2,379 reputation
11332
bio website berkeley.academia.edu/…
location Berkeley, CA
age 24
visits member for 3 years, 7 months
seen 11 hours ago

Currently a graduate student in mathematics at the University of California - Berkeley.

Previously obtained a MASt. in Applied Mathematics from the University of Cambridge (2013), and a B.S. in Mathematics and a B.A. in Physics from the University of Chicago (2012).


Nov
21
reviewed Approve suggested edit on is it possible to flow current in open circuit?
Nov
20
awarded  Custodian
Nov
20
reviewed Reject suggested edit on Why do grapes in a microwave oven produce plasma?
Nov
19
answered Density matrix: error with diagonalization claim and fixing it
Nov
17
answered Is the overall force of a test charge in a electromagnetic field always the same?
Nov
14
comment A question from Schwinger's particles, sources and fields monograph
I am confused. In some places you write $\phi ^\mu$ and in others you write simply $\phi$. Is there a scalar field $\phi$ and a vector field $\phi ^\mu$?
Nov
14
comment Calculating the Sun's emitted power in a wavelength range?
See wikiwand.com/en/Stefan%E2%80%93Boltzmann_law#/… . I believe this calculation is very similar to what you would like to do.
Nov
14
comment Which renormalisation techniques are available for 3+1 QED?
You should probably distinguish between re-normalization and regularization. Pauli-Villars is a method of regularization. Two other ones that come to mind are dimensional regularization and the usual cut-off regularization.
Nov
13
revised Where does the force to stop a constant velocity object come from?
added 512 characters in body
Nov
13
answered Where does the force to stop a constant velocity object come from?
Nov
12
comment Momentum conservation in an electromagnetic system?
Well, I honestly don't know why you would need to do this. Perhaps I misunderstand your question. I thought that you took note of the fact that momentum was not conserved, and was confused as to why that was not the case. And the reason of course is because we are applying a non-zero net force to the system. As a 'sanity check', I suppose you could actually calculate the change in momentum of those three things to verify that it does indeed come out to $f\Delta t$, but given that it's so tedious to do so, I don't know why you would want to do that.
Nov
12
comment Momentum conservation in an electromagnetic system?
So in particular, it shouldn't be balanced. They should differ by $f\delta t$. Also, I admittedly don't understand why you think that the momentum of the E&M field won't change unless the top charge accelerates to a non-negligible degree. The Liénard–Wiechert depend on the velocity, which, for the bottom particle, is changing to a non-negligible degree (though I guess it's possible that you might find this dependence 'cancels' when you do the actual computation).
Nov
12
comment Momentum conservation in an electromagnetic system?
. . . Then the momentum change of the E&M field would just have to be so that, after you add these three together, you get $f\Delta t$.
Nov
12
comment Momentum conservation in an electromagnetic system?
So I am admittedly trying to avoid details because I believe the actual computation will be at least slightly tedious. Nevertheless, I think it's easy to see that this is possible. The system has three things contributing to its momentum: the mechanical momentum of the top particle, the mechanical momentum of the bottom particle, and the momentum of the E&M field. If we declare that the positive direction is to the right, then the momentum of the bottom particle is increasing over time and the momentum of the top particle is decreasing over time . . .
Nov
12
comment Momentum conservation in an electromagnetic system?
@JohnEastmond That's right. The momentum of your entire system should change (in magnitude) by $f\Delta t$ over a time period of $\Delta t$.
Nov
12
answered Momentum conservation in an electromagnetic system?
Nov
11
comment Why do we have to use an integral in this scenario to figure out $v_{max}$?
@user42141 The kinetic energy does vary . . . $v$ depends on $r$.
Nov
11
comment Why do we have to use an integral in this scenario to figure out $v_{max}$?
@NeuroFuzzy Thanks for catching that.
Nov
11
revised Why do we have to use an integral in this scenario to figure out $v_{max}$?
added 71 characters in body
Nov
11
answered Why do we have to use an integral in this scenario to figure out $v_{max}$?