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.

View More On Wikipedia.org
  1. S

    A Does the theory of information have anything to offer for physics?

    Is there any use for this concept in classical branches of physics? Can it be of any help for a physicist in resolving problems (or, at least, in resolving them more efficiently when compared with traditional methods)? The word «classical» means exactly that, i. e. mechanics, hydrodynamics...
  2. chwala

    A Computing the Minimal polynomial - Ring Theory

    Am going through this notes...kindly let me know if there is a mistake on highlighted part. I think it ought to be; ##α^2=5+2\sqrt{6}##
  3. S

    I Coupled mode theory - question about an equation

    edit: Hello everyone! When I posted the question, latex equations that were visible in "preview" do not seem here. So, I upload a pdf version of the question. We consider zero free charges and currents: ρ=J=0 $$ \mathbf{\nabla} \times \mathbf{E} = -\frac{\partial \mathbf{B}}{\partial t}...
  4. G

    I Theory Without Spacelike Separations: Can It Exist?

    From what I understand only the past and future timelike separated events ever matter for me as an observer. Does that mean there could be a theory where a thing like spacelike separated events does not exist? I mean they never matter for any prediction anyway?
  5. Muu9

    Studying What math do I need to understand gauge theory?

    Note that I'm not interested in using it for physics, but instead for deep learning.
  6. Green dwarf

    I Predetermination in quantum theory and information theory

    My understanding of quantum theory and information theory is that, given complete information on the state of the universe at present, it is possible to predict its state at all times in the future and past. 3 questions: 1: is this true? 2: how are quantum-probabilistic outcomes accounted for...
  7. M

    A The double copy of (2,0) theory

    (2,0) theory is a six-dimensional field theory that has achieved a mild degree of notoriety. "(2,0)" is a notation for degree of supersymmetry, in dimensions where supersymmetries can have a "chirality" (left-handedness vs right-handedness); in this case, it means that this is a field theory...
  8. R

    Looking for basic theory on mixing of gases

    Hi, In my situation, I am dealing with two ideal gases traveling down a pipe at the same bulk velocities. I am only considering a 1-D treatment at the moment and I would like to find out at which point the two gases should be considered a well mixed, homogeneous mixture. Would anyone know...
  9. lindberg

    I Unruh, Haag et al.: No Room for Particles in Quantum Field Theory?

    In a paper by Bain (2011), particles are left with little ontological value because of the Reeh-Schlieder theorem, the Unruh effect and Haag's theorem. The author claims (and here I am copying his conclusion): First, the existence of local number operators requires the absolute temporal metric...
  10. warhammer

    I Query on Electromagnetic Theory (Dielectric Boundary Conditions)

    The given question from Electromagnetic Theory (which is based on Dielectric Boundary Conditions) is as follows: Interface b/w two dielectric medium has a surface charge density (suppose xyz C / (m ^ 2) ). Using boundary condition find field in 1 (relative permittivity =xyz) if field in 2...
  11. BadgerBadger92

    What Are Your Favorite Theories?

    I was just wondering what all of your guys favorite theory! For me it is a tie between special relativity and general relativity. I mainly want to know so I can look up any theories posted and learn about them. So what’s your favorite theory?
  12. A

    Book recommendations (abstract algebra and number theory)

    Hi, For an engineer who graduated and finished typical Cal A,B,C + Linear Algebra + ODE, what book do you recommend to start reading to be a transition to advanced pure math subjects like abstract algebra and number theory? I did deep google search & concluded that that book supposed to include...
  13. StanislavD

    A BCS theory of superconductivity and eternal supercurrents?

    In the BCS theory the Cooper pair density depends on temperature, meaning that pairs can be created/annihilated by temperature variations. Obviously, momenta of annihilated pairs dissipate on the atom lattice, so an initial supercurrent dissipates. On the other hand, in some experiments a...
  14. fresh_42

    Insights Évariste Galois and His Theory

    Galois died in a duel at the age of twenty. Yet, he gave us what we now call Galois theory. It decides all three ancient classical problems, squaring the circle, doubling the cube, and partitioning angles into three equal parts, all with compass and ruler alone. Galois theory also tells us that...
  15. F

    B The Many TOE's Theory: Examining the Possibilities

    Physicists search for explanations and a theory of everything, but how do we know that the 'everything' is any particular way? What if there is no ONE theory of everything. What if there is an infinite number of TOE's that can be shown to exist? How would we choose among them? For example what...
  16. malawi_glenn

    Ideas for group theory for high school math project

    Hi As high school teacher, I sometimes have those extremely talanted and self driven pupils. In their final year, they are required to make a science or math project, roughly one month full-time studies, approx 15-20 pages report. This academic year, one of my students have learned some group...
  17. P

    Is this computability theory proof correct?

