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 continue to expand indefinitely, resulting in the "big freeze" scenario below.
[1]
[edit] Big Freeze or Heat death
Main article:
Heat death of the universe
The Big Freeze is a scenario under which continued expansion results in a universe that
asymptotically approaches
absolute zero temperature. It could, in the absence of dark energy, occur only under a flat or hyperbolic geometry. With a positive cosmological constant, it could also occur in a closed universe. This scenario is currently the most commonly accepted theory within the scientific community. 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.
[edit] Big Rip: Finite Lifespan
Main article:
Big Rip
An animated impression of a galaxy undergoing the Big Rip
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 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.
[edit] Big Crunch
The Big Crunch. The vertical axis can be considered as either plus or minus time.
Main article:
Big Crunch
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.
[edit] Big Bounce
Main article:
Big Bounce
The Big Bounce is a theorized scientific model related to the beginning 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.
[edit] Multiverse: no complete end
Main article:
Multiverse
One multiverse hypothesis states that our uni-"verse" is merely one Big Bang among an infinite number of simultaneously expanding Big Bangs that are spread out over endless distances (open space).
Each "verse" may be either matter or antimatter, with an equal number in existence at any given time. As the "verses" expand they collide and matter and antimatter annihilate, releasing energy. Heat death of a finite universe would be predicted as entropy increases, however, the infinite size of the multiverse and the infinite number of "verses" could mean that new "verses" would be formed as old "verses" were annihilated.
A chain reaction multiverse would be analogous to a fireworks display (each explosion representing a Big Bang) that starts in one neighborhood and is followed by fireworks displays in surrounding neighborhoods and then in neighborhoods further out. The chain reaction of Big Bangs would continue to expand as Big Bang fuel is consumed. If the multiverse is open and the fuel is infinite then the chain reaction would expand forever. Of course, it is not known what the "fuel" is, but it is logical to assume that matter and energy are the product of a transformation from a real reactant, possibly the Higgs boson.
The multiverse as a whole may never end completely.
[edit] False vacuum
If the vacuum is not in its lowest energy state (a
false vacuum), it could
tunnel into a lower energy state.
[2] 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
[3].
[edit] Many-worlds interpretation of quantum mechanics
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.
[edit] Cosmic uncertainty
Each possibility described so far is based on a 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. It is also possible the universe may never have an end and continue in its present state forever.
How will the universe end?
Originally Posted by lomotel
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