (10 trillion) years. Coincidentally, this is comparable to the length of time over which star formation takes place. §IID. 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 white dwarf
s. The only objects remaining with more than planetary mass will be brown dwarf
s, with mass less than 0.08 solar masses, and degenerate remnants
: white dwarf
s, produced by stars with initial masses between about 0.08 and 8 solar masses, and neutron star
s and black hole
s, produced by stars with initial masses over 8 solar masses. Most of the mass of this collection, approximately 90%, will be in the form of white dwarfs. §IIE. 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 star burns 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. §IIIC; If the combined mass is not above the Chandrasekhar limit but is larger than the minimum mass to fuse
carbon (about 0.9 solar masses), a carbon star
could be produced, with a lifetime of around 106 (1 million) years., p. 91 Also, if two helium white dwarfs with a combined mass of at least 0.3 solar masses collide, a helium star
may be produced, with a lifetime of a few hundred million years., p. 91 Finally, if brown dwarfs collide with each other, a red dwarf
star may be produced which can survive for 1013 (10 trillion) years. §IIIC.
Over time, the orbit
s of planets will decay due to gravitational radiation, or planets will be ejected from their local systems by gravitational perturbations caused by encounters with another stellar remnant
., §IIIF, Table I.
Over time, objects in a galaxy
exchange kinetic energy
in a process called dynamical relaxation, making their velocity distribution approach the Maxwell-Boltzmann distribution. Dynamical relaxation can proceed either by close encounters of two stars or by less violent but more frequent distant encounters. In the case of a close encounter, two brown dwarfs or stellar remnants
will pass close to each other. When this happens, the trajectories of the objects involved in the close encounter change slightly. After a large number of encounters, lighter objects tend to gain kinetic energy
while the heavier objects lose it., pp. 85–87
Because of dynamical relaxation, some objects will gain enough energy to reach galactic escape velocity
and depart the galaxy, leaving behind a smaller, denser galaxy. Since encounters are more frequent in the denser galaxy, the process then accelerates. The end result is that most objects are ejected from the galaxy, leaving a small fraction (perhaps 1% to 10%) which fall into the central supermassive black hole
., §IIIAD;, pp. 85–87
The subsequent evolution of the universe depends on the existence and rate of proton decay
. Experimental evidence shows that if the proton
is unstable, it has a half-life
of at least 1034 years. If a Grand Unified Theory is correct, then there are theoretical reasons to believe that the half-life of the proton is under 1041 years., §IVA. Neutron
s bound into nuclei
are also expected to decay with a half-life comparable to the proton's., §IVA
In the event that the proton does not decay at all, stellar-mass objects would still disappear, but more slowly. See Future without proton decay below.
The rest of this timeline assumes that the proton half-life is approximately 1037 years., §IVA. Shorter or longer proton half-lives will accelerate or decelerate the process. This means that after 1037 years, one-half of all baryonic matter will have been converted into gamma ray
photon
s and leptons through proton decay.
Given our assumed half-life of the proton, nucleons (protons and bound neutrons) will have undergone roughly 1,000 half-lives by the time the universe is 1040 years old. To put this into perspective, there are an estimated 1080 protons currently in the universe. This means that the number of nucleons will be slashed in half 1,000 times by the time the universe is 1040 years old. Hence, there will be roughly ½1,000 (approximately 10−301) as many nucleons remaining as there are today; that is, zero nucleons remaining in the universe at the end of the Degenerate Age. Effectively, all baryonic matter will have been changed into photons and leptons. Some models predict the formation of stable positronium
atoms with a greater diameter than the observable universe’s current diameter in 1085 years, and that these will in turn decay to gamma radiation in 10141 years., §IID, IIE.
After 1040 years, black holes will dominate the universe. They will slowly evaporate via Hawking radiation
., §IVG. A black hole with a mass of around 1 solar mass will vanish in around 2×1066 years. However, many of these are likely to merge with supermassive black holes at the center of their galaxies through processes described above long before this happens. 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 1011 (100 billion) solar masses will evaporate in around 2×1099 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 photon
s and graviton
s. 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 1019 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 electron
s, positron
s, proton
s and antiproton
s., pp. 148–150.
will be able to rearrange their atoms and molecules via quantum tunnelling
, behaving as a liquid
does, but more slowly. However, the proton is still expected to decay, for example via processes involving virtual black holes, or other higher-order processes, with a half-life of under 10200 years., §IVF
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. Photons, neutrinos, electrons, and positrons will fly from place to place, hardly ever encountering each other. Gravitationally, the universe will be dominated by dark matter
, electrons, and positrons (not photons)., §VD.
