8
votes
0answers
59 views
What is the difference between scale invariance and self-similarity?
I always thought that these two terms are some kind of synonyms, meaning that if you have a self-similar or scale invariant system, you can zoom in or out as you like and you will always see the same ...
0
votes
1answer
25 views
Wigner characteristic function
I came across the "representation of a Gaussian state by its Wigner characteristic function". I don't know what Wigner characteristic function is and google results are not precise enough. Neither ...
-1
votes
1answer
33 views
Conservation of energy issue with pair creation/annihilation
Question: what is the energy balance in this situation?
(Fig A)
Two gamma rays collided and produced an electron/positron pair $(e-/e+)$.
(Fig B)
1. because all particles are accelerating ...
0
votes
0answers
29 views
Heisenberg Uncertainty Principle at a macroscopic level
At a macroscopic level, any physics interaction would require the two objects to be "measured" against each other, but what is what each macroscopic object perceives about the other one when it ...
1
vote
0answers
13 views
Calculate/Estimate the fractal dimention of the logistic map using box counting
This is the logistic map:.
It is a fractal, as some might know here.
It has a Hausdorff fractal dimension of 0.538.
Is it possible to calculate/measure its fractal dimension using the box counting ...
2
votes
1answer
70 views
Is glass a liquid?
I was told by a condensed matter physicist that glass is a liquid with a very high viscosity (it would be more precise to say that it is a supercooled liquid). The example given was that in cathedral ...
1
vote
1answer
33 views
Center of mass of a body on an incline
I am trying to reproduce a calculation by Carre et al. (1995) in which they calculate the shape of a droplet on an incline.
My issue is in the derivation of the potential energy (essentially the ...
1
vote
0answers
32 views
Maxwell-Boltzmann distribution
The short story is, that I have to calculate some transport coefficients, but using the the MB distribution as my distribution function.
What I currently need to solve is:
${{\mathcal{L}}^{\,\left( ...
0
votes
0answers
15 views
layered CMOS structure question
I am trying to understand the workings of a CMOS image sensor. I understand that increasing wavelength results in an increased penetration depth in the silicon often used in CMOS image sensors. What ...
0
votes
1answer
20 views
Lightning and Charge Displacement
There is something I don't really understand about flashes of lightning.
When a flash occurs, how come electricity be transferred at the speed of light since electricity's displacement is very slow ?
...
0
votes
0answers
53 views
Contour Integrals and Residues [closed]
I'm trying to figure out what it is all about, but my mind is blowing up. First of all, I have turned back and looked at the general definitions of integrals. Then I have looked to line integrals. ...
2
votes
1answer
60 views
Eigenvectors of a 4D rotation, and their interpretation
Let us define a 4D rotation by using two unit quaternions: $$\mathring{q}_l=\frac{a+ib+jc+kd}{\left|a+ib+jc+kd\right|}$$ and $$\mathring{q}_r=\frac{e+ib+jc+kd}{\left|e+ib+jc+kd\right|}.$$ They differ ...
0
votes
0answers
32 views
The imaginary time method and normalization [closed]
Hey there and thanks for giving time to look at my question.
I'm currently studying a 2D exciton spinor Bose-Einstein Condensate and am curious about the ground state of this system.
I'm using ...
1
vote
0answers
19 views
How sharp is the direction of magnetic field of a cone magnet?
I heard recently that cone magnets can be used to focus and direct the field sharply at one particular point in a particular direction. I jus want to kno how accurate and sharp this field is? And if ...
9
votes
2answers
235 views
Difference between $\Delta$, $d$ and $\delta$
I have read the thread regarding 'the difference between the operators between $\delta$ and $d$', but it does not answer my question.
I am confused about the notation for change in Physics. In ...
1
vote
0answers
38 views
Alternative interpretation of Off-shell internal QFT propagators?
In Quantum Field Theory in a (1, D - 1) space-time, to calculate transition amplitudes, we are using Feynman diagrams, where internal lines (internal propagators) corresponds to momenta which are said ...
2
votes
0answers
20 views
Equivalent of the Kirsch Equations for an elliptical rather than circular hole
Is there an equivalent set of closed form equations to the Kirsch Equations but for an elliptical hole rather than a circular hole?
4
votes
2answers
124 views
Why is the photon emitted in the same direction as incoming radiation in Laser?
