2
votes
3answers
101 views

Mathematical Formulation of Classical Spacetime

I have seen two formulations of Classical Mechanics: Newtonian spacetime (learned it from the lectures of Professor Frederic P. Schuller): Definition: A Newtonian spacetime is a quintuple $(M, ...
0
votes
0answers
47 views

Can electric heat pumps be more efficient than electric coil heaters

I have been reading about the heat pumps/air conditioners on the web. I found this article which seems to be telling something which looks like clear violation of laws of thermodynamics. The article ...
4
votes
1answer
68 views

What is the $10$ in the $\mathbf{4}\otimes\mathbf{4}$ tensor product of $SO(6)$?

This is the question 22.D in Howard Georgi's Lie Algebras book, I thought about for a minute, but couldn't come up with a plausible answer. It's a fact that the SO(6) and SU(4) algebras are ...
2
votes
2answers
85 views

What´s the origin of the four rays that come out of the reflection of candlelight in our TV?

The reflection of a candlelight in our TV shows four emerging rays. The rays vary spacial and periodical and have a repeating pattern of the colours of the rainbow. The further the flame is from the ...
0
votes
1answer
49 views

Definition of the S-matrix

when I think about scattering process I reach to slightly another definition to the S-matrix. because I understand my reasoning I hope someone could refine it to a correct one so that I can have a ...
1
vote
0answers
32 views

Definition for a trajectory in phase-space

When we say "a trajectory in phase space", when the parameter is time, do we mean the set of points in phase-space corresponding to a continuous segment in time? Does it have to be continuous? Does it ...
1
vote
0answers
35 views

Thermodynamics: Apartment Airflow: What Am I doing wrong air

Our apartment is a sauna. But sometimes it's much much hotter inside the apartment than it should be (night time it's 68 degrees outside but thermometer still says 90 inside!). I have 2 fans, one ...
0
votes
1answer
61 views

Schroedinger and Klein-Gordon equation and their complex conjugate

Let's consider the Schroedinger equation \begin{equation} i\hbar\frac{\partial}{\partial t}\psi=-\frac{\hbar}{2m}\nabla^2\psi \end{equation} If I have a wavefunction $\psi$ as a solution, then its ...
-3
votes
0answers
30 views

Please read the problem below,the approach and explain where it's wrong and what's the true concept behind? [on hold]

Where should (A B C or D) charge $Q$ be placed so that the flux of electric field through the hemisphere remain unchanged? there is a charge $q$ at the center of hemisphere's base. Here's the ...
0
votes
0answers
15 views

How to calculate light transmission in dBm if it goes through SMF to MMF or MMF to SMF?

The question might be very basic, but I could not conclude it after thinking and searching about a couple of hours. If a light in fiber optics is launched in an SMF, therefore, it is connected to an ...
0
votes
0answers
30 views

Density matrix and basis

Given an hermitian operator $\hat{A}$ I can span the Hilbert space in terms of the eigenvectors $\lvert a_i\rangle$. For example in a spin $1/2$ system I can choose to work in a basis from the ...
-2
votes
0answers
21 views

Why are cirrus cloud those that contribute the most to climate forcing?

I read everywhere that most of the forcing produced by clouds is done by cirrus but I can't figure out why. It's obviously related to their IR absorption - emission...
3
votes
0answers
27 views

Predict liquid film thickness outside a cylinder, under the influence of a) external gas flow and b) heating of the cylinder

I tried to post this question on Computational Science SE, but I was really unsure about the most appropriate SE site. The question didn't attract a lot of attention, and since Physics SE was my ...
0
votes
1answer
54 views

Bloch sphere representation of $\sigma_x$ operator on $|1\rangle$

I am trying to visualize a Hamiltonian H=$\hat{\sigma_x}$ $$ \hat{\sigma}_{x} = \left( \begin{array}{cc} 0 & 1 \\ 1 & 0 \end{array} \right) $$ acting on the state $| 1 \rangle$. I can write ...
0
votes
1answer
39 views

EFE and Local Minkowski

Suppose we view the Einstein Field Equations (EFE) in the context of a boundary value problem with a given stress-energy tensor and boundary conditions. The problem is solved by finding a ...
-2
votes
0answers
21 views

Book on thermodynamics for International Physics Olympiad? [duplicate]

I'm a junior in high school studying for the IPhO and I've started learning thermodynamics as part of my preparation. I have a guide to the exam that says things like this will be tested: Carnot ...
-2
votes
0answers
51 views

Is it possible for humans to jump from such an height and still be fine? [on hold]

This is the game Assassin's Creed Syndicate and here's a video showing how Evie Frye jumped from the Big Ben into a haystack - https://www.youtube.com/watch?v=JfCQe7Lqe60 Those who do not want to ...
1
vote
0answers
19 views

What shape does magnetic dust take under the influence of its own magnetic field?

