Theory Definition and 1000 Threads

In the 1970s, Ni formulated an alternative theory of gravity (The Astrophysical Journal {\bf 176}, 769 (passage on pages 791 f); see also Misner-Thorne-Wheeler, page 1070). Though in conflict with observation, I am interested in its fundamental properties. Ni has a scalar ##\Phi## as the...

I'm trying yo verify the relation \begin{equation} [D_{\mu},D_{\nu}]\Phi=F_{\mu\nu}\Phi, \end{equation} where the scalar field is valued in the lie algebra of a Yang-Mills theory. Here, \begin{equation} D_{\mu}=\partial_{\mu} + [A_{\mu},\Phi], \end{equation} and \begin{equation}...

I posted this earlier, but the thread has been closed. String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the...

Based on our current understanding of astrophysics, what's the largest possible rocky planet, theoretically speaking, with a surface gravity of 1g? The larger the planet, the lower the average density, and there's a structural lower limit to the density.

Hello, I am newish in group theory so sorry if anything in the following is not entirely correct. In general, one can anticipate if a matrix element <i|O|j> is zero or not by seeing if O|j> shares any irreducible representation with |i>. I know how to reduce to IRs the former product but I...

String theorists frame much of their studies in the context of Planck length. The theories are meant to fold together QM and general relativity. The equation for Planck length includes the gravitational constant, G. It seems to me the theorists are assuming the gravitational laws extend to...

First, I want to be pedantic here and underline the distinction between a set (in the model, or interpretation) and a sentence (in the theory) which is fulfilled by that set, and also constant symbols (in the theory) versus constants (in the universe of the model) Given that, I would like to...

Square law? i raise this question because of recently reading some QM, and realizing that for significantly short periods of time, it becomes hard to detect the mathematical patterns. E.g. in the double slit experiment, the standard pattern doesn’t appear after just a few photons. It takes...

Hi everyone! Sorry for the bad english! So, just a quick doubt... Does things collapse from a wave of probability into a quantum field or is the wave in the quantum field the probabilistic wave itself? An example to make it clearer: Suppose we have an atom, it enters an atom interferometer, it...

Hello, I am currently struggling to understand how one can write a Hamiltonian using group theory and change its form according to the symmetry of the system that is considered. The main issue is of course that I have no real experience in using group theory. So to make my question a bit less...

Can someone please direct me to ,or show, a proof that a Consistent and Sufficiently Strong AFT is not decidable. It presumably involves the Diagonal Argument, but I can't figure out how to apply it. Many thanks.

In the derivation of finding pressure exerted by a gas using kinetic theory of gases I am not understanding why the time between two collisions is taken as the time for rate of change of momentum when a particle bounces back from the wall. please help me

In the formulation of Euler-Bernoulli Beam Theory, there are two degrees of freedom at a point, w and dw/dx. Typically, the finite element model of this theory uses cubic polynomial for interpolation of $w$ using a two noded element as given in Chapter 5 of this book [1]. This element is a...

Greg Bernhardt submitted a new blog post The Sum of Geometric Series from Probability Theory Continue reading the Original Blog Post.

I have been following [this video lecture][1] on how to find gauge invariance when studying the perturbation of the metric. Something is unclear when we try to find fake vs. real perturbation of the metric. We use an arbitrary small vector field to have the effect of a chart transition map or...

Just when I thought there couldn't be any more quantum interpretations (I think @Demystifier listed 9 in his recent thread)... :smile: Lee Smolin and several others (Cohen, Cortês, Elitzur) have published a pair of related papers discussing dBB/Bohmian Mechanics and its ability to explain the...

In QED the maths suggests that a photon takes all possible paths, and all but one of the paths cancel out leaving the path we observe. Using this as an analogy:- The maths of quantum mechanics suggests a vast number of possible universes concurrent with our universe. Perhaps all these...

