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id stringlengths 1 6 | title stringlengths 15 150 | text stringlengths 30 20.1k |
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1 | What is spin as it relates to subatomic particles? | I often hear about subatomic particles having a property called "spin" but also that it doesn't actually relate to spinning about an axis like you would think. Which particles have spin? What does spin mean if not an actual spinning motion? |
100 | How is it possible to calculate the energy liberated by a given fission process? | How is it possible to calculate the energy liberated by a given fission process? For example, in the fission of a $^{235}$U induced by capturing a neutron? |
100000 | Difficult to visualize Franck-Condon overlap | The franc condon principle says about the vertical transitions, means the coordinates of the nuclei remains unchanged during an electronic transition. But, what is the physical meaning or how to visualize 1) Franck Condon overlap or Franck Condon Factor? 2) I specifically came across the vibrationally mediated photodis... |
100005 | Vertex for quartic interaction of complex scalar multiplet | Since I'm new to QFT and I tend to do a lot of errors during calculations, I would like you to tell me if I got the four-point vertex of the quartic interaction with a multiplet of complex scalar fields right: $$ L = (\partial_\mu \Phi)^\dagger (\partial^\mu\Phi) - m^2\Phi^\dagger\Phi-\lambda(\Phi^\dagger\Phi)(\Phi^\da... |
100009 | How does time dilate in a gravitational field having a relative velocity of v with the field? | Consider a Mass on earth. The time dilation on the surface of Earth is $$T' = T \sqrt{1 - \frac{2GM}{rc^2}}$$ Now if the mass is moving around the earth at velocity of v w.r.t Earth, what will be the time dilation within the mass as seen from the Earth? The object could be in free fall, orbit or in an escape velocity o... |
100012 | How can stars make up 0.5% of whole universe? | I was reading Wikipedia article about universe and stumbled upon pie chart which represents what universe contains. It says that stars make up 0.5% of whole universe. I tried to find average distance between stars in the universe, but came to some different numbers, but either way distance is more than 1 light year. At... |
100013 | Does Energy change sign when time is reversed? | In classical physics if one reverses time then energy does not change sign. For example in the formula for kinetic energy one has: $$E = \frac{1}{2}m v^2$$ If you reverse time the velocity $v$ changes to $-v$ but $E$ stays the same. What happens in quantum mechanics? In QM one has the formula: $$E = h \nu = \frac{h}{\D... |
100014 | Bottom magnetic levitation | There are many decorative devices, that keep a small metal sphere levitating in air by attracting it to a top electromagnetic coil while monitoring their height by optical sensors. There is also the 'levitron' where a passive permanent magnet spinning top is hoovering above some permanent magnets, it's orientation is c... |
10002 | Quantum Mechanics | Quantum Mechanics. Could anyone help me to understand the concept involved? Double slit experiment can be easily understood by Wave nature of light, but while explaining it with photons, it required a lot of mathematics (Englert–Greenberger duality relation). Can anybody tell me what is the physical interpretation of t... |
100023 | Status of time in a Universe at maximum entropy | In billions and billions (thanks Carl Sagan) of years I have heard that atoms will lose energy and their temperature will approach absolute zero and thus their entropy will approach a minimum level. If we take this to be true then it logically follows that there will be no way to distinguish one instant of time from a ... |
100025 | Horizon problem in the standard cosmological model | The horizon problem is usually stated as follows: Causally disconnected parts of the universe that we see today have the same temperature, so how could that be so if no information travels faster than the speed of light. But (without assuming inflation) wasn't the universe causally connected right after the big bag? An... |
100027 | Laws of addition of Vectors | How **Triangle Law and Parallelogram law of addition** of Vectors are different? _Ain't they._ Please don't tell me the things written in book......give me the appropriate reason.And how do i distinguish between the two while adding vectors,what am i trying to say is i get really confused where to use parallelogram law... |
100028 | How to derive the expression for the electric field in terms of the potential? | How can I derive that $$\vec{E}=-\vec{\nabla}\phi-\frac{\partial \vec{A}}{\partial t}$$ where $\phi$ is the scalar potential and $\vec{A}$ the vector potential? |