By this era, with only very diffuse matter remaining, activity in the universe will have tailed off dramatically (compared with previous eras), with very low energy levels and very large time scales. 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., §VF3. Other low-level annihilation events will also take place, albeit very slowly.
The universe now reaches an extremely low-energy state. What happens after this is speculative. It is possible that a Big Rip
event may occur far off into the future. Also, the universe may enter a second inflationary epoch, or, assuming that the current vacuum
state is a false vacuum
, the vacuum may decay into a lower-energy state., §VE. Finally, the universe may settle into this state forever, achieving true heat death
., §VID.
does not take place.
In 101500 years, cold fusion
occurring via quantum tunnelling
should make the light nuclei
in ordinary matter fuse into iron-56
nuclei (see isotopes of iron
.) Fission
and alpha-particle emission should make heavy nuclei also decay to iron, leaving stellar-mass objects as cold spheres of iron, called iron star
s.
to 
years from now
Quantum tunnelling should also turn large objects into black hole
s. Depending on the assumptions made, the time this takes to happen can be calculated as from
years to 
years. (To calculate the value of such numbers, see tetration.) Quantum tunnelling may also make iron stars collapse into neutron star
s in around
years.
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
will continue forever. If so, the universe will cool as it expands, eventually becoming too cold to sustain life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...
. For this reason, this future scenario is popularly called the Big Freeze.
The future of an expanding universe is bleak. If a cosmological constant
Cosmological constant
In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...
accelerates the expansion of the universe, the space between clusters of galaxies will grow at an increasing rate. Redshift will have stretched ancient, incoming photons (even gamma rays) to undetectably long wavelengths and low energies. Star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s are expected to form normally for 1 to 1 years, but eventually the supply of gas needed for star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
will be exhausted. Once the last star has exhausted its fuel, stars will cease to shine., §IID, IIE. According to theories that predict proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
, the stellar remnants
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
left behind would disappear, leaving behind only black holes which themselves eventually disappear as they emit Hawking radiation
Hawking radiation
Hawking radiation is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974, and sometimes also after the physicist Jacob Bekenstein...
., §IV. Ultimately, if the universe reaches a state in which the temperature approaches a uniform value, no further work
Work (thermodynamics)
In thermodynamics, work performed by a system is the energy transferred to another system that is measured by the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics. Thermodynamic work encompasses...
will be possible, resulting in a final heat death of the universe
Heat death of the universe
The heat death of the universe is a suggested ultimate fate of the universe, in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain motion or life. Heat death does not imply any particular absolute temperature; it only requires that...
., §VID.
Cosmology
Indefinite expansion does not determine the spatial curvatureCurvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...
of the universe. It can be open (with negative spatial curvature), flat, or closed (positive spatial curvature), although if it is closed, sufficient dark energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
must be present to counteract the gravitational attraction of matter and other forces tending to contract the universe. Open and flat universes will expand forever even in the absence of dark energy.
Observations of the cosmic background radiation by the Wilkinson Microwave Anisotropy Probe
Wilkinson Microwave Anisotropy Probe
The Wilkinson Microwave Anisotropy Probe — also known as the Microwave Anisotropy Probe , and Explorer 80 — is a spacecraft which measures differences in the temperature of the Big Bang's remnant radiant heat — the Cosmic Microwave Background Radiation — across the full sky. Headed by Professor...
suggest that the universe is spatially flat and has a significant amount of dark energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
. In this case, the universe should 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 concordance model
Lambda-CDM model
ΛCDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter, which is also known as the cold dark matter model with dark energy...
of physical cosmology
Physical cosmology
Physical cosmology, as a branch of astronomy, is the study of the largest-scale structures and dynamics of the universe and is concerned with fundamental questions about its formation and evolution. For most of human history, it was a branch of metaphysics and religion...
(Lambda-cold dark matter or ΛCDM), the dark energy is in the form of a cosmological constant
Cosmological constant
In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...
, the expansion will eventually become exponential, with the size of the universe doubling at a constant rate.
If the theory of inflation is true, 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
In the 1970s, the future of an expanding universe was studied by the astrophysicist Jamal IslamJamal Nazrul Islam
Jamal Nazrul Islam is a Bangladeshi mathematical physicist and cosmologist. He is a professor at Chittagong University and a member of the advisory board at Shahjalal University of Science and Technology...
and the physicist Freeman Dyson
Freeman Dyson
Freeman John Dyson FRS is a British-born American theoretical physicist and mathematician, famous for his work in quantum field theory, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists...
