instruction stringlengths 31 24.3k |
|---|
(Question at the bottom) The classical wave equation in 1+1D is:
$$\frac{\partial^2 y}{\partial x^2}=\frac{1}{v^2}\frac{\partial^2 y}{\partial t^2}.$$
It can be solved using the following method. Let's take $a = x+vt$ and $b = x-vt$. Now $a$ and $b$ are both functions of $x$ and $t$, $ a = a(x,t), b = b(x,t)$.
Now $y(x... |
I'm reading the book "Einstein Gravity in a nutshell" by Anothy Zee and I'm a bit stuck on one of the steps in the derivation for divergence in an arbitrary coordinate system. The proof goes as follows,
since we know
$$W^\mu\partial_\mu\phi$$
where $W^\mu$ is a vector field, $\phi$ is a scalar field, and $\partial_\mu... |
I've got a couple of basic doubts about single-mode optical fibers -
a) Why do single-mode fibers have lower attenuation than multimode fibers?
b) Why do light rays in single-mode fibers travel in a straight line?
c) Why do single-mode graded-index fibers not exist? Is it because the diameter and refractive index of su... |
Derivation of the Lindblad master equation starts with the assumption that at an initial time $t=0$, the total density matrix is the product of the density matrices of the system $\rho_S$ and that of the environment $\rho_E$ i.e. $$\rho_{\rm tot}(0)=\rho_S(0)\otimes\rho_E(0)\tag{1}$$
Question If we start with such a fa... |
Most people heard that we only see some % of an iceberg above water (10% etc). I suspect the exact % depends on the iceberg's shape (e.g. flat disc vs very narrow cylinder). But, assuming a similar, roughly spherical shape, does this % change with the iceberg's size? If you had roughly spherical icebergs, 1m, 10m, 100m... |
The Bogoliubov transformation picks a set of boson operators $\{a_{k},a^{\dagger}_{k}\}$ and transforms them into a new set of boson operators generally written as:
\begin{equation}
b_{k}=\sum_{l} u_{kl}a_{l}+\sum_{p}u^{\prime}_{kp}a^{\dagger}_{p}
\end{equation}
I was now thinking: is this the most general transformati... |
The set up is "A conducting sphere of radius $r_0$ is placed in an originally uniform electric field E, and maintained at zero potential. Show that the potential outside the sphere is:
$$\Phi(r,\theta,\phi)=|E|\bigg(r-\frac{r_0^3}{r^2}\bigg)cos(\theta)$$
where the $\theta=0$ is aligned with the direction of E."
I under... |
I don't understand how a particle can exist with negative kinetic energy.
Consider this scenario:
Here, an electron is tunneling through a potential barrier (The total energy of the electron is less than the potential barrier).
So the math works out pretty well and we find that the wave function has a finite value on ... |
In the theory of quantum vibrations (aka phonons) it is useful to divide up the vibrational normal modes of a crystal based on their representation within the symmetry group of the crystal. The representations signify how the phonon will transform under symmetry operations like reflection, rotation, inversion, etc. Fo... |
In Heisenberg representation we have:
$$\frac{d}{dt}A_H(t)=\frac{1}{i\hbar}\left[A_H(t),H_H(t)\right]+\frac{\partial A_H(t)}{\partial t} \ \ \ \ \ \ \ (1)$$
where I use the subscript $H$ to make as explicit as possible that we are working in Heisenberg representation. If we apply $(1)$ to the position operator $\hat{q}... |
The Lagrange density $\mathcal{L}$ of a scalar field $\phi$ in curved spacetime is
$$\mathcal{L}=\sqrt{-g}(-\frac{1}{2} g^{\mu\nu}\nabla_\mu\phi\nabla_\nu\phi-\frac{1}{2}m^2\phi^2-\xi R\phi^2)\tag{9.87}$$
where $g$ is metric determinant, $\xi$ is a constant and $R$ is the curvature scalar, and the signature convention ... |
I am trying to calculate the tree level scattering cross section for Moeller scattering using QED.
I have got some traces which I cannot evaluate.
e.g.$$Tr(\gamma^\nu \not{p_2}\gamma^\mu \gamma_\nu \not{p_1\gamma_{\mu}}).$$
I am able to evaluate traces which don't contain any slashed momentum in between. I know I have ... |
Is there a mathematically rigorous definition of turbulent or laminar flow?
