General Definition and 1000 Threads

I hear that philosophy refuse to "relativity concepts"(e.g relativity moral).Relativity theory says about the relativity of spacetime.I do not understand why special relativity does not contradict with general philosophy?(I know the theory Idea Form of Plato)

Actually, is not a doubt as a question, in which there is wrong or right. I just want to update myself with respect to the current physicists opinion about the Copenhagen interpretation of Bohr and Heisenberg. Summarizing, there is a consensus among the majority? In another words, there is still...

Good day, I'm starting my master in physics, and it's time for me to choose my courses. I will take one or two of the following three courses, which are: Statistical Physics, QFT and General relativity. Now, I'm finding it very hard to decide as on the one hand, I'm interested in QFT and...

Let's start with a configuration in which one tube, A, splits into two, B and C. We can write the relationship $$A_A v_A = A_B v_B + A_C v_C$$ When I first saw this formula (which was very recently), I wanted to solve for ##v_B## and ##v_C## given all other values. I can't of course. There are...

Hi, can i use a light clock made out of mirrors a distance appart to measure whether there is length contraction in different regions of spacetime? If the clock speeds up then the distance between the mirrors decreased. If the clock slows down the distance between mirrors increased.

I know that it will take 3 washings to reach the desired purity of sand, and that "N-1" is an exponent in the general expression, but I am stuck beyond that.

Hi. I have tried David Tong's note on QFT. I think it works well for me and lead me into QFT. Now I am confident to read Peskin's book. Now I am trying to learning GR. I planned to try David Tong's lectures on GR first and then read Sean Carroll's book. But I am not sure this plan now. I got...

I came to know of a old russian book "Physics : A general course" by Savelyev. I have heard that the book was popular in USSR. Strangely, I could not find any review or mention of this book in the internet (searched through Google, Yandex, DuckDuckGo). PhysicsForum - One post of one thread...

Hi! I know some theorists believe all quantum fields and gravitational field are different aspects of one universal field. What does that formally (e.g. mathematically) mean "to be different aspects of" and how can one prove, let's say, fields A and B are different aspects of C? By the way, I...

I have an long equation I managed to simplify to that form, but now I haven't the foggiest on how to solve for x, any help appreciated

As far as I understand it general relativity does not explain the origin of the inertial mass ##m_i## in Newton's law of motion ##\vec{F}=m_i\ d\vec{v}/dt## but rather it simply applies the concept to curved spacetime. For example if we have a particle with inertial mass ##m_i## and charge...

Consider a mass ##M## that generates a curvature of the space-time and an observer ##O##, fixed and positioned at such a great distance from ##M## that the time ##t## of its clock is not affected by ##M##. Suppose that the observer ##O##, in his polar coordinates reference system centred at...

All physical laws have to be Lorentz invariant according to a lecture I just watched. Why is general covariance (which is more general than Lorentz invariance) not a requirement for all laws of physics? Are there any quantum gravity theories that take the approach of adding general covariance to...

We relating to an electromagnetic radiation as waves. and in waves there is maximum point and minimum point but when there is permanent electromagnetic level there is no disorder or weave . so is it possible to measure it in blank space relative to other places

It seems that there are two distinct gravitational cases to consider: a) Object with no external contact with any type of stuff (e.g., a person in free-fall in a vacuum) b) Object WITH external contact (e.g., a person standing on the ground) I've enjoyed reading and listening to various...

I'm looking to learn how to do basic home maintenance such as: Roof repair Bathtub install Tile flooring Install wood flooring Shower stall demo and install How to add ceiling lights Driveway install Basic things that come with owning a home. I believe that the people who do these type of...

This equation, is non linear, non-separable, and weird. I would like to have a direction to start working on this. I tried writing sin(2y) = 2sin(y)*cos(y). See, ##xy' = x^3sin^2(y)-2sin(y)cos(y)## Can't separate. Writing in this way: ##(x^3sin^2y-sin2y)dx-xdy=0## Also, I checked that it is...

