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
Recent contents Top users
  1. MathematicalPhysicist

    A A question regarding Schwinger's Sources' Theory

    I was under the impression (false one appraently (I read Lubos Motl answer in stackexchange)) that Schwinger's theory which is covered in his three volumes called "Particles, Sources and Fields.", is really only a different interprataion to QFT, but the end results are the same. Now I read the...
  2. mertcan

    I M/G/C Queue Theory: Proving Results & Finding Sources

    hi, initially when I saw these statements , I got really amazed, and now I endeavor to find the proofs of these statements, bu I would like assure you of the fact that there are very very very few sources which evaluate M/G/K or M/G/infinite queue, mostly sources prefer to handle the subject of...
  3. O

    3 Phase Systems Theory and Procedure -- Determining Average Power

    Homework Statement Consider the 3 following Scenarios: 1. 2. rms value of line voltage is 208 V Three equal impedances, 60 +j30 W each, are delta-connected to a 230-V rms, three-phase circuit. Another three equal impedances, 40 +j10 W are wye-connected across the same circuit at the same...
  4. P

    Time-Dependent Perturbation Theory

    Note this isn't actually a homework problem, I am working through my textbook making sure I understand the derivation of certain equations and have become stuck on one part of a derivation. 1. Homework Statement I am working through my text (Quantum Mechanics 2nd Edition by B.H Bransden & C.J...
  5. PsychonautQQ

    Some true or false Field extension theory questions

    Homework Statement Let S= {e^2*i*pi/n for all n in the natural numbers} and let F=Q Is F:Q 1) algebraic? 2) finite? 3) simple? 4)separable? Homework EquationsThe Attempt at a Solution 1) Every element in S is a root of x^n-1 and every element of a in Q is a root of x-a, and thus I think...
  6. PsychonautQQ

    Galois Theory questions

    Homework Statement Let K be the splitting field in C of the polynomial g(X) = x^3 + 4 over Q a) determine the degree of the extension K:Q, b) determine the structure of the galois group Gal(K:Q) c) Using the Galois correspondence, determine all subfields of K d) Let r be an element of K and let...
  7. PsychonautQQ

    Understanding fixed fields (Galois Theory)

    Homework Statement Let's look at Q(a,c):Q where a is the third real root of 2 and c is a primitive cube root of unity. Then this extension is Galois and it's Galois group is isomorphic to ##D_3=S_3##. The proper subgroups of the Galois group are thus <(12)>,<(23)>,<(23)>,<(123)>. Let (12)...
  8. A

    A QFT as pilot-wave theory - one more time....

    I've recently read (portions of) the paper "QFT as pilot-wave theory of particle creation and destruction," available here: http://xxx.lanl.gov/pdf/0904.2287v5 This paper has been mentioned in a number of other threads, but I have a different question (not as an expert, unfortunately). The...
  9. LarryS

    I Classical vs. Quantum Defintion of Energy in Field Theory

    Classical fields are usually constructed using a collection of classical harmonic oscillators, e.g. masses connected to springs. The energy of a classical harmonic oscillator is proportional to the amplitude squared. QFT uses quantized versions of those same classical fields. But, in the...
  10. Run like hell

    Quantum Weinberg: The quantum theory of fields 2005 edition vs 1995

    Hi all, I'm about to buy the first volume of the series by Weinberg, but I'm a little worried about the edition, see I have a lot of requisites for a book before buying it. I've seen in the library the old hardcover edition and it looks fine for me: it's not written too small and the book even...
  11. Kevin McHugh

    I Unraveling the Mysteries of Leptons in String Theory

    Could someone explain or point me in the right direction on how string theory explains the leptons? TIA, Kevin
  12. wolram

    B Theory that challenges Einstein's physics could soon be put to rest

    Surly the variable speed of light is a dead dog, this article says it is not, and the theory can be tested But some researchers have suggested that the speed of light could have been much higher in this early universe. Now, one of this theory's originators, Professor João Magueijo from Imperial...
  13. Julie1703

