All Questions
236,815
questions
1
vote
0
answers
22
views
Quantum intrinsic spin
In the Stanford lecture:
https://www.youtube.com/watch?v=VtBRKw1Ab7E&t=940s (15m 40s)
Prof. Suskind claims that, with the emission of a photon, reverse-aligned particles flip from down to up.
But ...
0
votes
0
answers
19
views
Interpretation of degenerate metrics
I was studying the metric tensor and saw all about degenerate metrics. I would like what is the physical or geometrical intuition of a degenerate metric.
What is the meaning of $g(v,w) = 0$ for a ...
- 67
1
vote
0
answers
25
views
Asymptotic states and physical states in QFT scattering theory
Context
In the scattering theory of QFT, one may impose the asymptotic conditions on the field:
\begin{align}
\lim_{t\to\pm\infty} \langle \alpha | \hat{\phi}(t,\mathbf{x}) | \beta \rangle = \sqrt{Z} \...
- 88
0
votes
0
answers
14
views
Derivation of Einstein-Cartan (EC) action for parametrized connection $A$ & introduction of torsion
I have some trouble with one missing step when I want to get the teleparallel action from general EC theory, which I am not fully understanding.
The starting form of action is:
$$
S_{EC}=-\frac{1}{8\...
0
votes
0
answers
11
views
Is it possible to find a function that approximately describes data points in series?
With a pH sensor we measured the output voltage in dependence of temperature. By measuring over a temperature range we obtained a data series. That way we created several series by using different ...
- 1
0
votes
0
answers
24
views
Problem explanation from Estonian-Finish Physics 2003 olympiad [closed]
I am having trouble understanding problem 5.3 (Vibrations) from the Estonian-Finish 2003 Physics olympiad. Specifically in 5.3 they say "brick is kept in motion along(horizontal) $y$-axis by a ...
- 135
0
votes
2
answers
21
views
Different results of Range of a projectile
My question is from the Range of a projectile. Range is displacement of the projectile through X-axis. We all know the formula for the range $R$ of the projectile is $$R=\frac{v_0^2\sin(2\theta)}{g}$$ ...
0
votes
0
answers
14
views
Stress/forces on elements in continuum mechanics
When looking at small elements in continuum mechanics, why do we draw that the stress/force the way shown in diagrams? How do we know the "pairs" of forces on opposite faces always opposite, ...
- 11
-4
votes
0
answers
43
views
Could you please answer my questions (I have four questions)? [closed]
1.must the positive direction is always upwards when we study systems that have springs in a vertical way and we cannot assume that the positive direction is downwards?
If I understand correctly, how ...
- 1
0
votes
1
answer
41
views
$2\pi$-rotation of fermionic states vs. fermionic operators
Given a fermionic state $|\Psi\rangle$, a $2\pi$ rotation should transform it as
\begin{equation}
|\Psi\rangle \quad\to\quad -|\Psi\rangle \,,
\end{equation}
On the other hand, given a fermionic ...
- 393
0
votes
1
answer
22
views
Is the pressure at the top of the wings on Mars also lower than the local atmospheric pressure on Mars?
Generally speaking, on Earth, in order to fly, the pressure on the top of aircraft wings is lower than the local atmospheric pressure. So if we fly an airplane on Mars, will the pressure on the top of ...
- 2,040
1
vote
2
answers
38
views
Is the FRW metric, based on spatial homogeneity and isotropy, rotationally and translationally invariant? If so, how?
The spatial part of the Minkowski metric, written in the Cartesian coordinates, $$d\vec{ x}^2=dx^2+dy^2+dz^2,$$ is invariant under spatial translations: $\vec{x}\to \vec{x}+\vec{a}$, where $\vec{a}$ ...
- 11.8k
1
vote
1
answer
22
views
Weyl transformation of induced metric
Consider the Weyl/conformal transformation in four dimenions
$$\tilde{g} \enspace = \enspace \Omega^2 g \quad \Longrightarrow \quad \sqrt{-|\tilde{g}|} \enspace = \enspace \Omega^4 \sqrt{-|g|}$$
The ...
- 761
0
votes
0
answers
35
views
Where is the mass in a Black Hole without a "central" curvature singularity?
Not all black holes have a curvature singularity at their center (an example). But in principle, I thought that the curvature singularity was a direct result of the fact that the mass is concentrated ...
- 770
0
votes
0
answers
69
views
Physical intuition for the Minkowski space? [closed]
As the title suggests, I am looking for physical intuition to better understand the Minkowski metric.
My original motivation is trying to understand the necessity for distinguishing between co-variant ...
