Theories Definition and 457 Threads

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...

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...

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

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...

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...

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...

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...

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...

"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...

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?

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

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...

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...

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...

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...

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

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...

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...

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...

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!

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...

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?

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...

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...

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...

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...

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

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?

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?

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...

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...

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

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...

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

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...

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...

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...

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...

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...

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

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...

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...

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...

Once I've asked here why you physicist use Gauge theories with such confidence and the overall answer was "because it works". This probably is true but perhaps is also a bit disappointing to me because I was looking something more fundamental. I've recently thought of something that may be the...

I'm wondering if their are any unified physical theories that predict our universe to be a part of a multiverse in our own dimension? I'm looking for anything along the lines of stating that our universe is a star in a 'galaxy' of other universes that we can theoretically travel to if we could...

what theories out of the major two ( Bronsted-Lowry Theory of acids and bases and The Lewis Theory of acids and bases) should we use in common problems, and which one is more reliable ?

Dear PF, Could you please advise me good detailed reference on Grand Unified Theories... especially I want to see where for example SU5 potential is composed from two Higgs representations (two Higgs fields) and how symmetry breaking (minima of potential appears for both of fields) happens...

For my physics class, we are doing a large project for our finals. I wanted to do mine on dealing with stage lighting (theatre). I tried googling and doing some research, but couldn't find much. Does anyone know any theories related to the physics of stage lighting?

Hi there, I have a short thought that I want to share with all of you and see if there has been something written about it and, if not, why not?: A free particle spin is something that can take a discrete range of values, as it happens with electromagnetic or colour charge. However the other...

Do theories of quantum gravity require that space-time is a lattice instead of a continuum? I guess this question has been addressed elsewhere, but I would appreciate hearing different points of view. Please dummy down the responses so a philosopher can understand it.