Theory Definition and 1000 Threads

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. F

    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...
  2. 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...
  3. 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\{...
  4. 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.
  5. 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...
  6. 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...
  7. 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?
  8. 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...
  9. 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...
  10. 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...
  11. 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...
  12. 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...
  13. C

    Can gas kinetic theory explain heat transfer from gas to a container?

    If one considers the kinetic theory of gases, can a first order estimate of thermal transfer be performed by considering momentum exchange at the container's surface? I understand the basics of explaining and calculating pressure with the kinetic theory of gases, but if we assume energy is...
  14. F

    I Is this a new theory, an enhanced theory or just philosophy?

    I get new notification from new scientist usually about some virus or some weird anthropology theory. Once in a while a physics subject and this time I got this "https://www.newscientist.com/article/mg24132220-100-schrodingers-kittens-new-thought-experiment-breaks-quantum-theory/" Can somebody...
  15. andreia3aral

    Penetration Theory proposed by Higbie (1935)

    Hello, I have some questions related to the Penetration Theory proposed by Higbie (1935). I carried out laboratory experiments in a bubble column of 1.3 m filled with water and saturated with oxygen. Air bubbles were rising and the liquid was stagnant (its motion was just due to the rise of...
  16. J

    MHB Exploring Graph Theory to Identify Network Similarities

    Hi, I am very new in Graph Theory, and am currently trying to figure out it's potential to solve my research problem. Here it goes: I have a large physical network (10000 nodes, around 14,000 edges), it can be represented by an undirected weighted graph. Many portions of the network might have...
  17. J

    A Mean field theory in the Heisenberg model

    I have a problem about Heisenberg model.When applying mean field approximation,why does the average of spin flip terms be zero(<S+>=<S-> = 0 )? Thanks
  18. A

    Quantum Theory Of Semiconductor Quantum Dots + other books on this topic

    Hello, I have two questions into one. First I would like to know what books are considered the best to introduce the theory of quantum dots, so for example with the k.p method, tight-binding, empirical pseudopotentials, and other techniques, analytical derivations, optical properties, band...
  19. T

    I Problem of time in quantum field theory?

    Summary: Does the "problem of time in quantum mechanics" go for Lorentz-invariant quantum mechanical theories like QED? Everything I read about "the problem of time in quantum mechanics," i.e. absolute time in QM clashing with relativity's relative time coordinate and relativity of...
  20. D

    Why doesn't an electron influence itself in Maxwells theory?

    Hello everyone, for quite some time I am struggling with the following question: If we consider the action for a single particle in Classical Electrodynamics $$S[x(\tau),A(x)]=\int - m\ ds - \int d^4x\ A_{\mu}(x)j^{\mu}(x) -\frac{1}{4}\int d^4x F^{\mu\nu}(x)F_{\mu\nu}(x) $$ with $$ds=...
  21. S

    I Prove that a given graph contains a cycle using induction (Graph Theory)

    My Problem: Given a Graph G = (V,E), where the number of vertices is less than or equal to the number of edges, use induction to prove that the graph contains at least one cycle (the graph is not required to be completely connected). My attempt: For my base case, I used only one vertex with one...
  22. F

    Coding theory: Find the right code word

    Error correction can be performed on 1010101 after reception, i need to find the right code <br> i know that the polynomial for the received code is $$x^6+x^4+x2+1$$ when i try to find the error pattern,by long division, $$r(x)/g(x)$$ the remainder is $$z^2+z^2+1$$ xor $$z^2+z+1$$ so the...
  23. Vamsi9955

    B Can String Theory Be Tested and Solve Cosmic Mysteries?

    The fundamental building blocks of the universe is thought of super strings, if proved can solve the mysteries of the universe but if proved than how? And how can it solve the mysteries of dark energy &dark matter and black holes?
  24. DaTario

    A Thermal State in Relativity Theory: Can It Happen?

    Hi All, Considering a set of many many small hard balls which start colliding inside a box. The velocities of these balls being mostly greater than c/2. Is it possible, in this case, to speak of convergence to a thermal state in the same sense of ordinary thermodynamics (i.e., using...
  25. V

    Studying materials for basics physics: exercises, not theory

    Not sure if this thread belongs in this section. I was thinking who could give a better advice than the teachers themselves? Please do move the thread if it does not belong here. Thank you. I am first year non-physics student. I kind of never had any experience with physics. I have about 3...
  26. S

    A Is there any theory that can be modeled in any type of space?

    Is there any theory in physics that can be modeled in any type of space (Hilbert space, Euclidean, Non-Euclidean...etc)? And if yes, could that theory also contain/be compatible with all types of (physical) symmetries?
  27. Replusz

    Other Looking for ideas for new theory

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  28. fluidistic

    A Fermi liquid theory vs Hohenberg-Kohn theorems + Kohn-Sham equations

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  29. J

    A First order logic and set theory: who comes first?

    Goldrei's Propositional and Predicate Calculus states, in page 13: "The countable union of countable sets is countable (...) This result is needed to prove our major result, the completeness theorem in Chapter 5. It depends on a principle called the axiom of choice." In other words: the most...
  30. binbagsss

    Applying LSZ reduction - scattering particles - quantum theory

    Above
  31. J

    I Mistake in Schaum's Group Theory?

    Schaum's Outline of Group Theory, Section 3.6e defines {{\rm{L}}_n}\left( {V,F} \right) as the set of all one to one linear transformations of V, the vector space of dimension n over field F. It then says "{{\rm{L}}_n}\left( {V,F} \right) \subseteq {S_V}, clearly". ({S_V} here means the set...
  32. H

    Is Tonelli's Theorem a Useful Tool for Determining the Existence of Integrals?

