0
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0answers
2 views

How fast do molecules move in objects?

I guess it depends on the heat or the type of the material but can you give some examples or formulas to calculate it ? The best example would be the average speed of the air molecules (all types in ...
0
votes
0answers
3 views

Why rockets exploding in the sky sound is delayed?

I live in Israel, and we're currently in a war. There are rockets being launched at the country, and our missile defense system kills it named "Iron Dome". I just recorded the Iron Dome in action: ...
0
votes
0answers
3 views

Mathematical derivation of interference pattern for electrons?

One of the most famous experiments in quantum mechanics in the context of wave-particle duality is certainly passing a beam of electrons through two slits, which results in an interference pattern ...
0
votes
0answers
4 views

Philosophical thoughts on Reconciling Different Physical Theories—Example of Entropy

I always like to reason through the motivation behind equations, and during this process I began thinking about Wigner's 'unreasonable effectiveness of mathematics', and whether it can sometimes lead ...
0
votes
1answer
12 views

(Level: Undergrad) Continuity Conditions on the Wavefunction and Initial Values

I know that a physically meaningful $\Psi$ needs to be continuous. However, recently I came across a problem in which they were considering a wavefunction for the infinite square well potential and ...
1
vote
0answers
13 views

If I run away from gamma photons, I can see them, right?

Suppose Bruce Banner goes back in time, convinced that the Hulk is a stupid menace. Let's say he also borrows Quicksilver's speed abilities (maybe the Flash is more appropriate, but based on the ...
1
vote
0answers
6 views

How do geocentric theories explain seasons?

Did the geocentric theorists also use the fact that the earth had an axis tilt? Or was their explanation of some other kind?
2
votes
0answers
11 views

2 entangled electrons in QFT

In field theory, by quantizing a dirac field, we can obtain a creation operator for a single electron of definite momentum, of definite spin up or down, these respectively are: ...
2
votes
1answer
8 views

How would wormhole-based FTL violate causality?

We already have an answer why physically traveling faster than light would violate causality (the clock on board our hypothetical FTL spaceship would tick backwards to some outside observers). ...
0
votes
2answers
18 views

If outside a cylindrical solenoid exist an electrical field what does that mean to the Aharonov-Bohm Effect?

To the question "What is the electric field outside a cylindrical solenoid when inside is turned on a magnetic field" the answer is that outside exists a electric field. Does that mean that the ...
1
vote
1answer
29 views

Can speed be defined in the complex plane?

This question cropped up while I was playing with the equation for time dilation. If I set the speed to be $i$ (imaginary unit) the answer from the equation still makes sense, but does that matter if ...
0
votes
0answers
8 views

What is the most general definition of a bosonic Gaussian state?

I am reading this paper where the definition of the bosonic state is mentioned on page 2 here :- http://arxiv.org/pdf/0806.1625.pdf . From a general definition of any density operator in terms of ...
0
votes
0answers
6 views

Where does $R/\gamma^3$ come from in relativistic E&M?

I am starting to read many papers on electron beam physics; more specifically its motion in a magnet i.e. curved motion. The term $R/\gamma^3$ comes up a lot, but I don't know where they are coming ...
1
vote
0answers
7 views

Quasicrystals - Projections from higher dimensional regular crystals

Why are Quasicrystals Projections from higher dimensional regular crystals?
0
votes
0answers
4 views

Determining porosity in metals

I am in need of a book (preferably) or other reference material which would help technicians determine whether porosity exists in the fracture face of a tensile test bar for a variety of different ...
0
votes
1answer
15 views

Geomagnetic reversal?

I have always been told that the geomagnetic field acts "as if" there were a bar magnet inside the Earth. I now this is not true, but I feel that knowing what is actually going on would help me ...
0
votes
2answers
34 views

Can stimulated emitted photons be absorbed?

Typically a stimulated photon will be one of a pair with its stimulating photon. If the leading photon is absorbed by a particle in the ground state, will it then be re-emited by the stimulated ...
0
votes
1answer
5 views

All Andreev phenomena

Do You know any other Andreev connected phenomena apart from this listed below: Andreev reflection, Andreev bound states, Multiple Andreev reflection, Crossed Andreev reflection, Reflectionless ...
2
votes
1answer
20 views

Why do we need to prove the gauge invariance of QED (or all of the gauge theories) on the Feynman diagrams language?