As far as I understand, laminar flow - means, that the velocity fields varies smoothly along the distance and time. Layers of fluid move smoothly along each other, without mixing. It doesn't have to potential, may containt vortices or other top... |
What is the beta function for quantum electrodynamics?
I can't find it anywhere except on Wikipedia article on beta functions, where the one-loop beta function is given by:
$$\beta(\alpha) = \frac{\alpha^2}{3\pi}$$
However, using the definition of the beta function
$$\beta(\alpha) = \frac{d\alpha}{d\ln(\mu)}$$
one gets... |
In looking at page 2 of these lecture notes:
\begin{align}
\langle p | X | \bar p \rangle
&= \iint \frac{1}{\sqrt{2 \pi \hbar}} \, e^{-i p \bar x / \hbar} \, X \, \delta(\bar x - \hat x) \frac{1}{\sqrt{2 \pi \hbar}} e^{i \hat x \bar p / \hbar} \, d \bar x \, d \hat x \\
&= \frac{1}{2 \pi i} \frac{d}{d \bar p} \iint e... |
When the next type of calculation was possibly used for the first time? If 50% i.e. upper half of Moon were bright would the Sun-Earth to Moon-Earth distances ratio be calculated from just astronomicaly measuring the angle a if e.g. angle a' is set to 35° and if the Sun and Moon are viewed from opposite directions?I ... |
In Bootstrap and Amplitudes: A Hike in the Landscape of Quantum Field Theory there are few statements about analytical structure of amplitudes.
I want to understand statement:
Tree amplitudes must be rational functions of Mandelstam
variables.
What is the reason for such a property of tree level amplitudes? What is ... |
Lets say we have an homogeneous anisotropic medium where $\tilde\mu_r=\tilde\epsilon_r$ so we don't have to worry about polarization effecting anything. As such, the refractive index can be simply described by the 3x3 tensor $\tilde n$. Lets treat $\tilde n$ as a metric tensor to make some math easier.
$$\begin{matrix}... |
I would like to understand why a Bourdon tube works, the working principle is described on wikipedia as:
The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. This change in cross-section may be hardly noticeable, involvi... |
Im looking into Quantum Computing, where the BCS Theory is used to build Qubits with a BEC.
Why does the Bose-Einstein Condensate not interact with other particles and hence has no dissipation?
In other words how does the BEC form a superconducting material. Why is there no dissipation for BEC's?
|
I am currently going through this answer related to the Big Bang theory and from there a question arose in my mind:
Can the universe ever contract?
Can it ever contract to singularity?
I wonder, if it is possible, how it would happen? Is there any chance at all?
I am unaware about the physical reality of this quest... |
Looking at this picture from Kleppner's mechanics text, Δa is added to $A$ and it is suggested that:
"This causes a change of direction but leaves the magnitude practically unaltered if $ΔA$ is small."
What is practically happening in this sense? When looking at it from a calculus perspective, this makes total sense... |
Basically, why we treat them as independent quantities. I know what a partial derivative is, It means if a function depends on multiple variables, the partial derivative with respect to a particular variable will show how the function is varying with that variable while other variables are constant.
Now, we know $x=f(t... |
The standard argument about the vanishing of the magnetic field outside an infinite solenoid pertains to the longitudinal component, parallel to the solenoid axis. But there must be a non-zero toroidal field. However tightly the solenoid is wound, there is a net current in the longitudinal direction. Thus, by Ampere's ... |
Using dimensional analysis, determine the dimensional form of Young’s modulus given that:
Young's Modulus E= stress/strain
Am I correct in thinking that this could be written as
[M][L]^-1[T]^-2?
I'm just a little confused on how I got there :)!
|
For a scattering process let $S$ the scattering operator and $P_0$ the energy operator of the system. We define R to be a constant of motion if
$[R,P_0] = 0$
and we define C to be a conserved quantity if
$[C,S] = 0$.
