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String theory. In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just ...
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string theory, in particle physics, a theory that attempts to merge quantum mechanics with Albert Einstein’s general theory of relativity. The name string theory comes from the modeling of subatomic particles as tiny one-dimensional “stringlike” entities rather than the more conventional approach in which they are modeled as zero-dimensional point ...
In 1905 Einstein unified space and time (see space-time) with his special theory of relativity, showing that motion through space affects the passage of time. In 1915 Einstein further unified space, time, and gravitation with his general theory of relativity, showing 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. He envisioned one powerful framework that would account for space, time, and all of nature’s forces—something he called a unified theory. 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. Most of Einstein’s contemporaries considered the search for a unified theory to be a hopeless, if not misguided, quest.
In contrast, the primary concern of theoretical physicists from the 1920s 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 1960s the focus was on a different force—the strong force, which binds together the protons and neutrons within atomic nuclei. Gabriele Veneziano, a young theorist working at the European Organization for Nuclear Research (CERN), contributed a key breakthrough in 1968 with his realization that a 200-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. A few years later, three physicists—Leonard Susskind of Stanford University, Holger Nielsen of the Niels Bohr Institute, and Yoichiro Nambu of the University of Chicago—significantly amplified Veneziano’s insight by showing that the mathematics underlying his proposal described the vibrational motion of minuscule filaments of energy that resemble tiny strands of string, inspiring the name string theory. Roughly speaking, the theory suggested that the strong force amounted to strings tethering together particles attached to the strings’ endpoints.
String theory was an intuitively attractive proposal, but by the mid-1970s 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 universe, no matter how elegant the mathematical theory. Nevertheless, a small number of physicists continued to pursue string theory. In 1974 John Schwarz of the California Institute of Technology and Joel Scherk of the École Normale Supérieure and, independently, Tamiaki Yoneya of Hokkaido University came to a radical conclusion. 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.
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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). Rather than merely being a description of the strong force, these physicists contended, string theory required reinterpretation as a critical step toward Einstein’s unified theory.
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. This view was bolstered by string theory’s suffering from its own theoretical problems. For one, some of its equations showed signs 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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String theory is a mathematical framework that aims to unify quantum mechanics and general relativity by modeling subatomic particles as vibrating strings. Learn about its origins, predictions, difficulties, and prospects from Britannica's experts.
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String theory. String theory is perhaps the most high-profile candidate for what physicists call a theory of everything – a single mathematical framework capable of describing the entirety of ...
Learn about the bosonic string, conformal field theory, D-branes, scattering amplitudes, effective actions and compactification from these detailed lecture notes. Download the PDF files or watch the video lectures by other experts on string theory.
Apr 15, 2009 · Learn about the idea that the fundamental particles are tiny strings and that there are extra dimensions of space. Find out how string theory could explain our universe, its challenges and its prospects for testing.
Aug 29, 2019 · String theory is the idea that everything in the universe is made of vibrating strings in multiple dimensions. Learn how string theory emerged, what it promises and why it is controversial.
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