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87296 | Some conceptual questions in BEC | In Bose-Einstein condensate (BEC), people often say there is a well defined macroscopic phase. What exactly the macroscopic phase is? (a phase factor $\mathrm{e} ^{i\phi}$ in a many-body wavefuction?) Is the macroscopic phase the same as the coherent phase? | In a Bose-Einstein condensate (BEC), what is the significance of the macroscopic phase, and how does it relate to the phase factor $\mathrm{e}^{i\phi}$ in the many-body wavefunction? Furthermore, can you quantify the implications of phase coherence in terms of measurable properties of the BEC, such as interference patt... | 17,842 | cqadupstack-physics |
30167 | what is physical meaning of this partial derivative? | what is physical meaning of this partial derivative: $$\frac {\partial p_x}{\partial x}$$ i know how do i solve it when the case is just derivative but partial derivative is a bit Hectic!. | What is the physical interpretation of the partial derivative \(\frac {\partial p_x}{\partial x}\) in the context of fluid dynamics, and how does it relate to the behavior of pressure in a fluid in relation to spatial changes? | 37,495 | cqadupstack-physics |
78620 | Thermodynamics in a closed room - Why does the stale smell depend on Temperature? | Why does the stale smell disappears in a crowded room if you cool it via air- condition ? What's the physics ? | How does lowering the temperature in a crowded room using air conditioning affect the concentration of stale odors, and what physical principles explain this phenomenon? | 35,986 | cqadupstack-physics |
66058 | Why don't the components of these forces add up correctly? | > In the arrangement as shown in the figure below, the ends P and Q of an > inextensible string move downwards with uniform speed $u$. Pulleys A and B > are fixed. Mass $M$ moves upward with a speed: > > a. $2u\cos\theta$ > b. $u/\cos\theta$ > c. $2u/\cos\theta$ > d. $u\cos\theta$ > >  and the angle between the strings is \( 2\theta \), calculate the upward speed of mass \( M \). Choose the correct expression from the following options:
a. \( 2u \cos \theta \) ... | 26,098 | cqadupstack-physics |
65819 | What goes wrong when one tries to quantize a scalar field with Fermi statistics? | At the end of section 9 on page 49 of Dirac's 1966 "Lectures on Quantum Field Theory" he says that if we quantize a real scalar field according to Fermi statistics [i.e., if we impose Canonical Anticommutation Relations (CAR)], the quantum Hamiltonian is no longer any good because it gives the wrong variation of the cr... | What is the time evolution of the creation operator \(\hat{\eta}_{k}\) for a real scalar field quantized according to Fermi statistics, and how does it differ from the evolution obtained using Bose statistics? Please demonstrate your calculation step by step. | 16,550 | cqadupstack-physics |
123833 | About constraints of the first class and electrodynamics | Let's have some theory in hamilton formalism and let's assume that it has the constraints between canonical variables $Q, \pi$. By the Dirac terminology, the set of constraints $F_{a}(Q, \pi) \approx 0$ of the first class satisfies conditions $\lbrace F_{a}, F_{b}\rbrace_{P} \approx 0$, while the set of constraints of ... | In the context of Hamiltonian formalism with constraints, explain how the introduction of Dirac brackets allows us to convert the weak equality of constraints (denoted by $\approx$) to strict equality ($=$) in the case of a massive bosonic field, specifically in terms of the gauge field $A_0$. What are the implications... | 7,750 | cqadupstack-physics |
112571 | Effective Hamiltonian / Perturbation theory for non-degenerate case | Trying to wrap my head around the following situation. Consider first a case that I understand well: Let's assume a three level system where the lowest two levels are degenerate and individually couple to a third level, higher in energy by some large $\Delta$. The Hamiltonian may be written as $$\begin{pmatrix}0 & 0 &t... | In the given Hamiltonian $$\begin{pmatrix} 0 & 0 & t \\ 0 & \epsilon & t \\ t & t & \Delta \end{pmatrix}$$ where $\epsilon$ is a small energy offset and $\Delta$ is much larger than $t$ and $\epsilon$, how can you derive the effective Hamiltonian for the two low-energy states in the form $$\begin{pmatrix} 0 & t_{\rm ef... | 25,694 | cqadupstack-physics |
31419 | Higgs field questions | The Wikipedia article about Higgs field poses some questions to me. * The article says that the Higgs field is a "nonthermal" field, a field whose energy does not decrease as the universe expands, yet it claims that in the early universe Higgs field was stronger which led to inflation. How the field's strength could ... | If the Higgs field was stronger in the early universe and is described as a nonthermal field whose energy does not decrease with the expansion of the universe, how can we reconcile the idea that elementary particles had no mass during that early stage? Specifically, what mechanisms allow the Higgs field to provide mass... | 20,971 | cqadupstack-physics |
19773 | Work done by spring over distance | I'm working through a problem involving energy conservation. Unfortunately, I cannot calculate the work done by a spring. Before: +------------+ | | | spring | d1 | | +------------+ After: +------------+ | | | spring ... | Given a spring with a spring constant \( k = 200 \, \text{N/m} \) that is compressed from an initial distance \( d_1 = 0.1 \, \text{m} \) to a final distance \( d_2 = 0.3 \, \text{m} \), how can I calculate the work done by the spring during this compression? Please also explain the formula used to calculate the work d... | 11,329 | cqadupstack-physics |
23658 | Wave with mass transport? | I don't think this question has been asked on this forum before (at least I didn't find it). In the case of a tsunami, an earthquake generates a wave which will travel with the sea/ocean as the medium. However, what I remember from high school is that mechanical waves transfer energy but energy only. On a sectional vie... | How does the energy of a tsunami wave, generated by an underwater earthquake, cause significant horizontal movement of water, leading to flooding in coastal areas, despite the general principle that mechanical waves only transfer energy without displacing the medium horizontally? | 8,412 | cqadupstack-physics |
46792 | Tidal force on far side | I have a question about tidal forces on the far side of a body experiencing gravitational attraction from another body. Let's assume we have two spherical bodies $A$ and $B$ whose centers are $D$ apart, and who have radiuses $R_{A}$ and $R_{B}$, much smaller than $D$. Gravitation force has a law in $1/distance^{2}$. On... | How can we quantitatively derive the tidal force experienced by a mass $m$ located on the far side of a spherical body $B$ due to the gravitational attraction of another spherical body $A$, considering their distances and radii? Specifically, derive the difference in gravitational force acting on the mass $m$ at the cl... | 10,217 | cqadupstack-physics |
75082 | Why are magnetic fields only produced by moving charges? | Why do charged particles only produce magnetic fields while in motion? | What is the mathematical relationship that describes the strength of the magnetic field produced by a moving charged particle, and how does this relationship change with the speed of the particle? | 25,938 | cqadupstack-physics |
27359 | How to interpret vacuum instability of Higgs potential | If the Higgs mass is in a certain range, the quartic self-coupling of the Higgs field becomes negative after renormalization group flow to a high energy scale, signalling an instability of the vacuum itself. However, I don't know how to interpret the fact that the vacuum appears to be stable at a certain scale, and not... | What would be the critical value of the quartic self-coupling constant for the Higgs field to ensure vacuum stability at high energy scales, given the range of the Higgs mass and how does this value relate to the vacuum's behavior at different energy scales? | 15,025 | cqadupstack-physics |
