Chaotic Inflation theory

The Chaotic Inflation theory is a variety of the inflationary universe model, which is itself an outgrowth (or extension) of the Big Bang theory. Chaotic Inflation, proposed by physicist Andrei Linde, models our universe as one of many that grew as part of a multiverse owing to a vacuum that had not decayed to its ground state. In this theory, the peaks in the evolution of a scalar field (determining the energy of the vacuum) correspond to regions of rapid inflation which dominate, creating "bubble universes," making the structure of space fractal on the very largest scales, likely at scales larger than the observable universe. Chaotic Inflation (along with some other types of inflation) is usually a sub-class of eternal inflation,[1] since the expansion of the inflationary peaks exhibit positive feedback and come to dominate the large scale dynamics of the universe. Alan Guth's 2007 paper, Eternal inflation and its implications[1] details what is now known on the subject, and demonstrates that this particular flavor of Inflationary universe theory is relatively current, or is still considered viable, more than 20 years after its inception.[2] [3] [4]

History

Inflation, or the inflationary universe theory, was developed as a way to overcome the few remaining problems with what was otherwise considered a successful theory of cosmology, the Big Bang model. It is now known[by whom?] that Alexei Starobinsky, at the L.D. Landau Institute of Theoretical Physics in Moscow developed the first realistic Inflation theory in 1979[5][6] but failed to articulate its relevance to modern cosmological problems. Due to political difficulties in the former Soviet Union, regarding the free exchange of scientific knowledge, most scientists outside the USSR remained ignorant about Starobinsky’s work until years later. Starobinsky's model was relatively complicated, however, and said little about how the inflation process could start.

In 1979 Alan Guth of the United States developed an inflationary model independently, which did offer a mechanism for inflation to begin, the decay of a so-called false vacuum into 'bubbles' of 'true vacuum' that expanded at the speed of light. Guth coined the term, “inflation,” and he was the first to discuss the theory with other scientists worldwide. But this formulation was problematic, as there was no consistent way to bring an end to the inflationary epoch and end up with the isotropic, homogeneous Universe observed today. (See False vacuum#Developments of theory). In 1982, this "graceful exit problem" was solved by Andreas Albrecht and Paul J. Steinhardt and also independently by Andrei Linde.

In 1986, Linde published an alternative model of inflation that also reproduced the same successes of new inflation entitled "Eternally Existing Self-Reproducing Chaotic Inflationary Universe,"[7] which provides a detailed description of what has become known as the Chaotic Inflation theory or eternal inflation. The Chaotic Inflation theory is in some ways similar to Fred Hoyle’s Steady state theory, as it employs the metaphor of a universe that is eternally existing, and thus does not require a unique beginning or an ultimate end of the cosmos.

Quantum fluctuations of the inflation field

Chaotic Inflation theory models quantum fluctuations in the rate of inflation.[8] Those regions with a higher rate of inflation expand faster and dominate the universe, despite the natural tendency of inflation to end in other regions. This allows inflation to continue forever, to produce future-eternal inflation.

Within the framework of established knowledge of physics and cosmology, our universe could be one of many in a super-universe or multiverse. Linde (1990, 1994) has proposed that a background space-time "foam" empty of matter and radiation will experience local quantum fluctuations in curvature, forming many bubbles of false vacuum that individually inflate into mini-universes with random characteristics. Each universe within the multiverse can have a different set of constants and physical laws. Some might have life of a form different from ours; others might have no life at all or something even more complex or so different that we cannot even imagine it. Obviously we are in one of those universes with life.[9]
—Victor J. Stenger

Past-eternal models have been proposed which adhere to the perfect cosmological principle and have features of the steady state cosmos.[10][11][12]

Differential decay

In standard inflation, inflationary expansion occurred while the universe was in a false vacuum state, halting when the universe decayed to a true vacuum state becoming a general and inclusive phenomenon with homogeneity throughout, yielding a single expanding universe which is “our general reality” wherein the laws of physics are consistent throughout. In this case, the physical laws "just happen" to be compatible with the evolution of life.

The bubble universe model proposes that different regions of this inflationary universe (termed a multiverse) decayed to a true vacuum state at different times, with decaying regions corresponding to “sub”- universes not in causal contact with each other and resulting in different physical laws in different regions which are then subject to “selection” which determine each region’s components based upon (dependent on) the survivability of the quantum components within that region. The end result will be a finite number of universes with physical laws consistent within each region of spacetime.

