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Edwin Hubble discovered in 1929 that the universe in expanding and the light from the receding galaxies are red-shifted; their wavelengths become longer. How can light which is an electromagnetic wave be stretched or compressed like matter ? We observe the Doppler effect in sound waves, with the pitch increasing when... |
There is already a question similar to this.
I am wondering if there is any way to calculate the rebound force if the impact time is unknown. Here are the knowns:
mass of object
height of drop
height of rebound
final velocity and initial velocity for rebound
I cannot find a way to actually record the impact time in a... |
I know (but am quite confused) that static friction is greater than kinetic friction, but is this only true when the object is at rest/stationary? Please explain about this in detail while referring to the measure/amount of static friction and the kinetic friction with an example too if possible
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Carlo Rovelli is interviewed in this article (The illusion of time):
Alongside and inspired by his work in quantum gravity, Rovelli puts forward the idea of 'physics without time' This stems from the fact that some equations of quantum gravity (such as the Wheeler–DeWitt equation, which assigns quantum states to the U... |
I’m a bit confused on the effects of anomalous global symmetries. So take for instance the following theory
$$\mathscr{L}=\partial_\mu\phi\partial^\mu\phi^*+i\bar{\psi}\gamma_\mu\partial^\mu\psi-y \phi\bar{\psi}\psi+\text{h.c}-V(\phi)$$
with $V(\phi)=m^2|\phi|^2+\lambda |\phi|^4$
It has two global symmetries $U_V(1)$ w... |
Sidney coleman in his lecture 253a of QFT stated that " one-meson-to-one-meson S-matrix element, we should find it equal to 1" i.e $$\langle p'|S|p\rangle = (2\pi)^32E_p\delta^{(3)}(\vec{p}'-\vec{p})\tag{1}$$ for the scalar theory $$ \mathcal{L}=\frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi-\frac{\mu^{2}}{2} \phi... |
In the AdS/QCD correspondence, glueballs operators are given, for example, by $\text{Tr}[F_{\mu \nu}F^{\mu \nu}]$ for $0^{++}$ or $\text{Tr}[F_{\mu \nu}\widetilde{F}^{\mu \nu}]$ for $0^{-+}$. However, in this link1, figure 1, it is stated that glueball operators are made from linear combinations of these Wilson loops. ... |
When treating an atom as a point partcle, it is usually assumed that it cannot rotate about its axis. Is it that anything considered as a point particle cannot rotate about its own axis? If so, why is that the case?
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So let's say I have an infinite well with walls up at $x=-L$ and $x=L$. Suppose that inside the well, there is a time-dependent potential
$$ V(x,t)= \alpha_0\delta{(x)}f(t) $$
where $f(t)$ is a monotonically decreasing function. Then the time-dependent Schrodinger equation in the region $x \, \in \,[-L,L]$ is then
$$-... |
(My book uses the notation "ergosphere" as the hypersurface of static limit, "ergoregion" as the hypervolume within.)
Studying the Kerr BH, I've come to the part about horizons and singularities, and I think I understand the ring singularity, the two horizons, and the (outer) ergosphere, as shown here:
However, I also... |
I'm having a bit of trouble imagining the time evolution of non-gaussian wavepackets. For a free particle, I usually imagine a diffusing gaussian (in both $x$ and $p$ where $<p>(t)=p_0$) with it's peak having a velocity $p_0/m$. I want to see some more variety of initial wavefunctions and their time evolutions such as ... |
I read in this Wikipedia article:
In the late 1960s, experimentalists had found that hadrons fall into families called Regge trajectories with squared energy proportional to angular momentum, and theorists showed that this relationship emerges naturally from the physics of a rotating relativistic string.
This confuse... |
Do we know of any quantities that are conserved on the global scale of the universe? Is there an associated continuous symmetry?
I.e. momentum and energy are not globally conserved as the expansion of the universe breaks spacetime translation symmetry.
|
I found the following text regarding laser cavities. But I do not understand why they use the second derivate instead of the first. Since the second can take any positive or negative value.
