What is Theory: Definition and 1000 Discussions

A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may either be scientific or other than scientific (or scientific to less extent). Depending on the context, the results might, for example, include generalized explanations of how nature works. The word has its roots in ancient Greek, but in modern use it has taken on several related meanings.
In modern science, the term "theory" refers to scientific theories, a well-confirmed type of explanation of nature, made in a way consistent with scientific method, and fulfilling the criteria required by modern science. Such theories are described in such a way that scientific tests should be able to provide empirical support for it, or empirical contradiction ("falsify") of it. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge, in contrast to more common uses of the word "theory" that imply that something is unproven or speculative (which in formal terms is better characterized by the word hypothesis). Scientific theories are distinguished from hypotheses, which are individual empirically testable conjectures, and from scientific laws, which are descriptive accounts of the way nature behaves under certain conditions.
Theories guide the enterprise of finding facts rather than of reaching goals, and are neutral concerning alternatives among values. A theory can be a body of knowledge, which may or may not be associated with particular explanatory models. To theorize is to develop this body of knowledge.The word theory or "in theory" is sometimes used erroneously by people to explain something which they individually did not experience or test before. In those instances, semantically, it is being substituted for another concept, a hypothesis. Instead of using the word "hypothetically", it is replaced by a phrase: "in theory". In some instances the theory's credibility could be contested by calling it "just a theory" (implying that the idea has not even been tested). Hence, that word "theory" is very often contrasted to "practice" (from Greek praxis, πρᾶξις) a Greek term for doing, which is opposed to theory. A "classical example" of the distinction between "theoretical" and "practical" uses the discipline of medicine: medical theory involves trying to understand the causes and nature of health and sickness, while the practical side of medicine is trying to make people healthy. These two things are related but can be independent, because it is possible to research health and sickness without curing specific patients, and it is possible to cure a patient without knowing how the cure worked.

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  1. A

    I Architecture & Assumptions of General Relativity Theory

    Every theory, whether it is a physical, a psychological or a sociological theory, is defined in terms of an assumed architecture and in terms of a number of assumptions that apply within that architecture. An example from physics is the previously widely accepted dome theory to explain the...
  2. Diracobama2181

    Selection Rules (Time Dependent Perturbation Theory)

    I suppose my question is, since X commutes for H, does this mean that the selection rules are $$<n',l',m'|X|n,l,m>=0$$ unless $$l'=l\pm 1$$ and $$m'=m\pm 1$$, as specified in Shankar?
  3. M

    I Connection between General Relativity & Chaos Theory?

    I am very new to such ideas but was wondering if there is any connection to what I am asking. Taking two events, let's say at opposite ends of the globe. Would even A, only have a potential on event B, if light could travel between these event in the given time frame of these event occurring...
  4. Lynch101

    I Is Free Will a Foundational Assumption in Quantum Theory?

    Summary: Is "free will", as it is usually interpreted, a foundational assumption of QM? I've done a search using the term "free will" and have done a ctrl+f "free will" to go through those threads but I feel that the best way to find definitive clarification on my question is to ask specific...
  5. D

    I Quantum number and group theory

    Hi all, Group theory show us that irreducible representation of SO(3) have dimension 2j+1. So we expect to see state with 2j+1 degeneracy. But does group theory help to understand the principle quantum number n ? And in the case of problems with SO(3) symmetry does it explain its strange link...
  6. cookiemnstr510510

    Frontier Molecular Orbital Theory Problem

    Summary: How do I draw the HOMO of HO-. The problem asks about the HOMO of HO- interacting in different ways with the LUMO of H-Cl. I cannot proceed with the question without figuring out how to draw the HOMO of HO-. I have attached pictures. Hello All, I have been struggling with this problem...
  7. entropy1

    I Is Reality Real? Examining the MWI Theory

    Could MWI signify that there are not necessarily a (near) infinite number of real worlds, but rather that officially we can't tell if, or to what degree, the world we are in is real?
  8. C

    MHB Topology Munkres Chapter 1 exercise 2 e- Set theory

    Dear Everyone I am having some difficulties on exercise 2e from Topology 2nd ed by J. Munkres . Here are the directions: determine which of the following states are true for all sets A, B, C, and D. If a double implication fails, determine whether one or the other one of the possible...
  9. B

    B Is Human Height Ever Exactly Pi Feet?

