All Questions

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0answers
6 views

Vanishing of rotation of timelike unit vector in numerical relativity

I'm a bit confused. I don't think it is that difficult, but still don't manage :-( So the question is why the rotation of the timelike unit-vector in numerical relativity $$n_\mu=-\alpha \nabla_\mu t$...
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0answers
4 views

How do I get my femto camera experiment done?

Not sure how to set up light so that it's perfectly parallel and lined up and everything. Sent E mails to people who I could find through the internet that deal with a femto camera. Found out a nano ...
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0answers
10 views

What correlated systems have been offered to produce quantum mechanical predictions?

What correlated systems have been offered to produce quantum mechanical predictions? Are there any examples?
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0answers
18 views

Can someone explain Technicolor

I read the wiki on Technicolor (and understood some of it-not a scientist) Can someone give me a layman's definition? Is the technicolor theory dead now that the Higgs has been found? Can ...
0
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0answers
10 views

What is the current most accurate measurement of the cosmological transition redshift

Does anyone know what the current most accurate measurement of the redshift for when the Universe's expansion changed from decelerating to accelerating (with a reference)?
2
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0answers
16 views

Concept of polarization in microwave rotational spectroscopy

I am trying to understand the concept of polarization of molecules after they are excited by a microwave pulse. The context is: The complexes are produced in a pulsed supersonic jet expansion of a ...
1
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0answers
9 views

How to map the symmetry property of the lattice unit cell to the symmetry properties of eigen modes

For example, in $\mathbf{r}$ space, a honeycomb lattice (like graphene) has C6v symmetry about the center of the unit cell. The ground state (singlet) eigen mode has C6v symmetry and the 1st order ...
2
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1answer
31 views

Theoretical physics for better batteries?

It is Earth day, so I started thinking about the theoretical physics problems that could help reduce greenhouse-gas emissions and fight climate change. We actually have a reasonable range of ways to ...
0
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1answer
31 views

Could the LIGO design be also used to detect space - time distorsions (curvature) caused by a small gold sphere?

Suppose  you put  a gold sphere inside the LIGO interferometer, not in the path of the laser beams, but sufficiently close to  (in the vicinity of) one of the laser beams. Would the space  - time ...
2
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1answer
34 views

Why can an inner product of an eigenvector also be used as an eigenvector?

In quote box below, there is an inner product of an angular momentum eigenvector. Why can you use this inner product as a new eigenvector for the next part of the work? And why do they "of course" ...
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0answers
5 views

Using Isospin symmetry to determine the decay rate of a process [on hold]

Given some process $a\rightarrow b+c$. Using isospin symmetry how can one work out the decay rate $Γ(a\rightarrow b+c)$ ?
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2answers
45 views

Why is sound “loudness” measured in $dB$ instead of $[P]$?

From acoustics we know that sound is an elastic pressure wave. What our human senses perceive are "loudness" and "pitch" which are related to the amplitude and the frequency. While pitch can easily be ...
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0answers
20 views

Rotational acceleration with weight

I am having some issues with a question from my Physics homework. Question is: A wheel is hung up on an axis through the center. Above/over the wheel we hang a rope with 2 weights attached to each ...
1
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2answers
43 views

Computation in QFT

I'm always a mess with the upstairs and downstairs notation. To be specific, say I want to calculate the Euler-Lagrange equations of \begin{equation} \mathcal{L} = \frac{1}{2}\partial^\mu\phi \...
-1
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0answers
18 views

An easy dinamic problmem [on hold]

On a ladder of l=6m placed at the height of h=4.8m and with the mass of 50kg there is a man of mass 80kg at the point 0 in the mid of the ladder (l/2) and the point c where the gravity of the ladder ...
0
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0answers
39 views

Determining whether a particle is stable

The $Λ_b(5620)$ baryon is the hadronic state obtained by replacing the $s$ quark in the $Λ^0$ baryon with a $b$ quark, so it has quark content $udb$. One of the decay modes of this baryon has been ...
0
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1answer
36 views

Could six copies of the universe exist only interacting by gravity?

