datenwolf
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 May 22 comment the meaning of epsilon in this operator $\epsilon$ @fibonatic: Integrals are operators, and as such the integrative variable should be written immediately after the ∫ – the integral symbol and the d… are not a pair of parentheses enclosing some expression. I know it's taught in school that way, but it's ugly and in some cases even wrong. Mar 4 comment Is the electron wave function defined during photon emission @RonMaimon: You do realize that entanglement is a state of superposition? Measurement on one of the entangled particles collapses its wavefunction, hence also collapsing the other particle's wavefunction into the state orthogonal to that. Also every pure state can be trivially described of the superposition of all possible states, convoluted with a delta function located on that particular pure state (and in nature there's no such thing like a pure state, this is just a idealized picture). Feb 28 comment Is the electron wave function defined during photon emission @sonardude: Wow, good question. I honestly never considered this problem yet. I've also to admit, I'm "only" a experimentalist. But next time I have a chance to talk to somebody of the QED theory group I'll tap his or her brain about this. But I wouldn't be surprised, that if you evaluated the interference of the wavefunctions you'd see some oscillation in the probability flux that would act like a emitter for a photon. Feb 28 comment Is the electron wave function defined during photon emission Also the abstraction of a particle being in only a pure state is a mathematical idealization. In practice every real wavefunction is a superposition of. All those corrections found in QED and QCD are nothing else, than the contributions of additional superimposing wavefunctions to the ideal, pure state of the simple model. Feb 28 comment Is the electron wave function defined during photon emission @NickKidman: In terms of QED the wavefunction of a particle is the superposition of all possible states it can be at any given time, and what changes is the amplitudes of each of those elementary wavefunctions. Also try to understand a "quantum leap" as a tunnel process, specifically not as a tunnel process between orbital states, but tunneling into a free electron, borrowing energy from a virtual photon, then tunneling back into a lower energy state, giving back energy to the virtual photon and emitting the difference as a real photon. Feb 28 answered Is the electron wave function defined during photon emission Feb 28 comment In-flight damage to a supersonic jet "Flying at very high altitude aircraft (eg an SR71 or U2) the outside pressure would be too low to allow you to breathe, even with an oxygen mask." This is not true. In the mid 1990ies there was a record breaking hangglider flight, launched from over 20km high of a balloon. The pilots were all wearing masks. Also with those masks breathing works differently: You're no longer sucking air in, you're kind of force fed with air. To support exhalation there's a valve that reacts to the slightest pulmonary contraction, which effectly evacuate the lungs. So you've to relax to inhale. Oct 8 awarded Autobiographer Mar 7 comment Cellphone RF radiation GSM is a very traditional network design, where the intelligence is placed in the network and the end devices are kept rather dumb. This goes so far, that GSM even provisions for updating the mobile device's baseband firmware over the network. Mar 7 awarded Commentator Mar 7 comment Cellphone RF radiation Let me explain a bit: GSM uses time multiplex. Since the location of a single mobile equipment device (ME) is only slowly changing the RX and TX power there needs only little adjustments over time. However since a base transciever station (BTS) is serving up to 128 MEs, and those MEs are usually scattered over a large area, the different signal path conditions change significantly for every time slot. Since no TX and RX amplifier of reasonable price can adjust it's gain as fast as the time multiplex required, the adjustments are laid of to the MEs, but the BTS controls them. Mar 7 comment Cellphone RF radiation The GSM standard (6000 pages!), and the various talks around the OpenBTS openbts.sourceforge.net , OpenBSC openbsc.osmocom.org/trac and OsmoCom bb.osmocom.org/trac projects. What they do is implement a fully functional, open source cellular communication infrastructure. Also Harald Welte gave numerous talks on these topics, e.g. events.ccc.de/congress/2008/Fahrplan/events/3007.en.html Mar 5 comment Cellphone RF radiation The transmission power of the handset is controlled by the BTS, so that the signals from all the mobile devices in it's range arrive with similar power density at the BTS. Mar 5 awarded Editor Mar 5 revised Do photons interact with each other, or with themselves only? edited body Mar 4 answered Do photons interact with each other, or with themselves only? Feb 27 comment How does a honeycomb grid affect the travel of light? Indeed, but you didn't quantify it ;) Feb 25 comment How does a honeycomb grid affect the travel of light? Assume the honeycomb to consist of tubes of length l and diameter d, depending on the angle the visible/active cross section also get's smaller. Right now I'm too lazy to do the geometry, but I guess (educated / heuristicallly) that the distribution will be something like 1-sin^2(alpha*l/d) for the direct pass. Then there's the scattering term. Feb 25 comment What is the effect of polarization on diffraction by a narrow slit? The fence polarizer also works with superconducting wires. Once can explain this with the wires being excited oscillators with a 90° phase shift emitting waves both directions. In the forward direction the incident and the excited waves cancel out, where in the reflected direction one ends up with the familiar standing waves. This is the whole essence of reflection/transmission theory: There's some energy transfer yielding emittance of phase shifted waves. Feb 25 awarded Supporter