# All Questions

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### BPS sectors in $\cal{N}=4$ SYM

I am familiar with the idea of a BPS bound as in a lower limit on the mass of supermultiplets given by a certain function of the central charge and when I think of $\cal{N}=4$ SYM I see a complicated ...
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### Are non-supersymmetric GUTs ruled out due to lack of precise gauge coupling unification?

Does there exist any good proposal on how the gauge coupling unification can be fixed in non-supersymmetric GUTs? If not, can we assert that non-supersymmetric GUTs have been experimentally ruled out? ...
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Suppose I have an hourglass that takes 1 full hour on average to drain. The grains of sand are, say, $1 \pm 0.1\ {\rm mm}$ in diameter. If I replace this with very finely-grained sand $0.1 \pm 0.01\ ... 1answer 3k views ### Standard Deviation in Particle Physics I'm familiar with sigma, and how its usually calculated and used, but would like to know how it's applied to particle physics. I recall reading that the discovery of the Higgs would only be credible ... 1answer 448 views ### Electric field of a charged spherical surface [closed] Figure The dielectric shaped as on the figure has dielectric constant$\varepsilon=\varepsilon\left(r\right)$and free charge density$\rho=\rho\left(r\right)$. What is the electric field and ... 4answers 778 views ### Nature of Photons Why is it that photons are emitted in bundles? My physics teacher's answer was "it's complicated"... 2answers 181 views ### Does the Casimir effect allow to change the lifetime of a radiating atom? Is it true that a spontaneously light-emitting atom changes its lifetime if it is put between two parallel plates that are so near that they attract each other through the Casimir effect? Thus: does ... 2answers 628 views ### What is a Kustaanheimo-Stiefel transformation? What is a Kustaanheimo-Stiefel transformation? Which applications has it in physics? Can you point me to a reference, where this transformation is explained? 2answers 331 views ### Have CMB photons “cooled” or been “stretched”? Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ... 3answers 657 views ### Question on Conformal Field Theory Since every question has to be asked in a seperate topic, I'm asking a question refering to the following topic: Beginners questions concerning Conformal Field Theory In particula I'm refering to the ... 2answers 517 views ### Give me examples of crackpots who were right after all [closed] I am interested in examples of crackpots coming up with correct results in physics. Why do mainstream physicists look down so much upon "crackpots"? 1answer 197 views ### When do we expect to get results from the LHC? At the current LHC luminosities, will it take years to detect the Higgs boson, superpartners, or any other forms of new physics at the LHC? What should particle physicists do in the meantime? We ... 1answer 236 views ### Are valence electrons located solely in the s and p subshells? Or are they in all subshells?? 0answers 950 views ### Damping and stiffness constants of water I'm working on a simulation of water drops falling into a pool. I'm specifically interested in the waves generated by the impact of the drops. In order to calculate the vertical motion of the waves, I ... 4answers 588 views ### Isn't wave particle duality of light actually cheating? When answering questions about light, I see that we conveniently shift between wave and particle nature of light to match the answer-- isn't this really cheating? Or, is it the principle that the ... 1answer 290 views ### Does the Grand Canonical Ensemble allow for exchange of particles or not? I was doing some reading on wikipedia and found it interesting that one page says the Grand Canonical Ensemble does not allow for exchange of particles, however another page says it does. So I went on ... 1answer 295 views ### Determining Average Tidal Effects Maximum tidal heights vary widely across the globe, from 16 m in the Bay of Fundy to mere centimeters elsewhere. These variations are due to coastline and shoreline differences. This makes it ... 4answers 2k views ### Does mass affect speed of orbit at a certain distance? Does the mass of both the parent object, and the child object affect the speed at which the child object orbits the parent object? I thought it didn't (something like$T^2 \approx R^3$) until I saw ... 1answer 523 views ### Can observations of entangled particles affect their unobserved counterparts? There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them. Imagine an experiment ... 2answers 199 views ### What are the AFS values in the Atlas experiment? If you go to the Atlas experiment http://atlas.ch/ and click the status button, there's an AFS reading at the bottom with a current value 50ns_228b+1small_214_12_180_36bpi_8inj The 50ns seems to ... 1answer 445 views ### Expansion of multi-particle state vector as a sum of n-entangled states Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this: $$|\Psi\rangle = |\phi_{i_{0} i_{1} ... ... 1answer 531 views ### Is microcausality *necessary* for no-signaling? There are proofs in the literature that QFT including microcausality is sufficient for it not to be possible to send signals by making quantum mechanical measurements associated with regions of ... 1answer 2k views ### How does Telescope lens work? 1.How does a Telescope work? 2.What factors increase the magnification of the lens? 1answer 413 views ### Do all atoms in the universe gravitate each other? I understand that matter will gravitate toward matter. (ex: Earth gravitates a satellite toward it, and the satellite toward Earth.) Does this always apply, regardless of distance? Take two atoms, ... 3answers 585 views ### Nomenclature: Yang-Mills theory vs Gauge theory If you're writing about a theory with Yang-Mills/Gauge fields for an arbitrary reductive gauge group coupled to arbitrary matter fields in some representation, is it best to call it a Yang-Mills ... 3answers 212 views ### Making a “heavier-than-air” craft float How big would a hollow rigid object need to be to float, (not in water but in air) if all of the air was vacuumed out and the container sealed? 