Reputation
34,865
Next tag badge:
85/100 score
25/20 answers
Badges
5 67 161
Newest
 Nice Answer
Impact
~785k people reached

12h
revised Are ergs commonly used in astrophysics? If so, is there a specific reason for it?
added 1 character in body
13h
asked How many galaxies could be the source of the recent LIGO detection?
13h
asked Are ergs commonly used in astrophysics? If so, is there a specific reason for it?
1d
comment What is the correct statement of Kirchhoff's Law of Thermal Emission?
I certainly do not intend to enter a controversy (i.e. I won't respond further in this thread), but it bears mention that what makes this question unclear is the word "correct". Correct by whose standards? By what is in the literature? By what Kirchhoff himself would say if we asked him? By what the broader community understands the statement to mean? By what you think is correct? Your questions are dripping preconceptions and as such they are unlikely to find answers you're satisfied with. (Why are you asking? To find out, or to cause controversy? This site is not a venue for the latter.)
1d
reviewed Leave Closed Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false; and if it is not false why is it not false?
1d
comment Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false; and if it is not false why is it not false?
Stephen, I have edited in the reference. I find it extremely disingenuous that you attempted to hide your authorship of that document behind the link. Going beyond that, I don't think this is really the venue for the type of debate that you're looking for; we are not a substitute for the discussion that is currently taking place in the literature (cf. Johnson and Robitaille in the latest issue of Progr. Phys.). We are also not a substitute to peer review of your paper from last year. (You can try your luck at physicsoverflow and see what they say, maybe?)
1d
revised Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false; and if it is not false why is it not false?
Included reference.
1d
reviewed Edit Why is the speed of light exactly $299,792.458$ m/s and not faster or slower?
1d
revised Why is the speed of light exactly $299,792.458$ m/s and not faster or slower?
Small extra formatting fix.
1d
revised The question is related to quantum mechanics
added 1 character in body; edited tags; edited title
1d
comment Is there a phenomenon where physicists are only interested in the standard deviation of the quantity to be measured?
It bears mention that as a first approximation these resonances are often Lorentzian (a.k.a. Breit-Wigner), so formally they don't have a well-defined standard deviation. I'm not completely sure what they use as a width measure in practice, though.
2d
comment complex waveforms
Welcome! Note that this site uses LaTeX notation for mathematics, so $v=\sin(100\pi t)$ is produced using $v=\sin(100\pi t)$. A more thorough attention to spelling and clarity will make it much easier to tell what you're asking.
2d
comment Why are reciprocal lattice vector periodic, and time-frequency not?
k-vectors are periodic when there is a periodic potential. To have an analogous situation, you need a potential that's periodic in time. This is treated using Floquet theory where, indeed, the quasienergy is restricted to bands in the same way as k-vectors.
Feb
9
comment Do electrons in an atom always have the same 'direction'?
@Michael This is a (hopefully obvious) gross simplification of how angular momentum works inside atoms, to match the OP's terminology. Electron pairing is a relatively complex procedure, but indeed you can have two electrons with the same orbital angular momentum (but opposite spin). The description here applies only to the atomic ground states, and for any given atom you can always "spin up" the electron motion by driving to excited states. That said, any two (say) nickel atoms in their ground state will have the same amount of total angular momentum, differing only in its direction.
Feb
9
comment Do electrons in an atom always have the same 'direction'?
There are two contributions of angular momentum, orbital and spin. In a closed shell, each slot has two electrons of equal but opposite spin, and each slot with nonzero orbital angular momentum has a corresponding full slot with equal but opposite orbital angular momentum. The total angular momentum is therefore zero (for a full shell).
Feb
9
awarded  Nice Answer
Feb
9
revised Conservation of energy in quantum mechanics
Minor formatting fixes.
Feb
9
answered Conservation of energy in quantum mechanics
Feb
9
comment Can the permittivity tensor always be diagonalized?
You might be interested in reading about hyperbolic metamaterials, which sort of settles your second question. It would also be good if you can split the two questions as they are quite different in spirit and it helps to keep the discussions separate.
Feb
9
revised Do electrons in an atom always have the same 'direction'?
Formatting and spelling edits.