10003 | Olympic games and the local g | As you probably know, the two next Olympic games will take place in London and Rio. Randall, author of xkcd, did an interesting observation (that I had never thought of) in http://xkcd.com/852/ , arguing that the difference in latitude may influence comparisons between different world records in pole vaulting. As I sta... |
100031 | Shrinking and Expanding objects in a CFT | In a conformal field theory, is it possible to construct a machine that shrinks or expands objects? |
100034 | How do you know which atoms are in a specific piece of matter? | If you have a piece of matter in front of you, how can you know of which atoms it consists? And starting from nothing, how can I discover all the elements (or just a lot of them) of the periodic table? I can imagine some unefficient methods based on atom's characteristics (e.g. heat the matter till it becomes a gas, th... |
100035 | How to find the center of mass? | A massless rod of length $L$ attached to mass $m$ and with axle to cart of mass $M$. The cart has a shape of equilateral triangle (edge $L$). the cart is at rest and its center of mass is above $x=0$ and a rod is perpendicular to the ground. the cart is free to move without friction. at time t=0 the mass $m$ is release... |
100036 | How does pressure factor into mechanics? | We just started learning about pressure in our school, and i am a bit confused. I tried to google extensively, but i didn't really find much. In mechanics, so far in our school we've been taught about Newton's laws of motion and some related stuff, and suddenly we started learning about pressure. I asked this same ques... |
10004 | How to calculate the quantum expectation of frequency of a particle? | I know how to calculate the expectation of < $\Psi$|A|$\Psi$ > where the operator A is the eigenfunction of energy, momentum or position, but I'm not sure how to perform this for a pure frequency. In other words, what is the expectation of frequency? Indeed, is there an expectation, and is it solved using a fourier tra... |
100044 | Does specific heat change with pressure? If so, why? | As pressure is increased, do we require more energy to increase the temperature from given temperature for the same mass. For example, if we heat water at 1 atm to raise its temperature by 20 degree Celsius, will the heat required be the same when pressure is 3 atm? |
100048 | Why can we use the energy of a pendulum to calculate its frequency? | The question might sound rather vague; to calculate the frequency using the energy we simply use that the total energy is constant, set the derivative to zero and solve the equation of motion that follows. But my question is more about the why; how does the fact that the total energy is constant imply that we are able ... |
100053 | Absolute permittivity and permeability of free space | I'm reading about the propagation of EM waves in vacuum. We define the wave equation using two constants: $\epsilon_0$ and $\mu_0$. Of course they are absolute permittivity and absolute permeability of free space. I've read they have capacitive and inductive properties, I want to know how do we describe it **physically... |
100058 | Can we expect the discovery of something that moves faster than light/photons? | As our knowledge on M-Theory improves in the times ahead which may unfold some warped dimension, can we expect the discovery of something that moves faster than light/photons? |
10006 | physics- momentum ( a space question) | An astronaut is conducting repairs on a satellite 50.0m from a space shuttle. Her mass is 120kg (including space suit) and she is using a 0.5kg spanner. She realises that she only has 5 minutes oxygen supply remaining. With what velocity must the spanner be thrown for her to return to the shuttle safely. |
100061 | A paradox with spin: Is spin a physical degree of freedom? | Suppose I want to calculate the state associated with a spin particle under a magnetic field. I suppose the particle interacts via the Zeeman effect, and only through it. Then I want to resolve the Schrödinger equation: $$\mathbf{i}\hbar\dfrac{\partial\Psi}{\partial t}+\dfrac{\hbar^{2}}{2m}\dfrac{\partial^{2}\Psi}{\par... |
100064 | What are the current experimental limits on the polarizability of the vacuum? | Many (all?) materials are polarizable at some level; meaning that when we apply an electric field across the material, there is an induced dipole moment $$ \vec{p}=\alpha(\omega)\vec{E}, $$ where $\alpha(\omega)$ is the polarizability of the material at frequency $\omega$, $\vec{E}$ is the applied electric field, and $... |