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I'm looking a general definition of a reversible process for a (closed) system that wouldn't need to say anything about the environment and would be based on the intuitive notion of "reversing".
For adiabatic (no heat exchange) processeses, it can be done:
"An adiabatic process between two equilibrium states consisting... |
I am not in Physics major, and I wanted to know what is the difference between these two:
direct light reflected for the first time (like an object reflecting the light coming from the sun).
ambient light reflected for the second time (like an object reflecting the light coming from the sky).
My questions:
Are there... |
It is a rotational motion problem from Kleppner mechanics:
Two masses $m_a$ and $m_b$ are connected by a string of length $l$ and lie on a frictionless table. The system is twirled and released with $m_a$ instantaneously at rest and $m_b$ moving with instantaneous velocity $v_0$ at a right angle to the line of the cent... |
If one assumes continuous charge density inside some volume $V$, then is the electric field continuous inside that volume $V$? I know that the electric field is discontinuous whenever it passes through some charge.
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Here I post few lines from Rana and Joag classical mechanics page 40
The general velocity-dependent constraint is given by relation
$g(r,\dot{r},t) =0$. Then says this equation is a single scalar equation. But I am surprised if it depends on velocity then how is this scalar equation?
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Consider an inextensible rope with forces $ F_1, F_2... F_n$ acting along it's length, and, $ F_o$ and $ F'$ acting on it's left and right end respectively. Now, Does the equality that the tension at one end is equal to sum of forces along the rope ? [ the ropes shape does not vary w.r.t time ]
If so , how would I pr... |
A coulomb is 6.241 x 10^18 elementary charges. But what exactly is a coulomb? And what do we mean exactly by a charge? how was it measured?
|
Suppose a particle is described by a Lagrangian $\mathcal L(q_i, \dot{q_i}, t)$. Suppose that $q_i(t)$ is a trajectory (there might be more that one) along which the action integral is stationary for the paths connecting $(q_{i, 0}, t_0)$ and $(q_{i, 1}, t_1)$
Then, does the same path also make the action integral stat... |
Let's consider the following problem:
A spacecraft starts at time $t_0 = 0$ with speed $v > 0$ and moves along the $x$-axis. If the distance between spacecraft and earth equals $R$ (in the reference frame of the earth), i.e. at $t=\frac{R}{v}$ a frequency modulatated signal
$$
u \colon \left[ \frac{R}{v}, \frac{R}{v} +... |
So my Thermodynamics teacher said that on a $pV$ diagram, you can get adiabats crossing for a Carnot cycle, even if all the possible thermodynamic states of the system can be represented on a $pV$ diagram (2 dimensions). So this is NOT the case where a third state variable is needed to define the state of the system.... |
Friction on every surface is smooth and the wedge is not restricted to move so wedge can move. Also, the mass of the wedge is $m$, as is the mass of the block. The question is that sir? told that in the ground frame the block will experience acceleration in direction of $b$ and $a$. How can that be possible because I d... |
I was learning about plane waves in class and it was stated that $k$-vector is perpendicular to $E$ which is also perpendicular to $B$-field.
But is this always the case?
|
So I have tried searching for the working of a rainbow. I found many sources and the explanation was clear. I still have a problem though. Since dispersion happens due to different refractive indices for different colours, splitting should take place always independent of the angle. Then why is it possible at 40-42 deg... |
The first picture is that of my window while the second is its reflection as seen from the floor. The pattern depends on the angle. That is when I move a little closer then look at the reflection the left part of window becomes transparent and the pattern is only seen at the middle and the end.
What causes this?
I do... |
Can anyone recommend a book or paper where they compare a trapezoidal waveguide (angled wall) with one a rectangular waveguide?