114228 | Accleration and frequency | Recently, I was taught by my sir that the Acceleration of an electron of Bohr Atom is equal to its frequency. I am confused and didnt understand why it turns out to be equal | What is the relationship between the acceleration of an electron in a Bohr atom and its frequency, and how can we mathematically verify that they are equal? | 19 | cqadupstack-physics |
135337 | First variation of the action in relativistic notation - Landau & Lifshitz "Classical theory of fields" | In Landau & Lifshitz's book, _Classical theory of fields,_ the action for a free particle is defined as: $$\tag{8.1} S= \int ^b _a {-mc \ \text d s}=0,$$ where $$\text d s=c\,\text d t\sqrt{1-\frac {v^2}{c^2}}$$ is the the invariant space-time interval beetween points along the particles worldline. From the latter expr... | Given the invariant space-time interval for a free particle defined as \( ds = c \, dt \sqrt{1 - \frac{v^2}{c^2}} \), and knowing that the action \( S \) for the particle is given by \( S = -mc \int_a^b ds = 0 \), derive the expressions for the momentum \( p \) and energy \( E \) of the particle in terms of its velocit... | 31,741 | cqadupstack-physics |
54650 | Once I have the eigenvalues and the eigenvectors, how do I find the eigenfunctions? | I am using Mathematica to construct a matrix for the Hamiltonian of some system. I have built this matrix already, and I have found the eigenvalues and the eigenvectors, I am uncertain if what I did next is correct: I took the normalized eigenvectors, placed them in matrix form, and did matrix multiplication with the b... | What is the physical significance of convergence in the eigenvalues of the Hamiltonian matrix, and how does increasing the number of basis elements influence this convergence in the context of the particle in a box model? | 12,455 | cqadupstack-physics |
10063 | Inflation factor and doubling time | I get the general idea about cosmic inflation, but the numbers associated with it seem to be pulled out at random. For example, in The Elegant Universe, Brian Greene says that the universe doubled every 10^(-34) seconds about a hundred times to an overall factor of 10^30. Another astronomy text I read recently gives th... | What is the relationship between the duration of cosmic inflation and the total expansion factor, and how does this relationship influence the potential doubling times of the universe during that period? For instance, if the universe doubled every \( 10^{-40} \) seconds for a certain number of iterations, what would be... | 6,779 | cqadupstack-physics |
69497 | Query in Carroll Section 5.2 Birkhoff's Theorem | This is regarding the proof of Birkhoff's theorem. A part of the proof requires one to show that the most general spherically symmetric metric can be written in the form $$ ds^2 = -e^{2\alpha(t,r)} dt^2 + e^{2\beta(t,r)}dr^2 + r^2 d\Omega_2^2 $$ In order to show this, Carroll briefly describes how one would go about se... | In the context of Birkhoff's theorem and the properties of Killing vectors in a spherically symmetric metric, how can we mathematically verify that if the vectors tangent to the spheres $S_q$ and $S_r$ at a point are both orthogonal to a two-dimensional surface $O_p$, then they must remain orthogonal as $S_q$ and $S_r$... | 13,416 | cqadupstack-physics |
94954 | Assymptotic freedom significance | So I have read a bit on this, and get the idea and mathematical machinery leading up to this. I get that it sheds light on the relationship between coupling strengths and length scales. Can someone tell me the "deep insight", or some other consequence of this that commanded a Nobel prize. Are there other physical impli... | What is the significance of the relationship between coupling strengths and length scales in physical systems, and can you provide an example of a phenomenon or theory related to this relationship that has led to a Nobel Prize in Physics? | 32,611 | cqadupstack-physics |
17551 | units and nature | I am wondering whether the five$^1$ units of the natural unit system really is dictated by nature, or invented to satisfy the limited mind of man? Is the number of linearly independent units a property of the nature, or can we use any number we like? If it truly is a property of nature, what is the number? -five? can w... | What is the minimum number of fundamental units required to fully describe the physical quantities in the universe, and can you provide an example or argument to support this number? | 31,757 | cqadupstack-physics |
134306 | If it takes less than a year to accelerate to the speed of light at 1g why will it take the Voyager 10,000 years to reach Alpha Centauri? | Today I was doing my physics homework and there was a problem involving a space ship falling at 9.8 m/(s^2) to simulate gravity, and it asked how long would it take for the ship to reach to speed of light, and I calculated it to be just under a year. So if it takes less than a year to go to the speed of light at 9.8m/(... | Given that the acceleration due to gravity is 9.8 m/s², how long would it actually take for an object to reach the speed of light if it could accelerate continuously at this rate, and what are the implications of relativistic effects on this scenario? | 21,389 | cqadupstack-physics |
25384 | How is the shape of the universe measured by scientists? | I would like to learn how scientists go about measuring the large-scale curvature of the universe to determine if the universe is closed 'i.e. spherical', flat, or open 'i.e. saddle shaped'. My simplistic thought is that you could measure the corner angles of a really large triangle and see if they add up to <180, 180,... | How can scientists measure the large-scale curvature of the universe, and what methods or observations would they use to determine if it is closed, flat, or open? | 9,577 | cqadupstack-physics |
19906 | Effects of parallel superconducting plates | Assuming the existence of virtual particle field ( zero point energy field) Casimir force is produced by 2 parallel conducting plates excluding some of the frequencies between the plates, if these 2 plates are superconducting does that change the amount of frequencies being excluded? One theory I've read postulates tha... | How does the presence of superconducting materials between two parallel plates influence the Casimir force, and what impact does this have on the exclusion of virtual particle frequencies in relation to inertia of matter passing between the plates? | 9,433 | cqadupstack-physics |
22720 | Why does the d-spacing of a polymer decrease as its crystallinity increases? | I am currently investigating the annealing of a polymer (Parylene-C). In my reading I have found that when the polymer is annealed, there is a decrease in thickness of the film which results from a decrease in d-spacing. I don't have a background in polymer physics/chemistry and I was wondering if someone could explain... | What is the relationship between the crystallinity of Parylene-C and the changes in d-spacing, and how does this affect the thickness of the polymer film during the annealing process? | 33,610 | cqadupstack-physics |
82513 | Black-hole firewall and holographic principle | Can the firewall be viewed as the holographic boundary? Naively a hologram 3d image can not cross the hologram 2d surface that produces that image. According to the metaphor the boundary - 2d field quantum theory without gravity - could act as a firewall for the enclosed space - 3d string theory with gravity and black ... | What is the maximum entropy that can be contained within a black hole's event horizon, and how does this relate to the concept of the firewall as a holographic boundary? | 9,658 | cqadupstack-physics |