    I am proposing a new theorem of computability theory: THEOREM 1: There are numbers k and s and a program A(n,m) satisfying the following conditions. 1. If A(n,m)↓, then C_n(m)↑. 2. For all n, C_k(n) = A(n,n) and C_s(n) = C_k(s). 3. A(k,s)↓ and for all n, A(s,n)↑. Here C_n(∙) is a program with...
  18. G

    I Chaos theory has no fine edge -- does it fluctuate?

    Does nature err slightly beyond order into chaos in the context of chaos theory? And I'd like to proffer the idea that the point at which order tips into chaos actually fluctuates. Nothing in nature is absolutely perfect therefore do natural errors at the point in which order tips into chaos...
  19. joneall

    I Krauss's interpretation of gauge theory

    Lawrence Krauss, "The greatest story ever told ... so far", pp. 108-109. "Gauge symmetry in electromagnetism says that I can actually change my definition of what a positive charge is locally at each point of space without changing the fundamental laws associated with electric charge, as long...
  20. zaki belh

    A Question about kinetic theory and hydrodynamics (in plasmas)

    It is usual, in plasma physics, to combine the kinetic description for electron fluid and the hydrodynamic description for ion fluid, when studying the plasma properties or the dynamics of the electrostatic waves. I am wondering what are the physical meaning and limits of such an approach. Thanks.
  21. ohwilleke

    I Can Core Theory Be Derived From Nine Lines?

    Christoph Schiller, "From maximum force to physics in 9 lines -- and implications for quantum gravity" arXiv:2208.01038 (July 31, 2022). This paper asserts that nine propositions can be used to derive the Standard Model and GR and can point the way to quantum gravity, although he cheats a bit...
  22. M

    Meaning of time in the multiverse theory

    This statement got me thinking, would it be possible for 1 universe (out of the infinite collection of universes) to be stationary infinitely alternating between state A & B, or using the dice analogy throwing a 1 and a 2 over and over effectively making this universe appear looped in time...
  23. D

    I Does Heisenberg Have Ontological Commitments to Quantum Theory?

    Heisenberg is regarded as a major figure of the Copenhagen interpretation. In a certain degree, he is influenced by Logical positivism. Despite of that, has he any ontological commitments regarding the Quantum theory? Or, he considers the Quantum theory merely as calculation procedure for...
  24. LCSphysicist

    I Current theory of composite quarks and leptons

    "M. Shupe [Phys. Lett. 86B, 87 (1979)] has proposed that all quarks and leptons are composed of two even more elementary constituents:" (Griffiths) I am redoing the book of elementary particles from Griffths, and this exercise has showed really interesting to me. How is the currently status of...
  25. F

    Courses How useful is control theory in computational neurosciences?

    Hello, I have the opportunity of choosing an elective course on control theory before embarking for my master's program in computational neurosciences and I am weighing the pros and cons. I am looking for advice from PF members who specialized in this field. Since I have chosen enough courses...
  26. bigmike94

    Balancing Learning Theory & Problem Solving: A Student's Guide

    From experience how would you balance time on learning theory and problem solving? Maybe learn the theory enough that if you got stuck on a difficult problem you would be able to understand the solution without scratching your head too much? Im using University physics by young and freedman...
  27. H

    Proving that an Integer lies between x and y using Set Theory

    ## y-x \gt 1 \implies y \gt 1+x## Consider the set ##S## which is bounded by an integer ##m##, ## S= \{x+n : n\in N and x+n \lt m\}##. Let's say ##Max {S} = x+n_0##, then we have $$ x+n_0 \leq m \leq x+(n_0 +1)$$ We have, $$ x +n_0 \leq m \leq (x+1) +n_0 \lt y+ n_0 $$ Thus, ##x+n_0 \leq m \lt...
  28. Q

    I Is the CPT-Symmetric Universe Theory the Key to Solving the Antimatter Mystery?

    https://arxiv.org/abs/1803.08928. This is a simple and elegant theory, but there are some things I don’t understand. Why would the anti-universe exist before the Big Bang? From the viewpoint of the anti-universe, isn’t our universe time-reversed? Also, unless the total charge of...
  29. Delta2

    I Is a Unified Field Theory the Key to Understanding the Universe?

