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2answers
403 views

What the role of classical equation of motion in quantum field theory?

I've learnt quantum field theory for a semester but I still can't understand the role of classical equation of motion in QFT. I have looked up for several books. They all discuss classical field ...
0
votes
1answer
46 views

Why don't we use momentum to quantify inertia?

My understanding of Newton's 1st and 2nd laws have led me to believe that inertia and momentum are the same. 1st law: An external force is required to overcome an object's inertia 2nd law: Force is ...
1
vote
0answers
31 views

Using $c$ function to calculate $H$ spectrum in bosonic string theory

Ch-$8$ sec-$8.4$ Polchinski (String theory vol I) states In the canonical approach, focus on the zero-mode contribution to the world-sheet action. Inserting $$\color{red}{X^m(\sigma)=x^m(\sigma^2)+w^...
0
votes
3answers
62 views

How can you avoid a contradiction with relativistic length contraction?

I have a lot of confusion on special relativity. I am going to use the muon example because that's what was clearest for me to visualize. A muon generally decays too fast for it to reach the earth ...
7
votes
2answers
368 views

Energy gets paired with time and Momentum with space in both QM and SR.Any connections there?

In non-relativistic Quantum Mechanics, energy can be interpreted as a frequency in time, and momentum as a frequency in space. In Special Relativity, Energy turns out to be the temporal component, and ...
1
vote
0answers
17 views

Aerodynamic Problem in regards to a ping pong ball and and an open hole tube

I have a ping pong levitation system with a ping pong ball in a tube being pushed by a dc motor fan (shown below) and I'd like to define a relation of the balls height with the air velocity or airflow....
0
votes
0answers
36 views

Obtaining the unitary representation of the Lorentz group from infinitesimal transformations

My knowledge of Lie Groups and Lie Algebras is very limited, even more so when it comes to their representation theories. There is a difference that I can't quite understand, between the ...
0
votes
1answer
26 views

Commutation relation for Hamiltonian for fermion and boson

I feel like this is a dumb question since it isn't supposed to be this difficult. I am just confused on how the wavefunction is supposed to "interact" with the integral if you will. Since ...
0
votes
1answer
25 views

How does tank size relate to output velocity?

I'm comparing air compressors, and I don't understand why there isn't a correlation between tank size+max pressure and SCFM. Here are a few examples of some models: Model Tank (gallons) SCFM @ 90 ...
1
vote
0answers
28 views

Log-law entanglement with large central charge contradict bounds on the entanglement entropy

I am trying to learn more about entanglement entropy in large but finite-size systems at critical points. I am still relatively new to conformal field theory, so it is not unlikely I have ...
1
vote
1answer
56 views

Energy conservation in different reference frames

Suppose, I'm on top of a hill, and I drop a ball from some height. As there are no external forces acting on the Earth-ball system, I can safely claim that the total energy is conserved. I know that, ...
0
votes
1answer
54 views

What, exactly, is the Fermi Constant? What is its value? And what is the difference between $G_f$ and $G_f^0$?

There is no Wikipedia page for Fermi's Constant, and the page they DO have is confusing. From Fermi's Interaction: How can $G_f^0$ not be equal to $G_f$? What is the difference? And when they give ...
2
votes
4answers
69 views

Relationship between KG equation and Yukawa potential

If we start from Klein Gordon Lagrangian density and work through canonical quantization, we could arrive at field operators for scalar fields. Now, if we solve for the free propagator we arrive at (...
0
votes
1answer
30 views

Microstates and Macrostates in Canonical Ensemble

In the microcanonical ensemble for a system in equilibrium, the macrostate has a certain multiplicity, which represents the number of microstates that this system can be in. For the canonical ensemble ...
1
vote
2answers
36 views

Parton, detector and particle level at LHC

What is the difference between parton, detector and particle level in high energy physics? I found a similar question but I couldn't understand the explanation for detector and particle level given ...
0
votes
1answer
32 views

Crackle sound due to flow of charges

Why is a crackle sound generated when charges flow between surfaces? Does this energy comes from the loss in potential energy of electrons?
0
votes
1answer
31 views

On Calculating Expectation Values in Sakurai's Modern Quantum Mechanics

Expectation value $\langle A\rangle=\langle \alpha|A|\alpha\rangle$. Which can be written as $\langle A\rangle = \sum_{a}\sum_{b} \langle\alpha|b\rangle \langle b|A|a\rangle\langle a|\alpha\rangle$. ...
1
vote
2answers
34 views

