Theory Definition and 1000 Threads

What is the basic idea and purpose of the thermal field theory? I don't need a full in depth description of it, not at the moment at least. I am just trying to understand how it is relevant in the calculation of angular distribution of temperature of CMB(Comic Microwave Background) over the sky.

Homework Statement $$ L = -\frac{1}{2} (\partial_{\mu} A_v) (\partial^{\mu} A^v) + \frac{1}{2} (\partial_{\mu} A^v)^2$$ calculate $$\frac{\partial L}{\partial(\partial_{\mu} A_v)}$$ Homework Equations $$ A^{\mu} = \eta^{\mu v} A_v, \ and \ \partial^{\mu} = \eta^{\mu v} \partial_{v}$$ The...

I am 2nd year physics undergrad. Just want to study a bit about materials in my free time. I have no idea about engineering books. Please suggest some good books. Thanks.

So I have been reading '2D Topological Quantum Field Theory and Frobenius Algebras' by Joachim Kock recently and I couldn't help but wonder, how is this related to physics? I'm currently in the first chapter and he defined a TQFT as a monoidal functor. Now this seems somewhat abstract (which I...

Who am I kidding? Of course it is. But, everywhere I look, the series of increasing levels of orbitals is till σ*2pz only That's all. So if I need to find bond order of , say, some molecule with greater number of e- like BF3 with 24 electrons, how do I proceed?

One of the constants in chaos theory is symbolically labeled as beta, however I haven't found an official definition. The other constants Prandtl and Rayleigh deal with viscosity and diffusivity so they must be appropriate for the specific situation. Is beta simply a constant that can be changed...

In asking a question about analysis textbooks there was a bit of a chat about things like S = 1 - 1 + 1 - 1 ... = 1 - (1 + -1 +1 -1 ...) or 2S = 1 or S=1/2. I will say straight away the answer to what's going on - what infinite sums are, are simply definitions and believe it or not there are a...

What was the problem between Maxwell's EM theory and the principle of relativity? Why went the theory against the principle? I understand that the EM theory says that Light was a wave and ether is it's medium. On the other hand the principle of relativity says that there is no state of...

Allegedly, string theory (in it's simplest form) predicts that cosmological constant must be negative (or zero). Can someone explain where does this result come from? A reference would also be welcome.

Homework Statement A particle moves on the ##xy## plane having it's trajectory described by the Hamiltonian $$ H = p_{x}p_{y}cos(\omega t) + \frac{1}{2}(p_{x}^{2}+p_{y}^{2})sin(\omega t) $$ a) Find a complete integral for the Hamilton-Jacobi Equation b) Solve for ##x(t)## and ##y(t)## with...

How work AC/DC current in Quantum Field Theory

Art Hobson said that quanta propagate in space to infinity. (sorry can not give a link)

How work triboelectricity in QFT? Materialists exchange electrons as well as in classical theory?

It is very difficult for me to understand that a theory based only in "very logical" and "common sense" assumptions (S-Matrix theory, prestring era) makes (some) valid predictions in non-p QCD, while lattice QCD does not. Could the experts comment on this subjet? P.S.: Not interested in string...

Hello guys, I'm wondering if there are some important restrctions on the 'applicability' of first order perturbation theory. I know there's a way to deduce Schwarzschild's solution to Einstein's field equations that assummes one can decompose the 4D metric ##g_{\mu\nu}## as Minkowski...

The Klein-Gordon equation has the Schrodinger equation as a nonrelativistic limit, in the following sense: Start with the Klein-Gordon equation (for a complex function ##\phi##) ## \partial_\mu \partial^\mu \phi + m^2 \phi = 0## Now, define a new function ##\psi## via: ##\psi = e^{i m t}...

What is exactly Weizsäcker's ur-alternatives theory? How is it related to digital physics theories? Is it related to pancomputationalism? Does it defend that a universe can be described as being fundamentally made of qubits? Would this mean that that universe would be fundamentally made by...

Homework Statement Hi, I am looking at the attached question, parts a) and b).Homework Equations The Attempt at a Solution so for part a) it vanishes because in the ##lim \epsilon \to 0 ## we have a complete derivative: ## \int d\phi \frac{d}{d\phi} (Z[J]) ## for part b) we attain part a)...

Hello all, Can you tell me what is the best book to study QFT when you are thinking to follow a PhD in cosmology (Dark energy, scalar fields, extension to GR, string theory).

I find the de Broglie-Bohm pilot wave theory interesting but what I still feel missing in the descriptions I could find so far is that it reformulates what we already know but nobody speaks of new testable predictions that could eventually distinguish it from other interpretations (such as a new...

Hello guys, i`m currently making simulation of 2 dimension rolling disk on elastic sin/cosine plane. I`m just wondering if the theory applicable.

So during my PhD I've done one analytic based theory paper with one advisor and will now do an experiment paper with another advisor. I'm curious as to how this will look applying for postdocs. Would this allow me to apply for either theory or experiment? Or would it just make me look not...

Hello! I am reading Griffiths and I reached the Degenerate Time Independent Perturbation Theory. When calculating the first correction to the energy, he talks about "good" states, which are the orthogonal degenerate states to which the system returns, once the perturbation is gone. I understand...

Hello, I am currently taking a circuits class and I was looking for the solutions manual for the book Basic Circuit Theory by Charles Desoer. I haven't been able to find it anywhere but I really want it to practice more of the problems. I am able to do some but I never know if they are right or...

I am trying to read about and understand string theory. But in trying to understand how it reconciles with the world of quantum field theory and quantum mechanics, I am getting a little confused. How does the string move through and propagate through the quantum field? Does string theory...

