Newest Questions
246,675 questions
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Are there alternatives to the collapse of the wave function?
The equations of classical physics are time reversible -- unchanged when $t$ is replaced by $-t$. The Schrodinger equation in quantum mechanics is time reversible -- unchanged when $t$ is replaced by ...
- 297
2
votes
2
answers
15
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Does spectroscopy count as a measurement of electron spin?
There was some debate in my modern physics course about the statement
"The spin of an electron can only be measured in the presence of an external magnetic field".
So far in the course, ...
- 141
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votes
1
answer
20
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Rigid body and the need of the cross product
When one is introduced to rigid body mechanics many start by simply using Newton's second law :
$$\vec{F_i}+\sum_{j} \vec{f_{ij}}=m_{i} \frac{d^2}{dt^2}\vec{r_{i}}$$
Obviously if we now also sum every ...
- 132
1
vote
0
answers
33
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Variational Principle for the $\rm H_2^+$ ion
I am following the book "Introduction to the Quantum Theory" by David Park, and I've run into a problem. The text calculates the ground state potential energy of the $\rm H_2^+$ ion using ...
- 33
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1
answer
36
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Can we write powers of Yang-Mills Lagrangian in index-free differential form language?
The Yang-Mills Lagrangian can be written in index-free differential form language as
\begin{equation}
\mathcal{L} = - \frac{1}{4} F^{\mu\nu}_a F_{\mu\nu}^a \, \text{d}\omega = - \frac{1}{4} \text{tr} (...
- 2,617
2
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1
answer
26
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The density operator as a function of the Hamiltonian in equilibrium
I am studying statistical mechanics on my own with several books (Pathria, Huang, Reichl, etc..) and there is a conclusion which is stated in all these books is but never showed. This might be so ...
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0
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35
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Why does flowing water produce what sounds like white noise?
Why does flowing water produce what sounds like white noise? Is this due to a certain type of turbulence? Is there a proof that the noise produced is white (or pink or Brown?)?
- 2,227
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32
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Radii of points on moving rotating sphere
Imagine a solid sphere B moving uniformly in a straight line and rotating about its axis. The axis of rotation of B and the direction of motion of B are perpendicular to each other. Does this mean ...
-1
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0
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54
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A question about interstellar travel [duplicate]
If an observer $O'$, one light-year away, approaches $O$ at a speed close to that of light, the time elapsed for observer $O'$ would be practically zero. If $O$ is the one approaching, the opposite ...
- 105
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Restoring force in wave motion and transfer of forces
I am trying to understand about the forces that one body generates a force and gives it to the other one and receives a reaction, yes, these are not a cause effect pair as what sir Newton said and ...
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0
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66
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The arrow of geese. Four velocity and the arrow of time [closed]
As winter approaches geese fly south. As they fly they form an arrow which point in the direction of their velocity. Sometimes they fly east, or even north. Whichever way they fly they form an arrow ...
- 1,919
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37
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Canonical Electromagnetic Stress-EnergyTensor and Conservation Laws with Sources
Given the expression for the canonical Stress-Energy Tensor as:
$$T^{\mu \nu}=\partial^\mu \phi \frac{\partial \mathcal{L}}{\partial (\partial_\nu \phi)}-g^{\mu\nu}\mathcal{L}$$
where $\phi$ is a ...
- 11
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34
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Can the mass of a proton be used as a surrogate for the strength of gluon color charge? [closed]
If a proton has mass 938 MeV/c^2, and gluon energy makes up 99% of the mass of the proton, can we say that gluon color charge has a strength of .99 x 938 = 928 MeV in equivalent units, recognizing ...
- 5,048
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26
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How fast will an ideal gas move into a void (vacuum)? [duplicate]
Premise
Imagine we could magically / instantaneously create a void - a near-perfect vacuum - in the atmosphere (or any other similar space filled with a near-ideal gas).
Question
The instant after ...
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18
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How to formulate a massive vector field in extended GR such that $c_T = c$ while $v_{Vector} < c$? (GW170817 Consistency) [closed]
I am considering an extended framework of General Relativity (GR) coupled to a massive vector field (Proca field), which necessarily generates additional gravitational wave (GW) modes.
The theory must ...
-6
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0
answers
20
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Dimensional and Analytical Consistency Check: The Critical Informational Scale $S_{\text{crit}}$ derived from $\hbar$ and $G_N$ in a TVS Gravity Model [closed]
I have formulated an extended Tensor-Vector-Scalar (TVS) gravity theory that causally links Objective Reduction (OR) to Gravitation. The theory postulates the Critical Informational Density ($S_{\text{...
1
vote
0
answers
42
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Application of Reichenbach synchronisation
Suppose I adopt the Reichenbach synchronisation process so that light heading radially away from me- according to my clocks- travels with infinite speed, while light heading directly towards me ...
