General Definition and 1000 Threads

I have been wondering what effects a quantum mechanical system would cause in space time. Pick a general state of the system. This would not generaly be in one of the energy eigenstates -rather, it would be on a superposition of energy states. Now, each one of them would cause a different space...

Does General Relativity predicts that in the early universe vacuum energy was converted into matter? How does it relates to the Inflation Theory by Allan Guth? I'm asking this because I remember reading in a book on GR that there are ways of calculating the total amount of energy in the...

Homework Statement The equation of the line that goes through the points and can be written in general form . What are the values for A, B, and C? Homework Equations Ax+By+C=0 The Attempt at a Solution [/B] I think the answer is x=1. But how do i express that in general form?

My textbook states that an alternative definition of the change in potential energy is the work required of an external force to move an object without acceleration between two points. I am confused on why it says acceleration. Wouldn't that mean that the acceleration is 0 and therefore the...

Hi, I have a question about how to write down the following problem in a thesis. I have a standing sinusodial wave with amplitude: |\hat{q}_n| which I want to express as superposition of two traveling waves. Would you suggest do write the sum in the last line like I did, or has somebody a...

Hi All, Just curious on pros/cons of installing software designed for 32- bit systems in a 64-bit machine (Windows 8.1*)? * I have never been able to tell the difference, if any, between Win 8 and Win 8.1 .

Hello In evolution, the archetype rule is the "natural selection" rule. Are the other selection rules? (technological selection rules, cultural rules, etc) Thank you for your time. Regards, ORF

Hi all, Maybe most people would say that physics grad schools (PhD) programs don't care about your GRE writing score, but I have a sort of quick question: how much effort should I put into the Writing sections. I took my first GRE earlier this month, but messed up both of my writing sections...

Homework Statement Action attached: To find the EoM of ##\phi ## / ##\phi^* ## Homework Equations The Attempt at a Solution [/B] Without deriving from first principles, using E-L equations I have: ## \partial_{u}\frac{\partial L}{\partial_u \phi} - \frac{\partial L}{\partial \phi} =0 ##...

Hello everyone! I hope I write in right forum branch. The reason is that I have a question in my mind for a while. Maybe you can help to understand it. So, I am game developer, and one time I was using 2d physics engine to simulate motion in game. And I found out that in that engine, for...

Hi, My understanding is that when light (with some frequency and polarization) hits the interface between two media (each with some frequency-dependent material properties), the Fresnel equations apply. This tells us how much light reflects back versus refracts across the interface. I'm...

Suppose there is a charged particle far enough of any mass so that there is no gravitational interaction between the particle and any other body. The trajectory of the particle in space-time would appear to us like this (we are at the origin of our coordinate system). Consider that at...

(I don't know if this is the right place to post it, but I think the "textbooks" section is'nt. So I'm going to put it here.) I have been self studying S&G relativity for almost eight months, mostly from Weinberg's book on S&G relativity, but also from papers I occasionally find on web and from...

Hello PF. I'm a current sophomore in college studying aerospace engineering, but I was a physics major for most of last year. I am curious what would have become of that, since a lack of desire for low-paying employment opportunities trumped my aspirations in the field. I am curious, how many of...

I have a question about integration and I hope I can word it correctly. When we integrate over something (i.e. a line, a surface, or volume), what exactly do I integrate over? Is it the domain of that "thing"? I feel like it's something I've been told but I just can't remember. If this is the...

Homework Statement To show that ##K=V^uK_u## is conserved along an affinely parameterised geodesic with ##V^u## the tangent vector to some affinely parameterised geodesic and ##K_u## a killing vector field satisfying ##\nabla_a K_b+\nabla_b K_a=0## Homework Equations see above The Attempt at...

Is there any way to travel back in time in reality according to GR? Let me know!

Homework Statement question attached Homework EquationsThe Attempt at a Solution Attempt : Check if ##V^{\alpha}\nabla_{\alpha}V^u=0## Since Minkowski space, connection tensors/christoffel symbols are zero so this reduces to: ##V^{\alpha}\partial_{\alpha}V^u=0## where...

