# All Questions

27 views

### Dual methods in structure optimization

I am studying Structure Optimization, and the teacher took a few weeks to detail dual methods, but I don't get why it is useful. From an optimization problem with ...
391 views

### Can scattering amplitudes be simplified with 1PI diagrams?

I have been teaching myself quantum field theory, and need a little help connecting different pieces together. Specifically, I'm rather unsure how to tie in renormalization, functional methods, and ...
101 views

### Equation of motion in quantum system

The commutation relation between H and $L_i$ is $[H,L_i]$. I want to show the equation of motion. Is this right: $[H,L_i] = -i \frac{dL_i}{dt}?$
667 views

### Gravity force strength in 1D, 2D, 3D and higher spatial dimensions

Let's say that we want to measure the gravity force in 1D, 2D, 3D and higher spatial dimensions. Will we get the same force strength in the first 3 dimensions and then it will go up? How about if ...
758 views

### Bohmian loophole in PBR-like theorems

I'm reviving and expanding this question, because of the new paper today, by Aaronson et al. The more general question is: How does quantum-potential Bohmian mechanics relate to no-go theorems for ...
1k views

### Resistance between two points in an infinite metal sphere/cube

Let's imagine that we have a tridimensional metal object of infinite size, and decide to calculate the resistance between two arbitrary points. How would we go about doing this? I have thought of two ...
583 views

### Quick introduction to electromagnetism / Maxwell's equations [duplicate]

Possible Duplicate: Electrodynamics textbook that emphasizes applications I am a graduate student in applied mathematics and I am looking for a concise introduction to Maxwell's equations / ...
153 views

### What constitutes a 'reliable' instanton calculation?

In Modern Supersymmetry, John Terning, on pgs 151, and 153 performs a so called 'reliable' instanton calculation when dealing with the ADS superpotential 'since the gauge group is completely broken'. ...
224 views

785 views

### Non-commutative property of rotation

Addition of angles are non-commutative in three dimensions. Hence some other angular vector quantities like angular velocity, momentum become non-commutative. What is the physical significance of this ...
487 views

### Does a quantum phase transition have latent heat?

As the title says, I am thinking about the question that whether a quantum phase transition has latent heat. If so, at 0 temperature, we can drive the system by some parameter from disorder phase to ...
151 views

### Lightest flying solid material [closed]

I need to use a number of lanterns, to write something with it! I would like to use a light material which will bind the lanterns together (separated by space) so it looks like dotted letter. I know ...
21k views

### Is Keshe's technology for real?

http://www.youtube.com/watch?feature=player_embedded&v=UrN99RELqwo They clain they can create free energy using plasma reactors. Is this fake? M.T. Keshe said that several entities, ...
3k views

### Charge conjugation in Dirac equation

According to Dirac equation we can write, $$\left(i\gamma^\mu( \partial_\mu +ie A_\mu)- m \right)\psi(x,t) = 0$$ We seek an equation where $e\rightarrow -e$ and which ...
1k views

### charge density in a wire

If we have a infinitely thin and infinitely long straight wire on the $z$-Axis with given current $I(t)$, how can I compute the charge density? I figured out that the current-density is given by ...
364 views

### Why geometrically four acceleration is a curvature vector of a world line? And what is proper acceleration?

Why geometrically four acceleration is a curvature vector of a world line? Geometrically, four-acceleration is a curvature vector of a world line. Therefore, the magnitude of the ...
4k views

### Is the “How to break the speed of light” minute physics video wrong?

I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views. In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
128 views

### How creation of point defects in semiconductors is affected by strain?

When the effect of the strain on solids is discussed, normally the explanation is the following: increasing stress, first point defects created, then dislocations, then plastic deformation starts, ...
623 views

### Plate tectonics and water

In a couple of places already i've read the following assertion: It is believed that plate tectonics might play an important part in maintaining the presence of water on a planet's surface one ...
239 views

### Killing Vectors of BTZ black hole and their calculation in general

I was wondering what are the Killing vectors of BTZ black hole and how to guess them easily? Will it be the same as of AdS? What then will be Killing vectors for AdS-Schwarzschild e.g.?
740 views

### Physical explanation for capacitive circuit

In capacitive circuit, the voltage and current are out of phase. the current leads the voltage by 90 degrees. this can be explained by these two equations: $$V = V_{\max} \sin \omega t$$ I = ...
200 views

### Intervals as infinitesimals of same order (Landau & Lifshitz)

I don't understand the following statement in Landau & Lifshitz, Classical Theory of Fields, p.5: $ds$ and $ds'$ are infinitesimals of same order. [...] It follows that $ds^2$ and $ds'^2$ must ...
606 views

### What are thermal energy distributions?

I am trying to understand the photoelectric-effect deeply. My teacher used the Planck's law and integrated it to deduce the Stefan-Boltzmann law. He somehow showed some quantum-physical ...
80 views

### the poles of impurity system's Green's function

Denote the pure system as system 1, with both continuum and discrete eigen energy. $G_0$ is its Green's function. After introducing some impurities, we call the resultant system system 2 with new ...
1k views

### Noether theorem and classical proof of electric charge conservation

How to prove conservation of electric charge using Noether's theorem according to classical (non-quantum) mechanics? I know the proof based on using Klein–Gordon field, but that derivation use ...
226 views

### Calculating the $\frac{dp}{dT}$ slope using Clausis-Clapeyron

I've produced experimental data over how the boiling point of water varies with pressure and temperature and plotted this in a PT graph. I would like to verify my results using theory. The ...