# All Questions

206,019 questions
Filter by
Sorted by
Tagged with
27 views

### Why laplacian appear in so many places? [duplicate]

diffusion equation, Schrodinger equation, poison and laplace equation,sound wave equation these all equations are having one thing common, LAPLACIAN.why this quantity pops up everywhere? is there any ...
25 views

### What will happen if the inner walls of the perfect blackbody (shown in the image) is made perfectly reflecting?

I am curious about making the inner walls of this blackbody perfectly reflecting instead of perfectly absorbing. If I keep on giving in incident radiation,the photon density inside will increase, ...
• 408
18 views

### How is energy conserved in interference of light waves? [duplicate]

How is energy conserved during interference of light waves? I already know a textbook explanation that in constructive interference the resulting intensity is four times the initial intensity and for ...
• 408
24 views

### Confused about the scattering Operator in LSZ reduction formula

In Greiner's Field quantization book, Chapter 9 on the LSZ reduction formalism, he states $$S_{fi}=\langle q_1,...,q_m;\text{out}| p_1,...,p_m;\text{in}\rangle\tag{9.10}$$ where $S$ is the scattering ...
• 361
6 views

### Experiment on gravitational redshift with receivers at different altitudes

Is there a repeat of the Pound-Rebka experiment on gravitational redshift, where the receiver was placed at two different height distances from the transmitter? What was the result of the experiment?
• 8,475
1 vote
31 views

### Why are composite particles grouped with force carrying particles?

This Huge confusion with Fermions and Bosons and how they relate to total spin of atom says a hydrogen atom is a boson. I'm confused. I thought bosons were force carrying - e.g. a photon, gluon, etc?
• 123
47 views

### Force of an accelerating ball?

By Newton's second law, we know that $F=ma$. If I were to drop a ball from some height, it would accelerate to the ground with gravitational acceleration. But if I were to drop the same ball from a ...
15 views

### ·Can Physically Apply + Positive Newton's III Third Law of Motion as Cycle System in a Motor Engine [closed]

*Physically Can Apply Positive/in favor Newton's III Third Law of Motion as a Cycle System in a Motor Engine Device? 3rd Thermodynamic Law Applicate in a Power-Plant Device. The Reaction at From of ...
1 vote
44 views

### Do the null geodesics of photons emitted by Hawking radiation arise from the event horizon?

It is a well-known explanation of Hawking radiation that it originates from the quantum fluctuations near the horizon. Does it mean that one can look at the photons (part of the radiation) and follow ...
• 497
52 views

### To what extent can phase transitions be made rigorous?

It seems a lot of physical intuition in statistical mechanics, for example phase transitions, critical temperature, scaling hypothesis, renormalization group methods etc. should have a purely ...
• 361
22 views

### Can I treat fluid a rigid body calculating Moment of inertia? If not, how would I calculate it?

I wanted to set out calculating how much moment of inertia a bottle of water had so as to see how fast a bottle had to spin to create a non-zero constant angular velocity in the water. As I understand,...
7 views

### Confusion on FFT grid size used in ab initio calculations for periodic systems with planewave basis

Sorry it might be a long post, I'll try to write down all my thinking on this topic, and it is appreciated to point out whether and where I make mistakes. We are talking about algorithms used in ...
• 1
36 views

### Why does temperature remain constant in this case?

Consider two ideal gases of differing heat capacities. They occupy separate compartments of the same total volume. Assume their initial temperatures and that the amount of substance for both are the ...
• 187
438 views

### Do supermassive black holes at galactic centers and the galaxis containing them spin in the same axis?

If the galactic mass is rotating around a central supermassive black hole, should their spin axis not be the same, just as we would obtain for the rotation of a star and its planets ?
8 views

### Why does magnetic dipole's north pole pointing in the direction of magnetic field increases overall magnetic field?

I'm studying magnetic moment- current loop, electron/proton/charge revolving, magnetic dipole etc. This is about paramagnetism of materials. According to me magnetic dipole's south pole is attracted ...
1 vote
32 views

### What causes the flow of electrons from anode to cathode in a Daniell cell?

In a standard galvanic cell, I understand that electrons flow from the anode to the cathode. For example, in a Daniell cell, electrons flow from the Zn anode to the Cu cathode. Before the two half-...
1 vote
38 views

### Absence of velocity in energy conservation

Here we see a rod at rest hinged about a point. We want to know the angular speed of the rod when it becomes vertical as shown in the figure. The solution which is given in the books goes like this. ...
• 579
24 views

### Gravitational Aharonov-Bohm Effect and Conservation of Energy

Like for the electromagnetic Aharonov-Bohm effect of QED, the gravitational Aharonov-Bohm effect has recently been proven in an experiment done by Ch. Overstreet (2022), showing that the gravitational ...
• 738
113 views

### Can you see on Miller's planet?

I have read this question: Miller's world would be fried by a strong flux of extreme ultraviolet (EUV) radiation. The cosmic microwave background (CMB) would be blueshifted by gravitational time ...
• 25.4k
22 views

### Confusion on number of component of Cauchy stress tensor

The Cauchy stress tensor is often presented as a tensor having $(2,0)$ tensor having nine components in any given basis. However, I think it should actually be $6 \times 3 =18$ because a cube has six ...
• 5,558
10 views

1 vote
78 views

### How does string theory relate superposition and general relativity?

So I know that in general relativity, superposition cannot be true. However, since string theory supposedly connects quantum mechanics and gravity, how does it relate superposition and gravity?
46 views

### Finding Equation of motion from Lagrangian

I am given the following Lagrangian: $$L = \frac{ml^2}{2}\left((\dot\theta)^2 + \sin^2{(\theta)}\dot\phi^2\right) + \frac{I\dot\phi^2}{2} + mgl\cos{\theta}$$ which is meant to represent a simple ...
• 11