Reconstructing state from density matrix (and implications for Grover search)

If I am given a density matrix $\rho$ that I know corresponds to a pure state (i.e., $\rho = |\psi\rangle\langle\psi|$ for some $|\psi\rangle$), then is it possible for me to infer the state $|\psi\...
2
votes
1answer
71 views

Inertial vs gravitational mass at different temperatures

So, I know more energetic objects have more mass according to Einstein. I'm aware that this has been verified by weighing an object at different temperatures where the object weighed more at higher ...
0
votes
0answers
52 views

Asymptotic behaviour of a non-linear differential equation in Gravitation

I have been recently working on modifications to General Relativity, by adding new curvature terms in the Lagrangian density of the theory. In one of these theories (Einsteinian Cubic Gravity), the ...
2
votes
1answer
67 views

How do migratory birds fly in geodesics?

Recent studies point to cytochrome molecules in the eyes of migratory birds as a key component for birds to use when flying across the globe. It is thought they help the birds navigate using the earth’...
2
votes
0answers
23 views

Explanation for dark states in magneto-optical trap pumping the $\mathrm{^{85}Rb}$ $F=3 \rightarrow F'=4$ transition

The explanation given by Wikipedia on why you will find the $\mathrm{^{85}Rb}$ atoms going into the $F=2$ hyperfine state (and thus needing repumping) is that the detuning from the $F=3 \rightarrow F'=...
0
votes
0answers
36 views

Is $B=E/c$ true for all electromagnetic waves (in vacuum)?

The relation is true (and rather easy to prove using Maxwell's equations) for a plane wave. Since any wave can be written as a sum of plane waves, I figured it should hold for arbitrary waves, but a ...
0
votes
0answers
42 views

What are each of the following models used for in QCD? [closed]

What are the differences between the following models? Skyrme model in QCD MIT bag model Solitons for QCD R. N. quark model Chrial quark soliton model Non-chiral soliton quark model SLAC bag model
-2
votes
1answer
48 views

How can I calculate braking distance given a nonuniform acceleration

A braking distance equation can be represented below. $\mathbf {x_{braking} = \frac{(v_f^2-v_0^2)}{2a}}$ But how can I generalize this equation to be applied in instances where acceleration is ...
-2
votes
0answers
45 views

Why should the use of complex numbers in equations describing the physical world mean anything? [closed]

While I have not started studying physics at a high enough level to use complex numbers in it for myself, I'm aware they're a core part of quantum theory and are also used in electrodynamics. And ...
1
vote
2answers
54 views

Microstates of the canonical ensemble

In the micro canonical ensemble the microstates of a system in an arbitrary macrostate, are also eigenstates of the Hamiltonian. Does the same apply to the microstates of the canonical ensemble? Are ...
0
votes
1answer
16 views

ODE or PDE heat conduction

question about heat conduction. I was casually reading through an ebook and came across the following: Could you tell me where this last equation comes from? I can follow the solution to the problem ...
0
votes
0answers
15 views

Front impact analysis [closed]

Hello, so recently I have been doing one preetty simple project in FEA, my task was to do a front impact analysis on go-kart chasis. While the simulation itself isn't hard at all and to be honest I ...
0
votes
1answer
21 views

Distribution of current on a wire

Imagine a cylindrical wire with current flowing through it. What paths do the actual electrons take? My first thought is that the electrons only move along the surface of the wire; since that is where ...
0
votes
0answers
12 views

Quantum numbers for ${}^3P_2$ State of trivalent Praseodymium ion

I am trying to understand energy states in the Pr3+ Ion. The ground state is 3H4, which can only be achieved by giving the two electrons in the 4f-orbital the magnetic quantum numbers ml=2,3 or ml=-2,-...
0
votes
0answers
11 views

Motional e.m.f. & transformer e.m.f

According to wikipedia, there are two ways to generate induced e.m.f.: Keep the circuit stationary while moving the magnet, giving rise to transformer e.m.f. Keep the magnet stationary while moving ...
-4
votes
0answers
48 views

What are the differences between the notes of a piano in terms of waves? [closed]

The question in the title. 01001001 01110100 00100000 01101001 01110011 00100000 01101110 01101111 01110100 00100000 01101010 01110101 01110011 01110100 00100000 01000110 01110010 01100101 01110001 ...
1
vote
2answers
77 views

Why do guitar strings behave so nicely?

