http://en.wikipedia.org/wiki/Ultimate_fate_of_the_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.
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.
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.
The Big Bounce is a theorized scientific model related to the creation
of the known Universe. It derives from the oscillatory universe or
cyclic repetition 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.[citation needed] 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 universe collapses it
will spawn another universe in an event similar to the Big Bang after
a universal singularity is reached or a repulsive quantum force causes
re-expansion.
The multiverse hypothesis states that our universe is but one universe
among infinite 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.
If the vacuum is not in its lowest energy state (a false vacuum), it
could tunnel into a lower energy state.[citation needed] This is
called the vacuum metastability event. This has the potential to
fundamentally alter our universe; in more audacious scenarios even the
various physical constants could have different values, severely
affecting the foundations of matter, energy, and spacetime. It is also
possible that all structures will be destroyed instantaneously,
without any forewarning.
According to the many-worlds interpretation of quantum mechanics, the
universe will not end this way. Instead, each time a quantum event
happens that causes the universe to decay from a false vacuum to a
true vacuum state, the universe splits into several new worlds. In
some of the new worlds the universe decays; in some others the
universe continues as before.
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. 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.
Choosing among these rival scenarios is done by 'weighing' the
universe, for example, 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 any 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 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
Many religions have an end-of-the-universe prediction. The theological
study of the ultimate fate of the universe and/or ultimate destiny of
mankind is known as eschatology. Many religious beliefs are
cataclysmic, and some theists do not view the various scientific
theories about the end of the universe as contradicting their
religious beliefs. In fact, some theist argue that such scientific
theories validate end-of-the-universe predictions.
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.
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.
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, consisting of the fading out of the Sun to an
exhausted red ember and a vision of Earth as a cold and bland eroded
desert, to as recently as 2007 in the Doctor Who episode Utopia, with
the last remnants of society struggling to survive in a universe
without stars and few planets still capable of supporting life.
Religion is not wholly excluded from science fiction's explorations of
the end of our universe. Arthur C. Clarke's 1953 short story "The Nine
Billion Names of God" treats 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..
Isaac Asimov's short story, "The Last Question" was published in 1959.
Humankind builds a series of supercomputers to solve the question of
how to stop entropy, but are unsuccessful until long after the
universe (and humanity) has succumbed to heat death (the only
cosmological end-scenario articulated at the time). A computer built
in hyperspace finally discovers how to reverse the process and does
so: "'LET THERE BE LIGHT!' And there was light—".
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.
The end of the universe has been used for satirical and comedic
effect. In Douglas Adams's science-fiction series The Hitchhiker's
Guide to the Galaxy, the "Restaurant at the End of the Universe" and
its patrons are projected through time to the end of the universe, for
guests to watch the event 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 someone would observe an
entire range of mountains in one instant.
