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. SEYED2001

    I Is the Theory of Everything necessarily deterministic?

    Hi I am aware that QM isn't deterministic. Should a theory of everything be deterministic to be a theory of everything, and if yes, then how can it be when QM as a part of it is not deterministic? Thanks in advance Seyed
  2. Diracobama2181

    Phi 4 Theory Renormalization

    Let ##\phi_{+}=\frac{d^3k}{2\omega_k (2\pi)^3}\int(\hat{a}^{\dagger}(\overrightarrow{k})e^{ikx})## and ##\phi_{-}=\frac{d^3k}{2\omega_k (2\pi)^3}\int(\hat{a}(\overrightarrow{k})e^{-ikx})##. Then ##\phi^4=\phi_{1}\phi_{2}\phi_{3}\phi_{4}=(\phi_{1+}+\phi_{1-})(\phi_{2+}+\phi_{2-}...
  3. S

    What is the significance of using U/2I in four point probe theory?

    Dear Ladys and Gentlemans, I want to measure the sheet resistance R_square on a printed product. My measuring equipment consists a SMU to supply and measure and a four point Probe by Jandel. As output size I get the electrical resistance R (basically the measured Voltage U divided by the supply...
  4. A

    B Size of strings in string theory

    Quite a long time ago, I read about length of strings in string theory. And, if I remember correctly, expected length was in light years. I looked at Wikipedia today, and I see currently expected length of string is very small, around Plank size. Is it changed over time, or the expected length...
  5. N

    A General Covariance in Quantum Field Theory

    All physical laws have to be Lorentz invariant according to a lecture I just watched. Why is general covariance (which is more general than Lorentz invariance) not a requirement for all laws of physics? Are there any quantum gravity theories that take the approach of adding general covariance to...
  6. M

    Studying the theory behind batteries

    These days I've taken an interest in lithium ion batteries and the like, but I don't really know where to go to start learning about them. I saw the general engineering sources and the materials/chemical engineering sources threads, but there was nothing specifically about batteries- Does anyone...
  7. P

    MHB Exploring Finite Group Theory: Finding the Upper Bound of Groups of Order

    In the context of group theory, there's a theorem that states that for a given positive integer \(n\) there exist finitely different types of groups of order \(n\). Notice that the theorem doesn´t say anything of how many groups there are, only states that such groups exist. In the proof of this...
  8. MountEvariste

    MHB Is $p\equiv 3\pmod{4}$ a condition for $\pi$ to be an even permutation?

    Let $p$ be an odd prime number such that $p\equiv 2\pmod{3}.$ Define a permutation $\pi$ of the residue classes modulo $p$ by $\pi(x)\equiv x^3\pmod{p}.$ Show that $\pi$ is an even permutation if and only if $p\equiv 3\pmod{4}.$
  9. Pratyeka

    B Massive Gravity Theory: Explaining Universe Expansion

    I have started reading about Claudia de Rham's theory of massive gravity (https://www.imperial.ac.uk/people/c.de-rham) and how it can explain the mechanism of the expansion of the universe, among other thing. Lots of infos available on the above link. Has anyone found flaws in the theory or...
  10. Phylosopher

    Quantum Is Zuber's Quantum Field Theory textbook any good?

    Hi, I have been studying Quantum Field Theory this semester! It seems that Shwartz and Peskin are the most popular choices when it comes to studying QFT. But apparently my professor have another "old" preference. He strongly suggested that we learn QFT from Zuber's book. I have looked at the...
  11. A

    Particles on Deforming Surfaces: Theory & Analysis

    All books in analytical mechanics explain the case of a particle moving on a given static surface. But what happen if, for example, the surface is having some deformation?. I imagine that the principle of virtual work, and hence, D'Alembert are no longer valid since the normal force by the...
  12. H

    I Does quantum theory describe light as a wave?

    Hello! I recently had a discussion with a person who's well-read on quantum physics and I was suprised by his claim that "light is in no sense regarded as a wave" in quantum mechanics. His support for this claim was that there are no wave crest or wave trough, there is nothing moving. What...
  13. H

    A Eigenstates of ##\phi^4## theory

    What is known about the eigenstates of the ##\phi^4## theory in QFT? Is there an informal understanding of how these states are organized in the nonperturbative regime? For example, are there known to be any bound states in any dimensions? How does the energy of a multiparticle eigenstate (if...
  14. E

    Understanding Group Theory and its Applications in Quantum Field Theory

  15. PeroK

    A Amplitudes for ##\phi^4## theory

    This is QFT for the gifted amateur, chapter 19, which is generating the various Feynman diagrams and rules. Some calculations are given but I encounter various problems when trying to work them all out. The starting point is that we want to calculate: $$\langle q| \hat S | p \rangle = (2\pi)^3...
  16. dorteam

    Question about the theory of machines

    I couldn't do it
  17. F

    Does the theory of electromagnetism have this fundamental problem?

