Current observations suggest that the
expansion of the
universe
The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
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
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
—represented by the
cosmological constant
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant,
is a coefficient that Albert Einstein initially added to his field equations of general rel ...
, a ''constant'' energy density filling space homogeneously,
or
scalar fields
Scalar may refer to:
*Scalar (mathematics), an element of a field, which is used to define a vector space, usually the field of real numbers
*Scalar (physics), a physical quantity that can be described by a single element of a number field such a ...
, 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
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
will grow at an increasing rate.
Redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...
will stretch ancient ambient photons (including gamma rays) to undetectably long wavelengths and low energies.
Star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s are expected to form normally for 10
12 to 10
14 (1–100 trillion) years, but eventually the supply of gas needed for
star formation
Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
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
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov ...
, the
stellar remnants left behind will disappear, leaving behind only
black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s, which themselves eventually disappear as they emit
Hawking radiation
Hawking radiation is black-body radiation released outside a black hole's event horizon due to quantum effects according to a model developed by Stephen Hawking in 1974.
The radiation was not predicted by previous models which assumed that onc ...
.
[Adams & Laughlin (1997), §IV.] Ultimately, if the universe reaches
thermodynamic equilibrium
Thermodynamic equilibrium is a notion of thermodynamics with axiomatic status referring to an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable ...
, a state in which the temperature approaches a uniform value, no further
work
Work may refer to:
* Work (human activity), intentional activity people perform to support themselves, others, or the community
** Manual labour, physical work done by humans
** House work, housework, or homemaking
** Working animal, an ani ...
will be possible, resulting in a final heat death of the universe.
[Adams & Laughlin (1997), §VID.]
Cosmology
Infinite expansion does not constrain the
overall spatial curvature 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
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
must be present to counteract the gravitational forces or else the universe will end in a
Big Crunch
The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach absolute zero, an eve ...
.
Observations of the
Cosmic microwave background
The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...
by the
Wilkinson Microwave Anisotropy Probe
The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP and Explorer 80), was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic mic ...
and the
Planck mission suggest that the universe is spatially flat and has a significant amount of
dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
.
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
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...
.
If, as in the
concordance model of
physical cosmology
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...
(Lambda-cold dark matter or ΛCDM), dark energy is in the form of a
cosmological constant
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant,
is a coefficient that Albert Einstein initially added to his field equations of general rel ...
, the expansion will eventually become exponential, with the size of the universe doubling at a constant rate.
If the theory of
inflation
In economics, inflation is an increase in the average price of goods and services in terms of money. This increase is measured using a price index, typically a consumer price index (CPI). When the general price level rises, each unit of curre ...
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
In the 1970s, the future of an expanding universe was studied by the astrophysicist
Jamal Islam and the physicist
Freeman Dyson
Freeman John Dyson (15 December 1923 – 28 February 2020) was a British-American theoretical physics, theoretical physicist and mathematician known for his works in quantum field theory, astrophysics, random matrix, random matrices, math ...
.
Then, in their 1999 book ''
The Five Ages of the Universe
''The Five Ages of the Universe'' is a popular science book written by astrophysicists Fred Adams and Gregory P. Laughlin about the future of an expanding universe first published in 1999.
Book contents
The book ''The Five Ages of the Univer ...
'', the astrophysicists
Fred Adams
Fred C. Adams (born 1961) is an American astrophysicist who has made contributions to the study of physical cosmology.
Fred Adams is the Ta-You Wu Collegiate Professor of Physics at the University of Michigan, where his main field of research i ...
and
Gregory Laughlin 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
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...
when
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s had not yet formed. The second, the ''Stelliferous Era'', includes the present day and all of the stars and
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
now seen. 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
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
s,
neutron stars
A neutron star is the gravitationally collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star—combined with gravitational collapse—that compresses the core past white dwarf star density to th ...
, and
black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s. In the ''Black Hole Era'', white dwarfs, neutron stars, and other smaller
astronomical objects
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...
have been destroyed by
proton decay
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov ...
, leaving only black holes. Finally, in the ''Dark Era'', even black holes have disappeared, leaving only a dilute gas of
photons
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that ...
and
leptons
In particle physics, a lepton is an elementary particle of half-integer spin ( spin ) that does not undergo strong interactions. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), includin ...