The ratio of dark matter to matter is roughly in proportions $1:5.4$ This suggests that if there were about 6 Universes placed in the same space that were completely invisible to each other, except ...
-2
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0answers
17 views

How to get standard symplectic form so that one can get a vector field from a Hamiltonian function? [on hold]

In https://en.m.wikipedia.org/wiki/Hamiltonian_vector_field under 'Examples' a standard symplectic form w=(summation)dq(i)^dp(i) where p and q are the momentum and position of a particle. My question ...
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0answers
12 views

How much time does it take a light beam of a lantern at 1 light hour away from earth to hit a moving rocket sent from earth? [on hold]

Assume a stationary satelite in outer space at a distance of 299,792,458*3,600 meters from the earth. So basically the distance is the speed of light times 3600 seconds (or 1,079,252,848,800 meters) ...
-1
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0answers
32 views

Special relatvity

I am stuck on the following relativity problem: A body travels along the $X$-axis of an IF $S$ with velocity $v$. The $S$ observer emits a monochromatic pulse of light towards the body. The pulse ...
0
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0answers
22 views

Block sliding down a table

Disclaimer: I came up with the following problem on my own, so I don't know if there is a solution that makes sense our if my approach to solving it is correct... Any help is appreciated. Consider ...
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0answers
14 views

Bare Critical Masses of $^{241}$Am, $^{242m}$Am, $^{238}$Pu and $^{242}$Pu

$^{238}$Pu has 144 neutrons, and it has 2.8$\times$10$^{3}$ g$^{-1}$.s$^{-1}$ spontaneous fission neutrons and bare critical mass in 10 kg. $^{242}$Pu has 148 neutrons, and it has 1.7$\times$10$^{3}$ ...
-2
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0answers
22 views

Symplectic form on a Hamiltonian

What are the Hamiltonian equations with respect to standard symplectic form? What is the standard symplectic form?
0
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0answers
33 views

How do you determine the path of a particle placed in a vector field?

I have recently found a way of expressing newtonian gravity as a vector feild. First the Equation $$F=\frac{Gm_1m_2}{r^2}$$ I only want to know the accelleration in the equation since I only want to ...
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0answers
43 views

Why is the force of gravity the net force?

The first image is the diagram** in this FBD, use Fg on m1 as its net force (not concerning the friction). why do you not subtract the tension force in Mass 1?
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0answers
16 views

Planck's Constant is in units of Js does that mean photons are defined as 1 second of EM wave?

An EM wave delivers 6.626x10^-34 J per peak. This is true regardless of the EM wavelength. Each peak hits with the same energy, however the peaks are more tightly packed when the wavelengths are ...
0
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1answer
19 views

What imparts the linear motion or the tangential velocity to natural satellites like the moon to enable them to be in orbit around the earth?

From Newton's laws of motion & gravitation, it is clear that the force of gravitation provides the necessary centripetal force which acts along the line joining the centre of masses of the earth &...
0
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1answer
27 views

Electric Field for two identical charges

I have a task to find an electric field I don´t know how it should look like: We have 2 identical charges $q$ at a distance $d$, on x-axis at $(\frac{d}{2},0,0)$ and $(\frac{-d}{2},0,0)$. How can I ...
2
votes
3answers
87 views

Kepler's 3rd law: ratios don't fit data

I have been looking at satellite orbits around the earth, or any object around any planet in fact, and am trying to find the orbital radius, or semi major length of a given satellite. Kepler's third ...
0
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0answers
17 views

An rod is submerged into water in a graduated cylinder. Derive the total mass of the system as a function of depth of the rod [on hold]

I need help with this problem on a Buoyancy Lab. Consider an open graduated cylinder filled with 15 cm of water and is placed on the balance. A test rod is hung by a string and is partially ...
0
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0answers
27 views

Hierarchy problems: calculating the mass of the Higgs vs. other SM particles

While reading up on hierarchy problems in particle physics (wikipedia), I stumbled onto the statement that in the Standard Model, there is no hierarchy problem (or at least it cannot be formulated) ...
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0answers
19 views

Time Period of Oscillations ( A mechanical problem) [on hold]

So , basically I came across the following question : A massless rod (lying on a frictionless horizontal plane) is hinged at a point O. A string carrying a mass m at one end is attached to point A ...
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0answers
22 views

Why does the Earth not fall towards the Sun? [duplicate]

According to http://wtamu.edu/~cbaird/sq/mobile/2013/07/01/why-doesnt-the-earth-fall-down/ , the earth does not fall down because of the gravitational force of the sun. At the same time , earth's ...
0
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0answers
21 views

What is the algorithm for finding the constraint force using the method of Lagrange multipliers?