.
More recently, the astrophysicists Fred Adams
Fred Adams
Fred C. Adams is an American astrophysicist who has made contributions to the study of physical cosmology.- Biography:Fred Adams is professor of physics at the University of Michigan, where his main field of research is astrophysics theory focusing on star formation, background radiation fields,...
and Gregory Laughlin have divided the past and future history of an expanding universe into five eras. The first, the Primordial Era, is the time in the past just after the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
when star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s had not yet formed. The second, the Stelliferous Era, includes the present day and all of the stars and galaxies we see. It is the time during which stars form from collapsing clouds of gas
Molecular cloud
A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen ....
. In the subsequent Degenerate Era, the stars will have burnt out, leaving all stellar-mass objects as stellar remnants
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
—white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s, neutron stars, and black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
s. In the Black Hole Era, white dwarfs, neutron stars, and other smaller astronomical objects have been destroyed by proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
, leaving only black holes. Finally, in the Dark Era, even black holes have disappeared, leaving only a dilute gas of photons and leptons., pp. xxiv–xxviii.
This future history and the timeline below assume the continued expansion of the universe. If the universe begins to recontract, subsequent events in the timeline may not occur because the Big Crunch
Big Crunch
In physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity.- Overview :...
, the recontraction of the universe
into a hot, dense state similar to that after the Big Bang, will supervene., pp. 190–192;, §VA
Stelliferous Era
- From 106 (1 million) years to 1014 (100 trillion) years after the Big Bang
The universe is currently 1.37×1010 (13.7 billion) years old. This time is in the Stelliferous Era. About 155 million years after the Big Bang, the first star formed. Since then, stars have formed by the collapse of small, dense core regions in large, cold molecular cloud
Molecular cloud
A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen ....
s of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas. At first, this produces a protostar
Protostar
A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...
, which is hot and bright because of energy generated by gravitational contraction. After the protostar contracts for a while, its center will become hot enough to fuse
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
hydrogen and its lifetime as a star will properly begin., pp. 35–39.
Stars whose mass is very low will eventually exhaust all their fusible hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and then become helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s. Stars of low to medium mass will expel some of their mass as a planetary nebula
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
and eventually become a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
; more massive stars will explode in a core-collapse supernova, leaving behind neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s or black holes. In any case, although some of the star's matter may be returned to the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
, a degenerate remnant
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
will be left behind whose mass is not returned to the interstellar medium. Therefore, the supply of gas available for star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
is steadily being exhausted.
Milky Way Galaxy and the Andromeda Galaxy merge into one
- 3 billion years from now (17 billion years after the Big Bang)
The Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
is currently approximately 2.5 million light years away from our galaxy, the Milky Way Galaxy, and the galaxies are moving towards each other at approximately 120 kilometers per second. Approximately three billion years from now, or 17 billion years after the Big Bang, the Milky Way and the Andromeda Galaxy may collide with one another and merge into one large galaxy. Because it is not known precisely how fast the Andromeda Galaxy is moving transverse to us, it is not certain that the collision will happen.
Coalescence of Local Group
- 1011 (100 billion) to 1012 (1 trillion) years
The galaxies in the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
, the cluster of galaxies which includes the Milky Way and the Andromeda Galaxy, are gravitationally bound to each other. 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., §IIIA.
Galaxies outside the Local Supercluster are no longer detectable
- 2×1012 (2 trillion) years
Assuming that dark energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
continues to make the universe expand at an accelerating rate, 2×1012 (2 trillion) years from now, all galaxies outside the Local Supercluster will be red-shifted to such an extent that even gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s they emit will have wavelengths longer than the size of the observable universe
Observable universe
In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light from those objects has had time to reach us since the beginning of the cosmological expansion...
of the time. Therefore, these galaxies will no longer be detectable in any way.
Degenerate Era
- From 1014 (100 trillion) to 1040 years
By 1014 (100 trillion) years from now, star formation will end, leaving all stellar objects in the form of degenerate remnants
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
. This period, known as the Degenerate Era, will last until the degenerate remnants finally decay., § III–IV.
