ULTIMATE FATE OF THE UNIVERSE

The '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. Once the notion that the universe started with a Big Bang became popular among scientists, the ultimate fate of the universe became a valid cosmological question, one depending upon the physical properties of the mass/energy in the universe, its average density, and the rate of expansion. By extension, the fate of the universe is also a significant theme in science fiction.

Emerging scientific basis

The theoretical scientific exploration of the ultimate fate of the universe became possible with Albert Einstein's 1915 theory of general relativity. General relativity can be employed to describe the universe on the largest possible scale. There are many possible solutions to the equations of general relativity, and each solution implies a possible ultimate fate of the universe. Alexander Friedmann proposed a number of such solutions in 1922. In some of these the universe has been expanding from an initial singularity; this is, essentially, the Big Bang.
Observational evidence was not long in coming. In 1929, Edwin Hubble published his conclusion, based on his observations of Cepheid variable stars in distant galaxies, that the universe was expanding. From then on, the ''beginning'' of the universe and its possible ''end'' have been the subjects of serious scientific investigation. In 1931, Georges-Henri Lemaître set out a theory that has since come to be called the Big Bang theory of the origin of the universe. In 1948, Fred Hoyle set out his opposing steady state theory in which the universe continually expanded but remained statistically unchanged as new matter is constantly created. These two theories were active contenders until the 1965 discovery, by Arno Penzias and Robert Wilson, of the cosmic microwave background radiation, a fact that is a straightforward prediction of the Big Bang theory, and one that the Steady State theory cannot account for. The Big Bang theory immediately became the most widely held view of the origin of the universe.
When Einstein formulated general relativity, he and his contemporaries believed in a static universe. When Einstein found that his equations could easily be solved in such a way as to allow the universe to be expanding now, and to contract in the far future, he added to those equations what he called a cosmological constant, essentially a constant energy density unaffected by any expansion or contraction, whose role was to offset the effect of gravity on the universe as a whole in such a way that the universe would remain static. After Hubble announced his conclusion that the universe was expanding, Einstein wrote that his cosmological constant was his "greatest blunder".
An important parameter in fate of the universe theory is the density parameter, Omega (Ω), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω is equal to, less than, or greater than 1. These are called, respectively, the flat, open and closed universes. These three adjectives refer to the overall geometry of the universe, and not to the local curving of spacetime caused by smaller clumps of mass (for example, galaxies and stars). If the primary content of the universe is inert matter, as in the dust models popular for much of the 20th century, there is a particular fate corresponding to each geometry. Hence cosmologists aimed to determine the fate of the universe by measuring Ω, or equivalently the rate at which the expansion was decelerating.
Starting in 1998, observations of supernovae in distant galaxies have been interpreted as consistent with a universe whose rate of expansion is ''accelerating''. Subsequent cosmological theorizing has been designed so as to allow for this possible acceleration, nearly always by invoking dark energy, which in its simplest form is just a positive cosmological constant. In general dark energy is a catch-all term for any hypothesised field with negative pressure, usually with a density that changes as the universe expands.

Role of the shape of the universe

The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy it contains, and on the equation of state which determines how the dark energy density responds to the expansion of the universe. Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, concurrent with the Open Universe theory, and marked 'Accelerating' on the graph.

The ultimate fate of an expanding universe is determined by whether Ω is greater than, less than, or equal to 1.

Closed universe

If Ω>1, then the geometry of space is closed like the surface of a sphere. The sum of the angles of a triangle exceeds 180 degrees and there are no parallel lines; all lines eventually meet. The geometry of the universe is, at least on a very large scale, elliptic.
In a closed universe lacking the repulsive effect of dark energy, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch," by analogy with Big Bang. However, if the universe has a large amount of dark energy (as suggested by recent findings), then the expansion of the universe can continue forever - even if Ω>1.

Open universe

If Ω<1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of the universe is hyperbolic.
Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip," where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak binding forces.
Conversely, a ''negative'' cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a big crunch. This option is ruled out by observations, unless the universe undergoes an unexpected phase transition at some point in the future.