Recently, I came across some very powerful neodymium magnets (the flat cylinder kind), and I accidentally broke one by snapping two of them together quickly. What I noticed is that the two halves ...
-1
votes
2answers
20 views

Electricity and electric fields equations [on hold]

Whats the difference or relationship of $q$ between the equations $E=F/q$, $v=W/Q$ and $Q =ne$ ?
0
votes
0answers
44 views

Sum rule and dense limit

Is the finite size of lattice constant important for derivation of sum rules, for example, the sum rule for diagonal conductivity $\sigma_{xx}$: $$ \int \limits_{-\infty}^{\infty} ...
-2
votes
0answers
18 views

Gas thermodynamics: Kinetic energy change [on hold]

Think you have a rotating pipe and air at high pressure wants to flow from outer radius to inner radius close to the rotation center: question is here: Which of the following statement are correct ...
-1
votes
0answers
15 views

Warm and Hot dark matter density profiles

for Cold dark matter, density profiles are well known and easy to find information about - NFW,Burkert,Einasto, and others. but for some reason i couldn't find explicit expressions for the density ...
1
vote
1answer
31 views

p-cycles and Fluxes

I would like to ask why the existence of a non-trivial p-cycle leads to a non-trivial flux. I would say that e.g. for a five-form $F_{(5)}$ field strength , the flux is: ...
0
votes
2answers
43 views

Copper density modification

Can you increase the density of a material surface (metal) by surface treatment? For example commercial copper. If we take the ordinary OF copper (99.95%), I would expect not to have the tabulated ...
0
votes
0answers
20 views

How can I calculate the time domain correlation function in the frequency domain?

I have an operator $a(t)$, its correlation function is: $$<a(t)a^{\dagger}(t^{\prime})>=\delta(t-t^{\prime})$$ Now I need to find the correlation function in the frequency domain. i.e. to ...
0
votes
2answers
41 views

What does J cm-1 stand?

For an optical component, I got following number as an optical damage threshold from the company, damage threshold = 10 Jcm-1,20ns, 20Hz It looks like 20ns is ...
1
vote
3answers
43 views

Equations of motion derivation doubt

I just started on learning how to derive the equations of motion using calculus. This is my first time and I have a basic doubt. So $v = \large{\frac{dx}{dt}}$ Then, $dx = v dt $ What does this ...
-1
votes
2answers
53 views

Is it possible that there are stars working on fission?

Most/all stars are getting their energy from fusion of small atoms like our sun. But is it possible according to the laws of physics that there are stars getting their energy from fission fe with ...
1
vote
1answer
30 views

What is the Single Mode Approximation?

When Girvin and co-workers solved the excited collective modes called magneto-rotons in Fractional Quantum Hall liquids, they used something called the Single Mode Approximation (SMA). My question is: ...
4
votes
1answer
48 views

Can the efficiency of a thermodynamic cycle be worked out from a pV diagram?

Is it true that a pV diagram of a thermodynamic cycle with a specified scale on both axes is enough to calculate its efficiency (such as the one below)? Is it the area within the shape divided by the ...
0
votes
0answers
23 views

Are there explicit formulas for the eigenvalues and eigenvectors of a generic 4x4 density matrix? [migrated]

I have a 4x4 density matrix all of whose elements are nonzero. Its form is $$\begin{pmatrix} a & b & c & d \\ b^* & e & f & g \\ c^* & f^* & h & j \\ ...
3
votes
1answer
44 views

$W^{++}$ / $W^{--}$ Bosons in theory and experiment

I wonder whether there is any theoretical interest in and/or experimental search for double charged bosons, probably to be called $W^{++}$ and $W^{--}$. The latter would obviously turn an electron ...
-3
votes
2answers
44 views

Electric field $E$ due to a dipole moment

Why is the formula of $$E = kp/z^3~ ?$$ Why is it $z^3$ ? I want a physics answer not math please.
1
vote
0answers
53 views

Are tides just very very very weak spaghettification?

