534 reputation
16
bio website
location Sandy Eggo
age 56
visits member for 1 year, 11 months
seen Sep 3 '13 at 11:55

Know lots about GPS and other positioning technologies, lots about cellular air interfaces. Pretty new to Java/Android. Lots about Electromagnetics and Physics (Physics PhD, used to teach Electrical Engineering at University). Fair amount about superconductivity.


Apr
23
awarded  Yearling
Feb
11
asked Force of electromagnet on piece of iron
Nov
29
awarded  Caucus
Oct
4
answered What color would a proton be if it were visible to the human eye?
Sep
3
comment Does the uncertainty principle apply to photons?
@genneth of course you are right, I was wrong about why you are allowed to "violate" ∇⋅E=0, which is of course because $\nabla E=\rho/\epsilon_0$. So at time t=0 some charge shows up at the origin creating a delta function of electric field at the origin, and then run time propagation from there.
Aug
30
comment Does the uncertainty principle apply to photons?
@genneth ∇⋅E=0 is a static constraint, I am not talking about static fields. I am talking about an initial condition at time $t=0$ which will not be static at t>0. Every light beam and radio wave we know of violates ∇⋅E=0 in free space.
Aug
27
answered How come a photon acts like it has mass in a superconducting field?
Aug
27
comment Does the uncertainty principle apply to photons?
@dushya Consider an electric field in the $z$-direction at time 0 $E_z(x,y,z,0) = $\delta(x)\delta(y)\delta(z)$. It is a straightforward matter to calculate "classically" (and result is correct for quantum) the $E_z(x,y,z,t)$. You will never detect a photon at $r>ct$, the photons are localized inside the appropriate light-sphere. Please describe what is meant by "photons cannot be localized" in light of this simple experimental fact.
Aug
27
comment Does the uncertainty principle apply to photons?
@genneth There is no difference between light and electrons in anything you are saying, except it is very rare we see electrons coming from a source smaller than electron wavelength because electron rest mass makes its wavelength very small. A pulse of light 1 ns long is 30 cm long and is completely localised throughout its entire time of flight, you can put things in its path before and after it passes without stopping it, but put something in its path while it is passing and you stop the beam.
Aug
27
comment Does the uncertainty principle apply to photons?
@genneth can you give me a reference that goes beyond a single sentence saying it can't be done? I'd love to understand how a photon represented by a wave packet is any different from an electron represented by a wave packet.
Aug
26
comment Does the uncertainty principle apply to photons?
@AlecS I can't read the PRA ref, don't have login. In the google docs ref, what you cite is an unpublished one line quote from a referee of the paper. I call B.S. on the referee, and challenge you or anyone else to find a sensible refutation to what I say about localization.
Aug
26
revised Does the uncertainty principle apply to photons?
added 374 characters in body
Aug
26
comment Is it possible to change the path of a single photon?
@user8123 no reflection/refraction is "the same" photon. To "change" photons, photon should be absorbed, then re-emitted. But reflection and refraction happen without every absorbing the photon, just changing the evolution properties of its field, which is closely related to its wavefunction. That is to say, no energy from the photon is left behind in the object or material reflecting it or refracting it. (In lossy materials, some photons are absorbed and lost, but those successfully reflected or refracted retain all their original energy: their frequency is unchanged.)
Aug
26
revised Does the uncertainty principle apply to photons?
deleted 1 characters in body
Aug
26
answered Does the uncertainty principle apply to photons?
Aug
18
comment Direct exposure to the vacuum of space
and wearing white or green or black wouldn't change your equilibrium temperature, it would simply change the speed with which you approached equilibrium. It changes your albedo.
Aug
15
comment Squinting at street lights
I'm not sure everybody sees what you see. After I had Lasik surgery, I saw an irregular polygon with wiggly sides around each point source light. I attributed this to my pupil being open wider than the corrected part of my lens: so the inner part of my lens was correct and focused light to point and outside part of my lens was uncorrected by lasik and focussed light to a blur and I saw these overlapping.
Aug
2
answered Intuitive explanation to why superconductivity breaks at high temperatures
Jul
25
revised uncertainty of fields with many harmonic modes
fixed answer to respond to Ron's corrections.
Jul
25
comment uncertainty of fields with many harmonic modes
@RonMaimon I agree my original answer is not the answer to this question. (I was answering the question of why are the fluctuations in a single mode of the radiation field always finite).