General Definition and 1000 Threads

What is the deviation in the expansion of the universe exactly quantified, when I would assume general relativity and project it backwards? As a statistician I am asking for data, for either the backwards projected general relativity case and either the real expansion case, as it is...

I am posting this paradox as a brain teaser If we drilled a tunnel through the earth, to the other side, and measured gravity in the tunnel, gravity would be zero in the center of mass. This is Newtonian gravity and is connected to the vector addition of the gravitational force; cancels in...

Good afternoon people. I wanted to implement a physical system using control just to put into practice what I have learned in school. To be more specific: I would like to implement an inverted pendulum like the one on the photo In this system a control input (a force u) drives the cart (mass...

Homework Statement attached: I am stuck on question 2, and give my working to question 1 - the ##B(r) ## part I am fine with the ##A(r)## part which clearly is the same in both regions seen by looking at ##G_{rr}## , and attempt, however I assume I have gone wrong in 1 please see below for...

Hello Everyone, I conducted an experiment with a metal beam which had a motor attached to it in with an eccentric mass on it. The two ends of the beams were fixed with a roller and a hinge(as I remember). This was a one degree of freedom experiment. I had to collect data during free/forced...

Looking for a textbook or online pdf on general physics with calculus. I looked for Halliday and Resnick's Physics I and II from my past but did not find an affordable copy in good condition. If it includes advanced material, that is OK.

Homework Statement A solid cuboid has a volume of 40cm3. The cuboid has a total surface area of 100cm^3. One edge of the cuboid has length 2cm. Find the length of a diagonal of the cuboid. Give your answer correct to 3 significant figures. This question recently came up on my maths exam today...

Hi! I'm having a hard time with general solutions of a certain type, maybe it has to do with the constant in the particular solution? The equation is y''+2y'+y=xe-x+1 Is it right to assume that yh=(C1x+C2)e-x ? For the particular solution, I've tried all kinds of guesses for the form: yp=...

According to various sources, the Moon is separating from Earth 4 cm every year. I’ve searched for the explanation and I’ve found the following: The friction the seas and oceans from the Earth make with it’s soil causes the Earth’s rotation to slow down. This causes the Moon to speed up...

Homework Statement When if ever is the speed of the object increasing? Homework Equations Dot product result, cos(theta) acceleration perpendicular, acceleration parralel The Attempt at a Solution I solved the problems first three parts and found when the objects speed is constant using the...

Let us assume a "toy-metric" of the form $$ g=-c^2 \mathrm{d}t^2+\mathrm{d}x^2+\mathrm{d}y^2+\mathrm{d}z^2-\frac{4GJ}{c^3 r^3} (c \mathrm{d}t) \left( \frac{x\mathrm{d}y-y\mathrm{d}x}{r} \right)$$ where ##J## is the angular-momentum vector of the source. Consider the curve $$ \gamma(\tau)=(x^\mu...

Homework Statement For example, what type of filter is this: How can one tell, as a general guideline, without finding the transfer function? I think finding the transfer function is the only real way to tell for sure, but what is a quick way to make an educated guess? The Attempt at a...

Homework Statement I have an exam on vectors and 2 dimensional motion today. I NEED to know if it is possible to solve any GRAPHICAL VECTOR PROBLEM using only INTEGRATION AND MATH WITHOUT ADDING VECTORS TOGETHER GRAPHICALLY. So given any word problem that is supposed to be solved using that...

Homework Statement Find the general solution of the given differential equation. Give the largest interval I over which the interval is defined.Determine wether there are any transient terms in the general solution 5. \frac {dy}{dx} + 3x^2y = x^2 Homework EquationsThe Attempt at a Solution...

I am a working professional trying to get back to some physics that I used to enjoy a couple of decades ago. I still do remember the basic calculus (integrals, partial derivatives, basic ODE) and am interested in studying General Relativity. I have a decent understanding and memory of Special...

