0
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0answers
3 views

(A,B)-Representation of Lorentz Group: Coefficient functions of fields

I have a question regarding the construction of general causal fields in Weinberg's book on quantum field theory. In his conventions a field that transforms according to the irreducible (A,B) ...
0
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0answers
3 views

Derivation of Van der Waal's Equation from Helmholtz Free Energy

From the following equation $$ f(T,v) = f_{id}(T,v) - RT \ln\bigg(1-\frac{b}{v}\bigg)-\frac{a}{v}$$ how do I derive Van der Waal's equation. In the equation above, $f$ and $f_{id}$ are the Helmholtz ...
0
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0answers
4 views

Does magnet become weaker when exposed to para magnetic objects?

I was wondering whether magnets (permanent) become weaker as they are exposed to para-magnetic object? I was thinking this after seeing this: ...
0
votes
0answers
9 views

How does a vertical counter-weight system work?

How does a vertical counter-weight system work when you have variable weight on one side? From what I understand from this page elevators use a counter weight to counter-balance the cart and some ...
0
votes
1answer
20 views

The dimensional formula of distance travelled in $n$th second

I read that the dimensional formula of distance traveled in $n^{th}$ second is same as that of velocity. Okay, the formula for the distance traveled in $n^{th}$ second is $s_t= u+\frac{a}{2}(2t-1)$ ...
1
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0answers
20 views

U(1) anomaly in 4-d

I am reading U(1) axial anomalies in 3+1 d using the path integral method (fujikawa). Am i wrong in assuming that the anomaly can be cancelled by introducing a counter term in the lagrangian that ...
1
vote
0answers
13 views

What reflects/scatters sunlight most?

The difference between a white object and a mirror is mainly scattering versus reflection. If we neglect this difference and define the reflectivity by input energy minus transmitted energy minus ...
0
votes
1answer
26 views

Wave packets and amplitude

If a wave packet is given by: My question is basically how do we choose the write $A(k)$ to fit the particle we are looking at, or does it not matter (as my matter as my textbook seems to imply) ...
1
vote
0answers
35 views

What causes radioactivity? Is it a quantum mechanical effect?

I'm just curious what causes radioactivity. I've been told that in the case of alpha decay, since the nucleus is quantum mechanical, there is a probability that the configuration of protons and ...
1
vote
2answers
102 views

Is there any argument explaining why light speed is constant no matter how it is measured?

I know the hypothesis that the light speed is constant is retained by experiments. But is there any theory explaining why the light speed is constant no matter how an observer moves relative to light? ...
0
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0answers
25 views

Is there “stay” operator for quantum field operator when creation and annihilation operator exists?

The basic quantum field operator is like a superposition of creation and annihilation operators at each position. This basic quantum field operator seems to suggest that every time field is ...
2
votes
1answer
34 views

If light is an electric and (magnetic field), how can it be absorbed?

I was wondering how light or any electromagnetic radiation can be "absorbed" if it consists of electric and magnetic fields. For example if there is a charge at point A, and the light reaches point ...
0
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1answer
13 views

Elementary question about velocity

When we talk about the nonvanishing velocity of an object, are we assuming we are static relative to the object or not?
0
votes
1answer
12 views

How to find the final momenta of these objects?

Suppose two objects collide head on, where initially object 1 (mass $m_1$) is moving and object 2 (mass $m_2$) is stationary. Now assume that they have the same mass, so $m_1 = m_2$. Which ...
0
votes
2answers
46 views

On the coordinate independence of general relativity

I've been having a bit of trouble with the idea of coordinate independence in general relativity. Let me start with a simple example that I think illustrates my question conceptually: Say you have ...
0
votes
0answers
14 views

Help with a ring launcher [on hold]

I'm not sure if this is the right place to be asking this question, so close it if it's not, but I need help on a physics project. My current project is a ring launcher (Elihu Thomson Apparatus). I ...
0
votes
2answers
28 views

Faraday Effect does light bend or lose energy?