100065 | What does the $\Delta$ notation mean? E.g. for potential energy: $\Delta U$ vs just $U$? What is the difference? | I've seen in this article that potential energy is defined like this: $U=-\int _{\text{ref}}^r\overset{\rightharpoonup }{F}\cdot d\overset{\rightharpoonup }{r}$. However I've seen in other text books that potential energy is: $\text{$\Delta $U}$. What is the difference? Why is "Delta" used sometimes and sometimes not? ... |
100066 | Sign in the photon propagator | The Klein Gordon propagator is given (I use Peskin and Schroeder's conventions, if it matters...), \begin{equation} \frac{ i }{ p ^2 - m ^2 + i \epsilon } \end{equation} The photon propagator (using Feynman gauge) is \begin{equation} \frac{ - i \eta^{\mu\nu}}{ k ^2 + i \epsilon } \end{equation} The time-like component ... |
100072 | Energy-momentum tensor for dust | We all know that the energy-momentum tensor for dust is just $T^{\alpha\beta}=\rho_0v^\alpha v^\beta,$ where $\rho_0$ is the mass density in the dust's rest frame and $v^α$ is the dust's four-velocity. I'm trying to derive the dust energy momentum tensor from the equation $T_{αβ}=-\frac{2}{\sqrt{-g}}\frac{δS_M}{δg_{αβ}... |
100073 | How to get a function for the voltage across a capacitor connected to an AC voltage source? | I am looking for the way of obtaining a solution for $V_{c}$ ,as a function of $t$ depending of $\omega$, of the following differential equation related to an electrical circuit involving a low-pass filter : $ \frac{ d V_{c}(t)}{d{t}} + \frac{V_{c}(t)}{\tau} = \frac{V_{s}(t)}{\tau} $. where, $V_{c}$ is the voltage acro... |
100075 | How do wind turbines cause lightning? | I saw this paper about Lightning discharges produced by wind turbines More lightning strikes wind turbines than comparable non-moving structures. What would be the physical cause of this? Does it depend upon the motion of the wind turbine blades or is it because these are connected to the electric power grid? |
100076 | why galaxies look like discs rather than spheres? | Black holes have much gravitation to hold all stars and nebulas but why they are aligned in disc type shapes rather than spheres because gravitation is everywhere around black holes. Even on upper and lower sides. Even if rotation is the cause why cant they move above black holes in smaller circles. |
10008 | Why can't I see far when I look in a mirror? | I'm myopic. It's a fact. I understand exactly how it works because Internet told me light rays encounter themeselves too soon in my eyes... that is why I can't see far objects even if I see near objects very good. Yesterday, I was looking myself in a mirror (it seems that I'm a very narcissistic person :) ) and I disco... |
100080 | Bullet energy loss in solid materials | Does someone know simple model of energy loss in solid materials for a solid bullet? For example: I want to estimate momentum transferred to a thin plastic plate given by a small bullet. No matter how difficult model is. But it should depend only on plate/projectile parameters? **EDIT:** No precise solution is needed. ... |
100084 | Identifying an optics equation in a code refactoring project | I apologise if this a somewhat naive post. My knowledge of optics is limited, and I am learning on the job, so to speak. I'm a computational biologist, dabbling in a bit of physics. I'm currently reading Sonke Johnsen's "The Optics of Life" to try and get a better picture. I am involved in an academic project to refact... |
100086 | Are metals more heavy due to the Earth's magnetic field? | **Non-metal** objects are attracted to the Earth due to gravity. So the weight of non-metal objects can be only dependent on their mass. **On the other hand** metals can be attracted to the Earth's magnetic field, with the Earth acting as a giant magnet; causing metals to weight more than they normally should. In other... |
100088 | Compressed air in a volume: Can I determine its temperature? | Using a compressor, I augment the pressure in a volume (using atmospheric air). I only measure the pressure inside. I now that the density will increase however, the temperature decreases. Can any one give a hint how can I calculate any of the two if the only known values are the volume and the pressure. |
100089 | Final position of an object after aplying several horizontal forces | I'm given an object with a starting position. Several horizontal forces are applied to this object one after the other for different amounts of time. How can I determine the final position $x$? |
100098 | Lorentz transformation of the vacuum state | In general, the Hamiltonian $H$ has non-zero vacuum expectation value (VEV): $$ H \left.| \Omega \right> = E_0 \left.|\Omega \right>, $$ where $\left.|\Omega\right>$ is the vacuum state. The zero-point energy of the quantum oscillator is a good example to have non-vanishing VEV. The problem strikes me is that **how is ... |