False vacuum and true vacuum

Variants of the bubble universe model postulate multiple false vacuum states, which result in lower-energy false-vacuum “progeny” universes spawned, which in turn produce true vacuum state progeny universes within themselves.

Evidence from the Fluctuation Level in our Universe

It has shown that new inflation does not produce a perfectly symmetric universe, but that tiny quantum fluctuations in the inflaton are created. These tiny fluctuations form the primordial seeds for all structure created in the later universe. These fluctuations were first calculated by Viatcheslav Mukhanov and G. V. Chibisov in the Soviet Union in analyzing Starobinsky's similar model.[13][14][15] In the context of inflation, they were worked out independently of the work of Mukhanov and Chibisov at the three-week 1982 Nuffield Workshop on the Very Early Universe at Cambridge University.[16] The fluctuations were calculated by four groups working separately over the course of the workshop: Stephen Hawking;[17] Starobinsky;[18] Guth and So-Young Pi;[19] and James M. Bardeen, Paul Steinhardt and Michael Turner.[20]

The agreement of these models with the predictions of WMAP data adds weight to the idea that the universe is self caused by such a method. Although promising, many physicist take such evidence with a cautious optimism.[21]

References

^ a b Guth, Alan; Eternal inflation and its implications arXiv:hep-th/0702178
^ Holt, Jim. "The Big Lab Experiment. Was our universe created by design?". Slate.
^ Jones, Douglas S.. "Many worlds interpretation".
^ Guth, Alan. "Eternal inflation: Successes and questions".
^ Starobinsky, A. A. (1979). "Spectrum of Relict Gravitational Radiation and The Early State of the Universe". JETP Lett. 30, 682 (Pisma Zh. Eksp. Teor. Fiz. 30, 719).
^ Linde, Andrei (November 1994). "The Self-Reproducing Inflationary Universe". Scientific American: page 51.
^ Linde, A.D. (August 1986). "Eternally Existing Self-Reproducing Chaotic Inflationary Universe &". Physics Letters B 175: 395–400. Bibcode 1986PhLB..175..395L. doi:10.1016/0370-2693(86)90611-8.
^ Linde, A. (1986). "Eternal Chaotic Inflation". Mod. Phys. Lett. A1: 81.
^ Stenger, Victor J. "Is the Universe fine-tuned for us?".
^ Aguirre, Anthony and Gratton, Steven n (2003). "Inflation without a beginning: A null boundary proposal". Phys.Rev. D67 083515. arXiv:gr-qc/0301042. Bibcode 2003PhRvD..67h3515A. doi:10.1103/PhysRevD.67.083515.
^ Aguirre, Anthony, and Gratton, Steven (2002). "Steady-State Eternal Inflation". Phys.Rev. D65 083507. arXiv:astro-ph/0111191. Bibcode 2002PhRvD..65h3507A. doi:10.1103/PhysRevD.65.083507.
^ Gribbin, John. "Inflation for Beginners".
^ See Linde (1990) and Mukhanov (2005).
^ Mukhanov, Viatcheslav F. (1981). "Quantum fluctuation and "nonsingular" universe". JETP Lett. 33: 532–5. Bibcode 1981JETPL..33..532M.
^ Mukhanov, Viatcheslav F. (1982). "The vacuum energy and large scale structure of the universe". Sov. Phys. JETP 56: 258–65.
^ See Guth (1997) for a popular description of the workshop, or The Very Early Universe, ISBN 0521316774 eds Hawking, Gibbon & Siklos for a more detailed report
^ Hawking, S.W. (1982). "The development of irregularities in a single bubble inflationary universe". Phys.Lett. B115: 295.
^ Starobinsky, Alexei A. (1982). "Dynamics of phase transition in the new inflationary universe scenario and generation of perturbations". Phys. Lett. B117: 175–8.
^ Guth, A.H. (1982). "Fluctuations in the new inflationary universe". Phys. Rev. Lett. 49: 1110–3. Bibcode 1982PhRvL..49.1110G. doi:10.1103/PhysRevLett.49.1110.
^ Bardeen, James M. (1983). "Spontaneous creation Of almost scale-free density perturbations in an inflationary universe". Phys. Rev. D28: 679.
^ Beyond Belief: Science, Reason, Religion & Survival Speaker: Stephen Weinberg, Filmed in November 2006 at the Salk Institute. Presented by The Science Network.