All Questions

1
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0answers
39 views

Does an information-theoretical approach proof the equivalence of total order and total chaos?

In the light of information-theory, are a state with maximum and minimum entropy the same? In the case of gas (maximum entropy), one needs very little words to describe a part of the system, which ...
0
votes
1answer
49 views

How can a non-rotating black hole or singularity be created?

Every star or other massive body in the universe rotates, if only a little. If such a body collapses, its spin, any spin at all, and thus, angular momentum approach infinity as r approaches 0. Angular ...
1
vote
0answers
49 views

Time after which the 3 particles will meet? [on hold]

Problem is from Classical Mechanics: I am a beginner in Physics trying to understand the solution to the given below problem. Problem Statement: 3 particles are placed at the vertices of an ...
0
votes
0answers
29 views

Could black holes be driving the expansion? A different perspective than others that have asked [on hold]

Disclaimer: I'm not a phycisist. I'm a computer science major, going to an engineer school, that's taken the required physics with calc 1 and 2. This is just an interest. Please correct anything that'...
2
votes
3answers
69 views

What does it mean that charged particles in orbits undergoing acceleration would emit electromagnetic radiation?

One of the drawbacks of Rutherford's atomic model was that electron would emit electromagnetic radiation as it is continuously changing direction and therefore undergoing acceleration, in what form ...
1
vote
0answers
63 views

Dimensionally inconsistent!

This equation doesn't seem to be correct. Dimensionally inconsistent, in fact! How then, is it established? $$s_{t}=v_{0}+\frac{1}{2}a(2t-1)$$ (In case you don't know, this is the equation used to ...
8
votes
3answers
176 views

Are there cases where $\nabla\cdot\iiint\frac{\mathbf{J}(\mathbf{x}')}{\left|\mathbf{x}-\mathbf{x'}\right|}\mathrm{d}V' \neq 0$?

In Jackson's Classical Electrodynamics, Section 5.4 (Vector Potential), the author seems to assume that because $\nabla\cdot\mathbf{J} = 0$, the following holds for the current density (where the ...
0
votes
0answers
33 views

Using Kinematic Equations when acceleration is not constant due to drag force

If you drop a ball in a vat of oil with a mass of 50 g and it reaches terminal velocity of 0.032 m/s, how long would it take to reach 1/2 of terminal velocity? The drag force equals $F_d$ = Dv. I ...
0
votes
2answers
34 views

Frictional force between ground and sphere [on hold]

In this question I was asked to draw the free body diagram of the sphere. In the free body diagram, there were two forces in horizontal direction (1) normal reaction from wall (2) horizontal ...
0
votes
1answer
20 views

Force on Dielectric on pulling it out from capacitor

This is the text from Griffiths Electrodynamics for calculating force on dielectric on pulling it out from capacitor when the capacitor is connected to Battery so that voltage of capacitor is fixed: ...
0
votes
1answer
53 views

Change of basis in the many worlds interpretation?

Say we have two orthogonal states $|A\rangle$ and $|B\rangle$. In the many worlds interpretation, we can imagine two parallel universes in which we are either in state $A$ or $B$. But now if we ...
1
vote
2answers
61 views

Photoelectric effect confusion

I just have a quick confusion, so photoelectric effect says that light or photon act as particles not waves, however the photon energy is given by $E=hf$, so shouldn't the photon be initially a wave ...
-1
votes
0answers
43 views

Pressure required to form a black hole, explained to a ten year old

I could point to a mountain and say: gravity in a Black Hole is so strong, it would crush that mountain into the size of a grain of salt. But I am looking for something more concise, like the pressure ...
0
votes
1answer
66 views

Prove that a transformation is canonical by using $\mathbb{M}^T\cdot \mathbb{J}\cdot \mathbb{M}$ [on hold]

So, I was given the following problem to solve: A system with two degrees of freedom is described by the following hamiltonian \begin{equation} H=p_1^2+p_2^2+\frac{1}{2}(q_1-q_2)^2+\frac{1}{8}(...
-1
votes
0answers
17 views

Is there any graphs that demonstrate the Tsiolkovsky rocket equation? [on hold]

For example can you see the equation from analysis of a graph?
-3
votes
0answers
28 views

How much weight can we pick up with current tools? [on hold]

I'm curious about how much weight can we pick up with the tools have now. I tried to find it on the internet but no luck.
0
votes
0answers
21 views

How to estimate the error in the positioning of an airplane if there was no relativistic correction? [on hold]

I need to resolve this exercise on relativity. The position of an airplane in flight is made by triangulation. Radio signals are emitted by the airplane at regular time intervals and picked up by at ...
0
votes
1answer
22 views

Is there a superposition principle for the motion of interacting charges acted upon by external EM fields?

