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 Apr 10 comment Why glass is transparent? So why does light travel at a different velocity in the vacuum, if it's not absorbed in transparent materials? Nov 27 comment What's the point of hamiltonian mathematical formalism of classical mechanics? @LubošMotl I'm sure you already know that Dimensio1n0 was only 13 when he first joined here, yet was answering questions on the QED Lagrangian! Sep 26 comment Meaning of fourth component of velocity four vector He asked about the physical meaning of the fourth component, not the whole vector. Aug 16 comment Why define four-vectors to be quantities that transform only like the position vector transforms? Every frame uses the same Lorentz transformation when transforming events with the same lab space-time coordinates to other frames with the same relative velocity $v$. It's a transformation that doesn't change upon boosting to another frame, making it some kind of "Lorentz invariant". Maybe this isn't appropriate then? Aug 16 comment Why define four-vectors to be quantities that transform only like the position vector transforms? In $Q'=\rho(\Lambda)Q$, must the function $\rho$ be a Lorentz invariant if a physical law exists involving these quantities? Jul 22 comment Is the Maxwell Stress Tensor Coordinate Dependent? What is "the tensor itself"? Jun 26 comment Intuitive explanation for why centripetal acceleration is $\frac{v^2}{r}$ @OmarNagib the d/dt operator in Mark's explanation acts on a vector, and doesn't care about what it represents, only that it changes direction at a constant angular velocity $\omega$ with a constant magnitude. Perhaps Mark's brilliant explanation could be improved upon if it noted that both the position and velocity vectors rotate at the same angular velocity $\omega= v/r$, and therefore multiplied by this same factor. Jun 9 comment Calculating electric field using a given magnetic field equation (Maxwell-Faraday law) You're right when you say: "I don't think that having the magnetic field merely in the z^ direction, establishes any symmetry in the problem." for reasons given by Lubos in his answer in the link I gave. You should therefore be able to answer your own question in the answers below ;) Jun 9 comment Calculating electric field using a given magnetic field equation (Maxwell-Faraday law) Jun 1 comment Does a photon interfere only with itself? So Dirac was wrong; can you recommend a better QM text book? Apr 7 comment How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$ Archaic notation or not, I'm looking for an answer in the spirit of Dirac's method; but thanks for your effort. Apr 7 comment How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$ Thanks for your effort, but I was hoping for an answer based more around Dirac's procedure. Maybe you could have a quick glance at an online version of his book available on scribd.com? ;) Apr 3 comment Quantum Mechanics by Dirac Dirac's book is an introduction to QM for researchers and grad students. It was never used as a text book because he didn't have experience as a teacher of undergraduates and the problems they face; hence there's no exercises in the book. Even Feynman didn't understand Dirac's book when he read it as an undergraduate. The main thing going for it from what I've read is his more abstract view of the subject. Definitely a book only to be read by those with a good understanding of Hamiltonian mechanics and complex vector spaces (which he assumes the reader already knows about) Nov 26 comment EPR Paradox resolution: the spin is fixed at creation but its measurement isn't? So these states are probabilities of it being measured to have some spin; this doesn't mean the spin upon creation is in a superposition of spin states, does it? Nov 25 comment EPR Paradox resolution: the spin is fixed at creation but its measurement isn't? But aren't you using "state" here to mean the probability of what's measured? Nov 24 comment Does the total energy in an electromagnetic field depend on the acceleration of the sources? @ACuriousMind I'm trying to understand where the self-force for an accelerated charge comes from. Since the self-force increases with acceleration I thought this might be because more electromagnetic energy is created. Nov 12 comment Will a ball slide down a lumpy hill over the same path it rolls down the hill? The difficult part is showing that the constraint for no slipping and its angular momentum doesn't affect the path taken by the center of mass when it's allowed to slip. Nov 10 comment Will a ball slide down a lumpy hill over the same path it rolls down the hill? @RonMaimon I've done a search on Amazon.com for that reference in your answer, but I can't find it; is it an old rare book? Oct 27 comment Reading the Feynman lectures in 2012 @ArtBrown I've seen the book on Amazon.com and after looking at the contents, I'm still scratching my head over the whole point of it: Physicists use QED, engineers use CED and both models are brilliantly served by main stream text books. Oct 13 comment Should the eigenkets be weighted in $|P\rangle = \sum\limits_{r}|\xi^r\rangle$? every ket-vector can be expressed as a sum of a set of unity weighted eigenvectors? I find this hard to believe.