    B The dimension of time in String Theory

    I was doing some reading on String Theory...I'm not a scientist, but i enjoy it (so forgive me if my question is stupid) and i was wondering: Being time a dimension, could it be the dimension the strings exist in? And interaction between all particles and all forces determine how they vibrate...
  14. S

    A Free theory time-ordered correlation function with two internal fields

    Wick's theorem allows one to write a free theory time-ordered ##n##-point correlation function as a product of free theory time-ordered ##2##-point correlation function. The procedure involves the pairwise Wick contraction of fields such that external fields are not paired up each...
  15. T

    A Why General Relativity is non-renormalizable quantum theory?

    Hello I have not understand this.
  16. S

    A Free theory time-ordered correlation functions with derivatives of fields

    Consider the following time-ordered correlation function: $$\langle 0 | T \{ \phi(x_{1}) \phi(x_{2}) \phi(x) \partial^{\mu}\phi(x) \partial_{\mu}\phi(x) \phi(y) \partial^{\nu}\phi(y) \partial_{\nu}\phi(y) \} | 0 \rangle.$$ The derivatives can be taken out the correlation function to give...
  17. M

    B Learn Relativity Theory: Math Education Needed?

    What knowledge based are needed in relativity theory, not general public science education level, but true and mathematically. I have calculus and linear algebra education in university, Chinese engineering degree, quite rigorous in math education. Can I actually pick up relativity theory myself...
  18. James - STARS

    A The Inner Space of Garrett Lisi's E8 Theory

    Hi :) Does the 'inner space' and 'inner particle physics' which Mr. Lisi refers to in his TED Talk at Maui in 2013 refer to the 8 dimensional maximal tori within E8 and how they function? TED Talk at Maui in 2013 (video): Thanks.
  19. James - STARS

    A Antiparticles in Garrett Lisi's E8 Theory

    Greetings all :) I would like to know please how antiparticles fit into Garrett Lisi's E8 Theory. Thanks!
  20. J

    String Theory and Theoretical vs. Mathematical Physics

    Hello, I have a question about the the difference between mathematical physics and theoretical physics in general and about the difference between the MSc Theoretical and Mathematical Physics courses at Edinburgh in particular. I am planning to apply, however I am not sure which of the two...
  21. ltkach2015

    A Theory of Surfaces and Theory of Curves Relationship

    Hello I am interested in the Frenet-Serret Formulas (theory of curves?) relationship to theory of surfaces. 1) Can one arrive to the Frenet-Serret Formulas starting from the theory of surfaces? Any advice on where to begin? 2) For a surface that contain a space curve: if the unit tangent...
  22. 1

    Where do physics and game theory meet?

    This is going to sound really strange, but I don't want to have this question inside of me and never ask it. I love business/economics/game theory. However, the subject I've studied the most in my life at this point is physics. The question of what I want to write about for my PhD thesis is...
  23. V

    A doubt from Kinetic Theory of Gases

    I have read Average translation kinetic energy is 1/2RT per degree of freedom and Average translation kinetic energy for an ideal gases is 3/2RT.How? Does it imply f=3 for all ideal gases?
  24. S

    Newton's gravitational theory

    Homework Statement I wanted a proof that an object's center of gravity is the same as the center of mass by breaking the object into tiny pieces and then integrating over them. Homework Equations Well, the gravitational equation g=Gm1m2/r^2 The Attempt at a Solution I tried using some calc...
  25. T

    (2/3) as constant factor In Kinetic theory of gases

    Hi I'm in high school but what I'm going to ask you is probably being teached in college. General formula: p=(2/3)*(N/V)*Ek p- pressure N- amount of molecules V- volume of the container Ek - AVERAGE kinetic energy I've been told by my physics teacher, that 2/3 constant factor in kinetic theory...
  26. S

