2
votes
0answers
48 views

Difference between positron and electron scattering in Coulomb field

In first order of perturbation theory the S-matrix amplitude for electron scattering in the Coulomb field will be (up to normalization factors) $$ S_{fi} = \frac{iZ q^2}{\sqrt{2E_{f}2E_{i}}}\bar {u}(...
1
vote
3answers
43 views

What are the means to consider that a specific function is phase of an oscillator?

I hope the experts of the field forgive me for this n00b questions, but I am just trying to understand physics. Assume the following function: $$\phi(t)=\omega t+\cos(\omega t)$$ The above function ...
6
votes
2answers
204 views

A question to clarify the use of divergent series in calculating the casimir effect

Some time ago I posted a question here on this forum. I would like to ask some questions regarding the way the energy per unit area between metallic plates is calculated. The full calculation is on ...
3
votes
2answers
237 views

If energy is just a conserved quantity how can it have flux and density?

As I'm very well convinced for now, the better understanding of energy we have today in Physics is that of a conserved quantity, i.e, a numerical valued associated with a system that remains the same ...
2
votes
2answers
396 views

How can I tell that circular motion is a solution for a particle confined to the surface of a cone?

I'm working on a problem where a particle of mass $m$ is confined to the surface of an inverted half cone (and is circling downwards due to gravity), with the cone's half angle $\alpha$. I chose to ...
17
votes
7answers
723 views

What is potential energy truly?

I have a problematic question for which I have been unable to attain a satisfactory answer. What is potential energy truly? - I have read about how potential energy can be seen as the "highering" ...
2
votes
1answer
96 views

The question about quantization of free EM field

Let's have the free EM field theory with Coulomb gauge: $$ \partial^{2}A_{\mu} = 0, \quad A_{0} = 0, \quad (\nabla \cdot \mathbf A ) = 0. $$ One of the ways of quantizing the field is the following. ...
2
votes
1answer
504 views

Trace of Fermion Loops in Effective Field Theories

I'd like to know whether we need to take the trace of fermion loops in effective theory in the same way that we need to do so for renormalizable theories. At first thought, it seems obvious that ...
2
votes
1answer
165 views

What are “parity considerations” in deciding the form of the Hamiltonian?

In "introductory Quantum Optics", by Gerry and Knight, the Jeynes model is considered. In this model of electron-EM field interaction the electron is approximated by a two state system ($\lvert g\...
0
votes
0answers
57 views

motion of electrons [duplicate]

Do electrons move randomly, with no preference of directions? And why electrons don't fall into the nucleus? About this question, I read the article on Chemistry wiki, which says that when electron ...
0
votes
1answer
66 views

Current and Voltage of electrostatic discharge

I conducted an experiment , i put a silver foil on a a CRT TV , then i open the TV, charging the foil (acting like a capacitor plate), if i approach a grounded rod to it , it will discharge with a ...
0
votes
0answers
153 views

How to do this index notation differentiation?

I am studying classical Maxwell fields and I am stuck on this differentiating part. How can I derive the result given below ? $$\dfrac{\partial}{\partial(\partial A_{\mu}/\partial x_{\nu})} \left(2\...
9
votes
1answer
591 views

Double double-slit experiment

Suppose I have a double double slit experiment. That is, I have an electron gun in the center, that shoots entangled pairs of electrons in opposite directions, one to each double slit. I tried to ...
1
vote
0answers
86 views

Physical applications of the mathematical curvature

I was studying multivariable calculus last semester and had one of the topics talking about a curvature, but we had no applications on it. So how does it help in physics? E.g. curvature of curve: $k=...
2
votes
1answer
162 views

Is there a standard reference where entropy is set equal to zero in property tables?

For practical considerations, it seems that entropy is only meaningful as a difference between states, like $\Delta s$ going from state A to state B. For an ideal gas, for instance, standard formulas ...
4
votes
1answer
1k views

Correspondence between wave function and state vector

I am confused with connection between state $| \psi \rangle$ of a quantum system and corresponding wave function $\psi(x)$ (at a given time). I have been told that for every state $| \psi \rangle$ we ...
3
votes
0answers
328 views

ER = EPR and Time Travel

In Maldacena-Susskind paper arXiv:1306.0533, they propose an idea of $$\text{ER = EPR}$$ the relation between the wormhole and the quantum entanglement. which ER means Einstein Rosen (ER) bridges, ...
3
votes
0answers
106 views

Does quantum mechanics require classical measurement apparatus?

