What is Gr: Definition and 952 Discussions

1.a) Concider the 2-space consisting of a spherical shell at constan radius, r. In polar coordinates the line element on the surface can be written (a, b,∈ 1,2) Homework Equations ds2=gabdxadxb=r2dθ2+sin2θdφ2 calculate gab, Γabc, R1212, R2121, R11, R22, R The Attempt at a Solution...

I cannot get past thinking of it like air pressure

While studying the Einstein Equation, I noticed something curious, at least to me with little experience in General Relativity. Start with the usual formulation of the equation: R_{\mu\nu} - \frac{1}{2}g_{\mu\nu}R + g_{\mu\nu}\Lambda = \frac{8{\pi}G}{c^2}T_{\mu\nu} Then, apply the...

Hi. I have a question to ask the countless physics students on this forum. I just completed my gr 12 physics course (SPH 4U) and I absolutely loved it! The teacher was awesome, he had so much passion for the subject and he would go out of his way to tell us about how he majored in physics...

My question is to what extent the specifically non-linear properties of GR have been analyzed by theoretical physicists. Can they give rise to chaos and complexity, as many non-linear systems do? I also wonder: I've so far mostly read about linearized descriptions of gravitational waves...

I mean, why there are so many speculations? It must be 'shut up and press enter' :) For example, some people say that the second horizon in the Kerr black hole is not dangerous. Others claim that due to infinite concentration of energy there there is a real singularity there so everything...

How did Einstein come to pushish his general theory of relativity? Was it in a series of papers over a few years, or in one definite article? In either case, are these (or this) papers available on the internet in engligh? Thanks.

Hi all, I'm taking an introduction to general relativity course along with an elementary differential geometry course this term. I'm really interested in this stuff and I've been waiting 3.5 years to take these courses, so I'm really excited. Which textbooks have you all come across that...

As suggested by Marcus, I have read the whole paper and decided to start a discussion of Kober's paper by asking a few questions. The paper certaintly presents a very interesting view. Part of it is an extension of Heisenberg's work on unified QFT, that the mass originates from self-interaction...

So I was thinking about getting some textbook for self-study GR. I don't need to master it, I just wanted to get a look at it for the first time. Is there a particular textbook that anyone would recommend for me? Thanks!

As I try to understand GR, I find coordinate transformations just about everywhere. My question is simply: What is the reason coordinate transformations play such an important role in GR? Thanks.

If a stationary observer throws a rock out in the radial direction in a Schwarzschild geometry, what is the relationship between the energy of the rock and its speed in the observer's frame? I'm a bit confused because the book seems to say it's E = \frac{m}{\sqrt{1-V^2}}, but I thought that...

Another thought on the equivalency of gravity and acceleration and it's affect on light. If a beam of light was shot directly outwards from the moon, and partiallly reflected by a series of mirrors in it's path, would the apparent speed of light as observed by an external viewer (say Earth...

Homework Statement A cosmonaut spends a few years in an orbit above the Earth. We would like to estimate how his age will differ from his age if he had stayed on Earth. We will consider two separate effects. (a) First calculate the effect due to time dilation from Special Relativity. Let...

Eccentricity & GR precession; Mercury vs. GP-B How big a factor is the Eccentricity of Mercury orbit in contributing to its precession? GR precession has been confirmed in the Gravity Probe B orbit even though it has an eccentricity of zero. The GP-B used a gyroscope to take the place of a...

Hi all, I am having trouble proving the following proposition: \bar a is a generator of the additive group Z_m if and only if gcm(m,a)=1. Well, first let's start with what i know. I know how to prove the following: Let G=[a] be a cyclic group of order q. Show that a^s is a...

The first edition for this book was a nice primer to GR for ppl like me who are far from mastering the advanced math required to in deep understanding of GR. Prof. Edwin F. Taylor now has a drop site for electronic drafts of the second edition of the book, improved and updated with new...

If I understand things correctly, GR says that gravity isn't really a force at all, gravity is just particles moving in the geometry of spacetime. Given this, I don't understand the role of the graviton. I thought that gauge bosons were force mediators, that they somehow communicated and...

i might get confusing cause i don't understand this very much but here is the copy of my lab i need help with #1 & 6 of the POST-ALAYSIS here is the word doc. of my lab http://courses.digitaldapp.org/documents/Inquiry%20Lab%20-%20Experiment%2003%20-%20Composition%20of%20a%20Hydrate.doc...

1) If I plotted the time dilation at corresponding, radially symmetric coordinates surrounding a large mass, would it result in a geometry of space as a function of time? 2) I have heard GR defines the geodesic of a mass moving in the metric of another mass but as it is a geometry of masses...

arXiv:0809.3730 [ps, pdf, other] Title: Experimental Tests of General Relativity: Recent Progress and Future Directions Authors: Slava G. Turyshev Comments: revtex4, 35 pages, 10 figures Subjects: General Relativity and Quantum Cosmology (gr-qc) Einstein's general theory of relativity...

hi, recall the familiar round trip - it's more or less the same as in this arXiv article (http://arxiv.org/PS_cache/physics/pdf/0604/0604025v3.pdf) - round trip with acceleration g. me and my friends were wondering the following: imagine that the passenger abroad the rocket travels for 4...

I'm trying to learn some GR from Carrol's textbook, but I'm a little lost there. For example, this simple problem: In Euclidean 3-space, let p be the point with coordinates (x,y,z) = (1,0,-1). Consider the curve passing through p: x^i(\lambda) = (\lambda, (\lambda-1)^2, -\lambda)...

