1
vote
0answers
103 views

Debye Hückel Theory valid for ions?

I am wondering about the following: Is Debye Hückel Theory only used if you look at how an external "strong" field(like a potential by a sphere that has a charge that is 1000times higher than the ...
7
votes
1answer
133 views

Should all theories of gravity have Schwarzschild solution?

A consistent theory of gravity must include the Newton's classical theory of gravity as a weak field approximation. Moreover, to satisfy the experiments in the solar system, the Schwarzschild ...
0
votes
1answer
112 views

Inertial frame: Sun earth and moon

From the perspective of sun, is the moon orbiting the earth considered a single inertial frame or are moon and earth separate inertial frames? Or am I missing something completely fundamental?
1
vote
0answers
40 views

Choosing proper centripedal force in Newtonian gravitational forces [closed]

I am trying to do an orbit simulation, I took Newton's law of Newtonian gravitational forces. It seems to work correct, but I can't really determine the velocity of an object needed to stay in free ...
1
vote
4answers
996 views

How can a wave interfere with itself?

We know that waves can interfere with themselves to form interference patterns for example photons and electrons. How is this possible? I know it does happen but is there a proper representation or a ...
1
vote
1answer
152 views

Covariant derivative as a tensor

$$\nabla_{j} v^{i}~=~g^{ik}\nabla_{j}v_{k}.$$ Does this equality involve an intermediate step, where I take the metric inside the derivative, and then use the fact that covariant derivative of the ...
2
votes
1answer
76 views

Advantages of $e^-e^-$ or $e^+e^+$ collisions over $e^+e^-$ collisions?

Is there any (interesting) HEP process whose study would take advantage from $e^-e^-$ or $e^+e^+$ collisions with respect to $e^+e^-$ collisions?
2
votes
3answers
193 views

electron in the nucleus

In the event that the electron is in nucleus of the atom (via tunneling effects and other things I don't understand), How does QED deal with this situation?
2
votes
1answer
382 views

Phase factor for nearest neighbor hopping in the Haldane Model

In Haldane's model, he imagines a staggered magnetic field in graphene where the net flux through a unit cell is zero. To model this, he has a phase factor in next nearest neighbor hopping on the ...
1
vote
2answers
92 views

Alternative symmetries for the Maxwell Lagrangian?

I'm wondering about how to show that $A_a\rightarrow A_a+\alpha\partial_0A_a$, with $\alpha$ infinitesimal, is an infinitesimal symmetry of $\mathcal L=-\frac14F_{ab}F^{ab}$. \begin{equation} ...
1
vote
5answers
2k views

Time dilation at zero velocity (and zero gravity)

From what I've learned, the more an object travels closer and closer to the speed of light, the more time will slow down for that object.. at least from an outside perspective.. It was shown that ...
2
votes
2answers
570 views

Expectation Value of a Dynamical Variable

In quantum mechanics, we generally take about "expectation values of dynamical variables". However, by the postulates of quantum mechanics, every dynamical variable in quantum theory is represented by ...
0
votes
2answers
49 views

Relativistic momentum finding

Kinetic energy of an object $mc^2$. I want to evaluate the momentum. We know Kinetic energy, $$E_k = \frac{p^2}{2m}$$ $$mc^2 = \frac{p^2}{2m}$$ $$ p = \sqrt{2}mc$$ Note that the momentum is the ...
1
vote
0answers
117 views

Matrix Representations of Galilean group

The general group element (in the vector representation) $$ \left [{ \begin{array} {c} \bar x^1 \\ \bar x^2 \\ \bar x^3 \\ \bar t \\ 1 \\ \end{array} } \right] = \left[ ...
5
votes
3answers
263 views

Proving a step in this field-theoretic derivation of the Bogoliubov de Gennes (BdG) equations

In derivation of the BdG mean field Hamiltonian as follows, I have a confusion here in the second step: $H_{MF-eff} = \int ...
1
vote
1answer
330 views

What gives Maglev trains forward horizontal motion?

Maglev trains have superconductors which are immune to magnetic field lines with low enough temperature. Due to this property, they levitate on magnetic rails as magnetic field lines are bended below ...
0
votes
1answer
97 views

What is the longitudinal difference between the sub­solar point and the magnetic poles at time $t$ (hours)?