When an atom “lases” it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained?
How does the photon generated because of ...
1
vote
0answers
17 views
Why is Erbium Doped Fiber Amplifier (EDFA) preferred over Erbium Doped Waveguide Amplifier (EDWA)?
Why is Erbium Doped Fiber Amplifier (EDFA) preferred over Erbium Doped Waveguide Amplifier (EDWA)?
The question has been asked from an engineering point of view, but obviously I would also be ...
0
votes
0answers
19 views
Insert a conducting plate into a capacitor [closed]
A capacitor with capacitance C is connected to a battery of voltage E. After the capacitor is fully charge, a conducting plate of thickness $\frac{d}{3}$ is inserted slowly between the plates of ...
0
votes
0answers
18 views
Force being applied to an object [closed]
I am working on a project and I do not have a clue about Physics. I have a 3400lb,1542kg object traveling at 210mph. When it is stopped by another object that is not in motion, what is the force of ...
1
vote
2answers
50 views
Deriving $T = F\ r = I\alpha$ for a rigid body
For a single point mass :
$\tau=F_{t}r=ma_tr=(m r^2)\alpha = I\alpha$
For multiple point masses bound together : $\sum \tau_i = (m_ir_i^2)\alpha = I\alpha$
But how do we go from that to $I\alpha = ...
1
vote
1answer
39 views
Geometrical Representation Grover algorithm
I am studying the Grover algorithm and in my and others lectures, I've come across this picture.
If the dimension of the computational basis is greater than 2, why does the evolution algorithm ...
2
votes
0answers
90 views
Tensor equations in General Relativity
In the context of general relativity it is often stated that one of the main purposes of tensors is that of making equations frame-independent.
Question: why is this true?
I'm looking for a ...
0
votes
2answers
54 views
Planet in which satellite(moon) and star(sun) appear together once a year
With a hypothetical system, where the moon would be always on the opposite side of the planet than the sun, in a way that the moon would only be visible at night on the planet.
I don't know if this ...
0
votes
1answer
23 views
Why Quantum correlation is not uniform in this diagram?
Following diagram is from a Wikipedia article which shows Quantum Correlation for local hidden variables and Quantum Mechanics and experiments confirm Quantum Mechanics predictions.
My question is ...
1
vote
0answers
26 views
Is it possible to detect subjective decoherence? If yes, how?
In his paper from 1994 Thomas Breuer describes a phenomenon of subjective decoherence (p. 43). I wonder whether it can be measured, and if yes, how.
I also wonder whether it would allow to create an ...
0
votes
1answer
41 views
The Univere's mass-energy and uncertainty
A virtual creation with total mass-energy = $E$ is allowed as long as that virtual creation doesn’t last longer than $E/h$. Can the uncertainty principle also be used to estimate the mass-energy in ...
5
votes
4answers
151 views
Can a single molecule have a temperature?
A show on the weather channel said that as a water molecule ascends in the atmosphere it cools. Does it make sense to talk about the temperature of a single molecule?
6
votes
3answers
181 views
Group Theory in General Relativity
In Special Relativity, the Lorentz Group is the set of matrices that preserve the metric, i.e. $\Lambda \eta \Lambda^T=\eta$.
Is there any equivalent in General Relativity, like: $\Lambda g ...
3
votes
1answer
34 views
Intuitive explanation for why same force applied farther from a hinge causes larger angular acceleration than if applied closer?
A standard example of a problem involving torque is opening a door - the same force F applied far from the hinge causes a larger angular acceleration than if applied close to the hinge.
I always had ...
3
votes
1answer
27 views
Given mean insolation, can one place an upper bound on the daily peak insolation?
Photovoltaic panels are rated under standard conditions: eg a $100\mathrm{W}$ panel if irradiated with $1000\mathrm{W}/\mathrm{m}^2$ at $25^\circ\mathrm{C}$.
When the cost effectiveness of ...
3
votes
1answer
29 views
Magnetic field due to a conducting sphere in unpolarized light
From Jackson, problem 10.3:
A solid uniform sphere of radius $R$ and conductivity $\sigma$ acts as a scatterer of a plane-wave beam of unpolarized radiation of frequency $\omega$, with $\omega R ...
3
votes
0answers
32 views
Anyons as particles?