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... | When measuring the heat of combustion (∆H° combustion) of a substance at standard conditions, are the temperature and pressure kept constant throughout the entire combustion reaction, or do they change during the reaction until equilibrium is reached? | 17,106 | cqadupstack-physics |
679 | Learning physics online? | I'm thinking of following some kind of education in physics online. I have a master degree in Computer Science and have reasonable good knowledge in physics. I would like a program of 1-2 years and I'm more interested in particle physics. Is there any good online program that offer something similar? | What are the top three online master's programs in particle physics that can be completed within 1-2 years, and what are their average costs? | 8,520 | cqadupstack-physics |
15580 | What ring weave disposition should be the most resistant against stabbing and/or how to determine it | In a website that I am studying so I can build a Chain Mail, I have found a page featuring a lot of different Ring Weaves to build them. I want to determine which one is the best to provide resistance against stabbing strikes, so I wish to know if there are some calculations based on wire resistance, thickness and ring... | What calculations can I use to compare the effectiveness of different chainmail weaves, specifically Japanese 6 in 1 and Dragonscale, in terms of their resistance to stabbing strikes, considering factors like wire resistance, thickness, and ring size? | 7,696 | cqadupstack-physics |
64128 | Why there can't be infinitely small existing? | Why there can't be infinitely small existing? I am not suggesting it can or cannot. I am asking can there be an absolute or reasonable answer to that question. | Is there a minimum possible length or size in physical terms, such as the Planck length, and how does this limit our understanding of infinitely small measurements in the context of quantum mechanics? | 12,986 | cqadupstack-physics |
2055 | How are classical optics phenomena explained in QED (color)? | How is the following classical optics phenomenon explained in quantum electrodynamics? * Color According to Schroedinger's model of the atom, only particular colors are emitted depending on the type of atom and the state of its electrons. Then, how it is possible that the same type of matter changes color in relation... | How does the temperature of a substance like water affect its perceived color, and what quantum mechanical principles can explain this phenomenon in terms of photon interactions and atomic states? | 10,704 | cqadupstack-physics |
67690 | Non-local Lagrangian contact interaction | Conside a contact interaction given by a delta function on their worldlines. Use a gauge fixed Lagrangian for two point particles in terms of their proper times $t$ and $t^{\prime}$. **Is it possible to find proper equations of motion for this system?** For e.g. $$ S=\int dt \; \dot {x}^{2}+\iint\\! dt \;dt^{\prime}\; ... | Can you derive the equations of motion for a system of two point particles interacting via a delta function on their worldlines in a D-dimensional target space, and determine in which dimensions it is possible to integrate out the delta function? | 7,541 | cqadupstack-physics |
91015 | The origin of contact noise? | I was trying to measure the noise of a device with metal probes. I was not sure whether I should trust the results because I was told contact noise might contribute to some degree. I am a little confused about the notion of "contact noise". Is it because of the contact resistance (every resistor is a noise source)? Or ... | What is the origin of contact noise in electronic measurements, and how can the contribution of contact resistance and material properties be quantified in experiments involving metal probes? | 29,845 | cqadupstack-physics |
118734 | Why does a large train cause the ground to shake? | I work in a 4 story building that is approx. 150 feet away from a set of train tracks. When a large (40+ car) freight train goes by, the shaking in the building is perceptible. As I've watched the train go by, there does not appear to be any side to side movement and the speed is constant. What exactly is causing the v... | What are the factors contributing to the vibrations experienced in a building located 150 feet from train tracks when a large freight train passes by, and how can we quantify the impact of those vibrations compared to the train's motion? | 13,817 | cqadupstack-physics |
106270 | Kinematics, why must the final velocity be 50km/hr? | but I am reading a paper on optimization which involves physics. http://www.optimization-online.org/DB_FILE/2011/04/2997.pdf In page 17 (pg 16 bottom where it starts), just before the end of the first paragraph in the top it says > Similarly to the previous subsection, the final velocity Vf is fixed but in > this case ... | If the final position of an object is 100 meters and its final velocity \( V_f \) is fixed at 50 km/h, what is the required average acceleration during the motion if the object starts from rest? Assume constant acceleration. | 17,428 | cqadupstack-physics |
101406 | QHO in Microcanonical Ensemble: Problem with alternate derivation | I am working through Franz Schwabl's book on Statistical Mechanics, and he has a number of derivations of thermodynamic quantities that are different than those I have seen before. I am also having difficulty finding them repeated elsewhere. In particular, he has a method for calculating $\Omega(E)$, the number of stat... | Given a system of \(N\) independent Quantum Harmonic Oscillators, each with Hamiltonian \(\mathcal{H} = \sum_{j=1}^N \hbar \omega \left(n_j + \frac{1}{2}\right)\), derive an expression for \(\Omega(E)\), the number of states with energy \(E\), using both the combinatorial argument and Schwabl’s Fourier Transform approa... | 29,823 | cqadupstack-physics |
59695 | Probabilistic vs Statistical interpretation of Double Slit experiment | Why is it assumed that the results seen in the double slit experiment are probabilistic and not just a statistical result of some unknown variable or set of variables within the system. | What is the probability distribution of the photon hit locations on a screen in a double-slit experiment, and how does it support the interpretation of quantum mechanics as being inherently probabilistic rather than a result of hidden variables? | 3,883 | cqadupstack-physics |
77038 | Derivation of the Polyakov Action | As is usually done when first presenting string theory, the Nambu-Goto Action, $$ S_{\text{NG}}:=-T\int d\tau d\sigma \sqrt{-g} $$ ($g:=\det (g_{\alpha \beta})$ is the induced metric on the world-sheet and $T$ is a positive real number interpreted as the string tension), is introduced as the natural generalization of a... | How can you derive the Polyakov action \( S_{\text{P}} \) from the Nambu-Goto action \( S_{\text{NG}} \), given that your goal is to express \( S_{\text{P}} \) without involving a square root? | 35,097 | cqadupstack-physics |
87565 | Determining source of neutrinos | An article in Science, Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector, claims to have detected 28 neutrinos from an unidentified extra-solar location that has yet to be identified. From what I can gather, the only evidence for determining the origin of a neutrino is based only on the energy... | What is the probability density function for the energy values of atmospheric and solar-system-generated neutrinos, and how do the observed energy levels of the 28 neutrinos detected by the IceCube Detector compare to this function? | 18,858 | cqadupstack-physics |
116422 | Lagrangian for a system of particles | If a system of particles attracting each other under inverse square force, then prove that $$ 2<T> \+ <V> = 0.$$ | In a system of particles that attract each other according to an inverse square law, if the average kinetic energy is denoted as \( <T> \) and the average potential energy as \( <V> \), show that the relationship \( 2<T> + <V> = 0 \) holds true. What are the conditions or assumptions under which this relationship is va... | 27,257 | cqadupstack-physics |