Star formation ceases
- 1014 (100 trillion) years
It is estimated that in 1014 (100 trillion) years or less, star formation will end., §IID. The least massive stars take the longest to exhaust their hydrogen fuel (see stellar evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
). Thus, the longest living stars in the universe are low-mass red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
s, with a mass of about 0.08 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es, which have a lifetime of order 1013 (10 trillion) years. Coincidentally, this is comparable to the length of time over which star formation takes place. §IID. Once star formation ends and the least massive red dwarfs exhaust their fuel, nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
will cease. The low-mass red dwarfs will cool and become white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s. The only objects remaining with more than planetary mass will be brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
s, with mass less than 0.08 solar masses, and degenerate remnants
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
: white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s, produced by stars with initial masses between about 0.08 and 8 solar masses, and neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s and black hole
Stellar black hole
A stellar black hole is a black hole formed by the gravitational collapse of a massive star. They have masses ranging from about 3 to several tens of solar masses...
s, produced by stars with initial masses over 8 solar masses. Most of the mass of this collection, approximately 90%, will be in the form of white dwarfs. §IIE. 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 star burns 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
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
-oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
white dwarfs with a combined mass of more than the Chandrasekhar limit
Chandrasekhar limit
When a star starts running out of fuel, it usually cools off and collapses into one of three compact forms, depending on its total mass:* a White Dwarf, a big lump of Carbon and Oxygen atoms, almost like one huge molecule...
of about 1.4 solar masses happen to merge. The resulting object will then undergo runaway thermonuclear fusion, producing a Type Ia supernova
Type Ia supernova
A Type Ia supernova is a sub-category of supernovae, which in turn are a sub-category of cataclysmic variable stars, that results from the violent explosion of a white dwarf star. A white dwarf is the remnant of a star that has completed its normal life cycle and has ceased nuclear fusion...
and dispelling the darkness of the Degenerate Era for a few weeks. §IIIC; If the combined mass is not above the Chandrasekhar limit but is larger than the minimum mass to fuse
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
carbon (about 0.9 solar masses), a carbon star
Carbon star
A carbon star is a late-type star similar to a red giant whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds,...
could be produced, with a lifetime of around 106 (1 million) years., p. 91 Also, if two helium white dwarfs with a combined mass of at least 0.3 solar masses collide, a helium star
Helium star
A helium star or helium strong star is a class O or B star , which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope...
may be produced, with a lifetime of a few hundred million years., p. 91 Finally, if brown dwarfs collide with each other, a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
star may be produced which can survive for 1013 (10 trillion) years. §IIIC.
Planets fall or are flung from orbits by a close encounter with another star
- 1015 years
Over time, the orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
s of planets will decay due to gravitational radiation, or planets will be ejected from their local systems by gravitational perturbations caused by encounters with another stellar remnant
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
., §IIIF, Table I.
Stellar remnants escape galaxies or fall into black holes
- 1019 to 1020 years
Over time, objects in a galaxy
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
exchange kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
in a process called dynamical relaxation, making their velocity distribution approach the Maxwell-Boltzmann distribution. Dynamical relaxation can proceed either by close encounters of two stars or by less violent but more frequent distant encounters. In the case of a close encounter, two brown dwarfs or stellar remnants
Compact star
In astronomy, the term compact star is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass...
will pass close to each other. When this happens, the trajectories of the objects involved in the close encounter change slightly. After a large number of encounters, lighter objects tend to gain kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
while the heavier objects lose it., pp. 85–87
Because of dynamical relaxation, some objects will gain enough energy to reach galactic escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
and depart the galaxy, leaving behind a smaller, denser galaxy. Since encounters are more frequent in the denser galaxy, the process then accelerates. The end result is that most objects are ejected from the galaxy, leaving a small fraction (perhaps 1% to 10%) which fall into the central supermassive black hole
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
., §IIIAD;, pp. 85–87
Nucleons start to decay
- >1034 years
The subsequent evolution of the universe depends on the existence and rate of proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
. Experimental evidence shows that if the proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
is unstable, it has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of at least 1034 years. If a Grand Unified Theory is correct, then there are theoretical reasons to believe that the half-life of the proton is under 1041 years., §IVA. Neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s bound into nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
are also expected to decay with a half-life comparable to the proton's., §IVA
In the event that the proton does not decay at all, stellar-mass objects would still disappear, but more slowly. See Future without proton decay below.
The rest of this timeline assumes that the proton half-life is approximately 1037 years., §IVA. Shorter or longer proton half-lives will accelerate or decelerate the process. This means that after 1037 years, one-half of all baryonic matter will have been converted into gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s and leptons through proton decay.
