32,847 reputation
23896
bio website joshphysics.com
location Los Angeles
age 29
visits member for 2 years, 5 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.


5h
revised Coordinate Transformation of Scalar Fields in QFT
edited body
8h
awarded  Enlightened
Jun
26
awarded  Enlightened
Jun
26
awarded  Nice Answer
Jun
26
comment Doesn't Laplace's equation describe the local property of space?
Yes that's right.
Jun
26
comment Doesn't Laplace's equation describe the local property of space?
At any point where the charge density is zero, Laplace's equation holds, even if the charge density is non-zero elsewhere.
Jun
26
revised The magnetic field of a magnetic monopole
deleted 36 characters in body
Jun
22
comment Confusion about imposing constraint in the action
@psm Sure thing! By the way, I thought about the physics of this a lot more yesterday, and I think that you are changing the physics when you include the constraint because the "centrifugal" potential changes depending on the value of $c$. By varying the value of $c$, you can find paths that satisfy angular momentum conservation that you couldn't have had before because you've effectively added an additional force of constraint.
Jun
21
revised Confusion about imposing constraint in the action
Added related example
Jun
21
revised Confusion about imposing constraint in the action
added 57 characters in body
Jun
21
answered Confusion about imposing constraint in the action
Jun
21
comment Centripetal force in frame of reference of body moving In a circle
@1110101001 It seems you're making a common mistake -- a net force of zero does not mean you don't feel anything. As another example, suppose Alice is pushing you toward the left, and Bob is pushing you toward the right with a force of equal magnitude. Those to forces sum to zero, but you feel each of them.
Jun
20
comment Geodesic Equation from variation: Is the squared lagrangian equivalent?
Also nice, succinct answer. I somehow hadn't noticed it until just now when I completely re-wrote my own answer, scrolled down, and realized you basically say the same thing more compactly :)
Jun
20
revised Geodesic Equation from variation: Is the squared lagrangian equivalent?
added 44 characters in body
Jun
20
comment Geodesic Equation from variation: Is the squared lagrangian equivalent?
I think you're missing a factor of $L$ on the right hand side of the last equation (if I understand you notation correctly).
Jun
20
revised Geodesic Equation from variation: Is the squared lagrangian equivalent?
Error in previous version due to sloppiness with integration by parts. Rewrote answer using Euler-Lagrange equations themselves instead of variational problems for directness and clarity.
Jun
17
comment Geodesic Equation from variation: Is the squared lagrangian equivalent?
You're right, I made an error. I'm glad you caught that. It turns out that I did, in fact, neglect a certain term containing $dL/ds$ in integrating by parts, and I find, exactly as you indicate, that the EL problems are equivalent provided $dL/ds = 0$. Thanks for the careful read -- I will edit soon.
Jun
15
comment Classical and Semi-classical treatments of the ideal gas
@JánLalinský Interesting. I'll take a look at the reference. Thanks.
Jun
11
awarded  differential-geometry
Jun
5
comment Question about canonical transformation
@JessRiedel Not sure be be honest. I don't personally know of a physical situation for which the more general definition of canonical transformation is useful/necessary.