Hello Everyone. I Was Wondering how excatly the Gauge invariance of the trace of the Energy-momentum tensor in Yang-Mills theory connects with the trace of an Holonomy. To be precise in what I'm asking: The Yang-Mills Tensor is defined as: $$F_{\mu \nu} (x) = \partial_{\mu} B_{\nu}(x)-...

Besides the Feynman lectures on gravitation, I'm looking for modern and complete treatments of the topic of classical gravitation as a field theory in flat space time. Any suggestion?

Homework Statement Approximately 4% of the intensity of light is reflected at a glass-air boundary. Classically one expects roughly 8% of light to be reflected from a thin glass plate (4% at the front and back boundary). Outline briefly what quantum theory predicts for a single photon instead of...

I'm self-studying field theory and trying to solidify my understanding of index manipulations. So I've been told that there is a general rule: " If the index is lowered on the 'denominator' then it's a raised index". My question is whether this is just a rule or something that can make sense...

Homework Statement Homework EquationsThe Attempt at a Solution How to do part biii? I tried to find change of U and W, then use ΔU-W=Q=0. I can find the change in U by using the fact the rms of the x-component of the velocity is doubled. Therefore, originally, if isotropic <c2> =...

In Stanley Kubrick's Dr. Strangelove or : How I Learned to Stop Worrying and Love the Bomb, is depicted, rather comically, a mad scientist who understands that the doomsday weapon is actually an absolute deterrent against nuclear war. The only misfortune is that nobody knew about it in time as...

I'm wondering if one can arrive at E=mc^2 using only the physics of the late 19th century, in the following way: As light waves pass over an electrically charged particle, they push it in the direction of the wave motion, transferring both (kinetic) energy and momentum to the particle. Let's...

Am I understanding it correctly that if you keep acting with an internal 2-dimensional creation operator on a string you will get heavier and heavier particle from the 11-dimensional (26 dimensional) point of view? If so, how come we haven't observed those particles in the real life? Is it...

A quick question: are there known solutions to superstring theory that reproduce all the properties of the standard model at low energy? I mean: three families, gauge groups, pattern of symmetry breaking, correct quantum number assignments, etc. It may be that the question is not precise...

Prove that if a simple graph G has 6 vertices then G or its complement has a subgraph isomorphic to ##K_3##. The proof begins by noting that is must be the case that G or its complement as a vertex with degree at least 3. Why is this the case?

Prove in any axiomatic set theory that:2ε{a,2,b} , where a,b are letters

Quantum mechanics replaces the classical concept of cause and effect with probabilities. The best explanation: it just is. While the Heisenberg Uncertainty Principles hold in quantum field theory does QFT offer a different interpretation to this concept? Or at least mitigate some of the...

Hello! If the Library of Babel has 10^(2,000,000) books, does anyone think that it is possible to create a quantum state (with a quantum computer) that represents this Library? I think that in a classical way it is impossible, but in a quantum way? I find it quite interesting! What about you? :)

What exactly is the usefulness of formal logic theory? And how much useful is it? I believe that most of us have an intuitive sense of logic, which has to be very useful throughout our lives and just about for every situation we can think of. Given that, I came to wonder what more does formal...

Is the Theorey of relativity that there is no absolute movement, only movement of one frame relative to another or that there is absolute movement but we cannot measure it ?

Hi everyone. As a graduate student in statistics, I had taken a graduate course in measure-theoretic probability theory. In a conversation with the professor, he had remarked that if I wanted to pursue further research on some of the topics covered, it may be wise to do background reading or...

I’m often not sure what science writers mean when they use the word “observe.” I was recently re-reading Einstein’s book on relativity and it’s “observe” this and “observe” that, in a very simplistic sense. What’s “observable” to me is blue and green and red, etc., and the apparent spatial...

Consider a place where General Relativity is the appropriate theory, but suppose we consider just a tiny volume, so to speak, of space-time.. which is to say we are observing a phenomenum for a very short amount of time and the "laboratory" is also very small in space. Under these circumstances...

Homework Statement Homework Equations All needed are in the picture above (i hope so) The Attempt at a Solution to me it is extremely difficult because it is so complicated with many notations. Also, I actually don't know how to read the question properly to answer it Is E(beta) is the...

Homework Statement Find the known pythagorean triangles with sides of integers lengths, given the area of the pythagorean triangle is 60. Homework Equations Pythagorean triangles are right angled triangles. a primitive pythagorean triple is of the form: x=2mn y=m^2-n^2 z=m^2+n^2 gcd(m,n)=1...

I have found a general result for certain exponential integrals that may be of interest to those involved with using path integrals. I am not certain that I am applying it correctly but it appears to work, and I can reproduce results quoted in various textbooks , using it. This may however be...

As I understand it Horava Lifschitz theory breaks lorentz invariance at high energies. Does this mean we should see photons from gamma ray bursts leave a signal of varying speeds of light for different frequencies?

Hello, everyone! I am a lover of physics, specifically that of the quantum type. The very specific question I have is the exact scientific definition of "information" pertaining to string theory. Any insight is good insight!

Hello! What makes a theoretical model stand out compared to others. I was thinking about the Higgs mechanism and the fact that there were quite a lot of other models (proposed in the 60's-70's) to explain symmetry breaking, which (I assume based on the fact that they got published) were...

[Moderator's note: This thread is spun off from another thread since it was dealing with a more technical point that is out of scope for the previous thread. The quote that starts this post is from the previous thread.] I feel the same about transformations of Dirac matrices and Dirac field...