    A Factors in the theory of a complex scalar field

    The theory of a complex scalar field ##\chi## is given by $$\mathcal{L}=\partial_{\mu}\chi^{*}\partial^{\mu}\chi-m_{\chi}^{2}\chi^{*}\chi.$$ Why is it not common to include a factor of ##\frac{1}{2}## in front of the complex ##\chi## kinetic term? What is the effect on the propagator of...
  27. S

    A Correlation functions in an interacting theory

    Given the theory $$\mathcal{L}=\frac{1}{2}(\partial_{\mu}\phi)^{2}-\frac{1}{2}m_{\phi}^{2}\phi^{2}+\partial_{\mu}\chi^{*}\partial^{\mu}\chi-m_{\chi}^{2}\chi^{*}\chi+\mathcal{L}_{\text{int}},\qquad \mathcal{L}_{\text{int}}=-g\phi\chi^{*}\chi,$$ the time-correlation function ##\langle \Omega |...
  28. G

    A Wave of an outgoing anti-particle in quantum field theory?

    Hello. I'm studying a course of the Quantum Field Theory and I got a question in a canonical quantization of a scalar field. I don't write a full expression of the field quantization here but the textbook said terms with ei(p⋅x - Ept) are associated with an incoming particle and terms with...
  29. M

    MHB Is this theory regarding the graph and the square root valid?

    http://mathhelpboards.com/pre-algebra-algebra-2/find-value-squareroot-3-using-graph-drawing-suitable-straight-line-19973.html I guess I found a method to obtain the square root of any number using the above graph. $x^2-2x-3$ What I did to find the square root of 3 was replace $x^2$ with the...
  30. PeterDonis

    A H-theorem in quantum information theory

    An interesting paper has appeared on nature.com: http://www.nature.com/articles/srep32815 The abstract: I expect this to spawn plenty of pop science claims about "scientists say we can reverse entropy". But the paper itself looks like a good discussion of how the second law actually works...
  31. Math Amateur

    MHB Axioms of Set Theory: Separation Axiom and Garling Theorem 1.2.2 .... ....

    I am reading D. J. H. Garling: "A Course in Mathematical Analysis: Volume I Foundations and Elementary Real Analysis ... ...At present I am focused on Chapter 1: The Axioms of Set Theory and need some help with Theorem 1.2.2 and its relationship to the Separation Axiom ... ... The...
  32. Math Amateur

    I Set Theory: Separation Axiom and Garling's Theorem 1.2.2

    I am reading D. J. H. Garling: "A Course in Mathematical Analysis: Volume I Foundations and Elementary Real Analysis" ... ... At present I am focused on Chapter 1: The Axioms of Set Theory and need some help with Theorem 1.2.2 and its relationship to the Separation Axiom ... ... The...
  33. ShayanJ

    A Exploring the Dual Low Energy Limits of Superstring Theory

    Let's consider superstring theory on a 10 dimensional Minkowski background. And assume there is a D3-brane on which the open strings end and closed strings wander around freely in the background. I want to know, in what limit this gives a supergravity theory in which I can study it by using the...
  34. G

    MHB Number Theory for Electronic Signal Frequency Synthesis

    I am new to this forum. I am an electrical engineer designing frequency synthesizers for electronic test and measurement equipment. I have a design problem and I think that number theory could help me solve it. I'm not a mathematician, so I will state the problem the best I can. Definitions...
  35. A

    B Quantum field theory VS Quantum mechanics

    Hello I am little bit confused about one topic on theoretical Physics and that is If we want to describe our Quantum world (example atoms in metal) then should I use Quantum field theory or Quantum mechanics?
  36. wolram

    B Is supersymmetry a part of string theory

    Is supersymmetry part of string theory or does it have a place in the standard model
  37. Demystifier

    I Is probability theory a branch of measure theory?

