2
votes
3answers
95 views

Centrifugal force in Arthur C. Clarke's Rendezvous with Rama

I'm currently reading Arthur Clarke's Rendezvous with Rama. Rama is a 50 km long, 16 km diameter cylindrical alien artifact that is rotating fast enough to provide a 0.6G artificial gravity on its ...
2
votes
1answer
150 views

What is the QFT picture of a static electric field?

Accelerating charge generates electromagnetic waves and loses energy, in QFT terms it emits photons that carry it away. What of a static charge? Moving photons are usually associated with waves, which ...
1
vote
0answers
20 views

integrating small angular velocities

I know that for a constant angular velocity the following is true: $R=e^{W t} R_0$ where $W$ is an angular velocity tensor, $t$ is a time, and $R$ is a rotation matrix I believe the following is ...
0
votes
1answer
50 views

Is there an intuitive explanation for the direction of the B field around a wire?

A wire has cylindrical symmetry, therefore we should consider the possibility of the induced by field in the p,phi and z directions. I know from the right hand rule that we only get a field in the phi ...
5
votes
2answers
337 views

Where does a hadrons mass come from [duplicate]

So I've come to the understanding that a hadrons mass does not come from the constituent quarks but instead comes from a combination of things like binding energy and the mass energy of virtual gluons ...
0
votes
0answers
32 views

Determining Attitude from Angular Velocity History

I am doing an analysis concerning the torque-free motion of an axisymmetric body. The angular velocity is given by $\omega(t) = [\omega_t\ sin(\Omega t), \omega_t\ cos(\Omega t), \omega_{z0}]$ From ...
2
votes
1answer
82 views

Explicit derivation of the Feynman amplitude of $e^+e^-\rightarrow\mu^+\mu^-$

I'm trying to compute the Feynman amplitude of the process $$ e^+(p_1,s_1)e^-(p_2,s_2)\rightarrow \mu^+(q_1,r_1)\mu^-(q_2,r_2), $$ considering as interaction Lagrangian $$ ...
2
votes
2answers
102 views

Observer inside event horizon of an extremely large black hole [duplicate]

Imagine a very large black hole, with a mass equal to a large number of galaxies. Assume a space station is in orbit around the black hole some distance from the event horizon at a point A. An ...
1
vote
1answer
63 views

Kim delayed choice experiment

In Kim's delayed choice experiment as described in Wikipedia, you get interference patterns or not depending on whether you look at detectors D3 and D4 (which give you path information) or look at ...
0
votes
1answer
59 views

Homework: Rope falling on scale [closed]

I think I have a solution for the following question, but it seems suspiciously simple to me: Suppose we have fixed a rope of Length $L$ and Mass $M$ at the ceiling such that the tip of the rope just ...
2
votes
1answer
107 views

Derive the Boltzmann factor in classical statistical mechanics

In both quantum and classical statistical mechanics, the probability of an NVT system having an energy $E$ is proportional to $$ p(E)\propto e^{-E/T} $$ However, all of the derivations (that I can ...
2
votes
1answer
101 views

How far will the bullet travel before falling back to earth? [closed]

First, the question: A particular high performance rifle cartridge can be fired with a muzzle velocity of 1200 meters per second. The rifle is pointed straight up. Assuming there is no air ...
4
votes
1answer
134 views

Analytic proof that Lyapunov exponents in Hamiltonian systems pairwise sum to zero

I have read that in Hamiltonian systems, Lyapunov exponents come in pairs $(\lambda_i, \lambda_{2N-i+1})$ such that their sum is equal to zero. Is there a way of proving this analytically? EDIT: ...
1
vote
1answer
43 views

About superconductivity

If I take a magnet and a superconductor than it will expel the magnetic field lines of the magnet. now if there is a coil of wire on the other side of the superconductor and i start to warm up the ...
0
votes
1answer
24 views

Thermodynamics identities of magnetic materials

According to the chapter 2 of Yeosman, Statistical mechanics of phase transitions, dU = TdS - MdH if we consider the energy of magnetic dipole but dU = TdS + HdM if we consider the energy of ...
0
votes
1answer
47 views

Gravitational Time Dilation and Schwarzschild Coordinates

So I'm trying to use this equation for the time dilation of an object, but I don't know how to get the distance that I have (in meters) to a radial coordinate in terms of schwarzschild coordinates. ...
3
votes
2answers
104 views

Why specify the state of a particle in terms of position and momentum not velocity?

