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Unit 4: String Theory and Extra Dimensions

© Matt DePies, University of Washington.

Unit Overview

This unit continues our movement from experimentally proven understanding of nature's four fundamental forces to the theoretical effort to develop a "theory of everything" that brings all four forces under the same conceptual umbrella. The most prominent aspect of that effort is the family of string theories that envision the basic units of matter as minuscule stretches of threadlike strings rather than point particles. Introduced in the mid-1970s, the string concept has stimulated a great deal of theoretical excitement even though it has no connection to experiment so far. The unit introduces string theory in the context of quantum gravity and outlines its inherent multidimensional nature; the most promising approach involves a total of ten dimensions. The unit then covers the relationship of string theory to particle physics and introduces the idea of "branes," related to strings. Next, the unit focuses on cosmological issues arising from our understanding of the Big Bang, outlines the way in which the concept of rapid inflation very early in the universe can solve some major issues, and details links between string theory and cosmic inflation. Finally, the unit summarizes the understanding that string theory brings to fundamental understanding of gravity.