I was reading upon Faraday effect when it said Faraday effect causes a rotation of the plane of polarization That in mind, does this mean the light can be bent around or does the light loose ...
0
votes
3answers
30 views

How far can one hear sound?

I was thinking how far can I hear sound coming from a concert. Today I was walking at night and I could hear sound from somewhere very far. I started following the sound but sound used to disappear ...
0
votes
1answer
38 views

Landau's derivation of a free particle's kinetic energy- expansion of a function?

I was reading a bit of Landau and Lifshitz's Mechanics the other day and ran into the following part, where the authors are about to derive the kinetic energy of a free particle. They use the fact ...
0
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2answers
51 views

$F=ma$ calculation taking relativity into account?

Newton's second law of motion states that $f = ma$. However, in this equation, theoretically there could be a value of $f$ and $m$ that results in an acceleration that is enough to push an object past ...
0
votes
0answers
24 views

What is the physical interpretation of the fermion field Hamilton?

I am still unclear what the hamilitonian of a quantized field is, but what I do know is the hamilitonian of the boson field is defined as \begin{align} H_{\text{boson}} &=& ...
1
vote
2answers
37 views

Relativity of simultaneity example in Resnick

My question is a follow up to this question about simultaneity. I would have posted it as a comment to the replies for that question, but I wasn't allowed to. When Resnick introduces relativity of ...
3
votes
0answers
18 views

Which cosmological dark matter theory is most compatible with current particle physics?

This occurred to me while I was writing Why hasn't warm dark matter replaced cold dark matter as the standard model of cosmology? but I think this deserves a question of its own. The background ...
4
votes
0answers
31 views

Why hasn't warm dark matter replaced cold dark matter as the standard model of cosmology?

The $\Lambda\rm CDM$ (cold dark matter with cosmological constant) is the current standard model of cosmology because the model comes with a long list of phenomena successfully explained by it. ...
1
vote
0answers
42 views

Sufficient conditions for the energy to be not conserved?

I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics. Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. ...
0
votes
4answers
56 views

If the velocity vector of a moving particle is always perpendicular to the position vector, is the path a circle?

A Newtonian physics question: If the velocity vector of a moving particle is always perpendicular to the position vector, is the only possible path a circle? What if the magnitude of the velocity ...
0
votes
1answer
27 views

Thermal Velocity

What is thermal velocity? What is it's physical significance? Wikipedia says: The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles which make up a gas, ...
0
votes
1answer
42 views

Yang Mills theory and SU(N) groups [duplicate]

Trying to get a better understanding of the relation between a SU(N) Yang Mill theory and its number of "color" space. Most of the description I've found so far are either way to complex/specific. ...
0
votes
0answers
12 views

How to calculate average temperature of Nichrome 80 resistance wire? [on hold]

I know the following: I need the resistance wire to hold a temperature of 400C with a steady current The resistance wire is 1cm in length I have a 1500 mAh battery with 3.2V available What gauge ...
1
vote
0answers
52 views

Recent missed opportunities à la Freeman Dyson

There is an excellent paper by Freeman Dyson from 1972 (here) and therein the author cites old talks by Hilbert (here) and Minkowski (chapter 2 here) speaking about similar topics, namely how ...
0
votes
1answer
26 views

Would someone versed in relative motion consider it more accurate to say that a car slammed into, or collided with, a wall?

I've read that it's just as correct to think of A moving toward B (ie. A doesn't move, but B does) as it is to think about B as moving toward A (again, A doesn't move, but B does) or as the two moving ...
0
votes
0answers
28 views

Can observables with discrete and continous eigenvalues be commuting?

In Dirac's The Principles of Quantum Mechanics he often uses the notion of "a complete set of commuting observables". This means a set of observables $\{\xi_1, \xi_2, \ldots, \xi_v, \xi_{v+1}, \ldots, ...
-1
votes
0answers
39 views

Could Particles Really Spin in the Really Real World? The video in the link says they do [on hold]

In the video bellow the presenter indicates that particles really do spin. He also claims to calculate the energy release from a U 235 fission reaction. Could this be real? ...
0
votes
0answers
19 views

Why infrared absorption is a nonlinear technique?

