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i watched a video on YouTube https://www.youtube.com/watch?v=_A7wk40AeiI regarding the block universe where brian greene seem to be saying we live "forever" (i am probably misinterpreting his words ) can you please clarify if this is true? does he mean we experience our life over and over again "forever"? i know that ... |
Here I am asking about electrons, but of course this same question applies to muons and all the other spin one half particles.
I am aware that spin is defined as "an intrinsic property" of a particle. And I am also aware that multiple experiments are in agreement with the statement that electrons have spin one half, so... |
My understanding is that scalar-tensor/Jordan-Brans-Dicke gravity most closely resembles general relativity as the coupling constant omega approaches infinity. I am curious about how its predictions differ from those of general relativity when the constant is less than infinity. For example, is there a threshold at whi... |
Is it correct to say that the center of mass of any space rocket is stationary here on earth? roughly speaking, without external forces the motion of the center of mass is preserved, so since the rocket is stationary before the start, so is the center of mass still here?
|
In time dilation, does clock really run slow when it’s in high speed? Is that means the mechanical parts of the clock run slow?
Or , It’s just the other inertial observer who thinks that the other one’s clock is running slow.(because the successive light signal is taking more time to reach the destination)
And, If the ... |
I am new to special relativity, and I am trying to figure out if $\phi(x)=\frac{a \cdot a}{x \cdot x+a \cdot a-x^{0} a^{0}}$ is a Lorentz scalar, where $x$, and $a$ are four-vectors.
Since the dot product of any two four-vectors is a Lorentz scalar I only need to worry about the $x^0a^0$ term (I think), so I rewrote it... |
We can travel to the past and future then we can know the future at present moment (traveled in the future , knew everything and back again to the past). Then how can we say that we have free will? We have to perform the event which we seen from the future?
|
I follow the proof of Wick's theorem for a non-interacting case in "Many-Body Quantum Theory in Condensed Matter Physics (Bruus, Flensberg)", Ch 11.6.
In that chapter, above (11.75), the book states,
"Take now for example the case when $\tau_{i}$ is next to $\tau'_{j}$. There are two such terms in (11.72)..."
What (11.... |
I went to my Optometrist yesterday, and I noticed that they wanted to test my vision at 20ft. However, because they had a small room that could only accommodate 10ft, they used a vision chart that was reversed behind me, and effectively simulated 20ft by asking me to read the chart via the mirror.
Now, my question is: ... |
I found this question on this very site and was curious on how to solve it using D'Alembert's Principle
.I already know how to do it by balancing the torque about toppling point so please don't post the latter as an answer .
My attempt was to displace the upper sphere by $d\theta$ which gives its virtual displacement ... |
I am reading lecture notes on special relativity and I have a problem with the proof of the following proposition.
Proposition. If $X$ is timelike, then there exists an inertial coordinate system in which $X^1 = X^2 = X^3 = 0$.
The proof states that as $X$ is timelike, it has components of the form $(a, p\,\mathbf{e})$... |
Imagine you shoot a laser beam into space, and there is a target placed every 500 million light years from you.
In a static universe, the laser beam will reach the first target in 500 million years, the second target after another 500 million years, and so on.
But what about in an expanding universe? Because of the exp... |
I'm not asking you to solve this question, but here it is anyways for clarification purposes:
A rod of mass $m$ and length $2R$ can rotate about an axis passing through $O$ in vertical plane. A disc of mass $m$ and radius $R/2$ is hinged to the other end $P$ of the rod and can freely rotate about $P$. When disc is at ... |
From all my searching it seems like the most common explanation of virtual particles is that they are merely internal lines in Feynman diagrams and therefore just a convenient pictoral way of organising a perturbation expansion, and therefore they need not be considered 'real' in any way.
My only remaining confusion th... |
Can anyone tell me what is the physical meaning of the image below (Hikami boxes)? (Especially the dashed line.)
Furthermore (and this is less important), why are these boxes needed for weak anti-localization calculation?