I am trying to learn quantum mechanics and I have a question. Landau, in his quantum mechanics book says that it is in principle impossible to formulate basic concepts of quantum mechanics without ...
1
vote
1answer
103 views

Confusion about state of a quantum system

I am confused with the concept of state of a quantum system. First postulate of QM ussualy says that the wave function of the system contains all information about the state of the system. But reading ...
5
votes
1answer
1k views

How to derive Kepler's equation?

The Internet lacks, so far as I know, a derivation of Kepler's equation $$ M = E - e\text{sin}(E) $$ where $M$ is the mean anomaly, $E$ the eccentric anomaly and $e$ the eccentricity. Since there ...
4
votes
1answer
225 views

AdS3 soliton of Witten - for Hawking-Page transition

Are there explicit AdS$_3$ soliton solution? in the sense of Witten's Anti De Sitter Space And Holography and Hawking-page transition paper, by doing a $$\tau_E, y ,r \to y, \tau_E ,r$$ from a ...
7
votes
1answer
481 views

Was Einsteins work with relativity necessary for successful space travel?

So I know that Einstein and general relativity had huge impacts on the way we view the world, but how crucial were these scientific advancements to the success of our space programs? Would Newtonian ...
1
vote
0answers
80 views

According to Penrose, Weyl Tensor=0 is the start/end of the Universe. Must it =0?

If I understand Roger Penrose's theory, as the Universe expands and cools, matter is consumed by black holes. Eventually the black holes collide and evaporate so that there is only energy and the Weyl ...
2
votes
1answer
99 views

Killing vector contractions along isometric curves

Imagine $\xi_{\nu}$ is a Killing vector field on a manifold. Does $\xi_{\nu}\xi^{\nu}$ remain constant along any isometric curve defined by the Killing vector field? My guess is that yes since as ...
13
votes
3answers
595 views

Effect of linear terms on a QFT

I was always told when first learning QFT that linear terms in the Lagrangian are harmless and we can essentially just ignore them. However, I've recently seen in the linear sigma model, \begin{...
2
votes
2answers
651 views

What is relation between electrons and photon? [closed]

What is the relation between electrons and photons? Why do atoms get excited when their electrons come in contact with photons? Why do electrons go from a higher to lower energy level when emitting a ...
2
votes
1answer
255 views

What's an ideal wire?

I'm not talking about an ideal wire in a circuit (a wire with infinite conductance). I'm talking about an ideal wire in the case of the magnetic field of an infinite current carrying wire. What ...
0
votes
1answer
5k views

Why electrons get excited? [closed]

Why and how are electrons get excited and what happen inside an atom when electrons get excited?
1
vote
5answers
142 views

Why is the independence of orthogonal vector-quantities always implicit in books/lectures?

The "theorem" that I can "just" separately deal with orthogonal quantities (like horizontal and vertical force or velocity, etc), I never found explicitly mentioned, but just implicitly in the ...
2
votes
1answer
166 views

Do batteries lose charge?

Say I have a charge of +q and -q on the positive and negative terminals of a battery. If I connect wires to each terminal, but don't connect the wires (essentially creating an open circuit), the ...
4
votes
0answers
729 views

Time Evolution Operator in Interaction Picture (Harmonic Oscillator with Time Dependent Perturbation)

1. The problem statement, all variables and given/known data Consider a time-dependent harmonic oscillator with Hamiltonian $$\hat{H}(t)=\hat{H}_0+\hat{V}(t)$$ $$\hat{H}_0=\hbar \omega \left( \...
1
vote
2answers
932 views

Why do noble gases stabilize plasma discharges?