100099 | Power and speed | I'm asked to calculate how much POWER a 1210kg car needs to drive with a 85 km/s speed up a 655 meter long slope of 4.5°. I can find how much energy and work is required to do this, but isn't POWER=WORK over TIME? I don't have any time in my problem. So I ask: If I have a 1000kg car and I drive 500 meters...Could I go ... |
100105 | Is the potential energy of molecules related to its temperature? | Do ideal gases have a certain potential energy at a certain temperature? |
10011 | Famous physicists' quotations | I recently watched Sydney Coleman's 'Quantum Mechanics In Your Face,' and very much enjoyed it. (Highly recommended.) In it, Professor Coleman quotes a very clever comment by a philosopher called Ludwig Wittgenstein. Wittgenstein found it strange that people used to believe in geocentrism (Sun goes around the Earth.) W... |
100110 | Do particles rotate around themselves or they just move while the object rotates? | In this question, I'm not talking about particle spin. I guess, when an object rotates, its atoms also rotate. When an atom rotates, its particles must move in space. I wonder that if the particles have a direction. Can they rotate or do they just move position around the axis (middle) of a proton so we consider that t... |
100114 | How to achieve Gigavolts? | I was searching the internet when I found this article http://arxiv.org/abs/0804.1764, about achieving high voltage and power to ignite thermonuclear reaction by inertial confinement, the plan was to achieve it in a ultra vacuum and something that have to do with "taylor flow " which includes quantum physics which I re... |
100115 | Can a wave exist on the “face” of a wave? | It would seem that this would be possible with waves in water. What about other waves Clarification: Given a wave starting from a point of impact, in water, at: Time 0:00 and xyz 0,0,0 and the impacting “object” came from 0,0,h. At some time it would reach its first maximum wave height, say z=10. If at that instant a... |
100119 | Two pairs of projection operators of the Dirac equation | The Dirac equation may be interpreted as the action of projection operator $\frac{1 - \Delta}{2}\Psi = 0$, where $$ \Delta = \begin{pmatrix} 0 & \Delta_{b \dot {a}} \\\ \Delta^{\dot {b}a} & 0 \end{pmatrix}, \quad \Delta_{b \dot {a}} = \frac{i}{m}p_{b \dot {a}}, \Delta_{b \dot {a}}\Delta^{\dot {a} c} = \delta^{c}_{b} \R... |
10012 | What are the viable non-anthropic explanations for the tininess of the cosmological constant? | The cosmological constant is 10-120 times its natural value, but it is yet nonzero. Even TeV-scale supersymmetry breaking can't save it. The renormalization group would seem to imply it ought to be at the Planck scale, assuming naturalness, and no fine-tuning. The anthropic principle explains the size of the cosmologic... |
100124 | Time Dilation Effects from simply being on a spinning planet orbiting a star in a rotating galaxy in an expanding universe. | I am a layman, so take this with a grain of salt. I saw a TV show the other day which showed a Russian Cosmonaut who had spent more time in space than any other human. The relativistic effects of the low gravity and extreme speeds at which he had spent a decent part of his life had pushed him a small, but surprisingly ... |
100127 | What happens to a photon when it enters a black hole? | The photon has a mass of 0, but it has energy because of its motion. When it is sucked into the black hole and becomes a singularity, it loses its energy because it is no longer moving. It is not possible for something to be sucked out of a black hole, so it has no potential energy that the kinetic energy could have be... |
100130 | Standard Heat of Combustion | When considering tabulated standard values of heat of combustion (∆H° combustion) or any other similar value, the results are reported for species in their standard states (1 bar pressure, 25°C, etc). When something combusts, however, macro state variables such as pressure and temperature change. For the tabulated valu... |
100133 | Noether's Theorem in Field Theory | This question is regarding Noether's Theorem in general, but also in the application to an example. The example is: > _Find the conserved current for the Lagrangian_ > $$L=\bar{\psi}(\frac{i}{2}\gamma^{\mu}\partial_{\mu}-m)\psi.$$ Is my first step to find a transformation that leaves the action invariant? But isn't the... |
100137 | Sterile Neutrinos and Supersymmetry | Just read a Scientific American review of a recent article which suggests evidence for sterile neutrinos: http://www.nature.com/news/cosmic-mismatch-hints-at-the-existence-of-a- sterile-neutrino-1.14752 The article is a little unclear about exactly what evidence, but my question is more general. A sterile neutrino woul... |
