1
vote
0answers
6 views

What are the proper domains of the position and squared angular momentum operator?

I am looking at the position operator on a compact set $K \subset \mathbb{R}^n$ and the squared angular momentum operator ( so essentially the Laplace-Beltrami operator where I just look at the ...
-2
votes
1answer
12 views

How does it seem to be that space/time always equals c?

Bit of a noob question perhaps, but the way objects move they seem to be going all the same "velocity" so to speak, that velocity being the speed of light. Except, velocity is displacement/time, so if ...
0
votes
2answers
17 views

Does gravity stack?

If I am standing on a planet on the opposite side from its sun will I feel the downward pull of both the planet's gravity and the star's gravity? In other words, does gravity "stack" (Any D&D ...
1
vote
0answers
16 views

How should a math undergrad student prepare himself to study GR and QM?

I'm quite sure that similar questions like this have been asked for more than thousands of times on here but since each person's background and interests are unique I believe questions like this ...
1
vote
0answers
7 views

P-N junction voltage under polarization

All the books that deal with the p-n junction under applied bias asume that the same equations used for the equilibrium case (no bias) can be used for the biased case provided that the juntcion ...
2
votes
0answers
29 views

Counting Problems in Physics

What are some classic counting problems in physics? I'm trying to think of interesting examples to give in a math class on the matter, and I feel as if physics should have some ones to offer.
0
votes
0answers
23 views

what is the composition of magnetic field?

whenever I read electromagnetism topic then i was confused by magnetic field that what is the composition of it and why magnetic field forms from outside the current carrying conductor ...
2
votes
1answer
18 views

Reference on electrodynamics with tempered distributions

Back in my undergrad I had a course on classical electrodynamics where the fields had values in the space of tempered distributions. In this way one could correctly treat self-interaction and ...
1
vote
0answers
4 views

The DLCZ Protocol

I have been reading the article review for Optical Quantum Memory (http://arxiv.org/abs/1002.4659) when I came across this section about DLCZ protocol. I don't understand about Beam splitter. For what ...
1
vote
0answers
23 views

why do some of the dimensionful physical constants take on the values they do?

so this might have some duplicated inquiry that this question or this question had, and while i think i have some of my own opinion about it, i would like to ask the community here for more opinions. ...
1
vote
0answers
15 views

Derivation of the first term of the expansion of the conformal block

In the book Conformal Field Theory by Francesco, Mathieu, Senechal, how do we get equation 6.190 $$ \mathcal{F}_{1}=\dfrac{(h_{p}-h_{2}-h_{2})(h_{p}+h_{3}-h_{4})}{2h_{p}} $$ , the first term in the ...
1
vote
2answers
22 views

In terms of physics, does the phrase “time slows down” mean the same thing as “things happen more slowly?”

The common definition of "time" is a type of measurement, like size. But the sentence "size gets bigger" doesn't make any sense. Is "time slows down" an odd phrasing of "events occur more slowly" or ...
-6
votes
0answers
22 views

Potential Energy and Kinetic Energy [on hold]

how does potential energy related to height? how does kinetic energy related to velocity? how does potential energy related to those kinetic energy? how does potential energy and kinetic energy ...
2
votes
0answers
20 views

Why is Silver-108 unstable

Why is Silver-108 unstable if silver-107 and silver-109 are stable? I found it on crash course but no answer was given.
8
votes
2answers
270 views

Is topology of universe observable?

There is an idea that the geometry of physical space is not observable(i.e. it can't be fixed by mere observation). It was introduced by H. Poincare. In brief it says that we can formulate our ...
3
votes
0answers
32 views

Derivation of force law in special relativity

I've seen force defined in special relativity as the rate of change of 4-momentum $$ {\bf{F}} = \frac{d {\bf{p}}}{dt} $$ Can anyone comment on the following derivation of that relation? Take one ...
2
votes
1answer
28 views

Radiation emission and absorption

Any object can emit and absorb radiation and the power of emission can be represented by the Stefan-Boltzmann law: $$P=A\epsilon\sigma T^4$$ In many texts the net power radiated is the difference ...
6
votes
3answers
351 views

Why do bubbles make a sound?

