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I am dealing with an exercise about the ${\rm SU}(N)$ group. I have shown that the structure constants are given by
I am now asked to show that the following Jacobi identity is true:
The first thing I did was simply plugging them into the Jacobi Identity, but at some point I get stuck and have the feeling that it w... |
I can't quite wrap my head around Ohm's law. The relationship itself is quite intuitive to me. What I don't understand is when a system has dynamic voltages, currents, and resistances. I don't quite understand which variables are dependent and which are independent. For example, one could take multiple 9V batteries, co... |
Hi guys! One quick note before diving into the question. When you are answering this question please consider me as a layman and be as thorough as possible.
So, I have 2 cylinders; the smaller one rotating, without slipping, inside the larger one. I need to calculate the period of oscillation of the small cylinder. Th... |
Does the Ryu-Takayanagi conjecture only apply to vacua, or does it also apply to arbitrary excited states?
For excited CFT states, the entanglement entropy can be proportional to the volume, not surface area, or it can even be arbitrarily large.
|
I was studying surface tension the other day and this thought came to my mind.
What would happen if say a liquid like mercury which has higher cohesive forces than adhesive ones(hence the convex meniscus) and another like water, which has higher adhesive forces than cohesive ones (hence the concave meniscus) were mixed... |
I am currently studying Optics, fifth edition, by Hecht. In chapter 2.9 Spherical Waves, the author says the following:
$$\dfrac{\partial^2}{\partial{r}^2}(r \psi) = \dfrac{1}{v^2} \dfrac{\partial^2}{\partial{t}^2} (r \psi) \tag{2.71}$$
Notice that this expression is now just the one-dimensional differential wave equa... |
I am trying to understand why, in cosmology, it is said that the presence of fluctuations at scales above the Hubble distance would not be expected in the absence of inflation or something like it.
We treat density fluctuations using the density contrast $\delta = (\rho - \bar{\rho})/\bar{\rho}$ and then we Fourier ana... |
Suppose a body is moving with a constant velocity of 5 m/s in positive x direction.
Now after some time it changes it's direction from +x to +y keeping the magnitude same.
And it keep doing that motion i.e changing it's direction from +x to +y
Now how can i represent this motion graphically in a $v_{net}$-t graph.
The ... |
According to https://en.wikipedia.org/wiki/Up_quark the up quark can decay into a down quark plus a positron plus an electron neutrino. The problem is that the mass of the by-products is greater than the original particle. This would violate conservation of mass/energy unless some source of energy or mass was put int... |
Broadly speaking, what is actually being done when one analytically continues the external particles' momenta in scattering amplitudes in QFT?
Some associated more detailed questions:
When thinking of the quantum fields that go into the Green's functions that give the $S$-matrix by LSZ, these fields transform in the ir... |
The decay of $B \to J/\psi K_{S,L} $ is often referenced as "golden plate decay", for example in
If there is a B-decay into a CP-eigenstate, like the golden plate decay $B \to J/\psi K_{S,L} $, let [...]
(source: https://www.sciencedirect.com/science/article/pii/S0370269303017258)
Where does this expression come from... |
I thought about gravitational field. In Newtonian mechanics, gravitational energy between two matter is $U=-G\frac{M_1 M_2}{R^2}$ when mass of each matter is M1 and M2, having a distance R. With this equation, I was able to obtain the energy density of the gravitational field. But since Newtonian mechanics are good app... |
Lets start by considering the electromagnetic tensor $F^{\mu \nu}$:
$$F^{\mu \nu}=\begin{bmatrix}0 & -E_x/c & -E_y/c & -E_z/c \\ E_x/c & 0 & -B_z & B_y \\ E_y/c & B_z & 0 & -B_x \\ E_z/c & -B_y & B_x & 0\end{bmatrix}$$
And now consider Maxwell's equation:
$$\nabla \cdot \vec{E}=\frac{\rho}{\varepsilon _0}$$
$$\nabla \c... |
Something like an electron would act like a particle upon observation because the high energy light waves interfere with it. But what about Qubits? Why do they collapse into one state? And when do they collapse into one state, is it when they are rendered onto the screen? But why would that be the case bits/qubits are ... |
As particles gets toward each other, the potential energy decreases and kinetic energy increases. So that the net energy will be conserved. As a result, "black hole with mass $M$" and "system with same mass $M$ but nearly zero potential energy due to its large distance between particles", will have different net energy... |
Consider the situation when a ball hits a plane surface at an angle of incidence $\theta$ with speed $u$ and rebounds with the same angle. One can notice that there is a change in momentum in this scenario but I can't seem to find out what is the external force here? The ball exerts a force on the surface and by Newton... |
I would like to compute the partition function Z for the quadrupole moment, but it is not as easy as the one for the dipole. Could anyone help please?