100138 | is an electron gun dangerous? | Is an electron gun dangerous & what would be the repercussions to human tissue? If I were to do a DIY electron gun and put my hand in the beam would I regret it? |
100141 | Composition of kinetic energy | As kinetic energy is the "energy of motion", it cannot exist without matter. However, the energy in an E/M wave can. I understand that E/M waves have been described in structure as electrical and magnetic waves in a sinusoidal configuration. This means that kinetic energy cannot be made of EM waves or it would be mass-... |
100142 | Defining electric potential energy | When we say that the electric potential energy at a point is X is that assuming we are using a positive test charge? |
10015 | What really are some distant astronomical bodies that seems like dust clouds? | Looking at pictures like this  I bet it is a picture of a giant cloud of dust, bigger than a galaxy and made of asteroids and planets (instead of stars). But probably I'm wrong. What is that? |
100150 | Is it possible to have a negative attraction to gravity just like how magnets with same pole does? | Layman question here, is it possible for an object to be negatively attracted to a gravitational pull of another object? Like how same pole magnets repels each other, can it happen on gravity too? |
100154 | Good Source to Understand Angular Momentum | I am looking for a good source to understand angular momentum. I know the basics but I am looking for a sound in-depth knowledge like directions of angular momentum, when it is not parallel to angular velocity, differences between normal angular momentum and spin angular momentum, how one is intrinsic property and othe... |
100161 | How to get conductivity from Green function $\mathcal{G}(x_1,x_2,\tau)$ of inhomogeneous system? | I'd like to study an inhomogeneous system, i.e., momentum is not a good quantum number therein. Therefore, I tried to calculate temperature Green functions like $\mathcal{G}(x_1,x_2;\tau)$, or its twofold Fourier transformation $\mathcal{G}(p_1,p_2;\tau)$. But how can I get any transport property, e.g., conductivity, f... |
100163 | The relationship between the energy and amplitude of a wave? Derivation? | From multiple online sources I read that $$E \propto A^2$$ but when I mentioned this in class, my teacher told me I was wrong and that it was directly proportional to amplitude instead. As far as I know, every website I stumbled upon concerning this said that is the case. My teacher has a Ph.D and seems pretty experien... |
100166 | Molecules and electrons energy types | What are the types of energy that an atom or a molecule could have? For example they have kinetic energy, could they also have other types? |
100168 | Zwiebach scalar product notation | I am currently working through Zwiebach's a First Course in String Theory. He seems to use dot-product notation interchangeably with the "down-up" notation. For example, on pg 176/section 9.1, he talks about the "gauge condiction $n\cdot X = \lambda \tau$ fixing the string...", "points $X^\mu$ that satisfy $n_\mu X^\mu... |
100169 | Pendulum in a Turning Airplane | My friend and I are having an argument over what happens with a pendulum hanging inside an airplane during a turn. Assuming that the airplane is making a standard 1 G coordinated turn, how does the pendulum react? I believe because the pendulum is attached to the string, it is pulled by the plane and will be in exact a... |
100173 | Two distinguishable particles in a box | I would like to determine the number of energy states two free, distinguishable particles in a box of length $L$ have. I would then like to determine the number of states two free, indistinguishable particles, with spin $3/2$ each, have in that box at the elementary level. Finally, determine the number of states in cas... |
100175 | Different directions of frictional force when objects are rolling | My textbook has two instances of rolling bodies (smooth rolling). In the first, the body is rolling on the horizontal floor with some acceleration of its centre of mass. In this case, the book says that the friction will act in the direction the ball is accelerating. In the other instance, the ball is rolling down an i... |
10018 | A new idea on unifying sound and light | Got a new idea regarding the unification of light wave and sound wave into a single entity , may be probably a wave. Is it possible to proceed in that manner,and has it been done previously,like i have an idea of projecting.The light wave and sound wave and synchronizing their speeds,and let them meet at a point,formin... |
