What is Quantum theory: Definition and 226 Discussions

In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles and in condensed matter physics to construct models of quasiparticles.
QFT treats particles as excited states (also called quanta) of their underlying quantum fields, which are more fundamental than the particles. Interactions between particles are described by interaction terms in the Lagrangian involving their corresponding quantum fields. Each interaction can be visually represented by Feynman diagrams according to perturbation theory in quantum mechanics.

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  1. J

    What Are the Key References and Concepts in Algebraic Quantum Theory?

    Hi all, what would be your standard Ref. for algebraic approach to quantum theory (algebras, states, folia, etc.)? Haag or there is something better? Beyond the standard things, I'm interested in two aspects of algebraic theory when applied to non-relativistic MECHANICS: i) Classical...
  2. G

    Does Quantum Measurement Depend on the Observer's Consciousness?

    Hi, I'm writing something that touches on issues of quantum measurement (though the main theme is something different), and I want to be sure I'm not saying anything wrong about this very tricky subject. So I'm going to pose some thought-experiments to the physics experts on this forum. The...
  3. R

    Does the Potential Energy Increase or Decrease in Quantum Theory Problem 5?

    "5. Indicate whether the potential energy of the system increases (i) or decreases (d) in each of the following: a) two electrons move away from one another b) an electron is moved toward a proton c) two protons move away from one another d) a Na1+ ion moves toward a Cl1- ion Use...
  4. S

    Relativity vs. Quantum Theory: Which Reigns Supreme in Black Hole Physics?

    what do most physicists today believe in?
  5. B

    An impossible quantum theory of everything?

    No existing quantum mechanics or theory need be thought to sufficiently explain how it is that the subatomic of matter or photons of radiation can be detected and described as possessing their properties of behaviour called wave and spin or as being entangled in composite or singlet states, none...
  6. V

    Does quantum theory make bizarre events possible?

    Michio Kaku appeared on Part 1 of Einstein's Unfinished Symphony with the following interpretation of probabilities in quantum mechanics: Wouldn’t this be impossible, even in principle? Mars at its closest is at a distance of 55.7 million km, and if particles are limited by the speed of...
  7. R

    Unraveling the Mystery of Lasers & Quantum Theory

    How do lasers make use of the quantum theory of the atom. I tried to look it up but I couldn't understand what they were saying. :confused:
  8. T

    Negative Energy in Quantum Theory: A Puzzling Problem

    In the transition from "basic" quantum theory to quantum field theory, both in the derivation of the Gordon-Klein and of the Dirac-equations, there is a big problem with solutions with negative energies. Can anyone explain me why this is being considered a big problem in the first place (it...
  9. V

    Is superstringtheory a quantum theory ?

    A very naive question from a beginner: I only know a very limited amount of string theory, and as far as I know it, it is a quantum theory in the strictest sense, namely that we still have a state in Hilbert space which evolves unitarily ; it is just the "theory to be quantized" that changes...
  10. S

    Problem with this renormalize quantum theory

    Hi. I have a problem with this quantum theory, that is going to make me crazy!: Why we are allowed to renormalize every function after we find the solution. I mean, how we are sure that we have found all the solution exists. Thanks in advance. Somy :smile:
  11. C

    Can quantum theory be explained?

    Can quantum theory be explained? Is it possible to look at quantum theory and say "this calculation works because in terms of physics..."? (even if the physics does not entirely correlate with classical ideas) Eg - is it possible to explain in physics terms why electrons can only exist...
  12. Y

    Please help with these Quantum theory Qs please

    If someone could kindly spare some time and point out how to do these questions, most greatful. 1.After learning about de Broglie's hypothesis that particles of momentum, p, have wave characteristics with wavelength, h/p, a 76.00 kg student has grown concerned about being diffracted when...
  13. G

    Overlapping Quantum Theory & Relativity

    Question from an amateur: I often read that Quantum Theory can explain very accurately the very small but not the big, General Relativity very accurate for the big but not for the very small. How "wide is the band" in which both overlap, being both accurate? i.e how big is the size of...
  14. R

    Unification of Quantum Theory and General Relativity

    Mathematically speaking, the existence of a "dual" vector space, abstractly reflects the relationship between row vectors (1×n) and column vectors (n×1). The construction can also take place for infinite-dimensional spaces and gives rise to important ways of looking at different...
  15. S

    What is the Ontology of Spacetime in QFT?

    As I understand, QFT is formulated on a Minkowski background spacetime. This spacetime is not dynamical. So, what a priori reason is there for formulating QFT on a flat background spacetime? Is it a question of empirical evidence? Or of mathematical utility? Or both, something else? I have...
  16. Antonio Lao

    Can We Accurately Measure and Manipulate the Direction of Atomic Particles?

    Can "direction" be quantized? That is the main question of this thread. At the outset, we need to clarify (hopefully come to some sorts of agreement) the meaning of the word "direction" for two groups of people, (1) the mathematicians and (2) the physicists. I am considering myself...
  17. T

    Can Quantum Field Theory Be Applied to Gravity as It Was to Electromagnetism?

    [SOLVED] Quantum theory of gravity Does anyone know if the same field theory approach that was applied to the electromagnetic force (resulting in QED) has been attempted with gravity. This would entail ignoring GR and trying to develop a quantum field theory of gravity from scratch. Any insights?
  18. marcus

    New Markopolou/Smolin: Quantum Theory from Quantum Gravity

    New Markopolou/Smolin: "Quantum Theory from Quantum Gravity" http://arxiv.org./gr-qc/0311059 "Planck's constant turns out to be a derived quantity"
  19. A

    Consciousness and quantum theory

    I have just finished reading the ghost in the atom by P Davis and was intrigued by John Wheeler's interpretation of quantum theory where the wave function collapses when it enters the conciousness of an observer. I was wondering if since the book was published any progress has been made on this...
  20. M

    Theory of conduction of electrical energy not a quantum theory.

    When Maxwell showed that light was an electromagnetic wave it was necessary to identify some oscillator of atomic proportions to account for these waves. Henri Lorentz , considered that electrons which are normally held in an equilibrium position are capable of vibration when displaced under...
  21. I

    Exploring Issues in Quantum Theory: Advantages and Disadvantages

    I was just wondering what is wrong the quantum theory? What are its drawbacks?
  22. benzun_1999

    Tell me what is quantum theory?

    dear reader, can anyone tell me what is quantum theory? and what is time sciendifically?
  23. benzun_1999

    Understanding Quantum Theory: Exploring the Fundamental Concepts

    dear reader, could anyone say what is quantum theory exactly??[?] [?]
  24. wolram

    Explaining Quantum Theory Math

    i have found this link, the other one returned to german for some reason, http://quantumtheory.de/en.html i can't follow the math so can somone explain please ?
  25. C

    Polarization and Quantum Theory - confused

    Polarization and Quantum Theory -- confused This is what I'm getting hung up on: If you take a piece of vertically polarized glass and place it in front of a piece of horizontally polorized galss then NO light passes through the second glass because the light is at 90 degrees to the...
  26. E

    From quantum theory to stochatic equations

    cna we consider quantum physics as stochastic maths..being the x and p operator treated as if they satisfied stochastic equations..and treatign the Dx and Dp as "noise"..in fact could be the uncertaninty in quantum physics be treated as if it was chaos?-..
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