1
vote
1answer
289 views

$\pi$, $\sigma$ - atomic transitions with respect to the magnetic field axis

I am confused about the atomic transition with different polarized lights. I post the pictures as follows. There are four cases. In case 1, the right-handed circular polarized light ...
1
vote
1answer
50 views

Do zero gravitational-force points produce Naked singularities?

In between two singularities, does a particle experience gravity? If a particle is exactly at the midpoint between two singularities, will its net experience of the gravitational force (ignoring the ...
7
votes
2answers
1k views

Calculating diffraction patterns using FFT

I'm trying to write a piece of code that calculates a diffraction pattern similar to an X-ray experiment using a FFT. From my knowledge, the diffraction pattern for point particles can be calculated ...
1
vote
2answers
109 views

Laser cooling of atoms: more area or more power?

I want to optimise a Magneto-Optical trap. Laser beams come from the the x, y and z directions (positive and negative) and slow the atoms down. Would it be better to increase the beam spot-size ...
0
votes
1answer
56 views

Quasi-static and Poly-tropic processes

can we say all quasi-static processes are poly-tropic process?. since in a quasi-static process a smooth graph can be drawn between pressure and volume therefore, can we conclude that all quasi-static ...
4
votes
1answer
169 views

What empirical evidence is there for displacement current?

I wonder what more or less direct measurements of the displacement current exist. I know that the existence of em waves demonstrates its existence, though somewhat indirectly. I also know that there ...
1
vote
0answers
59 views

What sorts of problems does asymptotically safe gravity face as a potential quantum gravity solution?

I've recently read an article by Ethan Siegel over at Forbes (he also blogs at Starts with a Bang) on asymptotically safe gravity as a possible alternative to string theory. I read the author's blog ...
1
vote
0answers
42 views

Does it take energy to destroy the surface of a liquid jet? [closed]

Imagine we have a collision of a liquid jet with an obstacle Does it take time for the surface of the jet to be destroyed while collision?? Or it'll be destroyed immediately?
0
votes
1answer
53 views

How can I prove that the covariant acceleration is normal to the velocity?

I'm trying to show that the covariant acceleration is normal to the velocity for a massive particle. I think that I understand why this has to happen because I understand the covariant acceleration as ...
1
vote
1answer
212 views

Can a vacuum make a turbulent flow laminar?

When a vacuum is generated next to a turbulence, does the flow towards the vacuum become laminar? Imagine a vacuum cleaner tube is put next to turbulent air movement, does the "suction" change the ...
1
vote
0answers
35 views

Frozen water cooler bottle [closed]

My water bottle for my water cooler is frozen. Should I place it onto the water cooler while it is frozen, wait till it thaws a bit, or wait till it thaws completely?
1
vote
1answer
53 views

What is the coefficient of volumetric expansion of water? [closed]

What exactly is coefficient volumetric expansion? Is it $\gamma\,\Delta T$? Since water has maximum density at 4 C, is $\gamma=4\,{\rm C}^\circ$?
0
votes
3answers
99 views

What would be the capacitance of an unequal charged capacitor?

I searched for this question but I cannot get satisfactory answer. Say if we have a parallel plate or cylindrical capacitor and if I supply unequal charge to it how could I find its Capacitance. We ...
0
votes
1answer
99 views

How to calculate air flow from a pressurized tank?

I am writing an app that deals with simulated air brakes, and I need to simulate the release of air from one container of a given pressure into another container of a lower pressure. It doesn't have ...
1
vote
2answers
470 views

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, ...
4
votes
4answers
185 views

What allows us to assume spacetime is flat when no normal matter is present?

Dark matter causes a bend in spacetime. We see this through gravitational lensing. But what allows us to assume spacetime is flat when no normal matter is present? Why can't we say that dark matter ...
25
votes
5answers
3k views

Hole-and-nail paradox in special relativity

Yesterday we started relativity on our physics class, and my professor taught us a few concepts. We did some examples on how things changed by looking them from different reference systems, and a ...
20
votes
5answers
5k views

Can we create and destroy energy simultaneously at different points in a space?