59297 | Does String Theory explain spin? | The state of a particle will generally change if you rotate it. The details of how the state changes under an infinitesimal rotation are contained in the angular momentum operator **J**. This operator can be divided into two parts: an "orbital" angular momentum and a "spin" angular momentum. The orbital angular momentu... | If the angular momentum operator **J** is divided into orbital and spin components, how does the total angular momentum of a particle with spin-1/2 compare to that of a particle with no spin when both are subjected to a rotation of \(90^\circ\) about the z-axis? | 27,588 | cqadupstack-physics |
78483 | When sun is exactly overhead in my place in the tropics | What formula to use to find dates and times when the sun is exactly overhead in my place in the tropics? | What are the specific dates and times during the year when the sun is directly overhead at a location in the tropics, and how can I calculate them using the sun's declination? | 30,706 | cqadupstack-physics |
121969 | How does gravity slow light without an equal and opposite action? | This is regarding the gravity well sort of explanation. People claim that gravity doesn't slow light by saying it curves the road by which it travels but if space is indeed without properties and empty, it can exert no force upon light therefore the light would travel unless interacted upon by a force, there exists pus... | What are the theoretical implications of light curving around a gravitational field, and how does this relate to the concept of spacetime in the vicinity of a black hole's event horizon? | 34,562 | cqadupstack-physics |
33620 | What is happening over the 15 minutes it takes a neutron to decay? | I've read that free neutrons decay into a proton, electron and neutrino with an average lifespan of about 15 minutes. Is there anything physically different about a neutron that has existed for 14 minutes and one that has only existed for one minute? Does a random outside event trigger the decay or is something interna... | What is the probability that a free neutron will decay within the last minute of its average lifespan, given that it has already existed for 14 minutes? | 37,408 | cqadupstack-physics |
11939 | What is the Lagrangian for a relativistic charge that includes the self-force? | The usual Lagrangian for a relativistically moving charge, as found in most text books, doesn't take into account the self force from it radiating EM energy. So what is the Lagrangian for a relativistic charge that includes the self-force? | What is the expression for the Lagrangian of a relativistic point charge that accounts for the self-force due to its electromagnetic radiation? | 15,011 | cqadupstack-physics |
31830 | formula for transparency of very thin film of metal | Is there formula that gives transparency of very thin film of given metal (tens of nanometers) to the visible light/light of given wavelength ? Which properties of metals are needed for the formula ? I need to know which thickness of aluminium has 40% transparency to visible light. Thanks. | What is the formula for calculating the transparency of a thin film of aluminum with a thickness of tens of nanometers to visible light, and at what thickness does this film exhibit approximately 40% transparency? | 20,300 | cqadupstack-physics |
45896 | Can Parallel Transport always move a Vector Parallel to Itself? | Consider two tiny plane(flat) surfaces A and B meeting at a straight line L.We have a preassigned vector on A at some point P on it.Is it always possible to have a vector parallel to the first one and lying on B at some point on it(say Q)? [The first vector(that on A) is assumed as _not_ parallel to L] The two planes m... | Given two intersecting planes A and B at a line L, where a vector \( \vec{v} \) at point P on plane A is not parallel to line L, what is the necessary condition for the existence of a vector \( \vec{u} \) on plane B at point Q that is parallel to \( \vec{v} \)? Quantitatively determine under what geometrical constraint... | 10,792 | cqadupstack-physics |
38545 | Examples of manifolds and fluxes coming from generalized complex geometry | The paramount object in generalized gomplex geometry is the Courant algebroid $TM\oplus T^\star M$, where the manifold $M$ is called _background geometry_ I think (I am not sure). More generally this Courant algebroid can be twisted by a closed 3-form $H$ on $M$, which I suspect is called a _flux_ (I am not sure too). ... | Can you provide specific examples of a manifold \( M \) and a closed 3-form \( H \) such that the twisted Courant algebroid \( (TM \oplus T^*M, H) \) is relevant in the context of String Theory, and describe the significance of this combination? | 2,398 | cqadupstack-physics |
113522 | How can one rule out the possibility of there being neutral quarks? | This is a very simple question, which will most likely yield a prompt response from someone who knows more than I. The reason I ask:The quarks that we can detect (as they interact electromagnetically) are much lighter than the particles that they make up. From what I know, we say that gluons augment the energy level of... | What is the relationship between quark composition, gluon interactions, and the conservation of charge during particle decays, such as beta decay, particularly in the context of gauge bosons like the W boson? | 16,247 | cqadupstack-physics |
80672 | Can I Demagnetize a ferromagnet with a hammer? | If an iron is exposed to an external magnetic field, the iron's domains are all aligned with that ext-B . If I strike it with a hammer, will it be demagnetized? Comparing it with heat, I know the Tc point, but with vibrations what is the point like in heat? When would I expect the iron to be temporarily demagnetized? H... | What is the minimum force per unit area required to disrupt the magnetic domains in iron and achieve temporary demagnetization when struck with a hammer, given that the Curie temperature (Tc) is around 770°C? | 21,513 | cqadupstack-physics |
19228 | Physical meaning of the energy density of an electrostatic field | I understand the physical meaning of electrostatic energy of a system of charges (or a distribution with given density) as the energy stored in the system while working to carry the charges from infinity to their actual place in the system. According to this article on Wikipedia, in the case of a static field you can a... | How can the electrostatic energy density \( U = \frac{1}{2}\epsilon_{0}|\vec{E}|^2 \) be calculated for a system of point charges located at positions \( \vec{r}_1 \) and \( \vec{r}_2 \) with charges \( q_1 \) and \( q_2 \) respectively? If the distance between the charges is \( r \), what is the total electrostatic en... | 5,594 | cqadupstack-physics |
51196 | Orthogonality of modes | I want to know what it exactly means when it is said the modes of vibration are Orthogonal.I understand what it means mathematically but what is its physical interpretation? | In a system of coupled oscillators, if the normal modes of vibration are orthogonal, what does this imply about the energy distribution in each mode when the system is excited? Provide a quantitative explanation based on the characteristics of the modes. | 32,949 | cqadupstack-physics |
16616 | returning to physics research? | What the the most realistic and practical ways for a PhD in physics who has left the fold to return to a career of research in physics? The traditional employer of choice, universities won't hire such people. What alternative career choices are there for someone without an impressive track record so far? Are there alte... | What alternative career opportunities can a PhD in physics pursue to engage in research if they have recently left academia and lack an impressive publication record? Please provide at least three specific options and their potential income ranges. | 5,199 | cqadupstack-physics |