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2
answers
38
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To Find the power of a motion do we need to consider force into velocity or energy per time? [closed]
A trolley is moving at a constant velocity v and sand is being dropped in at m kg/s.So what is the power need to be supplied to keep the trolley moving at same velocity.I suggest two methods
Force x ...
-4
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0
answers
55
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Quantum Entanglement Field Theory by Ammar Hafeez [closed]
Is it possible for entanglement to be a dynamic field, suggesting that particles become entangled through their interaction with this field, as opposed to viewing entanglement as a direct, passive ...
3
votes
1
answer
168
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How is this ratio formula for two conducting balls true?
I recently skimmed through my tutor's physics book, it's not the greatest book out there since it doesn't provide much detail about how the physics works rather its more like a compilation for ...
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1
answer
57
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A problem with momentum conservation (Newtonian and relativistic) [closed]
Assume we have a large parallel-plate capacitor with a very high, uniform electric field. A nonconductive bar joins the plates at their centers. Now, assume that two small charges with negligible ...
- 2,920
-2
votes
0
answers
15
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Transforming Initial Cartesian Uncertainty into Delaunay Variables for Orbital Uncertainty Propagation [duplicate]
I am working on orbital uncertainty propagation where the initial uncertainty is given in Cartesian coordinates
(
𝑟
,
𝑣
)
(r,v), either as a covariance matrix or as bounded (non-statistical) ...
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0
answers
35
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Canonical quantization of abelian vector field in $R_\xi$ gauge
I am trying to do the canonical quantization of an abelian vector field $A_\mu(x)$ in the $R_\xi$ gauge. So the gauge-fixing Lagrangian is given by $$ \mathscr{L}_{gf} = -\frac{1}{2\xi} (\partial_\mu ...
- 303
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0
answers
29
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Visualise Hadamard gate as addition of $x$ and $z$ gate
I try to imagine the Hadamard gate on a Bloch sphere and it is obvious that it is the sum of the Pauli $x$ and $z$ gate matrices.
So that means we rotate the "vector" around the x axis and ...
3
votes
0
answers
27
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Why do random quantum circuits produce entanglement?
There's a lot of work done on random quantum circuits, and very often the story is that you start from a completely unentangled state, then random unitary gates act on it, and you generically end up ...
-8
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0
answers
51
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Binary entropy maximization gives ln 2 = 0.693, matching Ω_Λ. Coincidence or connection? [closed]
I'm working through a statistical mechanics problem and found something
that matches cosmological observations surprisingly well.
Binary Entropy Maximization
Consider N distinguishable patches, each ...
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0
answers
38
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Question about self-orthogonality in non-Hermitian systems [duplicate]
This is my second attempt at this question, the first one got deleted because my question was lacking detail. My knowledge of this subject comes entirely from these two sources: Nimrod Moisyevitch, ...
- 390
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1
answer
58
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Is this additive mixing or camera image sensor error
I have coupled RGB laser light into 3 gratings on chip and projected the light into the the farfield and put a camera sensor on top of the beam. Here is the setup and the experiment.
What I obsereved ...
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1
answer
134
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How does the concept of "coordinates" makes sense when considering large scales of the universe?
I will describe two instances, that led me to ask the question of relevancy or meaningfulness of coordinates when we are not local in our observation of the universe, but rather we consider a large ...
- 2,048
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votes
2
answers
73
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Free energy at 0 K from density functional theory and statistical mechanics
Helmholtz free energy of a system of atoms (for example — a perfect crystal) at $0$ K can be obtained by performing a static density functional theory (DFT) calculation (neglecting the effects of zero ...
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0
answers
54
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Relationship of space-time to energy and momentum [closed]
After reading Noether's theoram and many other examples like objects tendency to follow its geodesics in spacetime makes conserved quantities like momentum etc meaningful so , are energy and momentum ...
- 1
0
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0
answers
50
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Transforming Initial Cartesian Uncertainty into Delaunay Variables for Orbital Uncertainty Propagation [closed]
I am working on orbital uncertainty propagation where the initial uncertainty is given in Cartesian coordinates
(
𝑟
,
𝑣
)
(r,v), either as a covariance matrix or as bounded (non-statistical) ...
0
votes
0
answers
37
views
Practicality of zero-point for potential energy of a magnetic dipole in a magnetic field
Is there any practical significance of the convention of potential energy of a magnetic dipole in an uniform magnetic field?
Suppose, in a vacuum, a magnetic field runs in the $y$ direction. Now we ...
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2
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0
answers
73
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Does an EM wave "turn around" and go inside an open-ended tube?
I am struggling to resolve a thought experiment that deals with the behavior of an EM wave as it reaches the end of a tube.