All nucleons decay
- 1040 years
Given our assumed half-life of the proton, nucleons (protons and bound neutrons) will have undergone roughly 1,000 half-lives by the time the universe is 1040 years old. To put this into perspective, there are an estimated 1080 protons currently in the universe. This means that the number of nucleons will be slashed in half 1,000 times by the time the universe is 1040 years old. Hence, there will be roughly ½1,000 (approximately 10−301) as many nucleons remaining as there are today; that is, zero nucleons remaining in the universe at the end of the Degenerate Age. Effectively, all baryonic matter will have been changed into photons and leptons. Some models predict the formation of stable positronium
Positronium
Positronium is a system consisting of an electron and its anti-particle, a positron, bound together into an "exotic atom". Being unstable, the two particles annihilate each other to produce two gamma ray photons after an average lifetime of 125 ps or three gamma ray photons after 142 ns in...
atoms with a greater diameter than the observable universe’s current diameter in 1085 years, and that these will in turn decay to gamma radiation in 10141 years., §IID, IIE.
Black Hole Era
- 1040 years to 10100 years
After 1040 years, black holes will dominate the universe. They will slowly evaporate via Hawking radiation
Hawking radiation
Hawking radiation is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974, and sometimes also after the physicist Jacob Bekenstein...
., §IVG. A black hole with a mass of around 1 solar mass will vanish in around 2×1066 years. However, many of these are likely to merge with supermassive black holes at the center of their galaxies through processes described above long before this happens. 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 1011 (100 billion) solar masses will evaporate in around 2×1099 years.
Hawking radiation has a thermal spectrum
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
. 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 photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s and graviton
Graviton
In physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton must be massless and must have a spin of 2...
s. As the black hole's mass decreases, its temperature increases, becoming comparable to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's by the time the black hole mass has decreased to 1019 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 electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
s, proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s and antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....
s., pp. 148–150.
If protons do not decay as described above
In the event the proton does not decay as described above, the degenerate era will last longer, and will overlap the black hole era. In a timescale of approximately 1065 years, apparently rigid objects such as rocksRock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
will be able to rearrange their atoms and molecules via quantum tunnelling
Quantum tunnelling
Quantum tunnelling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount. This plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the sun, and has important...
, behaving as a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
does, but more slowly. However, the proton is still expected to decay, for example via processes involving virtual black holes, or other higher-order processes, with a half-life of under 10200 years., §IVF
Dark Era
- From 10100 years and beyond
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
, electrons, and positrons (not photons)., §VD.
By this era, with only very diffuse matter remaining, activity in the universe will have tailed off dramatically (compared with previous eras), with very low energy levels and very large time scales. Electrons and positrons drifting through space will encounter one another and occasionally form positronium
Positronium
Positronium is a system consisting of an electron and its anti-particle, a positron, bound together into an "exotic atom". Being unstable, the two particles annihilate each other to produce two gamma ray photons after an average lifetime of 125 ps or three gamma ray photons after 142 ns in...
atoms. These structures are unstable, however, and their constituent particles must eventually annihilate., §VF3. Other low-level annihilation events will also take place, albeit very slowly.
The universe now reaches an extremely low-energy state. What happens after this is speculative. It is possible that a Big Rip
Big Rip
The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, is progressively torn apart by the expansion of the universe at a certain time in the future...
event may occur far off into the future. Also, the universe may enter a second inflationary epoch, or, assuming that the current vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
state is a false vacuum
False vacuum
In quantum field theory, a false vacuum is a metastable sector of space that appears to be a perturbative vacuum, but is unstable due to instanton effects that may tunnel to a lower energy state. This tunneling can be caused by quantum fluctuations or the creation of high-energy particles...
, the vacuum may decay into a lower-energy state., §VE. Finally, the universe may settle into this state forever, achieving true heat death
Heat death of the universe
The heat death of the universe is a suggested ultimate fate of the universe, in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain motion or life. Heat death does not imply any particular absolute temperature; it only requires that...
., §VID.
Future without proton decay
If the proton does not decay, stellar-mass objects will still become black holes, but more slowly. The following timeline assumes that proton decayProton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
does not take place.