In the plasma literature, noble gases—usually helium or argon—are frequently said to 'stabilize' plasmas. For instance in this patent, the inventor states that the plasma can be stabilized "by adding ...
0
votes
1answer
81 views

If we hear a noise long enough, is it going to settle as tinnitus? [closed]

Some equipment sometimes have a high pitch ringing, and I was wondering out of curiosity: can noises (not only drive you crazy but also) settle and become permanent ringing in your ear if you are ...
0
votes
2answers
205 views

Function for curved line in log-log-plot

I've done experiments on the thermo-viscoelasticity of liver tissue and the following results ...
9
votes
3answers
301 views

Are there any serious alternatives to QCD nowadays?

I've read several posts here where people talk about the history of the developement of the theory of strong interactions. And they mention Regge theory, pomerons, S-matrix and so on. I'm confused ...
0
votes
2answers
398 views

What is the reason behind why a quantum particle cannot be at rest?

So I've seen different reasonings for this; which is correct, or are they both corollaries of each other? 1) For a particle to be at rest, we would know its momentum and therefore by Heisenberg's ...
2
votes
0answers
41 views

electrons in elecrtostatic force(please read specification given below) [duplicate]

when comb is rubbed with hair, and brought near small pieces of papers, small paper pieces gets a towards comb. Here the comb gets negatively charged and when brought near piece of paper where do ...
0
votes
1answer
139 views

Charging one thing with static electricity by using battery

How can I make one thing to get statically charged by using batteries but not friction ? For example charge a rod so it can attract shredding ?
3
votes
2answers
277 views

How to calculate the force acting on a magnet due to a solenoid

Can I assume both magnet and solenoid as magnetic dipole and use Coulombs law to find the force acting the magnet?
-1
votes
3answers
253 views

What is radiation(in simple words)? [closed]

I am a student who is interested in scientific facts. I want a simple definition for radiation. Neither too scientific, nor too simple.
0
votes
0answers
101 views

What is the most fundamental peice of matter? What is it that thing which can no more be sub-divided?

I know that there is theory that strings are the most fundamental particles. But if it is a string, then it can be 'cut' into pieces, and if it can be 'cut', then it can be cut at infinitely many ...
0
votes
0answers
31 views

Learning about group velocity, phase velocity and particle velocity [duplicate]

I am studying quantum physics and I would like to know a bit more in detail about group velocity, particle velocity and phase velocity. Can you guys suggest some books/online resources where I can ...
1
vote
0answers
194 views

Covariant Derivative with a Torsion Free Metric

Where $\triangledown$ is the covariant derivative and we are to assume that the connection is torsion free (that is, we can exchange the lower indices of the connection coefficients), how can I prove ...
3
votes
2answers
185 views

Quantum Philosophy a la John Bell

I recently discovered this website http://www.quantumphil.org/ and wondering whether Quantum Philosophy is an actual field, or just an aspect of QM? Apologies if this is in the wrong place.
0
votes
2answers
63 views

Why does chemical potential smaller than zero mean nondegeneracy and vice versa

In Mudelung's book, Introduction to Solid-State Theory, I have a confusion about the statement. Here, $x$ should be $\frac{\mu}{k_B T}$. I am cofused about his statement. Why does $x<0$ mean ...
4
votes
2answers
205 views

Why does $c_{-k,-\sigma}$ create a particle with momentum $k$?

In Mudelung's book, Introduction to Solid-State Theory, I am confused by the following statement. For many applications a further simplification is helpful. The concept of the hole presents us ...
0
votes
3answers
543 views

We need to find unit vector along the reflected ray [closed]

A ray of light on a plane mirror comes along a vector $i+j-k$ The normal on incidence point is along $i+j$ we need to find unit vector along the reflected ray. I am not able to solve and draw the ...
2
votes
3answers
2k views

Why do both plates of a capacitor have the same charge?

How do we know that both plates of a capacitor have the same charge? You could argue conservation of charge, but I don't see how conservation of charge implies the charge on both plates is the same. ...
-2
votes
1answer
109 views

If the wave function can be collapsed, can we collapse the particle function? [closed]

No doubt it's been questioned before so what is the theory or experiment? If there is an experiment.
0
votes
0answers
107 views

Field outside a solenoid?

Say you have a solenoid with diameter $d$ and length $L$. How can I show that as $d/L$ approaches 0, the field outside the solenoid is zero? I'm looking for a formal proof involving integration. ...

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