Can we create an amount of energy at a point in space and destroy an equal amount of energy at another point in space, with both the processes occurring simultaneously? This will not violate energy ...
2
votes
0answers
170 views

Could a falling office tower cause the melting of its iron or steel support structure? [closed]

Discussion on META: Questions related to geopolitical events Suppose you have an office tower, weighing around 300,000 metric tons, and has a height of ...
3
votes
3answers
150 views

Why didn't the glass break?

In the figure below, a needle has been placed in each end of a broomstick, the tips of the needles resting on the edges of filled wine glasses. The experimenter strikes the broomstick a swift and ...
1
vote
0answers
58 views
1
vote
2answers
94 views

How does a charge distribution evolve with time? (in classical electrodynamics)

It is often stated that, in classical electrodynamics, the electric and magnetic fields determine uni vocally the dynamics of a charge distribution distribution (how it evolves in time). I can more or ...
3
votes
1answer
121 views

Diffeomorphism group vs. $GL(4,\mathbb{R})$ in General Relativity

I am quite confused with the groups Diff$(M)$ and $GL(4,\mathbb{R})$ in the context of general relativity. I understand that the symmetries of GR are the transformations that leave the equations ...
0
votes
0answers
26 views

Einstein-Infeld-Hoffman Equations generalized coordinates

There are three (heavy,fast) bodies in a Cartesian coordinate system with position vectors $\{\mathbf{r_1},\mathbf{r_2},\mathbf{r_3}\}$, velocities ...
13
votes
2answers
272 views

What symmetry is associated with conservation of Lipkin's zilch?

The 'zilch' of an electromagnetic field is the tensor $$ Z^{\mu}_{\ \ \ \nu\rho}=^*\!\!F^{\mu\lambda}F_{\lambda\nu,\rho}-F^{\mu\lambda}\,{}^*\!F_{\lambda\nu,\rho} \tag1 $$ given in terms of the ...
4
votes
4answers
408 views

Does steady flow imply laminar?

Most secondary school textbooks, in their chapter about fluid dynamics, seem to suggest that "steady flow" and "laminar flow" are synonyms. Though I never received any fluid mechanics course when I ...
0
votes
1answer
73 views

Lens combination

Suppose there are two lenses touching each other as shown in the diagram below. the focal length of the lenses are $f_1$ and $f_2$ respectively. Now by using the formula for lens combination I ...
0
votes
2answers
49 views

$Ae^{\mathrm{i}\omega t}$ assumption for oscillating systems (formal & intuitive)

When we obtain a system of ODE's for $n$ masses connected with springs (or otherwise obtained by small amplitudes approximation), the next steps are usually assuming a solution in form $Ae^{i\omega ...
2
votes
1answer
66 views

Superpotential for Gaussian potential well? [closed]

so I am looking for the super potential of a Gaussian well, namely $V= -e^{-x^2/2}$, and the super potential has to satisfy the Riccati equation,$ − W′ ( x ) + W ( x ) = V ( x ) − a$. Somehow I ...
4
votes
3answers
509 views

What does it mean to say work is path-independent when pushing an object in different directions?

If I apply a straight upward(perpendicular to ground) force against gravity of $5\ \mathrm{N}$ and lift an object "A" 10 meters, then the work done is: $$ W = F \times S = 5\ \mathrm{N} \times 10\ ...
2
votes
2answers
44 views

The way planets rotate and revolve [duplicate]

Why is that the all planets move in the same plane?(correct me if I'm wrong) Why not some of them in anticlockwise direction and others in clockwise direction?
0
votes
1answer
57 views

Spectrum of Laplacian on one hemisphere

as is well-known, the spectrum of the Laplace operator on $S^2$, computed via $-\Delta f=\lambda f$, is positive and discrete. What happens to the spectrum if we just take one hemisphere into ...
0
votes
1answer
29 views

Refraction inside a refracting medium

After a light ray gets refracted at the boundary of a refracting medium, why do sent the light ray keep refracting inside. Cause if you divide the medium into many boundary layers then light should ...
1
vote
0answers
15 views