.
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 Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach absolute zero, an eve ...
, 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''

The
observable universe
The observable universe is a Ball (mathematics), spherical region of the universe consisting of all matter that can be observation, observed from Earth; the electromagnetic radiation from these astronomical object, objects has had time to reach t ...
is currently 1.38 (13.8 billion) years old.
This time lies within the Stelliferous Era. About 155 million years after the
Big Bang
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...
, the first star formed. Since then, stars have formed by the collapse of small, dense core regions in large, cold
molecular cloud
A molecular cloud—sometimes called a stellar nursery if star formation is occurring within—is a type of interstellar cloud of which the density and size permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, ...
s of
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
gas. At first, this produces a
protostar
A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The p ...
, which is hot and bright because of energy generated by
gravitational contraction. 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.
Stars of very low
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
will eventually exhaust all their fusible
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and then become
helium
Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
s.
Stars of low to medium mass, such as our own
sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
, will expel some of their mass as a
planetary nebula
A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...
and eventually become
white dwarfs
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place in a white dwarf; what ...
; more massive stars will explode in a
core-collapse supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original obj ...
, leaving behind
neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s or
black holes
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
.
In any case, although some of the star's matter may be returned to the
interstellar medium
The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...
, 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
Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
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
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...
is approximately 2.5 million light years away from our galaxy, the
Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
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 Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...
, 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
The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
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
In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is p ...
scenario, assuming a model of
dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
with
= −1.5.
False vacuum decay
In quantum field theory, a false vacuum is a hypothetical vacuum state that is locally stable but does not occupy the most stable possible ground state. In this condition it is called metastable. It may last for a very long time in this state, ...
may occur in 20 to 30 billion years if the
Higgs field
The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the excited state, quantum excitation of the Higgs field,
one of the field (physics), fields in particl ...
is metastable.
Coalescence of Local Group and galaxies outside the Local Supercluster are no longer accessible
: '' (100 billion) to (1 trillion) years''
The
galaxies
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...
in the
Local Group
The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of .
It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...
, 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
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
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
A cosmological horizon is a measure of the distance from which one could possibly retrieve information. This observable constraint is due to various properties of general relativity, the expanding universe, and the physics of Big Bang cosmology. ...
. 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
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and e ...
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
A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...
stars begin to die as
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
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
gamma ray
A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
s they emit will have wavelengths longer than the size of the
observable universe
The observable universe is a Ball (mathematics), spherical region of the universe consisting of all matter that can be observation, observed from Earth; the electromagnetic radiation from these astronomical object, objects has had time to reach t ...
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
Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
will end,
leaving all stellar objects in the form of
degenerate remnants. If
protons do not 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
Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...
will end. This period, known as the "Degenerate Era", will last until the degenerate remnants finally decay. The least-massive stars take the longest to exhaust their hydrogen fuel (see
stellar evolution
Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...
). Thus, the longest living stars in the universe are low-mass
red dwarf
A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...
s, with a mass of about 0.08
solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es (), 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
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
will cease. The low-mass red dwarfs will cool and become
black dwarf
A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently to no longer emit significant heat or light. Because the time required for a white dwarf to reach this state is calculated to be longer than ...
s.
The only objects remaining with more than
planetary mass
In astronomy, planetary mass is a measure of the mass of a planet-like astronomical object. Within the Solar System, planets are usually measured in the astronomical system of units, where the unit of mass is the solar mass (), the mass of the Sun ...
will be
brown dwarf
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...
s (with mass less than ), and
degenerate remnants:
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
s, produced by stars with initial masses between about 0.08 and 8 solar masses, and
neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s and
black holes
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
, 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
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
–
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
white dwarfs with a combined mass of more than the
Chandrasekhar limit
The Chandrasekhar limit () is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about (). The limit was named after Subrahmanyan Chandrasekhar.
White dwarfs resist gravitational collapse pr ...
of about 1.4 solar masses happen to merge. The resulting object will then undergo runaway thermonuclear fusion, producing a
Type Ia supernova
A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white ...
and dispelling the darkness of the Degenerate Era for a few weeks.
Neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s 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
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...