Often a particle's state is expressed in terms of position and momentum. Why not position and velocity? Momentum has a connection to the particle's mass which I wouldn't say is so important to the ...
0
votes
0answers
50 views

Is Rayleigh/Wood's anomaly simply the grazing order diffraction?

Is Rayleigh/Wood's anomaly simply the grazing order diffraction? I read some related papers but I am still confused, can I simply understand it as a surface wave propagating on the surface because of ...
2
votes
0answers
35 views

Why does a balance try to be horizontal? The moments are equal [duplicate]

Suppose we have an ordinary balance where equal weights are put in both sides. Now one side is slowly held down. When this force is not applied anymore, the balance tends to achieve horizontal ...
6
votes
1answer
125 views

Does Bekenstein bound imply that the number of possible states of a bounded system is finite?

Bekenstein bound limits the amount of information that can be stored in a system of bounded size and mass. Does that imply that the number of possible states is finite? Does that imply that the number ...
11
votes
3answers
347 views

Can someone clarify whether the recent experiment closing all remaining loopholes to Bell's Theorem really shut the door on local realism for good?

I saw this recent article on Phys.org that purports to close all remaining loopholes that previous experiments on violations of Bell's inequality left open. My question is, does this really close the ...
0
votes
0answers
135 views

Thermal state vs equibilibrium state

Could someone explain what's the difference between a thermal state and an equilibrium state? Or is it even the same?
1
vote
1answer
62 views

What actually happens in a capacitor?

I have this doubt wandering through my mind for a long time. A capacitor, according to the definition of physics, is a charge storage device. In a simple parallel plate capacitor, when electrons ...
0
votes
0answers
72 views

Probability current density and Hamiltonian commutator in 2nd quantization

If the current density operator is $$ \hat j(r) = \frac{1}{2i} [ \hat\psi^\dagger(r)\nabla\hat\psi(r) - \nabla\hat\psi^\dagger(r)\hat\psi(r)] $$ then how does it follow that $$ \langle \Psi(t) | [\hat ...
-2
votes
1answer
74 views

How to calculate the increase in temperature due to drop? [closed]

Question- Calculate the rise in temperature in celcius in a bucket of water after it is dropped from 50 m where acceleration due to gravity is 10. I know that I need to find the amount of energy ...
0
votes
0answers
98 views

Jim Gates' discovery of error-correcting codes in equations of supersymmetry

Can anyone explain what's going on here, in a way that isn't just a lot of gee-whiz? Here's the arXiv article. I'm more of a computer science person than a physicist, so error-correcting codes are ...
1
vote
1answer
47 views

Is specific heat really a constant?

When we calculate heat lost or gained by a body according to equation $q=mc\Delta T$ where $m$ = mass of body $c$ = specific heat $\Delta T$ = temperature difference In this equation, why do we ...
2
votes
1answer
82 views

Ideal Gas Law in a Rotating Galaxy Cluster

There is evidence that some galaxy clusters may experience some bulk rotation. If this is true, how valid is it to use the Ideal Gas Law to estimate the mass (actually, it calculates the acceleration ...
1
vote
0answers
25 views

Method of Transformed Impedances

So I am taking an advanced optics class at the moment, using the book Lasers and Electro-Optics by Chris Davis. At one point, while explaining the concept of impedance, he mentions something called ...
13
votes
0answers
101 views

Can one classify partial differential equations according to the causality properties of their solutions (and if yes, then how)?

Recently, I bumped into this interesting comment by Valter Moretti which made me wonder about the following, more general question (to which I suspect the answer is affirmative): Can we easily tell, ...
1
vote
1answer
95 views

How to derive the vertex factor for the four-field interaction in scalar QED?

I tried to find the Feynman rules using path integral. For scalar QED, I have an interaction term $e^2\phi^{\star}A_{\mu}^2\phi$. Generating function then can be written as $$ ...
2
votes
1answer
55 views

Local operation on bipartite quantum system [closed]

Suppose we have a state: $$ |\Psi_{1234}\rangle = \frac{1}{2}\left(|\Psi_{14}^+\rangle \otimes |\Psi_{23}^+ \rangle + |\Psi_{14}^-\rangle \otimes |\Psi_{23}^- \rangle - |\Phi_{14}^+\rangle \otimes ...
2
votes
2answers
170 views

Relativistic explanation of attraction between two parallel currents

This has been answered a lot of times, and I have been reading about it on many websites, including PSE, but I still don't get it. So please don't mark it as a duplicate unless it really is one. Two ...
10
votes
1answer
1k views

How can we speak use the notion of “particle” in LHC, given that we live in a curved spacetime?