I have no formal training in QFT so I would love to understand it.
https://doi.org/10.1103/PhysRev... |
I took multiple $B$ measurements for a constant $A$ value, which I simultaneously measured.
$A$ (in my case the resistance of a temperature sensor) was controlled by a PID controlled and slowly oscillated in the range 2596 to 2560.
It is tempting to just say that $A=2598\pm2$ but is this really correct? Because the val... |
Can 2 blocks, composed of different metals, have the same masses but different volumes and still have the same weight if hung on a spring balance?
|
Since in terms of units, $\tau = Nm$, $I=kgm^2$ and $\alpha=\frac{radians}{s^2}$:
$I\alpha = kgm^2\cdot \frac{radians}{s^2} = \frac{kgm}{s^2}m\cdot radians = Nm\cdot radians$
But... $\tau$ does not have radians? Where does it disappear?
|
Context
We have a particle of spin $1/2$ and of magnetic moment $\vec{M} = \gamma\vec{S}$.
At time $t=0$, the state of the system is
$$
|\psi(t=0) \rangle = |+\rangle_z
$$
We let the system evolve under the influence of a magnetic field $B_0$ parallel to $Oy$.
We are asked to find the state of the system at time $t$.
A... |
I am having a conceptual difficulty reconciling inelastic events and diffraction, particularly whether or not you can have inelastic diffraction.
Here is my thought experiment that I am working through (see cartoon picture below). Imagine you have a line of atoms spatially separated by a periodic spacing $a$, and that ... |
I'm confused whether the Jacobian is needed in a path integral representation of a dynamical system, as I've seen multiple conventions in the existing literature.
For simplicity, let's just consider the following ODE:
$$\dot{x} = F(x) + \eta(t),$$
where $F$ is some polynomial of $x$ of degree greater than $2$, and $\et... |
The question is in the title, so basically you drop a mass into a non rotating black hole, and then the distribution of mass inside the black hole will not be spherically symmetric (assume the mass did not reach the singularity yet). Will this information affect the gravitational field surrounding the black hole outs... |
Given that $\hat{H}\Psi = \hat{E}\Psi$
and that $E=\frac{p^2}{2m}$
Assuming a non-relativistic, system, does this mean that any eigenfunction of Energy is also an eigenfunction of momentum? Or does it work the other way and every eigenfunction of momentum is an eigenfunction of Energy?
If not, where does this break dow... |
Patches of normal space randomly condense out of the false vacuum of inflating space. What is the average distance between these patches? Another words, what is the average number of bubble patches per unit volume of inflating space?
I know we can't see other bubbles. I'm asking what Eternal Inflation Theory predicts.
... |
Let us assume that we have a symmetrical conducting hollow shell with a charge $Q$ on its surface. Now let us bring a point charge $q$ inside the shell cavity and place it at any point except at the centre (let say at $x=a$ assuming that origin is at the centre. I know that this will induce negative charges on the inne... |
Let us take a conducting spherical shell with no charge on it initially. Now if we put a charge $+q$ on its surface (by either method of induction or contact), would charges be induced on the inner surface of the shell? If charges are induced then aren't charges induced at the centre of the shell too? What happens insi... |
I am trying to prove Birkhoff's theorem in general setup.
Birkhoff's theorem states that every spherically symmetric vacuum solution to Einstein's field equation is the Schwarzschild. (i.e., it says spherically symmetric vacuum solutions admits static, asymptotically flat)
First I know from the classical textbook Carro... |
In quantum theory, physical states are elements of a Hilbert space, and the transformations must be unitary, implying that the states must transform under a representation of the symmetry group.
However, in classical physics, the states do not necessarily form a linear space, and even if they form a linear space, there... |
I read that the line integral in Ampere circuital law is applicable for a piece-wise continuous curve (loop). My question is whether the law is valid only for planar loops or does it hold good even for non-planar loops?
$$\oint B\cdot d\ell~=~ \mu_0I$$
|
I found this question on this very site and was curious on how to solve it using D'Alembert's Principle
Here's the link to OP(link)
.I already know how to do it by balancing the torque about toppling point so please don't post the latter as an answer .