    This is about possible problems with the equations of EM theory of Faraday and Maxwell. EM theory states that when an electron moves a magnetic field is generated. Does this field move with electron in the direction of the electron (if the electron is in motion)? Or, does it stay still in the...
  18. A

    Other Best journals in High Energy Physics (formal theory)

    Hello, I request inputs about selecting a journal to submit an article in High Energy Physics. This is in formal theory as opposed to Particle Phenomenology. The article is more than ten pages so PRL is not an option. How would you choose between JHEP and Physical Review D? Which is rated higher...
  19. U

    I Big bounce theory in light of the closed Universe finding

    As you all know: Planck evidence for a closed Universe and a possible crisis for cosmology https://www.nature.com/articles/s41550-019-0906-9 If confirmed, it would bring back the Big Bounce as a possible hypothesis for the evolution of the universe. This has long-term consequences being that...
  20. M

    What are the prerequisites to study quantum field theory?

    Summary:: What are the prerequisites to study quantum field theory? What are the prerequisites to study quantum field theory?
  21. T

    What are the key considerations for imaging with a condenser fresnel lens?

    Hello All, I am in need of an optics expert on imaging, and in particular a fresnel lens is being used as for an imaging device. From my understanding a condenser lens can be considered equivalent to a plano-convex lens. Setup: A condenser fresnel lens is used, for which both the fresnel and...
  22. Y

    Fastener Theory - Determining the Ideal Torque for a Bolt

    So this is for my car. If I have a bolt that I don't know what the ideal torque is supposed to be because the manufacturer of the car doesn't publish a torque, it's possible to calculate it? This can be done just give the specification of the bolt? Regardless of what the bolt is fastening? I'm...
  23. Haorong Wu

    I Need help with tensors and group theory

    I am reading Group Theory in a Nutshell for Physicists by A. Zee. I have big problems when learning chapter IV.1 Tensors and Representations of the Rotation Groups SO(N). It reads I can understand why ##D\left ( R \right )## is a representation of SO(3), but I hardly can see why the tensor T...
  24. Bruce Harvey

    A Can Quantum Mechanics Calculate the Frequency of an Atomic Clock?

    I have searched in vain for a detailed calculation of the frequency 9192631770 Hz from basic physical constants using Quantum Mechanics. Can anyone help with this please
  25. benorin

    Munkres Topology Ch 1 ex#7) part (c) — basic set theory Q

    Obviously the parenthetical part of the definition of ##F## means ##B\subset C## but we are not allowed to use ##\subset##. I do not know how to express implication with only union, intersection, and set minus without the side relation ##B\cap C = B\Leftrightarrow B\subset C##. This is using the...
  26. ShadownightPrograms

    I Many-Worlds Theory: Simulation Program in C#

    Here is the Code File in an txt. I can on request provied the whole Program, which includes the PSE, AtomFunctions and many useful but not all implemented Funtions to solve the Many Worlds Problem in C#. Please feel free to ask questions via here or email [e-mail address deleted by Mentors] I...
  27. J

    B String Theory & Elementary Particles: What's Real?

    If string theory is correct does it mean that elementary particles like photons, electrons, and quarks don't really exist or does it mean they do but are made of cosmic strings and so therefore are not elementary?
  28. T

    A Evaluating Matrix Spin Dependent Term in Dirac Quadratic Equation

    I derive the quadratic form of Dirac equation as follows $$\lbrace[i\not \partial-e\not A]^2-m^2\rbrace\psi=\lbrace\left( i\partial-e A\right)^2 + \frac{1}{2i} \sigma^{\mu\nu}F_{\mu \nu}-m^2\rbrace\psi=0$$ And I need to find the form of the spin dependent term to get the final expression $$g...
  29. sophiatev

    I The SO(3) group in Group Theory

    In Griffith's Introduction to Elementary Particles, he provides a very cursory introduction to group theory at the start of chapter four, which discusses symmetries. He introduces SO(n) as "the group of real, orthogonal, n x n matrices of determinant 1 is SO(n); SO(n) may be thought of as the...
  30. B

    I Citation for a knot theory statement

    Hello! Where can I find the source for this statement (i.e. a citation for it, ideally the original one): "any smooth k-sphere embedded in ##R^n## with 2n − 3k − 3 > 0 is unknotted". Thank you!
  31. MathematicalPhysicist

    A Is Stochastic String Theory the Key to Original Ideas in Physics?