I have been searching a lot with no success.
|
Question #1:
I'm actually surprised that nobody has asked this question before, but theoretically speaking, what would it be like to go past the speed of light? This is actually only one of a few questions that I'll ask (below), but I'm just curious. What would it look like? Would you actually travel back in time, (I s... |
As far as I understand, in classical (not quantum) physics the equations of motion are established experimentally (e.g. Newton's three laws and Newton's gravity law, Maxwell's equations). Then sometimes it turns out to be convenient to rewrite them as Euler-Lagrange equations for suitably chosen Lagrangian $L$. Howeve... |
If I have a Hamiltonian $H$ that only has kinetic energy and no potential energy, do the energy eigenvalues have to be non-negative? Could the ground state of Hamiltonian have negative eigenenergy? If so, is the negative value results from potential? What's the physical meaning of negative eigen-energy?
|
I was wondering if for example you rub a balloon on a wool surface and create a negative charge by getting some electrons from it and put the balloon near your arm for example, is it possible for the electrons on the balloon to go through the human body?
|
One typically solves waves (fields) equations in Fourier space. For example, the 1D wave equation
$\frac{\partial^2\phi(x,t)}{\partial t^2}-\frac{\partial^2\phi(x,t)}{\partial x^2} = 0$
in Fourier space becomes
$(\omega^2-k^2)\tilde\phi(k,\omega) = 0$,
from which one writes the general solution
$\phi(x,t)=\int dk (A(k)... |
I have this following problem:
Two blocks A and B of masses $m_a, m_b$ are placed as shown on a platform at a distance $r$ from the axis of rotation. Find the angular speed of the platform so that the blocks just begin to slide. Consider friction($\mu_s$) between all contact surfaces.
I couldn't decide which block m... |
Does a linearly accelerated charge radiate? And if yes, is the electromagnetic waves emitted detectable from both its non-inertial frame and from other observing inertial frame? And If yes, doesn't this contradict with Einstein Equivalence principle?
|
I saw this article and something really wierd came in my mind.
What would the sky look like on those planets of our solar system where rainfall of diamonds occur? Will it be full of rainbows? Has it been ever captured?
I don't know whether it will be full of rainbows or not but there can be surely more than two rainbo... |
If I want to calculate the number of boxes that have proper width, length and height of 1 that I can fit into some region of spacetime (assuming that for the first instant for which I'm trying to calculate the number of boxes they have a velocity of zero to avoid length contraction complications) given some metric,
Wou... |
The following is for $D=4$. The correlators at a fixed point are power laws of the form $x^{-2\Delta}$, where $\Delta$ is the scaling dimension. Suppose I wish to find the nature of the spectrum at the fixed point, for which I calculate the spectral function $\rho(p^2)$ which is defined so that $$\langle\phi(x)\phi(... |
Recently I have been trying to understand complex magnetic impedance and when I try to formulate the equations for it based off the similar equations for electrical circuits I keep coming up with some weird answers that don't make sense. I realize that two of the equations regarding electrical fields I found on Wikiped... |
What does it mean in thermodynamics when a derivative is computed "at constant $X$"? If I see
$\left.\frac{\partial S(E, N)}{\partial E}\middle| \right._N$
how is the derivation performed any differently? Other than forcing any derivatives of $N$ that happen to be present in the function $S$ to zero?
|
Consider the wavefunction of say two electrons in an external potential, associated with two possible states $\phi_a$ and $\phi_b$. Furthermore, each electron can have two spin states $\chi_1$ and $\chi_2$. A convenient basis for the anti-symmetric Hilbert space of the two electrons is (omitting the normalizations)
\be... |
We all know the earth is rotating around its own axis. From a physics energy point of view, some thing has to provide energy for the rotation. What provides the energy to rotate?
|
I've been struggling without any result on a formal problem about the relation between microscopic states of a system and the volume occupied by a macrostate in the phase space. I'm now very confused about everything.