I have an understanding of how bubbles work. They encapsulate air (or other fluids) in a membrane caused by surface tension. When they pop, there is often a sound. Sound is a type of energy, kinetic ...
-1
votes
0answers
22 views

How do I know which force to use in moments calculation?

I'm working on some Statics problem, with the method of joints, etc and for all of them, we use sum of moments = 0. However, I'm very confused about which forces I should use to find the sum of ...
2
votes
1answer
32 views

Fierz identity for Weyl spinors in tensor currents

Using Fierz identity I found that certain four-fermion operator with left $l_i$ and right-chiral $r_i$ Weyl spinors vanish $\bar{l}_1\sigma_{\mu\nu} r_2 \bar{r}_3 \sigma^{\mu\nu} l_4 =$ $ ...
2
votes
0answers
16 views

Electrochemical cell potential - Prigogine book

I'm trying to understand equation 10.2.14 from Prigogine book "Moder thermodynamics": $V=\frac{\tilde{A}}{nF}=\frac{1}{nF}\left(\mu_X^R+\mu_Y^L-\mu_{Xred}^R-\mu_{Yox}^L\right) - \left( \phi^R-\phi^L ...
2
votes
4answers
70 views

How much could one slow down aging using existing spacecraft?

Imagine that I board a spacecraft and head away from the Earth at top speed until I've aged twenty years, then I turn around and come back. How much younger will I be than the unexciting folk who hung ...
1
vote
1answer
29 views

Is there a textile like material that can act as a spring?

Imagine some sort of textile (as in very light, not metallic) that is tightly rolled up, can be easily unrolled by applying some force (i.e pulling it) but when released will eventually return to it's ...
1
vote
0answers
28 views

compact and non-compact gauge theory [on hold]

From the answer to this question, I see that the gauge theory has to be compact if the charges need to be quantized. I am not sure in what sense these are necessary and sufficient. So here is a ...
2
votes
1answer
35 views

Gas pressure and centrifugal force

I think about a rotating torus (simplified tire) filled with ideal gas. Mass of gas is $m$ and molar mass is $M$. Pressure in non rotating torus is $p_0$. Temperature is constant $T$. Inner radius of ...
1
vote
0answers
38 views

Notation for Translation Group Generators

The generators of the translation group $T(4)$ are given below: $P_0 \equiv -i \begin{pmatrix} 0 & 0 & 0 & 0 & 1 \\ 0 & 0 & 0 & 0 & 0 \\ 0 ...
1
vote
3answers
52 views

Convective heat transfer coeficient equation

I am attempting to model a situation, in which a sphere of some material of identifiable thermal properties is receiving heat at a constant rate. And that material is coming into equilibrium with the ...
2
votes
2answers
60 views

Is there a difference between Hertz and 'frames per second'?

It's not uncommon that the term 'frames per second' (sometimes abbreviated as fps or FPS) is associated with, or even equated to, the unit Hertz (Hz). I'm not exactly sure how these two concepts ...
1
vote
0answers
18 views

What is the physical significance of the fermi-field asymmetric stress-energy tensor?

Using the ideas from a previous question here it can be shown that if one takes the boson spin 1 stress-energy tensor of the form \begin{align} T^{\mu\nu}_{\text{spin one}} = \begin{bmatrix} ...
1
vote
1answer
108 views

Space-time curvature creates gravity or is it (could it be) vice-versa too?

Mass (Energy) creates space-time curvature and thus it forms the reason for gravity. Can it be vice-versa too? Like, mass created gravitational field, gravitational field created space-time curvature? ...
2
votes
0answers
31 views

Are there any applications of elementary number theory to science? [duplicate]

I've taken a class on elementary number theory (for fun), but now I wonder: was it at all useful to learn number theory for my future career in physics? More to the point, are there any applications ...
0
votes
1answer
32 views

About Shor's error correcting algorithm

In this paper, http://arxiv.org/abs/1301.4504 in equation 4.1 in what sense are the two states a "9-qubit state"? I did not understand this counting. Can someone explain what are the different $X_i$ ...
5
votes
4answers
249 views

“Lack of inversion symmetry” in crystal?