|
The Poynting vector is defined as $\vec{S}=c^2\epsilon_0 \vec{E}\wedge \vec{B}$ in vacuum. Can we replace $\epsilon_0$ by $\epsilon$ when we consider dielectric ?
|
I am currently studying Optics, fifth edition, by Hecht. In chapter 2.9 Spherical Waves, the author says the following:
$$\dfrac{\partial^2}{\partial{r}^2}(r \psi) = \dfrac{1}{v^2} \dfrac{\partial^2}{\partial{t}^2} (r \psi) \tag{2.71}$$
Notice that this expression is now just the one-dimensional differential wave equa... |
I am currently studying the conformal group, i.e the 15-dimensional group that is associated with the conformal symmetry of spacetime.
Before working on that group, I've work on the Poincaré Lie group. I've seen, for example, how, by requiring that the universe respects the Poincaré invariance, we obtain the irreductib... |
I am quite familiar with the position and momentum operators and expectation value or simply the average position or momentum
But sometimes experiments may require the mode too. But that is only possible after plotting the $|\psi(x)|^2$ on a graph. Is there any operator that can help us to find mode position or momentu... |
as you know, the ideal black-body has a lot of interesting properties. The most important of these is surely the Planck Law about its radiation:
Clearly the concept of black body does not exist perfectly in nature, but there are some objects that may approximate it. So we may say that a real non-ideal black body has a... |
Can it be shown that an angular momentum eigenstate $ | j, 0 \rangle $ with even $j$ is invariant to 180 degree rotations about the y axis (or any axis $\bot$ z)?
I was able to do this using properties of the Wigner D matrices but it seemed excessively complicated and lacking in physical insight. Intuition is telling m... |
I'm not a physicist, I don't know if this will make a lot of sense, so bear with me.
I'm just reading about how particles like the photon, electron, graviton, etc are each associated with their own fields. The gravity field can have a dent in it like the one caused by a massive body or waves traveling through it, gravi... |
On optical energy loss function, it is said that we don't see the surface plasmon. However, we can see the plasmon peaks on reflection electron energy loss spectroscopy.
My question is that why electrons can excite the surface plasmon on flat surface but photons cannot (at least we dont see it on ELF). The photon/elect... |
In constructing the total angular momentum operator, that is the sum of 4 independent angular momentum operators:
$$J=J_1+J_2+J_3+J_4 $$
one has the following set of commuting operators and eigenvectors in case of the uncoupled configuration:
$$ {\textbf{J}_1^2,J_{1z},\textbf{J}_2^2,J_{2z},\textbf{J}_3^2,J_{3z},\textbf... |
I recently started to study flight dynamics and I have to derive the equations of motion of a plane from the Hamilton's Principle. To better understand this principle, it is needed to have some knowledge in Variational Principle and that's a little confusing for me, especially when applied to vectors.
For example, here... |
Let's think that there is a black hole with mass $M$ and matter with mass $m$. Two objects have distance $R$. What is the gravitational potential energy between the black hole and the mass? How can I obtain the value?
For the convenience of calculation, few suggestions are followed.
The black hole is a Schwarzschild b... |
I see a lot of SUV's that has the structure as shown in the picture .I am talking about the the top back edge (right above the back window).
Wont't it worsen the streamlined design and causing more drag?