    Are we ever π feet tall? If so, does that mean that every exact measurement is irrational? If we are not, is there a base unit of the universe?
  10. AdamS

    A New BSM Theory: Investigating Claims

    http://sites.nd.edu/wtan/ take a look at the claims. and two published papers: https://doi.org/10.1016/j.physletb.2019.134921 https://link.aps.org/doi/10.1103/PhysRevD.100.063537
  11. C

    MHB Topology Munkres Chapter 1 exercise 2 b and c- Set theory equivalent statements

    Dear Every one, I am having some difficulties on exercise 2b and 2c from Topology 2nd ed by J. Munkres . Here are the directions: determine which of the following states are true for all sets $A$, $B$, $C$, and $D$. If a double implication fails, determine whether one or the other one of the...
  12. DifferentialGalois

    Studying Value of learning the Theory of Computation and Automata

    This may be a somewhat disorderly, unplanned out question, but nonetheless, I don’t know whether or not there exist any suitable academic advising websites that would be suitable for posting such. Would it be worthwhile investing time into learning theory of computation and automata via Neso...
  13. A. Neumaier

    B How to teach beginners in quantum theory the POVM concept

    [Edit 23.12.2019: A much extended, polished version of my contributions to this thread can be found in my paper Born's rule and measurement (arXiv:1912.09906).] Well, it is simpler than to introduce in full generality Born's rule. Everything can be motivated and introduced nicely for a qubit...
  14. D

    Trick for conserved currents in classical field theory

    First I found the equations of motion for both fields: $$\partial_\mu \partial^\mu \psi = -\frac{\partial V(\psi^* \psi)}{\psi^*}$$ The eq. of motion with the other field is simply found by ##\psi \rightarrow \psi^*## and ##\psi^* \rightarrow \psi## due to the symmetry between the two fields...
  15. D

    Calculating Divergent Amplitude in Phi-4 Theory

    For the diagram In scalar field theory, I have obtained an integral which looks like $$\int_{0}^{\Lambda} \frac{d^4 q}{(2\pi)^4} \frac{i}{q^2 - m^2 + i\varepsilon} \frac{i}{(p - q)^2 - m^2 + i\varepsilon}$$ I am required to calculate this and obtain the divergent amplitude $$i\mathcal{M} =...
  16. C

    A Could this unified theory be correct?

    First they got the higgs mass wrong (according to 2 independent measurements) but later they found a way to get the correct mass (after the mass already had been determined via LHC). https://arxiv.org/abs/hep-th/0610241 https://arxiv.org/abs/1208.1030 This looks too good to be true to me.
  17. G

    I Quantum field theory: an informative approach

    I'm looking for a book that describes the quantum field theory without going deeply in the theory with formulas or complex description of the mathematics under the theory. I know that this theory is really complex and it needs a deep knowledge of quantum physics in order to be understood. But...
  18. PGaccount

    A Understanding Membrane Theory: Main Concepts & Beautiful GI Results

    what are the main concepts of membrane theory? the most beautiful possible giresults. g → 1/g where g is the coupling constant ive read that this transformation changes a dirichlet membrane into fundamental strings. does this have something to do with evaporation of black holes?
  19. V

    B Special Theory of Relativity: Ques on Thought Experiment

    I have a doubt ,the thought experiment performed by einstein he thought that the clock was behind him and he is moving away from clock with speed of light what if he is approaching a clock with speed of light won't time run at very high speed
  20. piyush_1903

    Exploring Frequency & Temperature: Theory & Experiment

    So, my apparatus consists of a basic wooden plank with a nail on one end and a guitar tuner on the other. I plan on using a heating lamp to control the temperature of the apparatus, which is placed inside an insulation box, and use a non-contact infrared thermometer to measure the temperature of...
  21. K

    I Is Relativity a Complete Theory? Investigating Math Formulation

    Is it complete in the sense that there's nothing further to investigate in terms of its mathematical formulation? I mean, in the sense that we don't need to introduce new mathematical tools or review existing ones for the theory.
  22. J

    Algebra Book on how to write proper proofs in Group Theory

    I am trying to learn group theory on my own from Schaum's Outline of Group Theory. I chose this book because there are a lot of exercises with solutions, but I have several problems with it. 1) In many cases the author just makes some handwavey statement and I have to spend hours or days trying...
  23. A

    MHB Treatment of axioms of formal axiomatic theory

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  24. hugo_faurand

    B How a Lagrangian can represent a theory?

