0
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0answers
4 views

how is Helmholtz free energy related to grand partition function

According to my source of notes $$A = kT \left ( N \ln z-\ln Z(z, V, T)\right) $$ where $z=e^{\beta \mu}$, $\mu$ being chemical potential, $Z(z,V,T)$ is grand partition function. The derivation ...
0
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0answers
5 views

Energy conservation in Hubble Expansion

So space expands due to Hubble Flow. Some light is observed, which is seen to be red-shifted due to the space expansion. It is less energetic. Where did the energy go?
0
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0answers
2 views

Writing Breit-Pauli spin-spin-coupling Hamiltonian as a sum of irreducible spin tensor operators

The spin-spin interaction part of the Breit-Pauli Hamiltonian for two electrons is essentially (omitting constants and the contact term) \begin{equation} \frac{3(\mathbf S_1 \cdot \mathbf r)(\mathbf ...
0
votes
0answers
8 views

Feynman diagram; $\pi^0+\pi^0\rightarrow \pi^++\pi^-$

For the reaction below draw three Feynman diagrams, one that proceeds through exchange of a gluon, one through a photon and one exchanging a weak W-Boson. $\pi^0+\pi^0\rightarrow \pi^++\pi^-$ Which ...
-1
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0answers
7 views
0
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0answers
7 views

Is it necessary to consider relativistic effects when looking at an electron-photon collision?

I am looking at the collision of a photon into a stationary electron with the aim of computing the velocity of the electron after the collision in terms of the initial photon wavelength. Of course ...
0
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0answers
8 views

The existence of gravity waves has just been demonstrated by direct observation, 2016

How does the apparent confirmation of gravity waves effect String Theory today
0
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0answers
7 views

What is the proof of gravity being curvature of spacetime?

According to general relativity gravity is an illusion caused by curvature of space-time, rather than real force. As I understand there is overwhelming experimental evidence to support general ...
1
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0answers
16 views

How is it that gravitational waves can be detected by measuring distances?

If gravitational waves stretch space itself, how can they have an effect on the interference of two laser beams? According to my understanding, compression or dilation of space itself (as opposed to ...
1
vote
0answers
14 views

Is all energy quantised?

I'm wondering if all energy is quantized.Can a particle with kinetic energy have any value of kinetic energy or is kinetic energy also quantized?My reason for asking this is that if a particle is ...
-3
votes
0answers
19 views

Gravitational waves now detectated

Based on the information released so far, have we learned anything new from the detection of gravitational waves at LIGO?
1
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0answers
6 views

Electromagnetic Induction, specifically induced voltage

Why is it that if a conductor 'cuts through' (what does this mean?) a magnetic field that a potential difference is produced? I read this recently in a textbook...
0
votes
0answers
11 views

Special Relativity and the Light Clock and which direction was the laser pointing?

If I were to make a light clock, I would have some sort of laser pen attached to the top of one of two mirrors. That laser pen would be perpendicular to the surface of either/both mirrors. I would ...
-1
votes
1answer
5 views

What is the converted force from the weight force to the rotational force?

What is the converted force from the weight force to the rotational force? How far the 2,000 lbs (gross weight) car can drive (or move) with the rotational force that uses gears to converted from a ...
2
votes
0answers
14 views

How do large interferometers work?

In very large Michelson interferometer a such as LIGO, how can we keep the two light paths at the exact same distance in order to avoid any unwanted and noisy fringes shift? When I used to make ...
0
votes
2answers
47 views

At which point are gravitational waves generated when two black holes merge?

I was reading today's announcement of the gravitational waves and was wondering about this situation where there are two orbiting black holes. Did the wave come from the final merging or was it from ...
1
vote
0answers
20 views

The Ideal Gas Equation in higher dimensions

Basically I wanted to know whether or not the ideal gas equation, $PV=NkT$ would hold in higher dimensions? If so, how would you go about proving this? I can't see any reason as to why it shouldn't ...
1
vote
1answer
27 views

How did LIGO detect the source location of the black holes mentioned to be the cause of today's announcement?