Apparently (first paragraph of this article) the lack of inversion symmetry is some crystals allows all sort of nonlinear optic phenomena. Now. Does anyone know of an intuitive or just physical ...
0
votes
1answer
19 views

Impulse on adjacent objects

Let's say two objects are sitting adjacent (in contact) to each other. If we start pushing one of them, we know that both the objects move, remaining in contact to each other. But let's now consider ...
3
votes
0answers
86 views

Nature as a calculator [on hold]

I wondered whether physical experiments can find the outcome of otherwise intractable mathematical problems. For example, solitons or other non-perturbative effects in QFT cannot be seen at any ...
2
votes
2answers
68 views

Why do some hand dryers blow hot air?

I am not sure why some hand dryers are blowing hot air and not just air at room temperature. To me, hair dryers are just a way to dry one's hands using the same principle as when we shake our hands ...
0
votes
0answers
22 views

Confusion over Time dilation and energy to mass conversion [on hold]

Suppose a train starts approaching the speed of light. I kept on giving more and more energy so it is reaching towards speed of light. Now I have trouble understanding this further. Plz consider two ...
1
vote
1answer
26 views

Correlation in electron gas

In the textbooks that I read (namely Ashcroft/Mermin , Marder, etc.) it seems that a distinction is made between the correlations in electron gas and a Couloumb interaction between the electrons. What ...
2
votes
0answers
43 views

Intuitively proof that intensity of a wave is proportional to the square of its amplitude [duplicate]

Firstly I would like to know if this is valid for every kind of wave, or are there any conditions/exceptions where this is not valid. But the main question is, is it possible to prove this fact for a ...
1
vote
1answer
19 views

Thomas - Fermi screening

I read in Ashcroft & Mermin's Solid State text that for the Thomas-Fermi approximation to be applicable, the external potential needs to be "slowly varying," What does it mean for a function (in ...
-2
votes
0answers
38 views

Gravity as an absence of repulsive force [duplicate]

Could it be possible that the force we know as "gravity" is instead an absence of repulsive force from the direction "gravity" is coming from, so what we feel is a repulsive force from the opposite ...
-5
votes
0answers
18 views

what is the focal length of concave lense? [on hold]

I need just the formula . Please help me anybody ? And the sign convention used in the focal length formula. And any sites ?
4
votes
2answers
341 views

Neutrino annihilation and bosons

Would it be theoretically possible for a high energy neutrino and another high energy anti-neutrino to annihilate into a boson? Which boson(s) would be possible theoretically? - one or more photons ? ...
1
vote
3answers
36 views

Momentum acceleration in space?

I'm an engineering student and have a few ideas to bat at the scientific community. First premise is based upon common sense. I understand that if I am standing on a skateboard on a relatively smooth ...
1
vote
3answers
82 views

Do massless particles follow the curved spacetime or not?

I am assuming that zero (rest) mass particles don't interact gravitationally with each other and other particles. Does that mean they experience a "flat" spacetime instead of a curved one? I find it a ...
1
vote
1answer
36 views

How does acceleration affect the orbit?

I want to know what roughly happens if we hit an orbiting body a little. And how is it possible that most of the objects have seemingly circular orbits around. How do they stabilize? I ask because it ...
0
votes
2answers
41 views

Can friction be brought in to zero value by means of laboratory experiments?

By newton's first law, an object will continue to be in the state of motion of rest untill and unless an external force is acting on it. To prove or verify it experimentally today, is there any way ...
1
vote
0answers
56 views

Instantons in Witten's supersymmetry and Morse theory

I'm reading Witten's paper on supersymmetry and Morse theory and am confused about the details of the instanton calculation which he uses to define a Morse complex (beginning at page 11 of the pdf) . ...
4
votes
2answers
273 views

One question about sextupole

In multipole expansion, we use monopole, dipole, quadrupole or octupole to describe an electromagnetic field. But I saw someone use sextupole to describe transition states. If we expand an ...
3
votes
4answers
420 views

Is the potential in Schrödinger equation an operator?

In the Schrödinger equation in the position representation $$ i\hbar\frac{\partial}{\partial t}\Psi(x,t) ~=~[\frac{-\hbar^2}{2m}\nabla^2+V(x,t)]\Psi(x,t), $$ is the potential $V(x,t)$ an operator ...

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