    Hello everyone ! I recently read an article about Standard Model's Lagrangian. And it made me remember another article (that I read a long time ago) which said that a theory's Lagrangian "represent" the theory. But How ? Maybe I didn't get the sense of "represent". Also I know that there is...
  25. M

    A Gravitational dressing in quantum field theory

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  26. V

    Solid State Textbook on crystal field theory and degeneracy breaking

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  27. Robin04

    Perturbation theory for solving a second-order ODE

    I have to solve the equation above. I haven't heard about an exact method so I tried to apply perturbation theory. I don't know much about it so I would like to ask for some help. First I put an ##\epsilon## in the coefficient of the non-linear ##\xi^2(t)## term: ##\ddot{\xi}(t)=-b\xi...
  28. R

    I Does science disprove this person's theory?

    I was reading a forum post on a gaming website, and someone posted something I found interesting. Some have argued that it goes against scientific facts, specifically with regard to Quantum Mechanics. I don't know who's right, but I'd love to hear your thought on this? Human Wonder: "Random"...
  29. Guidestone

    Request for historical background on the concept of voltage

    Hi all. I'll get to the point. I've been interested in electricity since I was in college. Concepts such as current and resistance seemed easy to grasp for me but voltage remains a little bit obscure. It's thanks to this forum (specially forum members Jim Hardy r.i.p and SophieCentaur, sorry if...
  30. Hiero

    I Vector valued integrals in the theory of differential forms

    So I heard a k-form is an object (function of k vectors) integrated over a k-dimensional region to yield a number. Well what about integrals like pressure (0-form?)over a surface to yield a vector? Or the integral of gradient (1-form) over a volume to yield a vector? In particular I’m...
  31. forever_physicist

    A Fano Resonance Theory: Notes & Books

    Good evening. I wanted to study the theory about Fano resonances. I tried to read the paper but it doesn't seem very pedagogical to me and I coudn't understand all the details. Are there any notes or any good book where I can find a more precise theoretical description? Thank you
  32. OldBeginnings

    I Isn't the local no-hidden-variable theory inconsistent with standard QM?

    Consider a pair of entangled particles described by a local theory without hidden variables. Because there are no hidden variables, the results of an experiment on one particle of the entangled pair must be perfectly random. Due to locality, the particles also have no way of coordinating the...
  33. Demystifier

    A Is quantum theory a microscopic theory?

    Quantum theory is widely thought to be a theory of the fundamental microscopic constituents of matter. It is supposed to tell us something about how matter behaves at the fundamental microscopic level, from which the classical macroscopic behavior should somehow emerge as an approximation based...
  34. filip97

    A Spin Matrices & Higher Spin Tensors: Find Answers Here

    i can't find on internet why higher spin tensors are totally simetric. know this anyone ? I think that is connected to spin matrices.
  35. bagasme

    Courses Learning the Italian Language in order to Learn Music Theory

    Hello, When I attend art course in high school, on (Western) Music Theory subject, there are a lot of terms in Italian, especially on tempo (largo, adagio, moderato, allegro), dynamics (piano, pianissimo, forte, fortissimo, crescendo, decrescendo), and curves (legato, portato, staccato). Is it...
  36. T

    B In theory, could any element become unstable?

    Problem Statement: NA Relevant Equations: NA So just smashing through some info on particles and I have come across the term "decay" which seems to be used quite ambiguously. Decay is the process where a nucleus expells radiation as a means to redress the imbalance of forces occurring...
  37. matqkks

    I Why certain topics in elementary number theory?

    Why do all elementary number theory courses have the following topics - gcd, linear Diophantine equations, Fundamental Theorem of Arithmetic, factorization, modular arithmetic, Fermat's Little Theorem, Euler's Theorem, primitive roots, quadratic residues and nonlinear Diophantine equations?
  38. matqkks

    MHB Why certain topics in elementary number theory?