It is easy to see that there are constants of motion that are not conserved and the other way around, s... |
In quantum mechanics, there is a phenomenon called the 'Casimir effect'. As two metal plates have a very small distance, the plates work as a potential well, causing limited wave function between the plates while outside doesn't. As a result, two plates have a attraction force. (In some case it could be repulsive but t... |
Since the universe's entropy is going to increase indefinitely and it is going to be a continuous, does this mean that it will be equal to some power of pi or e or any other transcendental number?
|
In Quantum Mechanics - Concepts and Applications by Zettili, he states that an ideal blackbody can emit light across the entire spectrum. Why is this? In other words, what is the physical process that could cause this phenomena?
|
I'm looking for good papers on arXiv that tells the story of gravitational waves theoretical discovery and Einstein's (and others) doubts on their physical existence.
Of course, I searched the papers on arXiv, but only found these two:
J. L. Cervantes-Cota, S. Galindo-Uribarri and G. F. Smoot, "A Brief History of Grav... |
Consider the following quantum well:
Region 1 is a classically forbidden region, and hence the WKB wave-function will take the form of equation
$$\psi(x) = \frac{C}{\sqrt{q(x)}}e^{+\int_b^a q(x')dx'/\hbar} + \frac{D}{\sqrt{q(x)}}e^{-\int_b^a q(x')dx'/\hbar}. $$
Let us assume that there are no more classical
turning p... |
Problem 10.7 of the book "Problem Book in Relativity and Gravitation” by A. Lightman and R. H. Price reads:
If $\xi$ is a Killing vector, prove that $\xi_{\mu;\alpha\beta}=R_{\gamma\beta\alpha\mu}\xi^\gamma$.
The enclosed solution includes:
$0=\xi_{\sigma;\rho\mu}-\xi_{\sigma;\mu\rho}+\xi_{\mu;\sigma\rho}-\xi_{\mu;\r... |
Considering the following (magnetic field) hamiltonian: $\hat{H}=-\gamma B_z \hat{S}_z$ ($\gamma$ is a constant). Suppose an electron is in an eigenstate of $S_x$, and we ask ourselves the question whether the expected value of $S_z$ changes with time. This is not the case, as $[\hat{H}, \hat{S}_z]=0$.
Now suppose we a... |
I want to explore generalised Noether currents obtained from $q$-form symmetries in an action.
The regular way we obtain Noether currents is fairly straightforward: We have a 0-form symmetry $\phi \to \phi + \delta \phi$, and the action $S(\phi, \partial_\mu \phi)\to S(\phi + \delta \phi, \partial_\mu \phi + \partial_\... |
The Wikipedia article regarding the two-body problem in General Relativity states that the Schwarzschild metric "corresponds to the external gravitational field of a stationary, uncharged, non-rotating, spherically symmetric body of mass $M$".
My question is with regard to what reference frame does the mass $M$ have to... |
The von Neumann-Dirac Theory postulates that physical observables are represented by Hermitian operators. For example, let's assume the physical observable I am measuring is the spin of an electron, and my orthonormal basis is composed of the eigenvectors
$$ |\uparrow\rangle=\left(\begin{array}{c}
1 \\
0 \\
... |
Earnshaw's theorem states that there can be no stable equilibrium in an electrostatic field. Now consider an ion in a cubic lattice, eg, a sodium ion in NaCl. That ion is certainly in stable equilibrium, and it is acted on by the electrostatic field of all its neighbors. There must be something fundamentally quantum me... |
In the standard derivation of the Sackur-Tetrode equation, the accounting for the indistinguishability of ideal gas molecules adds an extra factor of $N!$ in the partition function. This is usually approximated by Stirling's approximation.
Let us assume that the volume of the box is very large so that the energy spacin... |
After a recent post and watching several videos about AC circuits my understanding is better, however there is something I’m not sure on.
Picture an AC circuit distributed to a household. I’m in the UK so let’s say 230 volts, with a frequency of 50hz.
Now, the neutral is grounded, meaning close to earth potential. Why ... |
I am thinking of purchasing Messiah's book. How relevant is the material discussed in it? Has anything in the book been proven wrong? If so, what book should I supplement it with, or should I even get it at all (not an opinion, based solely on what is outdated and what is not)?
|
Is there a single word to describe materials which both have a homogeneous and isotropic permittivity and permeability?
