What is Theories: Definition and 485 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. W

    Reality Scorecard for Physics Theories

    After reading Lee Smolin's Time Reborn and Rodney Brook's Fields of Color, a question occurred to me. Has anyone compiled a "reality" scorecard for the differing theories out there, both current and historical? For example, QFT proponents would consider the following things as real: fields...
  2. M

    Fundamental theories are gauge theories

    Hi folks -- I was reading some (non-technical) work by Frank Wilczek, in which he stated that any fundamental theory -- that is, well behaved in the E →∞ limit -- must be a local gauge theory. Does anyone know of the reasons for why this is thought to be the case? Even sketchy remarks...
  3. F

    Theories on the beginning of the universe before the Big Bang Theory

    Hello everybody, I'm doing a little research for an Astrophysics course and I am supposed to talk about some older theories that have been developed to try to explain the beginning of the universe before the big bang theory became widely accepted. Sadly, when I look for them, most of what I...
  4. JimiJams

    Implications of Einstein's Theories

    What little I've read about Einstein, out of a textbook, regarded his theories on motion at the speed of light. I'm not sure if this is general or special relativity, but it involved observations such as time dilation and length contraction, as well as changes to momentum and energy. I...
  5. R

    Is Planck Time Not Considered in Mainstream Physics Theories?

    Hello! I was told, that there are no mainstream physics theories, in which time is discrete. My question is this: At any present or any given future scenario, there will always exist the smallest amount of time, that a machine is able to measure. How come this variable, is not a main...
  6. G

    ∃ a Good Book on Alternative Theories to SR and/or GR?

    What is a good book on alternative theories of Special and/or General Relativity?
  7. B

    Primary constraints for Hamiltonian field theories

    I am currently trying to carry out the construction of the generalised Hamiltonian, constraints and constraint algebra, etc for a particular field theory following the procedure in Dirac's "Lectures on quantum mechanics". My question is the following: I have momentum variables that depend on the...
  8. S

    What are good time travel theories to use for Science Fiction?

    Hello! Sorry, I'm not not exactly sure if this post is in the right thread. But I would just like to ask what time travel theory is appropriate, and hopefully much easier to use, for science fiction? I am planning to write a semi sci-fi short story, and it involves using time travel: to the...
  9. J

    Why aren't state-reduction theories refuted by diffraction experiments

    Spontaneous collapse theories like GRW postulate that elementary particles have a 10 to the -16 probability per second for spontaneously collapsing in the position basis, where the collapse function involves multiplication by a Gaussian. Entanglement then guarantees that macroscopic objects are...
  10. M

    (Philosophical?) Question on effective field theories

    I've just acquainted myself with 'effective field theories', and have found myself thinking about the following question. In the effective field programme we generate low-energy theories from high-energy theories by 'integrating out' the high-energy modes, and this process is said to be...
  11. naima

    Can hidden variable theories assign values to observables?

    hi PF I read the no-go Kochen theorem using 18 vectors projection (here). One attribute a value to an observable A: v(A) This function is supposed to be linear and verify v(AB) = v(A) v(B) so v(AB - BA) = v(A)v(B) - v(B)v(A) = 0 (v is a real number function) v must assign v(id) = 1 because v(A...
  12. marcus

    Why do gauge theories win out?

    "Gauge" is normally understood as "mathematically redundant" Why are gauge theories so prevalent? Why do they always seem to win out in the contest to describe the world? In a theory with some group of gauge symmetries, only the gauge-invariant quantities are considered physically...
  13. R

    Theories out there that view time as a particle?

    Conceptually hard to grasp... are there any theories out there that view time, like a particle, as having a rest mass, and possibly spin and charge?
  14. C

    Recommended reading on Kaluza-Klein theories.

    Hi guys! I'm looking for a good introduction to Kaluza-Klein theory(ies) and would like any recommendations. Thanks :)
  15. Z

    What are the accepted theories for the source of gravity?

    I have very little knowledge of physics so the simpler you can keep your replies the better for me. Newton put forth a gravity theory that essentially said that there is a force that pulls on us to keep people on the Earth and this is gravity. Einstein came along and included in his theory...
  16. S

    Classification of Gravitational Theories

    hi there are many gravitational theories such as 1- modified gravity { massive gravity, dilaton gravity, ... } 2-conformal gravity 3-emergent gravity 4-lower and highest dimensional gravity 5-... is anybody know about this gravitational theories? is there a general classification of...
  17. J

    Where is a good place to go to get input on theories?

