![]() ![]() As the universe expanded and cooled, protons and neutrons formed atomic nuclei, which then combined with electrons to form neutral atoms. Prior to that time, photons and the fundamental building blocks of matter formed a hot, dense soup, constantly interacting with one another. The cosmic microwave background (CMB) radiation is electromagnetic radiation left over from when atoms first formed in the early universe, according to our standard model of cosmology. The three spatial dimensions we are familiar with from daily life are essentially infinite, while compactified dimensions are curled up, and have a finite size that ranges from a few microns (10-6 m) down to the Planck length. In string theory, the term compactification refers to how an extra dimension is made small enough that we cannot perceive it. Open strings and closed strings have different properties, and give rise to different sets of fundamental particles. Unlike open strings, closed strings are not attached to other objects however, a closed string can be broken apart to form an open string. ![]() In string theory, a closed string forms a loop. For example, a string is a 0-brane, a membrane is a 2-brane, and we could live on a 3-brane. The “p” in p-brane stands for the number of dimensions that brane has. In string theory, branes are fundamental objects that exist in a specific number of spatial dimensions. ![]() The peak of the spectrum is higher and at a shorter wavelength as the temperature increases. The spectrum of light emitted by a blackbody is smooth and continuous, and depends on the blackbody’s temperature. If a small volume of space contains enough mass, general relativity predicts that spacetime will become so highly curved that a black hole will form.Ī blackbody is an object that absorbs all incident electromagnetic radiation and re-radiates it after reaching thermal equilibrium. These black holes are thought to have formed when massive stars reached the end of their cycle of evolution and collapsed under the influence of gravity. Black holes have been detected through their gravitational influence on nearby stars and through observations of hot gas from surrounding regions accelerating toward them. AdS/CFT has also been used the other way, with black hole calculations providing insight into complicated particle collisions and condensed matter systems that are difficult to understand with the conventional field theory approach.Ī black hole is a region of space where gravity is so strong that nothing can escape its pull. Although AdS/CFT describes an artificially simple situation-we appear to live in flat space, not Anti-de Sitter space-the mathematical correspondence between the two descriptions of physics has allowed relatively straightforward field theory calculations to shed light on problems associated with the quantum mechanics of black holes. A conformal field theory is the type of field theory used in the Standard Model. Anti-de Sitter space has negative curvature (a two-dimensional plane is curved in a saddle shape rather than flat), and is one of the simplest geometries in which the equations of general relativity can be solved. According to AdS/CFT, a string theory in a region of Anti-de Sitter (AdS) space is equivalent to a conformal field theory (CFT) on the boundary of that region. Finally, the unit summarizes the understanding that string theory brings to fundamental understanding of gravity.Īnti-de Sitter/Conformal Field Theory (AdS/CFT) is a mathematical relationship between two separate descriptions of the same physics. 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. The unit then covers the relationship of string theory to particle physics and introduces the idea of “branes,” related to strings. 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. 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 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. This unit continues our movement from an 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. ![]()
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