31,989 reputation
23491
bio website joshphysics.com
location Los Angeles
age 28
visits member for 2 years, 2 months
seen 1 hour ago

New project: phermi.com

Let me know if you know of any hard physics problems with clever solutions. (email listed to the left)

Personal website: joshphysics.com

Currently a lecturer at the UCLA Department of Physics and Astronomy.

Ph.D. theoretical high energy physics, UCLA.

BA/BS in physics/math, UC Berkeley.


Mar
23
awarded  Nice Answer
Mar
18
comment Differential geometry of Lie groups
@WetSavannaAnimalakaRodVance Interesting, thanks for the link.
Mar
16
comment Justifying the notation $\langle x\ |\ \psi\rangle$
possible duplicate of Meaning of inner product $\langle \vec{r} | \psi(t)\rangle $
Mar
15
awarded  Good Answer
Mar
12
revised Information content of the electrostatic Maxwell equations vs Coulomb's Law vs Poisson's Equation
added 72 characters in body
Mar
11
comment Why is the “complete metric space” property of Hilbert spaces needed in quantum mechanics?
Comment on question (v1): Regarding your first question, every inner product space is automatically a metric space because every inner product automatically induces a norm (length) in a natural way: $\|x\| = \sqrt{\langle x,x\rangle}$, and a norm induces a metric in a natural way: $d(x,y) = \|x-y\|$. The second question is more involved, but I think it's answered in the duplicates suggested by Qmechanic.
Mar
8
revised Divergence theorem in complex coordinates
deleted 170 characters in body
Mar
3
comment When can one write $a=v \cdot dv/dx$?
@Martín-BlasPérezPinilla I'm somewhat inclined to agree, although I think the abuse has at least two possibly advantages: (1) it's easier and simpler to write and therefore a bit more readable (2) I think it can benefit one's intuition if one knows what he's doing. Having said this, I completely agree that it's often extremely confusing to students, along with a lot of other physics derivative conventions.
Feb
27
awarded  Nice Answer
Feb
26
comment potential inside a cylindrical shell in terms of the surface potential?
It's hard to know what "easy" means to you. There is more than one way to do this 1) Determine the Green's function for the Dirichlet problem on the interior of the cylinder and then compute an integral 2) Expand the the potential in appropriate orthogonal functions (involving Bessel functions in this case), and compute the coefficients in the expansion by doing some integrals. If the potential is sufficiently simple, both of these methods shouldn't be too bad.
Feb
19
revised Why is the harmonic oscillator so important?
added 18 characters in body
Feb
16
awarded  Popular Question
Feb
4
comment When can one write $a=v \cdot dv/dx$?
@KDN Nowhere do I claim that a function must be invertible to be differentiable, nor is that implied by my answer. In order for one to define velocity as a function of the position in some neighborhood of a point $x_0$ along the trajectory of a particle, the position must be an invertible function of time in some neighborhood of $t_0$ such that $x(t_0) = x_0$. If not, the trajectory could intersect itself at say $x_*$, and the velocity at $x_*$ would be ambiguous.
Feb
3
comment Problem understanding sign of volume integral in Minkowski space
@BerrickFillmore Not off the top of my head, but I'll let you know if I dig anything up.
Jan
29
comment How does one calculate the full perihelion shift of Mercury, including perturbations from other planets?
It seems it was Le Verrier who recognized this first: en.wikipedia.org/wiki/Urbain_Le_Verrier#Precession_of_Mercury
Jan
27
comment Is $∣1 \rangle$ an abuse of notation?
@JamalS I know :(. Teaching has been taking up all of my time. Hopefully I can add more soon.
Jan
27
comment Is $∣1 \rangle$ an abuse of notation?
@IllegalImmigrant You're imposing unnecessarily harsh restrictions on the use of symbols as labels. If I write $|\mathrm{stuff}\rangle$, where $\mathrm{stuff}$ can be any symbols whatsoever you can write, then $\mathrm{stuff}$ is simply being used as a label. It could be a number, a sequence of numbers, a happy face, a portrait of your grandmother...
Jan
26
revised Uniqueness of the equivalence class of inertial frames
added 218 characters in body
Jan
26
comment What is Convective acceleration of flow velocity?
@ArthurMabentsela There is a dot above the $\mathbf{x}$ which denotes a time derivative. The equation $\dot{\mathbf x}(t) = \mathbf v(\mathbf x(t), t)$ is simply the statement that if the particle is moving with the fluid, then its velocity matches that of the fluid.
Jan
25
revised Uniqueness of the equivalence class of inertial frames
deleted 44 characters in body