Is there a general procedure one can follow to find the force of constraint for a classical holonomic system with the nonconstraint forces derivable from a potential energy $U\left(\mathbf{r}_1, \dots ...
1
vote
1answer
39 views

Hypercharge renormalization for $SU(5)$ GUT

Reading about $SU(5)$ unification, texts says that they use the renormalization factor $\sqrt{3/5}$ for weak hypercharges in order to embed SM into a $SU(5)$ group. This implies a new $U(1)_Y$ ...
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0answers
13 views

help: calculating surface temp for rotating planet from solar constant 1366 w/m2

I'm interested in calculating the maximum surface temperature for a rotating planet from the solar constant. I can calculate the solar constant for a planet at any distance from the sun, no problem, ...
-1
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0answers
29 views

Exoplanets by the transit method [on hold]

Many exoplanets have been discovered by the transit method, wherein one monitors a dip in the intensity of the parent star as the exoplanet moves in front of it. The exoplanet has a radius R and the ...
0
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1answer
29 views

Lorentz Transformation: sent before finish line

As she wins an interstellar race, Mavis has a “hooray” message sent from the back of her 300m long ship as she crosses the finish line at v=0.6c. Stanley is at the finish line and at rest relative to ...
1
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2answers
85 views

Modern arguments against Geocentrism?

In ancient times, the arguments for geocentrism were primarily from observation. It looks like the heavens revolve around the Earth, so "heavens revolve around Earth" is a reasonable first model. ...
5
votes
1answer
330 views

Is the Born rule indeed wrong?

This is a question about the validity of a preprint, arXiv:quant-ph/0509089, which claims that the "Copenhagen Interpretation of QM is incorrect" (same title, authored by Guang-Liang Li and Victor O.K....
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0answers
13 views

Non-trivial content of AdS/CFT for a generic EFT on AdS

I have a very generic and naive question on the actual content (and usefulness) of the AdS/CFT conjecture in the low energy approximation where one considers a low energy QFT on AdS, comprising ...
1
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0answers
18 views

Combinatorics geometric series two-point function

In this answer Proof of geometric series two-point function it is said: Now what about the coefficients in front of each Feynman diagram? Due to the combinatorics/factorization involved it ...
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0answers
20 views

Transformer Equation Confusion

I have read some posts on here which I think to revolve around my problem too but couldn't really understand the explanations. So basically, I have seen how the Transformer equation is derived: $\...
1
vote
1answer
25 views

Interchanging $\epsilon_F$ and $\epsilon$ when deriving Density of States (DOS) of Free Electron Fermi Gas (FEFG)

When deriving the Density of States for a Free Electron Fermi Gas, Kittel seems to flamboyantly interchange $\epsilon$ and $\epsilon_F$ when going between equations. I am specifically puzzled as to ...
0
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1answer
29 views

Substituting into quantum harmonic oscillator

I'm a bit confused by the substitution that is often performed with the harmonic oscillator. This step is usually skipped over, but it has me a bit confused. I attached a picture to show what is ...
0
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0answers
9 views

Confusion regarding torque given by M×B

The magnetic torque acting on a loop of magnetic moment M placed in a magnetic field B, is given by τ=M×B. My question is, about which axis does this give the torque about? Is it the instantaneous ...
-2
votes
2answers
36 views

Does this graph represents only the magnitude of the friction force?

Friction force acts in the direction opposite to the relative motion between surfaces. For example, when a block is attempted to move from left to right with a force $F$, there will be an opposing ...
0
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0answers
17 views

Confusion on conservation of energy in the beta decay process

In a question,regarding the beta decay process, it is given that. Assuming the anti-neutrino to be massless and possessing negligible energy and the neutron to be at rest, momentum and energy are ...
0
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0answers
11 views

Euclidean Feynman Rules derivation using Wick Theorem

When studying perturbation theory and Feynman rules, the standard derivation seems to start from the S-Matrix element in the interaction picture, and expands it into some series, after which Wick's ...
0
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0answers
20 views

Inductance problem confusion

I am preparing for my upcoming finals and I have no idea how to do these two inductance problems I am so confused. Its an MCQ, here are the problems: I am confused with problems 2 and 3, the rest I ...

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