There are just too many "homogeneous and isotropic materials" and "homogeneous and non-isotropic materials" in my text. And it's the worst in headlines.
|
There is a particle moving within this inverted circular cone with an initial tangential velocity of $v$ at an initial height of $h$, and we see that the cone forms an angle of $\theta$ with the horizontal.
The problem is this: to find the final height of the object when it stops climbing up or sliding down the inclin... |
In Peskin & Schroeder, "An Introduction to Quantum Field theory", chapter 4, the author derives the 2 point correlation function:
$$\langle \Omega|P{\phi(x)\phi(y)}|\Omega \rangle = \lim_{T\rightarrow \infty(1-i\epsilon)} \frac{\langle 0|P \left [U(T,x^0)\phi_I(x)U(x^0,y^0)\phi_I(y)U(y^0,-T)\right ]|0\rangle}{\langle... |
Two important unimodular lattices are $E_8$ and the Leech lattice.
One can take 10D superstring theory and compactify it over the $E_8$ torus.
One can also take 26D bosonic string theory and compactify it over the Leech Latice $\Lambda_{24}$.
In both cases one ends up with a 2 dimensional theory.
(Due to the variou... |
Why is the component of contact force is not like contact force cos theta and contact force sin theta but here they have no trigonometric values like we normally make components for a force.Like F
contact
cosθ
F
c
o
n
t
a
c
t
cos
θ
and
F
contact
sinθ
F
c
o
n
t
a
c
t
sin
θ
.Since here we have normal force and frict... |
The normal force for the case of pushing a crate across a floor with an applied force $F_{app}$ at an angle $\theta$ above the horizontal is given by Newton's second law:
$$ \sigma F_y = 0 = n - mg + F_{app}\sin(\theta) $$
Thus:
$$ n = mg - F_{app}\sin(\theta) $$
If the angle of $F_{app}$ is below the horizontal, we ge... |
Imagine a bead, free to move along the length of a horizontal rod, pivoted at one end. The system is initially at rest, with the bead at some distance from the end. Now, a constant torque is applied to the rod. I want to find the equation of the motion of the bead.
My attempt: (The mass of the bead is $m$, and the mo... |
If we take a (lets imagine cylindrical) resistor in DC (steady state), we have that the electric field follows Ohm’s law:
$\mathbf J_f=\sigma \mathbf E$. where $\mathbf J_f$ is the free electron current density.
Since it is in steady state it also follows from the continuity equation that $\nabla \cdot \mathbf J_f=0$
... |
I've seen values online for the coefficient of kinetic friction for wood on wood (0.2) as well as glass on glass (0.4), but can't seem to find the value for wood on glass.
|
We are learning electrdynamics and maxwell eqation. I understand how this euation of divegence makes sense
$\nabla \cdot E = \partial_i E_i = 2\pi\rho$
is just
$\partial_x E_x + \partial_y E_y + \partial_z E_z = \rho$
I can see how repeated indices are just summed over, but for the equation (curl)
$\nabla \times \vec E... |
Current is defined as the rate of flow of charge through a point. Now say we've got a surface charge density $\sigma$ which moves around on a surface.
According to the above definition the current anywhere on the surface should be zero because the amount of charge flowing across a point is zero since a point has no are... |
If we have a cubic container and then put in there some quantity of hydrogen molecules (10$^{22}$ molecules) an then all of them collide at the same time with a rigid wall of the cube, if them collide at 90° in one case an 45° in another, in which case the molecules transfer more quantity of linear momentum?
|
Lagrangian for $d=1$ $\mathcal{N}=4$ SUSY model on a $n$-complex dimensional Kahlerian target space is given as (see p.213, eqn. (10.251) in the Mirror Symmetry book (pdf))
$$\begin{equation}
L= g_{i\bar{j}} \dot{\phi}^i \dot{\bar{\phi}}^{\bar{j}} + i g_{i\bar{j}} \bar{\psi}^{\bar{j}} D_t \psi^i + ig_{i\bar{j}} \ba... |
My textbook states that:
...The capacitance $C$ depends only on the geometrical configuration (shape, size, separation)of the system of two conductors. [As we shall see, later, it also depends on the nature of the insulator (dielectric) separating the two conductors.]...