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
fuse carbon (about ), a
carbon star
A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose Stellar atmosphere, atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monox ...
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
A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...
stars, which can survive for (10 trillion) years,
[ or by accreting gas at very slow rates from the remaining ]interstellar medium
The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...
until they have enough mass to start hydrogen burning
In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a ...
as red dwarfs. This process, at least on white dwarfs, could induce Type Ia supernovae.
Planets fall or are flung from orbits by a close encounter with another star
: '' (1 quadrillion) years''
Over time, the orbit
In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
s of planets will decay due to gravitational radiation
Gravitational waves are oscillations of the gravitational field that travel through space at the speed of light; they are generated by the relative motion of gravitating masses. They were proposed by Oliver Heaviside in 1893 and then later by ...
, or planets will be ejected from their local systems by gravitational perturbations caused by encounters with another stellar remnant
In astronomy, the term compact object (or compact star) refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a ...
.
Stellar remnants escape galaxies or fall into black holes
: '' to (10 to 100 quintillion) years''
Over time, objects in a galaxy
A galaxy is a Physical system, system of stars, stellar remnants, interstellar medium, interstellar gas, cosmic dust, dust, and dark matter bound together by gravity. The word is derived from the Ancient Greek, Greek ' (), literally 'milky', ...
exchange kinetic energy
In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion.
In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...
in a process called dynamical relaxation, making their velocity distribution approach the Maxwell–Boltzmann distribution
In physics (in particular in statistical mechanics), the Maxwell–Boltzmann distribution, or Maxwell(ian) distribution, is a particular probability distribution named after James Clerk Maxwell and Ludwig Boltzmann.
It was first defined and use ...
. 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
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter ()not big enough to sustain nuclear fu ...
or stellar remnants 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 energies 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
''The Five Ages of the Universe'' is a popular science book written by astrophysicists Fred Adams and Gregory P. Laughlin about the future of an expanding universe first published in 1999.
Book contents
The book ''The Five Ages of the Univer ...
'', New York: The Free Press, 1999, .
Because of dynamical relaxation, some objects will gain just enough energy to reach galactic escape velocity
In celestial mechanics, escape velocity or escape speed is the minimum speed needed for an object to escape from contact with or orbit of a primary body, assuming:
* Ballistic trajectory – no other forces are acting on the object, such as ...
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
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...
. It has been suggested that the matter of the fallen remnants will form an accretion disk
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...
around it that will create a quasar
A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...
, as long as enough matter is present there.
Possible ionization of matter
: ''> years from now''
In an expanding universe with decreasing density and non-zero cosmological constant
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant,
is a coefficient that Albert Einstein initially added to his field equations of general rel ...
, matter density would reach zero, resulting in most matter except black dwarf
A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently to no longer emit significant heat or light. Because the time required for a white dwarf to reach this state is calculated to be longer than ...
s, neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s, black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s, and planet
A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...
s ionizing and dissipating at thermal equilibrium
Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in t ...
.
Future with proton decay
The following timeline assumes that protons do decay.
: ''Chance: (100 nonillion) – years (1 tredecillion)''
The subsequent evolution of the universe depends on the possibility and rate of proton decay
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov ...
. Experimental evidence shows that if the proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
is unstable, it has a half-life Half-life is a mathematical and scientific description of exponential or gradual decay.
Half-life, half life or halflife may also refer to:
Film
* Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang
* ''Half Life: ...
of at least years. Some of the Grand Unified theories
A Grand Unified Theory (GUT) is any model in particle physics that merges the electromagnetic, weak, and strong forces (the three gauge interactions of the Standard Model) into a single force at high energies. Although this unified force has ...
(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
Supersymmetry is a Theory, theoretical framework in physics that suggests the existence of a symmetry between Particle physics, particles with integer Spin (physics), spin (''bosons'') and particles with half-integer spin (''fermions''). It propo ...
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.
Nucleons start to decay
Neutron
The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...
s bound into nuclei are also suspected to decay with a half-life comparable to that of protons. Planets (substellar objects) would decay in a simple cascade process from heavier elements to hydrogen and finally to photons and leptons while radiating energy.[Adams & Laughlin (1997), §IV-H.]