I am looking for a good explanation and/or reference quotation explaining why infrared absorption technique is essentially nonlinear (eg. for carbon monoxide quantification). When using ...
10
votes
1answer
518 views

Why don't the black holes appear black in color in images of galaxies taken from HST?

According to NASA a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area According to the documentary Space Unraveling The Cosmos about ...
0
votes
1answer
16 views

Flow rate is calculated only using the parallel component of the velocity vector

Flow rate is calculated using only the parallel component of the velocity vector to the area vector. Why is this? How can I mathematically prove this? Namely, how do I prove any perpendicular ...
2
votes
1answer
39 views

Finding the stabilizer group given a state

Consider general pure state $|\psi\rangle$ in some hilbert space $\mathcal{H}$ (which could be a tensor product of other Hilbert spaces) I would like to know whether there is a way to ...
2
votes
1answer
33 views

How fast do molecules move in objects?

I guess it depends on the heat or the type of the material but can you give some examples or formulas to calculate it ? The best example would be the average speed of the air molecules (all types in ...
0
votes
0answers
24 views

Mathematical derivation of interference pattern for electrons?

One of the most famous experiments in quantum mechanics in the context of wave-particle duality is certainly passing a beam of electrons through two slits, which results in an interference pattern ...
0
votes
0answers
43 views

Philosophical thoughts on Reconciling Different Relativity and Quantum—Motivation behind String Theory [on hold]

I always like to reason through the motivation behind equations, and during this process I began thinking about Wigner's 'unreasonable effectiveness of mathematics', and whether it can sometimes lead ...
0
votes
1answer
27 views

(Level: Undergrad) Continuity Conditions on the Wavefunction and Initial Values

I know that a physically meaningful $\Psi$ needs to be continuous. However, recently I came across a problem in which they were considering a wavefunction for the infinite square well potential and ...
3
votes
1answer
63 views

If I'm running away from chasing gamma photons, I can see them, right?

Suppose Bruce Banner goes back in time, convinced that the Hulk is a stupid menace. Let's say he also borrows Quicksilver's speed abilities (maybe the Flash is more appropriate, but based on the ...
4
votes
1answer
41 views

How do geocentric theories explain seasons?

Did the geocentric theorists also use the fact that the earth had an axis tilt? Or was their explanation of some other kind?
4
votes
2answers
40 views

2 entangled electrons in QFT

In field theory, by quantizing a dirac field, we can obtain a creation operator for a single electron of definite momentum, of definite spin up or down, these respectively are: ...
6
votes
2answers
372 views

How would wormhole-based FTL violate causality?

We already have an answer why physically traveling faster than light would violate causality (the clock on board our hypothetical FTL spaceship would tick backwards to some outside observers). ...
0
votes
2answers
27 views

If outside a cylindrical solenoid exist an electrical field what does that mean to the Aharonov-Bohm Effect?

To the question "What is the electric field outside a cylindrical solenoid when inside is turned on a magnetic field" the answer is that outside exists a electric field. Does that mean that the ...
1
vote
1answer
54 views

Can speed be defined in the complex plane?

This question cropped up while I was playing with the equation for time dilation. If I set the speed to be $i$ (imaginary unit) the answer from the equation still makes sense, but does that matter if ...
0
votes
0answers
14 views

What is the most general definition of a bosonic Gaussian state?

I am reading this paper where the definition of the bosonic state is mentioned on page 2 here :- http://arxiv.org/pdf/0806.1625.pdf . From a general definition of any density operator in terms of ...
0
votes
0answers
11 views

Where does $R/\gamma^3$ come from in relativistic E&M?

I am starting to read many papers on electron beam physics; more specifically its motion in a magnet i.e. curved motion. The term $R/\gamma^3$ comes up a lot, but I don't know where they are coming ...
1
vote
0answers
13 views

Quasicrystals - Projections from higher dimensional regular crystals [on hold]

Why are Quasicrystals Projections from higher dimensional regular crystals?

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