    I am self educated. I have created the Grand Unified Field Theory. I wrote a paper explaining the Theory in under 500 words. I have made that paper public. I would like to share it with other scientists. The rules on these forums clearly state not to use this place to share unpublished papers...
  18. marcus

    Why gravity codes renormalization of conformal field theories

    http://arxiv.org/abs/1305.6315 Why gravity codes the renormalization of conformal field theories Henrique Gomes, Sean Gryb, Tim Koslowski, Flavio Mercati, Lee Smolin (Submitted on 27 May 2013) We give a new demonstration that General Relativity in d+1 dimensions with negative or positive...
  19. N

    What are wave and particle nature of light theories?

    hello everyone i want to ask that what are the theories that proposes the wave nature of light and also those which proves the particle nature of light? list all the theories please ! P.S i don't want a complete description about those theories. thank you
  20. G

    Can combining Tesla models and designs produce free energy?

    know i know I'm on the lower end of the IQ scale in this forum but try to bear with me. I'm trying to combine few Testla models and designs to produce "free" energy. My plans are to measure the energy output from a antenna "the size you would find on a old house" then building a Testla coil that...
  21. nomadreid

    Model Theory: relation between two theories with the same models?

    This is a question out of model theory. (This preamble is due to the fact that "model" and "theory" are used in different ways in different fields.) Is there any specific relationship between two theories which have the same models? A knee-jerk reaction would be to say that they are isomorphic...
  22. A

    Principal Virtual Work Theories - Cylindrical Pipe Application

    Dear All, I did post this issues in the physics forum, however there is somebody ask me to post it in the engineering forum. With this I re-post it here. Does anyone here familiar with a theory called Principal Virtual Work (Equilibrium theory) ? I read somewhere that with this theory, i...
  23. A

    Principal Virtual Work Theories - Cylindrical Pipe Application

    Dear All, Does anyone here familiar with a theory called Principal Virtual Work (Equilibrium theory) ? I read somewhere that with this theory, i could relate(for pipeline application - collapse & buckling) the components for ovalisation, external pressure and hoop strain. Appreciate if...
  24. S

    What is the most counter-intuitive concept in the relativity theories?

    Thanks! Please answer, Mr. Donis! Also, if someone could simplify the difference between a reference frame (used today) and a reference body (used in Einstein's book) please do so!
  25. K

    Simplified theories for gravity?

    Hey, I was wondering, are there any major theories about gravity that actually try to simplify it all? Like, I recently heard that potentially the universe is expanding exponentially. It got me thinking. Couldn't this be translated to what gravity is? I mean, we know that gravity depends on the...
  26. L

    Multiple Dimensions in Quantum Theories

    Will someone please explain to me how a theory, such as a quantum field theory, be expressed in more than three dimensions? Is this referring to the spatial dimensions we live in now, or what? And how does someone even begin to ponder these multiple dimensions?
  27. JK423

    Different interpretations? No, different theories

    I was reading Everett's paper http://rmp.aps.org/abstract/RMP/v29/i3/p454_1 on the "Relative State" Formulation of Quantum Mechanics, and i realized that this is not an interpretation experimentally equivalent to other "interpretations" like the Copenhagen.. These are different theories that...
  28. D

    How much can we rely on theories?

    Modern physics is trying to understand and describe domains that we cannot observe, therefore we have trust our powers of reasoning, deduction of the mathematical facts. Im wondering how much we can rely on physics theories created from mathematical models compared to theories created through...
  29. S

    Theories of the origins of the universe

    Hi everybody, I have a high school physics project in a few months and I need your help. As you can see from this post's title, its about Theories of the origins of the universe. I've read Hawking's "Brief history of time" and I did some research on Internet but I only found famous Big Bang...
  30. C

    How do the tidal forces warming moons theories hold when []

    How do the “tidal forces warming moons” theories hold when [..] How do the “tidal forces warming moons” theories hold when apart from heating from expansion, there may be also cooling from contraction? I can understand a temporary heating, from the tital forces exerted on the moon but...
  31. samalkhaiat

    Non-abelian Local Gauge Invariance in Field Theories

    These are notes I made when I was studying the subject 20 years ago. They seem fine considering that I was student then. I believe they can be useful for those who are studying Yang-Mills and other related material. Sam
  32. I

    Macroscopic superpostion and hidden variable theories

    I have been reading: http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199560561.001.0001/acprof-9780199560561-chapter-20 It appears Pilot wave theories have no way to explain macroscopic superpostion. Any thoughts or opinons on this?
  33. I

    Do hidden variable theories reject superposition of states?

    do Hidden variable(local and non local) theories say all objects exist as a single objects in a single location rather than many locations at the same? unlike objects in superpostion?
  34. MTd2

    How to recover time paradoxes in canonical theories of gravity?