Assume a wave starts out traveling along the outside of a copper tube. The ...
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0
answers
111
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Path integral in quantum mechanics and expectation values
How to calculate any expectation value from path integral in quantum mechanics? In QM path integral the initial and final points are fixed and points between them are varied. But as far as i ...
- 367
3
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1
answer
121
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What is the link between the vector field generating the group action and the covariant derivative
I am currently working through Witten's "Two Dimensional Gauge Theories revisited". He defines an operator (p.28, but the redefinition is for p.32)
\begin{equation}
D = \sum_i \psi^i \frac{\...
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0
answers
65
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Time-domain algorithm to generate noise with Power Spectral Density (PSD) $S(\omega,T) \propto \coth(\omega/T)$ sequentially
I need to numerically generate colored noise with a Power Spectral Density (PSD) $S(\omega,T) \propto \coth(\omega/T)$ (quantum thermal noise). I cannot use standard Spectral Synthesis (Inverse FFT) ...
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0
votes
0
answers
48
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Degrees–of–freedom counting and Goldstone structure for $SU(3)$ broken by a complex $3\oplus\bar{3}$ Higgs
I am studying the Higgs mechanism in a single $SU(3)$ gauge theory with 2 scalars being a complex fundamental $\phi \sim 3$ and its complex conjugate $\psi \sim \bar{3}$. I would like to understand in ...
- 55
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0
answers
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How the energy-momentum tensor comes from the action in Kalb-Ramond (KR) gravity? [closed]
The action
\begin{align}\label{action}
S=\int d^4x\sqrt{-g}\bigg[\frac{1}{2\kappa}\bigg(R-\varepsilon\, B^{\mu\lambda}B^\nu\, _\lambda R_{\mu\nu}\bigg)-\frac{1}{12}H_{\lambda\mu\nu}H^{\lambda\mu\nu}-V(...
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1
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85
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Questions about the behavior of a void (vacuum) in atmosphere [closed]
Introduction
I've been doing some research on this topic and I want to:
Confirm my findings
Answer some lingering questions
Premise
Imagine we could magically / instantly create a void in the ...
- 105
-4
votes
0
answers
82
views
The cat thought experiment [duplicate]
This thought experiment was made with the purpose of trying to understand whether the ideal gas law holds in relativistic frames.
Suppose you have two observers, a box that is perfectly insulative and ...
2
votes
1
answer
69
views
Will a magnet levitating in an actively-controlled field always have a "free axis" of rotation?
I recently saw an advertisement for a fun gadget: a 20-sided die levitating (via active magnetic control) over a pad (with an array of electromagnets, I assume). In the video demonstrating the gadget,...
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83
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How the universe could work without dark matter? [closed]
I have a 7 page document that outlines the current 4 major anomalies. Universal expansion (dark matter), voids, early star formation, and local galactic environment) and a possible radical explanation ...
3
votes
1
answer
125
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Riemann 2-manifold volume form: complex vs real
Question 1: is it always possible to write the metric in that form? Is it sufficient the local conformally-flat form to obtain the volume?
Question 2: Is the volume form in (4.1) well-defined? Going ...
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1
answer
84
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If two sounds are identical, with one having a higher amplitude, would they both have the same frequencies? [closed]
Given homework question, "A certain sound is recorded by a microphone. The same microphone then detects a second sound, which is identical to the first one except that the amplitude of the ...
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5
votes
2
answers
454
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A (probably wrong) proof that the fundamental Poisson brackets are independent of the special choice of the canonical variables
In Wolfgang Nolting's book Theoretical Physics 2 - Analytical Mechanics, the following theorem is stated:
While the formal definition of canonical trasformation is given only several pages later in ...
- 51
2
votes
0
answers
76
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Operations with the hard sphere potential
In statistical mechanics (in particular I'm interested in applying the Landau Kinetic Equation to a hard spheres gas), it is often useful to get the gradient or the Fourier transform of the ...
0
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0
answers
52
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Is there a connection between Ehrenfest equation and von Neumann equation? [closed]
I understand how Ehrenfest is sort of giving a correspondence between classical and quantum whereas von Neumann is more like a quantum mechanical equivalent of Liouvilles equation. But do they share ...
- 1
9
votes
2
answers
742
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Permanence of the basic forces
I am a highly interested layperson in Germany focusing on the fundamental principles that govern our everyday reality.
I have a specific question regarding the permanence of the basic forces of ...
- 107
-1
votes
0
answers
72
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Relativistically spinning top? [duplicate]
Assuming a spinning top with a rigid radius, not changing due to centrifugal forces, of 2 cm at the equator measured at rest, is spinning hypothetically at approximate $0.866c$ the speed of light in ...
- 4,685