My attempt was to displace the upper sphere by $d\theta$ which giv... |
In the paper https://arxiv.org/abs/1912.11034 authors introduce a new conserved current for the massless Dirac fermions. This Lagrangian
$$
\mathcal{L} = \frac{i}{2} (\bar{\psi} \gamma^{\mu} \partial_\mu \psi - \partial_\mu \bar{\psi} \gamma^{\mu} \psi)
$$
is claimed to be invariant in addition to the conventional vect... |
What are some free and open-source interactive simulations, illustrations, animations, demonstrations, videos, calculators and other resources for experimental physics and mathematics like the Wolfram demonstration project
|
While solving the particle in a ring we get a general solution of the form:
$$\psi(x) = A\exp(imx) + B \exp(-imx)$$
Where $m=\left(\frac{2iE}{h}\right)^.5$. Imposing the boundary condition I get that $m$ should be an integer, but most of the books drop one of the terms in the general solution. Why is that? They write t... |
The Schwarzschild solution in GR only has a singularity at the origin $r=0$: otherwise there is no matter content. The right-hand side of Einstein's equation is hence almost everywhere zero, but I would expect a Dirac-delta like matter distribution at the origin. The vacuum Einstein's equations are
$$R_{\mu\nu} - \frac... |
I know that Cosmology has a role in Horava-Lifshitz Gravity, but do Black Holes play a significant role in the applications of Horava Lifshitz Gravity, if so, what will be the mathematical equations describing it?
|
Consider a metal stick, say iron or aluminum. From the experience, even if it's resilient, bend it forward and backward a couple of times, it would be broken.
However, consider a thin iron foil or thin aluminum foil. From the experience, we know that it could be bend forward and backward for almost as many time as time... |
In my text book magnetic flux density is defined as the number of field line per units of area. what I know is the field line is just a conceptual imagination , which doesn't really exist, but then how can we "count" the number of field lines to know how much flux density is there?
|
The magnitude of the gravitational acceleration $g$ at which the falling mass is accelerated towards the center of the gravitating mass can be found if we know the mass and radius of the gravitating mass in the equation of $g=GM/R^2$ formulated by Newton. It doesn't even depend upon
The magnitude of the gravitational ... |
Let $H$ be the Hamiltonian of a specific atom (not hydrogen) and $J$ the total angular momentum. Since $H$ and $J$ commute, they have common eigenstate.
So we can label the atomic states by their energy and total angular momentum $\phi_E^J$.
My question is, suppose we have a state $\phi_E^J$ and another state $\phi_{E'... |
If I have a spring that I displace by $x$ from its equilibrium and then let go, what position will the spring be at after $n$ time. (taking friction into account)
I made a quick Illustration to explain the problem further:
We know that following Hoeke's law
$$F = -kx$$
with $k$ being the stiffness
since
$$F = ma$$
We ... |
In equilibrium, there can be no net current in a semiconductor. Accounting for both drift and diffusion current, the following relationships can be derived relating the electron density, $N_{e}$, the hole carrier density, $N_{h}$, and the electrostatic potential, $\varphi$:
$$
N_{e}\propto e^{\frac{q\varphi}{\kappa T}}... |
How does the buoyant force come into action all of a sudden when an object is immersed in a fluid?
|
I have been researching for almost a week looking for some variable that might affect the time period in a pendulum other than length and the only thing I found is the medium and that is due to resistivity. Does anyone have an idea of a variable that might have an effect on the time period of a pendulum?
Thanks a lot.
|
Suppose we have a gauge theory defined in the UV and it flows to an interacting CFT in the IR, i.e. the beta function vanishes for some finite value of the coupling. I am confused about the meaning of this. Isn't a CFT by definition scale independent? But we have the CFT only at a particular energy scale where the beta... |
I should show that the density operator $\rho \in \text{Herm}(\mathbb C^d)$ is positive semi-definite if and only if $\text{Tr}[\rho A^\dagger A] \geq 0 \quad \forall A\in L(\mathbb C^d)$.
