0
votes
0answers
17 views

What does “Field theory limit” means in D/M-branes or supergravity theories? [on hold]

What does "Field theory limit" means in D/M-branes or supergravity theories? Reading some papers related with D/M-branes, they often mention field theory limit, $i.e$, limit of $\alpha\rightarrow 0$,...
1
vote
0answers
53 views

Conformal group in 2D being a subgroup of Diff/Weyl - Polchinksi's 'String Theory' [on hold]

In the appendix on page 364 of 'String Theory', Polchinski defines the conformal group (Conf) in two dimensions to be the set of all holomorphic maps. On page 85 he explains how Conf is a subgroup of ...
3
votes
1answer
29 views

Cold dark matter halos and cusps

Cold dark matter is one of the preferred candidates for dark matter. Yet, models such as the NFW and isothermal predict that halos will contain cusps, where the density tends towards infinity, despite ...
0
votes
0answers
42 views

Are 3 waves that have the same frequency (and wavelength) but different phase differences coherent? [duplicate]

Waves 2 and 3 have different phase differences which remain constant (since the frequency and wavelength is the same) as compared to wave 1 so to get to the point, are the 3 waves coherent?
0
votes
2answers
57 views

Is the relation between expansion of a liquid with temperature linear?

Say I have a liquid with certain volume. If I heat it, will it expand with a constant rate? $$ \frac{T}{V} = k.$$ It is true for gases, is it also true for liquids? And if yes then: is it true for ...
2
votes
1answer
60 views

Calculating the ground state energy in an electron gas (Jellium)

$\renewcommand{\phi}{\varphi} \newcommand{\vec}[1]{\textbf{#1}}$ This is pretty lengthy because I kept having ideas while writing this. Consider an electron gas in a cube of side length $L$, $V=L^...
0
votes
0answers
25 views

Coin frequency distribution [on hold]

When considering the coin frequency distributions for coins of different masses, does the surface on which the coins are dropped influence the power spectral analysis of the sound waves thus produced?
0
votes
0answers
24 views

A fundamental theory of superunification [on hold]

So, an year ago I was searching over the Internet about anti gravity (just out of curiosity).. And I stumbled upon this article: http://theoryofsuperunification-leonov.blogspot.bg/2015/01/russia-...
0
votes
0answers
18 views

Photoelectric effect - elastic collision [on hold]

In an elastic collision, since the electron leaves with the same amount of energy as it originally had, does that mean the photon receives no energy? Does this even result in a photon emission, if so, ...
0
votes
0answers
32 views

How to calculate position of object that have linear and angular acceleration at the same time?

Let's imagine that we have a boat with two engines: main and rotary engine. Main engine gives boat acceleration $a$ m/s² up to constant linear speed $V$ m/s. When engine turns off, boat slows down ...
0
votes
0answers
26 views

How to calculate the heating power of a metal plate in nature?

I like to heat up a part of a metal plate to a given temperature. For that I want to use an electric heater. The metal plate is located outside in nature. For that I need to take in account the wind ...
0
votes
0answers
20 views

Electrical field in coaxial cavity

I already asked this question at electrical engineering SE, but I got the recommendation that in the Physics SE there will be a better chance to get answers. I have a geometry as follows: This is ...
0
votes
1answer
60 views

How can we detect electric field in electromagnetic wave?

Electromagnetic wave have magnetic and electric component but what is the proof for that? How "non electrostatic" electric field can be detected around coil?
2
votes
1answer
43 views

Why does Higgs field have 4 components and written in a doublet?

I'm studying the Higgs field and I encountered some problems. My book says that the Higgs field has four components which are conveniently arranged into a two-component vector as: $$\phi=\binom{\phi^{+...
1
vote
0answers
53 views

Lagrangian of a coupled pendulum

I am trying to find the Lagrangian for a coupled pendulum: the two pendulums have the same characteristics (length $l$ and mass $m$) and are attached to the same roof at a distance $d$. In addition, ...
3
votes
0answers
21 views

Is there an analog of the Komar mass for conformal Killing Fields?

Is there an analog of the Komar mass for conformal timelike Killing vector Fields? For a stationary spacetime M, the Komar mass may be given as: $$M=\oint_{\partial M}\sqrt{g_{00}}(2T_{\mu\nu}-g_{\...
1
vote
0answers
52 views

What are the different definitions of torsion-free connections in GR? [on hold]

What are the different definitions of torsion-free connections in GR? I am summarizng torsion-less condition in various context, if you know anything about it please let me know. One typical ...
0
votes
4answers
95 views

Can a person in a car hitting the interior of the car move the car?