100180 | Lagrangian formalism and Contact Bundles | In his Applied Differential Geometry book, William Burke says the following after telling that the action should be the integral of a function $L$: > A line integral makes geometric sense only if it's integrand is a 1-form. Is > $Ldt$ a 1-form? Well, that's the wrong question. The correct question is: On > what space i... |
100181 | Is it possible that there is no theory of quantum gravity? | {{Under Construction}} Short question: What published works and what research groups are investigating the possibility of inexistance of gravity at quantum level? Long question: I am no phisicist, but of what I read and understand of the subject, no one has been able to fit graviton into the standard model, it seems th... |
100186 | Is time dilation real? | If a body with an accurate clock is moving away from A which is stationary, then the time in B would be slower than that in A. Since relative to B A would have an equal velocity time in A would be slower than that in B. This results in a contradiction. This is the argument given in this website. Can someone say how thi... |
10019 | Do sound waves bend and/or diffract? | Sound waves are normally mechanical wave i want to know whether the sound wave bends if it bends does it undergo diffraction just like light wave? |
100194 | How to relate second variation to quadratic terms? | I am working on a physics problem, but my issue is math-related. My professor skips some steps based on 'intuition' that I lack: In a conservative system, to find out the nature of equilibrium points, we are looking at the potential energy functional, in general form given by $P[f(s)] = \int F(f(s)) ds$. (The problem i... |
100203 | Container in a Vacuum in a Container Problem | My friend puzzled me with this: Say I have a container that contains a vacuum and another container inside. And this inner container contains air. Also the outer container material is just barely strong enough to not implode due to the vacuum. If I remove the air from the inner container to outside of the outer contain... |
100205 | Can I applicate the law of action and reaction on energy? | It is clear that if you push on some object, there is reaction of the same force. But is it the same energy? Thanks a lot. |
100206 | Force exerted by a capacitor on a polar object | I was reading about capacitors and wondered what the force an electrostatic field created by a capacitor would be on an object with a certain charge and mass. If it can exert a force on a polar object then surely it can move charged objects around. So please could someone tell me whether it is possible to do this and w... |
10021 | Online QFT video lectures | I'm aware of Sidney Coleman's 1975/76 sequence of 54 lectures on Quantum Field Theory. Are there any other high-quality QFT lecture series available online? |
100213 | Can walking provide electrical energy? | This is more of a theoretical question, but is it possible to convert the energy you use to walk into electrical energy to say, power a light bulb? |
100216 | Is there current flowing though a power source? | Would there be any current flowing though an ideal voltage source? I am asking this more specifically when you are analyzing a circuit and you are doing nodal analysis. I know i=v/r, but since the source is ideal, resistance would be zero or infinity? |
100217 | On the distinction of past and future: could one theoretically reverse direction of particles and cause time to appear to go backwards? | Based on my understanding of physics after seeing _The Distinction of Past and Future_ on Project Tuva, there is no distinction between past and future on a fundamental level- all particle interactions can occur in reverse. So my question is whether or not one could theoretically reverse the direction of all particles ... |
100219 | Can $\langle\Omega|f|\Omega \rangle$ always be reduced to $\langle0|f|0\rangle$? | I've not come across any expression involving $\langle\Omega|f|\Omega\rangle$ in Srednicki's QFT book (please correct me if these exist there). On the other hand, they are abound in Chapter 7 of Peskin&Schroeder, in relation to the LSZ reduction formula. Here $|\Omega\rangle$ is the ground state of the interacting theo... |
100229 | What if the surface charge on a conductor is positive? | This site says that if the field at the surface at the conductor has a parallel component, then the surface charge will move, which is impossible if the conductor is at equilibrium. But I learnt that positive ions can't move in a conductor, only electrons can. I asked my prof and he said that if the field has a paralle... |
100230 | Help with momentum question involving vectors/trig | The problem: A car with a mass of 1200 kg and speed 10 m/s runs into a traffic barrier at an angle of 45 degrees, and is thrown outwards at an angle of 45 degrees relative to the barrier with a speed of 5.0 m/s How big was the change in momentum of the car during the collision? I tried decomposing the momentum, but fai... |
