Universe: Mixmaster

Theoretical Cosmology:

Universe: Mixmaster

Published:
Updated: April 21, 2009, 8:45 pm
Topics: Theoretical Cosmology

Introduction

Rather than the initial state of the universe being carefully tuned in a specific initial configuration of fields and forces, it may have been a fully chaotic state where all possible initial conditions were realized, but only one was lucky enough to survive. Today we observe a universe that is surprisingly uniform, but it may not have started out that way. Cosmological models based on the so-called "Kasner metric" were first studied in 1958 and led to fully anisotropic universes. A variety of dissipation mechanisms were advanced to smooth out this anisotropy by the present epoch as the universe expanded. Near the Singularity itself, the degree of anisotropy is maximal.

In 1969-70 Charles Misner and others described a universe in which the metric near the Singularity changed with time from one anisotropic state to another. This sequence of changes continued all the way back to time zero.

"Whether the universe is infinitely old by this standard remains to be determined... The Mixmaster cosmological model does have an infinite past history in this sense, since each "bounce" from one Kasner motion to another is a recognizable event, of which an infinite number exist between the present epoch and the Singularity." 

Near the initial Singularity, the universe is represented by an infinite sequence of Kasner Epochs during which the universe is in a chaotic regime.

According to studies by Szyolowski and Kapeta in 1991, the universe evolves towards the Initial Singularity along a sequence of spacetimes in which it expands in some directions, collapses in others, or even oscillates. This chaotic behavior breaks down if the dimensionality of spacetime is greater than 4, but in general the chaotic behavior will persist if spacetime dimensionalities are in the range from 4 to 9. For dimensionalities greater than 10, the process is not chaotic. This work builds upon the investigations into Mixmaster cosmology, and although it does not do away with the Initial Singularity, it shows that even without quantum effects, the dimensionality of spacetime may have undergone considerable change. As a chaotic system at high density and temperature, the universe could have jumped from one chaotic Kasner mode to another, between strange attractors, undergoing an almost infinite number of oscillations before "breaking-out" and expanding in the Big Bang.

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Preview Image

"Artist's concept of the first stars in the Universe turning on." - (Source: NASA/WMAP Science Team.)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Universe: Mixmaster." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published February 14, 2008].
<http://www.cosmosportal.org/articles/view/138905/>

 

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