# All Questions

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### Image formation [duplicate]

What is the real cause behind the formation of an image? It is explained as" when rays of light focus at a point image is formed." So here we have two events, one focusing of light and another ...
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### Sign convention for basic Dirac equation

The dirac equation;$$(i\gamma^\mu\partial_{\mu} - m)\psi=0$$ is just; $$(i\gamma^{0}\partial_{0} - i\gamma^{i}\partial_{i} - m)\psi=0$$ in a (+,---) metric right?
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### Magnetic Pole Emission from Pulsars

I've been reading up on some pulsar emission theory (admittedly written in the 70's and 80's, but I figured that's a good place to start), namely this review by Curtis Michel as well as the book Black ...
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### 2-body interaction energy of 3 particles

If only two-body interaction is considered then what's the energy if I put three particles on one site? Assume delta-interaction and interaction strength is proportional to scattering length $a_F$ ...
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### How does the Luminosity Function relate to the tristimulus sensitivity function?

In colorimetry, the irradiance spectrum is weighted with the luminosity function to obtain the perceived luminosity, and the tristimulus sensitivity functions to obtain the perceived ...
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### How is the equation of motion for a real scalar field derived from the Lagrangian?

The Lagrangian for a real scalar field is: $$\mathcal{L}=\frac{1}{2}\eta^{\mu \nu}\partial_{\mu}\phi\partial_{\nu}\phi-\frac{1}{2}m^2\phi^2$$ How can I derive the dynamics of this field from this ...
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### Calculating the minimum Lawson parameter for sustained d-d fusion

Calculate the minimum Lawson parameter for sustained deuterium-deuterium fusion in a plasma with an energy of 10 keV. I have been given the above question as part of a homework assignment and help ...
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### Have we observed another supernova explosion since SN 2008D?

I read the wikipedia article about SN 2008D which says: "Now that it is known what X-ray pattern to look for, the next generation of X-ray satellites is expected to find hundreds of supernovae every ...
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### How the boundary term in the variation of the action vanishes

In David Tong's QFT lecture notes (Quantum Field Theory: University of Cambridge Part III Mathematical Tripos, Lecture notes 2007, p.8), he states that We can determine the equations of motion by ...
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### What will be the shape of liquid if there is no gravitational force [duplicate]

We all know that liquid will take a shape of container in which its filled, but What will be the shape of liquid if there is no gravitational force?
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### What can be the smallest chaotic system?

As I am talking about 'smallest' can I expect that it should be a quantum system? I understand that we use quantum chaos theory instead of perturbation theory when the perturbation is not small. For ...
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When I learned Special Relativity, it was taught in terms of basic linear algebra, without any mention of the Minkowski space, proper time as integration on the metric, etc. However, when I am trying ...
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### When drift velocity equals thermal velocity?

In some papers, I can see the drift velocity of electrons equaling thermal velocity. Can anyone tell me when both almost equal each other?
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### Fermi and Boltzmann distribution of carriers in semiconductor

What are the requirements for describing charge carriers (e.g. electrons) in a semiconducting material by - Fermi distribution - Boltzmann distribution When do we apply the one or the other? If the ...
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### Relativistic kinematics of particle decay

Suppose a particle decays to three other particles. The masses of all particles are assumed to be known and we work in the rest frame of the parent particle. So there are 12 parameters for this ...
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### Are quarks the limits? The end of the fundamental science. For collisions on more higher energies will lead to black holes after all?

Are quarks the limit and the Plank scale is believed to be the limit of distance when the very concept of space and length cease to exist (10^-19) Any attempt to research the existence of shorter ...
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### Is there any theory about extra-Universal place? [closed]

I mean you can probably imagine cells and extracellular space between them. In biology some things can go through the cell membrane in and out. What if universe/s are "similar" and some form of ...
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### Weyl Ordering Rule

While studying Path Integrals in Quantum Mechanics I have found that [Srednicki: Eqn. no. 6.6] the quantum Hamiltonian $\hat{H}(\hat{P},\hat{Q})$ can be given in terms of the classical Hamiltonian ...
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### Why there is so much “nothingness” in the Cosmos?

I mean look how big is the Cosmos and hof few planets and suns are outthere, compared to the vast "nothingness" between them. With "nothingness" I mean no standard particles like atoms, electrons ...
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### Period of Transmission of signals in different frames

A radar transmitter (T) is fixed to a system $S_{2}$ which is moving to the right with speed v relative to system $S_{1}$. A timer in $S_{2}$, having a period $\tau_{0}$ (measured in $S_{2}$) causes ...
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### Speed of Universe Expansion [duplicate]

How much is the universe expanding every second (Earth second)? If you could be a bit simple in the answer that would be good.
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### Are oscillations of electron chirality experimentally observable?

Is there any plausible experiment by which chirality oscillations in electrons could be observed experimentally, such as through some analogy to neutrino oscillation experiments?
Let's say we are traveling in a train. The path has two parts: one at ground-level and the other moving up on the ramp. The ramp has an inclination of $\arctan\frac{a}{g}$ with the horizontal, where ...