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Works Related Introduction to String Theory

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    First, the author¡¯s summary: String theory (superstring theory) is actually not experimental at present, and the important definition of science is repeatability, experimentation, and digitization.  Then, the statement that it is only pure theory without experimentation may be more biased towards hypothesis, and the origin of string theory is actually inseparable from philosophy and metaphysics.  In fact, in the modern physics world, many theories draw ideological nourishment from philosophy and metaphysics; and this just proves that "rationality" is constantly expanding in the direction of "super-rationality".  The mission of modern physics is to "explore"; while social sciences are more about "imploding (inplore, created-by-somebody, not-nobody, but-I-do-not-konw-who-  he-is. )¡± dig deeper within.  If human beings want to break through the existing and restricted cognition, they must find new ways to understand the world from religious ideas that have been abandoned and rejected, and even from primitive witchcraft worship String theory is a developing theoretical physics.  A branch that combines quantum mechanics and general relativity into quantum gravity.  String theory uses segments of "energy strings" as the most basic unit to explain that all microscopic particles in the universe, such as electrons, protons and quarks, are composed of this one-dimensional "energy lines".  In Chinese literature, it is generally written as "string" or "string".  The particle theory established earlier believes that all matter is composed of zero-dimensional point particles. It is currently a widely accepted physical model and has successfully explained and predicted many physical phenomena and problems. However, this theory  The particle model it was based on encountered some unexplainable problems.  In comparison, string theory is based on a wave model and therefore avoids the problems encountered by the former theory.  The deeper string theory theory not only describes string-like objects, but also includes point-like and film-like objects, higher-dimensional spaces, and even parallel universes.  It is worth noting that string theory has not yet been able to make accurate predictions that can be experimentally verified. This will be explained below.  The prototype of string theory was discovered by Gabriele Veneziano in 1968.  It is said that he was originally looking for a mathematical function that could describe the strong force in the nucleus, and then found the 200-year-old beta function (Euler) in an old mathematics book. This function could describe what he wanted.  The strong force needs to be solved.  This was not the case. According to Venechino himself, this function was the result of years of hard work, and rumors of "accidental discovery" and "discovery from mathematics books" made him very unhappy.  Soon after, Leonard Su Shikan discovered that this function can be understood as a small elastic "line segment" that can twist and shake like a rubber band, which later developed into "string theory".  Although string theory was initially intended to solve the mode of action of the strong force, subsequent research has discovered all particles (including antiparticles), such as quarks and anti-quarks, electrons and positrons (electrons, positrons), and anti-neutral particles.  Microns, etc., as well as the four basic force particles (gluons, intermediate bosons, photons, gravitons), can be expressed in a similar way as a small section of energy string that is constantly vibrating, and the various particles are different from each other.  The only difference is the length, vibration parameters and shape of the string.  The earliest string theory is called Bose string theory, and Nanbu Yoichiro gave the earliest action quantity, [source request] However, this action quantity is difficult to quantize within the framework of field theory.  Afterwards, Alexander Polyakov gave an equivalent action, whose geometric meaning is to treat the space-time coordinates as a scalar field on the world plane, and satisfy the general coordinate transformation rules of general relativity on the world plane.  In addition, if this action quantity is required to be invariant under the change of Weyl, then it will naturally require that the world surface is a two-dimensional surface.  Bose string theory is the simplest string theory model. Its most important physical image is that physical particles are not simple point particles, but excited states generated by the vibration of strings.  Obviously it has great shortcomings. One is that it only briefly describes the scalar boson and does not introduce fermions into the framework; the other is that it does not include the gauge symmetry in general quantum field theory; the third is that when studying its mass  When observing the spectrum, it was discovered that its vacuum state is a group of unstable tachyons with a mass square less than zero.  All these problems are well explained after being extended to superstring theory.  Superstring Theory In addition, the term "string theory" refers to the original 26-dimensional Bose string theory and superstring theory that adds supersymmetry.  In the recent physics world, "string theory" generally refers to "superstring theory". To facilitate the distinction, the earlier "Bose string theory" is called by its full name.  In the 1990s, inspired by string duality, Edward Witton conjectured the existence of an 11-dimensional M theory. He and other scholars found strong evidence showing five different versions of 10-dimensional superstring theory and 11-dimensional supergravity theory.  In fact, it should be six different limits of M theory.  These discoveries led to the second innovation of superstring theory.  String Theory and Grand Unification String theory attracts so much attention, mostly because it has the potential to become a grand unified theory.  String theory may also be one of the solutions to quantum gravity.  In addition to gravity, it naturally and successfully describes various forces, including electromagnetic forces and those that exist in nature.??Other various forces.  Superstring theory also includes fermions, one of the fundamental particles that make up matter.  