0
votes
1answer
9 views

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 ...
0
votes
1answer
9 views

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 ...
0
votes
0answers
8 views

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 ...
0
votes
1answer
17 views

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 ...
2
votes
0answers
11 views

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? ...
1
vote
0answers
11 views

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 ...
2
votes
2answers
36 views

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 ...
0
votes
0answers
12 views

AC wire radiation

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 ...
0
votes
0answers
18 views

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 ...
0
votes
0answers
34 views

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 ...
-2
votes
0answers
47 views

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
0
votes
0answers
12 views

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 ...
2
votes
3answers
233 views

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. ...
0
votes
1answer
32 views

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 ...
1
vote
1answer
39 views

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 ...
0
votes
1answer
13 views

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 ...
2
votes
2answers
41 views

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 ...
0
votes
0answers
25 views

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 ...
0
votes
1answer
40 views

Finding the spectrum of a curious hamiltonian

I wish to analyse the following hamiltonian, i.e. find its eigenvalues and eigenstates. $$H = \frac{1}{2}\epsilon(\sigma _z \otimes \mathbb{1} + 1\otimes \sigma _z) - \Delta (\sigma _x \otimes \sigma ...
0
votes
0answers
18 views

How to calculate the atomic form factor of Lithium? [on hold]

I have a density function, $\rho=e^{\frac{-2r}{\pi a^3}}$, and I have also two numbers, but I don't know what they mean. They are: $a_k=0.2 \mathring A$ angstrom, $a_l=1.6 \mathring A$ . And teacher ...
2
votes
2answers
51 views

Why is an electron negatively charged, and what is the difference between negative and positive charges?

Nobody has yet defined the actual meaning of a charge, or why a negative charge is different from a positive charge. Everybody knows that positive charge is due to protons and negative charge is due ...
2
votes
0answers
37 views

Why can't we reach the ends of rainbow?

Rainbows are spectacular things. But I imagine why we can't reach to the ends of rainbows. Do rainbows have no ends ? If so, why can't we reach at them? If you go closer,they will go further. Why?
0
votes
0answers
32 views

How to deal with $\nabla(\delta\Psi)$ in functional derivatives?

I am trying to compute the functional derivative of the following functional $$F[\Psi]=\int{}d^nx\Psi{}e^{(\nabla\Psi)^2}.$$ What I have tried up till now is the following ...
3
votes
1answer
348 views

How quickly does gravity extend from created mass? [duplicate]

I apologize in advance if this is a stupid or off-topic question. Since Energy can be converted into matter according to $E=mc^2$, how fast does it take for the gravity of that new matter to extend ...
11
votes
2answers
128 views

Underdetermined forces in a statics problem

I was trying to cook up a good exam problem on Newtonian mechanics, and I came up with one that I didn't fully understand myself. Always fun when you can outsmart yourself. In the figure a cylinder ...
0
votes
0answers
17 views

Calculating time of being in a lift only by weight & travel distance

If someone is in a lift and normally weighs 90kg, when the lift starts accelerating the person weighs 100kg. After the lift has maintained a constant speed for a while it starts slowing down. While ...
-1
votes
0answers
13 views

A car collides with a net [on hold]

A little car of 500 grams with a speed of 2 m/s collides with a net with a spring constant of 400 N/m. If the force is bigger then 40 N, the net breaks. 1) Prove that the net brakes 2) What is the ...
2
votes
0answers
13 views

I would like to know what variables to consider when I experiment with pouring from bottles and the “glug” effect?

I am a middle school science teacher and want to model a science fair project for my students. Specifically I want to investigate using a vent in the top of the handle of a gallon milk jug to ...
4
votes
2answers
465 views

Would using Cherenkov radiation for lighting be feasible?

Could Cherenkov radiation be used for general illumination, for example, to replace LEDs, light bulbs etc? I.e. are there, or could there be, methods to produce substantial amount visible light with ...
2
votes
0answers
25 views

What prevented the early universe to become a black hole before inflation? [duplicate]

I am an ignoramus on this subject, and I assume that these statements quoted from wikipedia are more or less accurate:(http://en.wikipedia.org/wiki/Inflaton) 1) Prior to the expansion period, the ...
0
votes
0answers
18 views

primordial perturbations

According to cosmic inflation, primordial perturbations are adiabatic. As in, the fractional number density of all types of particles is the same, n_baryons = n_photons etc. But what would it mean if ...
0
votes
3answers
50 views

Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?

In classical physics we often cast an analogy between translational and rotational systems Force < > Torque Energy < > Rotational Energy Momentum < > Angular Momentum and considering SI ...
2
votes
1answer
16 views

A paradoxical equation in RNS string fermionic part

It is well known for RNS string, $i.e.$, worldsheet supersymmetry formalism, the open string NS sector has worldsheet fermion expansion: \begin{equation} \psi^{\mu}_{\pm} = \frac{1}{\sqrt 2} \sum_{r ...
1
vote
0answers
20 views

Why is the limit to observe quantum phenomena $k_B T < \hbar \omega_0$?

Eg. in cavity QED you have to cool down the appartus so that quantum effects may be observed in a way that $k_B T < \hbar \omega_0$. I suppose that $\omega_0$ here means the frequency which the ...
0
votes
0answers
23 views

Magnetic field of magnetic screwdriver?

I wanted to know what is the typical strength of the magnetic field generated by the tip of a magnetic screwdriver, but couldn't find it anywhere on the manufacturers' webpages. So I was wondering, ...
0
votes
1answer
22 views

Why voltage become multiply when connect batteries or capacitor in series but not in parallel?

As i understand, the different voltage between two object is caused by the total different charged between two object. Thus, the higher extra electron between two opposite charged object, the higher ...
1
vote
2answers
160 views

Why do corn flakes clump together in milk when stirred? [duplicate]

The Cheerios Effect is the name the scientific community has given to this phenomenon. When cornflakes or oats are mixed with milk and stirred, they tend to clump together. Why does this happen? Can ...
1
vote
2answers
45 views

Non-invariance of the Interaction term in QED lagrangian

The interaction term in the QED Lagrangian $$\mathcal{L}_{int}=e\bar\psi\gamma^\mu A_\mu\psi$$ changes under a gauge transformation $$A_\mu\rightarrow A_\mu+\partial_\mu\chi$$ Doesn’t it affect the ...
3
votes
2answers
176 views

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 ...
1
vote
0answers
26 views

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 ...
2
votes
0answers
25 views

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 ...
1
vote
1answer
26 views

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?
0
votes
0answers
14 views

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 ...
0
votes
0answers
32 views

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 ...
0
votes
0answers
13 views

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 ...
1
vote
0answers
23 views

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 ...
0
votes
1answer
24 views

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?
0
votes
1answer
28 views

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?
0
votes
0answers
30 views

Loop quantum gravity- is the critical density sufficient to form a 'black hole'?

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 ...
-3
votes
0answers
29 views

How to calcuate uniform circular motion? [on hold]

Given: Ideally, I maintain a speed of 265km/hr and 285 km/hr. Roughly, 73.6 m/s and 79m/s. I make a turn and experience around 4.5g's to 5.5g's, roughly 45 and 55 m/s^2, for about 7 seconds. I ...

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