78943 | Why doesn't sound infinitely loop? | Let say we have a microphone and a speaker. The microphone will receive the surrounding sound, and the speaker will amplify it. Assume we have unlimited power for the microphone and speaker, so they can work forever. When we speak to the microphone, the sound should be repeated by the speaker. While the speaker generat... | In a system where a microphone and a speaker are set up to create a continuous loop of sound, what physical principle or phenomenon prevents the sound from circulating indefinitely, and how does this relate to concepts such as feedback and stability in sound systems? | 23,518 | cqadupstack-physics |
122370 | How do you levitate a foam rock? ('Endless Second' artwork) | I saw this in an art museum:  How is this possible? The materials used to make this were foam, wood, stone dust, paint, electromagnets, and metal. I would like to know how this was make and how I could make something similar. Thank You. | What principles of electromagnetism and material science could be applied to create an object that appears to float, utilizing materials such as foam, wood, stone dust, paint, electromagnets, and metal? Please provide a quantitative analysis of the necessary specifications for the electromagnets, including their streng... | 32,877 | cqadupstack-physics |
116333 | Information faster than light? | Imagine that you have two typewriters on the other side of the galaxy. Their typebars are connected by ropes (stretched to the maximum), so anything you type will instantly appear at the second typewriter. Are the sentences information? If so, why not send information faster than light? If not, I'd at least ask if such... | If two typewriters located at opposite ends of the galaxy are connected by an idealized "instantaneous" rope system, what is the maximum speed at which information can be transferred from one typewriter to the other, in terms of the speed of light (c)? | 12,409 | cqadupstack-physics |
96190 | Non-Constant Acceleration due to Gravity | Recently, I had the first physics lab for my university physics course. This lab was fairly simple, as we were merely using a computer and a distance sensor to graph the position, velocity, and acceleration of a cart as it moved along a linear track. One of the situations we captured data for involved starting the cart... | In an experiment measuring the acceleration of a cart rolling up and down an inclined ramp, the observed acceleration was approximately \(0.546 \frac{m}{s^2}\) while moving upwards and \(0.486 \frac{m}{s^2}\) while moving downwards. Considering that gravity is the only force acting on the cart, what could explain the d... | 1,883 | cqadupstack-physics |
94863 | What is the center of Earth's landmass? | I have read, several times, that the Great Pyramid is located at "the center of Earth's landmass". How do we define "Earth's landmass"? And once defined, how do we find the center of it? | What are the geographical coordinates of the center of Earth's landmass, and what method can be used to calculate it accurately? | 2,558 | cqadupstack-physics |
78826 | Are CCDs approaching the sensitivity of photomultiplier tubes? | I still see photomultiplier tubes (PMT) used for even benchtop spectroscopy experiments. How much more sensitive are they to CCDs? I found a post which claims about 1.5 x more sensitivity for PMTs, but any references or more complete understanding of the problem would be really appreciated. I'm also wondering if they n... | What is the comparative sensitivity of photomultiplier tubes (PMTs) to charge-coupled devices (CCDs) in terms of photon detection efficiency, and how does this relate to their cooling requirements and signal-to-noise characteristics in spectroscopic applications? | 34,323 | cqadupstack-physics |
104722 | Do gravitational waves cause time dilatation? | The effect of gravitational waves in transverse traceless gauge on matter is represented by the expansion and contraction of a ring of test particles in the direction of polarization of the wave. This result is obtained by choosing a gauge which in GR is a choice of a coordinates. Does that mean that choosing another c... | How do gravitational waves in transverse traceless gauge affect the measurements of time dilation for uniformly moving observers compared to accelerated observers, considering both the weak field approximation and the full non-linear case? Quantitatively, what would be the difference in time dilation effects observed i... | 2,817 | cqadupstack-physics |
126718 | Are the ideas of the speed of light and the absolute top speed inside the universe equivalent? | The idea of the speed of light being as fast as something can go is pretty well accepted. I'm wondering if the top speed might be (very slightly) higher? Lemme explain. I was reading about particle acceleration, and how accelerating a particle to the speed of light would require infinite energy. According to a quick Go... | If the speed of light in a vacuum is \( c = 299,792,458 \) meters per second, what is the minimum amount of energy required to accelerate a particle with a rest mass of 1 kg to a speed of \( 0.9999999999999999c \)? Assume that the particle's relativistic kinetic energy is described by the equation \( KE = \gamma mc^2 -... | 26,046 | cqadupstack-physics |
114253 | How do you calculate the energy output if you know the volts, amps and time? | How do you calculate the energy output if you know the volts, amps and time? | If you have a circuit that operates at 12 volts and draws a current of 3 amps for 10 hours, how much energy in watt-hours does the circuit output? | 23,351 | cqadupstack-physics |
130710 | Flow velocity out of a pipe | For a compressible homoentropic gas is the flow velocity out of the pipe the same as the velocity into the pipe? | For a compressible homoentropic gas flowing through a pipe with varying cross-sectional area, how does the velocity of the gas at the exit compare to the velocity at the entrance, and what principles govern this relationship? Provide a quantitative example using the ideal gas law and the continuity equation. | 36,120 | cqadupstack-physics |
126316 | Heisenberg Uncertainty Principle | Question: The uncertainty in position is equal to the uncertainty in momentum. What is the uncertainty in velocity? What I did: I know that the uncertainty in position multiplied by uncertainty in momentum is equal to $\frac{h}{2\pi}$ As momentum is mass times velocity, and mass is constant and definite, the uncertaint... | In a particle confined within a one-dimensional box of length \( L \), the uncertainty in position \( \Delta x \) is approximately equal to \( L \). If the mass of the particle is \( m \) and Planck's constant is \( h \), what is the expression for the uncertainty in velocity \( \Delta v \) of the particle in terms of ... | 28,996 | cqadupstack-physics |
89659 | Eigenfunctions of the Runge-Lenz vector | The hamiltonian for the hydrogen atom, $$ H = \frac{\mathbf{p}^2}{2m} - \frac{k}{r} $$ is spherically symmetric and it therefore commutes with the angular momentum $\mathbf{L}$; this causes all its eigenfunctions with equal angular momentum number $l$ but arbitrary magnetic quantum number $m$ to be degenerate in energy... | What are the eigenvalues and corresponding eigenfunctions of the hydrogen atom's Hamiltonian \( H \) and the Laplace-Runge-Lenz vector \( \mathbf{A} \), and how can these be related to the classical eccentricity of the orbit? Additionally, what uncertainty principles apply to the components of \( \mathbf{A} \) when in ... | 22,562 | cqadupstack-physics |