When an object is thrown or propelled upwards and it meets the point at deceleration and drops; what is that point called, where the object is not moving in either direction?

Is it really hard to find a solution of a GR equation maybe two planet system ? Or It could be a different system.I just wonder 1-How much its difficult ( Like can a person calculate those solutions) 2- Whats the boundries (Like we can solve 2 planet system but not 5 etc ? ) 3- Can...

Hi, i got little confused after this conversation in https://www.physicsforums.com/threads/some-questions-about-light-and-relativity.918094/page-2 There was also this conversation: So i want to clear the confusion. As was pointed out to me, in STR mass is defined as m2=E2 - p2, which...

General relativity passes test at Milky Way’s central black hole by Ken Croswell For the first time, astronomers use stars orbiting a supermassive black hole to test Einstein's general theory of relativity, finding no sign of a fifth fundamental force. Links: John Batchelor Show...

Hello, I have a mess in interpretation of constants in description of movement in GR. First of all I define Lagrangian ##l=1/2g_{\mu\nu}u^{\mu}u^{\nu}##, and I would like to talk about axial smyetric spacetime (for example Kerr black hole) ##l(r,\theta)##. l is independent from ##t## and...

Dark matter and dark energy are fudge factors to solve problems in general relativity such as unexplained mass and drag. Is this correct or am I missing something?

I have read Special Relativity from Resnick and Halliday's book Fundamentals of Physics. Now I want to read general relativity. I tried reading Einstein's book "Principles of Relativity", but sad to say, many things went tangentially above my head because I couldn't follow many equations, as...

$\tiny{17.1.08}$ $\textrm{ Find the general solution of the given equation?}$ \begin{align*}\displaystyle y''+100y&=0 \end{align*} $\textit{The auxiliary equation is:}$ \begin{align*}\displaystyle x^2+100x&=0\\ x(x+100)&=0\\ x&=-100 \end{align*} $\textit{Answer by EMH}$...

Homework Statement Consider a system of N isolated conductors,with arbitrary shape and position. We specify the charge Qi on the ith conductor for each i. The capacitance Cij is: Qi= ΣCijVj, sum over j. To prove: Cij = Cji Hint: Consider how much energy is needed to start with the system...

Last year I've finished the undergraduate course in Mathematical-Physics and Mathematics and this year I've started on graduate school on Physics in order to obtain a master's degree. What I'm really interested are two main topics: general relativity and quantum field theory. I also like...

So in differential calculus we have the concept of the derivative and I can see why someone would want a derivative (to get rates of change). In integral calculus, there's the idea of a definite integral, which is defined as the area under the curve. Why would Newton or anyone be looking at the...

Hello, Reviewing for the test and there are still some things I'm not sure about so I thought I'd ask here and hopefully come across someone that can help. I swear I knew this, but I have not been diligently reviewing as much as I should so I think I forgot and became confused. When a...

Homework Statement :[/B] Find the general solution of the Trigonometric equation: $$3\sin ^2 {\theta} + 7\cos ^2 {\theta} =6$$ Given andwer: ##n\pi \pm \frac {\pi}{6}## Homework Equations :[/B] These equations may help: The Attempt at a Solution :[/B] Please see the pic below: It...

Homework Statement :[/B] Find the general solution of the equation: $$\tan {x}+\tan {2x}+\tan {3x}=0$$ Answer given: ##x=## ##\frac {n\pi}{3}##, ##n\pi \pm \alpha## where ##\tan {\alpha} = \frac {1}{\sqrt {2}}##. Homework Equations :[/B] These equations may be used: The Attempt at a...

Homework Statement :[/B] Find the general solution of the Trigonometric equation $$\sin {3x}+\sin {x}=\cos {6x}+\cos {4x} $$ Answers given are: ##(2n+1)\frac {\pi}{2}##, ##(4n+1)\frac {\pi}{14}## and ##(4n-1)\frac {\pi}{6}##. Homework Equations :[/B] Equations that may be used: The...

Homework Statement Homework Equations see above The Attempt at a Solution Using the conservation equation for ##p=0## I find: ##\rho =\frac{ \rho_0}{a^3}##; (I am told this is ##\geq0## , is ##a\geq0## so here I can conclude that ##\rho_0 \geq =0 ## or not?) Plugging this and ##p=0## into...

