# All Questions

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### Brane-world interaction: What is it?

I have read some articles about the string theory (In my opinion it is by far the most nonsensical theory of physics) and heard about brane-world interactions. What is a brane-world interaction? Is it ...
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### Why trajectories approach to origin tangent to the slower direction?

I am reading non-linear dynamics from Strogartz. Suppose, I have two solutions of a non linear system: $x(t) = x_0e^{at}$ and $y(t) = y_0e^{-t}$, where $a\in \mathbb{R}$. Now it is clear that,for ...
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### How can one produce a projected electric field?

How can one produce an electric field? I understand that there is a method involving metal sheets and running an electrical current through the parallel sheets. However, is there a simple way to ...
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### Are all maximally symmetric spacetimes constant curvature spacetimes?

A $d$ dimensional maximally symmetric spacetime is a spacetime with the maximum allowed number of Killing vectors. This number is $\frac{d(d+1)}{2}$. Constant curvature spacetimes are spacetimes ...
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### What subatomic particle is a blackhole composed of?

In a black hole, what is the "state" in which the mass that is present is in? Are they there as tightly packed neutron or soup of quark or are particles broken down into 10D strings and coiled as ...
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### Singularity function [on hold]

If $$h(t)= \begin{cases}0 ,& t<0 \\ 4 ,& 0< t <2 \\ 6-t ,& 2< t <6 \\0,& t>6\end{cases}$$ Express $h(t)$ in terms of the singularity functions. (Unit ...
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### Path of EM wave propagation in a circuit wire

The image is my visualization of drift velocity and electromagnetic (EM) propagation of charge wave in a closed circuit. The slow drift velocity of the electrons follows the path of the circuit (a ...
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### Will the block #3 move? [on hold]

Hey, On my test I've been assigned to calculate acceleration of the box with mass = m3(I'll call it block #3). The problem is, I can't even imagine the block moving, as I cannot find any force ...
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### Relative speed of Geostationary satellite with respect to earth?

I was wondering whether relative speed of geostationary satellite with respect to earth is zero or not.Since angular velocity of satellite about earth is same as angular speed of earth about its own ...
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### Determinant of a propagator

Say I have a path integral $\int D \phi \exp(i S_0)$. $S_0$ is the usual free action $$S_0=\frac{1}{2}\int\phi (-\Box-m^2) \phi=\frac{1}{2}\int \phi G^{-1} \phi,$$ and at the moment I'm not ...
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### Machine readable database of gamma lines

Friends of mine did a lab experiment where they recorded $\gamma$-spectra in the range from 0 to 1500 keV with a soil sample. The data contains some background and a couple sharp peaks at different ...
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### Expectation to uncertainty

We know that in the case of $O$ being an operator, $\langle O^2\rangle-\langle O\rangle^2$ equals to uncertainty as long as $\langle\rangle$ means the mean value (expectation value). if we have $A$ ...
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### Does limiting to infinity violate laws of physics?

It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$. So if I want to find the limit of ...
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### $\rho g h$ and shape of container inconsistency?

The Scenario Suppose I have a cylindrical beaker and a conical flask (which cross-sectional area is bigger at the bottom), each located on an identical digital weight scale. Both of them have the ...
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### Help me select a motor! [on hold]

I am having trouble selecting a motor to power a crank-rocker system I am building. I honestly don't know much about DC motor selection so would you guys be able to help me out? I am looking for a 12 ...
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### Can momentum have a complex expectation value?

I'm making examples of wave functions to incorporate in a QM exam. I came up with the following wave function, which gives me some troubles: \psi(x,0) = \begin{cases} A(a-x), & -a \leq x \leq ...
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### Why is it useful to study spatially inhomogeneous spacetimes? [on hold]

There are many scholars who have dedicated their efforts towards finding solutions to the Einstein Field Equations that are spatially inhomogeneous. Current cosmological observations indicate that on ...
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### What do you actually mean by DC voltage again and AC voltage gain? [migrated]

What do you actually mean by DC voltage gain and AC voltage gain? I know their formulas but I do not understand what they actually are? That is, basically I do not understand what is their ...