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4
votes
2answers
546 views

What are the pros and cons of Einstein-Cartan Theory?

As an alternative to General Relativity, i hear that it can avoid the initial big bang singularity as well as the singularities in black holes, so why does it appear to be talked about so little? If ...
0
votes
0answers
10 views

What is the effect of dopant on the crystalite size?

Crystal size decreases with doping and then increases with increase in dopant concentration, why? the ionic radii of dopant is greater than the host atoms.
0
votes
3answers
63 views

Finding energy Eigenvalue from two spin Hamiltonian

Let's consider a system of two spins, named spin 1 and spin 2. Let's also consider, in a Hamiltonian, spin part has been defined as $\sigma_1 \cdot \sigma_2$. For example: $$H= E_0 + \sigma_1 \...
0
votes
0answers
35 views

How to solve a general planet orbit differential equation? [on hold]

According to Newton's gravitation law, the following differential equation can be made $$\frac{d^{2}}{d t^{2}} \mathbf{x}{\left(t \right)} = - \frac{G M }{\left|{\mathbf{x}{\left(t \right)}}\right|^{...
2
votes
1answer
56 views

Which form of Lagrangian should I choose for uniform magnetic field?

Here's the problem and corresponding question. Let's consider a uniform magnetic field $\vec{B}=B_0\hat{z}$. Looking for the solution of vector potential satisfying $\vec{B}=\vec{\nabla}\times \vec{A}...
0
votes
1answer
57 views

Finite-time Fourier transform of a wavefunction

Can someone explain this formula to me? Given a wave packet whose time evolution is $g(t)$, a partially resolved spectrum is found by Fourier transforming its overlap with the same wave packet at ...
0
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0answers
15 views

Polarisation circularly polarised light

How to distinguish between circularly polarized light and unpolarised light when passed through rotating nicole prism?
2
votes
0answers
14 views

Time reversal symmetry of the Faddeev-Popov determinant

I am studying the Faddeev-Popov procedure to quantize a non-Abelian gauge theory, and I got confused by the status of the time reversal symmetry. People have different definitions of the time reversal ...
0
votes
1answer
20 views

How to design material to avoid (light) reflections?

I wondered how a material (maybe for example a glass window) must be made to provide none or very few reflections. And while I think about it I don't really know which interaction is behind reflection....
0
votes
1answer
17 views

How does a moisture-wicking base layer reduce the evaporative cooling effect?

I read that moisture wicking base layers help keep you warm by keeping you dry, and therefore countering the effect of evaporative cooling. That made sense to me, until I SPECIFICALLY read somewhere ...
1
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0answers
40 views

Particle in a box

There is one box filled with N number of atoms and having energy E then if we open the box in free space or where there is no particle to interact with those atom of box then still atoms has energy E?
2
votes
0answers
69 views

Doesn't electrical energy gets lost due to slackening of local electrical wires hinged between street electric poles?

I am talking about the wires which get somewhat loose or somewhat like parabolic shaped due to earth's gravity. What I think is due to slackness of wires there is a net increment in resistance which ...
1
vote
1answer
10 views

Does increasing height of column in a brita filter decrease the time it takes to filter?

Using conservation of mass Min=Mout I would think not but with Bernoulli's equation I get confused. (due to density being constant and same with the area I'd think the velocity has to stay constant. ...
2
votes
3answers
117 views

How long does it take for an electron to reach equilibrium with blackbody radiation?

While teaching a course on electrodynamics, I thought of an interesting question that I think deserves some attention. Consider an ensemble of electrons all with momentum $\hbar \mathbf{k}$ ...
0
votes
1answer
52 views

A simple though experiment: molecular sieve + buoyancy = perpetual motion?

The picture below is a low-effort mock-up I made showing a closed loop with uniform ambient room temperature and top-down gravity containing two species of gas—although the idea may apply equally to ...
-3
votes
0answers
35 views

Magnetic Effects of Electric Current [on hold]

An electron being accelerated through 100V enters a unifiorm field of 0.004Tesla perpendicular to the direction of the motion. Calculate the radius of the path.
0
votes
1answer
53 views

Breaking down QFT into a single multiparticle equation of state

I'm trying to fit QFT into a familiar mathematical framework: Newtonian Mechanics (Single Particle): We have a set of particles $X$ whose locations at given moment in time is $\hat{X}(t)$ and whose ...
0
votes
1answer
45 views

Catching the beat! [on hold]

I'm lately fascinated with the whole "beat" concept, and have been doing some experiments. I'm trying to capture the beat waveform on an oscilloscope in run mode, but am having no luck. I'm putting a ...
0
votes
1answer
19 views

Are you warmer or colder when there's too much dead air insulation?