What's the benefit of this structure?
|
My question is two-part. First, imagine a bipartite quantum state $|\Phi \rangle_{AB}$, made of $2n$-qubits, shared between Alice and Bob (with $n$-qubits each). Alice performs some unitary operation $U$ on her part of the state and then performs $Z$-basis measurements. As a result, Bob's state collapses to a mixed sup... |
Fidelity is measure of distance between density operators. it is a measure of the "closeness" of two quantum states, the input state $\rho_{in}$ and the teleported state $\rho_{out}$.
where it's generally defined as :
$ F(\rho_{in} , \rho_{out})$= ${ [tr(\sqrt{\sqrt{\rho_{in}} \rho_{out} \sqrt{\rho_{in}}}]^2} $,
for $ ... |
In the following question, the capacitor $C_2$ is is initially charged to a potential difference to $2\epsilon$, when the switch was open. The solution to the problem takes the rate of change of charge on both capacitors to be equal when the switch is closed.
How can you be certain of this? Wouldn't there be two curre... |
We all know the classical four-dimensions used to locate objects in space: Length, width, height and time. It occurred to me that electric field acts also like a kind of dimension does it not? Every point in space corresponds to a vector with a certain magnitude and direction.
|
Suppose we are given the Hamiltonian
$$\hat H = \hat H_0 + \hat H_p(\varepsilon) = \frac 1 {2m}(\hat p_1^2 + \hat p_2^2) +\frac 1 2 m \omega^2(\hat x_1^2 + \hat x_2^2) + \varepsilon m\omega^2\hat x_1\hat x_2 $$
and, after switching to CM coordinates,
$$
\begin{split}
\hat X= \frac {\hat x_1 + \hat x_2}{2}, &\qquad \hat... |
Recently I chewed the fat with a physics student and got intrigued by him mentioning "the Devil's problem," which he described as a simply worded mechanics problem that is extremely difficult to solve and has an answer of exactly 13 despite the formulation having no numbers and being very natural. That's kinda crazy, s... |
In order to solve this problem, I tried assigning a variable to the masses of the four sections of the meterstick and the constant, 1 kg, to the rock
rock = 1 kg, 1/4 of stick = x
From here I thought the mass of the meter stick was 4x.
Turning the problem into an equation, I got: 1kg + x = 3x.
Isolating x, I got 1kg= ... |
If one twin is on earth at 1 g and the other twin accelerates away from earth following a great big elliptical counterclockwise trajectory. He travels at .9 g for 20 years(according to earth time) as well as some small amount of left acceleration (.44 g since $\sqrt{0.9^2+0.44^2}=1$) to make the first semicircle . He t... |
Things tend to be more classical the bigger they are, so I guess the area where the Drude model (the one that explains resistivity with classical scattering) would work best is when the charge carriers are big. One example of that is ionic compounds dissolved in liquids. There, the charge carriers are whole atoms, plu... |
So I've heard two different explanations of the uncertainty principle, both of which make sense on their own, but I'm having a hard time figuring out how they're connected. The first is that the uncertainty principle is really a statistical principle. Basically, we can measure the position of a particle any individua... |
Say I have a large mirror and in front of the mirror, there is an object and I'm standing at a different position in front the mirror. At what position should I look in the mirror so that I can see the object in the mirror?
For example: If I stand at the point $(2,6)$ and object is at $(4,9)$ and the mirror is on the x... |
Can the attractive property of gravity be explained using lines of force?
Or is it only possible to explain it through the quantum field theory?
I am doubtful because the lines of force of two bodies of positive mass are similar to the lines of force of two positive charges. Do they repel like the charges?
