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-3 votes
0 answers
30 views

What if proton is heavier than neutron? [closed]

What really happens to the atom if proton gets heavier than a neutron. I've heard that proton emits radiation. Plz explain
1 vote
0 answers
18 views

Is angular velocity about any point in a rigid body always the same?

Suppose I have a disc that is in translational as well as rotational motion. Doubt 1 If we talk about the angular velocity of the disc, about which point is this angular velocity measured? (I mean to ...
1 vote
1 answer
32 views

Question on special relativity

I am trying to learn special relativity. If we consider two inertial reference frames with spacetime co-ordinates $(t,x,y,z)$ and $(t',x',y',z')$ and let there be 2 observers who measure the speed of ...
0 votes
3 answers
18 views

Convergence of rays at focal plane after reflection from concave mirror

My teacher taught us that rays parallel to each other(but not necessarily parallel to the principal axis), after reflection from a concave mirror,get converged at a sharp point somewhere on the focal ...
0 votes
0 answers
3 views

Will the electrical potential difference between the Windward and Leeward sides of a mountain range generate electrical current?

I would like to know if its possible that the electrical potential difference between the Windward side and the Leeward side of a mountain range would be enough to generate a constant electric ...
0 votes
1 answer
228 views

Wheel rolls hitting curb, how is the force of the curb on the wheel related to the initial velocity of the wheel?

To find the force for a wheel to scale a curb one must find where the force forwards produces a torque that is larger than that of the weight of the wheel but how can one relate this to the intitial ...
0 votes
2 answers
33 views

Can the Strong CP problem be explained by the cancellation of quark electric dipoles by dipoles from some as yet undetected matter surrounding quarks?

I am not a mathematical physicist but from popular science articles I get the impression that CP violation occurs because quarks unexpectedly don't produce an electric dipole. If this is correct could ...
0 votes
0 answers
5 views

Calculating temperature change out of a room

Currently I'm trying to find how the outside temperature affects the internal temperature of a room through its walls. I'm trying to use the convection heat transfer equation to find the exterior wall ...
-2 votes
2 answers
35 views

Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
2 votes
1 answer
78 views

Looking for papers that claim that spacetime is emergent

This article states: It’s really striking that for most of the plausible theories of quantum gravity that we have, in some sense their message is, yeah, general relativistic spacetime isn’t in there ...
1 vote
1 answer
522 views

Finding the state space representation of a dynamic model with the force and angle as control inputs vector

I am trying to design a controller to control the angle of the force on my mobile rigid body. I some questions: I am not sure how to write the state space representation with the force, $F$ and angle,...
1 vote
2 answers
128 views

Vertical trajectory of a projectile with quadratic drag

I was wondering is there is an equation (or function) that can predict the apogee time and height of an object given its current acceleration and the usual constants ( mass, drag coefficient, cross ...
14 votes
4 answers
975 views

Molecular origin of solid-liquid and solid-vapour surface tension

I understand that surface tension arises at the liquid-vapour interface due to the asymmetric nature of long-range attractive forces and the short-range repulsive forces acting on the interface where ...
0 votes
1 answer
64 views

Gauge transformation rule for $dA$, where $A$ is the gauge field

Let $G$ be a non-Abelian simple compact gauge group and $\{ t^\alpha\}$ be a normalized set of generators for its Lie algebra $\mathfrak{g}$. Let $C^{\alpha \beta}_\gamma$ be the coupling constant for ...
0 votes
2 answers
39 views

Entangled Photons passing different polarizers

Consider two entangled photons leaving a source. Both are polarized at angle 0. One travels to the left and the other to the right. The one on the left encounters a polarizer at 30 degrees and the one ...
0 votes
2 answers
109 views

Doubt on conservation of angular momentum for Kepler's laws

Just before proving Kepler's laws, my Professor claimed that if $\vec{F}$ is a central force with center $O$ and it is the only force acting on a point $P$, then the trajectory of $P$ is a curve plane....
9 votes
1 answer
3k views

Deriving Virasoro algebra question

I'm reading a book Lie groups, Lie algebras, cohomology and some applications in physics by Azcarraga and Izquierdo, and on page 347, when deriving the exact form of the central extension term I came ...
0 votes
2 answers
624 views

Electric field inside current carrying conductor

Is the electric field inside current carrying conductor changing electric field or it is a constant electric field? And how this electric field produce magnetic field?
0 votes
1 answer
27 views

Moving laser beam passing over stationary circular opening

I am in need of help with the following situation. I appreciate any insight. Imagine a circular laser beam of diameter d1 moving at velocity v passing over a stationary circular opening of diameter d2 ...
0 votes
1 answer
336 views