To explain the harmonics on a guitar string, we use 2D models of the string. For example we assume that the string can only go up and down. But the string is inherently a 3D object and it could ...
2
votes
1answer
33 views

Seeing gauge-covariance of the wavefunction for a uniform magnetic field

Consider the Hamiltonian $$H=\frac1{2m}(\mathbf p-q\mathbf A)^2+q\phi$$ and let $\psi$ be a solution to the Schrödinger equation $$i\hbar\frac{\partial\psi}{\partial t}=H\psi$$ Then if we gauge ...
3
votes
1answer
35 views

Airflow across a horizontally placed solid cone

I need an equation to solve the following: I have a solid cone wherein I place the pointed section horizontally. I then switch on a horizontal airflow across the cone so that the flow strikes the ...
0
votes
1answer
24 views

Definition of conductivity: Derivative or Ratio of $V$-$I$-curve?

I was wondering if the conduvtivity $\sigma\propto dI/dV$ or $\propto I/V$ where $I$ is the current and $V$ the voltage?
0
votes
0answers
33 views

Orthogonality of basis functions of irreducible representations

Lets say I have two irreducible representations of a finite group $G$. Let the group have $l$ elements. The elements of the representation shall be linear operators $L$ that act on some function ...
0
votes
0answers
12 views

Measurement of two different spin components of entangled particles

Consider two entangled spin 1/2 particles. Of one I measure the z-component, of the other the x-component, at the same time. Because they are entangled, the z- and x-component of the other are will ...
-4
votes
0answers
60 views

Would a change of the spacetime topology inside a black hole be a possible consistent solution with quantum mechanics of the information paradox?

Would a change of the spacetime topology inside a black hole be a possible consistent solution with quantum mechanics of the information paradox and why and how is this explained? What would this ...
1
vote
1answer
47 views

Addition of angular momentum for 4 spins

I have a system of $4$ spin $\frac{1}{2}$ particles, whose Hamiltonian looks like this: $$ H = \alpha (s_1 \cdot s_2 + s_1 \cdot s_4 +s_2 \cdot s_3 +s_3 \cdot s_4 )$$ In order to find its eigenvalues ...
1
vote
2answers
80 views

Is it possible securely detonate a hydrogen bomb inside a very, very thick iron armor to get the armor only rise its temperature and not break apart? [closed]

Is it possible securely detonate a small hydrogen bomb inside a very, very thick iron armor, preferabely a sphere, to get the armor only rise its temperature and not break apart? Would it be a hazzard ...
0
votes
1answer
37 views

How do we apply force on a body?

We know that force is apllied either by pushing or pulling anything. But how do we push or pull or apply force on anything. I imagine the object A that is pushing and another object B that is getting ...
0
votes
0answers
11 views

How can neutral, even-numbered atoms like strontium be trapped in a magnetic trap?

Since the beginning of this year, there has been a lot of attention paid to newly-created 'Pauli crystals', also known as 'Pauli-blocking crystals'...... Using ionized atoms, or at least odd- numbered ...
0
votes
0answers
24 views

Connection between Symmetry Breaking and RG flow

I was wondering if this interpretation of how RG flows connects to the conventional symmetry breaking description of phase transitions is correct. Say I am an experimentalist and I move through ...
1
vote
1answer
40 views

What happens to initially static plasma around a wire?

Consider an infinitely long, cylindrical wire which goes through the $z$-axis with current, $I$, and radius $a$. Hence, in cylindrical coordinates, the magnetic field is given by $$\begin{aligned} \...
0
votes
1answer
27 views

Difficulty understanding molar volume

Suppose I am at STP and I am dealing with an ideal gas and I have a 22.4L container (with a movable piston attached on top) filled with 1 mol gas. Now, I will try to change the molar volume in two ...
0
votes
0answers
13 views

EPR Bohm's variant question

I've been doing some research on the EPR paradox and there is an instance that I do not understand. Say we have a positron electron pair that are entangled, conservation of angular momentum tells us ...
0
votes
1answer
21 views

Is RPM or Torque more useful for a Gravity driven launching mechanism?

for a project I need to create a launching mechanism which operates based on gravity. After some initial designing I have come up with a design where a counterweight (250g) is dropped about 85cm, ...
0
votes
0answers
15 views

Statistical Mechanics: Thermodynamic Probability for Air divided into leaky cells [closed]

Air at standard conditions circulates freely in a large box subdivided into leaky cells of volume 1 cmଷ. The thermodynamic probability, W_eq, for the distribution of equal numbers of molecules, N_eq, ...

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