Let's have the QED lagrangian. It has explicit gauge invariance, so, by the naive thinking, all of the EM processes must satisfy the property of gauge invariance. So why do we need to recheck of gauge ...
1
vote
0answers
16 views

Analytical solution of transient barometric formula for fluid in one dimension

Consider a column of fluid of length $L$, with initial density $\rho_0$ and initial velocity ($u_0 =0$) everywhere. Now at time $t=0$ gravity is switched on. No flux boundary conditions are assumed at ...
3
votes
3answers
218 views

Calculate loudness of sound: why am I getting contradictory answers?

I know of events that are happening about 45 KM away from me which are said to be 210 or 213 dB at 75 meters distance from multiple sources. I think that I can hear them, so I did the obvious: $$ ...
0
votes
2answers
20 views

What are experimental techniques to probe band structure of solids?

What are experimental techniques to probe band structure of solids? I am not looking for exhaustive list. Few simple to understand techniques will suffice.
0
votes
2answers
26 views

Straight line on 8-axis [on hold]

How would a straight line appear in a 8-axis co-ordinate system. Will it continue to look like a straight line or will it appear like zig-zag line. We can see that straight line appears like a dot in ...
3
votes
5answers
152 views

About the definition of expectation value in quantum mechanics

In quantum mechanics, the expectation value of a observable $A$ is defined as $$\int\Psi^*\hat A\Psi$$ But in probability theory the expectation is a property of a random variable, with respect to a ...
4
votes
1answer
48 views

AM Receiver and sideband frequencies

How sorry for "dummy" question. I have difficulty to understand how the AM receiver. Being a child I was taught that AM receiver resonates only with the radio frequencies it is tuned to, and "passes" ...
3
votes
3answers
78 views

How to understand the definition of vector and tensor? [duplicate]

Physics texts like to define vector as something that transform like a vector and tensor as something that transform like a tensor, which is different from the definition in math books. I am having ...
0
votes
0answers
28 views

Research Topics In Theoretical Physics [on hold]

Could someone with a broader overview of the subject, and with more academic experience list research topics in Theoretical Physics? I'm a third year undergrad thinking about future research. I don't ...
0
votes
0answers
15 views

Trouble understanding phase matching equation

consider a 2nd order non linear optical material, i.e. a material in which it holds that $ P = \epsilon_0 E + 2dE^2$. In the Born approximation, the non linear contribution to the polarization density ...
0
votes
1answer
49 views

Showing Dirac equation's Lorentz invariance and use of unitary matrix $U$

Dirac equation is $i \hbar \gamma^\mu \partial_\mu \psi - m c \psi = 0 $ To show its Lorentz invariance, we convert spacetime into $x'$ and $t'$ from $x$ and $t$ and then $( iU^\dagger \gamma^\mu ...
0
votes
0answers
13 views

Is there some other name used for “ping rigidity”?

In MTW, p. 398, "Box 16.4 (continued)", there's an interesting sketch (which can also be seen on p. 15 of this excerpt (www.pma.caltech.edu/~ph236/yr2008/readings/MTW_Chapter16.pdf). (It's not the ...
1
vote
0answers
32 views

Defining axes for conservation of energy [on hold]

Problem: A bungee-cord jumper is on a bridge that is $y_1$ above water level $y_2$. The bungee cord obeys Hooke's law with spring constant $k$ and has a relaxed length $L$ The jumper stops before ...
2
votes
4answers
39 views

Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
-1
votes
0answers
17 views

Solve the given differential equation by using Green's function method [migrated]

I am really struggling with the concept and handling of the Green's function. I have to solve the given differential equation using Green's function method $$\frac{d^{2}y}{dx^{2}}+k^{2}y=\delta ...
0
votes
1answer
73 views

Quantum states and state vectors

Does a state vector correspond to only one quantum states and the components in the state vector correspond to different states of this quantum state or is it that the components of the state vector ...
0
votes
0answers
11 views

How much inductance and capacitance generate in copper strip? [on hold]

I have 60m long copper strip and cross-section area of 25mm x 3mm. and also it has some 90 degree turn after 10m distance. So, How much inductance and capacitance will be generated in strip.? and we ...
0
votes
2answers
51 views

What is the electric field outside a cylindrical solenoid?