    Well there was today some lecture on String theory which I got late since I was reading something else in Condensed matter physics and then I looked at a book that I have of stochastic Integration with jumps and by associativity of ideas I searched google for Stochastic String Theory and got to...
  32. E

    Nonlinear scalar equation in field theory

    Thank you very much
  33. Adwit

    A Quantum Field Theory: 3-4 Equation Steps Explained

    I understand how do 3 no. equation come from 1 & 2 no. equation. But I am struggling to understand how do 4 no. equation come from 3 no. equation. Will anyone do the steps between 3 no. equation and 4 no. equation, please ?
  34. A

    Quantum physics and the theory of evolution

    How did you find PF?: Searching a way to share own thoughts I was wondering if we could gather all the laws of the universe and try to link anything to everything. I'm thinking of the possibility of finding links between quantum physics and the theory of evolution. It reminds me of the...
  35. A

    I Perturbation Theory and Zeeman Splitting

    Suppose we have a hamiltonian $$H_0$$ and we know the eigenvectors/values: $$H_0 |E_i \rangle = E_i|E_i \rangle $$ We then add to it another perturbing Hamiltonian: $$H’$$ which commutes with $$H_0.$$ According to nondegenerate first order perturbation theory: $$\langle H \rangle \approx...
  36. J

    Voltage theory for an LCR circuit

    Summary:: I say the answer is A because these are reactive components that take and give back energy from the circuit so no voltage drop across the 2- L & C. Please let me know yours thoughts- thanks Hello I am a newby to electronics taking a class. Please review my thinking on this problem. I...
  37. E

    Can Humans Achieve Flight Through Theory Crafting?

    Hi, smart people This quarantine has got me thinking: Can we get people in the air? I have 3 questions that may or may not help answer this question. But I do appreciate any insight. 1. How would one accelerate (the average human) 100 feet in the air and sustain their position? Under normal...
  38. J

    I Group Theory Appearing in Griffith's Elementary Particles (2nd Ed.)

    Hello, I'm trying to make sense of some of the group theoretic discussion found in Griffith's Introduction to Elementary Particles. I have had a fair amount of exposure to elementary group theory, but no representation theory, and have some specific questions related to this which refer to the...
  39. Philip Koeck

    Deriving vdW-equation from kinetic theory

    Does anybody know of a derivation of the van der Waals equation from the molecular kinetic theory of gases, but without using the tools of statistical physics (such as partition functions)?
  40. M

    A Eric WEinstein's Geometric Unity theory

    Eric Weinstein finally released a video of his 2013 Oxford talk on "geometric unity". There are many fans and skeptics out there, looking in vain for a genuinely informed assessment of the idea. I admit that so far I have only skimmed the transcript of the video, being very pressed for...
  41. Replusz

    I Vacuum amplitudes in \phi^4 theory

  42. PainterGuy

    Stats on Students Understanding Theory of Relativity

    Hi, I'm not sure if it's a good idea to start a thread about the following problem but I didn't want to PM anyone. Some time ago I came across a thread which had stats related to the problems faced by students learning the theory of relativity. It showed like how many undergraduates really...
  43. John Greger

    A Solving Problems in "Conformal Field Theories" by Francesco

    I have been following the book called "Conformal Field Theories" by Francesco, also known as "the yellow pages". I do this for fun but, of course, sometimes it gets rather technical. Do there exist solutions to the problems in this book? I haven't found a solutions manual available. Many...
  44. Z

    Perturbation Theory - expressing the perturbation

    Hi, I just need someone to check if I am on the right track here Below is a mutual Coulomb potential energy between the electron and proton in a hydrogen atom which is the perturbed system: ##V(x) = \begin{cases} - \frac{e^{2}}{4\pi\epsilon_{0}}\frac{b}{r^{2}} \text{for } 0<r \leq 0 \\ -...
  45. Phylosopher

    I Why perturbation theory uses power series?

    I am revising perturbation theory from Griffiths introduction to quantum mechanics. Griffiths uses power series to represent the perturbation in the system due to small change in the Hamiltonian. But I see no justification for it! Other than the fact that it works. I searched on the internet a...
  46. electrogeek

    I 2nd Order Perturbation Theory Energy Correction

    Hi everyone, I'm struggling with the proof for the second order energy correction for perturbation theory when substituting in the first order wavefunction. I have attached an image of my current proof for it below, but I'm not sure whether this is the correct approach for it (the H's in the...
  47. P

    I Minimization of free energy in Landau theory

    Thanks in advance for any insight! Following Pathria's discussion of phase transitions, I'm getting tripped up on the discussion of Landau's theory. Pathria begins with a zero-field free energy ##\psi = A/NkT## where ##A## is the Helmholtz free energy. He proceeds to characterize the...
  48. danielristic

    I Is this a typo? (Quantum Theory for Mathematicians by Brian C. Hall)

    Hello, After reading a few vulgarisation books, I'm looking into familiarising myself with the more mathematical aspects of quantum physics so I've started reading Quantum Theory for Mathematicians by Brian C. Hall. I'm only 9 pages in but I've already spotted what I think is a typo. I checked...
  49. K

    I Is there some agreement on properties of a theory of quantum gravity?

    Having read many times that there is no theory of quantum gravity, yet physicists at Physics Forums must have some ideas of what a theory of quantum gravity will contain. Is it allowed to discuss these questions at Physics Forums? Wikipedia does allow some current theoretical work to be...
  50. G

    I Confused by Notation? Perturbation Theory Explained

    Looking at. <psi|AB|theta>, under what conditions would this be equal to <psi|A|theta> * <psi|B|theta> I’m just getting into perturbation theory and am running into confusing notation. Thanks john
Back
Top