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Meaning of the discrete Fourier transform in condensed matter

I'm in a CMP course now and I think I'm taking for granted what it means for a creation/annihilation operator to be Fourier transformed. I understand what a Fourier transform is for some function, but ...
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0answers
3 views

Could Planck Relics prevent a contained particle of anti-matter from interacting with exterior matter?

The need for some quirky asymetry to exist in the way matter and antimatter cancelled out to result in the universe having matter seems... well, weird. During the big bang, a bunch of microscopic (...
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1answer
15 views

the constants of the matrix 4*4

I have the following matrix \begin{equation} A= \begin{pmatrix} 0 &1  &0  &0  \\ 1 & 0 &0 &0\\ 0 &0&0&1\\ 0&0&1&0 \end{pmatrix} \end{equation} The ...
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1answer
10 views

Why is Sellmeier's equation an even function of $\lambda$?

According to Sellmeier's formula, the dispersion formula of a transparent material can be written as $$n^2(\lambda) = 1 +\sum_i\frac{B_i \lambda^2}{\lambda^2 - C_i},$$ where $B_i$ and $C_i$ are ...
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0answers
13 views

Magnetic Dirac operator rotationally invariant?

Let $\omega=e^{2\pi i/3}$ be the third root of unity. We consider the two-dimensional Dirac operator with homogeneous magnetic field $$ H = \begin{pmatrix} 0 & 2 D_{\bar z} -Bx_2 \\ 2 D_{z} -B_{...
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1answer
19 views

Double slit experiment: effects of changing path difference between slits on diffreaction pattern

I know that interference pattern maxima occur due to path difference of integer number of wavelengths, causing constructive interference, and minima due non-integer number of wavelengths, causing ...
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0answers
32 views

Driving a quantum system

I don't understand the mathematical form of an external driving force on a quantum system. For example, say we were driving a quantum harmonic oscillator. You would have the Hamiltonian for the ...
3
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3answers
68 views

In classical physics (classical electrodynamics), why linearity of Maxwell's equations prevent interaction of electromagnetic waves?

In classical physics (classical electrodynamics), electromagnetic waves don't interact. In quantum mechanics, they could. In this article on light-by-light scattering: https://arxiv.org/abs/1702.01625 ...
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0answers
31 views

Laplace's equation solution for square

I wanted to solve Laplace equation $\Delta u(x,y)=0$ on the square $0≤x,y≤1$ with boundary conditions $u(x,0) = u(x,1) =0,∂_{x}u(0,y) = sin(πy), ∂_{x}u(1,y) = sin(3πy)$. I'v written I wanted to solve ...
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1answer
18 views

Do both selection rules need to be satisfied for a transition to be allowed?

The selection rules for electron transition are $\Delta l=\pm 1$ and $\Delta m = 0,\pm1$. Do both conditions need to be satisfied for a transition to be allowed? For example, is the transition from ...
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3answers
97 views

Why is a nuclear fusion reactor not currently possible?

Nuclear fission reactors are fairly common, but what technological/physical limitations are currently impeding developing the nuclear fusion reactor? The H-bomb is capable of creating nuclear fusion ...
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1answer
34 views

Relativistic Accelerating Frame (non-inertial frame)

One way to resolve the Twin paradox is to count in the effect of acceleration when velocity suddenly changes. I am therefore searching for a relativistic version of "accelerating frame" or ...
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1answer
47 views

Relighting a candle from its smoke, and being burned?

Having been extinguished, a candle can be relit from the resulting trail of smoke, even from meters away. However despite this apparently high level of heat, paper, bystanders, etc… are never ...
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2answers
68 views

Why are atoms stable?

I will ask my question in a way that's all handwaving and no math, and I will welcome handwaving answers. I'm interested in visualizing the concepts. A long time ago we had an idea about the atom as a ...
1
vote
1answer
44 views

Gauge fixing in the classical $U(1)$ gauge theory

My question concerns the gauge fixing in classical v.s. quantum $U(1)$ gauge theory. I will ask about the gauging fixing in quantum $U(1)$ gauge theory in a separated Phys-SE post. For the classical $...
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0answers
8 views

Calculating the base peak from a mass spectrometry

Consider we have the following fragmentation of propane, obtained by mass spectroscopy: Which, if I haven't made mistakes, leads us to the following mass spectrum: It's clear that the molecular peak ...
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2answers
26 views

Oscillating disc on flat table

Suppose we have a uniform disc of mass $2m$ and radius $R$, and we place a small piece of putty of mass $m$ onto the disc at a position very close to the rim. Now let's say the disc with putty is now ...
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0answers
11 views

How to calculate path-dependent integrals in thermodynamics (from 3D simulation results)?