4184 | Why should the Standard Model be renormalizable? | Effective theories like _Little Higgs models_ or _Nambu-Jona-Lasinio model_ are non-renormalizable and there is no problem with it, since an effective theory does not need to be renormalizable. These theories are valid until a scale $\Lambda$ (ultraviolet cutoff), after this scale an effective theory need a UV completi... | What is the significance of renormalizability in the Standard Model of particle physics, and how does it relate to the requirement for a UV completion at high energy scales? | 3,086 | cqadupstack-physics |
103845 | How to prove wave nature of large object? | In double slit experiment only small sized particles were used. however if we use large objects such as a tennis ball, the expected pattern is not observed. Why the wave nature is not visible for large objects in double slit experiment ? How do I then prove that large objects also have wave nature? | In the double slit experiment, how does the de Broglie wavelength of a large object, such as a tennis ball, compare to its size, and what implications does this have for observing wave-like behavior? Calculate the de Broglie wavelength of a tennis ball with a mass of 0.057 kg moving at a speed of 10 m/s, and discuss wh... | 21,505 | cqadupstack-physics |
19635 | What narrow-linewidth laser system runs at 2100nm with 1W of power? | For an experiment at our university we need a laser that runs at about 2.1 μm (about 20nm higher or lower would be fine too. We have found a multitude of lasers that achieve this (typically Thulium- or Holmium-doped solid state or fiber lasers), but they don't meet the requirements that we have. Specifically, we need: ... | What are the key parameters and features that a laser, operating around 2.1 μm with a power output of at least 500 mW, must meet to be suitable for a specific experimental application requiring continuous wave, single-mode emission with about 0.1 nm linewidth and polarized output? Additionally, how would one go about m... | 10,779 | cqadupstack-physics |
78932 | What happens if an already excited electron gets hit by another photon (lasers)? | Slightly vague title but it is the best I can do. My question stems from some interest in how 3 stage lasers function. A photon from the pumping source comes in and strikes a atom in the active medium. The photon is absorbed, an electron is excited, and the energy instantly falls to a metastable state. My question is w... | In a three-stage laser, if an electron in the metastable state is struck by a second pump photon that has enough energy to promote it to a higher energy state, what are the possible outcomes for the electron? Specifically, does it jump to this higher energy state, or is the active medium designed in such a way that the... | 1,607 | cqadupstack-physics |
135277 | The variation of the Lagrangian density under an infinitesimal Lorentz transformation | I'm trying to introduce myself to QFT following these lectures by David Tong. I've started with lecture 1 (Classical Field Theory) and I'm trying to prove that under an infinitesimal Lorentz transformation of the form $$\tag{1.49} {\Lambda^\mu}_\nu={\delta^\mu}_\nu+{\omega^\mu}_\nu,$$ where $\omega$ is antisymmetric, t... | Given the Lagrangian density \( \mathcal{L}(\phi, \partial_\mu \phi) \), under an infinitesimal Lorentz transformation characterized by the antisymmetric parameter \( \omega^{\mu}_{\nu} \), the variation of the Lagrangian density is defined as
\[
\delta \mathcal{L} = -\partial_\mu(\omega^{\mu}_{\nu} x^{\nu} \mathcal{... | 13,704 | cqadupstack-physics |
126562 | paradoxical results in different applications of the 2nd law of thermodynamics | Assume two closed systems adjacent to each other together forming one adiabatic system. Both systems are assumed to have their volumes fixed and can therefore communicate with each other through heat transfer only. Now let study this simple example with three different formulation: 1. The first formulation is what I ... | In a closed adiabatic system consisting of two adjacent systems with fixed volumes, if heat transfer occurs from system 2 to system 1 such that the heat exchanged, \( \delta Q \), is \( 100 \, \text{J} \), and the temperatures of system 1 and system 2 are \( T_1 = 300 \, \text{K} \) and \( T_2 = 350 \, \text{K} \) resp... | 23,869 | cqadupstack-physics |
78577 | Proof that the momentum operator is Hermitian | I am trying to prove that the momentum $p_x$ operator is Hermitian, my approach is the following $$<p_x>~=~\int \Psi^*(\vec{r},t)[-ih\frac{\partial}{\partial x}]\Psi(\vec{r},t)\, d^3r.$$ I try to do integration by parts but I cannot resolve the differential, as the integration is in respect to $\vec{r}$ and the partial... | Can you show that the momentum operator \( p_x = -i\hbar\frac{\partial}{\partial x} \) is Hermitian by evaluating the integral \( \langle p_x \rangle = \int \Psi^*(\vec{r},t) p_x \Psi(\vec{r},t) \, d^3r \) and using integration by parts to demonstrate that it satisfies the condition \( \langle p_x \rangle = \langle p_x... | 37,931 | cqadupstack-physics |
32989 | What is the status of Mpemba effect investigations? | There is this puzzling thing that is called Mpemba effect: paradoxically, warm (35°C) water freezes faster than cold (5°C) water. As a physisist, I've been asked about it several times already. And I have no definite answer to that, apart from the standard: "there are many things that can influence it". So, does anyone... | What factors contribute to the Mpemba effect, and how can the freezing rates of warm (35°C) and cold (5°C) water be quantitatively compared in an experiment? | 5,004 | cqadupstack-physics |
92889 | Partition function for a microcanonical ensemble | Is it possible to write down a partition function for a microcanonical ensemble? | What is the expression for the partition function of a microcanonical ensemble, and how does it relate to the number of accessible microstates and the total energy of the system? | 6,985 | cqadupstack-physics |
74144 | What is the difference between air pressure and atmospheric pressure? | I remember studying that air pressure and temperature are inversely proportional. Now I saw in book that "Atmospheric pressure decreases as we go higher and higher." But in height the temperature is less, and so the air pressure is high. But it is given atmospheric pressure increases with altitude. I googled and unders... | How does the relationship between air pressure and temperature change with altitude, and can you explain the differences between air pressure and atmospheric pressure in terms of their properties? | 35,639 | cqadupstack-physics |
17087 | "Slightly off-shell"? | I'm not new to QFT, yet there are some matters which are quite puzzling to me. I often come across the statement that real particles (the ones we actually measure in experiments, not virtual ones) are "slightly off-shell". What does this actually mean? To my knowledge, something being off-shell means that it violates t... | In quantum field theory, real particles are often described as being "slightly off-shell." Given that being off-shell implies a violation of the relativistic energy-momentum relation \( E^2 = p^2c^2 + m^2c^4 \), can you explain how this concept applies to real particles, including examples or experimental evidence that... | 33,635 | cqadupstack-physics |
71236 | Saturation of the Cauchy-Schwarz Inequality | Going to as little details as possible, here is a statement from Wald's text on QFT in curved spacetimes(I am not quoting the book) He considers two vector spaces ${\cal S}$ and ${\cal H}$. > Note - For more details about ${\cal S}$ and ${\cal H}$, read this box. I > believe for most part of the question, the following... | Given the inequality \( \mu(y_1, y_1)\mu(y_2, y_2) \geq \frac{1}{4} \Omega(y_1, y_2)^2 \), what does it imply about the relationship between \(\mu(y_1, y_1)\) and the maximum value of \(\frac{\Omega(y_1, y_2)^2}{\mu(y_2, y_2)}\) for \(y_2 \in {\cal S}\) such that this inequality is saturated? Specifically, can you deri... | 14,373 | cqadupstack-physics |
