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Cyclic model
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Cyclic model refers to several cosmological models in which the universe follows infinite, self-sustaining cycles (for example: an eternity of Big Bang-Big crunches).
new cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. It was proposed in 2001 by Paul Steinhardt of Princeton University and Neil Turok of Cambridge University. The theory describes a universe exploding into existence not just once, but repeatedly over time.
The Steinhardt-Turok model
As Richard C. Tolman showed, the earlier cyclic model failed because the universe would undergo inevitable thermodynamic heat death.
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Encyclopedia
Cyclic model refers to several cosmological models in which the universe follows infinite, self-sustaining cycles (for example: an eternity of Big Bang-Big crunches).
Overview
One new cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. It was proposed in 2001 by Paul Steinhardt of Princeton University and Neil Turok of Cambridge University. The theory describes a universe exploding into existence not just once, but repeatedly over time.
The Steinhardt-Turok model
As Richard C. Tolman showed, the earlier cyclic model failed because the universe would undergo inevitable thermodynamic heat death. However, the newer cyclic model evades this by having a net expansion each cycle, preventing entropy from building up. However, there are major problems with the model. Foremost among them is that colliding branes are not understood by string theorists, and nobody knows if the scale invariant spectrum will be destroyed by the big crunch, or even what happens when two branes collide. Moreover, like cosmic inflation, while the general character of the forces (in the ekpyrotic scenario, a force between branes) required to create the vacuum fluctuations is known, there is no candidate from particle physics. Moreover, the scenario uses some essential ideas from string theory, principally extra dimensions, branes and orbifolds. String theory itself is a controversial idea in physics.
Lynds Cyclic Time model
Peter Lynds has proposed a model in which time is cyclic, and the universe repeats exactly an infinite number of times. Because it is the exact same cycle that repeats, however, it can also be interpreted as taking place just once. Lynds argues that his model addresses a number of problems in cosmology that other models are unable to, including the question of the origin of the universe. A key feature of Lynds' model is his treatment of thermodynamic time reversal. Rather than the second law of thermodynamics possibly be violated and entropy decrease, the order of events reverse so that entropy can continue to increase. As the laws of physics are time reversible (with the exception of the second law of thermodynamics), Lynds argues that this causes no problems, while also avoiding some.
See also
Further reading
Reissued (1987) New York: Dover ISBN
0-486-65383-8.
- Lauris Baum and Paul H. Frampton, Phys. Rev. Lett. 98, 071301 (2007).
External links
- , Department of Physics, Princeton University
- , Department of Physics and Astronomy, The University of North Carolina at Chapel Hill
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