100232 | How can we get the mass of an uncharged proton? | How can we get the mass of an uncharged proton, i.e. how varies the mass of the charged proton if i remove the electric charge? For the isotopic spin theory neutron and proton have the same mass and it is possible to distinguish that particles only for the different values of the third component of the isotopic spin. T... |
100236 | Which component shows spin squeezing under twisting Hamiltonian? | Given a many body spin system, a collection of N spin-1/2 particles, under the interaction of the twisting Hamiltonian: $$H_{int} = \sum_{i,j=1}^Na_{i,j}\sigma_{z,i}\sigma_{z,j}= A J_{z}^{2}$$ assume all $a_{i,j}$ are equal and define: $$\mathbf{J} = \sum_{n=1}^{N} \mathbf{\sigma}_{n}$$ the collective spin operator, $\... |
10024 | Figuring out North and South Magnetic Poles for Earth | I currently make my living as an electrophysicist, so am a bit embarassed at having not thought this one through, before. Magnetically, the North pole is.... North. We get out our compass, and wait for the North-seeking needle to line up. I've always thought of this end of the needle as the north end. In a current carr... |
100243 | Computing power based on weighted averages | I'm struggling to understand the reason why I'm getting different results with two apparently similar ways to compute the power consumption (over multiple time intervals) of an electrical circuit. Let's assume I have a DC circuit with one power supply and one 10-ohms resistor. During the first 3 seconds the voltage is ... |
100244 | If Black Hole never forms, how important will be to study Black Hole paradoxes? | I recently came across a paper Black Hole - Never Forms, or Never Evaporates. It is claimed that under general evaporation conditions, before particles come into the Black Hole, the Black Hole itself will completely evaporate. In other words, Black Hole cannot form from gravitational collapse. If this paper was correct... |
100248 | Do atoms have an outter shell or boundary? | Do atoms have boundaries or an outer shell? If so, how do photons react to it? Also, if not, then does the atom always have the same set of electrons or do the electrons keep on changing? What I mean to ask is, are there any boundaries which are defined? If there are, then how will it react to an incoming photon. And i... |
100249 | From Dirac to Klein-Gordon in curved spacetime | Is there an easy/elegant way of showing that "squaring" the Dirac equation in curved spacetime yields the Klein-Gordon equation, just like it happens in Minkowski space? A brute force approach would require a lot of tedious algebra dealing with the spin connection, the veilbein formalism and the Dirac matrices. |
100250 | Ampere's Circuital Law | I'm having trouble understanding the surface used for Ampere's Circuital Law. In classes, we've been using simple circular or rectangular loops. Is the surface supposed to be area of the circle or the rectangle? Or is it a simple case of the law? A example would be the surface used for displacement current. This one is... |
100254 | Gravitational compression / compression in general | How exactly does gravitational compression, or compression in general, increase temperature? It seems counter-intuitive seen as temperature usually increases from the solid to the gas phase. |
100262 | Quantum wave interference in 3d space | Why, in the double slit experiment, is there an interference pattern only along the horizontal axis and not along both axes? |
100264 | Renormalizing QED with on-shell fermions | When renormalizing QED, we calculate the 1 loop correction to the fermion- fermion-photon vertex using the diagram, $\hskip2in$  When doing the calculation we typically let the photon go off-shell but demand that the fermions be on-shell. In other words... |
100265 | Determining $y$ coordinate of charged particle motion | I've tried several different ways, with a tutor, and with other colleagues. One of my colleagues has even gone to the professor with whom he worked out an equation for the component, and it was later confirmed to be incorrect. Here is the question: > A proton ($q = 1.6 \times 10^{-19}$ C, $m = 1.67 \times 10^{-27}$ kg)... |
100266 | Propulsion force | My physics instructor gave us a general problem > A box is sitting motionless on a rough, horizontal patch of ground. You give > it a good kick, so that it slides to the right with an initial speed of 4.5 > m/s. The box slows and eventually comes to a stop after traveling 14m. As > the box nears the end of its motion, ... |
