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 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? May 27 revised If time-like paths are geodesics, what physical principle applies to space-like intervals? edited title May 27 asked If time-like paths are geodesics, what physical principle applies to space-like intervals? May 26 awarded Notable Question Apr 8 revised What's the interpretation of Feynman's picture proof of Noether's Theorem? Corrected wrong logic Apr 7 accepted How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$ 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) Dec 15 asked How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$ 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 25 asked EPR Paradox resolution: the spin is fixed at creation but its measurement isn't? Nov 25 awarded Inquisitive 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 24 revised Does the total energy in an electromagnetic field depend on the acceleration of the sources? edited title Nov 24 asked Does the total energy in an electromagnetic field depend on the acceleration of the sources?