    In another math thread https://www.physicsforums.com/threads/categorizing-math.889809/ several people expressed their opinion that, while statistics is a branch of applied mathematics, the probability theory is pure mathematics and a branch of analysis, or more precisely, a branch of measure...
  38. zoobyshoe

    The Rubber Band Theory of Bow Strings

    When I was 6 or 7 I decided to make a bow and arrow one day. I had never seen or handled one in real life, but it was intuitively obvious to me from TV that they way to do this was to tie the ends of a stretched rubber band to the ends of a stick. This would have worked, after a fashion...
  39. C

    Applicability of potential flow theory (fluid dynamics)

    To start this question off, I'll just state what I do understand about potential flow theory 1.) I understand that the navier stokes equations are really difficult to solve analytically except in degenerate cases where the assumptions about the flow cancel out the non-linear terms. 2.) I...
  40. Jorge07

    A Calculating Waiting Time with Weighted Servers in Queueing Theory

    Hi all, I'm a software developer and i am working on a project which use queueing theory. I was reading some stuff about that but I could not find anything related to my problem or I didn't know how to search it. For example If a bank customer service have 2 counters. The first counter have the...
  41. arpon

    Most Beautiful Theories in Math & Physics

    What's the most beautiful theory in Physics or Math you have ever read? For me, they are the Prime Number Theorem and the Theory of Relativity.
  42. D

    A Quantum Field Theory - Why quantise fields?

    As I understand it, the need for quantum field theory (QFT) arises due to the incompatibility between special relativity (SR) and "ordinary" quantum mechanics (QM). By this, I mean that "ordinary" QM has no mechanism to handle systems of varying number of particles, however, special relativity...
  43. haushofer

    Insights General Relativity as a Gauge Theory - Comments

    haushofer submitted a new PF Insights post General Relativity as a Gauge Theory Continue reading the Original PF Insights Post.
  44. R

    B Can the theory change over time

    i and me teacher was in debate vs each other my teacher say we shouldn't believe in big bag because it is just a theory and it may change i say to him the theory is a collection of fact and model that have been on test then he say to me i have a B.S in physics do you know more than me .
  45. J

    Solve Set Theory Homework: Right Hand Side of "Or

    Homework Statement ##C \subseteq A \cap B \implies A \cap B \cap C = C## Homework Equations How do I get rid of the "belongs to" term on the right hand side? I know I need to prove either the left hand or the right hand side of the "or" term is correct, I'm just not sure how to get there. The...
  46. S

    A Partition function in quantum field theory

    Why is the partition function ##Z[J]=\int\ \mathcal{D}\phi\ e^{iS[\phi]+i\int\ d^{4}x\ \phi(x)J(x)}## also called the generating function? Is the partition function a q-number or a c-number? Does it make sense to talk of a partition function in classical field theory, or can we define...
  47. S

    A Feynman rules for a 0-dimensional field theory

    Consider the partition function ##Z(\lambda)## of the ##0##-dimensional scalar ##\phi^{4}## theory ##Z(\lambda)=\frac{1}{\sqrt{2\pi}}\int^{\infty}_{-\infty}d\phi\ \exp\{-\frac{1}{2}\phi^{2}-\frac{\lambda}{4!}\phi^{4}\}.## It can be shown that...
  48. RoboNerd

    Theory in approaching Faraday law/circuit question

    Homework Statement I have a square conducting loop of size L that contains two identical lightbulbs 1 and 2. The magnetic field that goes into the page varies B(t) = a*t + b. Lightbulbs have resistance of R0 Here is a question and the sample response. Disregard the part of the question that...
  49. M

    Proof of A Union of A Intersection B Equals A

    Homework Statement Prove that ##A \cup (A \cap B) = A## Homework Equations In the previous exercise, we proved: Let A, B be sets. Then, the following statements are equivalent: 1) ##A \subseteq B## 2) ##A \cup B = B## 3) ##A \cap B = A## The Attempt at a Solution The proof of ##A \cup (A...
  50. F

    Video about pressure in kinetic theory

    Hi, I am looking for a video helping intuition on pressure, in the context of kinetic theory of gases. I remember seeing a video where someone poured a bucketful of little hard balls (lead sinkers for fishing?) onto an electronic scales (a dynamometer, really) showing that this corresponds to...
Back
Top