    Canonical theories of gravities imply a foliation of spacetime into 3 hypersurfaces, each one labeled by time and related by lapse functions. It happens that this makes time unlike space, which is bad, since in GR, time is another coordinate. It also makes closed time like surfaces to...
  35. S

    Aether Theories: Consensus on What Space is Made Of?

    No, I'm not talking about the original luminiferous aether disproven by the Michelson-Morley experiments. I'm asking what the consensus is on whether 'empty' space is actually made of something: http://en.wikipedia.org/wiki/Aether_theories To what extent is there a consensus on what space...
  36. Islam Hassan

    Relationship Between QED/QCD and Field Theories

    Are QED/QCD themselves field theories or sub-field theories of other more general field theories? What are the formal theories/theoretical frameworks that completely characterise the Standard Model in our present state of knowledge? IH
  37. Y

    Compactified String Theories - Generic Predictions for Particle Physics

    A review paper by Bobby Samir Acharya, Gordon Kane and Piyush Kumar http://arxiv.org/pdf/1204.2795v1.pdf 12 April 2012 This is my first post here in a long time. I learned of this paper from yesterday's Lubos Motl blog. It is the most instructive string theory paper I have ever read...
  38. P

    Nikodem Poplawski's theories

    What do people think of Nikodem Poplawski's proposal that adding torsion to GR (in the form of ECSK gravity) leads to, among other things, black holes that "bounce", and an alternative to inflation for the flatness/oldness problem? Published in Physics Letters B...
  39. Chronos

    Another nail in the coffin of alternative redshift theories

    Cosmological redshift is often targeted by crackpot physics zealots. Here is a sober discussion worthy of review: Direct Determination of Expansion History Using Redshift Distortions, http://arxiv.org/abs/1210.6596
  40. C

    The line between insane conspiracy theories and credible human rights violatio

    What is the formal definition of the line between insane conspiracy theories and credible human rights violations? What usually distinguishes the two, and makes some rational, and others not? For example, 9/11 conspiracy theories don't seem to be credible nor believable at all. However, US...
  41. FalseVaccum89

    Should I Go With My Crazy Theories?

    I am currently working towards a double major in Mathematics and Physics, so that I will have a very good background in both. My reasons are twofold: 1) I want to be well-prepared to study in a Mathematical Physics Ph.D. program like the one at Virginia Tech 2) I have a deep and abiding passion...
  42. X

    On modified theories of gravity

    I am confused about the modified theories of gravity. We all know there is the Schwarzschild solution for GR. The solution can give right prediction for the solar-system experiments, such as Light deflection, perihelion shift of the Mercury and gravitational time delay. Whether all kinds of...
  43. N

    Faster Than Light Travel, Theories.

    Any one who has been following my other Thread (Simulated Gravity) knows that I've trying to write a Hard(ish) Science Fiction novel. I'm looking for help in firming up my "FTL Drives" and trying to use current Real world knowledge Currently there is two ways to "cheat" the speed of light...
  44. Y

    Photon properties from gauge theories

    Hello everyone, I read on Wikipedia that a lot of the properties of photons are explained by them being the quanta of an abelian gauge field (link). Does anyone happen to have a good source on this? I haven't learned anything about gauge theories yet, so I'm looking for an introductory text...
  45. T

    Are Lawrence Krauss' theories accepted in physics academia?

    How could something possibly come from nothing? He reminds me of the Sokal Affair.
  46. R

    Effective field theories, eliminating fields using equations of motion

    First year grad student here, I've taken two terms QFT. I'm studying some effective field theories, and one of the techniques I've seen used for writting down the effective lagrangian is identifying some fields or components of fields that are "small" and removing them from the lagrangian by...
  47. C

    Most Elegant Physics Theory: Research Today

    What part of physics that is still actively researched today, is the most mathematically elegant in you opinion.
  48. jfy4

    Lattice field theories and the continuum limit

    I have heard generally that it is possible to put different physical theories on a lattice and after renormalization get the same continuum theory. I mean, different lattice theories that lead to the same continuum theory. Is this true for, say, qcd, or other particle theories? Are there...
  49. M

    SR for cl. rel. field theories.

    I read basic stuff about relativity (time dilitation etc.) in a HS textbook. I want to do some relativistic dynamics and go up to Einsteins field equations (GR). For GR I will definitely need tensor analysis. However, what is the math involved in the SR that I need to get to classic...
  50. Z

    Can stars predict the future of our world and universe?

    I have been wondering lately is it possible to predict happenings in world and universe by the position of the stars,and if so how? :confused: Please help thanks:smile:
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