As I remember, on old day explanation, a person in a car hitting the interior of the car cannot move the car, because there is no action and reaction force between the car and ground. But I doubt the ...
2
votes
0answers
46 views

Experiment using a laser beam [on hold]

I need to come up with an experiment to conduct for my physics class. So far, I'm stuck at the use of lasers. What plausible experiments can be done using lasers that haven't been done before, and ...
0
votes
1answer
44 views

Do Black Holes emit Hawking radiation while engulfing normal mass?

As I read on various sites ,all of them say that Black Holes emit Hawking radiation as one of the instantly created virtual particles near Event Horizon escapes from it.One goes inside it and other ...
-1
votes
0answers
55 views

Linear motion in a constant acceleration [on hold]

a car start to move from rest and travels along a straight horizontal road with a constant acceleration. Velocity of the car after t seconds is vms-1. Find the displacement of the car during the ...
0
votes
0answers
39 views

Where I can find quantum entanglement, real experimental raw data

For analysis purpose, I am looking for raw data from real entanglement experiment with spin measured at two detectors, at various combinations of angles, but preferably at a single combination of ...
0
votes
1answer
151 views

Universe spawned from the death of a hyper black hole?

Some Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole a scenario that would help to explain why the cosmos seems ...
1
vote
3answers
108 views

Finding the Expectation value of harmonic oscillator [on hold]

What is the expectation value for $e^{{\alpha}a^{\dagger}}e^{-\alpha^*{a}}$ of any two states of harmonic oscillator (let say $|n\rangle$ and $|m\rangle$) given below, $$\langle n|e^{{\alpha}a^{\...
9
votes
2answers
1k views

Green dot on photos when taking photo facing the sun

When taking a photo towards the sun, I found there is a green dot on the photo. I'm pretty sure this is caused by the sun, the camera has no problem. Question: what is the cause of this green dot? why ...
1
vote
0answers
21 views

Explanation of a match between shadows and wet floor at Niagara Falls

The question is about the cause of a wet-floor phenomenon. My vacation trip started at Niagara Falls (Canadian side, horseshoe fall on the upper left corner). It was around 10-11 AM, not too sunny yet....
2
votes
3answers
33 views

Do all smoothly curved pieces of transparent material have a focal point?

I understand that a lens by definition has a focal point but do all pieces of glass with smoothly curved surfaces have a single point at which all parallel rays of light passing through it in a ...
1
vote
1answer
27 views

Applying Ampere's Law for Two Parallel Wires

This seems a simple question but I'm not able to understand it properly. Say we have two parallel wires carrying same current I in different directions. We need to calculate the magnetic field at any ...
1
vote
1answer
29 views

Find velocity of ambulance from the observed frequencies?

I have a problem where an ambulance with a siren is traveling past me (a stationary observer) at a constant velocity. When the ambulance is approaching, I measured the frequency at 1000 Hz and as it ...
-1
votes
0answers
77 views

Skeptical of the “Cannon Shot Rule” [on hold]

What I consider a highly suspect figure was imparted to me today in a lecture and it very immediately did not sit well with me. To wit, this cannon shot rule (see here for a reproduction of the ...
-2
votes
2answers
64 views

Can the Copenhagen interpretation and the many-worlds theory be somehow reconciled? [on hold]

Is it possible that, at the moment of observation, a timeline is created where an object is in a state which contrasts its state in the current timeline? Using Schrodinger's cat as an example, let's ...
1
vote
0answers
35 views

Experimental tests of electric and magnetic fields in a gravity field

Has anyone experimentally verified that the measured values of the electric and magnetic fields do not change due to gravity, that there is no post-Newtonian effect on the strength of either $E$ or $B$...
0
votes
1answer
29 views

Do III-V based photovoltaics “glow” (photo-luminesce) when illuminated but not loaded?