What is the formal definition of Coupling efficiency

Does anyone knows the formal definition of Coupling efficiency? I have been reading the term in photonics devices and optics. I have been searching for it, but I could not find any. Thanks for the ...
2 votes
0 answers
156 views
+50

Missing counterterms in $\phi^3$ + $\phi^4$ theory in 1PI effective action

I hope I'm just overlooking something. The Lagrangian is as follows: $$\mathcal{L}=\frac{1}{2}(\partial_\mu \phi)^2-(\frac{1}{2}m^2\phi^2+\frac{1}{3!}g\phi^3+\frac{1}{4!}\lambda\phi^4)$$ and I just ...
0 votes
0 answers
10 views

Loop Effect of Photon Propagator in T-channel of $\Phi 3$ theory

In Schwartz's QFT chapter 16, he calculates the loop effect of photon propagator, with the choice of Pauli-Villars regulator, the scattering amplitude would be $$\mathcal{M}_{\text{loop}}(p) = \frac{g^...
0 votes
1 answer
134 views
+50

Do lasers with optical isolator or synchrotron radiation sources allow for Rabi cycles?

In Rabi cycle two-level system cyclically transitions between ground and excited state - bringing question where their energy difference goes during these transitions? For transition from ground to ...
0 votes
1 answer
54 views

Are there closed simply connected 2D manifolds that do not require a third dimension?

In the context of cosmology, space is commonly described as potentially having a global curvature that can be positive, zero, or negative. A common way that textbooks describe positive curvature is by ...
3 votes
2 answers
429 views

Are there Schwarzschild solutions to EFE with the Landau-Lifschitz Pseudotensor?

I read that solving the Einstein Field Equations can sometimes lead to the problem of non-conservation of energy and that the Landau-Lifschitz Pseudotensor resolves this problem. I can't however find ...
5 votes
3 answers
430 views

Trouble understanding the classic approximation of a black body as a hole on a cavity

While studying the Rayleigh-Jeans attempt to explain the spectral energy distribution of black bodies I have trouble understanding the concept of a black body as a small hole on a cavity. We define a ...
0 votes
0 answers
31 views

Sources for different treatments of thermodynamics [duplicate]

Clarification: I know that information entropy and entropy are different, yet there is clearly a relation. Hence why I am asking about that relation and how heat comes into it. I don't really ...
3 votes
1 answer
242 views

Chirality oscillations in weak interaction

As far as I have understood, the mass $m$ of a fermion causes a coupling of the both chiralities $\psi_L$ and $\psi_R$. This coupling would induce an oscillation of the chirality within a time scale ...
0 votes
1 answer
29 views

What force or field is associated with the weak hypercharge?

So what is the force or field associated with the weak hypercharge in post-SSB?
0 votes
1 answer
43 views

Elastic vs inelastic scattering in particle physics

Does elastic scattering occur via the Z boson and inelastic scattering via the W boson? If so, why? Does it have something to do with the fact that interactions via the Z boson don't change quark ...
0 votes
1 answer
596 views

Calculating the expectation value of a spin operator in a uniform magnetic field

I'm trying Usually for these types of questions, I'm used to the field being in a specific direction. For example, if the field was in the $z$ direction, I could find this solution by checking $|\...
0 votes
2 answers
56 views

Quantum Mechanical Current Normalisation

Consider an electron leaving a metal. The quantum-mechanical current operator, is given (Landau and Lifshitz, 1974) by $$ j_x\left[\psi_{\mathrm{f}}\right]=\frac{\hbar i}{2 m}\left(\psi_{\mathrm{f}} \...
0 votes
1 answer
9 views

Doppler shift from a moving reflector and source if only the relative velocity is known?

Suppose there is a device which is producing and listening to sound (sonar), a reflector is moving with respect to device and the velocity of reflector and device with respect to the air is not known, ...
-1 votes
0 answers
39 views

Does this equation imply non-linear waves? [closed]

For one-dimensional bounded domain $x \in [0, L]$ consider $\partial_{t} v = -\frac{1}{\rho}\partial_{x}\rho - v $ $\partial_{t} \rho = -\partial_{x}\rho v$ with initial and boundary data as $v(0, t)=...
0 votes
0 answers
47 views

How to expand $(D_\mu\Phi)^\dagger(D^\mu\Phi)$ in $SU(2)$

I would like to calculate the following expression: $(D_\mu\Phi)^\dagger(D^\mu\Phi)$ where $D_\mu\Phi = (\partial_\mu-\frac{ig}{2}\tau^aA_\mu^a)\Phi$ and $A_\mu^a$ are the components of a real $SU(2)$ ...
0 votes
0 answers
22 views