Effect on mass near a black hole [duplicate]

When an object falls inside the event horizon with already huge terminal velocity directed towards the black hole, the gravity must accelerate to near light speeds which should almost increase its ...
1
vote
0answers
34 views

Single Photon Counting Module [closed]

I have a single photon counting module from Picoquant (tau-SPAD) . When it is powered on, the TTL output has a constant value of around 4 volts (as opposed to occasional TTL spikes indicating photon ...
2
votes
3answers
109 views

Is time created by movement through a higher dimensional object? [closed]

In a comment I read on this page, someone mentions a theory where time is created by moving through and slicing "moments" of a higher dimensional object. For analogy, a 2-D creature living on a plane ...
1
vote
1answer
87 views

About quantum measurement problem, proper or improper mixture?

Generally a quantum measurement is regarded as resulting in a definite outcome due to "state collapse" and the post-measurement state is described as a proper mixture with the ignorance of the ...
3
votes
4answers
393 views

Is simulating the entire universe possible?

Is it physically possible that we may one day simulate the entire universe with every single particle, field and law of physics factored in? Can n number of particles (say the number of particles that ...
1
vote
1answer
97 views

Does a spaceship travelling at near lightspeed see the universe aging slow or fast?

Now I know this probably is well trodden territory, but this question has bugged me for some time, and I couldn't find a similar question in the archives (although plenty about relativistic time ...
5
votes
1answer
226 views

Do all celestial objects have stationary orbit?

Do all celestial bodies of sufficient mass such big asteroids, moon, planets etc. have orbit such that the period of revolution is same as the sidereal period of that object (such as geostationary ...
0
votes
2answers
55 views

Equilibrium on a fixed wedge

While solving a question I came acrross this doubt.For a block in equilibrium on an inclined wedge, the summation of forces should be equal to zero.I am confused because I got two different results ...
3
votes
1answer
152 views

What is the deep reason of length contractions and time dilations? [duplicate]

In the theory of relativity, a spacetime can have length contractions or length expansions and time can have time dilations or expansions. In theory of special relativity, any physical object with ...
1
vote
1answer
34 views

Low frequency video transmission

Can a video signal be transmitted for a short distance ($30\,\mathrm{cm}$) by a very low frequency carrier ? Here my concern is about frequencies $1\,\mathrm{hz} - 100 \,\mathrm{hz}$ . Transmission ...
0
votes
0answers
13 views

Electric field in a sphere embedded in a medium

Consider a system where a sphere of conductivity $\sigma_i$ is embedded in a large medium of conductivity $\sigma_e$. An electric field $E_0$ is applied and the question is, what is the electric field ...
7
votes
1answer
661 views

Quantum Error Correction: Surface code vs. color code

Recently, two groups working on quantum computers published results on quantum error correction. The first was Rainer Blatt's group, who used trapped ions to perform a topologically encoded qubit ...
3
votes
1answer
83 views

Superposition State in Coin Toss

I was reading the following lines from Quantum Computation and Quantum Information by Nielsen and Chuang on page 278 of chapter 7. A coin has two states and makes a good bit but a poor qubit ...
0
votes
0answers
28 views

Is there any reason (other than convenience) to assume the universe is paracompact?

In this discussion on MathOverflow, it is mentioned that the universe, being a Riemannian manifold, must be paracompact. But is there any reason to assume the universe is globally 'small enough'? In ...
1
vote
1answer
60 views

Angular Momentum and Kepler's Second Law

Let me preface by saying that I get the gist of the conservation of angular momentum, at least qualitatively. To better illustrate my question, I will consider the case of a planet orbiting a star. ...
3
votes
2answers
91 views

Questions regarding the Feynman-Stueckelberg interpretaion

I am studying for an introductory particle physics exam, and I am having some problems with the Feynman-Stueckelberg interpretation of antiparticle states. Background: The course was being thaught ...
0
votes
1answer
32 views

is it possible to get energy by lowering temperature

Is it true that I have a pressure meter that is precise enough and measures fast enough, if I use it to measure the pressure of atmosphere, the measure will vary because gas molecules hit my pressure ...

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