I observed that:
In general entropy is defined as $S = k_b \log(\Omega(E))$ where $\Omega(E)$ is the ... |
I'm a teaching assistant in calculus and my students who are studying mechanical engineering asked me to explain the multivariable chain rule. So I thought it could be fun if I could give an example of its use in classical mechanics; by considering some classical system. It should be simple classical mechanics since th... |
Assuming that $g_{\mu \nu}(x) = η_{\mu \nu} + h_{\mu \nu}(x)$, determine the first-order form of $R_{\lambda \mu \nu}^{\rho}$ in $h_{\mu \nu}$. The resulting theory is known as linearized gravity.
From the definition of the Riemann tensor and the connection coefficients in terms of the metric tensor, I have that the Ri... |
So, I have a spectrum calculated from an underwater sensor, $S_{vv}(f)$, and want to convert it to $S_{vv}'(k)$, where $k$ is wavelength and $f$ frequency.
I assume Taylor hypothesis for frozen turbulence, i.e. turbulent structures are unchanged when advected by the mean flow. Thus:
$$U = \frac{2 \pi f}{k} $$
and
$$\fr... |
I do understand how quantum entanglement works, but I don't understand how this can help us communicate. Just because you know the value of the other, there's no way to change it (as far as I know), so it would be the same, so you couldn't send a bit. I know there's something I'm missing, but I'd really like to underst... |
What is the physical significance of requiring Casimir operators (of e.g. Poincare group or the conformal group) to be Hermitian? What breaks down if we do not impose this condition?
EDIT:
To be perhaps a bit more specific, one of the Poincare Casimir operators is momentum squared, with eigenvalue negative mass squared... |
Quoted from BU-104b: Battery Building Blocks:
The electrode of a battery that releases electrons during discharge is
called anode; the electrode that absorbs the electrons is the cathode.
Based on the definition for cathode and anode above, why is the cathode filament in an x-ray tube negatively charged (and discharg... |
So we have a train going 5 m/s that gets loaded with 20,000 kg of coal while going over a 10m platform for 2 s. There is a 50,000 N horizontal force applied to the train during that period in order to keep the train going a constant 5 m/s.
That 50,000 N force does 500,000 J of work. But the KE of the coal at the end of... |
The fields of relativistic field theory (scalars, vectors, tensors, and spinors) are all defined via their transformation properties under the restricted Lorentz group (which excludes discrete spacetime transformations, namely, parity and time-reversal). This classification is done completely classically.
However, when... |
According to what I've learned, when two electrons repel each other, photons are exchanged between the electrons, and gluons are exchanged between quarks in a nucleus. However, in beta decay, it seems like W (plus or minus) bosons are just emitted from quarks and the W bosons quickly decay into a pair of leptons.
Q1. S... |
For a $LC$ harmonic oscillator, the energy spectrum is evenly spaced by
$$ \Delta E = \hbar \omega \quad \omega = {1\over \sqrt{LC} } $$
For two inductively coupled $LC$ harmonic oscillators with mutual inductance $M$, starting from:
$$\begin{cases}
\quad (i\omega L_1 + {1\over i\omega C_1})I_1 + i\omega M I_2 &= U... |
While reading Griffith's Electrodynamics, I didn't quite understand how magnetic fields were introduced.
Electric Fields were introduced as an intermediary calculation to finding the electrostatic force, and their detection makes sense in a way, because the Field and Force are in the same direction. Specifically, the e... |
My original Lagrangian is this, but I want to obtain nonlinear terms considering small oscillations : $$ L = ma^2[\dot \theta^2(1+ 2\sin^2\theta) + \Omega^2\sin^2\theta + 2\Omega_0\cos\theta] . $$
Now, equilibrium point of potential energy $U$ is $\cos\theta_0 = \frac{\Omega_0^2}{\Omega^2}$. Now if $\Omega_0 = \Ome... |
When I first looked into number theory, I was surprised about why mathematicians are so obsessed about integers, primes and so on. As far as I understand, (almost) all integers in the real world arise as an approximate description of composite dynamics.