In this nice answer I started to learn about how the silicon photovoltaics cells on the International Space Station are managed. In that case, the cells are generally either delivering useful power to ...
0
votes
0answers
16 views

Lightning, Electrical breakdown, and Current

Recently a discussion came up about this gif: http://i.imgur.com/r9Q8M4G.gifv This lead to a few questions about electrical breakdown of insulators. The disagreement we're having is whether or not a ...
1
vote
0answers
47 views

Can I use an electromagnet as a shark repellent? [on hold]

I scuba dive, and also spearfish. Doing these sports in the ocean presents obvious challenges since Sharks exist in the ocean. I know about a product called shark shield which uses magnetism to ...
-3
votes
1answer
52 views

Are black holes causing expansion? [on hold]

If the universe is sufficiently large enough, there should be a black hole in every direction of the sky. So, could there be a game of tug-of-war going on between all of the black holes in the ...
0
votes
4answers
26 views

Are elements of statistical ensemble fixed or dynamic?

I will use the simplest example I can think of to explain what I am trying to understand. Consider a system with ~$10^{23}$ particles in an equilibrium with fixed values of pressure, volume and ...
0
votes
1answer
23 views

Heat transfer direction in fins

I'm unsure of what exactly is changing the heat transfer direction in the triangular fin. $$q_{x} = -kA(x)\frac{dT(x)}{dx} (1)$$ $$q_{x+dx} = -kA(x)\frac{dT(x)}{dx} - k\frac{d}{dx}[A(x)\frac{dT(x)}{...
4
votes
0answers
20 views

What Is the Roche Limit Factor for a Tension-Free Solid Rubble Pile?

I have reached a confusion when searching for derivations of the Roche Limit, which differ in value and explanation. All equations are given of the form: $ P = r_{M} \sqrt[3]{f\frac{\rho_{M}}{\rho_{...
-2
votes
1answer
57 views

Why $\epsilon_0 = 1/(4\pi k)$ instead of $\epsilon_0 = 4\pi k$? [on hold]

In my physics book, they consider a positive point charge $q$ and a spherical surface of radius $r$ centered on this positive charge. Then the flux through this surface is given by $$\Phi = \iint \vec{...
3
votes
1answer
22 views

Why is the molecular partition function only broken down into translational, rotational, vibrational, and electronic states, ignoring configurations?

Per Atkins and others, energy is the sum of contributions from the translational, rotational, vibrational, and electronic modes of motion. Since the formula for the partition function is $Q=\sum_i e^{\...
0
votes
0answers
27 views

Non-singlet and singlet flavor combination [duplicate]

In the perturbative QCD, specific partonic distribution functions (pdf) linear combination is called "flavor singlet" or "flavor nonsinglet" combination. What is the combination, and why are they ...
1
vote
1answer
49 views

I cannot verify if given transformation is canonical (CT) [on hold]

I'm going on a list of exercises and there's 6 days that I can't figure to this. Prove that given transformation is canonical: $\Large Q=\frac{p}{mw}\sin(\frac{mwq}{P})$; $\Large P=p\cos(\frac{...
1
vote
0answers
44 views

What is wrong with my formulas for a mathematical model of a double pendulum? [on hold]

I tried mathematics but I've had no response in a month. I wanted to create a computer simulation on Matlab, using a model for a pendulum from this study (A double pendulum model of tennis strokes. ...
1
vote
1answer
58 views

String Theory Vs. Holographic Theory of the Universe. Compatibility [on hold]

String Theory claims strings to be one dimensional objects vs. dimensionless point particles of the Standard Model. String Theory also needs 10 or possibly more spatial dimensions to operate in. ...
3
votes
2answers
49 views

Meaning of “Metrically defined” matrix

I got stuck on understanding stuff from Methods of molecular quantum mechanics written by R. McWeeny. The content is: It must be stressed that the representation property embodied in $\mathcal{A} \...
3
votes
0answers
27 views

Homotopy Theory for Topological Insulators

I'm trying to understand topological insulators in terms of homotopy invariants. I understand that in 2 spatial dimensions, we have Chern insulators since $$\pi_2(S^2) = \mathbb{Z}$$ One subtlety that ...
4
votes
1answer
40 views

LHC: Clumps of protons or continuous stream?

I am curious about the Large Hadron Collider and whether the proton (anti-) beams are clumps of protons (grouped together) or are they roughly equally distributed around the circumference of the ring. ...
9
votes
2answers
74 views

Why can we approximate dynamics of massive particles by masless and vice versa?

I am puzzled by the following observation. Our descriptions of massless and massive particles are very different. For example, masless particles have only two polarizations, which we call helicities. ...
2
votes
0answers
14 views

Energy-band diagrams of heterojunctions

I'm studying heterojunctions and I'm struggling with drawing their energy-band diagrams. I've been looking for books or something to look up how the diagrams can turn out to be with different types of ...

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