|
I have seen the equation for de Broglie wavelength derived through equating Einstein's $E=mc^{2}$, and Planck's $E=hf$, using a substitution from $c=f\lambda$ to make things in terms of wavelength. From this the following result is derived:
$$ \lambda = \frac{h}{mc} $$
This makes sense to me under the assumption that s... |
I am currently studying Optics, fifth edition, by Hecht. In chapter 2.9 Spherical Waves, the author says the following:
The outgoing spherical wave emanating from a point source and the incoming wave converging to a point are idealizations. In actuality, light can only approximate spherical waves, as it can only appro... |
The way I understand the uncertainty principle is that it's not even really about quantum mechanics specifically -- it's just a property of waves. e.g. A periodic wave doesn't even have a well defined position, so in order for wave-function to have a well-defined position, we have to represent it as the superposition ... |
I am having a conceptual problem. I understand why the definition of the velocity of a body moving in one dimension is the derivate of its position coordinate. But I don't get why the velocity vector is defined as the derivative of the position vector. Is it that the derivative of a position vector was just found to be... |
I have some trouble understanding what happens to the phase of a BEC when some particles are removed. The motivation of the question is the experiment of observing interference between two BECs. In my current picture, a BEC is a state $\Phi(r)e^{i\varphi}$, where $\Phi(r)$ is the N-fold tensorproduct of the single part... |
im having difficulty understanding the criteria of signs settled down by BSL transport phenomena in the derivation of Stokes law in chapter 2
at the page 59 it takes the molecular momentum-flux tensor negative when integrating the normal force on the solid of the sphere
but at page 60 when the book makes the integratio... |
Consider the resistive force modelled by the function $\vec{F} = -b\vec{v}(t)$.
The curl of this function, $\nabla \times \vec{F}$, is
$$[\frac{\partial}{\partial y} (\frac{dz}{dt}) - \frac{\partial}{\partial z} (\frac{dy}{dt})] \hat{i} \ + \ ...$$
I wrote the $x$-component only because it is too time-consuming to wri... |
Suppose that a particle is in uniform circular motion and the magnitude of the centripetal component of the net force increases. Does this increase the tangential speed or decrease the radius of the circular path?
One case that comes to mind is moving a ball attached to a string, moving in a circle. In that case, the r... |
I am reading a book titled "Relativity Demystified --- A self-teaching guide by David McMahon".
He explains the derivation of electromagnetic wave equation.
$$
\nabla^2 \, \begin{cases}\vec{E}\\\vec{B}\end{cases} =\mu_0\epsilon_0\,\frac{\partial^2}{\partial t^2}\,\begin{cases}\vec{E}\\\vec{B}\end{cases}
$$
He then comp... |
In Harvey Reall's Black Holes lecture notes, he defines static spacetimes as follows
A spacetime is said to be static if it admits a hypersurface-orthogonal timelike Killing vector field.
I am not sure why this would not be true for a stationary rotating spacetime. Assume for instance that we had a 2+1 dimensions spa... |
If one has a gauge theory with a specific symmetry group and we add to it a scalar field with a non-zero VEV, how do we know in general to which symmetry group will the original symmetry be spontaneously broken?
|
Since $ds=\frac{dq_{rev}}{T}$ for reversible processes it seems we can have reversible isentropic processes that are not adiabatic provided the temperature changes in such way that the sum of $\frac{dq}{T}$ is zero but the sum of $dq$ itself is not zero. Is this possible? What are some example of such a process used/fo... |
In his General Relativity notes, on page 149, David Tong remarks that when we look for solutions to Einstein's equations, we can't just take any metric, such as $g_{\mu \nu} = 0$; we must pick one such that $\det g_{\mu \nu} < 0$ (with Minkowski signature). He writes further on this:
Other fields in the Standard Model... |
I've already got the electric fields and magnetic fields derived from the Lienard-Wiechert potentials:
$${\bf E}=\frac{q}{4\pi\epsilon_0}\frac{R}{(\bf R\cdot u)^3}[(c^2-v^2){\bf u}+\bf
R\times(u\times a)]$$
$${\bf B}=\frac{\bf R}{cR}\times\bf E$$
where ${\bf R=r-r'}$ and ${\bf u}=\frac{c\bf R}{R}-\bf v$.
I wonder if ... |
I want to define the dynamics of a system to follow a specific trajectory in the state space indicated by a point cloud/previous measurements/observations that lie on a manifold, given some initial and final points.
Let us consider a simple example:
In the following figure, i have noisy measurements from an oscillating... |
Based on my previous question here, lets us step back a little bit.
The speed of light $c=1/\sqrt{\mu_0\epsilon_0}$ is assumed as a value that does not depend on the observer because it is just a product of two constants.