I don't know how to begin to proof this. I think I'm missing some properties of Traces. The only thing I notice is that the operato... |
I have often seen people showing how much of an object one can see at a given distance due to earth's curvature (actually, this was mostly in discussions with flat-earthers).
How can I calculate this? Let's for example say, a building of known height $h$ is at a known distance $d$. How would I find out how much of the ... |
In the 1995 paper 'Almost any Quantum Logic Gate is Universal' by Seth Lloyd, the author imagines a setup where we can apply two Hamiltonians $A$ and $B$ to a quantum system. By repeatedly and alternately applying these Hamiltonians, a unitary of the following form can be performed on the system:
\begin{align}
U = .... |
Is there math proof that we can cancel out units in Physics? For example:
$\require{cancel}distance = \frac{meters}{\cancel{second}} * \cancel{second}$.
So we see that seconds cancel out and we left with meters which is correct but how is it possible if it is not actually division (meters per second) it is only our int... |
In quantum statistical mechanics we often define a density matrix as
$\rho = \sum_{i} p_{i} | \Psi_{i} \rangle \langle \Psi_{i} | $.
Its time volution is determined by the equation:
$\rho \left(t\right) = U \left(t\right) \rho U^{\dagger} \left( t \right) $ and it allows us to determine the expectation value of any ob... |
2 people pulling a spring with equal forces from opposite ends is identical to pulling it from a rigid wall, but how to calculate its extension if its pulled from both ends with different forces? Should the mean of the forces be taken?
|
The Rayleigh-Jeans law is derived for a box with reflective walls. This system is designed to be able to accumulate electromagnetic radiation because of reflection for wavelengths that "fit in the box" and so interfere constructively. For this very very specific system, because of this accumulation, these wavelengths c... |
Let us assume that a ship is traveling relative to earth at the speed close to C.
My understanding is that according to special relativity it should be impossible to tell whether a ship is moving and earth is stationary or vice verse (all laws of physics should behave exactly the same in both cases).
However, if we tak... |
If a spaceship left Earth for the galactic center at 3pm one day, traveling at extremely close to the speed of light (say 99.9999999%), then a second spaceship left at 4pm, would they arrive an hour apart, or would time dilation interfere?
|
If the universe is expanding uniformly, then wouldn't the rate of expansion of the universe change if you were to move closer to a point that is currently moving away from us faster than light?
For example:
Say A, B and C are all equally far apart. A is moving away from B at just under the speed of light (say 90%), and... |
My question is the following. I consider a system S in contact with a thermostat, the system receives a heat $Q$ from it.
What we can write is:
$$\Delta S_S \geq \frac{Q}{T}$$
This is exactly the second principle.
However, for the thermostat, I have often read that $\Delta S_{T} = -\frac{Q}{T}$
Why are we sure to have ... |
I am reading a book and it makes the following question:
"A friend asks to
borrow your precious diamond for a day to show her family. You are a bit
worried, so you carefully have your diamond weighed on a scale which reads
8.17 grams. The scale’s accuracy is claimed to be more or less 0.05 gram The next day you
weigh t... |
Let's consider the heat equation on a $\Omega \subset \mathbb{R}^2$ manifold with a boundary $\Gamma$, with initial and boundary conditions
\begin{align}
\dot{u}(\mathbf{r}, t) &= \Delta u(\mathbf{r}, t)\quad \mathbf{r}\in\Omega\\
\lim_{\mathbf{r}\to \Gamma} u &= 0\\
\lim_{t\to 0}\left<T_u, \varphi\right> &= \left<\del... |
This question is in the context of performing simple rotational spectroscopy on molecules, but could be extended for more general cases.
