1
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0answers
4 views

Anyon Lagrangian

The discussion of 2D quantum mechanics of two identical particles may be started (as written in the following article) with Lagrangian $$ L_s = \frac{\theta}{\pi} \dot{\phi} $$ where $\phi$ is ...
1
vote
3answers
19 views

Are fields intuitive choices to explain forces?

Fields are used to explain all the forces with respective particle being their facilitators. However, are fields intuitive choice to explain the forces? The physical significance is not very apparent. ...
0
votes
0answers
11 views

Srednicki's QFT: LSZ Reduction Formula for an Interacting Field Theory

I'm reading the chapter on Scattering Amplitudes and Feynman Rules from Srednicki's Qunatum Field Theory. Here's an excerpt from the chapter: I'm not sure of how $(10.6)$ has been written or ...
0
votes
0answers
6 views

What is the ultimate “matter reaching diameter” (radius) for a laser beam with information sent out today compared to the observable universe?

Diameter (radius) refers here to the distance the laser beam can travel to reach matter before Dark Energy will make this impossible. Hubble's Konstant implies an expanding universe in which ...
0
votes
1answer
10 views

Number of free parameters in a Standard Model with Neutrino oscillation

In two related questions, it was asked how many free parameters the standard model has. Without Neutrino oscillation, there are 19 free parameters. Now it turned out that Neutrinos have a mass aswell, ...
0
votes
1answer
14 views

Relativistic invariance of cannonical field quantisation

When I read Mukanov's book in "Quantum effects in gravity", I found the following interesting remark at p. 57. Remark: Lorentz invariance.To quantize a field theory, we use the Hamiltonian ...
0
votes
0answers
8 views

How to explain implicit time dependence to someone?

I am trying to explain what implicit time dependence is and how it differs from explicit time dependence, but I'm unsure how "sound" my explanation is. Here is what I said: Suppose I have a function $...
0
votes
0answers
6 views

Scalar power spectrum in Starobinsky inflation

I am trying to find the scalar power spectrum $P_S$ for Starobinsky inflation in terms of k, so that I can derive the scalar spectral tilt using the equation $P_s \propto k^{n_s-1}$ I can only find a ...
1
vote
0answers
25 views

How does a bicycle remain stable when in motion?

I could understand it at a theoretical standpoint but how can one represent the dynamic stability of the bicycle mathematically using a vector diagram ?
-2
votes
0answers
19 views

If the (space, spacetime) is origin of every things, then what is the physical propertiese of (space, spacetime)? [on hold]

If the (space, spacetime) is origin of everythings, then what is the physical properties of (space, spacetime)?
2
votes
1answer
26 views

What does a physical surface look like at a subatomic level?

At the macroscopic level, we are all quite familiar with the concept of a physical surface. From wikipedia: https://en.wikipedia.org/wiki/Surface_(topology) In mathematics, a surface is a ...
0
votes
1answer
9 views

Current flow in a Bridged T filter

Currently Learning about circuits and have been given the following question. "The circuit below is a bridged T filter. Label all of the current directions and use complex impedance analysis to ...
0
votes
1answer
16 views

Distance covered by a wheel in time t rotating at a certain angular frequency

I'm a web developer who has lost his touch with Physics 6 years ago and now I'm implementing a certain animation, I just want to know whether I'm calculating it correctly Given a wheel of radius $r$, ...
-1
votes
0answers
17 views

Work In Vertical Circular Motion [on hold]

A body of mass 2 kg is moving in a vertical of radius 2 m. The work done when it moves from the lowest to the highest point is?
0
votes
0answers
20 views

Microscopic form of Ohm's law

Microscopic form of Ohm's law is: $$\vec j = \sigma \vec E$$ Where $\vec j$ and $\vec E$ is the electric density and electric field at a point on the conductor respectively. $\sigma$ is the ...
0
votes
2answers
45 views

Difference between measurement and expectation value?