Today LIGO announced discovery of Gravitational waves. What method was used to determine the source location of the waves?
0
votes
2answers
25 views

Can two different objects or system of molecules have different temperatures, but having same internal kinetic energy?

If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and ...
0
votes
0answers
8 views

Force required for balancing a three-bodied frictionless and gravityless system

Hello everyone, I made calculations over calculations but I think my free body diagrams were wrong. There are three bodies here: on two of them (the 2 and 3) are applied two forces (F2 and F3) ...
2
votes
1answer
27 views

Redshift of merging black holes

How did they found that the gravitational waves where emitted at redshift $z=0.09$? I understand the measurement of redshift for an electromagnetic wave where we have measured in a lab various ...
0
votes
0answers
4 views

Gibbs isotherm and calculating interfacial tension change from first principles

Question: Is it possible for a solid particle to change the surface tension between two phases? (or: Does a solid particle have a chemical potential?) This question stems from the more ...
2
votes
0answers
55 views

Einstein's original papers predicting gravitational waves?

I came across the original handwritten papers in which Einstein predicted gravitational waves: and since LIGO announced they've detected a signal confirming the predictions I was wondering if ...
1
vote
0answers
19 views

Question on in and out states in chapter 10 of Weinberg's QFT volume 1

In chapter 10 section 2 (on pomology) of Weinberg's QFT volume 1, he shows $G$ has a pole when the external line goes on shell. In the proof, he inserted a complete set of single-particle states ...
-1
votes
0answers
16 views

What is collimated/paralell beam of atoms?

This question is related to following exercise: "The intensity of the collimated, paralell beam of atoms of potassium was reduced by 3% by a layer of argon at 1 mm thickness and pressure $6,0\cdot ...
1
vote
0answers
28 views

Does gravitational time dilation have a direction?

I understand that higher the gravitational potential, "slower" time runs. So a clock on international space station will run "faster" than a clock at sea level. However does it matter where the ...
0
votes
0answers
19 views

Question about a solution of a partial differential equation by separation of variables

I'm trying to understand this text: http://www.ekayasolutions.com/UCDMath/HeatCondSphere.pdf But I'm having problem with this part: Whe have to solve: \begin{equation} \dfrac{\partial ...
-1
votes
0answers
17 views

What happens to the average kinetic energy if you double the temperature?

I've always wondered what would happen to the average kinetic energy if you double up the absolute temperature of an ideal gas. My hypothesis is that, since the temperature is proportional to the ...
1
vote
1answer
15 views

Why does narrower slit give a wider diffraction pattern in single slit diffraction?

I was reading on this website and it said that one of the characteristic of single slit is narrower slit give a wider diffraction pattern but why? ...
1
vote
3answers
49 views

Graviton and photon

I understand that photon is the carrier of a change in the EM field. Is the graviton a carrier of the gravitational field itself or a carrier of a change in the gravitational field?
-1
votes
0answers
8 views

Diffraction grating location of maxima for arbitrary number of slits

Say I have a diffraction grating with 8 slits. I want to find the location of the maxima. What do I do? Can I use the equation $d\sin\theta = n\lambda$? I know it works for 2-slits and for ...
1
vote
0answers
4 views

Effect of paint on drag force

Aerospace engineering as well as automobile engineering gives a particular significance to the shape of a vehicle to enable proper and more effective transportation.What I want to know, is, about the ...
4
votes
1answer
62 views

So Black Holes Actually Merge! In 1/5th of a Second - How?

I've read a lot of conflicting answers in these forums. However, today saw the awesome announcement of gravitational waves. Two black holes merged: ...
0
votes
0answers
7 views

If the torsion of the straight line is undefined what happens with the information about the torsion?

