# Gravity: Dimensionally-Extended

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## Introduction

In the spirit of the Nordstrom-Kaluza-Klein theory which involved adding a 5th dimension to spacetime, physicists discovered that SO(8) in 4-D could be recast as the far-simpler SO(1) theory, but in 11-D. By adding additional dimensions to the mathematics, the compliment of fundamental fields became much simpler in 11-dimensions, but when it was reduced back to a 4-dimensional theory, you could recover the full compliment of fields predicted by the more complex SO(8) theory. Still, there were problems that seemed insurmountable no matter what trick you tried to work.

During the late 70's an increasing fraction of theoretical attention became focussed on the search for a self-consistent, infinity-free GUT. Supergravity and Supersymmetric GUTS (SUSY GUTS) were the object of a veritable feeding frenzy of activity as this new motherlode was mined. A bewildering number of ideas were spawned that impacted the theoretical structure of spacetime and the vacuum. New phase transitions were identified at energies between 100 and 10^{15}GeV implying new patinas of vacuum states litering spacetime. Dimensional-extension was applied to Supersymmetry theory, but required spacetime to have far more than 4-D; perhaps as many as 11. These additional dimensions would be rolled-up into sub-spaces resembling tiny spheres attached to each point in spacetime, but other more exotic geometries for these sub-spaces were also investigated. These ideas resulted in an explosion of popular articles as physicists boldy went into a landscape previously reserved for science fiction authors.

A Scientific American article "The Hidden Dimensions of Spacetime" written by Daniel Z. Freedman and Peter van Nieuwenhuizen tried to set the record straight on what all of this meant, but any intuitive understanding of 11-D spacetime seemed to elude the grasp of even the most ardent science popularizers.

## Related EoC Articles

- Gravity: Canonical Quantization
- Gravity: Covariant Quantization
- Gravity: Dimensionally-Extended
- Gravity: Gauge Field
- Gravity: Graviton
- Gravity: Kaluza-Kline Theory
- Gravity: Quantization ca. 1990
- Gravity: Quantum
- Gravity: Renormalization
- Gravity: String Theory
- Gravity: Superspace Quantization
- Gravity: Supersymmetry
- Gravity: What is Gravity?

## Image Preview

Gravitational waves are propagating gravitational fields, "ripples" in the curvature of space-time, generated by the motion of massive particles, such as two stars or two black holes orbiting each other. Gravitational waves cause a variable strain of space-time, which result in changes in the distance between points, with the size of the changes proportional to the distance between the points. Gravitational waves can be detected by devices which measure the induced length changes. Waves of different frequencies are caused by different motions of mass, and difference in the phases of the waves allow us to perceive the direction to the source and the shape of the matter that generated them. (Source: NASA-The Laser Interferometer Space Antenna (LISA).)

Citation

Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Article Name." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published February 12, 2008].

<http://www.cosmosportal.org/articles/view/135644/>

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