Hello, I have read a fair chunk of Munkres' Topology book and took a short introductory course during undergraduate, but I would like to learn point-set topology a little better. I have quite a bit of mathematical maturity, so that isn't an issue for me. I had a larger list of potential books to...

I've recently been wondering about the notion of measurement in quantum mechanics. While I'm aware that understanding and precisely defining the concept of a quantum mechanical measurement is at the heart of interpreting the subject, I would like some feedback on some aspects of this topic I...

Pardon my ignorance, but why would nuclear energy be better option, I hear a lot of fears from the general public of why it is not safe? How would someone convince someones fear about the safety of nuclear power, considering what happened in Japan? cheers,

I just read the following paper that was written in 2014: https://arxiv.org/abs/1403.4687 It proposes that wave-particle duality and the momentum-position uncertainty (entropic) principle are physically the same phenomena. The paper was discussed at some length in this forum in the following...

Hi, i have this problem..., giving two circle (example radius 1 = 500 units, radius 2 = 200 units, distance between centers = 275.73 units) find Euler Spiral (aka Cornu spiral, aka Clothoid https://en.wikipedia.org/wiki/Euler_spiral) tangent giving circle (unknown tangent points). For this...

Hi there guys, I'm struggling! I've been looking at the International Earth Rotation Services (IERS) "standards" for motion of a satellite in GR. the expression is far from trivial and I'm battling to determine where to even start with this bad boy. The expression is given by \Delta...

I have proved for myself the following theorem, generalizing Galois theorem to general algebraic extensions. My question is: is it true, and is there some reference to this theorem in the literature? Theorem: Recall that a subfield ##M## of a field ##L## is a perfect closure in ##L## if there...

Suppose i have an equilateral triangle and i want to find the principal axes of rotation passing through one of the vertex. How can i do that? I am thinking along the following lines but I'm not too sure: 1)Since the equilateral triangle has symmetry about a median, that definitely is one...

First of all, I would like to admit that my understanding of general relativity is limited, though this will hopefully be remedied this summer when I take a GR class. I think we have all seen a sci-fi movie where the characters are stuck in a space where they are trapped in a sort of "warp...

The international Journal of Greenhouse Gas Control. It has an Impact Factor of around 4, but what's the perception? Is it respected? Is it considered a good journal? There isn't a qualitative judgment online. My boss seems to look down on it, but it has a good impact factor.

Hi everybody! I am (like many) very fascinated by the cosmic microwave background, but there are many aspects of it that I do not understand yet. I'm currently in 4th semester of my physics studies, and just starting quantum physics now. Some of those questions might be stupid or (mis)leaded by...

i'm trying to understand the solution to this problem: http://physweb.bgu.ac.il/COURSES/StatMechCohen/ExercisesPool/EXERCISES/ex_2065_sol_Y13.pdf (link to the problem and the solution of it) All my questions come from the partition function: 1) From where the term (2*pi)^d comes from?, I...

Consider the Einstein-Maxwell action (setting units ##G_{N}=1##), $$S = \frac{1}{16\pi}\int d^{4}x\sqrt{-g}\ (R-F^{\mu\nu}F_{\mu\nu})$$ where $$F_{\mu\nu} = \nabla_{\mu}A_{\nu}-\nabla_{\nu}A_{\mu} = \partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}.$$ This describes gravity coupled to...

In general relativity, does momentum conservation mean conservation of 4-momentum or 3-momentum

Hello there, suppose we take ##M## to denote the spacetime manifold. Suppose also that ## ds^2 = g_{\mu \nu} dx^\mu dx^\nu##. I have some confusions with regards to the metric and the line elements. My main confusion is at which points in the manifold are ## ds^2## defined? Is it correct that...

I want to prove that ##E = -g_{\mu \nu}u^\mu p^\nu## is the energy measured by an observer with velocity ##u^\mu## of an object with momentum ##p^\mu##. My reasoning is that in special relativity we know that ##\gamma m = E##. We can transform to coordinates where ##u'^\mu = (1,\vec{0})##. Since...