Flat universe

If the average density of the universe exactly equals the critical density so that Ω=1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines never meet.
Absent dark energy, a flat universe expands forever but at a continually decelerating rate, the rate of expansion asymptotically approaching zero. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe. In 2005, the Fermion-boson fate of universe theory was proposed, positing that much of the universe would ultimately be occupied by Bose-Einstein condensate and the fermion quasiparticle analog, perhaps resulting in an implosion.

Theories about the end of universe

The fate of the universe is determined by the density of the universe. The preponderance of evidence to date, based on measurements of the rate of expansion and the mass density, favors a universe that will not collapse.

Big Freeze or Heat Death

Main articles: Big Freeze, Heat death of the universe

The Big Freeze is a scenario under which continued expansion results in a universe that is too cold to sustain life. It could, in the absence of dark energy, occur only under a flat or hyperbolic geometry, because such geometries then are a necessary condition for a universe that expands forever. With a positive cosmological constant, it could also occur in a closed universe. A related scenario is Heat Death, which states that the universe goes to a state of maximum entropy in which everything is evenly distributed, and there are no gradients — which are needed to sustain information processing, one form of which is life. The Heat Death scenario is compatible with any of the three spatial models, but requires that the universe reach an eventual temperature minimum.

Big Rip: Finite Lifespan

In the special case of phantom dark energy, which has even more negative pressure than a simple cosmological constant, the density of dark energy increases with time, causing the ''rate'' of acceleration to increase, leading to a steady increase in the Hubble constant. As a result, all material objects in the universe, starting with galaxies and eventually (in a finite time) all life forms, no matter how small, will disintegrate into unbound elementary particles and radiation, ripped apart by the phantom energy force and shooting apart from each other. The end state of the universe is a singularity, as the dark energy density and expansion rate becomes infinite. For a possible timeline based on current physical theories, see 1 E19 s and more.

Big Crunch

The Big Crunch. The vertical axis can be considered as either plus or minus time.

The Big Crunch theory is a symmetric view of the ultimate fate of the universe. Just as the Big Bang started a cosmological expansion, this theory postulates that the average density of the universe is enough to stop its expansion and begin contracting. The end result is unknown; a simple extrapolation would have all the matter and space-time in the universe collapse into a dimensionless singularity, but at these scales unknown quantum effects need to be considered (See Quantum gravity).
This scenario allows the Big Bang to have been immediately preceded by the Big Crunch of a preceding universe. If this occurs repeatedly, we have an oscillatory universe. The universe could then consist of an infinite sequence of finite universes, each finite universe ending with a Big Crunch that is also the Big Bang of the next universe. Theoretically, the oscillating universe could not be reconciled with the second law of thermodynamics: entropy would build up from oscillation to oscillation and cause heat death. Other measurements suggested the universe is not closed. These arguments caused cosmologists to abandon the oscillating universe model. A somewhat similar idea is embraced by the cyclic model, but this idea evades heat death, because of an expansion of the branes that dilutes entropy accumulated in the previous cycle.

Big Bounce

The Big Bounce is a theorized scientific model related to the creation of the known Universe. It derives from the oscillatory universe interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe.
According to one version of the Big Bang theory of cosmology, in the beginning the universe had infinite density. Such a description seems to be at odds with everything else in physics, and especially quantum mechanics and its uncertainty principle. It is not surprising, therefore, that quantum mechanics has given rise to an alternative version of the Big Bang theory. Also, if the universe is closed, this theory would predict that once this incarnation of the universe collapses it will spawn another universe in an event similar to the Big Bang after a universal singularity is reached or a repusive quantume force causes re-expansion.

Multiverse: no complete end

The multiverse hypothesis states that our universe is but one universe among numerous parallel universes, possibly with different physical laws. Whatever the ultimate fate of our universe may be, almost all parallel universes will have different fates. And while many universes may be closed, many others may be open. The multiverse as a whole may never end completely.

