The ultimate
fate of the universe is a topic in cosmology. Rival scientific theories
predict whether the universe will be of finite or infinite duration. Once
it was accepted that the universe had a beginning a finite time ago, the
ultimate fate of the universe becomes a valid cosmological question, one depending
upon the universe's average density of matter and rate of expansion.
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
The Big Freeze is a scenario under which continued expansion results in
a universe that is too cold to sustain life. It could occur under a flat or
hyperbolic geometry, because such geometries are a necessary condition for
a universe that expands forever. A related scenario is Heat Death, which
states that the universe goes to a state of maximum entropy in which there
are no energy gradients needed to sustain information processing, of which
life is the most interesting form.
Big Rip: infinite time, finite lifespan
In an open universe, general relativity predicts that the universe will
have an indefinite future existence, but will approach a state where life
as we know it cannot exist. Under this scenario, a cosmological constant causes
the rate of expansion of the universe to accelerate. Taken to the extreme,
an ever-accelerating expansion means that all material objects in the universe,
starting with galaxies and eventually all life forms, no matter how small,
will disintegrate into unbound elementary particles. The end state of the
universe is then a gas of photons, leptons and protons (or only leptons and
photons, if protons decay) growing ever less dense. For a possible timeline
based on current physical theories, see 1 E19 s and more.
Big Crunch: finite time and lifespan
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.
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. Of course, it is meaningless
to distinguish between a Big Crunch and a Big Bang; we should only speak
of recurring singularities.
Multiverse: no complete end
The Multiverse (or parallel universe in the singular case) scenario states
that while our universe may be of finite duration, it is but one universe
among many. Moreover, the physics of the multiverse may permit it to exist
indefinitely. In particular, other universes may be subject to physical
laws differing from those that apply in our own universe.
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
disaster. This would fundamentally alter our universe; the various physical
constants could have different values, severely affecting the foundations
of matter.
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.
Barrow and Tipler (1986) propose a Final anthropic principle: the mergence
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.
Frank J. Tipler's Omega point scenario (Tipler 1994) concludes that the
reverse 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.
Even if 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.
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. [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.
