Ultimate fate of the universe

Many religions have postulated an end to the Universe. According to some, the end of the world will cause the end of the Universe. See the article on eschatology for discussion of these issues. This article is about scientific theories of the end of the Universe.

The ultimate fate of the Universe is a subject of study in the field of cosmology. Either the Universe will exist forever, or it will cease to exist at some time. It is unknown which of these possibilities will hold true. It is also not known whether the Universe will continue to support life.

Scientific theories

Until fairly recent times, the mainstream scientific view of the universe was of an eternal and unchanging existence, now known as the Steady state theory. After Edwin Hubble's discovery of universal expansion, however, the notion of a beginning and a possible end became an important subject of scientific investigation.

The beginning of the Universe is most commonly referred to as the Big Bang. Theories about the end can be divided into five major groups:

1. Despite observations, the universe is eternal as believed before.
   • steady-state universe
2. The Big Bang was preceded by a Big Crunch and the Universe will eventually undergo another Big Crunch and Big Bang sequence.
   • oscillatory universe
3. Our universe may end, but it is only one amongst numerous others which are not, as a collection, subject to physical laws that could cause a total end.
   • multiverse
   • parallel universe
4. The Universe will not end, but its contents will reach a uniform equilibrium which renders life impossible.
   • heat death of the universe
   • Big Rip
5. The Universe will end in some way.
   • Big Crunch

All theories must come to terms with general relativity, which provides a common background for cosmological speculation. Most of these theories are solutions of GR equations, only differing in their parameters (such as average density or the value of the cosmological constant).

The first three groups are not discussed in this article, as they nullify the very concept of an "ending of the Universe". In such theories, some kind of meaningful activity can last forever.

Infinite time, but finite lifespan

In an open Universe, General Relativity shows that the Universe can exist indefinitely in the future, but will settle down into a state where life as we know it will cease to exist; for a possible timeline based on current physical theories, see 1 E19 s and more.

In 2003, New Scientist magazine reported a preprint by Robert R. Caldwell, Marc Kamionkowski and Nevin N. Weinberg which puts forward the hypothesis that the end of the Universe may occur as a "Big Rip", which will shred the physical structure of the Universe.

In this model, a cosmological constant causes the Universe's rate of expansion to accelerate. Taken to the extreme, an ever-accelerating expansion means that all physical objects in the Universe, starting with galaxies and down to individual human beings, bacteria, and grains of sand, will eventually be torn to pieces and then to elementary particles. The Universe will be then reduced to single elementary particles forever accelerating away from one another.

Finite time and lifespan

The Big Crunch theory is a symmetrical view of the life 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 a cosm-wide contraction.

It is unknown what the end result would be: a simple extrapolation would have all the matter and space-time in the Universe collapse into a dimensionless singularity, but at these scales quantum effects should be considered. Some people use this opportunity to postulate an oscillatory Universe, that starts again to expand. Indeed, if symmetry is to be followed, it is meaningless to make a distinction between a Big Crunch and a Big Bang, and so any endpoint may progress to a new universe.

Life in a mortal Universe

Some well-known physicists have speculated that an advanced civilization could use a finite amount of energy to survive for an effectively infinite amount of time. The strategy is to have brief periods of activity, alternated by longer and longer periods of hibernation (see Dyson's eternal intelligence for more information).

The reverse is true for a civilization finding itself in the middle of the Big Crunch. Here, an effectively infinite amount of subjective time can be extracted from the finite remaining time, using the enormous energy of the Crunch to "speed up" life faster than the limit is approaching (see Frank J. Tipler's Omega point).

Even if possible in theory, it is unclear whether these possibilities could practically be developed by any civilization, regardless of technological advancement. However, effective solutions may become indistinguishable from the present state of our universe.

Recent work in fields such as inflationary cosmology , string theory, and quantum mechanics has pushed the debate into an entirely distinct realm from the scenarios discussed in Dyson's and Tipler's hypotheses. Physicists such as Eric Chaisson and David Layzer have noted that an increasing "entropy gap" arises in an expanding spacetime, casting doubt on the heat death hypothesis. In conjunction with work by Ilya Prigogine on far-from-equilibrium thermodynamics, their analysis suggests that the gap itself may contribute to information and the formation of structure.

Meanwhile, physicists such as Andrei Linde, Alan Guth, Edward Harrison , and Ernest Sternglass have demonstrated 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 de novo generate and transmit information into a distinct universe. Moreover, recent theoretical work on the unresolved quantum gravity problem and the Holographic Principle has indicated 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 cosmic models.

Popular culture

Several science fiction authors and humorists have written parodies involving the end of the Universe.

• In Terry Pratchett's Discworld series, the term big bang is imbued with a sexual connotation. The Discworld is situated on top of four elephants, who in turn stand upon the back of a great Turtle. As the gender of the Turtle is not known, it leads to speculation about what position the Turtle would assume should there be another big bang.

• The novel The Restaurant at the End of the Universe, the second work in Douglas Adams' Hitchhiker's Guide to the Galaxy series, features a restaurant whose patrons can repeatedly watch the end of all things as part of an after dinner show. Another entry in the fictional Hitchhiker's Guide to the Galaxy, (from which the novel gets its name), is for the creation of the Universe: The entry mentions the Jatravartid people of Viltvodle VI, who believe that the Universe was sneezed out of the nose of a being called the Great Green Arkleseizure. These same people are said to live in perpetual fear of a time they call the Coming of the Great White Handkerchief.

Observational Constraints on Theories

Some cosmologists, like Yun Wang and Max Tegmark, are now working on how recent observational data constrain the theoretical possibilities, for the nature of dark energy, and its possible effects on the ultimate fate of the universe, as a Big Crunch, flat vanilla state, or Big Rip.

"... Using the spectacular new high redshift supernova observations ..., CMB and galaxy clustering data, we make the most accurate measurements to date of the [dark energy density] rho_X as a function of cosmic time, constraining it in a rather model-independent way, assuming a [flat universe]. We find that Einstein's vanilla scenario ... remains consistent with these new tight constraints, and that a Big Crunch or Big Rip is more than 50 gigayears away for a broader class of models allowing such cataclysmic events ..."

See also

• arrow of time

Recommended reading

• Fred Adams & Greg Laughlin, The Five Ages of the Universe
• John Barrow, Impossibility
• Stephen Baxter, Deep Future
• Eric Chaisson, Cosmic Evolution
• Paul Davies, The Last Three Minutes
• Alan Guth, The Inflationary Universe
• Edward Robert Harrison, Masks of the Universe: Changing Ideas on the Nature of the Cosmos
• David Layzer, Cosmogenesis
• Andrei Linde, Particle Physics and Inflationary Cosmology
• Ilya Prigogine and Isabelle Stengers, Order out of Chaos: Man's New Dialogue with Nature
• Ilya Prigogine, Is Future Given?
• Lee Smolin, The Life of the Cosmos
• Lee Smolin, Three Roads to Quantum Gravity

External links

• Phantom Energy and Cosmic Doomsday by Robert R. Caldwell, Marc Kamionkowski and Nevin N. Weinberg
• A Brief History of the End of Everything, a BBC 4 Radio series