# All Questions

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### Help needed to understand the dispersion curve of a 1D lattice with diatomic basis

I am trying to understand the dispersion curve (as shown below) of a 1D lattice with diatomic basis. Here are my questions: Can both optical and acoustic branch of phonon simultaneously exist in ...
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### What is the Quantum Transition Time for Photon Emission?

When an electron in an atom changes energy states to emit a photon, how long does the process take? Is this question even meaningful?
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### Few particle fermion system wavefuction

Suppose I have 3 fermions($\left|\psi_1\right\rangle$, $\left|\psi_2\right\rangle$, $\left|\psi_3\right\rangle$) and a system with 3 states ( $\left|1\right\rangle$, $\left|2\right\rangle$, ...
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### Length contraction

I am trying to work out the length contraction using the Lorentz transformations. Here is how I stated the problem: Suppose a bar (whose proper length is $L$) is moving at speed $u$ (to the right) ...
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### Group representations as vectors

This might be something basic, but it is unclear to me. So I am used to work with representations of groups as matrices. These matrices represent the structure of the Lie algebra by satisfying the ...
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### Find the current/ potential difference across each bulb [on hold]

I need help solving this problem: Two identical bulbs are connected in parallel to a different source, one with E = 8.0 V and internal resistance 0.8 ohm. Each light bulb has a resistance R = 2.0 ohm ...
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### Calculating the distance that a telescope can detect [on hold]

A typical 4-meter telescope is capable of detecting stars with apparent ￼magnitude of +24 with an exposure time of 5 minutes. Using this exposure time, ￼out to what distance (in pc) can this telescope ...
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### Compute convective heat transfer coefficient for a condensing steam

I have a question about convective heat transfer coefficients. I am trying to figure out how much steam I can condense in this specific heat exchanger. Steam at 9 MPa is condensed in a 1 shell pass, ...
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### Dynamics of modifing a Hamiltonian

I am working on quantum mechanics right now, and I am wondering if there is a qualitative way to think about off diagonal term of a Hamiltonian matrix? I know that we can diagonalize a matrix, then ...
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### Pedagogical introduction to vertex, domain wall, and kink

Recently, Majorana fermion becomes hot in condensed matter physics. The concepts: vertex, domain wall, and kink often appear in these articles about Majorana fermion. I have no idea about the ...
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### Electric Field Resulting from a Conductor

In preparation for an upcoming exam, I've been attempting to visualize the electric field produced by a conductor in a variety of situations. I asked myself the following question and attempted to ...
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### Where does the energy from a parachute go?

When a parachute slows the velocity of an object where does the energy go? If it's a falling object the acceleration from gravity is roughly constant. How does air drag "dissipate" the extra energy?
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### Local unitary transformation that maximizes overlap

Could anyone point me in the right direction (reference to papers would suffice) regarding the following: Given two quantum states $|\psi\rangle ,|\phi\rangle \in (\mathbb{C}^d)^{\otimes n}$, where ...
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### Normal Ordering the phi^4 interaction

I am trying to quantize the quartic potential $\frac{\lambda}{4!}\phi^{4}$ in a box of side length $L$, with periodic boundary conditions. I have expanded the field ...
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### Is my interpretation of how a gravitational wave is formed correct?

I'm sure many here are familiar with the following image showing the 2D representation of how the fabric of spacetime is warped by the presence of mass:- Can this fabric be interpreted as an ...
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### Right Hand Rule for Proton Magnetic Field

I thought that right hand rule was for find the magnetic field generated by a current, where your thumb point in direction of the current. However, I was watching something that said we can curl our ...
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### How can we tell if a molecule is in thermodynamic equilibrium from scattering data?

We have a molecule that is emitting/absorbing photons. We know the Hamiltonian and that there are several levels. We count the emitted photons at different angles and frequencies. We can also do ...
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### What does “shortwave radiation” mean to a meteorologist?

I'm have an empirical model developed using surface observations of radiation (400-1100nm). I tend to think of this as visible, near infrared, and a little bit of shortwave infrared. I now need to ...
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### Charged particle singularity

Is it possible to manipulate magnetic/electric fields, similar to magnetic confinement technologies/penning traps, to compress charged particles into black holes?
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### How is anti-hydrogen captured?

Knowing that the overall charge is zero, what mechanisms/technologies are used to capture anti-hydrogen? Where is it stored until annihilation? I am aware of magnetic traps being used to edge the ...
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### Relativistic Doppler Effect and the Sagnac effect

What I think I know about the Sagnac effect can be found here. It occurs to me that the equations for calculating the time do not take the Doppler effect into account. I'm familiar with the very ...
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### What is the role of exotic hadrons in particle physics? [on hold]

As the title! I like lots of detail. Thanks folks! EDIT: As user23873 brought to my attention, I am referring to tetra/penta quarks and others like those recently discovered at CERN.
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### How do we 'watch ' atomic interactions?

I'm relatively new to objective physics and it's measuring and imaging abilities.. Specifically I don't know if we can 'watch' inter/or intra molecular exchanges like the photonic and electronic. I ...
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### How to see the ground state degeneracy (GSD) from a $BF$ theory in $2+1$ $d$?

I have seen many times the $BF$ theory has non-trivial ground state degeneracy (typically on torus), but I can not see how the conclusion come out. Recently I found a paper by Hansson, Oganesyan and ...
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### Circuit Diagram [on hold]

Three resistor are put into play, two in parallel and another in series to them. One of the resistors in parallel is decreased. what will happen to the voltage and current.
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### How can light have the same speed for all observers? [duplicate]

I'm a little confused on this. If you're travelling at, say, 10% of the speed of light then light is travelling at 3x10^8 ms^(-1) relative to you. If you're moving at 80% of the speed of light and ...
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### Interaction Lagrangian forms

When a charge motion is given (known), the electromagnetic field can be explicitly found (Retarded potentials, etc.). The interaction Lagrangian density is $j\cdot A$ or in the action it may look like ...
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### Theory on what would happen if a proton touches anouther [on hold]

I came up with a theory on what would happen if two protons touched each other. I want to know if it is scientifically valid. If two protons repel each other, then the closer you bring them together, ...
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### Electric Field due to volume charge [on hold]

Electric Field at point P due to volume charge Since,the Electric field at point (0,0,z) is dE = ρvdvaR/4πε0R2 aR = cosα az + sinα aρ where aR means unit vector R can anyone derive the above ...
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### Dry Ice Sublimation time, practical calculations [on hold]

I would like to send a parcel to a family abroad with frozen (to the temperature of -18 ° C.) products.The products are small balls having a diameter of 4 cm. Balls are made from pizza dough.Total ...
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### Why do we believe in a “force” driven universe? [on hold]

Why do we not believe in the potential for a "unified force field" universe, to the exclusion of the belief in the potential for a mechanical, gear driven universe, if the correct shape for the gear ...