I have been reading up on the kinetic theory of gases, and I'm unsure whether I have correctly understood why particle velocities become correlated after colliding. Is it because during the collision they exchange momentum and thus their velocities (and hence trajectories) are altered in a...

I have read about LISA Pathfinder. Can a satellite with gravitational test instruments, such as a torsional pendulum, test the MOND theory at L1 and L2? Maybe both MOND and dark matter are needed to explain velocities of some remote stars and the formation of large galactic structures.

Can anyone please suggest which books or articles can be taken which would start from a preliminary one for a newcomer like me for understanding the Brans-Dicke theory . Thanks.

Yesterday I have seen the excellent documentary "The Swedish theory of love". (Yes, you can find the full documentary on YouTube, and no, it's not about sex!) Perhaps the most interesting part in the documentary is this graph. And guess which country is right in the middle? Croatia! If that is...

Is there a historical example of a theory that physicists all over the world pursued and developed in a concerted and organized research for more than 20 years without results, but then turned out to be correct? I get frequently as an answer the heliocentric vs. geocentric model, it took...

Hello everyone, I am currently finishing my Masters in Theoretical Physics and looking forward to continue in a PhD. I always thought I would love String Theory, and now that i am actually doing it I see that my feeling was correct. I do not know why but trying to understand its concepts...

Hi. I'd like to ask what are the differences between Particle Physics, Quantum Field Theory and the Standard Model. I see these names of physics courses but I want to confirm if I understand the difference. My understanding is that when students learn particle physics in their undergraduate...

Earlier in the forum Urs Schreiber discussed criticism of KKLT, and claims that string theory does not allow de Sitter vacua https://www.physicsforums.com/threads/no-metastable-type-iib-de-sitter-vacua.950271/ The following recent claims to address these concerns, and claims KKLT allows de...

please suggest me a good book on the high energy physics where group theory is discussed for the beginner.

I've been looking at another Penrose's theory/model called twistor theory (https://en.wikipedia.org/wiki/Twistor_theory) that seems very interesting. From what I've read it seems to me that literally everything can be represented by twistors (or, rather, variations of twist theory). The only...

Hello everyone,Upon my comment on the insight "Applying for Physics Graduate School - Comments", Mr. Bill (bhobba) suggested that I need to write an individual post regarding my inquiry. I am looking for physics graduate programs (PhD). My senior project/thesis was on classical field theory and...

Find dfa's for the following language on $\sum$={a,b}; c) L={w:${n}_{a}$(w) mod3 < 1;

Homework Statement Show that the 2nd order nondegenerate perturbation theory corrections are given by: ##E_n^2 = \sum_{k \neq n}^{\infty} \frac{|\left < \phi_n | \hat{H} | \phi_k \right> |^2}{E_n^0 - E_k^0}##[/B] and ## C_{nm}^2 = \frac{C_{nm}^1 E_n^1 - \sum_{k \neq n}^{\infty} C_{nk}^1...

Dear Everyone, Here is the question: "Prove that if $k$ divides the integers $a$ and $b$, then $k$ divides $as+bt$ for every pair of integers $s$ and $t$ for every pair of integers." The attempted work: Suppose $k$ divides $a$ and $k$ divides $b$, where $a,b\in\mathbb{Z}$. Then, $a=kt$ and...

in the tv show "The Big Bang Theory", Sheldon wrote a book called "A proof the algebraic topology can never have a non self-contradictory set of abelian groups". Is this just a random set of words that is meant to sound smart but in reality means nothing or is it accurate? If it is, what does it...

When deriving the kinetic theory of gases, we take the change in momentum of a particle as it hits one side of a box and divide it by the time over which the collision takes place. The time is derived by taking the total distance the particle traveled in the box (i.e. from one end, off the side...

Hi, I'm reading Lamarsh's book "Introduction to nuclear reactor theory" and in chapter two there is a brief description of neutron scattering theory. I have a few questions about it. 1) In the book the author says that it is easier to analyze the interaction process in the center of mass frame...