James Clerk Maxwell deduced that the unit of mass has the dimensions of (L^3)(T^-2). But he assumed Newton's Law. What would it be under general relativity?

Hello everyone, Heisenberg's uncertainty principle tells us that we cannot measure the position and the momentum of a particle to infinite accuracy. My question is, can we use general relativity to overcome this difficulty? From what I know, any mass can curve spacetime even if it was small, and...

Hi. What are the math courses should I take in order to understand the mathematics involved in a book such as Sean Carroll in general relativity. Thanks

Hello! (Wave) Suppose that we have the recurrence relation $a_k=3^k-a_{k-1}, a_0=1$. By replacing the terms of the sequence we get that it is equal to $a_k=3^k-3^{k+1}+3^{k+2}-a_{k-3}$. How do we get that it is equal to $a_k=3^{k}-3^{k-1}+3^{k-2}- \dots+ (-1)^k$ ? :unsure: Also, why is the...

I am trying to study "religiously" the book by Sachs and Wu, but I am finding the Exercises very much of a challenge. Does anyone know if there exists a source for solutions one can consult when stuck?

For a system of two or more particles, it is customary to define potential energy functions ##V_{ij}## between pairs of particles, so that the total conservative force (not necessarily total) on any given particle is $$\mathbf{F}_i = \sum_{j\neq i} -\nabla_i V_{ij}$$as a sum over all other...

My struggle here comes from finding the bending moment ##N(x)##. My working is as follows. We want to find the bending moment on an element a distance ##x## away from the axis of rotation. To do so, let us consider the bending moment due to the force on an element ##\xi>x## away from the axis...

For a general body, there exists the notion of centre of mass work; that is, computing the work done if all of the forces on the body act through the centre of mass. If we separate the total kinetic energy into that of the CM and that relative to the CM, ##T = T_{CM} + T*##, we can show by...

576 Find the general solution $2y'+y=3t^2$ Rewrite $y'+\frac{1}{2}y=\frac{3}{2}t^2$ So $u(t) = exp\left(\int \frac{1}{2} dt \right)=e^{t/2} $

Find the general solution of the given differential equation, and use it to determine how solutions behave as $ t\to\infty$ $y'+y=5\sin{2t}$ ok I did this first $u(t)y'+u(t)y=u(i)5\sin{2t}$ then $\frac{1}{5}u(t)y'+\frac{1}{5}u(t)y=u(i)\sin{2t}$ so far ... couldn't find an esample to follow...

The calculations for the magnetic field produced by a uniformly rotating charged sphere can be found in basically every book on electrodynamics. I wonder what happen with the magnetic fields produced by rotating rigid solid that also present precession and nutation movements. The question comes...

Hi, if I want to construct the most general Lagrangian of a single scalar field up to two fields and two derivatives, I usually see that is $$\mathscr{L} = \phi \square \phi + c_2 \phi^2$$ i.e. the Klein-Gordon Lagrangian. My question is, would be valid the Lagrangian $$\mathscr{L} = \phi...

Summary:: I want to learn special and general relativity I am curious what is the best way to learn special and general relativity. https://www.coursera.org/learn/einstein-relativity/home/info I started this course but it seems relativity easy so far. Only on week 2. Being easy is not bad I...

First of all, please understand that I am not good at English so I used the translator. (EDITED by mentor: small edits + added latex...) After I studied free particles, I wanted to apply what I learned to other situations. But as you know, to determine the solution of the free particle, you...

Is it ##(n-1)d^{1->10}ns^2 \ or \ (n-1)d^{1->10}ns^{0->2}## ? My textbook says it is the latter. But I feel like it should be the former. Moreover, period 6 and 7 has the presence of f-orbitals. So adding## (n-2)f^{0->14}## would make it more general. Isn't it? And also what about the f-block...