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
A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s and leptons
In particle physics, a lepton is an elementary particle of half-integer spin ( spin ) that does not undergo strong interactions. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), includin ...
through proton decay.
All nucleons decay
: '' (10 tredecillion) years''
Given our assumed half-life of the proton, nucleon
In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number.
Until the 1960s, nucleons were thought to be ele ...
s (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, none will remain at the end of the Degenerate Age. Effectively, all baryonic matter will have been changed into photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s and lepton
In particle physics, a lepton is an elementary particle of half-integer spin (Spin (physics), spin ) that does not undergo strong interactions. Two main classes of leptons exist: electric charge, charged leptons (also known as the electron-li ...
s. Some models predict the formation of stable positronium
Positronium (Ps) is a system consisting of an electron and its antimatter, anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two part ...
atoms with diameters greater than the observable universe's current diameter (roughly 6 metres) in years, and that these will in turn decay to gamma radiation in years.
If protons decay on higher-order nuclear processes
: ''Chance: to years''
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 atom
Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
s and molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s via quantum tunneling
In physics, a quantum (: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of quantization". This me ...
, and may behave as liquid and become smooth sphere
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
s due to diffusion and gravity. 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
Supersymmetry is a Theory, theoretical framework in physics that suggests the existence of a symmetry between Particle physics, particles with integer Spin (physics), spin (''bosons'') and particles with half-integer spin (''fermions''). It propo ...
possibly with a half-life of under years.
: ''> years from now ''
2018 estimate of Standard Model
The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...
lifetime before collapse of a false vacuum; 95% confidence interval is 1065 to 10725 years due in part to uncertainty about the top quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...
mass.
:''> years from now''
Although protons are stable in standard model physics, a quantum anomaly may exist on the electroweak
In particle physics, the electroweak interaction or electroweak force is the unified description of two of the fundamental interactions of nature: electromagnetism (electromagnetic interaction) and the weak interaction. Although these two forc ...
level, which can cause groups of baryons (protons and neutrons) to annihilate into antileptons via the sphaleron
A sphaleron ( "slippery") is a static (time-independent) solution to the electroweak field equations of the Standard Model of particle physics, and is involved in certain hypothetical processes that violate baryon and lepton numbers. Such proces ...
transition. Such baryon/lepton violations 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.
Black Hole Era
: '' (10 tredecillion) years to approximately (1 googol
A googol is the large number 10100 or ten to the power of one hundred. In decimal notation, it is written as the digit 1 followed by one hundred zeros: 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000, ...
) years, up to years for the largest supermassive black holes ''
After years, black holes will dominate the universe. They will slowly evaporate via Hawking radiation
Hawking radiation is black-body radiation released outside a black hole's event horizon due to quantum effects according to a model developed by Stephen Hawking in 1974.
The radiation was not predicted by previous models which assumed that onc ...
. 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 black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s 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 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 photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s and hypothetical graviton
In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with re ...
s. As the black hole's mass decreases, its temperature increases, becoming comparable to the Sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
'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 electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s, positron
The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
s, proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
s, and antiproton
The antiproton, , (pronounced ''p-bar'') 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.
The exis ...
s.
Dark Era and Photon Age
: ''From years (10 duotrigintillion years or 1 googol years) and beyond''
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. Photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s, lepton
In particle physics, a lepton is an elementary particle of half-integer spin (Spin (physics), spin ) that does not undergo strong interactions. Two main classes of leptons exist: electric charge, charged leptons (also known as the electron-li ...
s, baryon
In particle physics, a baryon is a type of composite particle, composite subatomic particle that contains an odd number of valence quarks, conventionally three. proton, Protons and neutron, neutrons are examples of baryons; because baryons are ...
s, neutrino
A neutrino ( ; denoted by the Greek letter ) is an elementary particle that interacts via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small ('' -ino'') that i ...
s, electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s, and positron
The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
s will fly from place to place, hardly ever encountering each other. Gravitationally, the universe
The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
will be dominated by dark matter
In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
, electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s, and positron
The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
s (not proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
s).[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
Positronium (Ps) is a system consisting of an electron and its antimatter, anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two part ...
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.