Now I wanted to know if these were the only tw... |
On page-274 Kleppner and Kolenkow, An introduction to classical mechanics, it is said that we can apply the rotational work-energy theorem and translational work-energy theorem separately in many problems.
However, how do you decide if on a given problem that if it can be applied separately or not? I came across some p... |
In Continuous-Variable quantum information, a general Gaussian measurement is described by the POVM elements (say on a single mode for simplicity)
$$ \Pi(\alpha) = \frac{1}{\pi} D(\alpha) \Pi^0 D^{\dagger}(\alpha)$$
where $D(\alpha)$ is the displacement operator and $\Pi^0$ is any (generally mixed) density matrix of a ... |
I am faced with the following problem:
A cylinder containing $n_{0} = 4$ moles of ideal monoatomic gas, at temperature $T_{0} = 280\ \mathrm{K}$ and pressure $p_{0} = 150\ \mathrm{kPa}$, is equipped with a safety valve that causes the gas to escape into the surrounding atmosphere when the internal pressure exceeds $p_{... |
The figure shows the tungsten filament with a constant diameter except for a piece of it which has half of the diameter as the rest of the wire. Assume the temperature is constant within each part and changes suddenly between the parts. If the temperature of the thick part is 2000K, the temperature of the thin part of... |
An object in free-fall drops from rest. The origin is at the starting point and the $y$-axis points downwards. The $y$-coordinate of the ball is,
$$ y = \frac{1}{2} g t^2$$
The total time of flight is $6$ $seconds$.
Question: What is the probability that the object is in between $y = \frac{1}{2} g$ and
$y = 2 g$ metres... |
I am a CG artist working on a specific shoot, that I have no clear answer to how it would look. And I seek your help. :D
The idea for the shoot is a flyby of two Interstellar Vessels named ITV Europa and ITV Lea Sudux.
Europa is flying back to Earth while Sudux blast to where Europa is coming from. Thus I figured that ... |
I was told in my physics class that the force does not change between the two plates but wouldnt the electric field not change between them bc it gets divided by the dielectric constant?Hence the force should change as well. Why this does not happen?
|
I am studying this classical paper by Regge and Wheeler Stability of a Schwarzschild singularity.
In the second page they introduce their formalism with spherical harmonics and generalization thereof. In particular in eqns. (7) and (8), they introduce vector spherical harmonics, with the definitions:
$$\psi^M_{L,\mu}\p... |
Let us say we have the two bosonic annihilation operators $a$ and $b$ with $[a,b^\dagger]=[a,b] =0$. Does a unitary transformation with
\begin{equation}
a = UbU^\dagger
\end{equation}
exist? And what is its explicit representation?
|
A free, non-relativistic wave packet of a quantum particle is usually thought of as having spherical shape. What happens for a particle moving relativistically? For an outside observer, is the wave packet oblate (flattened in the direction of motion) or prolate (elongated in the direction of motion)?
In a few words: is... |
Suppose a rod with length $L$ moving toward a hole whose radius is $L$. The paradox is, from the ground frame, the length of the rod is contracted hence rod will fall into the hole. However, from the rod's frame, it is the length of the hole contracted, so the rod will not fall. Now, ask to find the vertical motion of ... |
This question is related to this other one in math.SE. I'm having troubles studying the "macroscopic" case for a magnetic potential vector and verifying what the Maxwell's equations yields.
Particularly I have
$$\vec{f} =\vec{\nabla} \times \vec{\nabla} \times \langle \vec{A}_M (\vec{x}) \rangle$$
where
$$ \langle \vec... |
When we study a relativistic point particle (say, at the beginning of a string theory course), we looked at einbeins, and that's because they were equivalent to the action $\int d\tau\sqrt{\eta_{\mu\nu}\dot{x}^\nu\dot{x}^\nu}$ then the einbein action worked. However why doesn't the action $\int d\tau ~\eta_{\mu\nu}\do... |
I would like to know if a small electric current can be created in a closed loop of wire by using a strong electric field to move the free electrons within the closed loop of wire.
To create this strong electric field, a high voltage DC power supply could be used, one that say generates 100 kV. The power supply's two e... |
I was told that diffraction through a slit occurs as follows-
When the 'point sources' of the planar wavefront at the location of the slit emit secondary wavelets we find bright and dark spots at unusual locations(which is according to Huygens' Principle).