Matter decays into iron
- 101500 years from now
In 101500 years, cold fusion
Cold fusion
Cold fusion, also called low-energy nuclear reaction , refers to the hypothesis that nuclear fusion might explain the results of a group of experiments conducted at ordinary temperatures . Both the experimental results and the hypothesis are disputed...
occurring via quantum tunnelling
Quantum tunnelling
Quantum tunnelling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount. This plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the sun, and has important...
should make the light nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
in ordinary matter fuse into iron-56
Iron-56
Iron-56 is the most common isotope of iron. About 91.754% of all iron is iron-56.Of all isotopes, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei....
nuclei (see isotopes of iron
Isotopes of iron
Naturally occurring iron consists of four isotopes: 5.845% of 54Fe , 91.754% of 56Fe, 2.119% of 57Fe and 0.282% of 58Fe. There are 24 known radioactive isotopes and their half-lives are shown below...
.) Fission
Fission
Fission is a splitting of something into two parts.Fission may refer to:*In physics, nuclear fission is a process where a large atomic nucleus is split into two smaller particles....
and alpha-particle emission should make heavy nuclei also decay to iron, leaving stellar-mass objects as cold spheres of iron, called iron star
Iron star
In astronomy, an iron star is a hypothetical type of star that could occur in the universe in 101500 years. The premise behind iron stars states that cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into iron-56 nuclei...
s.
Collapse of iron star to black hole
to years from nowQuantum tunnelling should also turn large objects into black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
s. Depending on the assumptions made, the time this takes to happen can be calculated as from
years to years. (To calculate the value of such numbers, see tetration.) Quantum tunnelling may also make iron stars collapse into neutron starNeutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
s in around
years.Graphical timeline
See also
- Timeline of the far futureTimeline of the far futureWhile predictions of the future can never be absolutely certain, this list of predictions follows from present scientific understanding and models...
- Big RipBig RipThe Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, is progressively torn apart by the expansion of the universe at a certain time in the future...
- Big CrunchBig CrunchIn physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity.- Overview :...
- Big BounceBig BounceThe Big Bounce is a theoretical scientific model of the formation of the known universe. It is implied by the cyclic model or oscillatory universe interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe.- Expansion and contraction...
- Big BangBig BangThe Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
- Cyclic modelCyclic modelA cyclic model is any of several cosmological models in which the universe follows infinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 theorized a universe following an eternal series of oscillations, each beginning with a...
- Dyson's eternal intelligenceDyson's eternal intelligenceDyson's eternal intelligence is a concept that states an intelligent being would be able to think an infinite number of thoughts in an open universe....
- Entropy (arrow of time)Entropy (arrow of time)Entropy is the only quantity in the physical sciences that requires a particular direction for time, sometimes called an arrow of time. As one goes "forward" in time, the second law of thermodynamics says, the entropy of an isolated system will increase...
- Final anthropic principle
- Graphical timeline of the Stelliferous Era
- Graphical timeline of the Big BangGraphical timeline of the Big BangThis timeline of the Big Bang shows the sequence of events as predicted by the Big Bang theory, from the beginning of time to the end of the Dark Ages....
- Graphical timeline from Big Bang to Heat DeathGraphical timeline from Big Bang to Heat DeathThis is the timeline of the Universe from Big Bang to Heat Death scenario. The different Eras of the Universe are shown.Usually the logarithmic scale is used for such timelines but it compresses the most interesting Stelliferous Era too much as this example shows. Therefore a double-logarithmic...
. This timeline uses the double-logarithmic scale for comparison with the graphical timeline included in this article. - Graphical timeline of our universeGraphical timeline of our universeThis more than twenty billion years timeline of our universe shows the best estimates of the occurrence of events since its beginning, up until anticipated events in the near future. Zero of the scale is the present day. A large step on the scale is one billion years, a small step one hundred...
. This timeline uses the more intuitive linear time, for comparison with this article. - Heat death of the universeHeat death of the universeThe heat death of the universe is a suggested ultimate fate of the universe, in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain motion or life. Heat death does not imply any particular absolute temperature; it only requires that...
- Timeline of the Big BangTimeline of the Big BangThis timeline of the Big Bang describes the history of the universe according to the prevailing scientific theory of how the universe came into being, using the cosmological time parameter of comoving coordinates...
- The Last QuestionThe Last Question"The Last Question" is a science fiction short story by Isaac Asimov. It first appeared in the November 1956 issue of Science Fiction Quarterly and was reprinted in the collections Nine Tomorrows , The Best of Isaac Asimov , Robot Dreams , the retrospective Opus 100 , and in Isaac Asimov: The...
, a short story by Isaac Asimov which considers the inevitable oncome of heat death in the universe and how it may be reversed. - Ultimate fate of the UniverseUltimate fate of the universeThe ultimate fate of the universe is a topic in physical cosmology. Many possible fates are predicted by rival scientific theories, including futures of both finite and infinite duration....