Is it possible to solve a problem of overcoming of speed of light with solid objects using faraday cage Theory with equivalent charge?

Hey all I previously asked about some math structure fulfilling some requirements and didn't get much out of it ( Graph or lattice topology discretization ). It was a vague question, granted. Anyway, I seem to have stumbled upon something interesting called geometric group theory. It looks...

Hi all, I have stumbled upon Artin's book "Algebra" and was wondering if I could use it to do some self-study on Group Theory. Some background: I am a physics undergraduate who has some competence in elementary logic, proofs and linear algebra. It seemed to me that ideas related to Group...

I've heard in a general way that string theory can describe the properties of the fundamental particles through standing waves or resonances of strings. Is this in fact the case, and if so, can someone provide a link to the relevant research papers?

Homework Statement Show that the force resisting change of the minimum distance h between the surfaces of two rigid spheres of radii a and b which are nearly touching is: $$6\pi\frac{\mu}{h({a^{-1} + b^{-1}})^2}\frac{dh}{dt}$$ provided $$\frac{\rho h}{\mu}\frac{dh}{dt}$$ Homework Equations...

I'm interested in pursuing graduate studies in Relativistic Quantum Information (looking into universities affiliated with the ISRQI) as well as other fields related to quantum information theory (Quantum Computing - QKD protocols, Quantum Channels). I think it would be cool to apply QIP to...

I recently started reading Feynmans book QED. There are a couple of questions I have regarding his theory on the percentage of light that is reflected of two surfaces of glass. My question is as follows, A piece of glass in fact has four surfaces. The front of the glass the back side of...

It is my understanding that in both Classical Field Theory and QFT the Lagrangian must be Lorentz invariant in order for the fields to be considered relativistic. Buy what about the field itself (φ or ψ)? As complex-valued functions of space and time do they also have to be Lorentz invariant...

The theory regarding two persons experiencing different amounts of time dilation due to the two persons being influenced by different amounts of gravity states that while one person stays on Earth under its gravity and another person travels through space under less influence of gravity (less...

Homework Statement [Answer is V = 25m/s, however, how do I get that answer? Thank you!] A police cruiser sets up a novel radar speed trap, consisting of two transmitting antennas at the edge of a main north-south road. One antenna is 2.0 m [W] of the other. The antennas, essentially point...

This is the provocative question posed by Sabine Hossenfelder in her article in Forbes, covering the ongoing debate of inflation critics like Paul Steinhardt (once one of the theory founders) and scientists who develop models of inflation. Link to her article...

https://imgur.com/a/oSioYel I am trying to understand this proof, but am tripped up on the part that says "Consider the action of ##G## on ##\operatorname{Syl}_2(G)## by conjugation." My question is, how is this a well-defined action if ##\operatorname{Syl}_2(G)## is not normal? Isn't this...

Hello, I am contacting you because I would like to know if there is a way to simulate quantum loop theory. Indeed, the S-Knots are much more complex objects than graphs because between the points there is a curve that can be knotted. S-Knots are graph embeddings in 3D and I do not see how such...

Homework Statement Let ##G## be a group. Let ##H \triangleleft G## and ##K \leq G## such that ##H\subseteq K##. a) Show that ##K\triangleleft G## iff ##K/H \triangleleft G/H## b) Suppose that ##K/H \triangleleft G/H##. Show that ##(G/H)/(K/H) \simeq G/K## Homework Equations The three...

Just looking for extra critique here: I'm a 2nd year math and physics student at a good uni in Canada. My average is in the 70s (B range, hoping to bring up to an 80/A- by the end of second year). The good thing is that Canadian unis will only look at my most recent 4 semesters or so (though I'd...

Hi folks. I am trying to reconcile the additive colour theory of light with more traditional grade school colour mixing. For example, we all know that blue paint plus yellow paint makes green paint. How do we explain this from the perspective of light? So the yellow paint appears yellow because...