116367 | Relative speed when approaching the speed of light | According to this chart of the Lorentz factor as a function of speed:  If a spacecraft neared (roughly) 0.85c, would it appear to be traveling at 1.7x the speed of light from the perspective of those on board - i.e. covering 0.85c distance, but in half the time amoun... | If a spacecraft is traveling at a speed of 0.85c, what would be the Lorentz factor for that speed, and how would this affect the perception of speed for passengers on board compared to an observer at rest? | 13,447 | cqadupstack-physics |
1223 | Which PPN parameters are least well determined? | There are by now (late 2010) many tests of GTR. GTR is holding up quite well! But, surely, we do not yet have it cornered in every possible way. In terms of the PPN parameters used to characterize low-order deviations of any theory of gravity from Newtionian ideals, where are the loosest screws? Which PPN parameter is ... | Which of the Parameterized Post-Newtonian (PPN) parameters used to characterize deviations in gravitational theories from Newtonian principles is currently the least constrained by experimental data, and what specific experiments could be designed to better constrain it? | 28,531 | cqadupstack-physics |
78245 | What is the theoretical justification for a fluid flow's being irrotational? | I am not a fluid dynamicist, and I really just began thinking about this problem as my curiousity drew me into building an answer for the question What really allows airplanes to fly?. It is very clear from the answers to the following questions: When is a flow vortex free? Does a wing in a potential flow have lift? th... | In fluid dynamics, what are the necessary conditions for a flow to be considered irrotational, and how can the Navier-Stokes equations be decomposed to analyze vorticity in a similar manner to the Maxwell equations in electromagnetism? | 12,578 | cqadupstack-physics |
76662 | Total angular momentum - single electron | I have been dealing with total angular momentum of the single electron which is outside the closed shells in which sum of the angular momentums is zero. My book says that total atomic angular momentum is $\mathbf{J}=\mathbf{L+S}$ and its magnitude $J=\sqrt{j(j+1)}\hbar$ where quantum number $j$ can have half-integer va... | Given an electron in a p orbital with quantum number \(\ell=1\), which can have total angular momentum values \(j=\frac{3}{2}\) and \(j=\frac{1}{2}\), calculate the corresponding magnitudes of the total atomic angular momentum \(J\) and the possible values of the magnetic quantum number \(m_j\) for each case. Specifica... | 34,217 | cqadupstack-physics |
80406 | Does a battery in a vacuum produce a current? | I've always assumed that the strong resistance of air is the reason there is no flow of electrons between the terminals of a battery until a wire is connect. However, in a vacuum there is no resistive substance to impede the flow of electrons. Does this mean that in a vacuum an average AA battery will spontaneously hav... | If an AA battery is placed in a vacuum, will there be any flow of electrons between its terminals, and if so, how does this flow compare to that in a normal atmospheric environment? | 5,193 | cqadupstack-physics |
83824 | almost same mass, same distance, different energy needs | Imagine a car, driving 10 km at constant speed in 6th gear. There will be a measurable fuel consumption. Now imagine the same car driving 10 km again at a constant speed (same as above) in the 1st gear. The fuel consumption will be MUCH higher. I would expect a higher consumption because the internal organs of the engi... | Why does a car in 1st gear consume significantly more fuel than in 6th gear when both are driven at the same speed over a distance of 10 km? Please consider the effects of engine efficiency, gear ratios, and frictional losses in your explanation. | 32,830 | cqadupstack-physics |
39138 | how far away can something be from the earth and still be in orbit? | Just as the title asks, How far away can, say, a satellite be and still be in "orbit" ? How about for a given velocity? _Fun Facts_ 200 miles (320 km) up is about the minimum to avoid atmospheric interference. The Hubble space telescope orbits at an altitude of 380 miles (600 km) or so. _potentially helpful numbers_ ma... | What is the maximum altitude at which a satellite can orbit the Earth while maintaining a circular orbit, and how does this altitude change if the satellite's velocity is altered? Provide calculations based on the gravitational force and centripetal acceleration. | 27,467 | cqadupstack-physics |
30477 | If gravity is a bend in Space-time then what is magnetism? | Einstein postulated that gravity bends the geometry of space-time then what does magnetism do in to the geometry of space-time, or is there even a correlation between space-time geometry and magnetism? | How does the presence of a magnetic field influence the curvature of space-time according to the framework of general relativity, and can you quantify this effect using the magnetic energy density? | 16,942 | cqadupstack-physics |
13283 | Modeling a spray painted polyurethane surface reflection | I'm modeling light interaction/reflection from a fiberglass surface with polyurethane epoxy (that is very reflective) that has been spray painted with a matte black paint. I'm looking for some input - is it reasonable to approximate this as specular reflection from the polyurethane with a loss factor from the paint abs... | How can I quantitatively model the reflection of light from a fiberglass surface coated with a polyurethane epoxy and then covered with matte black paint, specifically regarding the contributions of specular reflection and absorption? What parameters should I consider, and how can I incorporate a loss factor into my Mo... | 9,657 | cqadupstack-physics |
95259 | How do you find a particular representation for Grassmann numbers? | This question is more general in the sense that I want to know how one finds a particular (say matrix) representation for any object. For the case of Grassmann numbers we have from Wikipedia the following representation: > Grassmann numbers can always be represented by matrices. Consider, for > example, the Grassmann a... | Given two Grassmann numbers \(\theta_1\) and \(\theta_2\) represented by the following matrices:
\[
\theta_1 = \begin{bmatrix} 0 & 0 & 0 & 0\\ 1 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 0 & 0 & 1 & 0\\ \end{bmatrix}, \quad \theta_2 = \begin{bmatrix} 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0\\ 1 & 0 & 0 & 0\\ 0 & -1 & 0 & 0\\ \end{bmatrix}
\... | 29,339 | cqadupstack-physics |
119105 | Decompression speed (rate) | I've heard that decompression speed or rate in which the gas will leave the greater pressured container is equal to the speed of sound. For example, if the spacecraft gets damaged the air cannot exit out to vacuum faster than about 340 m/s I don't understand how the flow rate of the fluid is determined by the density. ... | What is the maximum speed at which air can escape from a spacecraft into the vacuum of space if the decompression speed is equal to the speed of sound in air, and how does the density of the air affect this flow rate? | 19,187 | cqadupstack-physics |
104303 | Calculating pitch and roll with accelerations greater than +/- 1g | I'm looking to compute the pitch and roll of a device fitted with a three axis accelerometer when it is not at rest or moving at a constant velocity. Most applications I've seen so far are for stationary tilt sensing... genuinely stuck on this one! Aiming to use it for a python program I'm working on. For a stationary ... | How can I calculate the linear vertical acceleration of a device equipped with a three-axis accelerometer, accounting for pitch and roll when the device is not at rest or moving at a constant velocity, given the formulas for roll and pitch? | 2,699 | cqadupstack-physics |