I am still wondering why Maxwell assumed that $\mu_0$ and $\epsilon_0$ are constant that do not de... |
I would like to calibrate a low-temperature Hall effect measurement using a Fe SRM.
Are there any standardized Hall measurements of SRM's available?
|
Assume that a point electrical charge is at rest WRT an observer inside a uniform gravitational field. Using Einstein's equivalence principle (EEP), this scenario is equivalent to an electrical charge located in a uniformly accelerating shuttle. However, it is evident for an inertial observer outside the shuttle that t... |
Given the Boltzmann equation:
$$\frac{\partial}{\partial t} f_s (p,t) -H p \frac{\partial}{\partial p} f_s (p,t) \\
= \sum_i \int \Gamma_i (p'_\alpha ,p) f_\alpha (p'_\alpha , t) [ 1-f_s (p,t)]d^3 p'_\alpha -
\int \Gamma_i (p'_\alpha ,p) f_s (p , t) [ 1-f_\alpha (p'_\alpha,t)]d^3 p'_\alpha$$
Where I am told th... |
I was thinking today about configurations where one measures that a certain observable is not in a certain state.
I was getting confused about what this means for decoherence.
If I observe a detector and I measure when a particle does not interact with it, then, I don’t understand how this can be entirely equivalent to... |
I have a nanoribbon (NR) which is constructed of $N$ 1D chains. The Hamiltonian is written as the following:(for only N=3)
$$
H=
\begin{bmatrix}
H_0&H_{12}&0\\
H_{21}&H_0&H_{23}\\
0&H_{32}&H_0
\end{bmatrix}
$$
here $H_0$ is the bulk Hamiltonian and $H_{ij}$ is representing hopping between $i$ and $j$ chains. I have cal... |
If we consider a particle to be point-like, wouldn't it produce a Schwarzschild spacetime in it's vicinity?
What does spacetime look-like in the vicinity of point particles? What experiments have been done in regards to detailing spacetime geometry in the vicinity of point particles?
|
To explain my question, I wish to use the case as shown above. I am able to solve the numerical based on the above and similar cases, but still, I have a conceptual doubt regarding the workings of an Inductor.
Suppose in the case above, the battery is connected for a very long time and a steady-state is reached in the... |
I am wondering if it is possible for a massless boson to change the particle interacting with it, into another type of particle. In other words, is it possible to have a pair production process (in S channel) similar to the diagram below:
where $\gamma’$ is a massless guage boson similar to photon, and $\chi$ and $\ps... |
Consider a semi circular ring with radius R and charge Q distributed uniformly on the ring boundary and now, -Q charge is introduced at the centre ( q=Q)
Now what I did was I split the ring up into many small segments of length 'dl' having charge 'dq' and I paired that up with -Q charge in middle and found resulting... |
Black holes are formed when energy is put in a small region of space, I was wondering if there is a threshold to how much energy should I add in a certain volume of space to get a black hole, I read about the Schwarzschild radius formula that tells us the radius of event horizon of black hole formed by a star of mass $... |
The two Lorentz invariants are $\mathbf{E}^2-\mathbf{B}^2$ and $2\mathbf{E}\cdot \mathbf{B}$.
It is common in the literature to construct a complex vector:
$$
\mathbf{F}=\mathbf{E}+i\mathbf{B}
$$
whose square produces the Lorentz invariants:
$$
\mathbf{F}^2=\mathbf{E}^2-\mathbf{B}^2+2i\mathbf{E}\cdot\mathbf{B}
$$
Since... |
I am reading the papers about black hole in $AdS_2$, which can be regarded as a solution in JT gravity. More concretely I am reading this paper https://arxiv.org/abs/1908.08523 "Jackiw-Teitelboim model coupled to conformal matter
in the semi-classical limit" by Moitra et.al. In conformal gauge the solution of JT gravit... |
I am currently exploring the mathematical structure of Quantum Mechanics on an introductory level. A couple of books and online sources (including this website) stated how the Uncertainty Principle is a consequence of two non-commuting operators like position-momentum or the spin operators. But in some books including ... |
I am reading Decoherence and the Quantum-To-Classical Transition, which describes the experiment of investigating the dynamic of decoherence by making interference of fullerene molecules. Such experiment is described in this paper and is based on Talbot-Lau effect.