Does measurement mean simply acting on a wave function by a physical observable? Or finding the expectation value of the physical observable? I understand the result is same if the function is an ...
0
votes
2answers
36 views

Danger Zone for Aircraft

Question Statement:- An enemy jet is flying at a constant height of $250\text{ m}$ with a velocity of $500\text{ m/s}$. The fighter jet passes over a n anti-aircraft gun that can fire at any time ...
0
votes
0answers
13 views

Simulating a lens effect given its light transmission curve

What is the algorithm for processing image so it appears like viewed through the lens with specific light transmission curve? It is possible to convert some wavelength to RGB color but what are the ...
1
vote
2answers
41 views

Equation of motion of a simple pendulum

Consider a simple pendulum of length $l$ moving in $(x,y)$ plane. Assume its point of attachment is being jiggled by external forces with prescribed acceleration $a(t)=(a_x(t),a_y(t))$. Let $\theta(t)$...
1
vote
2answers
20 views

Charge on capacitors in series

'When there are 3 capacitors connected in series, charge across each capacitor is the same.' Okay so say we consider three caps made of plates of the same conducting materials and same dielectric ...
2
votes
0answers
51 views

The Feynman propagator and the $i\epsilon$ prescription

The Feynman propagator is usually represented in the i-epsilon form and texts solve the integral in this form (as opposed to doing the Feynman (time-ordered) contour on the real axis). Restricting ...
0
votes
1answer
38 views

What does it mean to say “the fundamental physics is contained in…”?

This is very common to show up in books. Here's one example from Thomson's Modern Particle Physics. When talking about the general expression for the $a \rightarrow 1+2$ relativistic decay $$\Gamma_{...
0
votes
0answers
23 views

Understanding a Derivation of the Wave Equation for Longitudinal Oscillations

I am working through problem 4.2 in Barton Zwiebach's "A First Course in String Theory." The problem goes as this: Consider a string with uniform mass density $\mu_0$ stretched between $x = 0$ and $...
2
votes
0answers
19 views

Why the changing magnetic flux horizontal component does not induce electricity?

Textbooks just seem to utter that change in the magnetic flux that is 'piercing' the plane contributes to electricity induction. They don't explain why. Is there any intuitive explanation?
1
vote
1answer
41 views

Does the medium a magnetic field is propagating through affect its speed?

I'm wondering if a material's magnetic susceptibility or magnetic permeability would have an effect on the speed a magnetic field would propagate through it. I know it won't speed it up but I'm ...
0
votes
0answers
35 views

Doing a physics project with Machine Leaning [on hold]

for my studies I can choose a question or a problem which I can then try to solve in a project. Since I am interested in machine learning I thought that one could combine this project course with my ...
0
votes
1answer
27 views

Integer number of wavelengths after the wavefunction is normalized in a cubic box

One of the steps when learning quantum mechanics in three dimensions is to normalize $\psi$ in a cubic box of side $a$. In math terms $$\int\limits_0^a\int\limits_0^a\int\limits_0^a \psi^*\psi dxdydz=...
1
vote
0answers
41 views

Susskind's Theoretical Minimum, Error in General Symmetries Section?

On page 136 of Leonard Susskind's The Theoretical Minimum, Suppose the coordinates of an abstract dynamical system are $q_i$. The general idea of an infinitesimal transformation is that it is a ...
1
vote
0answers
26 views

Diagonal lorentz invariant matrix

Is there any general way to show that diagonal Lorentz invariant matrix must be proportional to $g^{\mu \nu}$? I can show it is true, but my proof is not clean enough for such a simple problem.
1
vote
3answers
68 views

Would it be possible to pull Mars and Earth closer each other?

The burden of travelling between Mars and Earth comes from the distance. If the planets were closer, life could spread to Mars more easily, ensuring the survival of the intelligent lifeforms. What ...
0
votes
3answers
38 views

Is a light wave's amplitude stretched, along with the “red shift” stretch - making it brighter?

When light waves are stretched and "red-shifted", is the amplitude of the light wave stretched as well, affecting the intensity/brightness of the light wave?
0
votes
0answers
23 views

Coleman-Mandula theorem and mass gap

I had a couple of naive questions about Coleman-Mandula theorem. One of the assumptions of the theorem is the non-existence of massless particles in the spectrum. Since we do have massless photons ...
0
votes
0answers
34 views

Bose-Einstein condensate effect

Does every boson gas go through the condensate effect? Could there be a boson gas with high energy (photons for example) that would have enough energy to be at different quantum states even at 0 K?
5
votes
1answer
45 views

Is there a delay in the effect of the gravitational or electromagnetic force if a secondary body suddenly appears? [on hold]

If the sun were to suddenly vanish in our solar system, it would take about 8 minutes for the Earth to exit its orbit. This is because the gravitational field of the sun would vanish at a rate of $c$. ...
4
votes
1answer
70 views

Why would speed of light be directional if spacetime is discrete?

