The 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 and Neil Turok. Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ... According to the Big Bang theory, the Universe originated in an extremely dense and hot state (bottom). ... The ekpyrotic universe or ekpyrotic scenario is a cosmological theory of the origin of the universe. ... 2001: A Space Odyssey. ... Paul J. Steinhardt is the Albert Einstein Professor of Science at Princeton University and a professor of theoretical physics. ... Neil Geoffrey Turok (1967) is a South African cosmologist. ...

The model

In the cyclic model, two parallel orbifold planes or M-branes collide periodically in a higher dimensional space. The visible four-dimensional universe lies on one of these branes. The collisions correspond to a reversal from contraction to expansion, or a big crunch followed immediately by a big bang. The matter and radiation we see today were generated during the most recent collision in a pattern dictated by quantum fluctuations created before the branes. Eventually, the universe reached the state we observe today, before beginning to contract again many billions of years in the future. Dark energy corresponds to a force between the branes, and serves the crucial role of solving the monopole, horizon, and flatness problems. Moreover the cycles can continue indefinitely into the past and the future, and the solution is an attractor, so it can provide a complete history of the universe. In topology, an orbifold is a generalization of manifold. ... Branes are objects in M-theory and its offshoot, brane cosmology. ... P-branes or branes are terms from quantum superstring theory used to refer to membrane-like structures of one to eleven dimensions that arise in equations of this heavily mathematical theory. ... In cosmology, the Big Crunch is a hypothesized collapse of the universe upon itself after its expansion eventually stops —a counterpart to the Big Bang. ... According to the Big Bang theory, the Universe originated in an extremely dense and hot state (bottom). ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ... In physics, magnetic monopole is a term describing a hypothetical particle that could be quickly clarified to a person familiar with magnets but not electromagnetic theory as a magnet with only one pole. In more accurate terms, it would have net magnetic charge. Interest in the concept stems from particle... When we look at the CMB it comes from 15 billion light years away. ... The flatness problem is a cosmological problem with the Big Bang theory, which is solved by hypothesising an inflationary universe. ... In dynamical systems, an attractor is a set to which the system evolves after a long enough time. ...

An earlier cyclic model of Richard Tolman failed because the universe would undergo inevitable thermodynamic heat death. However, the 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. Richard C. Tolman was California Institute of Technology professor of physical chemistry and mathematical physics. ... Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of temperature, pressure, and volume changes on physical systems at the macroscopic scale. ... The heat death is a possible final state of the universe, in which it has reached maximum entropy. ... The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work. ... Branes are objects in M-theory and its offshoot, brane cosmology. ... In physics, scale invariance is the feature of physical objects of laws that do not change if the space is magnified, i. ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles... In physics, Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify the two fundamental forces of gravitation and electromagnetism. ... In topology, an orbifold is a generalization of manifold. ...

Originally, ekpyrotic models described two branes separated along a fifth dimension which collide once. Crucially, both the ekpyrotic and cyclic models create the fluctuations we observe today in a contracting "ekpyrotic" phase. However, in the ekpyrotic model, while a future collision with a different brane could conceivably happen in the future, ending our epoch in a conflagration, this happens randomly, not periodically. There were problems with the old ekpyrotic picture having to do with the very special, nearly supersymmetric initial state required in order to end up with a nearly homogeneous universe: the problems solved by cosmic inflation, such as the monopole, flatness and homogeneity problems were shifted to a set of fine-tuned initial conditions. The ekpyrotic picture was not connected to the issue of dark energy. In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... In particle physics, supersymmetry is a hypothetical symmetry that relates bosons and fermions. ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ... In theoretical physics, fine-tuning is a necessary procedure of fudging and very accurate adjusting of the values of the parameters of a theory in order for various physical quantities to be very small. ... In mathematics, boundary conditions are imposed on the solutions of ordinary differential equations and partial differential equations, to fit the solutions to the actual problem. ... In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ...

There are other technical differences having to do with the nature of the branes. For example, in the ekpyrotic model, they are D-branes; while in the cyclic model, they are orbifold planes. In theoretical physics, D-branes are a special class of p-branes, named for the physicist Johann Dirichlet. ... In topology, an orbifold is a generalization of manifold. ...

External links

• Paul J. Steinhardt, Department of Physics, Princeton University http://feynman.princeton.edu/~steinh/