The Fundamental Theorem of Quantum Measurement is stated as follows: Every set of operators ##\{ A_n \}## ##n =1,...,N## that satisfies ##\sum_n A_n^{\dagger}A_n = I## describes a possible measurement on a quantum system, where the measurement has ##n## possible outcomes labeled by ##n##. If...

If I am wasting anyone's time, please advise so I can leave and find another source to assist me in my quest. I have been thinking about the theory of General and Special Relativity for most of my life. When I was 16 years old, I saw a documentary about Einstein and how he used his thoughts as...

Homework Statement Say I have four categories which make up a "whole" that I'll call a unique "deal". Each deal can have "I" properties, "J" investors, "K" mortgages, and "L" credit lines, where "I" and "J" must be integers greater than zero and "K" and "L" are non-negative integers (i.e. 0 or...

If we have a system of masses in motion, will the velocity of the center of mass always be given by the net momentum divided by (1/c^2 times) the total energy of the system?

The following, regarding quantum measurement, is stated in the paper "Limitation on the amount of accessible information in a quantum channel" : "Our discussion of measurement will be based on a specific physical model of measurement, to which we now turn. Suppose we have a quantum system ##Q##...

The discussion here https://www.physicsforums.com/threads/general-relativity-the-sun-revolves-around-the-earth.245334/ concludes that in general relativity there are no privileged reference frames so that, for example, it would be valid to use the Earth as a reference frame and say that...

I was looking at my student status today and saw that I'm now a Sophomore, although I haven't started my major yet (have completed almost all the gen ed requirements). What struck me as odd was that in purely doing gen ed requirements, it raised me a full class rank, and took a full school year...

From Verifying the Theory of Relativity by Chandrasekhar Sir J.J. Thomson, as President of the Royal Society at that time, concluded the meeting with the statement', I have to confess that no one has yet succeeded in stating in clear language what the theory of Einstein's really is'. And...

I need to simulate the Friedman equations under different conditions of flat space. Can someone please tell me a good package in MATLAB, Mathematica or stand alone. I am most well versed in MATLAB but have coded in Mathematica before.

What is the best book to learn general relativity for undergraduate and graduate students ? And why?

I've always read that these two theories are incompatible, and how General Relativity works for large scales while Quantum Theory represent reality in extra-small cases. So my question is where is the limit where General relativity ceases to exist and Quantum Theory gives a better portrait of...

why is the general theory of relativity is so complicated i feel that it's very simple no thing hard in it there is a whole website to make people understand it i read the articles and i didn't found any thing complicated knowing the i am 13 so it should be very hard to understand

1) Reduce the quadratic system to its normal form; $x'=y+x^2 +y^2$ $y'=xy$ 2) Consider the following vector field on $R^2$ $x'=\mu x -y-x(x^2 +y^2)$ $y'=x+\mu y -y(x^2 +y^2) $ where $\mu\in\Bbb{R}$. Define the cross section $\Sigma$ to the vector field by $\Sigma=\{(r, \theta) \in \Bbb{R}$x$...

Homework Statement Consider the metric ds2=(u2-v2)(du2 -dv2). I have to find a coordinate system (t,x), such that ds2=dt2-dx2. The same for the metric: ds2=dv2-v2du2. Homework Equations General coordinate transformation, ds2=gabdxadxb The Attempt at a Solution I started with a general...

How can I collapse macroscopic absorption cross-section of 4 groups into two ? Assuming that the first two groups are fast groups and the other twos are thermal . I am suffering with the following : 1- Do I have to assume that the groups are directly coupled ? 2-Does what apply on the two...

One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...

Many have recommended me Resnick for intro physics book, however I already have Kleppner for mechanics, so should I continue just getting a book for thermodynamics and then for EM when I need them or should I get sth like Halliday Resnick? I have noticed, that separate books per subject tend to...

Hi All, Sorry for the vagueness of the post; I promised privacy to a friend who just obtained a patent. She asked me to find a way of testing the product. Since I have no access of any sort to a lab, I am considering doing Mathematical simulations. I wonder if anyone knows about this and/or has...