    Hi I am sitting with a homework problem which is to show if I can actually integrate a function. with 2D measure of lebesgue. the function is given by ##\frac{x-y}{(x+y)^2} d \lambda^2 (x,y)##. I know that a function ##f## is integrable if ##f \in L^{1}(\mu) \iff \int |f|^{1} d \mu < \infty##...
  33. E

    MHB Isomorphism of logic, arithmetic, and set theory

    Has anybody ever heard of this? I learned about it in a discrete math class in grad school, and I've never heard of it anywhere else !? For example, logical disjunction (OR) and set-theoretic UNION are isomorphic in this sense: 0 OR 0 = 0. {0} UNION {0} = {0}. Similarly, logical AND & set...
  34. N

    A Block Diagonalization - Representation Theory

    How does one go about finding a matrix, U, such that U-1D(g)U produces a block diagonal matrix for all g in G? For example, I am trying to figure out how the matrix (7) on page 4 of this document is obtained.
  35. matqkks

    I What should I say about elementary number theory?

    I need to give an option talk about elementary number theory module. I will discuss how it is study of positive integers particularly the primes and give some cryptography applications. What is a good hook to stipulate in this talk regarding an introduction to elementary number theory?
  36. matqkks

    MHB What should I say about elementary number theory?

    I need to give an option talk about elementary number theory module. I will discuss how it is study of positive integers particularly the primes and give some cryptography applications. What is a good hook to stipulate in this talk regarding an introduction to elementary number theory?
  37. QuasarBoy543298

    Exploring Gauge Symmetry in Classical Field Theory

    hi, I'm currently taking a classical field theory class (electromagnetism in the language of tensors and actions and etc) and we have just encountered the gauge symmetry, that is for the 4 vector potential we can add a gradient of some smooth function and get the same physics (if we take Aμ →...
  38. Calculuser

    I Well-formed Formulas Set in Formal Theory

    There is a statement on page 26 in Elliott Mendelson's book of "Introduction to Mathematical Logic" as shown: What I got from the statement above, which is obvious, I guess, is that in the sequence of \mathcal{B}_1,\mathcal{B}_2,...\mathcal{B}_k there are "SOME" well-formed formulas (wfs)...
  39. Zeynaz

    A theory question about gasses and pressure

    I am struggling to answer questions about gasses. In this case the only way i can think of is, it has to do with the change in atmosphere right? because if we think about the formula P/T=P/T as the temperature decreases the pressure should increase. But in this case we have a smaller pressure...
  40. Rob S

    A Exploring Enrico Fermi's Beta-Decay Theory: A Search for Missing Links

    In 1933 Enrico Fermi published a paper on his theory of beta-decay. He describes it as a contact force, which means he didn't think there was a mediator as there was for the electrodynamic forces. Somewhere along the line, there must have been someone who suggested a mediating particle such as...
  41. S

    A Is M-Theory more fundamental than String Theory?

    M-Theory is a theory of membranes which are the fundamental objects of the theory (M2 and M5 branes), however these objects are considered solitons, solutions of supergravity. How can membranes be "fundamental" if they are solitonic solutions of supergravity? Or am I missing something? And is...
  42. GiacomoPaini

    I forgot the name of a theory in Magnetism

    Can you help me I don't remember a theory The name was something like Theory ok kamp (Kemp? ) Something like this This theory is about magnetism, more precisely about how two sources shield and influence the field) Do you know the name thank Jacky Thank you
  43. J

    Mussardo's Statistical Field Theory

    I have been browsing this book, and it seems a quite interesting one. The traditional Statistical Mechanics is quite traditionally treated (so only average) but then, the linking of Statistical Mechanics with QFT, and the exact solutions in Conformal Field Theory, are quite nice. But I do not...
  44. A. Neumaier

    A Macroscopic systems in the quantum theory book by Asher Peres

    From here: From here: Peres writes on p.11: And on p.58: Note that Peres says that these issues are not yet fully understood! On p.63, Peres writes: On p.424: And on the next page: The footnote quoted by Peres says: And on p.25, where Peres introduces ensembles, he says (like Gibbs...
  45. A

    I De Broglie-Bohm theory and Bohm-like models - how is vacuum treated?

    Hi all, I've been looking at de Broglie-Bohm theory and more recent attempts at Bohm-like models that are relativistic and attempt to reproduce QFT. What I'm not clear on (non-expert) is how the vacuum is modeled in these cases? If we have a set of infinite quantum harmonic oscillators...
  46. chwala

    How to explain collision theory?

    What activities can one use in explaining collision theory to secondary level students?
  47. Z

    Schools What are some good solid state theory masters schools in Europe?

    What are some good solid state/condensed matter theory schools in Europe ?
  48. P

    I Electrostatic in string theory or LQG

    How the repulsion between electrons occurs in String theory and in the loop quantum gravity? The electrons will also create electrostatic fields, or will it be the another mechanism?
  49. S

    I Stewart's Galois Theory doesn't make sense

    I am going through this book, and on page 38, there is LEMMA 3.15 Let K be a subfield of C, f an irreducible polynomial over K, and g, h polynomials over K. If g divides gh, then either f divides h or f divides h. OK, so I have proven that f must divide over g or h - i.e., if f doesn't divide...
  50. P

    I Is the Minkowksi/Einstein Block Universe theory science?

    Hermann Minkowski (Einsteins math instructor and a mathematical physicist himself): The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself...
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