    Why do all elementary number theory courses have the following topics - gcd, linear Diophantine equations, Fundamental Theorem of Arithmetic, factorization, modular arithmetic, Fermat's Little Theorem, Euler's Theorem, primitive roots, quadratic residues and nonlinear Diophantine equations?
  39. fresh_42

    I Chameleon Theory: Detecting the Particle with Astronomical Surveys

    I came across the following paper by Christian Arnold, Matteo Leo & Baojiu LiRealistic simulations of galaxy formation in ##f(R)## modified gravity https://www.nature.com/articles/s41550-019-0823-y From what I have read on Wikipedia about the chameleon theory, it only left one question: How...
  40. R

    B Multiple Histories theory by Richard Feynman

    Summary: There is some thing i did not get about Multiple History theory Summary: There is some thing i did not get about Multiple History theory I am reading big answers to the big questions from Stephan Hawking. He has mentioned very little about Multiple History theory. I could not...
  41. J

    I Trying to get the point of some Group Theory Lemmas

    There are two related Lemmas in Schaum's Outline of Group Theory, Chapter 4 that seem excessively convoluted. Either I am missing something or they can be made much simpler and clearer. Lemma 4.2: If H is a subgroup of G and {\rm{X}} \subseteq {\rm{H}} then {\rm{H}} \supseteq \left\{...
  42. M

    A Developments to unify quantum theory with General Relativity?

    Have there been any recent developments in the attempt to unify the standard model of quantum theory with General Relativity? It appears the no progress has been made recently in string theory or loop quantum gravity.
  43. Demystifier

    I What is the current experimental evidence for quantum trajectory theory?

    [Moderator's note: Spin off from previous thread due to topic change.] Recent experimental confirmation of the quantum trajectory theory: https://www.quantamagazine.org/how-quantum-trajectory-theory-lets-physicists-understand-whats-going-on-during-wave-function-collapse-20190703...
  44. J

    A Geometry of Classical Physics in terms of Gauge Theory geometry?

    Reading the interesting book "Groups_and_Manifolds__Lectures_for_Physicists_with_Examples_in_Mathematica", in the introduction it is stated: (...) we have, within our contemporary physical paradigm, a rather simple and universal scheme of interpretation of the Fundamental Interactions and of...
  45. I

    Is gravity a result of composition and temperature? Share your thoughts!

    I have this theory; gravitation is a result of the right composition and amount of elements, combined with the right temperature with a flux of course. This means there are many possibilities to create gravity, and anti-gravity if switched 180 degrees. Am I far out? what's your thoughts?
  46. M

    I Time independent perturbation theory in atom excitation

    Hello! In Griffiths chapter on Time independent perturbation theory, he has a problem (9.20) in which he asks us to calculate the first order contribution to the electron Hamiltonian in an atom if one takes into account the magnetic dipole/electric quadrupole excitations, beside the electric...
  47. A

    A What topics in Quantum Gravity don't require QFT or string theory?

    Full quantization of gravity is a big issue, but that's not what I'm asking here. I'm asking about quantum effects that involve any form of gravitation (Newtonian or GR) but that don't require a full quantization of GR or anything like that. Things like gravitational neutron interference or the...
  48. matqkks

    I What to include in an introduction on number theory?

    I am writing an introduction to a first course in elementary number theory. The topics are linear Diophantine equations, modular arithmetic including FLT and Euler's Generalization, quadratic residues and Non - linear Diophantine equations. How can I write an introduction to this showing linkage...
  49. FourEyedRaven

    Particle Thomson (Modern Particle Physics) & Schwartz (Quantum Field Theory)

    Hi. Are these two books complementary, or do they have too much in common? https://www.amazon.com/dp/1107034264/?tag=pfamazon01-20 www.amazon.com/Quantum-Field-Theory-Standard-Model/dp/1107034736/ My problem is that I still don't quite understand the difference between university courses in...
  50. D

    Other Textbooks for tensors and group theory

    Hello, I am an undergraduate who has taken basic linear algebra and ODE. As for physics, I have taken an online edX quantum mechanics course. I am looking at studying some of the necessary math and physics needed for QFT and particle physics. It looks like I need tensors and group theory...
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