100269 | The physics of sound boards | As a kid I was bemused at why soundboards worked. A small sound could be demonstrably amplified simply by attaching the source to a surface that is rigid and not too thick. How could the volume increase so much given that there was no extra energy added? As an adult I kind-of-think I know, but there are still many nagg... |
10027 | In a low pressure (near vacuum), -20°C vessel, would sublimated moisture rise to the top or fall to the bottom? | If I have a strong vessel that I've cooled to say -20°C, and lowered the pressure below 0.006 atmospheres, the water in food placed inside will sublimate and freeze dry the food. But what happens to the water vapor? Does the moisture rise to the top or fall to the bottom of the vessel itself? Or does it just expand to ... |
100270 | The shape of speaker cones | This is related to another question I just asked, but they are different enough I thought it deserved its own spot. Speaker elements seem to always be shaped like a cone with a portion of a sphere at the center. What is the physics reasoning behind this shape being so standard? Is it a precise shape that all speaker el... |
100271 | Ampere's Law and net current? |  If the current through a closed Amperian curve is zero, the net circulation around the closed curve should be zero. In the image, above the entire field is perpendicular to the Amperian curve when it enters the curve, but is not entirely perpendicular ... |
100274 | Conversion of Moving coil galvanometer to ammeter | A galvanometer can be converted into an ammeter by connecting a low resistance (called shunt resistance) in parallel to the galvanometer.  Firstly, why do we need to connect the resistance? If a resistance is connected in parallel, then some of the curr... |
100276 | What happens to gas molecules after ionization? | I know that gas molecules conduct electricity after they get ionized but what will happen if we keep increasing the voltage even after ionization? Will it explode? If it will then how much energy will be released? Assume I have neon gas in Crookes tube. |
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CQADupstackPhysicsRetrieval — BEIR, unified schema
A normalised copy of the dataset behind the mteb task CQADupstackPhysicsRetrieval, one of the tasks of the BEIR benchmark as mteb defines it (a member of the aggregate task CQADupstackRetrieval). Same queries, documents
and relevance judgements as the benchmark evaluates — reshaped into one strict schema shared by every dataset
in this collection.
| Source | mteb/cqadupstack-physics @ 79531abbd1fb (the revision pinned in mteb) |
| Domain · languages | stackexchange · eng |
| Queries / documents / qrels | 1,039 / 38,316 / 1,933 |
| Qrels per query | min 1 · mean 1.86 · max 72 |
| Score values | 1 ×1,933 |
| Layout | queries · corpus · qrels, split test |
| License | cc-by-sa-4.0 |
Schema
| config | columns | rules |
|---|---|---|
queries |
id: string, text: string |
ids unique and non-empty; every query has ≥ 1 qrel |
corpus |
id: string, title: string, text: string |
title is always present ("" when the source has none) |
qrels |
query-id: string, corpus-id: string, score: int32 |
referential integrity to both tables; no duplicate pairs; no floats |
Files are Parquet, sorted by id, zstd-compressed, sharded at 500 MB. Every rule above is enforced by a validator
before publishing; provenance.json records the source file hashes, what changed, and the output file hashes.
What changed from the source
- byte-preserved all text — no whitespace, newline, or control-character normalisation
- cast
qrels.scoredouble -> int32 - kept 2 documents whose text is identical to another document's — a property of the source; note that models embed such documents identically and retrieval ties among them are broken by corpus order
- renamed
_id→id - renamed source splits (
queries←queries/queries,corpus←corpus/corpus) totest
Load it
from datasets import load_dataset
queries = load_dataset("Hyukkyu/beir-cqadupstack-physics", "queries", split="test")
corpus = load_dataset("Hyukkyu/beir-cqadupstack-physics", "corpus", split="test")
qrels = load_dataset("Hyukkyu/beir-cqadupstack-physics", "qrels", split="test")
License and attribution
The data is redistributed under the source's terms — cc-by-sa-4.0. All credit belongs to the
original authors; see the source repository and the references in mteb's task metadata (http://nlp.cis.unimelb.edu.au/resources/cqadupstack/).
This repository is an independent repackaging and is not affiliated with the RTEB or MTEB maintainers.
License discrepancy. The upstream dataset card declares
cc-by-sa-4.0whilemteb'sTaskMetadatadeclaresapache-2.0. This card carries the upstream value as the more conservative choice.
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