I think anyone here understands why individual macroscopic objects... |
If $$\psi(x)=A\exp(-x^2/a^2)\exp(ikx)$$
$\langle{p}\rangle=0$ since
$\langle{x}\rangle=0$, since the integrand is an odd function and Ehrenfest theorem states $\frac{d\langle{x}\rangle}{dt}=\frac{\langle{p}\rangle}{m}$.
But explicit calculation of $\langle{p}\rangle= \int^{\infty}_{-\infty}\psi^*(x) \hat{p} \psi(x)dx$ ... |
I'm working on the Eq.9.77 in Peskin (page 304):
To demonstrate this, we need only apply standard identities from linear algebra. First notice that, if a matrix $B$ has eigenvalues $b_i ,$ we can write its determinant as
$$
\det{B}
~=~ \prod_{i}{b_i}
~~= \exp{\left[ \sum_{i}{\log{b_i}} \right]}
~=~ \exp{\left[ \opera... |
It may be a very stupid question, but still. Given a periodic table
Why there is a well/hole of missing elements in atop of periodic table ?
(Pictured as green area). Is this just a side-effect of standard element distribution logic in a table ? Can something be put in these missing places, like different isotopes of ... |
I have been studying about quantum circuits, and I have come across resonators or microwave resonators multiple times. I do have a vague idea about them but I am not able to understand what is their basic purpose in quantum circuits and how to deploy them in the circuits?
|
Starting from First Law of Thermodynamics, we have
ΔQ = ΔU + ΔW
Where, ΔW is the work done "by gas" on the surrounding.
Now, for an isobaric process, it is given by
ΔW = ∫PdV = PΔV
here P is the external pressure, which remains constant. Here is my doubt. Why do we take P as external pressure while calculating work... |
So ive been encountering several exercises where we have a particle decay (into two other particles) and we're asked to calculate the, say, CM orbital angular momentum of the outgoing 2 particles (based on our knowledge of spins of the particles in question and angular momenta algebra). This is a straightforward exerci... |
We observe that as the current through the filament is increased, the filament gets hotter and brighter. Also the color of light changes from red to orange to yellow. It only gets till yellow-white, but never any bluer. Even when the temperature reaches 2000 degree centigrade in a black body radiator, using a power o... |
Does anyone know of a wind tunnel experiment on a wing or airplane that measures the absolute amount of lift (not the lift coefficient); and demonstrates conclusively that the lift generate by a wing equals the weight of the aircraft (Lift = Weight).
Thanks.
|
I do not mean to know how they vary (inversly or directly), I need to know if there is a function relation for the rate of condensate formation.
|
As you know, the ratio of gravitational force to Coulomb repulsion force between two protons is very small. This means that the source of nuclear stability cannot be the force of gravity. Can some neutrons be added to increase this ratio? If yes, how many?
|
This question is in reference to eq. (2.52) on the bottom of page 27 in Peskin and Schroeder.
To evaluate the Klein-Gordon field propagator along a spacelike interval we wrap the contour around the branch cut at $p=+im$. My question is (possibly a mathematical one) why it is necessary to move the contour in the first p... |
I have been working through a problem. It has asked me to determine the eigenstates and corresponding eigenvalues of the number operator in a quantum harmonic oscillator;
$$\hat{n}=\hat{a}_+\hat{a}_-$$
I have been looking for some literature on it but I can't seem to find anything! I know what solution I am expecting. ... |
Consider a laser source emitting a laser beam in the horizontal direction. If we are given the power of the laser source, we can calculate the force on the laser beam.
Now consider that the laser beam is moving horizontally with a 0.5c. Would the force on the laser source change by the emitted laser beam?
Since the fre... |
Summary:: I find two different expressions for the EM tensor for dust, and both derivations seem right to me.
Given the action for a system of dust $$S =-\sum m_q \int \sqrt{g_{\mu\nu}[x_q(\lambda)]\dot{x}^\mu_q(\lambda)\dot{x}^\nu_q(\lambda)} d\lambda,$$
where I use the $(+,-,-,-)$ sign convention.