Consider a system of charges interacting with one another via their EM fields together with external EM fields applied to the system from outside. Suppose we work out the equations of motion ...
4
votes
2answers
88 views

Gauge fixing, invertibility and Green's functional

consider the photon in QED and the corresponding EOM of its Green's functional in k-space: $$(k^\mu k^\nu-k^2g^{\mu\nu})\Delta_{\nu\rho}(k)=i\delta^\mu_\rho.$$ Now, I understand that $U^{\mu\nu}(k):=...
0
votes
0answers
37 views

Unsolved problems in physics [reference request] [on hold]

I'm looking for a comprehensive reference outlining the unsolved problems in physics by category. I stumbled into this site which does the same, but for maths. I know that wikipedia has a pretty ...
2
votes
1answer
43 views

To see if a system behaves chaotically does one have to vary (in a tiny way) the initial momenta of ALL constituents of the system?

Consider a deterministic system (a gas, a liquid, or a solid, each of which can have an arbitrary form; for example, the atmosphere, a waterfall, or a double pendulum) which consists of a huge number ...
0
votes
1answer
34 views

Third Law of Thermodynamics and Thermal Pollution

Unlike coal power plants which produce CO2 and intensify the greenhouse effect, every engine produces thermal pollution because of the constraints on engine efficiency. No engine can convert 100% of ...
2
votes
1answer
81 views

Why is $\rm{Conf}(\mathbb{R}^{1,1}) = \rm{Diff}(S^1) \times \rm{Diff}(S^1)$ and not $ \rm{Diff}(\mathbb{R}) \times \rm{Diff}(\mathbb{R})$?

The Minkowski metric for $\mathbb{R}^{1,1}$ is $$ ds^2 = dt^2 - dx^2 = du dv $$ for coordinates $$ u = t + x \hspace{1cm} v = t - x $$ If you do any coordinate transformation that acts independently ...
-1
votes
0answers
24 views

Magnetic field of a ring ( tricky) [on hold]

here in this question the ring is rotated along axis perpendicular to the normal axis . This ring has charge q and rotated with angular velocity w . Then we have to magnetic field on a point on normal ...
2
votes
2answers
61 views

Why is horizontal pressure the same as vertical pressure in a static fluid?

In a static fluid, I know that because it is not moving, the pressure from the top equals the pressure from the bottom. Also, using the same logic, the pressure from the sides must be the same. Why ...
1
vote
0answers
35 views

Spacetime manifolds of 1+1 d systems for writing TQFT partition functions

Are the spacetime manifolds of two unentangled systems disconnected? This arises in the context of thinking of an operator whose expectation value we wish to take by writing this quantity in terms ...
7
votes
4answers
2k views

Does a proton have a binding energy?

When calculating the $Q$-value, $Q = \Delta M \cdot c^2$, of this reaction: $$ ^6Li \ (\alpha, p)\ ^9Be \quad \iff \quad \alpha + \ ^6Li \ \longrightarrow \ ^9Be + p $$ The $Q$-value can also be ...
0
votes
0answers
16 views

How to plot Majorana energies for Kitaev chain as function of mu?

My first attempt was, using the Python library Kwant, getting the lowest eigenvalues for the 1D p-wave superconductor as a function of the chemical potential mu (In the image below I show what I got). ...
1
vote
0answers
27 views

Resonance and energy flow

In this post, Alfred Centauri describes the resonance as a phenomenon which appears when 'the energy flow from the driving source is unidirectional' and then shows that this is the case for $\Omega=\...
0
votes
1answer
48 views

Photon creation operator physical realization

I am trying to self study QED so I apologize if my question seems silly. As I realize, all physical processes should stem from some "hermitian" operator in the quantum language. As it is well known, ...
0
votes
0answers
24 views

What's wrong with my work? (calculate spring stiffness constant) [on hold]

So the prompt is as follows: A 1100 kg car moving on a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.3 m. What ...
-1
votes
1answer
62 views

Convert emotion into energy? [on hold]

if it were possible to quantify emotion, would it be possible, theoretically, to then convert it into usable energy?
2
votes
2answers
61 views

Are there more than 3 dynamical pictures of quantum mechanics?