The principle of Talbot-Lau effect is that if you send... |
I'm trying to understand intuitively why the peak reflected light from a thin-film decreases in wavelength with increasing angles. To me, it seems it should be the opposite. I know the peak reflectance is given by the equation $2nd\cos(\beta)=(m-1/2)\lambda$, where beta is the angle of the refracted ray in the film. In... |
We know that the lowering and raising operators in quantum mechanics are defined as
\begin{array}{l}
a =\frac{1}{\sqrt{2}}(X+i P) \\
a^{\dagger} =\frac{1}{\sqrt{2}}(X-i P),
\end{array}
respectively.
I was reading in this book page 257 about the different quantization schemes and he mentioned that the Wick-ordered quant... |
How can I determine the concentration of dust? Let's say it's for general forest residue chips (biofuel). Perhaps the question is vague, but I am not sure. I am still new to the site, so I am not sure if this is an appropriate tag, at least it's close to what I am working with. I have the most data I need, but I could... |
Consider the ${\rm 2D}$ isotropic oscillator. The hamiltonian is $$H=\frac{1}{2}(p_x^2+p_y^2+x^2+y^2)$$ and the phase space is $4$ dimensional. In this case, the set of all linear canonical transformations that preserve the form of Hamilton's equations form a group ${\rm Sp}(4,{\rm R})$. On the other hand, the group of... |
I'm currently working on a project on my own where I'm interested in finding information about an object based on a spectrum. Namely, I want to use the spectrum that I input into my program to be able to analyze what atoms are present in the analyzed object. (I know this is probably hard but it's a fun project). Howeve... |
I'm not sure where else to ask this question but I thought this might be sort of a relevant place. It's a question that's bothering me for a long long time.
I'm staying in an apartment where there's a large penthouse above our flat occupied by one of the builder-partners of the apartment. In fact, the penthouse in ques... |
Suppose I have the ground state $\psi$ of some Hamiltonian $H$ and I want to get energy eigenvalue of $\psi$ without doing $H \psi = E \psi$.
De Broglie’s formula $$
E = \hbar \omega,
$$says I can get $E$ provided I know $\omega$. How do I calculate this $\omega$ in that case? I imagine the Fourier transform would give... |
The Rutherford experiment proved that the Thomson model was incorrect and the Rutherford model was the right one, this because the $\alpha$ particles were deflected by the nucleus and in the Thomson model this was not possible. The question is: since in the Thomson model we have the electrons, which have negative charg... |
Usually, when I'm thinking about a quantum measurement, I see a sort of particle that is being hit by a photon. The more energy the photon carries, the more the momentum of the particle is disturbed, but at the same time the more precise is the measurement of the particle's position.
But recently, I was thinking about ... |
Displayed is the context
My question is, why doesn't the electric field from the electrons permeate throughout the cold plasma?
Surely there will be flux on the RHS of the boundary as there is an unbalanced amount of electric charge inside the region?
|
I'm sure how fast a particle moves must have some relativistic effect, or maybe also classical ones too. Suppose you fixed the positions of two charged particles. Suppose you're in a lab frame and in a paradoxical but analytically useful way, you fix the position of a particle but change its velocity towards or away fr... |
There is a difficulty with the pressure of the Einstein crystal model. The model does not include any simple way to evaluate the derivative in Eq. (28.2-7e). We might try to
evaluate the pressure by finding the difference between G and A, since G = A + PV .
For a one-component system, G is given Eq. (26.1-29) as
\begi... |
This question is primarily mathematical in nature. I have been reading Quantum Field Theory for the Gifted Amateur and I am reading about Feynman’s path integral approach. The definition of the “sum over all paths integral” is given as including a capital pi symbol. For example,
I am familiar with the pi function as a... |
I recently read a paper where it says "if space is universally Euclidean, then time is universal" and I don't understand some key points about the implication.