I would like to calculate some path-dependent thermodynamical quantities from the results of a fluid dynamics simulation (single fluid, single phase). One of these quantities is the head $$y_{12} = \...
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1answer
32 views

Who is the person behind the so-called “Boure's Law”?

When I was in college, specifically in Rigid Body Kinematics, I was taught that Boure's law or formula, which looks something along these lines: $$\left(\frac{\mathrm{d}\boldsymbol{\omega}}{\mathrm{d} ...
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0answers
7 views

Do the Misner-Sharp mass and ADM mass asymptote to one another for static spacetimes

I know for asymptotically flat spacetimes, one can define the Arnowitt-Deser-Misner (ADM) mass of the spacetime $M_{ADM} = \frac{1}{16\pi} \lim_{r\to\infty} \int d^2\sigma r^a \gamma^{cd}\left( \...
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0answers
31 views

Is entropy maximized for steadily driven systems?

Suppose we send an electric current through a piece of metal. If we knew only the average energy and current through the sample, it would seem natural to assume the state of the sample is described by ...
2
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0answers
12 views

Wien's law and colors

I know there are a Wien's law for frequency and one for wavelenght, but I'm wondering which one is the most accurate when it comes to our perception of colors. For instance for the Sun, the Plank ...
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0answers
8 views

Transforming a general four-impulse to the center of mass frame

I'm currently stuck on a problem. It's about two particles colliding with each other, where particle $A$ is traveling in the positive $x$-direction and particle $B$ in the negative $y$-direction. The ...
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0answers
4 views

Nanoscale Melting Point Depression

Changing the size of a bulk material lowers the melting point of it. However there is only mention of this happening to metallic nanoparticles. Is this exclusive to metallic elements or can it also ...
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0answers
18 views

Container divided into 2 parts with $p, \ V, \ T$ known, what is the final temperature

So, this problem was given to 10th graders in a town physics olympiad. A thermally insulated container is divided by a thin thermoconductor wall in 2 compartments with volumes $V_1 = 3L$, respectively ...
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1answer
29 views

Can accelaration of a falling mass be positive when upwards direction is positive? What am I missing?

As shown in the figure: (+) direction is upwards displacement is y time=t Let's say that $ y=30-5t^{2} $ , thus the second derivative will give acceleration as -10 which is (-) as expected. Now let'...
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2answers
55 views

Eigenvectors as basis vectors

I know this kind of question has been asked before but I did not understand it completely. So while studying operators and eigenstates, I came across two formulas, $\hat{A}|\psi\rangle = |\phi\rangle$ ...
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2answers
37 views

Understanding the Israel Junction Conditions

The well known and frequently used Israel Junction conditions are the equivalent of Einstein's field equation on a membrane in the brane-world picture. All the sources have this notation: $K_{ab}^{(i)}...
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0answers
38 views

Physics history — the Ultraviolet Catastrophe [duplicate]

I will ask my question in a way that's all handwaving and no math, and I will welcome handwaving answers. I'm interested in visualizing the concepts. We had an idea about the atom as a massive nucleus ...
0
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0answers
18 views

Dirac spinors completeness relation for $d>4$

In $d=4$ and in the rest mass frame, the four Dirac spinors $u_s(0)$ and $v_s(0)$ satisfy the completeness relation $$ \sum_{s=1}^{2} u_s(0) \overline{u}_s(0) - \sum_{s=1}^{2} v_s(0) \overline{v}_s(0)...
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0answers
11 views

Need help with understanding the equation below. Here $h$ is the film thickness of fluid left behind in a fluid fluid displacement

A simple equation for the evolution of the interface described by $$r=R(z,\phi,t)=a-h(z,\phi,t)$$ where $a$ is the radius of the cylinder and $h$ is the typical film thickness – can be found in terms ...
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0answers
17 views

Testing space-time warp on a smaller scale, “Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein-Maxwell-Plasma Theory”

So according to this paper it creates a warp drive without the need of negative energy to operate which many think does not exist in reality. So my question is what would you do to experimentally ...
4
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1answer
37 views

Exceeding the Kerr black hole spin limit

It is well known that the limit on the angular momentum for a Kerr black hole is given by \begin{equation} 0 \leq a^* \leq 1 \quad \text{where} \quad a^* \equiv \frac{cJ}{GM^2} \end{equation} and $J$ ...
-1
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1answer
28 views

How does time dilation apply at the centre of a black hole?

