# All Questions

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### Quantum field theory quote

I have read this in scientific American: According to quantum field theory, all particles spend a little time as combinations of all other particles" Is this right? How long? And how can they be a ...
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### UV light penetration into silicon

I'm in need of some information about UV (particularly UVA) light's ability to penetrate into silicon. Specifically, I am looking for a relationship between wavelength and penetration depth. Also, if ...
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### Magnetic engine

Is it possible to mimic crrent engine design (to some extent) by replacing the cylinders with opposed magnets? A device interupts their natural desire to push away from each other allowing them to ...
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### Cosmic Inflation: Lower Expansion Rate with than without?

When I read the Cosmic Inflation diagram at https://en.wikipedia.org/wiki/File:Horizonte_inflacionario.svg which I rotated to make it readable: where the Hubbleradius, and therefore also the ...
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### Stable Nuclei - Deviation from equal protons and neutrons

While studying the semi-empirical mass formula for nuclei, I came across an "asymmetry term" whose function, as far as I understand, is to build in the fact that nuclei "prefer" to have equal numbers ...
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### Relativistic Lagrangian transformations

I need to study the relativistic lagrangian of a free particle. It's $\ L= - m c^2 \sqrt[2]{1- \frac{|u|^2}{c^2}}$ I need to study the translation, boost and rotation symmetry. I say it doesn't ...
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### Specular intensity [closed]

Im currently studying for an exam and have been going through some past papers on the subject, however i have come across a question that has recursively come up each year and the notes on it are not ...
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### Is electromagnetism a dead research field?

Are there any phenomena, we consider as electromagnetic and have no explanation for ?
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### Showing Hubble constant is time-independent

I have the following question for homework: Show that the Hubble constant $H$ is time-independent in a universe in which the only contribution to energy density comes from vacuum energy. So in ...
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### Quantum mechanics and everyday nature

Is there a phenomenon visible to the naked eye that requires quantum mechanics to be satisfactorily explained? I am looking for a sort of quantic Newtonian apple.
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### Equivalent RC circuit to a RRC circuit?

I'm in doubt about a situation that I've seen sometimes: imagine we have a resistor in parallel with a resistor and a capacitor in series. Since I don't know how to generate figures of circuits to ...
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### electrostatic repulsion [closed]

Consider a homogeneous ring of radius $R$ made of a thin wire of cross section $A$ with $R^2≫A$. A charge $Q_1=10\mu C$, uniformly distributed over the ring, broke it apart due to electrostatic ...
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### Categorizing solutions to Hierarchy problem

We know that no gauge symmetry can prevent a term $m_\phi^2|\phi|^2$ for a scalar field, and that, given the quadratic loop corrections, the natural scale is $m_\phi \sim M_P$. This is related to the ...
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### An application of Toeplitz operators

I want to find an application of the Toeplitz operators. All I need is a known problem (not an open problem) which solution use the theory of Toeplitz operators. I don't need all the details but I ...
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### How to numerically solve a laser driving semi-classical two-level system using Floquet formalism?

Consider the semi-classical laser driving two-level atom, where the laser is treated classically and the atom is treated quantum mechanically. The effect of laser on the atom is a dipole coupling:  ...
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### A double-sided lever and multiple forces [closed]

Assume a double-sided lever where the left arm has a length of a and the right arm has a length of b + c. Please refer to this ...
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### Difference between velocity vectors, relative speed

Consider two particles moving in the same direction instantaneously but one of them follows a circular path and one follows a straight path. If I adopt a rotating frame of reference in which the ...
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### How does the volume change affect an adiabatic process?

A gas consisting of rigid diatomic molecules was initially under standard conditions. Then the gas was compressed adiabatically, 5 times the original volume. Find the mean KE of rotating molecules ...
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### Historical aspect of wave theory of light

Huygens thought light as a wave. Wave is a propagation of physical disturbance. We now know that light is electromagnetic field. Electric and magnetic field fluctuates here. What Huygens really ...
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### Dividing values with units

I'm reading about the subject of heat in a basic physics book. If I am not mistaken the formula to work out how much energy is required to increase the temperature of water is ...
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### What really is the Magnetic Force on a wire?

I have a doubt regarding the significance of a force on a wire. Well, first of all, I know that if I have a particle and if there are several forces acting over it, then we can compute one total force ...
### Derivative of $\epsilon$ in lennard jones equation
I just want to calculate the derivative of epsilon for the following Lennard Jones equation: LJ = $4\sqrt{\epsilon_{ii} \epsilon_{jj}}$ $[(\sigma/ r)^{12}-(\sigma/r)^{6}]$ with respect to ...