I was wondering as to why there are two tidal bulges instead of just one on Earth, and then I saw this diagram: The oval shape that the Earth's water is transformed into in this image reminded me of ...
2
votes
1answer
41 views

Different postulates and statistical interpreations of quantum mechanics

Hi I have a query about the difference of two aspects of the statistical interpretation of quantum mechanics given in the popular introductory quantum mechanics books "Introduction to Quantum ...
0
votes
0answers
15 views

How does electrical energy develop by concentrating ions on one side of a biomembrane?

In biology there is a topic called oxidative phosphorylation. In the first step of this process substrates such as isocitrate is oxidised and the electrons are transferred to coenzymes NAD+ or FAD ...
1
vote
1answer
36 views

Tractrix - velocity pointing to pulling point

It is said the tractrix is the curve described by a mass being pulled by a string, where the end of the string being pulled moves with constant speed, and the mass suffers a friction force. What is ...
2
votes
0answers
33 views

Integrating out heavy fields while preserving symmetries

The basic a-b-c for integrating out heavy fields what one learns when making the example of Fermi theory, is that if you have a Lagrangian $L= -\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+\frac{1}{2}M^2 V^\mu ...
-5
votes
0answers
29 views

On Carnot engine and heat pollution [on hold]

Suppose a power plant uses a Carnot engine to generate electricity, using the atmosphere at 300 K as the low-temperature reservoir. Suppose the power plant produces 1 × 106 J of electricity with ...
-1
votes
1answer
25 views

Global Hyperbolicity in spacetime Manifold [on hold]

If space time is timelike or null geodesically incomplete but cannot be embedded in a larger spacetime then we say that it has singularity. What does incompleteness means here?
1
vote
2answers
58 views

What is more basic thing to explain phenomenons : Energy or Force?

You know many physical happening are explained by considering forces or we can explain these phenomenon using energy (like energy conservation, etc.). so i was wondering that explaining the physical ...
1
vote
0answers
32 views

Very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth

I need a very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth. Currently, thanks to the algorithm which generates the position ...
-3
votes
0answers
20 views

Books for students [duplicate]

Can any one please suggest me books for physics. I need a book for good theory and concept . And a book for practice , it should contain some solved questions. The both the books should contain ...
1
vote
0answers
10 views

What is exactly the difference between an active and passive frequency standard?

In the case of passive atomic frequency standard, we take an atomic reference which has a resonant frequency response centered at certain particular frequency. Then we take a local oscillator and tune ...
1
vote
0answers
35 views

What to do when the fields are arranged in a matrix?

I am dealing with a Lagrangian in which the fields are arranged in an $N\times N$ matrix and i have to find the minima of the potential. Usually i would write the Lagrangian in components and then ...
-2
votes
0answers
17 views

Mathematical formula for maximum sound pressure level [on hold]

I googled a math equation for calculating Maximum Sound Pressure Level but couldn't help myself. What is it?
0
votes
1answer
45 views

Scattering in Schrödinger picture [on hold]

If we look at a scattering process in the Schrödinger picture for a Hamiltonian $H = H_0(t) + V(t)$ where $H$ is independent of time (because we examine a theoretical situation after accelerating ...
0
votes
1answer
38 views

Are pure Dirac fermions (electrons, quarks, …) allowed to have effective Majorana mass?

Charged particles such as electrons and quarks are not allowed to have a hard Majorana mass (see here). With 'hard' I mean an explicit mass term in the Lagrangian which would break the corresponding ...
36
votes
4answers
3k views

Why does LIGO do blind data injections but not the LHC?

The LIGO group has a team that periodically produces fake data indicating a possible gravitational wave without informing the analysts. A friend of mine who works on LHC data analysis told me that ...
0
votes
0answers
35 views

Noether current for a transformation for the Klein-Gordon Lagrangian

I have this Lagrangian density $$\mathcal{L} = \frac{1}{2}(g^{\mu\nu}\partial_\mu\phi\partial_\nu\phi^* - \mu_0^2\phi^*\phi)$$ with $g_{\mu\nu} = g_{\mu\nu}(x^\alpha)$ and I need to get the Noether ...

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