# All Questions

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### How to Find how far away could binary system be?

Human eye resolution is about one arcminute. Two stars in a binary system are separated by 10 AU. How far away can they be such that your eye could still distinguish them as two separate stars rather ...
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### What is the relative speed of the galaxy with respect to the Earth

Consider a distant galaxy. Though this is a bit contrived, suppose that an astronomer measures the fourth transition of the Brackett series of transitions from n > 4 to n = 4 in Hydrogen at a ...
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### Landau's Problem - Poisson bracks of a spherical symmetry function and angular momuntum in z axis

In landau's Mechanics, there's a problem: I think, if the function has the property spherical symmetry, or: $\phi(r,p)=\phi(-r,-p)$ The form suggested by landau follow this property, but I can't ...
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### How tachyons violate causality?

Something to move faster than light should have imaginary mass,like photons have zero mass and thus travel at 'c'. i have read the article of physicist E. C. George Sudarshan. he said taking mass to ...
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### highest density of water

If temperature is decreased, volume decreases. so density increases. But in case of water, its density increases till 277 K, then decreases. Why does this happen? Why 277 K is water's highest density? ...
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### Temperature in CFT

Non-vanishing Temperature can break conformal symmetry(Can anyone show this point explicitly), my question is that in AdS/CFT the temperature of boundary field theory is non-zero, why the boundary ...
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### What make us fall when we move on ice?

This is a common phenomenon and most of the people have encountered this while moving on ice:falling down! Why does this occur? According to me, it is due to lack of static friction. But why will it ...
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I'm trying to test my recently installed MEEP program for a very simple AC current. I know that for DC current, Ampere's law dictates that the magnetic fields must drop off as 1/r. How does this ...
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### Mechanism of Supersymmetry Breaking (F-term, D-Term, Mediated)

I will make my question clear. SUSY is broken symmetry because we haven't seen superpartners. As far as I know, there are two mechanism of SUSY breaking, F-term and D-Term. Besides, there are some ...
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### Schrodinger Wave Functional (quantum fields) - Solving Functional Gaussian Integrals

Okay, So i'm doing some research that involves the Schrodinger representation in quantum field theory. The ground state wave functional for the Klein Gordon field is a generalized gaussian in position ...
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### A new interpretation of QM [on hold]

Do you think that this new interpretation of quantum mechanics has solved the measurement problem completely as it claims? http://article.sapub.org/10.5923.j.ijtmp.20140405.04.html
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### Currents inside real conductor in transmission line?

At first, consider transmission line with two conductors where TEM mode is established and conductors are perfect. As we know, on surface of conductors we will have surface currents (connected to ...
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### How to derive Schrodinger equation?

Schrodinger equation is the basis to understanding quantum mechanics, but How we can derive it? I asked my doctor but he told me that it is came from the experience of Schrodinger and his experiments. ...
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### Really quick question about the order of operations in the Lorentz force

I'm trying to calculate the Lorentz force for a particle in a uniform electric Field, E and magnetic field B. The formulas is $$F=q(E+v\times B)$$ I'm just wondering what the order of operations is ...
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### One step in deriving the Einstein-Hilbert action

In this amazing first principles derivation of the Einstein-Hilbert action there is one small manipulation needed to show $$c g_{ab,cd}\left(\eta^{ac}\eta^{bd} - \eta^{ab}\eta^{cd}\right)$$ is ...
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### Net Electric Field of Multiple Charges [on hold]

Question: Four charges, each of magnitude +Q are placed at the corners of a square of side a. Obtain an expression for the electric potential at the centre of the square and at the mid point of one ...
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### Deriving the Coulomb force equation from the idea of photon exchange?

Since Newton's law of gravitation can be gotten out of Einstein's field equatons as an approximation, I was wondering whether the same applies for the electromagnetic force being the exchange of ...
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### Interpretation of angular momentum in semi-classical vector model

My Professor said that when we calculate the total angular momentum of multiparticles, in this case i.e. 2 particles, we can add total angular momentum by thinking this way, if both spins allign they ...
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### 1D Infinite Square Box Discrete Energy levels but Continous Momenta?

In the 1d particle in the box the energy of the particle should be completely determined by the momentum of the particle that you observe correct? So how can you have discrete energy levels and a ...
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### What's the difference between insulators and topological insulators?

What's the difference between insulators and topological insulators? When I asked some people about this, they told me that "because the topological insulators have gapless edge states,...", but what ...
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### Sum of energy for 2 solids in rotation

I would like to compute the sum of energy of the following case: Two solids are turning (disks). Yellow solid is turning at $-w1 rd/s$ around its center of gravity and blue solid is turning at ...
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### Speed of sound and Break the sound barrier

What happens when plane exceeds the speed of sound? and What is the interpretation of the conical shape that appears behind the plane?
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### Recommend books on thermodynamics [duplicate]

I want to take on thermo I will be analysing boilers, gas cycles ,ic engines etc. I want to Analyse all of these by using the basic laws gof thermo on my own (if i could) .I have cengel boles book and ...
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### Metal with the biggest positive and negative charge per atom (ion)

Which metal has the highest positive and negative charge per atom? i know that Arsenic can have a positive charge of +5 and negative charge of -3 but is there any metals that can have more electric ...
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### What are the different types of beam splitters? [on hold]

I want to know the differences in the various types of beamsplitters, especially amongst the following types: Polarizing Beam Splitter Non-Polarizing Beam Splitter Plate Beam Splitter Pellicle Beam ...
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### Accelerating disk [on hold]

A disk of radius $R$ is accelerating to the right over a plane. At $t=0$ the speed and the acceleration of the axle are $v_1$ and $a_1$ what is the velocity and the acceleration of each point (1-4 ...
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### Is it possible to build an ion thruster jetpack already? [on hold]

s it possible to build an ion thruster jetpack already? If not, what are the current challenges?
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### Example of a state which is positive but its partial transpose is not positive

Could any one give me an example of a state whose density matrix is positive semidefinnite but partial transpose is not positive semidefinnite?
I think in loop quantum gravity the rate of expansion of the universe is found from: $H^2=\frac{8\pi G}{3}\rho\left(1-\frac{\rho}{\rho_c}\right)$ And I was wondering whether the critical density ...