What is the electric field outside a cylindrical solenoid when inside is turned on a magnetic field? The question is related to the question aharonov-bohm-effect-electricity-generation
1
vote
0answers
246 views

Fourier Transform of Poisson Equation [migrated]

While trying to solve the Poisson Equation by using Green's Function I have to Fourier transform the equation i.e $$-\nabla^{2}\phi(r)=\rho(r).$$ In the book after Fourier transform, the solution ...
2
votes
1answer
103 views

Lorentz group representations in QFT: what's the vector space?

In QFT, a representation of the Lorentz group is specified as follows: $$ U^\dagger(\Lambda)\phi(x) U(\Lambda)= R(\Lambda)~\phi(\Lambda^{-1}x) $$ Where $\Lambda$ is an element of the Lorentz group, ...
0
votes
1answer
44 views

Why point mass leaves it's own gravitational well? [on hold]

I suppose that point mass has its own gravitational well. Why this point mass is still attracted by other gravitational waves. I expect that this point mass is surrounded by "gravitational hills". Why ...
0
votes
0answers
18 views

Double slit experiment with monchromatic light and wave packet of a few photons. How are they different?

I am confused about the de broglie wavelength of photon and the wavelength of the electromagnetic wave after reading this experiment. In a double slit experiment, when light falls on the two slits, an ...
1
vote
1answer
82 views

A Spin up particle in QFT

This appears like a question that is rarely addressed in field theory pedagogy (perhaps because the answer is obvious): how does one describe a particle of definite spin in quantum field theory? For ...
1
vote
2answers
65 views

Why does the earth have to feel a pull when something falls?

Heck, I'm not even worried about the speed of a reaction. But remember that if I fall towards the earth, with a force, the earth has the same force exerted upon it in the opposite direction. I was ...
-1
votes
0answers
15 views

why does muon hop rate in metals change with temperature like this

you can find this figure in this pdf we use μSR to study the superconductor properties,,but I don't quite understand the T^-9 slope, does muon trapped in an interstitial site and hop rate drop with ...
1
vote
1answer
63 views

How to compute observables from the boson field operator?

I think I understand that if given the two boson wavefunction of two different states \begin{align} \Psi(\boldsymbol{r}_1,\boldsymbol{r}_2) = \dfrac{ \psi_1(\boldsymbol{r}_1)\psi_2(\boldsymbol{r}_2) + ...
1
vote
1answer
51 views

Help with ideal gas law manipulation

Equation 1 represents an improvement over the intial assumption of constant mass velocity (i.e., $\rho v=\rho_o v_o$). We can now improve Eqn. (2) to get to Eqn. (3). My question is: what are the ...
0
votes
0answers
14 views

What is the way to make a semi-transparent object to appear white? [on hold]

Can an object appear opaque white to the eye but still be transparent ; i.e. pass light through (like a one-way mirror effect) In other words, is there any other way for an object to appear white, ...
0
votes
0answers
18 views

Quantum Energy Teleportation and Stress-Energy tensor divergence

This question is about a paper from last year about Quantum Energy Teleportation. If I understand the main assertion of what QET is supposed to involve, basically you are teleporting energy as ...
-1
votes
2answers
57 views

Projectile Motion with air Resistance - Adjust only the Angle to hit a target

OK, let me preface this by saying i am not a physics student, nor have i ever been. I am a software engineer working on a development degree. So this is homework but the assignment was just to create ...
0
votes
0answers
10 views

Regimes of Josephson junction

There are several formulas to describe critical current in Josepshon S-N-S junction mainly based on Elianberger and Usadel equations. The starting point is the Nambu-Gorkov equation and then some ...
0
votes
2answers
73 views

Why angular momentum about three independent axes?

The generic commutation relations for the angular momentum operator are $[J_x, J_y] = i \hbar J_z$, where the $J_i$, $i = x,y,z$ are the components of the angular momentum vector operator, $\mathbf ...

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