Does anyone know of a general expression for the unit dyadic, given in terms of the language of general curvilinear coordinate systems?Perhaps an expression for its components?Perhaps an expression, just appropriate for use with orthogonal coordinate systems?$$~$$ In cartesian coordinates the...

I require your help to list all phenomena described as interferences in physics ( as teached nowadays ) with their citations in scholar documents if they are not well known by non-specialists. I am open to adjacent domains like information theory and mathematics. There are already light...

There are two kind of singularities which are familiar in General Relativity. One of them is the singularity of Black Holes and the other is at the beggining of the universe. I'm confortable with the former singularity --it seems to make sense. But as with the latter, I'm not so confortable...

Please don't kill me here...I am really just a curious creature...QFT and GR are mutually incapabatable ergo they cannot both be correct...so best is that one is used for low energy large scale predictions (as per theory) and small scale high energies ( as part theory) ...(BTW I know what the...

Homework Statement Killing Equation is: ##\nabla_u K_v + \nabla_v K_u =0 ## In flat s-t this reduces to: ##\partial_u K_v + \partial_v K_u =0 ## With a general solution of the form: ##K_u= a_u + b_{uc} K^c ## where ##a_u## and ##b_{uv}## are a constant vector and a constant tensor...

I thought about the geometry of Earth by definition and thought of the implications of 'curved space-time'. I understand a trajectory of a satellite and other objects to be straight geodesics through warped space-time. Would the Earth then therefore be able to described as a straight surface in...

Homework Statement Homework Equations flux = int(b (dot) ds) The Attempt at a Solution I just wanted clarification on finding ds. I understand why ds is in the positive yhat direction (just do rhr) but I don't understand where the dxdz come from. How do we find ds in general?

Hi guys, A real easy one. Are the following postulates completely true about general relativity as they are pretty amazing to me. 1) Black holes are a solution to his field equations for GR (or are predicted by the theory) 2) His field equations also suggested the universe was expanding 3)...

Hello! I just had my general GRE and I got 158 on the verbal part. How good/bad is it? I want to apply for a phD in physics, should I retake it? I got 170 for math and I am talking about graduate schools as MIT and Caltech. Thank you!

1. The problem statement, all variables, and given/known data Homework Equations The Attempt at a Solution So basically I took vertical direction formula and I solved for "t". I then took the horizontal direction formula and solved for "x" or we can also call x the "Range" since that's...

Hello, I'm a freshman and I'm struggling with some questions. I'm trying to relate all I'm learning from my Physics classes to the real world (that is the mathematical connection and its expanations with the real world). I have some especifics questions but also a general answer I think could be...

(This is not a homework problem). I'm an undergrad physics student taking my second course in quantum. My question is about operator methods. Most of the proofs for different commutation relations for qm operators involve referring to specific forms of the operators given some basis. For...

Homework Statement In each cycle, the heat given to the system from the reservoir is dQ##_i##. So, why is the total work given by summing ##dQ_i ## over the cycle,why not only ##dQ_i##? Homework EquationsThe Attempt at a Solution

I've been doing many Kinematic problems for physics class on like projectiles, falling objects, cars/people/boats,etc. The thing I'm most confused about is that there are many physics problems involving the x and y directions for velocity, acceleration, position... but like i get confused on...

So, I'm going to learn general relativity but I'm confused in which book I start with Bernard Schutz book seems excellent but I'm more interested in d'Inverno book, And Misner/Throne Book Seems complete but its giant and good for reference, So I think I will go with d'Inverno , but first I need...

Homework Statement Modify the initial conditions (for the diffusion equation of a circle) to have the initial conditions ## g(\theta)= \sum_{n=-\infty}^{\infty}d_{n}e^{2\pi in\theta} ## Using the method of Green's functions, and ## S(\theta,t)= \frac{1}{\sqrt{4\pi...

What is the force acting on an object according to general theory of relativity? If there is a such a force, can we predict the motion of an object in general relativity just using the modified Newtons laws of mechanics i.e using relativistic mass of an object instead of rest mass ?