Naturally, this effect will be greater when the wavefront is la... |
A proton of mass $m$ collides elastically with a particle of unknown mass at rest. After the collision the proton and the unknown particle are seen moving at an angle of $90^o$ with respect to each other. What is the mass of unknown particle in terms of the mass of proton?
|
Question: Let $\{\vert\psi_1\rangle, \vert\psi_2\rangle \}$ be an orthonormal basis. Define Hamiltonian $\hat{H} = \alpha \left( \vert\psi_1\rangle \langle\psi_2\vert + \vert\psi_2\rangle\langle\psi_1\vert \right)$ for some real, positive $\alpha$. Find the eigenvalues and eigenkets $\{ \vert E_1 \rangle, \vert E_2\ran... |
After a lot of brainstorming, We haven't quite been able to figure out the relation between torque and direction in the picture below:
We have two connecting rods between a wheel and an axle (B). These are are hinged in the point C.
Rotating the wheel 180 degrees by axle A either CW or CCW, how are the forces transfer... |
I have some questions about normal ordering in quantum field theory: I already read this very good question with very very good answers and this other question with other very good answers (I read also this one and many others, but without understanding much).
For what I understood, normal ordering is more a simbolic o... |
So I’ve been reading about the many worlds interpretation of quantum mechanics, and I keep seeing that they say that all worlds would come about. In repeatedly seeing the notion of all options, I wondered, could you have seemingly absurd outcomes where things like life history had this elaborate design in it. Just to c... |
I am trying to understand Lemma 16 of this paper, "Exponential Decay of Correlations Implies Area Law", and I'm getting stuck on the recursion step. The essential bit is going from Equation (B9) to Equation (B10). I don't see how we can keep on doing recursion to smaller and smaller regions until we get to the size $l_... |
While reading about the Bohr model I noticed the following equation:
$$
{m_\mathrm{e} v^2\over r} = {Zk q_e^2 \over r^2}
$$
Is it possible to explain which formula they used? How from the speed and radius they got an equation depending $Z$ (the number of protons)?
I understand that $F=ma$ and then $\frac{kq_e^2}{r^2}=... |
I will premise this question with the fact that I am trained in mathematics and not physics.
Right now I am reading Chapter 1 of the book Optical Radiation Detectors about radiation noise in blackbody sources. The author's state:
The Bose-Einstein expression for the probability that the total photon energy at a specif... |
--Unsure if this is a question for Physics or for language/English stackexchange, asking this in Physics as I assume more people here are familiar with these notions in scientific talk--
I have a 2D figure (labeled 'Figure 1') that represents the discrete values of the Electric field E (on the ordinate) at different po... |
In Jackson Electrodynamics, chapter 3.
We saw that for an azimuth symmetry, we have,
$$
\Phi(r, \theta) = \sum_{l=0}^{+\infty} \left(A_l r^l + B_l r^{-(l+1)} \right) P_l \cos(\theta)
$$
Then in the books, it says that the potential in $\vec{x}$ due to a charge in $\vec{x}'$ is given by
$$
\frac{1}{|\vec{x}-\vec{x}'|}... |
What is happening at atomic Level between two bodies when there is friction force acting between them?
|
I read recently about neutrino pair exchange. What is neutrino pair exchange? Can this exchange induce forces stronger than electromagnetic forces between electrons which in turn form attractive electronic bodies?
Could someone here please explain for me? Thank you.
|
The Casimir effect causes a limited number of wave functions, causing fewer particles between plates than outside and this could be considered as a negative mass. Then, if we have a technology good enough so that the total energy of the system is negative, will the system have acceleration towards the opposite directio... |
Considering the Weyl connection $\Gamma^{\lambda}_{\mu\nu}$ in a torsion-free space, defined by the covariant derivative of the metric tensor and a vector field $A_{\lambda}$:
$D_{\lambda}g_{\mu\nu}=A_{\lambda}g_{\mu\nu}$
How can I find the explicit expression for this connection?
|
wrt: https://www.youtube.com/watch?v=xfxEPjyIaZM&ab_channel=KhanAcademyIndia-English
$\tau$ is Relaxation Time (time between 2 successive collisions)
The video shows derivation of drift velocity of an electron as:
$$V= \frac{\sum (u + at)}{N}$$
where $V$ is drift velocity of an electron , $a$ is acceleration caused by ... |
Einstein told us that a spring balance under free fall shows zero deflection and thus derived that gravity is a curvature in the fabric of spacetime and all those stuffs.