Future without proton decay
If protons do not decay, stellar-mass objects will still become black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s, although even more slowly. The following timeline that assumes proton decay
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov ...
does not take place.
:'' years from now''
2018 estimate of Standard Model
The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...
lifetime before collapse of a false vacuum; 95% confidence interval is 1065 to 101383 years due in part to uncertainty about the top quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...
mass.[Manuscript was updated after publication; lifetime numbers are taken from the latest revision at https://arxiv.org/abs/1707.08124.]
Degenerate Era
Matter decays into iron
: '' to years from now''
In years, pycnonuclear fusion
Pycnonuclear fusion () is a type of nuclear fusion reaction which occurs due to zero-point oscillations of nuclei around their equilibrium point bound in their crystal lattice. In quantum physics, the phenomenon can be interpreted as overlap of ...
occurring via quantum tunnelling
In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, shoul ...
should make the light nuclei in stellar-mass objects fuse into iron-56
Iron-56 (56Fe) is the most common isotope of iron. About 91.754% of all iron is iron-56.
Of all nuclides, 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
Natural iron (Fe) consists of four stable isotopes: 5.845% Fe (possibly radioactive with half-life > years), 91.754% Fe, 2.119% Fe and 0.286% Fe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are Fe (half-life 2 ...
). Fission and alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...
emission should make heavy nuclei also decay to iron, leaving stellar-mass objects as cold spheres of iron, called iron stars. Before this happens, however, in some black dwarf
A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently to no longer emit significant heat or light. Because the time required for a white dwarf to reach this state is calculated to be longer than ...
s the process is expected to lower their Chandrasekhar limit
The Chandrasekhar limit () is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about (). The limit was named after Subrahmanyan Chandrasekhar.
White dwarfs resist gravitational collapse pr ...
resulting in a supernova
A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
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
: '' to years from now''
Quantum tunneling should also turn large objects into black hole
A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
s, 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 neutron star
A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s in around years.
Dark Era (without proton decay)
: '' to years from now''
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
In quantum field theory, a false vacuum is a hypothetical vacuum state that is locally stable but does not occupy the most stable possible ground state. In this condition it is called metastable. It may last for a very long time in this stat ...
). The expansion of the universe slowly causes itself to cool down to absolute zero
Absolute zero is the lowest possible temperature, a state at which a system's internal energy, and in ideal cases entropy, reach their minimum values. The absolute zero is defined as 0 K on the Kelvin scale, equivalent to −273.15 ° ...
. The universe now reaches an even lower energy state than the earlier one mentioned.
Beyond
: ''Beyond years if proton decay occurs, or years without proton decay''
Whatever event happens beyond this era is highly speculative. It is possible that a Big Rip
In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is p ...
event may occur far off into the future. This singularity would take place at a finite scale factor.
If the current vacuum state
In quantum field theory, the quantum vacuum state (also called the quantum vacuum or vacuum state) is the quantum state with the lowest possible energy. Generally, it contains no physical particles. However, the quantum vacuum is not a simple ...
is a false vacuum
In quantum field theory, a false vacuum is a hypothetical vacuum state that is locally stable but does not occupy the most stable possible ground state. In this condition it is called metastable. It may last for a very long time in this stat ...
, the vacuum may decay into an even lower-energy state.[Adams & Laughlin (1997), §VE.]
Presumably, extreme low-energy state
A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy, called energy levels. This contrasts with classical particles, which can have any amount of energy. The ...
s 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.[
The universe could possibly avoid eternal heat death through random ]quantum tunneling
In physics, a quantum (: quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. The fundamental notion that a property can be "quantized" is referred to as "the hypothesis of quantization". This me ...
and quantum fluctuation
In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space,
as prescribed by Werner Heisenberg's uncertainty principle. ...
s, given the non-zero probability of producing a new Big Bang creating a new universe in roughly years.
Over an infinite amount of time, there could also be a spontaneous entropy
Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the micros ...
decrease, by a Poincaré recurrence
Poincaré is a French surname. Notable people with the surname include:
* Henri Poincaré (1854–1912), French physicist, mathematician and philosopher of science
* Henriette Poincaré (1858–1943), wife of Prime Minister Raymond Poincaré
* L ...
or through thermal fluctuations
In statistical mechanics, thermal fluctuations are random deviations of an atomic system from its average state, that occur in a system at equilibrium.In statistical mechanics they are often simply referred to as fluctuations. All thermal fluctu ...