At the direct centre of a black hole, you have $0$ GPE, and the net gravitational force is $0$. So how does time dilation work there (or is this another physics mystery)? Specification: I refer to how ...
2
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2answers
76 views

Are chaotic systems examples of complex systems?

I am struggling to find a proper source or reference where examples of complex systems which are chaotic are given. Based on my understanding, complex systems consist of interacting components, each ...
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1answer
20 views

Positional is not equivalent to conservative in dimensions greater than one

I've just started writing dynamical systems and I was trying to find an example to show that if we are in a $2$ or $3$ dimensional real space "positional do not implies conservative". In ...
1
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0answers
51 views

Why the Warp-drive uses a 3D shape to distort space instead of a 4D shape?

I know that warp-drives are just a theory and that they would require exotic mass (that is also a theoretical material), but, as said in this video, after some re-calculations, it was theorised that ...
0
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2answers
46 views

Speed of electromagnetic wave in a medium

Speed of electromagnetic wave in a medium (for example air) is different for different frequency (for exmaple red light is faster in air than blue light). So how can we calculate the speed of light ...
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0answers
31 views

A question about collisions and probability, from an élite university admission test [closed]

Good afternoon, I have come across this question, from a recent admission exam to my country's top physics university, which I have found particularly interesting as the text seems to be deliberately ...
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0answers
56 views

Cosmology - The Geodesic Equation Derivation

My question relates to the derivation of the Geodesic Equation given on pages 121-122 of Baumann's cosmology. $$\frac{d^2x^i}{d\tau^2} = -\partial^i \Phi (dt/d\tau)^2 + O(\Phi^2). \tag{A.2.43}$$ On ...
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2answers
31 views

Why is the SI unit of Magnetic Pole Strength Ampere-meter?

Till now I was silent because I thought the SI unit of pole strength to be Ampere-Second and due to everything in analogy with electrostatic, it was ok, but when I looked closely, it changed to Ampere ...
0
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1answer
43 views

ISO an elegant derivation of the Geodesic Equation from the Einstein Equation

Assuming a particle filled with perfect pressure-less fluid can the Geodesic Equation be derived from the Einstein Equations?
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1answer
19 views

Coefficient of thermal expansion

Is the coefficient of thermal expansion of a particular material under constant pressure constant?
0
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0answers
24 views

Ideal gas partition function

I am studying how to calculate the density of states and the partition function of $N$ non-interacting particles. My question is why the integral of the momentum, in the density of states calculation, ...
1
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0answers
15 views

Low energy strong coupling asymptotic

The low-energy behavior ($Q^2<\text{1GeV}^2$) of the strong interaction coupling constant predicted by LFHQCD, $\alpha_S = \pi \exp(-Q^2/4\kappa^2) $, where $\kappa=M_\rho/\sqrt{2}$, is in ...
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2answers
39 views

Why is volume of gas independent of its molecule size?

According to the ideal gas law: $pv = nRt $ My question is, why is the volume $v$ independent of the volume of individual components of the gas, i.e. molecules? As the sizes of individual molecules ...
0
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1answer
29 views

SUSY Kinetic and $W$ potential terms: RG flow — free or interacting

In this Seiberg's SUSY lecture, the professor said that the following theory with Kinetic and $W$ potential terms: $$ K=|\phi|^2 $$ $$ W=m\phi^2+g \phi^3 $$ "It is not a valid theory in $4d$, ...
0
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2answers
63 views

How to perform experiments near absolute zero temperature when the background temperature of the universe is 2.7 K?

The cosmic microwave background (CMB) radiation as a remnant from an early stage of the universe (Big Bang) is filled all space and has a thermal black body spectrum at a temperature of $2.72548±0....
0
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1answer
40 views

Why do we need to equation of state (EOS) equation?

I cannot understand why we need the equation of state of star for the numerical solution of TOV equation. In fact, I do not know how EOS equation helps with solving TOV equation. How is EOS equation ...
0
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2answers
23 views

Definition of metallic state

What is the physical and chemical definition of a metallic state? I found this term in various books and, although the idea is intuitively clear to me, I would prefer to have a precise and complete, ...

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