I'm trying to convert geomagnetic coordinate to geographic, but there are some steps in the paper which I'm reading, that I don't understand. I have the geomagnetic latitude centered around the ...
3
votes
2answers
139 views

Electron Shell Configuration

Is there a way to predict the electron configuration of an element, for example Copper is 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^10 ?
1
vote
1answer
92 views

The gravity waves from the big bang? How can we know?

The latest news says that scientists detected gravitational waves from the Big Bang. My question is how do they know the waves originated in the big bang verses any number of supernovae and or ...
5
votes
2answers
5k views

Determining the direction of friction

I had a question which has always been of slight confusion to me. Say you are dealing with your typical block-on-an-angled-plane setup. You have a block with mass m that is initially at rest. The ...
1
vote
0answers
46 views

EMF & Magnetic force at the same time?

A conductor is placed in a magnetic field, current starts to flow, and the wire experiences the Lorentz force of $x$ Newtons. However, what confuses me is that $x$ is a value that is calculated from ...
3
votes
1answer
52 views

Are photons absorbed by expanding space?

Can a photon/EM-field-excitation redshifted by spatial expansion be completely dissipated? Does the energy reach a minimum value (Planck's constant) and continue on as normal? Does expansion also ...
2
votes
1answer
253 views

Heuristic equation for Friction force between materials

I'm programming a game where different types of objects will be sliding over different types of terrains (Top-down in two dimensions). At my current level of physics education we are given the ...
7
votes
3answers
855 views

Do gravitational waves cause time dilatation?

The effect of gravitational waves in transverse traceless gauge on matter is represented by the expansion and contraction of a ring of test particles in the direction of polarization of the wave. ...
1
vote
3answers
424 views

Can virtual particles, in particular gravitons, interfere?

Question 1. Can virtual particles, in particular gravitons, interfere? Virtual particles are created and annihilated in a distance too small and a time too short to be measured. Their existence is ...
4
votes
1answer
99 views

Derivation of metric of space time with a point source in 2+1 dimension using ADM formalism

In "Quantum Gravity in 2+1 dimension" by S Carlip, Sec 3.1 (where the metric of a spacetime with a point source is derived, using the ADM formalism), equation 3.8 states that (this is the momentum ...
0
votes
2answers
207 views

Can electromagnetic fields be used to shield electromagnetic radiation?

Can electromagnetic fields be used as shielding for electromagnetic radiation?
8
votes
1answer
1k views

Why is the Hodge dual so essential?

It seems unnatural to me that it is so often worthwhile to replace physical objects with their Hodge duals. For instance, if the magnetic field is properly thought of as a 2-form and the electric ...
2
votes
1answer
3k views

Magnetic field of uniformly charged rotating hollow sphere

I want to compute the magnetic field due to a homogeneously charged, rotating sphere with radius $R$, angular velocity $\vec{\omega} = \omega\hat{z}$ and total charge $Q$. I want to use Biot-Savart ...
1
vote
1answer
583 views

Finding angular momentum about the center of mass?

If we have a couple of particles of an equal, unknown mass: $$r_{+} = (c + e^{-Bt} \cos({\theta}))\textbf{x} + (d + e^{-Bt} \sin({\theta}))\textbf{y}$$ $$r_{-} = (c - e^{-Bt} ...
2
votes
0answers
116 views

Transformation law for spinor functions multiplication

Let's have Dirac spinor $\Psi (x)$, which formally corresponds to $$ \left( 0, \frac{1}{2} \right) \oplus \left( \frac{1}{2}, 0 \right) $$ representation of the Lorentz group. What representation is ...
15
votes
1answer
947 views

Why doesn't breath condense around poop of flies on the window's glass?

One day it was raining outside and I was breathing on the glass of my window. I noticed that around the spots of fly poop there is a circle where vapor does not condense. With time the circle becomes ...
1
vote
1answer
331 views

Why is the orbital angular momentum of a pi electron along the axis of two atoms' molecule one?

I'm reading quantum chemistry. The book says that the orbital angular momentum of a $\pi$ electron along the symmetry axis of a molecule made up of two atoms is $\pm 1$. I think this is a primary ...
4
votes
2answers
158 views

Where does the $50^*$ in $SU(5): 10\otimes10= 5^*\oplus45^*\oplus 50^*$ in A. Zee QFT?