Confusion about time reversion and the Feynman-Stuckelberg interpretation

The Dirac equation $(i\hbar\gamma^{\mu}\partial_{\mu}-mc)\psi(\mathbf{x},t) = 0$ admits solutions with positive and negative energies. In the Feynmann-Stuckelberg interpretation we view negative ...
2 votes
1 answer
433 views

Komar Charge Derivation from Killing Current

We can define a divergence-less current from any Killing vector field $\xi^a$ by $$ J^a[\xi] = \xi_b R^{a b}$$ I would like to show that \begin{equation}\star J = \mathrm{d}\star\mathrm{d} \xi.\...
0 votes
1 answer
26 views

Why in two block system, both block tends to have same velocity at maximum potential energy when no external force is applied? [closed]

Consider a hemispherical bowl and a block placed inside it if the bowl is given velocity $v$ and given that there is no friction, the block will gain kinetic energy and then will rise to a maximum ...
0 votes
0 answers
35 views

How well does a cavity with a hole approximate a black body?

Cavity with a hole is a frequently cited approximation to a black body (more precisely, it is the hole that is the black body here): Is there a simple estimate of how well such a cavity approximates ...
7 votes
2 answers
1k views

Hermitian conjugation in Radial Quantization

I'm a little confused about Hermitian conjugation in a radially quantized CFT. Now, in the Minkowski theory, Hermitian conjugation leaves the coordinates invariant, i.e. $t^\dagger = t$ and $x^\dagger ...
0 votes
4 answers
150 views

Proper Time Along a Trajectory with Changing Velocity

I'm relatively new to SR and just encountered the Twin Paradox. I don't think I had trouble understanding the resolution to the paradox, but I was curious how an observer in an inertial reference ...
0 votes
1 answer
356 views

Circular motion and banked roads question

I can't work out c) for the following question, and I'd just like some help clarifying why my solution is wrong. Part a) and b) are fine. A car rounds a bend on a road that follows the arc of a ...
-7 votes
0 answers
54 views

Have I correctly integrated Quantum Mechanics with General Relativity by involving the expectation value of the the energy-momentum tensor from QFT? [closed]

Have I correctly integrated Quantum Mechanics with General Relativity by involving the expectation value of the energy-momentum tensor from quantum field theory? Why the Energy-Momentum Tensor is a ...
0 votes
1 answer
33 views

Dipole term in light-matter interaction

I have a question regarding the description of the term “dipole” in light-matter interactions. If I understand it correctly, there are 3 different things that one can declare as a dipole during light-...
0 votes
0 answers
23 views

Energy of the gravitational field within a sphere of radius $R$ in the Schwarzschild metric

The Landau-Lifshitz energy-momentum pseudotensor $t^{μν}$ is defined by $$16πt^{μν} = -2G^{μν} - g^{-1} \left[ -g \left( g^{μν}g^{αβ} - g^{μα}g^{νβ} \right) \right]_{,αβ}$$ where $g=\text{det}[g^{μν}]...
8 votes
2 answers
2k views

Current geometry and Ampere's law

Under the right circumstances, Ampere's law $\oint \vec H\cdot d\vec \ell=I_{encl}$ can be used to deduce the field $\vec H$ at a point from the current enclosed by the circuit which produces $\vec H$....
1 vote
0 answers
27 views

Energy output calculations for the very big heat exchanger

It recently emerged the concept of using deep wells as heat exchangers. It can be visualized as a long (2000 m) vertical tube with an inner diameter of 162 mm (the outer pipe diameter is 177.8 mm, ...
1 vote
0 answers
60 views

Why does a moon's orbit get more circular with time?

I understand that there is a transfer of energy between a moon and a planet depending on whether the moon is orbiting faster or slower than the spin rate of the planet. This would obviously change the ...
2 votes
1 answer
104 views

Derivation of Schrödinger equation in Feynman-Hibbs

I am going through the derivation in chapter 4-1 of "Quantum Mechanics and Path Integrals. Emended Edition" by Feynman and Hibbs. The chapter starts with a proof of the equivalence of the ...
8 votes
5 answers
1k views

Do you always experience the gravitational influence of other mass as you see them in your frame?

You see a galaxy far away. That galaxy is attracting you with a certain amount of gravity. I'm wondering if the gravity influence of the galaxy on you, as measured by you, always ends up being what ...

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