False vacuum

If the vacuum is not in its lowest energy state (a false vacuum), it could collapse into a lower energy state. This is called the vacuum metastability event. This would fundamentally alter our universe; the various physical constants could have different values, severely affecting the foundations of matter.

Cosmic uncertainty

Each possibility described so far is based on very simple form for the dark energy equation of state. But as the name is meant to imply, we know almost nothing of the real physics of the dark energy. 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. Could the same happen again? Recent decades have taught cosmologists that the universe is stranger than they thought.

Observational constraints on theories

Choosing among these rival scenarios is done by 'weighing' the universe, i.e. measuring the relative contributions of matter, radiation, dark matter and dark energy to the critical density. More concretely, competing scenarios are evaluated against data on galaxy clustering and distant supernovae, and on the anisotropies in the Cosmic Microwave Background.

Life in a mortal universe

Dyson's eternal intelligence hypothesis proposes that an advanced civilization could survive for an effectively infinite period of time while consuming only a finite amount of energy. Such a civilization would alternate brief periods of activity with ever longer periods of hibernation.
John Barrow and Frank J. Tipler (1986) propose a Final anthropic principle: the emergence of intelligent life is inevitable, and once such life comes into being somewhere in the universe, it will never die out. Barrow and Tipler go even further: the eventual fate of intelligent life is to permeate and control the entire universe in all respects but one: intelligence cannot halt the Big Crunch. Moreover, it will not want to do so because the main source of energy in a universe undergoing a Big Crunch will be a hot spot in the sky arising from an asymmetrical contraction of the universe. They speculate that the required asymmetry will be engineered by some form of intelligent life.
Tipler's Omega point scenario (Tipler 1994) concludes that the reverse of the eternal intelligence scenario would be the case for a civilization caught in the final stages of a Big Crunch. Such a civilization would, in effect, experience an infinite amount of "subjective" time during the remaining finite life of the universe, using the enormous energy of the Crunch to accelerate information processing faster than the approach of the final singularity.
Though possible in theory, it is not obvious whether there will ever exist technologies that will make either of these scenarios feasible. Moreover, effective solutions may be indistinguishable from the present state of our universe. In other words, if beings cannot stop the universe from collapsing, at least they can use the energy of the collapse to simulate future universes (roughly reminiscent of the Matrix movies) that resemble the ending universe, but with artificial or compressed time scales.
Recent work in inflationary cosmology, string theory, and quantum mechanics has moved the discussion of the ultimate fate of the universe in directions distinct from the scenarios set out by Dyson and Tipler. Theoretical work by Eric Chaisson and David Layzer finds that an expanding spacetime gives rise to an increasing "entropy gap", casting doubt on the heat death hypothesis. Invoking Ilya Prigogine's work on far-from-equilibrium thermodynamics, their analysis suggests that this entropy gap may contribute to information, and hence to the formation of structure.
Meanwhile, Andrei Linde, Alan Guth, Edward Harrison, and Ernest Sternglass argue that inflationary cosmology strongly suggests the presence of a multiverse, and that it would be practical even with today's knowledge for intelligent beings to generate and transmit ''de novo'' information into a distinct universe. Alan Guth has speculated that a civilization at the top of the Kardashev scale might create fine-tuned universes in a continuation of the evolutionary drive to exist, grow, and multiply. This has been further developed by the Selfish Biocosm Hypothesis, and by the proposal that the existence of the fundamental physical constants may be subject to a Darwinian evolution of Universes.^[1] Moreover, recent theoretical work on the unresolved quantum gravity problem and the Holographic Principle suggests that traditional physical quantities may possibly themselves be describable in terms of exchanges of information, which in turn raises questions about the applicability of older cosmological models.

Religious perspective

Virtually every major religion has an end-of-the-universe narrative. The theological study of the ultimate fate of the universe and/or ultimate destiny of human kind is known as eschatology. Many religious groups are torn as to whether their theological beliefs about the end of the world can be made compatible with the scientific theories of the end of the universe. For example, a text that reads "and all the stars fell from the sky" might on the one hand show a misunderstanding of what stars are (as merely points of light). But if that text has actual true implications from a divine intelligence, it might reference any one of a number of modern secular theories about the end of the universe.