(see also fluctuation theorem
The fluctuation theorem (FT), which originated from statistical mechanics, deals with the relative probability that the Entropy (statistical thermodynamics), entropy of a system which is currently away from thermodynamic equilibrium (i.e., maxim ...
).
The possibilities above are based on a simple form of dark energy
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure format ...
. However, the physics of dark energy are still a very speculative area of research, and the actual form of dark energy could be much more complex.
Graphical timelines
If protons decay:
# ImageSize = width:1100 height:370 # too wide
ImageSize = width:1000 height:370
PlotArea = left:40 right:235 bottom:50 top:50
Colors =
id:period1 value:rgb(1,1,0.7) # light yellow
id:period2 value:rgb(0.7,0.7,1) # light blue
id:events value:rgb(1,0.7,1) # light purple
id:era2 value:lightorange
id:era1 Value:yellowgreen
DateFormat = yyyy
Period = from:-51 till:1000
TimeAxis = format:yyyy orientation:horizontal
ScaleMajor = unit:year increment:100 start:0
ScaleMinor = unit:year increment:10 start:-50
AlignBars = justify
BarData =
bar:Era
bar:Events
TextData =
fontsize:M
pos:(0,260)
text:"Big"
text:"Bang"
# pos:(880,260)
pos:(780,260)
text:"Heat"
text:"Death"
# pos:(880,90)
pos:(780,90)
text:" log"
text:"year"
PlotData=
textcolor:black fontsize:M
width:110
bar:Era mark:(line,white) align:left shift:(0,0)
from:-51 till:8 shift:(0,35) color:era1 text:"Primordial Era"
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"
from:100 till:1000 shift:(0,-45) color:era1 text:"Dark Era"
width:110
bar:Events
color:events align:left shift:(43,3) mark:(line,teal)
at:-8 shift:(0,35) text:"One second"
at:8 shift:(-2,15) text:"First star began to shine"
at:10 shift:(-2,-5) text:"13.8 billion years, the present day"
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"
If protons don't decay:# ImageSize = width:1100 height:370 # too wide
ImageSize = width:1000 height:370
PlotArea = left:40 right:235 bottom:50 top:50
Colors =
id:period1 value:rgb(1,1,0.7) # light yellow
id:period2 value:rgb(0.7,0.7,1) # light blue
id:events value:rgb(1,0.7,1) # light purple
id:era2 value:lightorange
id:era1 Value:yellowgreen
DateFormat = yyyy
Period = from:-170 till:5500
TimeAxis = format:yyyy orientation:horizontal
ScaleMajor = unit:year increment:1000 start:0
ScaleMinor = unit:year increment:100 start:-100
AlignBars = justify
BarData =
bar:Era
bar:Events
TextData =
fontsize:M
pos:(0,260)
text:"Big"
text:"Bang"
# pos:(880,260)
pos:(780,260)
text:"Heat"
text:"Death"
# pos:(880,90)
pos:(780,90)
text:" log log"
text:"year"
PlotData=
textcolor:black fontsize:M
width:110
bar:Era mark:(line,white) align:left shift:(0,0)
from:-170 till:90 shift:(0,35) color:era1 text:"Primordial Era"
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"
width:110
bar:Events
color:events align:left shift:(43,3) mark:(line,teal)
at:-87 shift:(0,35) text:"One second"
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
*
*
*
*
*
*
*
* ''The Last Question
"The Last Question" is a science fiction short story by American writer Isaac Asimov. It first appeared in the November 1956 issue of ''Science Fiction Quarterly'' and in the anthologies in the collections ''Nine Tomorrows'' (1959), ''The Best ...
'' – A short story by Isaac Asimov which considers the inevitable outcome of heat death in the universe and how it may be reversed.
*
*
*
Notes
References
External links
* by melodysheep
{{Portal bar, Stars, Outer space, Solar System, Science
Articles which contain graphical timelines
Astronomy timelines
Physical cosmology
Ultimate fate of the universe