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The theory envisions that a string undergoing a particular mode of vibration corresponds to a particle with definite properties such as mass and charge. While string theory is still a vibrant area of research that is undergoing rapid development, it remains primarily a mathematical construct because it has yet to make contact with experimental observations.
In Einstein unified space and time see space-time with his special theory of relativityshowing that motion through space affects the passage of time. In Einstein further unified space, time, and gravitation with his general theory of relativityshowing that warps and curves in space and time are responsible for the force of gravity. These were monumental achievements, but Einstein dreamed of an even grander unification. For the last three decades of his life, Einstein relentlessly pursued this vision. Although from time to time rumours spread that he had succeeded, closer scrutiny always dashed such hopes.
In contrast, the primary concern of theoretical physicists from the s onward was quantum mechanics —the emerging framework for describing atomic and subatomic processes. Particles at these scales have such tiny masses that gravity is essentially irrelevant in their interactions, and so for decades quantum mechanical calculations generally ignored general relativistic effects. Instead, by the late s the focus was on a different force—the strong forcewhich binds together the protons and neutrons within atomic nuclei.
Gabriele Veneziano, a young theorist working at the European Organization for Nuclear Research CERNcontributed a key breakthrough in with his realization that a year-old formula, the Euler beta function, was capable of explaining much of the data on the strong force then being collected at various particle accelerators around the world.
String theory was an intuitively attractive proposal, but by the mids more-refined measurements of the strong force had deviated from its predictions, leading most researchers to conclude that string theory had no relevance to the physical universeno matter how elegant the mathematical theory.
Nevertheless, a small of physicists continued to pursue string theory.
They suggested that one of the supposedly failed predictions of string theory—the existence of a particular massless particle that no experiment studying the strong force had ever encountered—was actually evidence of the very unification Einstein had anticipated. Although no one had succeeded in merging general relativity and quantum mechanics, preliminary work had established that such a union would require precisely the massless particle predicted by string theory.
A few physicists argued that string theory, by having this particle built into its fundamental structure, had united the laws of the large general relativity and the laws of the small quantum mechanics. The announcement was universally ignored.
String theory had already failed in its first incarnation as a description of the strong force, and many felt it was unlikely that it would now prevail as the solution to an even more difficult problem. For one, some of its equations showed s of being inconsistent; for another, the mathematics of the theory demanded the universe have not just the three spatial dimensions of common experience but six others for a total of nine spatial dimensions, or a total of ten space-time dimensions.
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