Now let's assume we have a spring balance in gravity-free space (though there is a gravitational force between me and the balance) as shown below. I... |
The basic physics concept I hope almost every one might be aware of i.e "water tend to expand instead of freezing just below and above 4 degree celsius".
My question is why exactly at 4 degrees this phenomenon occur? Why not at some other temperature also what makes it to behave that way?.
Any explanation for the reaso... |
Context: The atmosphere of Venus wasn't always as warm as now: a few hundred million years ago it was much more habitable. I am interested in how fast the interior of the planet warmed up, after it's climate changed.
Model:
Venus is a uniform sphere with some heat conductivity $\alpha$, temperature distribution $f(r)$ ... |
According to General Relativity I am being accelerated upwards by planet earth while writing this question. But a curious person on the the other side of the planet relative to me would have the same experience. That means we are accelerated in opposite directions, although earths diameter do not seem to increase. How ... |
Suppose we define a temperature field that varies as a function over space.. now, the steady-state is the state where the temporal variations of this function are zero, that is the function only varies as we move across space.
So, once we are in steady-state there is a 'set' spatial distribution of temperature. My ques... |
the photoelectric effect was explained by Einstein as $$\frac12mv^2=\hbar\omega - W$$ where $W$ is the binding energy of the atom that the electron is in, and $\hbar\omega$ is the energy of the photon that strikes said electron. I know that in order for the electron to leave its atom, $\hbar\omega>W$ and if $\hbar\omeg... |
Pluto is locked in 3:2 resonance with Neptune, so that means that it should be possible to generate a simple looping animation that shows what movements Pluto would make given 2 orbits of Neptune.
I can find some animations of Pluto's orbit, but none that show Neptune locked in Position
Wikipedia has a similar animatio... |
In Bootstrap and Amplitudes: A Hike in the Landscape of Quantum Field Theory there are few statements about analytical structure of amplitudes.
I want to understand statement:
In a local theory of massless scalars, they can have simple poles and the residue of such a pole is, by
unitarity, a product of lower-point am... |
It is known that gravity is not a force, but a bending of 4D spacetime. Could charge (as well as mass) have an analog in this regard? Why does mass bend spacetime but charge does not?
Sorry for the blue-sky question.
Thank you
|
Hi i'm not clever enough to think outside of my finite existence. Can someone explain the bounds of my logical thinking that infinity is a paradox like the question: "are you lying?". Is my understanding of multiverse even correct?
|
I was always taught that classically all electromagnetic phenomena are encapsulated in the Maxwell equations and the Lorentz force formula for point charges:
$$ \vec{F} = q\left(\vec{E}+\vec{v} \times \vec{B}\right)$$
but according to this equation the magnetic field doesn't do any work. So I have two seeming contradic... |
I have been trying to solve the heat equation for a uniform sphere. My setup: sphere has an initial temperature distribution, and the surface is kept at constant temperature. I am interested in how the temperature changes within the sphere over time. The below video is the visualisation of my results.
https://www.youtu... |
Suppose there's a clock on a spaceship and a clock on earth. The spaceship is moving toward earth at a constant relativistic velocity, and both clocks start simultaneously from the reference frame of earth. The spaceship passes the earth after a certain time. From the reference frame of the ship, how long ago did the e... |
Given a combination of metals or metals combined with one or more other elements, how do you calculate the theoretical work function of the alloy?
|
Every subatomic particle which interact with the 3 quantum interactions has a cloud of virtual particles.
How big is that cloud and where is its density bigger?
|
My question
Why can't effects propagate backwards in time, within the backwards light cone of a cause? For example, when I turn on a flashlight, why doesn't the light travel backwards in time just like it does forwards in time? I don't see why this is prohibited by the laws of physics.
I have a feeling this question ac... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.