See A. Zee, QFT in a nutshell, Appendix B, eq. (24) (p. 469 in first edition with a typo $55^*\to50^*$, cf. Zee errata; p. 530 in second edition.) Where does the $50^*$ in $SU(5)$: $$10\otimes10= ...
3
votes
1answer
171 views

Mode groups in an optical fiber

I know what modes in an optical fiber mean but what are exactly mode groups in an optical fiber? From what I read until now, I have the impression that modes that have close propagation constants ...
2
votes
3answers
305 views

What is sound in terms of acoustic sources?

Sound is nothing more than small amplitude, unsteady pressure perturbations that propagate as a longitudinal wave from a region in space which created it (called the source region) into a quiescent ...
3
votes
4answers
169 views

Help understanding proof in simultaneous diagonalization

The proof is from Principles of Quantum Mechanics by Shankar. The theorem is: If $\Omega$ and $\Lambda$ are two commuting Hermitian operators, there exists (at least) a basis of common eigenvectors ...
2
votes
1answer
149 views

Enthalpy in thermodynamics!

What does enthalpy tell us about? According to definition; it is the total heat content of a system, if it is the total heat content of a system then what is Internal Energy? Since we know, ...
0
votes
0answers
61 views

Questions about four-momemtum

I am reading a note about Kerr metric, following is some screen shot where I have problems. First of all, I think the author made a mistake. It should be $$ E=-u_\mu k^\mu=u^t\;\;\;L=u_\mu ...
0
votes
1answer
222 views

Help deriving the general linear wave equation $d^2y/dx^2=(1/v^2)d^2y/dt^2$ [closed]

How do I derive the General Linear Wave Equation $$d^2y/dx^2=(1/v^2)d^2y/dt^2?$$ My teacher differentiated the general wave function $f(x + vt)+g(x - vt)$ twice with respect to both variables to get ...
9
votes
1answer
164 views

Proof of renormalizability based on analyzing the symmetry of effective action: isn't regulator also important?

In QFT Vol2 written by Weinberg(Chap 16-17), or very much similarly in Adel Bilal's notes(Chap 7), a powerful way of proving renormalizability is presented: Analyze the symmetries of the quantum ...
4
votes
1answer
2k views

What exactly does Aaron D. O'Connell's experiment show?

I watched a TED talk by the scientist Aaron D. O'Connell about actually seeing quantum superposition. The link to the talk is :- ...
0
votes
1answer
223 views

Matter-antimatter asymmetry problem

As we know that matter-antimatter asymmetry is one of unsolved problems in physics. One possible solution to this problem is given as baryogenesis which produce asymmetry in rate of creation between ...
4
votes
7answers
6k views

How do I see things of the bright room, being in the dark room?

Visible light emitted or reflected from the objects around us provides information about the world. If I sit in a dark room, and see the bright room outside, I am able to see all the objects of ...
2
votes
0answers
78 views

Questions about deduction the dual form of Frobenius's Theorem

I am reading Page 435, General Relativity by Wald. Let $T^*\subset V^*$ be a subspace of the dual tangent space of a manifold, $W\subset V$ be the subspace of the tangent space annihilated by $T^*$, ...
0
votes
1answer
391 views

Information carried by single photon

In Quantum Information we can use photons for quantum bits (qubits). What i often read is that each photon can carry one unit of information, i.e. using the polarization state of a single photon. I ...
0
votes
0answers
43 views

What does Bell's Theorem really violate? [duplicate]

Well this is a fairly straightforward question. I know it states that either hidden variables is wrong or Quantum Mechanics. But indirectly hidden variables is a part of QM due to uncertainty. So what ...
1
vote
2answers
156 views

EM Radiation and Heat

If there is EM radiation, will there always be a heat exchange between the wave and its surroundings? If you have an extremely energy-efficient light bulb that converts ALL the energy it receives into ...
1
vote
2answers
190 views

Will the way you make a coil affect magnetic induction?

We had an experiment about magnetic induction. We discoved that as the number of coils you make the induced voltage and current increases. But I'm wondering if I made the coil messy or made the ...
5
votes
2answers
275 views

Does vortex shedding exist along the surface of an object?

Vortex shedding occurs due to the detachment of flow. The typical example is for the oscillating wake behind a cylinder, and has a frequency related to the size of the object. I want to know, if a ...

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