I understood from lectures that the metric of a spacetime was absolute: It does not depend upon the test charge we put inside. Indeed, all the calculation our professor carried out were independent of ...
0
votes
1answer
184 views

Position of centre of mass during toppling

Does the centre of mass shift in any way when it's about to topple, because a body toppling would simply mean that the weight vector is acting in a direction towards a point on the surface outside the ...
0
votes
0answers
49 views

Chiral multiplet : Fundamental and adjoint representation and its Lagrangian

In supersymmetry theory, consider $4d$ $N=1$ theory, we know that chiral superfield (In fundamental representation $\Phi \rightarrow e^{i\alpha} \Phi$) $\Phi$ and its lagrangian is given as ...
0
votes
0answers
22 views

How are mass and density treated in general relativity? [duplicate]

Background: I am confused by how mass relates to the equations in general relativity. For example, given a certain mass density distribution, I am unsure how to express a system in terms of GR. ...
0
votes
4answers
177 views

Is the centripetal force a pseudo force? [duplicate]

So I'm having a bit of struggle understanding the origin of the centripetal force. Is the centripetal force a pseudo force? Somebody told me that both the centrifugal and the centripetal forces are ...
1
vote
1answer
125 views

A problem related to Center of Mass?

A Man is standing on the ground( Mass m) next to a rope-ladder(length l) attached to a hot air balloon ( Mass 3m). If he starts climbing the ladder and covers half of the rope, find the distance that ...
0
votes
3answers
62 views

Examples of non-linear field symmetries?

Consider a Lagrangian theory of fields $\phi^a(x)$. Sometime such a theory posseses a symmetry (let's talk about internal symmetries for simplicity), which means that the Lagrangian is invariant under ...
0
votes
1answer
73 views

Why don't we include the adhesive and cohesive force while calculating rise in a capillary tube?

The contact angle of a liquid solid interface is explained by saying that the liquid surface must be perpendicular to the resultant of adhesive cohesive and gravitational forces acting on it, since it ...
0
votes
1answer
60 views

What is voltage in a circuit?

What is voltage in a circuit? We just started learning about electricity in my school. From what I understand; potential is potential energy per Coulomb and voltage means difference in potential. So, ...
1
vote
0answers
111 views

How do instantons look in real time/spacetime?

Instantons, as I understand it, are mathematical constructions in Eucledean spacetime. Does it imply that instantons do not exist in real spacetime or instanton tunneling effects are does not have ...
0
votes
1answer
38 views

Why does the light beam moves diagonally?

In almost all articles that explains Relativity or Time dilation. They start by saying the the Light is absolute and isn't affected by the inertial frames of reference yet when they start to explain ...
2
votes
0answers
53 views

The properties of light photons [duplicate]

Please consider a closed room with light reflecting walls and in the centre of the room there is a Lighting Bulb. Now if I switch on the bulb, the room is obviously illuminated with light. When I ...
0
votes
2answers
231 views

Behavior of two gases in a closed container

If two ideal gases with different molecular weights (i.e. nitrogen and argon) are injected into a closed container (of any given size, but assume ~1L), what will happen over time, assuming all ...
0
votes
3answers
127 views

Can Bernoulli fly a car?

I need to settle an argument. How much influence, if any, does the Bernoulli principle have in sending a stock car traveling at 200 MPH sailing through the air when the air pressure unexpectedly ...
0
votes
1answer
25 views

Distortion of non-circular cross sections upon torsion

True or false? Non-circular cross sections can be non-planar when torsion is applied. This was on a quiz today and I wasn't sure of the answer. I guessed true by intuition, but does anyone have a ...
1
vote
1answer
94 views

A heavy crate (mass m) is placed inside the flatbed of a truck but not tied down

A heavy crate (mass m) is placed inside the flatbed of a truck but not tied down. As the truck pulls away from a stop sign the crate remains in place and does not slide on the truck bed. What force ...
0
votes
1answer
53 views

Deriving Loop Equations in a Circuit with 2 batteries?

First time posting here, so please help with formatting. I need help deriving loop equations for this becaue the 2 batteries/power supplies are throwing me off. https://i.imgur.com/MJH6mIM.jpg The ...

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