I'm trying to understand the basics of anyons physics. I understand there is neither a Fock space they live in (because Fock is just the space of (anti-)symmetrized tensor product state, see e.g. ...
2
votes
1answer
78 views
Complex masses for Dirac and Weyl spinors
I'm trying understand how to rotate Dirac fields to absorb complex phases in masses. I have a few related questions:
With Weyl spinors, I understand, $$ \mathcal{L} = \text{kinetic} +
...
6
votes
2answers
62 views
Is particle entanglement a binary property?
Is the particle entanglement a boolean property? That is, when we consider two given particles, is the answer to the question "are they entangled" always either "yes" or "no" (or, of course, "we are ...
4
votes
2answers
83 views
Is there a general systematic approach how to calculate the individual terms in an operator product expansion?
Is there a general systematic procedure or approach to obtain the analytic functions $c_{ijk}$
as well as the corresponding operators $$A_i(z)$$ that appear in the operator product expansion (OPE)
$$
...
1
vote
0answers
38 views
How the “Standard Model” get that name? [closed]
I want to know how the Standard Model theory got such "generic" name?
0
votes
2answers
38 views
Using the Normalization Condition with Wavefunction
I'm very confused with this problem and I was looking for some guidance.
$$\psi(x) = Ae^{ikx}e^{-x^2/2a^2}$$
Use the normalization condition to find A.
So I understand that you use the normalization ...
1
vote
0answers
25 views
Finding the force of an object? [closed]
Sorry if my initial question was seen as a "homework question" but I don't really know how to go about asking this type of question. I have a feeling I have to use Newtons law but there is no ...
3
votes
0answers
23 views
Hall conductivity from Kubo: Bulk or edge?
Using the Kubo formula, Thouless, Kohmoto, Nightingale, and den Nijs (TKNN, PRL 49 405-408 (1982)), proved that upon summing all the contributions of the filled states of an insulator, the Hall ...
2
votes
0answers
17 views
Boundary Condition for Perfect Conductor in Uniform Magnetic Field
When I was studying the perfect conductor scattering (Section 10.1) in Jackson's book, I was confused by the calculation for magnetic dipole induced by the incident wave. He simply said like "set the ...
0
votes
1answer
34 views
Current in AC circuit
The problem is to find the current on the capacitor. $I''$ should be correct, but I don't know how to construct the formula for $I'$.
I managed to get the value for $I_c$ using Thevenin and Norton ...
1
vote
1answer
43 views
How to derive the expression for Bose-Einstein distribution variance?
Can anyone point me to a derivation of this expression? $n_s$ is the number of bosons in a state.
8
votes
1answer
67 views
Hexadecapole potential using point particles?
We can get monopole $1/r$, dipole $1/r^2$, quadrupole $1/r^3$ and octupole $1/r^4$ potential falloff by placing opposite point charges at the corners of a point, line, square and cube, respectively. ...
4
votes
2answers
72 views
Tensor fields on space-time
I'm reading landau electrodynamics . For the investigation of the dynamics of a charged particle in an electromagnetic field , the author introduces a four vector potential field on spacetime . The ...
7
votes
3answers
146 views
Where does the extra equation come from to determine the forces from an object on a table?
I have a question about basic statics but somehow I cannot manage to find the answer on my own (btw, this is not a homework. It's been so many years since school for me...).
The problem is very ...
5
votes
0answers
62 views
Why do we identify symmetric 2nd rank tensors with spin-2 particles in string theory?
I am going through Tong's lecture notes on String Theory and came across the following irrep decomposition (Chap 2, p.43) of the bosonic string first excited states:
$$\text{traceless symmetric} ...
1
vote
1answer
90 views
Path Integral Quantization
I was reading through my notes on the path integral quantization of bosonic string theory when a general question about path integral quantization arised to me.
The widely used intuitive explanation ...
2
votes
0answers
32 views
Gauge fields and strings: Loop equations
I am trying to derive Eq. (7.25) (p. 117) of Polyakov's book:
$$ \delta \Psi (C) = \int_{0}^{2\pi} {\rm P} \left(F_{\mu\nu}(x(s)) \exp \oint_C A_\mu dx^\mu \right)\dot{x}_\nu \delta x_\mu(x) \, {\rm ...