If the torsion of the straight line is undefined what happens with the information about the torsion? It is known that the information conserved in a system can be nor created, neither destroyed. ...
0
votes
0answers
10 views

Quadrupole configuration

The general solution to the 2D Laplace equation, $\nabla^2 \psi = 0$ is \begin{align} \psi(r,\theta) = P_0 \ln r + \sum_{k = 1}^\infty \dfrac{Q_k \cos(k\theta)+R_k\sin(k\theta)}{r^k} \end{align} The ...
1
vote
2answers
59 views

Why is the speed of light exactly $299,792.458$ m/s and not faster or slower?

Why is the speed of light $299,792,458$ metres per second, and not faster or slower. Why not $500$ trillion kilometers per second or $120$ miles per hour? This has been 'bothering' me for a while. ...
-1
votes
0answers
11 views

How do we acquire c-coefficients (“weights”, “probabilities”), when dealing with superposition of stationary states?

I searched quite a lot textbooks to answer this question, but I couldn't find anything satisfactory. This could be more general question, but it will be easier to just restrain to particle (say ...
4
votes
1answer
47 views

Are there waves of time?

If I understand correctly, gravitational waves are ripples in the fabric of space-time itself created by the movement of mass. Moreover, space and time are just dimensions of the same space-time ...
1
vote
1answer
39 views

Is there absolute proof towards gravitational waves?

As you probably know gravitational waves seem to have been proven unless you've been living under a rock for the past day. The experiment involves the reflecting off mirrors and waves of light and it ...
0
votes
0answers
10 views

How much light is necessary to form a black hole [duplicate]

I suppose that enough light in a small enough volume could create a black hole. What is the good quantity that can tell when light can or cannot make a black hole? Energy density? But there must be ...
1
vote
1answer
21 views

Does the size of a black hole change depending on its charge or spin?

I was talking to this friend of mine who said that the size of a black hole could vary depending on its "charge" and spin. He said the size of a black hole would reduce if it had a spin or charge. The ...
0
votes
1answer
5 views

Question about the way the inner stress in an axially loaded member is defined

When a member is in tension, such as in a tensile test of a piece of metal, its freebody-diagram would show a force of P in both directions. Why then is its internal stress not $\frac{2 \cdot P}{A}$? ...
0
votes
2answers
33 views

Confusion over basis sets in quantum mechanics

In a sense, I feel like I understand every step in the following (fairly typical) calculation, but I don't understand the conclusion. I consider a vector space spanned by two basis vectors ...
4
votes
2answers
371 views

How strong were the gravitational waves that LIGO detected at the source?

Congrats to the LIGO team on the announcement of their discovery of gravity waves! The articles I've read say that the distortion we see here is much smaller than a proton. What about at the source? ...
2
votes
2answers
82 views

What will be the role of gravitational waves in future physics? [on hold]

What does this discovery mean for us? Can it lead to a better understanding of the cosmos?
-2
votes
0answers
22 views

Find the period of a pendulum system

How to solve the following problem, A mathematical pendulum is formed by a cable with length $l$ and a sphere at it's end with mass $m$. While the pendulum swings at it's position of ...
0
votes
0answers
7 views

Rotational spring in inertial reference with Euler angles

I am thinking about how to exprime the moment produced by rotational springs using the Euler angles. Consider a rotating rigid body A, a local reference $B$ $(o,x,y,z)$ is attached at the center of ...
1
vote
1answer
12 views

Example of a system where we cant measure the total possible microstates of a system but can measure the microstates of most probable state?

I have been reading about entropy and I read that entropy is basically a measure of total possible microstates but there was an approximation that when no. of particles become very large we take ...
4
votes
0answers
57 views

How were gravitational waves discovered?

It was announced today that gravitational waves were discovered. The article gives the following explanation of the experiment: When a gravitational wave passes LIGO, the tunnels deform ...
2
votes
1answer
6 views

How is the energy spectrum of a gamma ray in a material?

I'm trying to solve the following problem for a course in radiation physics. A thin ray of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity and the energy of the ...

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