In rotational (microwave or IR) spectroscopy of molecules, the energy levels are discrete and given by
$$E_J=BJ(J+1)$$
where $B$ is the rotational constant, and $J$ is the angular mom... |
The thing about infrared thermometers that bugs me is how can you get the same temperature reading regardless of the distance to the object. Shouldn't there be a difference when measuring from two different standing points since energy flux density decreases with ${1\over distance^2}$ and infrared thermometers work by ... |
Let $\Lambda$ be an element of the Lorentz group and $\eta$ the flat metric. I need to show that the condition $$\Lambda_\rho^\mu\Lambda_\sigma^\nu\eta_\sigma^\rho=\eta^{\mu\nu}$$ for an infinitesimal $\Lambda_\beta^\alpha=\delta_\beta^\alpha+\omega_\beta^\alpha$ implies that $\omega$ is antisymmetric.
So here's what I... |
From what i understand recently, greenhouse gases traps the sun heat (infrared radiation) on earth, by making it harder to dissipate back into space, reflecting most of them again. The exact same process happen in hydroponic greenhouse
If that's the case - why then, hydroponic greenhouse inner temperature don't keep in... |
When I look at Snell's law
$\frac{\sin\theta_2}{\sin\theta_1} = \frac{v_2}{v_1} = \frac{n_1}{n_2}$
I don't see any reference to wavelength.
If red and blue have the same speed in the same medium, why they refract differently?
What am I missing?
|
The Maxwell-Boltzmann probability density function for the energy is
$$
f_{MB}\left(E\right)=2\left(\frac{1}{\text{K}_{B}T}\right)^{3/2}\sqrt{\frac{E}{\pi}}\exp\left(-\frac{E}{\text{K}_{B}T}\right)
$$
In this expression it is usually implied that the energy levels are continuous. However, in statistical physics it is s... |
Let $\psi=a_1\phi(1s(2) \ ^1S)+a_2\phi(1s(1)2s(1) \ ^1S)+a_3\phi(2s(2) \ ^1S)
+... $ be a state of the helium atom. Applying variationally calculus we can found the energy expectation value of this state is almost exact to the experimental value.
Is by this comparation that we know that the total angular momentum $J$ ... |
Imagine you have a particle in a 1D potential well with infinitely high walls. Such a particle would have an energy of
\begin{equation*}
E_n = \frac{\hbar^2 \pi^2}{2m a^2}n^2
\end{equation*}
if the mass of the particle is $m$ and the well has a width of $a$. Now assume $n=1$ for that particle. What would happen if we l... |
For the free particle in 3d, I follow Robinett's page 491 to find that the solutions to the radial equation are the spherical Bessel function $j_l(z)$ and $y_l(z)$ where $z=kr$ and $k=\sqrt{\frac{2mE}{\hbar^2}}$.
If I allow for a constant potential $V=V_0$, and consider the $E<V$ case, then since the state are bound, I... |
This seems like a rather straight-forward question, but I cannot seem to find any literature on the subject.
It's well-known that a low-energy EFT like chiral perturbation theory, for example, can be re-expressed in terms of a Yang-Mills theory coupled to fermions that form a pion condensate at low energies. I am curio... |
Why does a tower of building blocks (cubes) fall?
Theoretically, as long as the center-of-mass is above the blocks' bottom faces, and as long as one does not shake the tower too much, it should not fall. This means that, with sufficient care, one can build a tower infinitely high. @Bernhard has suggested the link confi... |
I, for a while now, wanted to build a little Farnsworth desk fusor. Nothing too powerful, simply a small "desk lamp" if you will. As the fusor needs 2 grids, I was wondering, if it might be possible to position the outer grid outside of the vacuum chamber, as to make the inner grid a bit bigger. Just an idea, nothing s... |
Today we know biological factors of aging like DNA methylation increases & chromosome telomere shortens, that is we have an intrinsic clock. But Einstein suggests time stops at light speed & so should do aging. Question is on which clock, on our watch or body clock? Who has shown DNA methylation stops at high speeds? W... |
I thought that the individual lepton numbers $L_e$, $L_{\mu}$ and $L_{\tau}$ are individually conserved for each vertex.