Moved from technical math section, so missing the homework template Summary:: Find a general formula for the nth derivative Hi everyone! How would I approach and answer a Q such as this I began by rewriting the expression in a different form, then used chain rule to each given term I...

If an astronaut travels to a 10 ly distant star with a speed very close to light speed, then he will measure a distance to his star much smaller than 10 ly (length contraction) so his time for reaching the star will be smaller than 10 years, let's say 1 year. Then, without delay, he returns back...

I've been reading about the sophisticated double-slit experiments currently being conducted by a team of physicists led by Tom Campbell. It's no secret of course that Campbell hopes that the findings of these experiments will strengthen the argument that our universe is a computer simulation...

I always was confused on how objects fall on Earth due to curvature of space. All I see everywhere is a flat stretched piece of fabric and balls going round and round the central massive ball. But that does not explain anything, how objects actually fall. Finally I saw this video where it...

Since the spherical wave equation is linear, the general solution is a summation of all normal modes. To find the particular solution for a given value of i, we can try using the method of separation of variables. $$ ψ(r,t)=R(r)T(t)ψ(r,t)=R(r)T(t) $$ Plug this separable solution into the...

One obvious difference is that gravity is more general, because there are alternative theories of gravity that differ from general relativity. In this sense general relativity can be thought of as a subset of gravity. But I am interested in a different type of difference. I am interested in a...

Every theory, whether it is a physical, a psychological or a sociological theory, is defined in terms of an assumed architecture and in terms of a number of assumptions that apply within that architecture. An example from physics is the previously widely accepted dome theory to explain the...

a) P(X<18) = (18-20)/sqrt25 =-2/5 =-0.4 then you use the standard normal table and find that; P(X<18)=0.3446 b) P(X>27) = (27-20)/5 = 7/5 = 1.4 P(Z>1.4) =P(Z<-1.4) =0.0808 C) =(13<X<23) =13-20/5 , 23-20/5 =-7/5 , 3/5 =-1.4 , 0.6 P(Z<0.6)-P(Z<-1.4) =0.7257-0.0808 =0.6449

I'm a bit confused about the notation used in the exercise statement, but if I'm not misunderstanding we have $$\begin{align*}(\psi^+_1)^{-1}:\begin{array}{rcl} \{\lambda^1,\lambda^2\in [a,b]\mid (\lambda^1)^2+(\lambda^2)^2<1\}&\longrightarrow& \{\pm x_1>0\}\subset \mathbb{S}^2\\...

Attempt: I don't know what they mean by effective Lagrangian. I am aware there is something called 'the lagrangian' that goes as L=g_ab * dx^a/dk * dx^b/dk, but i don't see how this gives me any of the chrostoffel symbols... cheers

I am very new to such ideas but was wondering if there is any connection to what I am asking. Taking two events, let's say at opposite ends of the globe. Would even A, only have a potential on event B, if light could travel between these event in the given time frame of these event occurring...

Hi everyone, While finding the solution for one of my exercises, I found the following answer. I'm seriously questioning if the equations provided in that answer are reversed. According to my understanding, if two vectors ##\vec{S}## and ##\vec{T}## are parallel (same direction) the magnitude...

Hello. I've recently been reading this paper... https://arxiv.org/pdf/gr-qc/0001099.pdf ...in the hope that I can begin to understand some the role of the energy conditions in General Relativity. But I'm not making much progress and so I've turned to this paper...

"their scalar product is..." why?

Source = John R. Taylor, Classical Mechanics, page 651 + page 677 Trying to solve, A mass m is thrown from the origin at t=0 with initial three momentum p_0 in the y direction. If it is subject to a constant force F_0 in the x direction, find its velocity \mathbf{v} as a function of t, and by...

Question.

For a harmonic oscillator with a restoring force with F= -mω2x, I get that the solution for the x-component happens at x=exp(±iωt). But why is it that you can generalise the solution to x= Ccosωt+Dsin(ωt)? Where does the sine term come from because when I use Euler's formula, the only real part...