qftme
Reputation
690
Top tag
Next privilege 1,000 Rep.
Create new tags
8 19
Impact
~28k people reached

• 0 posts edited
• 3 helpful flags
• 374 votes cast

# 230 Actions

 Jun 24 comment Why is the decay of neutral kaons (violates CP invariance) seemingly not sufficient enough for certain people to describe matter-antimatter imbalance? +1 for "..this is a family site." Haha Jun 24 comment Does particle indistinguishability and quantised enery levels (in bound states) violate the Pauli Exclusion Principle? @Gigacyan: Sure is, duly accepted. Cheers Jun 24 accepted Does particle indistinguishability and quantised enery levels (in bound states) violate the Pauli Exclusion Principle? Jun 22 comment electron orbits Hyperphysics has a nice exposition on this: hyperphysics.phy-astr.gsu.edu/hbase/hyde.html Jun 22 comment electron orbits @dmckee: I did say it was a simplistic answer ;-) Jun 22 comment Ascent rate and size of balloon @Cameron: You could calculate a rough estimate by doing a little experiment - Get one of the balloons you intend to use and inflate it until it pops. If you know the pressure difference between inside and out when it pops, you could predict at what height this same pressure difference would occur. Since measuring the pressure in the balloon may be difficult in practise, you could calculate it if you measured the size and (negative) weight of the balloon, up until the moment it bursts. Jun 22 comment electron orbits A simplistic answer: if a single electron, bound to a proton, absorbs a photon, the electron will be excited into a higher energy state. If the photon absorbed is higher than the ionization energy, the electron will be liberated from the atom. Therefore the highest energy state the electron could occupy, without being ionised, would be the state closest to the ionization energy (from below.) Jun 22 comment Function of electric water pump That just depends on which way around you connect the two pipes to it. Jun 21 comment Energy produced by a swing? Hi @Seb, the GPE and KE are the two forms the energy could be in. The total energy available in the system is $E=GPE+KE$. When the swing is high it is changing direction, which implies the velocity is zero and therefore the KE is zero. All the total energy is therefore all in the form of the GPE at this moment. When the swing is low, the velocity is maximum, and therefore so is the KE. The GPE is necessarily zero at this point. All of E, GPE and KE are energies - so yes, they are all measured in Joules. Jun 19 comment a question on Lagrange's equation when the time derivative of the generalized co-ordinates is constant I see what you're getting at but this is too brief to be an answer. Perhaps you could change it to being a comment or edit your answer to elaborate. -1 until then I'm afraid. Jun 18 comment Formulas for ball rolling in a bowl? @Dane: See also this question physics.stackexchange.com/questions/11227/… Jun 18 comment Analyzing the motion of a ball rolling without slipping inside a hemispherical bowl Closely related: physics.stackexchange.com/q/10798 Jun 16 comment Does particle indistinguishability and quantised enery levels (in bound states) violate the Pauli Exclusion Principle? @gigacyan: Having just finished another read-through of this page I wondered whether you would edit your answer to include the essence of our discussion in its comments. After which, I would be happy to accept it :) Jun 16 comment heliocentricity and the theory of relativity I would go as far as to say this is a duplicate of the question in @Qmechanic's comment. @statichippo: regarding your last paragraph - indeed, no need to worry about that here :) Jun 15 comment What happens when two D-branes annihilate? @Hiatus: To my mind, your comment seems sufficient for an answer. Jun 15 comment Stronger than Newton's laws? @Marek: Here, here! I'd vouch for those to comments to be posted as an answer (minus the 1st sentance perhaps ;) Upon seeing it, I will certainly cast a +1 vote on it. Jun 15 comment Stronger than Newton's laws? Continued.. I suspect, however, that in practice this would be of very limited use - Newton's Laws work fine as they are and their power, in some respect, comes from their simplicity and ease of use. Given that QFT is already complex enough to solve for elementary particle interactions, it would likely be extremely difficult to show that it can be reduced to Newton's 2nd Law for the many-particle systems, that comprise the macroscopic bodies, to which Newton had intended it to apply. In summary, I don't feel this question is worth losing much sleep over, even if it is solvable analytically Jun 15 comment Stronger than Newton's laws? @Vladimir: For the record, I dislike refering to running couplings/masses as an "anti-Newton" law even more than I disliked calling it "t'Hooft's law." QFT and Newtonian mechanics are both fundemental but have very different realms of applicability. Both make firm and accurate predications when used at the appropriate energy scale for which they were developed. Of course, in principle, it should be possible to derive Newton's Laws from QFT. ... Jun 14 comment Stronger than Newton's laws? I agree with the sentiment of @Rasko's comment. However, I don't think it's appropriate to refer to running masses and couplings as "t'Hooft's law". Perhaps I'm being pedandic, but that's how I feel. Jun 13 comment Can a planet cover the whole sky as seen from its satellite @Philip: No, the effect of an atmosphere with increasing density at lower altitutes would increase the extent of the sky covered by the large planet. (Before I wrote it above I too had to take a minute to consider in which direction the light would refract.) Imagine you're standing on the satellite looking at light from the very edge of the planet; almost parallel to the surface of the satellite. As it enters a medium of higher refractive index, at an oblique angle, it will bend towards the normal-to-the-surface. I.e. into the surface of the satellite, thus preventing you from seeing it.