The Energy-Momentum... |
I'm reading a review on the Ising model and came across a section where they discuss Legendre transforms of thermodynamic potentials. Now I'm familiar with the classical thermodynamic relations such as $F = U - TS$ (Helmholtz), $G = F + pV$ (Gibbs) and so on, but fail to see the connection with the ones proposed for sp... |
When discussing systems which we want to be cold, but which lose cold by taking in heat from the ambient environment, what's the "I'm a smart physicist" way of saying "cold loss"?
If I were discussing loss of heat from a kiln or an oven to the ambient environment, I would say "thermal loss to the environment".
If I wan... |
The vast majority of uranium is U-238, and most of the rest is U-235, U-232, U-234, etc....
So how can the averaged atomic weight be a little over 238?
|
Nuclear weapons and reactors get their chain reactions underway via neutron radiation, but do other radiation particles ever contribute?
|
For part a and b the answers are fig.(a) and fig(b) respectively. Can anyone explain me the graphs in more details? Like for a why is there lines in graph on the 2nd and 3rd quadrants and why is the vector going outwards from the origin? Similarly for b
|
I found this problem when I was trying to prove that the gravitational attraction on an object is the gravitational attraction on the center of mass of that object (I had doubts on it). And in doing so I ran into this problem which shows that the effect on the center of mass isn't equal to the effect on the whole thing... |
I am told that, in cold weather, I should let my faucet trickle a little to prevent pipes from freezing, especially if some portion of my above-ground pipes are likely to get cold.
Are there any rules of thumb I can use to estimate the flow rate at which I should trickle my faucet to keep pipes from freezing? If such a... |
There's this theory that electromagnetic waves can't make through holes that are smaller than their wavelength its supposed to be how microwaves stop microwave radiation from coming out... But that doesn't make sense. I mean it would make sense if the theory said that em waves couldn't make through holes smaller than ... |
We study in thermal physics that no natural processes are reversible i. e. they are irreversible, so size of universe, it's also natural process. Why we still say big crunch theory a theory, why can't we just neglect it and say that universe is expanding and will expand forever on the basis of principle I put forward a... |
An airplane travels 200 miles due west and then 150 miles 60° north of west. The direction i get is 21.64° north of west but the book's answer is 25.17° north of east....I don't understand how so?
|
Deriving the equation of geodesic deviation one looks at two test masses on positions $x^\mu$ und $\tilde{x}^\mu$ and defines the separation vector $\boldsymbol{\chi}$ as
$$\tilde{x}^\mu=x^\mu+\chi^\mu$$
I don't really understand how this can be a vector since I have been told that vectors can only exist in one tangent... |
The Schrodinger equation:
$$-\frac{\hbar^2}{2m}\nabla^2\Psi(r)+V(r)\Psi(r)=E\Psi(r)$$
$$\textit{kinetic energy} + \textit{potential energy}=\textit{total energy}$$
Is one of my favourite equations, but there's one term I don't understand: the $V(r)$ term which is supposed to mean potential energy... but what type of p... |
I am having issues in giving correct physical meaning to the associated sigma matrices:
\begin{equation} \sigma_+ = \begin{pmatrix} 0&1\\ 0&0\end{pmatrix} \text{ and } \sigma_-=\begin{pmatrix} 0&0\\ 1&0\end{pmatrix}\end{equation}
Is the $\sigma_+$ related to emission and $\sigma_-$ to absorption or is it the opposite? ... |
If we are interested in preparing the electron state $|+\rangle=|s=1/2,s_z=+1/2\rangle$ in the laboratory, the obvious thing is to apply a magnetic field along the positive $z$-axis (${\vec B}=B\hat{z}$). Having done that, can we be sure that the resulting state is $|1/2,+1/2\rangle$ but not $|1/2,-1/2\rangle$? I have ... |
I'm trying to derive a classical model to describe diamagnetism, and I'd like to understand if it is possible to understand the basic properties of diamagnetic materials with it i.e.:
''A diamagnetic material placed in an external magnetic field $B_{ext}$ develops a magnetic dipole moment directed opposite $B_{ext}$. I... |
