# All Questions

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### Can the question of a gravitationally accelerated charge radiation be tested experimentally?

I know that the question of radiation from a gravitationally accelerated charge has been discussed extensively at Does a charged particle accelerating in a gravitational field radiate?. Yet the ...
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### Which experiments of harmonic generation at low frequency are preceeding Franken SHG?

In "The principles of Nonlinear Optics" by Shen, he says that that generation of harmonics at low frequencies were long known before Franken did SHG in optical range. "Franken's idea was simple. ...
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### what is the reaction force of electromagnetic force created on a conductor in a magnetic field?

If a force is created on a conductor carrying a current in a magnetic field, what does the reaction of this force act on?
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### Why , under constant light intensity and constant frequency, do electrons emitted from a metal surface travel at different speeds?

I was playing around with this PheT simulation: https://phet.colorado.edu/en/simulation/photoelectric Under a certain threshold wavelength and an intensity at 20%, the electrons were being emitted ...
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### Does 'real' photon electromagnetically interact with matter?

Consider the standard description of Compton scattering - radiation is constituted of stream of photons (these are supposed to 'real' as contrasted to 'virutal' photons of the QED). One of these ...
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### Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...
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### pendulum acceleration vector

I'll make this quick, I want the acceleration vector for a pendulum WITHOUT using angle acceleration and angle velocity, just using the tension and gravity forces.
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### Flame composition types

Can anyone define the atomic structure of a carbon fuelled flame. I have studied variations of flame patterns but this type seems to stand out.
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### What is a good book to self-teach optics?

I'm interested in camera lenses and how things like barrel distortion and lens flare happens, but know that one cannot just start there. I'm a math major and I've worked out of Strauss PDE book so I ...
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### Why are LIGO's beam tubes so wide?

Gravitational wave detectors and particle accelerators have at least one thing in common -- they require long vacuum tubes through which a narrow beam is fired (a laser in the gravitational wave case, ...
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### Optical bandpass filter at focal point of lens

Optical bandpass filters are designed for a particular angle of incidence (AOI), e.g. see Fig 4 here. However that is for the ray picture of light. Imagine I have a thin bandpass filter positioned ...
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### A Take on Dark Energy [on hold]

Extreme over-simplification alert (the full proof is hundreds of pages long and it’s quite unfinished as of yet). Okay, I have a simple (enough) explanation of what dark energy is, but I am not sure ...
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### How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...
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### Which one of these energy formulas is correct?

Which one of the following formulas is correct? What do they mean/represent? How are they used? $E=mc^2$ $E^2=m^2c^4+p^2c^2$ $E=\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$
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### Why cannot a fundamental string couple to the R-R gauge field $C_{\mu\nu}$?

People usually say that D-branes can carry R-R charges, or can couple to R-R sector gauge fields. But why a fundamental string cannot couple to a 2-form R-R sector gauge field? What's the essential ...
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### Is using nonlinear crystals considered nonlinear optics according to you?

Ok let me rephrase would you consider interaction of nonlinear crystals with light that does not have enough intensity to induce nonlinear polarization ?
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### Why can´t we call the energy released after the annihilation of a particle and its antiparticle pure energy?

As a particle and its antiparticle annihilate each other a huge amount of energy is released, and no mass is left. This energy always comes in the form of force mediating particles (photons, gluons). ...
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### Partial trace with unitary

We know that $\mathrm{Tr}_B(\rho(t))\neq\rho _{S}(t)$ in general. But why if we include the unitary in the partial trace: \begin{eqnarray} \mathrm{Tr}_B( U_B^\dagger (t)\rho(t) U_B(t)) &=& ...
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### Will this approach to gauge-gravity duality work?

This is a question on whether quantum gravity has an internal symmetry structure given by gauge fields. I set up the basics of the idea first. Let us consider the complex 3-dim space $E^3$ with the ...
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### How thin lens model work when there are two images with different distances from the lens?

I am trying to understand how thin lens camera work. From what I understand of thins lens model, the image is formed on image plane that obey the equation $$\frac1S_1 + \frac1S_2 = \frac1f$$ So ...
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### What are Superstring Theory's equations which provide the successful unification between general relativity and quantum mechanics? [duplicate]

This is NOT a duplicate question. The thrust of this question is "What are Superstring Theory's equations which provide this successful unification between general relativity and quantum mechanics?" ...
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### Laplacian equations and transformation invariance and homogeneous functions

Functions whose Laplacian is zero are said to be harmonic. 1) Do harmonic functions always imply a conservation law and transformation invariance of some kind? 2) Homogeneous functions do not admit ...
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### QFT Weinberg scattering thoery

I have a question about beginning of chapter 3 (scattering) of QFT.vol.1 by Weinberg i think (am i wrong?) $\Psi_\alpha$ means a collection of particles each whit a definite $p^\mu$ specially $p^0$ ...
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### Wave speed derivation using x^2, x^3, etc

The derivation below uses a circle approximation of the curve. How would you do it with a parabolic, cubic, or higher order approximation(x^4, x^5, etc.)? I've heard one would just approximate the ...
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### Can we bring the distribution of the landing places of falling leaves from a tree bring in connection with a Lorenz attractor?

I have already asked a few weeks ago if the motion of a falling leave is chaotic. Wich it is. But if we consider the collection of the trajectories of all the falling leaves, a pattern emerges on the ...
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### How can the concept of locality be used for feature engineering the concept of spacetime?

Can spacetime be described in terms of (some sort of) evolution of locality (being able to observe the local things only)?
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### A lot of high power microscopes have 2500x magnification, why that specific number?

I've been shopping around for a microscope, and I've noticed something I didn't really expect. Across different brands, across different times (look at some "vintage stuff"), many many microscopes ...
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### Does changing a closed surface in the manner outlined contradict Gauss' Law?

As I understand it, Gauss' Law states that the electric flux on any arbitrary closed surface is equivalent to the sum of all charges enclosed within the surface times a constant. Mathematically, this ...
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### Topological insulators and high symmetry points

I've been reading about topological insulators (topological systems in general) and one signature (or the defining signature?) is that an odd number of surface states cross the Fermi energy between ...
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### At which points Normal reaction acts on a moving object is more , if possible give an image for this , A,B,C,E . Thanks For Answering [on hold]

At which points Normal reaction acts on a moving object is more , if possible give an image for this , A,B,C,E . Thanks For Answering.
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### Can we use radiation pressure to push human

I want to know, at least in theory, are there any safe em wavelength that could affect human body as net force and do no harm To put it bluntly I want to know is it possible for levitate human on ...
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### Photons are self-conjugate but neutrinos may or may not: why is that?

Caution: This may be a very naive question but I find it confusing. Moreover, I believe this question is based on potential misconception. I would like it to be clarified. Although the neutrinos are ...