119723 | Subgroups of the Clifford Group | We recall the definition of a Clifford group (over $n$ qubits) is the set of unitary transformations: $$\\{U: UPU^\dagger\in\mathcal{P}\\}$$ where $\mathcal{P}$ denotes the corresponding Pauli group (again over $n$ qubits). What progress has been made in characterizing the subgroups of the Clifford group, and in partic... | What is the number of distinct subgroups of the Clifford group that are isomorphic to the Pauli group for a system with \( n \) qubits? | 9,359 | cqadupstack-physics |
30556 | What does AdS/CFT have to say about quantum gravity in our world? | The Ads side of the AdS/CFT correspondence is a model of quantum gravity in 5 dimensional antidesitter space. What can it say about quantum gravity in our 4-spacetime dimensions? Or is it just a toy model to better our understanding of quantum gravity as a whole? | What quantitative predictions can be made about the behavior of black holes in a 5-dimensional anti-de Sitter space, and how do these predictions compare to our understanding of black holes in 4-dimensional spacetime? | 37,430 | cqadupstack-physics |
64574 | Definition of the entropy | In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is defined as $$H(X)=-\Sigma_x P(x)log_2 [P(x)]$$ bits, where $P(x)$ is the probability that $X$ is in the state $x$ , and... | Consider a discrete random variable $X$ that can take on the values $x_1, x_2, \ldots, x_n$ with corresponding probabilities $P(x_1), P(x_2), \ldots, P(x_n)$. If the probabilities are $P(x_1) = 0.5$, $P(x_2) = 0.25$, $P(x_3) = 0.125$, and $P(x_4) = 0.125$, calculate the Shannon entropy $H(X)$ in bits. What does this va... | 23,606 | cqadupstack-physics |
20877 | How to write classical dynamics of solids in tensor form (relation of stiffness and viscosity tensor)? | This is a question about dynamics. If I have understood correctly there should be a tensor that describes the dynamics of a (solid?) body (= viscosity ?). I mean, tensor that includes the time dependence. I would do it in a following way: $$ \sigma_{ij} = (C_{ijkl}(t) + \frac{\partial C_{ijkl}(t)}{\partial t} t + \frac... | How can the time-dependent behavior of stress in an anisotropic elastic solid be modeled using a Taylor expansion of the stiffness tensor, and what are the implications of including higher-order time derivatives of the strain tensor in this model? Specifically, what would the terms following the linear viscosity term r... | 33,280 | cqadupstack-physics |
27735 | Heuristics for definitions of open and closed quantum dynamics | I've been reading some of the literature on "open quantum systems" and it looks like the following physical interpretations are made: * **Reversible** dynamics of a **closed** quantum system are represented by a **group of automorphisms** (of a $C^∗$-algebra, von Neumann algebra, or $B(H)$, depending on whom you read... | Can you provide an example of a physical system that illustrates irreversible dynamics in a closed system, and explain how its behavior can be represented by a semigroup of endomorphisms within the framework of quantum mechanics? | 28,957 | cqadupstack-physics |
111147 | Charge Distribution On Hollow Sphere | Say we have a hollow conducting sphere (with some finite thickness). If this object has an excess charge amounting to +Q coulomb, and there is no extra electric field in the surroundings (due to other charges), how will the charge be distributed? Intuitively it seems that the charge will be symmetrically distributed..(... | How is the charge distributed on the surface of a hollow conducting sphere with an excess charge of +Q, and why is the electric field zero inside the hollow part? Can you explain how the symmetry of the charge distribution leads to this outcome, possibly involving the concept of solid angles and the mathematical relati... | 753 | cqadupstack-physics |
104598 | In the B mode power spectrum, what is the relationship between the multipole number and the wavelength of the seed gravitational waves? | One of the key datasets of the recent BICEP2 results is the B mode power spectrum shown below. The existence of these B modes implies the existence of gravitational waves prior to inflation. My question is: what is the relationship between the multipole number of the B mode and the wavelength of the gravitational waves... | What is the mathematical relationship between the multipole number of B modes in the cosmic microwave background and the corresponding wavelength of the gravitational waves that produced them, considering the scaling factor related to the expansion of the universe? | 19,119 | cqadupstack-physics |
109043 | What's the total Cosmic Microwave Background energy? | This is a part of my wider attempts at accounting matter in the observable universe. The total light ever emitted by stars and other space objects is capped around 1% of baryonic mass (in energy equivalent). How much light is there in space and how heavy is it? How does the CMB compare to that? How would we calculate i... | What is the total energy output of all stars in the observable universe, expressed in joules, if it constitutes about 1% of the total baryonic mass, estimated to be approximately \(4 \times 10^{53}\) kg? Additionally, how does this energy output compare to the energy density of the Cosmic Microwave Background (CMB), wh... | 28,209 | cqadupstack-physics |
97909 | Theoretical reasons for charge quantization | I'm aware of Millikan's oil drop experiment and I've read that quarks have fractional eletric charge, but I was wondering if there's any theoretical argument that makes us believe charge is quantized. I've also read about Dirac's famous work in which he demonstrated that if a magnetic monopole exists then electric and ... | What are the theoretical arguments or principles that support the quantization of electric charge beyond the existence of magnetic monopoles? Provide at least two distinct reasons or frameworks that lead to the conclusion that charge is quantized. | 31,924 | cqadupstack-physics |
104304 | Without seeing the lightning, can you tell how far away it struck by how the thunder sounds? | Is there any way to tell how far away a lightning strike is by how its thunder sounds? I thought one way might be by using the fact that higher frequencies travel faster than lower frequencies. Would you have to correct for the fact that thunder may not take a straight path? (If so, this would affect the distance calcu... | Given that the speed of light is approximately 3.00 x 10^8 m/s and the speed of sound in air is approximately 343 m/s, if you observe a lightning strike and hear the thunder 5 seconds later, how far away was the lightning strike in meters? Assume that the sound travels in a straight path. | 36,746 | cqadupstack-physics |
87697 | The universe being finite | 1. I always thought we didn't know if the universe is finite or infinite. However is it true that the universe (not just the observable one) is finite with no boundaries? 2. The articles arXiv:0901.3354 and arXiv:1101.5476 don't quite suggest an infinite universe. Would someone please explain? 3. Also, is it true t... | Is the universe finite and without boundaries, and what evidence from recent astronomical studies or theories supports this claim? | 9,906 | cqadupstack-physics |
22538 | Event-by-Event Simulation of Quantum Phenomena | I just recently stumbled over http://rugth30.phys.rug.nl/dlm/ and http://www.sbfisica.org.br/bjp/files/v38_26.pdf As the title suggests these are presentations of mathematical models capable of simulating quantum "effects" on an event-by-event basis using "Deterministic Learning Machine" Models. What is the state of di... | What are the potential advantages and disadvantages of using Deterministic Learning Machine Models to simulate quantum phenomena compared to traditional quantum mechanics approaches, and how might these models influence our understanding of quantum effects? | 30,788 | cqadupstack-physics |
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