There are 3 well known dynamical pictures of quantum mechanics: the Schrödinger picture, the Heisenberg picture and the interaction picture. In above wikipedia article, their connection is nicely ...
0
votes
0answers
12 views

What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)?

What is the critical temperature for a BKT transition in the 2D quantum XY model with $S=1$ (not $S=1/2$)? For instance, the classical XY model has KTc/J = 0.898 and the quantum XY model with S=1/2 ...
0
votes
1answer
37 views

$N$ independent spins, mean value of $m_N$

We have $N$ independent spins $s_i$ which can take on values $-1$ and $1$ with probabilities $p(s_i=1)=p$, $p(s_i=-1)=q$. For the total magnetization $M$ we can get N+1 different values $-N,-N+2,...,N-...
0
votes
0answers
27 views

Interaction picture counter rotating terms

In the interaction picture, we often do the rotating wave approximation where terms like $e^{i(\omega_1 + \omega_2)t}$ are ignored because they represent rapidly oscillating terms which ends up ...
1
vote
5answers
128 views

Capacitance for infinitely large plates

Let's say you have two infinitely large plates. I understand the formulas for capacitance. What I don't understand is the intuition behind the fact that when you increase the distance between the ...
0
votes
3answers
27 views

The Lagrangian for gravitational potential energy in a double pendulum

For a double pendulum what would be the gravitational energy. I am trying to work out the Lagrangian for the double pendulum. I got the kinetic energy but I am struggling on the gravitational ...
0
votes
0answers
17 views

Damped forced vibration Calculating amplitude and phase angle

Consider that we have the following forced vibration with preload ($kxo$) spring. $$m\ddot{x}+c\dot{x}+k( x+xo) = F_0 \sin{(\omega t)}$$ Assuming that the solution must be a harmonic form but with ...
3
votes
4answers
116 views

Cheap classroom demonstrations of quantum mechanics

In a few weeks I'm going to be teaching a week-long class on quantum mechanics at a summer program for very mathematically talented high school students. I'm planning to focus on the finite-...
-1
votes
2answers
74 views

What exactly is $p$?

Consider the Bernoulli equation of fluid dynamics. One of the terms is $p$. I know it is pressure. But what type of pressure is it? Is it pressure due to height or a completely different concept?
-2
votes
1answer
85 views

Why don't green and anti-green gluons immediately annihilate each other?

I can't believe I haven't found an answer elsewhere..... I have read repeatedly about blue/anti-blue gluons, etc., but no reason as to why they don't destroy each other immediately..... Or maybe ...
0
votes
2answers
54 views

Hamiltonian in Piers Coleman - Introduction to Many-Body Physics book

In the book "Piers Coleman - Introduction to Many-Body Physics (2016, Cambridge University Press)" in page 491 When an electron pair is created, electrons can only be added above the Fermi ...
2
votes
4answers
120 views

Is there a limit to the amount of mass we can concentrate in a region of space?

Black holes are solutions to Einstein's Field Equations. Black holes contain a singularity hidden from the outer universe. As I understand, these singularities are infinitesimal and contain a very ...
1
vote
3answers
83 views

Initial conditions for wave equation

One of the common initial conditions given for the wave equation, $$\frac{\partial^2 p}{\partial t^2} - \nabla^2 p = 0,$$ is $p(\overline{x},t=0) =0$ and $p^\prime (\overline{x},t=0) =0$. What is ...
-4
votes
1answer
28 views

What are typical atomic densities of solids and gases? [on hold]

What are average values for the number of atoms per cubic cm for typical solids and gasses at atmospheric pressure?
0
votes
0answers
47 views

Does water pressure have any effect on the size of a permanent magnet's magnetic field?

If a permanent magnet is dropped into a deep body of fresh water such as Lake Superior, as it descends down, the rising water pressure should continually reduce the size of the magnetic field ...
0
votes
0answers
10 views

Shell model label symmetry

I'm working through the quark model Hadron wavefunctions, and trying to figure out the flavour-spin part of the wave functions. This is easy enough for S shell spatial states, since the space wave ...
0
votes
1answer
54 views

Ferromagnetism and induced magnetism

According to Wikipedia: A magnetic domain is a region within a magnetic material where individual magnetic moments of the atoms are aligned with one another and point in the same direction thus ...
1
vote
0answers
50 views

Black Holes without Schwartzschild Radius condition? [duplicate]

Reading this comment makes me ask what does that actually mean that In fact, if you are close enough to $c$, the mass-equivalent of your kinetic energy may be enough to make you appear as a black ...

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