So I want to describe the premise better. By a helicopter I mean something that can stay suspended in air perfectly and can move around in any direction freely. To generalize the motion of the helicopter mathematically, assume that the position of the helicopter in each dimension is a continuous and differentiable func... |
A general form of wave equation is
$$Y = A \sin(ωt-kx+φ)$$
Now if $t = 0$ is taken at the instant when the left end is crossing the mean position from upward to downward direction, $φ = π$ and the equation will be
$$Y = A \sin(kx-ωt)$$
now the above equation is taken to prove the frequency of standing wave why we dont ... |
In Introduction to Solid State Physics, eighth edition, by Kittel, page 141, eqs. (20,21), the density of states for electron in conduction in three dimensions is
$$D(\epsilon)\equiv \frac{dN}{d\epsilon}=\frac{V}{2\pi^2}\left(\frac{2m}{\hbar^2}\right)\epsilon^{1/2}=\frac{3}{2} \frac{N}{\epsilon}.$$
The same argument co... |
Suppose I have two Hamiltonian pieces $H_1$ and $H_2$ such that $[H_1,H_2]=0$. Then we know that the two pieces have shared eigenbasis. Assume both $H_1$ and $H_2$ have eigenvalues 2 and -2. Let $|\psi\rangle$ be an eigenstate of $H_1$, then I think if $|\psi\rangle$ is not an eigenstate of $H_2$ then we can conclude t... |
Whilst working on an experiment with pipe flow from a basin, I noticed that with large enough pipe diameters, the fluid would begin to form open channel flow instead of filling the pipe entirely.
Does anyone know the causes of open channel-flow, or could point me towards relevant literature?
Thank you.
|
In my problem we look at a relativistic particle of charge $q$ and mass $m$ in the presence of a second particle of unit charge and mass $M\gg m$, which is fixed at the origin. I need to find an expression for the total energy E of the first particle in terms of canonical coordinates using the Hamiltonian (and ignoring... |
Consider the above image
This is a pretty standard diagram but it makes no sense to me. I have some questions regarding it.
Why are we taking surface tension of air-solid interface into consideration for finding the shape of the drop? It appears to me that it is not acting on the drop but on solid.
Which surface ar... |
I am working in a higher derivative quantum gravity theory, and I'm having trouble with the variation of d'Alembertian operator.
Suppose we have the following action:
\begin{equation}
\mathcal S[g]=\int d^4x \sqrt{-g} R \: \square^kR
\end{equation}
When varying this with respect to the metric in order to find the assoc... |
I'm writing my bachelor's thesis and working on Srednicki's discussion about area laws for a massless scalar quantum field with Hamiltonian
The field is in a spherical lattice of discrete points with spacing a;
The UV cutoff is thus $a^{-1}$ and the IR cutoff is $L^{-1}$ where $L=(N+1)a$
The starting Hamiltonian is
$$H... |
If I understand correctly, wetsuits insulate their wearers when they are immersed in water. I assume that the same is true when they are not immersed in water (especially when dry); is that true? What major factors affect this?
|
I'm curious why the so-called 'information paradox' is a paradox. I know that it's regarded as a paradox due to the fact that Hawking radiation seemingly violates the unitarity of the time-evolution of quantum states. But isn't it the case that QM already contradicts unitarity if the Copenhagen interpretation is accept... |
I have been trying to understand the implications of general relativity. I unfortunately don't have a good knowledge of advanced topics and I may have made some silly assumptions.
As far as I understand, spacetime dictates the trajectory of an object, and the object curves spacetime. Objects follow the shortest path, a... |
Imagine a box designed to make vacuum state inside. Is it possible for us to lock the photons up inside something completely enclosed?
|
I recently learned of lattice field theory wherein quantum fields are defined on a discrete spacetime. Naively this sounds to me a lot like certain numerical methods for solving differential equations (e.g. the finite-difference method) where you start with continuum field equations and solve them approximately on a di... |
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