In Feynman's Simulating Physics with Computers, Feynman states that "we might change the idea that space is continuous to the idea that space perhaps is a simple lattice and everything is ...
-2
votes
0answers
42 views

What is the time for which this plane is in danger of being hit by this cannon shell? [on hold]

A fighter plane is flying horizontally at a height of $250~\mathrm{m}$ from ground with a constant velocity of $500~\mathrm{m/s}$. It passes over a cannon which can fire a shell at any time in any ...
0
votes
3answers
46 views

gauss law and electric flux

Can you please explain me what is electric flux. I know it is $\oint\mathbf{E}\cdot\mathrm{d}\mathbf{S}$, but in many place its given flux means to flow. But how does electric field "flow"? Also if we ...
-2
votes
0answers
26 views

Parallel combination of cells [on hold]

In this circuit suppose that $E_1 >E_2$. This means that the positive terminal of $E_1$ will have a greater potential than the positive terminal of $E_2$. Then current should flow from the ...
5
votes
1answer
49 views

Use my example to explain why loop diagram will not occur in classical equation of motion?

We always say that tree levels are classical but loop diagrams are quantum. Let's talk about a concrete example: $$\mathcal{L}=\partial_a \phi\partial^a \phi-\frac{g}{4}\phi^4+\phi J$$ where $J$ is ...
6
votes
4answers
1k views

Is the deformation of spacetime, elastic deformation or plastic deformation?

Is the deformation of spacetime, elastic deformation or plastic deformation?
0
votes
0answers
32 views

Swirl velocity from circulation - Vortex

I have a vector field in cartesian coordinate $(x,y)$ with coordinate origin at vortex core. For calculating the swirl velocity $v_\theta$ I followed below steps, Step 1: Find the circle coordinates ...
0
votes
0answers
19 views

Calculating effective dielectic constant

I have a system of metallic nano-particles supported on glass where I have observed a difference in the in-plane dielectric constants of the metal ($\varepsilon_x$ is different from $\varepsilon_y$ ...
2
votes
1answer
33 views

Why do we get a diffraction pattern with a slit whose width is not comparable to the wavelength of the incident light?

In single slit experiments with sodium light whose wavelength is of order micrometer and slit width of order of hundreds of micron, we still observe the diffraction pattern. How do we explain this?
0
votes
1answer
36 views

Acceleration of a pulley system

The figure above shows a pulley system consisting of 3 masses ($m_1$, $m_2$ and $m_3$), a homogeneous wheel (radius R, mass M) and 2 massless pulleyes which are connected by a massless rope. Mass $m_1$...
3
votes
2answers
43 views

Infer the shape of a solid given the moments of inertia

Let's say we have a solid with uniform mass distribution, but we don't know its shape. However, we know the moment of inertia of the solid with respect to as many axes of your choosing as you want (e....
1
vote
0answers
24 views

Collision term in Boltzmann Equation

In Dodelson's Book, chapter 3, we have the collision term in Boltzmann equation is written as $$\int\frac{d^3p_1}{(2\pi)^32E_1}\int\frac{d^3p_2}{(2\pi)^32E_2}\int\frac{d^3p_3}{(2\pi)^32E_3}\int\frac{...
0
votes
2answers
104 views

Intuition for the identity $\epsilon_{ijk}\epsilon_{ilm}=\delta_{jl}\delta_{km}-\delta_{kl}\delta_{jm}$? [on hold]

One of the popular Kronecker delta and Levi-Cevita identities reads $$\epsilon_{ijk}\epsilon_{ilm}=\delta_{jl}\delta_{km}-\delta_{kl}\delta_{jm}.$$ Now, is there an intuition or mnemonic that you use,...
0
votes
0answers
15 views

Can a single photovoltaic semiconductor junction ever produce a voltage much above it's own band gap?

A simple model for a photovoltaic cell is a current source with a series resistor, and a few more items. The current from the current source is some fairly constant proportionality constant of the ...
2
votes
0answers
13 views

Modeling Optical Properties of Doped Crystals

I am interested in modeling the optical properties of crystals doped with lanthanides to investigate their luminescent properties. What would be the best way to pursue this? EDIT (In response for a ...
1
vote
1answer
52 views

If I spin around why do the stars not dissappear?

Galaxies at the far limit of the visible universe are moving away from us near the speed of light. There may be some beyond that that are moving away from us faster, so the universe appears to have an ...

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