The end of the universe in science fiction

Scientific speculation about the ultimate fate of life in the universe merges almost seamlessly into science fiction. Many works describe the end of the universe—occasionally purely educational exercises describing theories of the day, more often exploiting its potential as the ultimate sense of wonder plot device, or satirising the pretensions of humanity in general and cosmologists in particular. At its best (and sometimes at its most bombastic) science fiction can try to suggest a scientific eschatology that searches for meaning in the face of the new knowledge. Countless sci-fi and fantasy works use the ''threatened'' destruction of the universe as their plot device, usually with an evil supervillain and/or the incompetence of humanity as the cause, and usually with human ingenuity saving the day.

Books

The topic of heat death was explored in science fiction as early as 1895 in H G Wells' ''The Time Machine'', which includes an evocation of the heat death of the universe as imagined by scientists like Lord Kelvin at that time. In the absence of a modern dynamic cosmology, this consisted of the fading out of the Sun to an exhausted red ember, and a vision of Earth as a cold and bland eroded desert. As the understanding of cosmology increased, so too did the scope of science fiction. Isaac Asimov's short story, "The Last Question" was published in 1959, and posits a universe experiencing heat death, and a future human computer technology so powerful that it finally discovers how to reverse the process by igniting what is, in effect, a new Big Bang. When Asimov published this story, in 1959, heat death was still the only scenario discussed in this entry to have been articulated.
The Big Crunch as the fate of the Universe was explored in science fiction as early as Poul Anderson's 1970 novel ''Tau Zero'' which posits a cyclic universe where the big crunch will be surrounded by a cloud of hydrogen, and that a starship could navigate a course to avoid the singularity and emerge into the new universe after the subsequent big bang.
Religion is not wholly excluded from science fiction's explorations of the end of our universe. Arthur C. Clarke's short story "The Nine Billion Names of God" takes non-scientific eschatology seriously. Its famous last line ominously chronicles the end of the universe as observed by mankind: ''Overhead, without any fuss, the stars were going out.''
Not only a source of fear or hope, the end of the universe has been used for satirical and comedic effect. Milliways, ''The Restaurant at the End of the Universe'', is a fictional location in Douglas Adams's science-fiction series ''The Hitchhiker's Guide to the Galaxy''. The entire restaurant and its patrons are projected through time via a "time bubble" to the point at which the Universe ends. The ceiling is made of glass so the restaurant guests can watch the universe end as dinner entertainment.
The concept of an end to the universe has inspired some authors to explore the more human-centric topics of fate and free will, In Kurt Vonnegut's classic novel ''Slaughterhouse Five'', the primary character is a war veteran who is contacted by aliens from the planet Tralfamadore who claim that one of their scientists will accidentally destroy the universe while testing a new type of spaceship fuel. Tralfamadorians are aware of this event because they perceive all of time instantaneously, in a similar way to how a human being would observe an entire range of mountains in one instant.

Movies and TV shows

★ Woody Allen's movie ''Annie Hall'' (not science fiction) has the young Alvy Singer complaining to a doctor that if the Universe is expanding, there is no point in doing his homework. His mother asks "What business is that of yours?" and "What has the universe got to do with it?"; his cigarette smoking doctor postulates that we should just enjoy life.

★ In the TV series ''Red Dwarf'', and also in the Red Dwarf book ''Backwards'', the crew happen upon a reality where time is traveling backwards. Kryten theorises that this is some time in the future of their universe, where it is heading to a Big Crunch, causing time to go in reverse. Another aspect of the show entered into the idea of the Multiverse, delving into the idea of an infinite number of parallel universes, each separated by different forks in the "destiny line."

★ In the TV series ''Lexx'', episode 2.20 "The End of the Universe", all of the matter in the universe, except the main characters and their ship, is converted into flying autonomous robotic arms with a single consciousness of the main villain Mantrid. The gravitational force of these arms closing in on each other causes a Big Crunch with the Lexx in the center. The Lexx is somehow sent to an alternate universe to continue season three of the series.