These 2 statements are both true, but I'm having trouble reconciling them, please help: When you're sleeping in a sleeping bag, you want the sleeping bag to be form fit (hence the mummy shape). If it'...
-4
votes
2answers
75 views

Is it possible that this electromagnetic field propulsion system would not violate any conservation laws? [on hold]

I have recently come up with a design of a conceptual electromagntic field propulsion system which should not violate any conservation laws, particularly the Law of Conservation of Momentum and the ...
2
votes
2answers
79 views

Can Newton's laws be reformulated with reference to “relative” frames

I was reading: https://arxiv.org/abs/1205.2326 page 2 which gives thorough discussion of the three laws. In particular there is a refutation of the (paraphrased) 2nd law implies the first because ...
0
votes
0answers
18 views

Plasma Cannon Concept

I would like to know if once a plasma is created, could it be placed into a fiberglass bullet/casing via magnetic fields then fired by a stronger electro-magnetic field. I know that the plasma will ...
-2
votes
0answers
32 views

Rotational inertia [on hold]

Consider two bodies, A and B, of equal mass set at a short distance. Body A is spinning and body B is at rest. Then, through some kind of electromagnetic device, a strong repulsive force is ...
0
votes
1answer
80 views

Greatest relativistc mass possible for a single photon

I have been told that photons can not be blue shifted to the point where they become black holes, although a photon with a Planck scale wavelength would also have a relativistic mass equal to a black ...
0
votes
0answers
13 views

Where can I find the calculation of the holographic dual to the circular 't Hooft loop?

I know that for a Wilson loop, in the fundamental representation, the dual is a string worldsheet ending on the loop at the boundary of AdS. Similarly, I guess that the object corresponding to ’t ...
-5
votes
0answers
62 views

What is exactly meant by “time is relative”?

Let's say we are traveling to the galaxy X - which will take 4 years for us to reach. However, it will take 100 years for the observer on the earth. How come is it possible? How 4 years can be ...
0
votes
0answers
31 views

What would I need to pickup to understand the theory of topological insulators? [on hold]

I am a mathematician who does mostly analysis, so excuse me for my ignorance. I was wondering where I could start learning about topological insulators. I have finished reading up on the operator ...
0
votes
0answers
17 views

creating eh-pairs in a semiconductor -> conduction or valence band?

When a beam ray respectively a photon creates an electron-hole pair in a semiconductor, e.g. for silicon the ionization energy is 3.6 eV, is the electron then directly in the conduction band? So does ...
0
votes
1answer
24 views

Deeply Virtual Compton Scattering

what are Transition Distribution Amplitudes respectively Deeply Virtual Compton Scatterings ? I'm so unsure about the terms I can't even distinguish (in case they are not really related to each other)....
-1
votes
0answers
35 views

Are quarks from two different nucleons less distant than the quarks inside a nucleon?

I am curious about atomic nucleus and the possibility that baryons could be very close to each other, but no so close. And, are protons positioned favoring the surface and neutrons more in the center ...
1
vote
0answers
32 views

Intuitive explanation of superficial degree of divergence

Consider $\varphi^p$ theory in dimension $D$. For a Feyman diagram $\Gamma$ one can introduce the superficial degree of divergence $deg(\Gamma)$. It is defined as $DL-2I$ where $I$ is the number of ...
0
votes
1answer
44 views

How can velocity and momentum be in opposite direction for antiparticles as given in the solutions of Klein Gordon Equation?

This is given in Greiner, Relativistic Quantum Mechanics For a free particle solution and antiparticle solution with momentum $\vec{p}$ the current is given by $e\frac{c^2\vec{p}}{E_p}$. The current ...
5
votes
2answers
86 views

Naming symmetries in quantum systems, e.g. $\mathbb{Z}_2$ or $U(1)$

I'm constantly confused by some of nomenclature that is associated with symmetries in quantum Hamiltonians and was hoping someone could set me straight. Specifically, we often have something like a ...
0
votes
0answers
16 views

Why does the phenomenon of localized energy producing particles and antiparticles lead to the creation of an infinite number of particles?