To put in context, the author argues, based on historical sources, that the name of Galilean transformations is misleading and it would be more appropriate to c... |
$$\frac{d\langle p\rangle}{dt}=-i\hbar \int_{-\infty}^{\infty}\frac{d\psi^*}{dt} \frac{d\psi}{dx}+\psi^*\frac{d}{dt}\Bigr(\frac{d\psi}{dx}\Bigr)$$
I didn't know the coding of partial derivative which are inside the integral
There is a question about this on site, but I don't have much experience with bra -ket notation... |
I remember expositions on Feynman diagrams (like Flip Tanedo's https://www.quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams/) and others representing electron-positron anihilation with emission of a gamma (with time running from left to right) as 'similar' to an electron being scattered by a gamma (with time run... |
I've recently worked on obtaining the S-wave and D-wave functions of the deuteron and determine its magnetic dipole moment and electric quadrupole moment. I've considered a one-pion exchange potential between the nucleons only. Of course, I found slight deviations from the experimental values which I've read are due to... |
If two particles are quantum entangled...let’s call them particle A and particle B. You measure the state of particle A.
At this point, can you know the exact time at which the particle B goes from superposition into a known state due to the remote measurement of particle A, only by waiting on particle B without know... |
I am reading "On the electrodynamics of moving bodies" and have got to page 6 and become stuck. Is anyone able to please help explain how:
Einstein went from the first line of workings to the second line (I can see how the first line is created but not what or how the second line is created by which rule of different... |
I have been following a course on GR that at one point discusses the metric derived for the outside of a physical, non rotating uncharged massive object with spherical symmetry. For this situation I have seen the Schwarzschild metric derived, in Scharzschild coordinates.
From the form of the metric, it is observed that... |
In a free scalar field theory, Wick's theorem guarantees that $\langle \hat\phi(x)\rangle = 0$ and $\langle \hat\phi(x)^2\rangle = \infty$. Given that $\hat \phi(x)$ creates a particle at $x$, these have the relatively straightforward interpretations
$$
\langle 0|\text{particle at x}\rangle=0
$$
and
$$
\langle \text{pa... |
When we walk or run, are there any forces that counteract the static friction between our feet and the ground? I can’t seem to think of any, but if not, why is it that we still need to push on the ground to walk or run, even at a constant velocity?
|
I was told that in real life, there isn't always high symmetry in what one wants to work with. So why do we spend so much time dealing with highly symmetric problems that have elegant, straightforward solutions when this is usually not possible in practice? Shouldn't we get used to dealing with more realistic, complex ... |
Chapter 4 of the Feynman Lectures
Feynman defines the following:
We imagine that there are two classes of machines, those that are not reversible, which includes all real machines, and those that are reversible, which of course are actually not attainable no matter how careful we may be in our design of bearings, leve... |
(This question may lose me some physics knowledge points, but please be patient with me, my training is mostly in chemistry)
What is the purpose of using the electromagnetic tensor over simply directly working with electric and magnetic fields? Specifically in the quantum electrodynamic Lagrangian we use the tensor. 1 ... |
Setup: an official ping pong ball is floating inside a party plastic cup filled with clean water, which is then dropped from a certain height onto a soft mat.
Observation: the ping pong ball shoots up to a height which is much higher than its initial position.
Question: why does the ping pong ball do that? Why didn't t... |
In renormalization, we are forced to set several quantities in the Lagrangian to infinite values in order to account for physical results. In QED, for example, we start with a Lagrangian like this:
$$
\mathcal{L} = \bar{\psi}\left(i\gamma^\mu \partial_\mu -e \gamma^\mu A_\mu -m\right)\psi - \frac{1}{4}F_{\mu\nu}F^{\mu\... |
What exactly is a Baryon number? I looked up definition from wikipedia and still struggle to understand this. And how does this differ than the
electromagnetic charge?
My textbook did the following computation:
It is calculating the electromagnetic charge right and not the Baryon number?
|
I am currently learning QFT, and after watching the wonderful lectures by Leonard Susskind (https://theoreticalminimum.com/courses/advanced-quantum-mechanics/2013/fall), I am still struggling to see the connection between multi-particle (Fock) states and harmonic oscillators. When constructing Fock states, prof. Susski... |
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