★ In the TV series '' episode "Chrysalis," a number of genetically engineered humans determine that the Universe will collapse into the Big Crunch and attempt to develop a way to alter the cosmological constant of the universe to keep its mass from collapsing in on itself.

★ In the infamous Ed Wood film ''Plan 9 from Outer Space'', alien invaders raise the dead in order to prevent humans from destroying the universe through a device that can "explode sunlight."

★ In the 2006 season of Doctor Who, the Torchwood Institute acquire a mysterious orb that the Doctor identifies as a "void ship", a vessel intended to exist outside of space/time and thus outlive the universe. He suggests that the universe is cyclical or oscillatory, saying that in the Void ship you could survive the end of the universe and the creation of the next one. In the 2007 episode ''Utopia'', the Doctor travels to the year 100 trillion on the planet Malacarrisso at the end of the universe. The stars have all burnt out, keeping it permanently dark. Here, the last humans rely on elderly Professor Yana to get them to the place called Utopia. By 100 trillion, most humans have devolved into cannibals called Futurekind. After the rocket reaches Utopia, the humans find nothing apart from the cold and darkness. They cannibalise themselves into spherical cyborgs nicknamed the Toclafane.

★ In the 1981 episode of Doctor Who, Logopolis, our universe is revealed to have already passed the heat death point, and entropy is channelled into other universes. When The Master destroys Logopolis, entropy begins to flood into our universe and destroy it.

Video games

★ Durandal, the rampant AI in Bungie's ''Marathon'' series shows concern, and even obsession, with escaping the closure of the universe, which he insists is inevitable, but can be avoided by means unknown to the player.

★ In the video game ''Chrono Trigger'', the End of Time area corresponds with the end of the universe. The End of Time is seen as a small square with a streetlight in the middle, with three paths. One path leads to the various portals used by the characters to traverse time, another leads to a being known as the "Master of War" who watches the various wars and battles throughout time and teaches the characters magic. Finally, the last path leads to the place where the characters park their Time Machine, the Epoch. There is little else, except for a dark abyss in which there is absolutely nothing.

★ The plot of the PlayStation 2 RPG trilogy ''Xenosaga'', particularly '' deals with several characters trying to prevent the end of the universe by continually resetting time and never allowing the universe to age beyond a specific date (c. 6000 AD).

★ Anthropic principle ★ Arrow of time ★ Big Bang ★ Big Crunch ★ Big Freeze ★ Big Rip ★ Big Bounce ★ Cosmology ★ Doomsday event ★ Dyson's eternal intelligence ★ Esoteric cosmology ★ False vacuum	★ Final anthropic principle ★ General relativity ★ Heat death of the universe ★ Kardashev scale ★ Models of the Universe ★ Multiverse ★ Omega point ★ Shape of the universe ★ Timeline of cosmology ★ Timeline of the Big Bang ★ Deep ecology	Scientists ★ John D. Barrow ★ Freeman Dyson ★ Alan Guth ★ Andrei Linde ★ Frank J. Tipler

References

1. http://www.universetoday.com/am/publish/printer_advanced_civilization_become.html

External links

★ Baez, J., 2004, "The End of the Universe."

★ Caldwell, R. R., Kamionski, M., and Weinberg, N. N., 2003, "Phantom Energy and Cosmic Doomsday," ''Physical Review Letters 91''.

★ Hjalmarsdotter, Linnea, 2005, "Cosmological parameters."

★ Malm T. M., Spiral Rotation Model.

★ Vaas, R., 2006, "Dark Energy and Life's Ultimate Future," in Burdyuzha, V. (ed.) ''The Future of Life and the Future of our Civilization''. Springer: 231-247.

★ An in depth look at what the future holds for the universe.

★ A Brief History of the End of Everything, a BBC Radio 4 series.

★ Cosmology at Caltech.

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