At least this is how I explained to myself that this Feynman diagram, corresponding to the process $e^{+}e^{-} \rightarrow \mu^{+}\mu^{-}$, is not allowed:
Now I saw on Wikipedia that this Feynman d... |
Einstein's equivalence principle is often illustrated by pointing out that a person trapped in an elevator has no way of telling whether they are on the surface of the earth or in deep space in a rocket ship accelerating at 9.8 m/s2. A third alternative is that the elevator is at the end of a very large centrifuge arm... |
I'm a beginner wrapping my head around how general a definition a "function" really is when connected to the real world, please help.
I am trying to connect the mathematical definition of a function to real-world occurrences. Here is the Wikipedia definition of "function":
a function[note 1] is a binary relation betwe... |
Consider the Hamiltonian for the classic planar harmonic oscillator:
$$H = H_x + H_y$$
where $$H_x~=~\frac{1}{2}(p_x^2+x^2), \qquad H_y~=~\frac{1}{2}(p_y^2+y^2).$$
So it is possible to obtain a set of action-angle variables $(H_x, H_y, \phi_x, \phi_y)$ .
My question is, how does the trajectory look in such coordinates?... |
I have only seen examples and references to the Navier-Stokes equations in two and three dimensions. Do we know if these equations work in one dimension or greater than three dimensions?
|
If we have a normalized entagled state:
$$ |a\rangle=N (|1\rangle|2\rangle+|1\rangle|-2\rangle+|1\rangle|2\rangle-|-1\rangle|2\rangle) $$
Where $|2\rangle, |-2\rangle$ describes particles A and $|1\rangle, |-1\rangle$ particle B.
If we measure this system and find out that particle A is in the state $|2\rangle$, the s... |
A box with mass $25$ kg on a ramp at an angle of inclination $30^\circ$ to the horizontal is pulled with a force of $75$ N at an angle of $20^\circ$ to the ramp. What is the frictional force if it is pulled up the ramp at constant speed?
I've constructed a free-body diagram:
(not drawn to scale, and please ignore th... |
Does anyone know how to compute analytically or numerically the following integral (for $T=10^4$K)?:
$$n_\gamma=\frac{1}{\hbar^3\pi^2c^3}\int\limits_{2.1789\cdot 10^{-18}}^{+\infty}\dfrac{E^2\mathrm{d}E}{e^{\frac{E}{kT}}-1}$$
I tried with R, MATLAB, Maxima, Maple and Wolfram but I failed. I also search an analytical so... |
A few years ago I asked on Reddit about the behavior of wave propagation in even and odd dimensions. I received this answer:
"The answer lies in the solutions to the wave equations. Essentially, in odd dimensions a wave will propagate at a single characteristic velocity $v$, while in even dimensions it propagates with ... |
I have a general question regarding such type of calculations, but let me start with a concrete question. Consider the $bc$- free fermion CFT so that $b(z)$ and $c(z)$ are free fermions with OPE,
$$b(z) c(w) \sim \frac{1}{z-w}$$
and thus commutation relations,
$$\{b_r, c_s \} = \delta_{r,-s}.$$
One can construct a weig... |
The dark matter in galaxies causes the starts to orbit with a higher orbital speed. Now, assuming that there is a constant force from the dark matter on the starts, there should be constant acceleration on stars. This, in a long period of time, should cause the start to orbit faster and faster, eventually reaching infi... |
A particle is free to move on x-axis in which of the cases the particle will execute oscillation about $x=1$?
$(1)\,\,\,\,\,F=(x-1)$
$(2)\,\,\,\,\,F=-(x-1)^2$
$(3)\,\,\,\,\,F=-(x-1)^3$
$(4)\,\,\,\,\,F=(x-1)^3$
Here's my work:
The particle starts motion about $x=1$.
This means that after $x=1$ force will be restoring,... |
In mechanical terms, what machine element can we consider a bicycle rim to be?
Like can we design it based on the assumption that it is a curved beam/ a hoop?
|
Is there a method to "decompress" the acceleration scalar? For example, I am computing the scalar as:
$\sqrt{a_x^2 + a_y^2 + a_z^2}$
where $a_x, a_y$ and $a_z$ are the components of the acceleration vector. If I have the scalar value (norm), is there a way to determine the $a_x, a_y, a_z$ components? A colleague mentio... |
let's consider a classic mercury thermometer.