    Is there any approach in any books out there, where we consider that in universe exists only one field, let it be called the Unified Field (UF), in which all of the known fields (gravitational, EM field, quark field, gluon field, lepton field, Higgs Field, e.t.c.) are just components (pretty...
  30. J

    Why do scientists call evolution a "theory"?

    Why do scientists refer to evolution as a theory which leads to the argument that evolution is "just a theory"? Why don't they use a less confusing word?
  31. M

    For ## n\geq 1 ##, use congruence theory to establish....

    Proof: Let ## n\geq 1 ## be a natural number. Note that ## 5^{2}\equiv 4\pmod 7\implies (5^{2})^{n}\equiv 4^{n}\pmod {7} ##. Now observe that \begin{align*} (3\cdot 2^{5n-2})&\equiv (3\cdot 2^{3}\cdot 2^{5n-5})\pmod {7}\\ &\equiv [3\cdot 2^{3}\cdot (2^{5})^{n-1}]\pmod {7}\\ &\equiv [24\cdot...
  32. M

    For ## n\geq 1 ##, use congruence theory to establish....

    Proof: Let ## n\geq 1 ## be a natural number. Then \begin{align*} 6^{n+2}+7^{2n+1}&\equiv (6^{n}\cdot 6^{2}+(7^{2})^{n}\cdot 7)\pmod {43}\\ &\equiv (6^{n}\cdot 36+49^{n}\cdot 7)\pmod {43}\\ &\equiv (6^{n}\cdot 36+6^{n}\cdot 7)\pmod {43}\\ &\equiv (6^{n}\cdot 43)\pmod {43}\\ &\equiv 0\pmod {43}...
  33. M

    For ## n\geq 1 ##, use congruence theory to establish....

    Proof: Let ## n\geq 1 ## be a natural number. Then \begin{align*} 2^{5n+1}+5^{n+2}&\equiv (2^{5n}\cdot 2+5^{n}\cdot 5^{2})\pmod {27}\\ &\equiv [(2^{5})^{n}\cdot 2+5^{n}\cdot 25]\pmod {27}\\ &\equiv (32^{n}\cdot 2+5^{n}\cdot 25)\pmod {27}\\ &\equiv (5^{n}\cdot 2+5^{n}\cdot 25)\pmod {27}\\...
  34. M

    For ## n\geq 1 ##, use congruence theory to establish?

    Proof Let ## n\geq 1 ## be a natural number. Then \begin{align*} 3^{n+2}+4^{2n+1}&\equiv 3^{n}\cdot 3^{2}+(4^{2})^{n}\cdot 4\pmod {13}\\ &\equiv (3^{n}\cdot 9+16^{n}\cdot 4)\pmod {13}\\ &\equiv (3^{n}\cdot 9+3^{n}\cdot 4)\pmod {13}\\ &\equiv (3^{n}\cdot 13)\pmod {13}\\ &\equiv 0\pmod {13}...
  35. gremory

    A S-Matrix in Quantum Field Theory

    Hello, i need help with the S-matrix. From what i understand, with the S-matrix i would be able to compute the scattering amplitude of some processes, is that correct? If so, how would i be able to do that if i have some field ##\phi(x,t)## in hands? Is that possible?
  36. MathematicalPhysicist

    Suggestions for future reading — Supergravity by Freedman or A First Course in String Theory by Zweibach?

    What do you recommend to read first, Supergravity by Freedman or A First Course in String Theory by Zweibach? For future consideration.
  37. alan123hk

    Roughly how many people in this world actually know about string theory?