It is still unknown whether string theory can successfully explain the universe composed of all the forces and matter currently known in the physics world.  So far, researchers have not been able to find a string theory model whose low-energy limit is the Standard Model.  Extra dimension Extra dimension is a concept proposed relative to "four-dimensional space-time". It generally refers to other dimensions expanded by the theory on the basis of four-dimensional space-time.  Einstein proposed that the universe is a "four-dimensional space-time" composed of space and time.  In 1926, German mathematical physicist Theodore Kaluza added another spatial dimension to the four-dimensional space-time, that is, added a fifth dimension, and rewritten Einstein's equations of relativity. The rewritten equation could  The two known fundamental forces, electromagnetic force and gravity, are naturally unified in the same equation.  Up to this point, the additional dimensions existing in the theory are collectively referred to as "extra dimensions."  In superstring theory, it is one-dimensional time and ten-dimensional space or nine-dimensional space.  D-Brane Since the space-time dimension of superstring theory is 10, it is natural to think that there are 6 extra dimensions that need to be compacted.  When compactifying closed strings, the so-called T-duality can be found; while compactifying open strings, it can be found that the endpoints of open strings stay on these hypersurfaces and satisfy the Dirichlet boundary conditions.  So these metasurfaces are generally called "D-branes".  Researchers call the dynamics of D-branes "matrix theory" (M theory), which is one of the sources of the word "M".  Before it is experimentally confirmed, string theory belongs to the category of philosophy and cannot be completely regarded as physics.  One reason for the lack of experimental proof is that no one yet understands string theory well enough to make correct predictions, and another is that current high-speed particle accelerators are not powerful enough.  Scientists are using a new generation of high-speed particle accelerators currently and in preparation to try to find the superparticles predicted by the main supersymmetry theory in superstring theory.  But even if superparticles are really found, this still cannot be regarded as strong evidence that can confirm string theory, because it only finds a particle that originally exists in this universe, but it at least means that the research direction is not wrong.  While string theory has historically been a branch of physics, some argue that string theory's current non-experimental status means it should (strictly speaking) be classified more as a mathematical framework than a science  .  A valid theory must be empirically proven through experiments and observations.  Many physicists advocate confirming string theory through some experimental methods.  [1] Some scientists hope to use the Large Hadron Collider of the European Organization for Nuclear Research (CERN, Conseil European Pour Recherches Nucleaires) to obtain corresponding experimental data - although many people believe that any theory about quantum gravity requires higher orders of magnitude of energy  Let¡¯s investigate directly.  [2] In addition, although string theory is generally recognized [original research?  ], but it has a lot of equally possible solutions.  [3] Therefore, some scientists argue that string theory may not be falsifiable and has no predictive power.  [4][5][6][7] Since the predictions made by any string theory that are different from other theories have not been confirmed experimentally, the correctness of the theory has yet to be verified.  In order to see the nature of strings in particles, the energy levels required are much higher than what is currently possible in experiments.  String theory has many features of mathematical interest and naturally contains most properties of the Standard Model, such as non-Abelian groups and chiral fermions.  Because string theory may be difficult to prove experimentally in the foreseeable future, some scientists[8] ask whether string theory should even be called a scientific theory.  It cannot yet be falsified in Popper's philosophical implications.  But it also implies that string theory is seen more as a framework for building models.  In the same form, quantum field theory is a framework.  [9] The ideas of string theory have brought a huge impact on physics that is suggested to go beyond the Standard Model.  For example, although supersymmetry is an important part of string theory, scientists have also studied supersymmetric models that have no obvious connection with string theory.  Therefore, if supersymmetry were detected at the LHC, it would not be seen as a direct proof of string theory.  However, if supersymmetry is not detected, its absence will not prove string theory wrong, since there is a vacuum in string theory where supersymmetry can only be seen at much higher energies.  Conversely, if the Sun's gravity is not observed to deflect light by the predicted angle during a solar eclipse, Einstein's general theory of relativity will be proven wrong.  (General relativity has of course been proven correct.) At a more mathematical level, another problem is that, like much quantum field theory, large parts of string theory are still perturbatively formulated (i.e.  is an approximation to continuity rather than an exact solution).  While there have been considerable advances in non-perturbative techniques¡ªincluding conjecturing a complete definition of spacetime that satisfies certain asymptotic properties¡ªa non-perturbative, adequate theoretical definition.It is certainly lacking.  A central problem with applications of string theory in physics is that the context in which string theory is best understood preserves most of the underlying theory of supersymmetry derived from "time-invariant spacetime": currently, string theory cannot handle it well  Issues of time dependence and cosmological background.  The two points mentioned earlier involve a more profound problem: in string theory's current conception, it may not be truly fundamental due to its dependence on background¡ªit describes perturbative expansion with respect to a fixed space-time background.  Some regard background independence as a fundamental requirement for a quantum theory of gravity; this is especially true since general relativity is already background independent.
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