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Oct
25
comment Learning how to use Levi-Civita symbol
Oh also the first chapter of Landau's EM book has a footnote which contains some Levi-Civita stuff. I know that sounds obscure, but it's actually the first place I always go to when I need to know something about it!
Oct
25
comment Learning how to use Levi-Civita symbol
Maybe you need to look at an intro GR book - there is a lot more tensor calculus in such courses, so it will give you a better introduction. Check out the first couple chapters of Sean Carroll's review article: arxiv.org/abs/gr-qc/9712019, or the text that grew out of it.
Oct
18
comment Why doesn't topological phase transition break any symmetry? Hidden symmetry?
Not an answer, but just a clarification - we do not "assume" hidden variables do not exist. They have been proven repeatedly to NOT exist, unless the theory is nonlocal (Bell's theorem and experimental results). This is a strong constraint, in many people's opinion.
Sep
30
awarded  Explainer
Sep
22
comment Degeneracy in One Dimension
Just a slight rephrasing of #2: "At infinity the wave functions are zero so that left side of the last equation is identically zero. That "constant" is constant in $x$, so must be everywhere zero"
Aug
22
comment Why is static friction called self adjusting force?
I actually think this is a good question. Perhaps keep the title, and allow the question to be "I have heard static friction called a "self-adjusting force". How can this be? How does the force "know" how large to be? They way I understand it....".
Aug
1
reviewed Reviewed Shallow water wave question from Acheson's book
Jul
31
revised Problem with shell model and magnetic moment of Lithium-6
Just added math tags.
Jul
31
reviewed Reviewed Problem with shell model and magnetic moment of Lithium-6
Jul
31
suggested suggested edit on Problem with shell model and magnetic moment of Lithium-6
Jul
27
comment What strategy should I use to approach this problem? If my straight line approximation doesn't work
This answer is very close to what my comment was getting at. The equations (2) and (3) are the equations of the lines touching the steps. You have in your diagram equation (3); equation (2) is parallel to the steps but touches the upper corner of each step rather than the lower corner, which (3) does. You "derive" them with the equation for a line $y=mx+b$, where $m=1$ and there are two different $y$-intercepts, $-99$ and $-100$.
Jul
27
reviewed Reviewed How do I calculate motor efficiency from voltage, current and RPM?
Jul
27
comment How do I calculate motor efficiency from voltage, current and RPM?
"Useful work" is whatever is possible to get out of the motor, not what is actually gotten out of the motor. At least, that's a reasonable interpretation. The efficiency of a motor should not suffer just because you forgot to hook it up to something right?
Jul
26
comment What strategy should I use to approach this problem? If my straight line approximation doesn't work
I think you want to find the intersection of your equation for the motion of the projectile (assuming it's correct...) with the equation of a line starting 1 foot before you have the line in the diagram - meaning, "at the top of each step" instead of at the bottom. Then you can be sure of which step you land on.
Jul
26
reviewed No Action Needed Relativity of simultaneity example in Resnick
Jul
25
comment How to calculate the 2-point function of gravitons?
Ok well you might just be reduced to checking out arXiv articles until you find one that references something. Check out Brandt and Frenkel from 1993, they seem to use Birrel and Davies "Quantum Fields in Curved Spacetime" - you check that one out yet?
Jul
24
comment How to calculate the 2-point function of gravitons?
The graviton does not exist in "GR", it only exists in QFT. I seem to remember that Peskin and Schroeder has a section on it, but just check out some of the more extensive QFT textbooks (Weinberg maybe?)
Jul
24
reviewed Reviewed Mass generation by Chern-Simons theory
Jul
23
reviewed No Action Needed Pool in a submarine
Jul
22
comment What is the path integral exactly?
I won't downvote but it does seem like "a poetic description of a mathematical device" is pretty unclear. The path integral is not poetry, so it must be the mathematical device? So what is the poetry? Path integrals describe reality to $10^{-9}$ (or whatever); they must be more than poetry!