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seen Jun 28 at 16:46

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)
related: induced E from changing uniform magnetic field
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.
Oct
5
comment Why does Dirac write $\langle\xi'|\overline{f(\xi)} = \overline f(\xi ')\langle\xi'|$?
@KyleKanos Why doesn't Dirac just substitute $\xi'$ into $\overline{f(\xi)}$ as for (34)?
Oct
5
comment Why does Dirac write $\langle\xi'|\overline{f(\xi)} = \overline f(\xi ')\langle\xi'|$?
@KyleKanos Dirac uses $\xi$ for a real linear operator, ' to label objects connected with eigenvalues-- $\xi'$ for an eigenvalue, $\langle\xi'|$ for an eigenbra
Sep
23
comment How does Dirac form this conjugate imaginary equation?
@ACuriousMind This is page 30 of his book where the basic mathematical framework is based around there being a function of a ket, amongst other things. You really need to have a look at the book to see what I mean.
Sep
20
comment What axiomatizations exist for special relativity?
Nowadays, we'd say there is a universal speed limit c that light happens to travel at, making its measurement convenient.
Sep
18
comment How can (in Dirac's terminology) the product of two “real” linear operators be “not real”?
This answers my question. It would help if you could put $\alpha = \bar\alpha$ in brackets after Hermitian.
Sep
3
comment How does Dirac show that $\langle B|\bar{\bar{\alpha}}|P\rangle\;=\; \overline{\langle P|{\bar{\alpha}}|B\rangle}\;=\; \langle B|{\alpha}|P\rangle$?
Indeed; I assumed that the adjoint of an adjoint cancelled like the inverse operator. It seems obvious now that the adjoint of an adjoint should initially be assumed to give a different linear operator since its still just a linear operator.