Penrose says the following (paraphrased) in "Road to Reality" on pg 611 of the first American edition A particle and anti particle may combine to produce energy, as given by general relativity. ...
-3
votes
0answers
40 views

Which of the following is not conserved ( for the following options) [on hold]

A smooth tube of certain mass is rotated in gravity free space and released. The two balls shown in the figure move towards ends of the tube. For the whole system which of the following quantity is ...
5
votes
1answer
667 views

Why are there fixed target experiments?

Collider experiments put all their energy into $ \sqrt{s} = 2E $ while target experiments only provide $ \sqrt{s} = \sqrt{2Em+m^²} $. Yet, there are fixed target experiments. Why?
0
votes
1answer
21 views

Quantum Interference Pattern with Perpendicular Sources

Imagine that there is a photon detector in front of me. Also imagine that there is a test photon traveling from my left to my right. As this test photon passes, I fire other photons right at the ...
1
vote
0answers
26 views

How polar researchers were able to pinpoint the south magnetic pole in 1900s?

I am reading a few books on polar explorations done in 1900s and one of the aim of these explorers was to locate the south magnetic pole. I wonder how able to pinpoint the location of south magnetic ...
0
votes
1answer
27 views

Reading energy Eigenvalues from a Hamiltonian matrix for 1D harmonic oscillator

After a perturbation $V(x)$ added to the system, a matrix element $H_{nn}$ calculated in unperturbed Eigenstates for one-dimensional harmonic oscillator is given as: $$\epsilon \hbar \omega_0\begin{...
0
votes
0answers
26 views

Do flat plates result in less drag than concave surfaces?

Do flat plates (A) result in less drag than concave surfaces (B)? Intuitively, i think flat plates produces less drag than concave surface because the concave surface makes the fluid move backwards, ...
0
votes
0answers
38 views

Colombeau Algebra for physics students

I have an undergraduate degree in physics, taken 2 years of calculus, and a rigorous course in linear algebra. I have not taken a math course in analysis, though have read a bit about it on my own. ...
0
votes
0answers
33 views

How can energy be negative for antiparticles in the solutions of Klein Gordon equation?

Although similar questions have been asked before I'm still confused. This is from Greiner, Relativistic Quantum Mechanics $E^2=c^2\sqrt{\vec{p}^2+m_0^2c^2}$ Consequently, there exist two possible ...
-1
votes
1answer
86 views

Can unitary probability theory (quantum mechanics) emerge from a lack of information about a deterministic process? [duplicate]

My initial question below appears to be unclear so I am rewording in more succinctly here. The pre-edit question remains below. There exists two types of probability theory: 1-norm (classic ...
2
votes
0answers
36 views

Possible values of the total orbital angular momentum quantum number $L$

I'm reading Gerhard Herzberg's "Atomic spectra and atomic structure" (can be accessed on archive.org, the relevant part is from p.82-87) and I don't quite grasp how to determine the possible values of ...
1
vote
0answers
47 views

What's the covariant derivative of a normalized, timelike Killing vector?

I'm reading The large scale structure of spacetime and in page 72 the author says: A static metric admits a timelike killing vector $K$. We define the timelike unit vector $V$ as $V=K/f$, where $f^...
1
vote
1answer
37 views

Some counting of field degrees of freedom for a classical spin-1/2 Dirac field

A classical real scalar field admits a decomposition $$\phi(x)\sim a_pe^{-ip\cdot x}+a_p^*e^{+ip\cdot x}$$ which tells that at each $x$, there exists a real number i.e., one degree of freedom at each ...
1
vote
0answers
21 views

Relationship between bridge pylon and water flow

Recently, I was met with the following question: When observing water flow around a bridge pylon, of the following statements, which one(s) are true: a) The bridge pylon applies force to ...
0
votes
0answers
22 views

Will a pump work with the added friction due to different cylinder dimensions? Pumped from wide to smaller diameter pipe. (Math & photo included) [on hold]

A simple pump that lifts 1,178 gallons per lever stroke. I ask this question because the bottom chamber has a larger diameter than the cylinder it's pumping water up into.(PHOTO) The math makes ...
1
vote
2answers
50 views

Centre of mass of a solid cone using a symmetrical method [duplicate]

When we rotate a right angled triangle about its perpendicular we get a solid cone. For a right-angled triangle the centre of mass is at its centroid i.e., at $(\frac h3, \frac b3)$. If we consider a ...
2
votes
0answers
48 views

Physics behind rays of light in the photographs taken in the darkness

What is the physics behind these rays of light visible in the photographs of objects that emit light? What justifies their shape and amount of rays? Very well known effect in a sense, but I did not ...

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