    Roughly how many people in this world actually know about string theory? I'm guessing no more than a few hundred because the math of string theory is so esoteric.
  38. marcosdb

    I Jefimenko's Theory of Gravitation: Continued Discussion

    This is a continuation of this post, which has been closed to replies: I am also really curious to better understand Jefimenko's theory of gravitation; I have the book, which apparently is no longer available on amazon, and I updated the wikipedia page to include his generalized gravitation...
  39. K

    Classical Looking for a physics textbook which shows how to develop theory

    I was wondering if there is any such textbook which shows how a real physicist actually goes about developing models and or theories to explain experimental observations. I want to see how it is done in practice. Is there such a book? At a level that an undergraduate can understand. It is great...
  40. K

    I String theory calculation of Extremal black hole entropy problem

    one of the claimed successes of string theory is its ability to derive the correct Hawking-Bekenstein equations to calculate the quantum entropy of a black hole without any free paramenters, specifically Extremal black hole entropy using supersymmetry and maximal charge. I was wondering if...
  41. chwala

    I Prove the given properties - Ring Theory

    Ok for ##1##, we also have, ##a⋅0=a⋅(0+0)=a⋅0 + a⋅0 ## We know that ##a⋅0=0 ## by additive cancellation. For ##2.11##, Number ##2##; We first show and prove that ##-b=-1⋅b## adding ##b## on both sides, ##-b+b=0## for the lhs ##-1⋅b +1⋅b=b(-1+1)=b(0)=0## for the rhs therefore...
  42. Y

    Help Understand Bearing Theory

    Hi, Sorry if this is a stupid question, but I haven't taken fluid mechanics classes and mechanical engineering ones. I understand that sometimes bearings get "dry" and you can regrease them. However I did some searching online and found that it's possible to over grease a bearing which can...
  43. K

    I More doubts in perturbation theory

    Townsend, quantum mechanics " In our earlier derivation we assumed that each unperturbed eigenstate ##\left|\varphi_{n}^{(0)}\right\rangle## turns smoothly into the exact eigenstate ##\left|\psi_{n}\right\rangle## as we turn on the perturbing Hamiltonian. However, if there are ##N## states ##...
  44. chwala

    I Understanding zero divisors & ##\mathbb{Z_m}## in Ring Theory

    Homework Statement:: See attached Relevant Equations:: Ring Theory Trying to go through my undergraduate notes on Ring Theory ( in appreciation to my Professor who opened me up to the beautiful World of Math)...anyways see attached... I need some clarity on the zero divisor. I am aware that...
  45. K

    I Doubt in understanding degenerate perturbation theory

    McIntyre, quantum mechanics,pg360 Suppose states ##\left|2^{(0)}\right\rangle## and ##\left|3^{(0)}\right\rangle## are degenerate eigenstates of unperturbed Hamiltonian ##H## Author writes: "The first-order perturbation equation we want to solve is ##...
  46. T

    MHB Recreational Number Theory, Unsolved Problem

    Find a perfect power k^m > 1 where k, m, k^m do not contain 2 in their decimal digits, nor do share any decimal digit, no matter if k^m might possibly be expressed in more than one way for some value, e.g. 8^2 = 4^3. I do not know if such an integer exists at all, or how many and how large they...
  47. A

    I Discussing Information Theory with non-scientists

    Do you have an opinion about my summary above? Do you understand the relation between irreversible logic and irreversible process? According to Landauer, logical irreversibility implies physical irreversibility. This is still a topic of debate it seems to me. Is the debate also about what logic...
  48. strangerep

    A Meaning of "symbol" in algebraic field theory?

    I'm probably inadequately equipped to understand this paper by Bucholtz, Longo and Rehren on "Causal Lie products of free fields and the emergence of quantum field theory", but I decided to give it a try. Alas, I got stuck in the 1st para of sect 2 where it says: Although I've seen the term...
  49. yucheng

    Studying Balancing Theory and Applications?

    Merely studying formalism and theory in quantum mechanics is too dry and demotivating for me. I would appreciate being able to do more practical calculations and realistic applications instead of canned problems. Is there a way to balance this theory and applications? I have thought of doing...
  50. Tan Tixuan

    I Classical field in quantum field theory?

    In quantum field theory, we have the following expansion on a scalar field (I follow the convention of Schwarz's book) $$\phi(\vec{x},t)=\int d^3 p \frac{a_p exp(-ip_\mu x^\mu)+a_p^{\dagger}exp(ip_\mu x^\mu)}{(2\pi)^3 \sqrt{2\omega_p}} \quad p^{\mu}=(\omega_p,\vec{p})$$ With commutation relation...
Back
Top