I do not understand why it does not behave like a "normal" thermometer which exploits volume dilatation. In a normal thermometer, I'd say that the mercury length would be proportional to its temperature.
Therefore, I should be able to measure, for instance, 37 of body temp... |
With the double slit, experiment we show the double nature of light and matter as wave and particle. In particular, the so called "which way" thought experiment illustrate the complementary principle. In my book, this experiment is analyzed putting a series of particles in front of one of the two slit, so when the elec... |
In papers they often say things about the analytic structure of S matrices - things like resonances are poles on the unphysical sheet, particle channels cause a square root branch cut etc.
I've seen this demonstrated in a couple of simple cases but I was wondering if there was any book/notes where this is talked about ... |
TL;DL
In an inertial frame of reference, one fundamental law that always holds is the conservation of momentum. If you take the reference frame of one of the interacting objects the conservation of momentum no longer holds, so it is possible to detect accelleration (or a force). If this is true then why (in general rel... |
As described by the GR theory, gravity is the curvature of space-time.
On the other hand in quantum mechanics gravity tends to be described as a force, related to it's hypothetical particle called graviton...if that's the case i.e if gravity is a force then what is space-time according to QM?
|
I have just started a course in statics and dynamics. I find the course book we have lacking much more than I had anticipated with respect to rigour and giving mathematical arguments when making statements. I have decided to try to work with the book An introduction to mechanics (Kleppner, Kolenkow) on my own "on the s... |
I'd like to show that the position operator $ X = x$ and momentum operator $ P = \frac \hbar i \frac \partial {\partial x}$ are Hermitian/Self Adjoint when acting in the Hilbert Space $H = L^2(R)$. I would like to show this in the general case $\langle \phi |X \psi \rangle = \langle X\phi | \psi \rangle$ where $\phi, \... |
If i would point a basic red laser at a wall i would see a red point, but how? The photons from the laser cant reach my eye unless the laser is aimed very specificlly, Other photons can't bounce of the laser into my eye since light doesnt bounce of from light, so what is happening?
|
I happened to mention the term ‘matter’ in a question about black holes recently. A friendly user told me that the Schwarzschild model is a pure vacuum solution.
This threw me somewhat.
Such a statement being true would mean that a black hole is equivalent to any region of spacetime in the vacuum state - with maxima... |
The paper Null Geodesics of the Kerr Exterior shows the equation
$$Q = p_ \theta^2 - \cos^2\theta(a^2 p_t^2 - p_\phi^2 \csc^2\theta),$$
where $p$, the four-momentum of a photon, has superscript 2 and subscript $\theta$. I understand the 2 symbolizes the third part of the momentum, but what does the $\theta$ part mean? ... |
I am in high school. So in my book, there is just the definition of decay constant. But I don’t understand the concept of it.
|
This previous question about the effective mass of a photon traveling through glass has a few answers that say we can think of it as a quasiparticle with an effective mass. Photons are spin-1, but because they move at the speed of light, we only get two polarizations. In glass, is the resulting quasiparticle also spi... |
I'm not a physicist but I was attempting to write a story that includes some special relativity shenanigans that I hoped someone could verify.
The gist of it is that people in a spaceship with a 60 day head start need to outrun a signal sent from their starting point, by accelerating for $t_1$ time (as perceived from w... |
For the classical Klein-Gordon field, the motion of a wavepacket is constrained slower than the speed of light for $m^2 >0$ and constrained to exactly the speed of light for $m = 0$ (the equation of motion is the wave equation in that latter case). However, in quantum mechanics, in determining amplitudes of propagation... |
I was reading some texts explaining that since our region of the world is overwhelmingly dominated by matter, and not by anti-particles, this suggests that in some region of the universe, there will be a region dominated by anti-matter.
Why must there exist a region dominated by anti-matter?
I could guess at an answer,... |
Why isn't force $F=m\vec v$ instead of $F=m\vec a$?
If I'm standing in a wind that's blowing at a steady 100 mph, would that not impart a force on me?
|
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