4answers 734 views ### Voltage drop along an idealized resistance-free wire in a circuit? If you connected the positive terminal of a battery to the negative terminal to a battery with a wire with (hypothetically) no resistance, and are asked to give the voltage drop of a segment of wire ... 5answers 469 views ### Is special relativity an exact description of reality? In discussing relativity with a (somewhat mathematical) friend the other day, I ran into a problem showing why special and/or general relativity could be considered as exact descriptions of reality ... 0answers 81 views ### A question about the relativity of time [duplicate] Possible Duplicate: Invariant spacetime - distance - Circular Motion I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance ... 5answers 878 views ### Why is the contribution of a path in Feynmans path integral formalism \sim e^{(i/\hbar)S[x(t)]} In Feynman's book "Quantum Mechanics and Path Integrals" Feynman states that the probability P(b,a) to go from point x_a at time t_a to the point x_b at the time t_b is P(b,a) = ... 2answers 1k views ### Invariant spacetime - distance - Circular Motion I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance will compress by the same factor. My question is, if something travels in a ... 1answer 212 views ### Why can you assume that the angular momentum vector of a top will always track its axis of rotation? My favorite physics 101 textbook (Giancoli) explains precession in terms of a spinning top whose axis is tilted from the vertical. The way the book sets things up, L (angular momentum) points along ... 5answers 1k views ### Is there the smallest particle that can be guaranteed to be unable to be broken down into smaller particles? Is there the smallest particle that can be guaranteed to be unable to be broken down into smaller particles? 6answers 3k views ### Are human eyes the best possible camera? I am not a physiologist, but whatever little I know about human eyes always makes me wonder by its details of optical subtleties. A question always comes to mind. Are human eyes the best possible ... 2answers 235 views ### Does the lack of modular nuclearity in string theory mean anything? Nuclearity is a postulate in algebraic quantum field theory (AQFT). Basically, it says thermal states at any temperature always have a thermodynamic limit with extensive quantities. This is violated ... 4answers 433 views ### Can a disk like object (like UFO's) really fly? UFOs as shown in movies are shown as disk like objects with raised centers that emit some sort of light from bottom. Can such a thing fly? My very limited knowledge in physics tell me that a disk ... 1answer 800 views ### Why does the water in the toilet move around so much on stormy days? On calm days, the water in the toilet looks completely still. But when it's rainy and windy out, the water looks like it moves and pulsates. Why is this? 1answer 385 views ### The superconformal algebra How does one derive the superconformal algebra? Especialy how to argue the existence of the operator S which doesn't exist either in either the supersymmetric algebra or the conformal algebra? ... 2answers 440 views ### Is energy exchange quantized? In the photoelectric effect there is a threshold frequency that must be exceeded, to observe any electron emission, I have two questions about this. I) Lower than threshold: What happen with lesser ... 4answers 1k views ### If all conserved quantities of a system are known, can they be explained by symmetries? If a system has N degrees of freedom (DOF) and therefore N independent1 conserved quantities integrals of motion, can continuous symmetries with a total of N parameters be found that deliver ... 0answers 98 views ### How to compute the heat flow for a specific material for some given boundary temperature? Assume I have a bounded material with heat sources inside. The material is known (i.e. I know heat capacity and all relevant data) and the temperature of the boundary is fixed. I solved the (steady ... 1answer 1k views ### What is the resistivity coefficient of graphene? What is the resistivity coefficient of graphene? 4answers 913 views ### How do I correctly interpret \rho = \psi_1^* \psi_2? Summary: This turned out to be a rather trivial one indeed. As Marek mentioned in the comment, the continuity equation is trivial. And it indeed turns out be so. Godfrey Miller elaborates on this, ... 1answer 4k views ### Newton's color Disk How does Newton's color disk work? Newton's disk - Take a circular white color disk, make 7 equal intersections and paint section with respective VIBGYOR colors, now when you spin the disk in certain ... 1answer 108 views ### Where can I get the most accurate measurements of parton distribution functions? Where would I look to get the most accurate experimental values of parton distribution functions for the proton? I know these functions aren't measured directly, but I'd basically like to find a fit ... 2answers 931 views ### Rocket engines: air & vacuum Could you please help me understand what is the difference between rocket engines designed to work in air (first stage) and vacuum (later stages)? 1answer 816 views ### Open shells in Quantum mechanics of multielectron atoms This question: How do electron configuration microstates map to term symbols? And the discussion of multielectron effects here: Quantum Computing and Animal Navigation Inspired me to try to understand ... 4answers 10k views ### What's the difference between the five masses: inertial mass, gravitational mass, rest mass, invariant mass and relativistic mass? I have learned in my physics classes about five different types of masses and I am confused about the differences between them. What's the difference between the five masses: inertial mass, ... 1answer 622 views ### Temperature vs AC energy consumption I'm need to understand the following: to keep the room at confortable temperature (70 degree, for example), how does the amount of energy consumed by the AC grow as the outside air temperature rises ... 3answers 500 views ### What is the difference between |0\rangle and 0? What is the difference between |0\rangle and 0 in the context of$$a_- |0\rangle =0~?$\$

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