(This was originally posted in https://www.physicsforums.com/showthread.php?t=248625&page=2" but I started a new thread as it was going slightly off topic) Einsteins equation for gravity is g=ρc2+3P (basically energy density plus 3 times the pressure)- The equation for Newtonian gravity...

Hi! This is a question for the physicists. What types of math do I need to study the physics of ... let's say loop quantum gravity, string theory, quantum electro dynamics/ chromodynamics and general relativity on the basic level? Tnx

In SR, coordinates are unambiguously defined with reference to a lattice of rigid steel rulers with synchronized clocks at each vertex. How does the situation change in GR? Consider e.g. the Scharzschild metric ds^2 = g(r) c^2 dt^2 - \frac{dr^2}{g(r)} - r^2(d\theta^2 + \sin^2\theta...

I have read in various places that according to General Relativity space contracts around large bodies. And moving further out of the gravitational field, space dilates. What is the logical basis for this? Is it in fact even true and can it be measured? Does anybody know of any sources on...

Question about "pressure" in GR On http://math.ucr.edu/home/baez/einstein/node3.html it says "Given a small ball of freely falling test particles initially at rest with respect to each other, the rate at which it begins to shrink is proportional to its volume times: the energy density at...

I'm looking for a reasonably challenging problem that will help me apply concepts of GR. Difficulty wise, I'm looking for something that would compare to a QED cross-section calculation. Can anyone suggest such a calculation? I'm considering the problem posed in MTW to figure out the...

Hello! I know nowadays physicists try to make the grate unification - all 4 forces in a single theory that would govern all of their interactions :) However many people say QM and GR are incompatible. Can anyone of you please explain to me why this is so? I know that QM is a probability...

Specific examples please

Hello folks, I was wondering about a possible probe sent to alpha centauri which would be able to do a deep scan of the system, maybe for a month, and then send back results. I then wondered, that if the probe was exposed to different gravitational conditions, let's say favourbly, would...

I have to find the vertical displacement of a potato shot out of a potato launcher (Gr. 11 Physics assignment). It would make sense (and make this easier) to assume that the potato went straight up and down and I am allowed to assume that air resistance is negligible. My main problem is proving...

If I want to consider the velocity of distant receding galaxies which may be receding at velocities close to the speed of light can I use SR? I know you are not suppose to use SR with when velocities are close to the speed of light. If a velocity is due to universal expansion does that make a...

Since SR physics has considered motion strictly as the separation of bodies, no longer can a body move through space except with reference to another body. Consider an infinite number of frames (A, B, C, ... A1, B1, C1,...An) with common x axis. All move near the speed of light relative to...

M. Chodorowski argues in his http://arxiv.org/abs/astro-ph/0610590v3" that the concept of "expansion of space" is not necessary to explain the expansion of the universe, and therefore Occam's Razor tells us that we should consider discarding the concept entirely. He says that expansion is...

In GR, what is the energy of a system of two identical bodies rotating around their center of mass with regular angular frequency? (assuming such a system is possible). Please take into consideration that I don't know GR at all. Thanks.

Stumped about GR "contradiction"--help please Apparently some crackpot blew some $$ on a full page ad in a science magazine, claiming to show that there black holes don't exist because GR contradicts itself about them. I haven't seen the ad, but there's also a blog about it and a thread about...

According to GR, how do changes in the mass of an energy density become reflected in its gravitational field? Is the dissemination of the change in mass throughout the gravitational field c-limited? If so, what geodesic does the dissemination of the change travel. Is the geodesic the same as...

Question: 1. A gravitational interaction causes two energy densities to accelerate towards each other. 2. This increases their relative velocity. 3. By special relativity, increasing relative velocity increases (relativistic) mass. Even if the energy involved is small, the energy...

http://http://arxiv.org/abs/0803.2701v1" is a new, well-written explanation by R. J. Cook and M. S. Burns as to why the accepted physical attributes of GR are entirely frame-dependent. This concept is fundamental to understanding GR. Jon

So after hearing a few theories, I had this idea that seems to make some sense. The problem is that all of the math involved is waaaay beyond anything I've done, and I don't even know where to start. So basically I have this theory that seems to make a lot of qualitative sense but I have no...

I quite often hear that GR is formulated in terms of tensors because laws of physics expressed in terms of tensor equations are indepedent of choice coordinates because they `transform nicely'. I thought the motivation for tensors was that since spacetime is curved, we locally linearize it by...

1. How would a general relativist explain why an object falls towards the earth? 2. Is it correct to say that it is not the apple that falls towards the Earth but it is the Earth that accelerates towards the apple? Why is this ok to say?

I'm doing a research project for a class in advanced differential geometry, and have chosen to cover dynamical systems. However, I've found that the relationship between dynamical systems is limited to exploring flows on manifolds in the most abstract sense. As a result, I was hoping on expand...

Since the WMAP 5 year data is now out and contains no nasty new surprises, what does everyone think about the current and future status of gravity? Please read these more detailed descriptions of the poll options before you vote! Note that these options are all basically beyond what we can know...

We describe mass as creating "curvature" in the universe. Taking a simplified lower dimensional analogy, the universe at a point in time could be seen on average as being like the surface of a ball, but at a more detailed level the surface could consist of shallow cones (made of locally flat...

I have a question about classical gravity versus GR. If we use Newtonian gravity for a sphere, gravity is zero in the center due to vector addition. So if we were to plot the gravity force versus distance, from far space, to the center of a spherical planet, it starts near zero, climbs until we...

Well as every physical theory has some phenomonas that it can't explain/describe, what are those phenomena in GR? I mean besides the what goes inside the event horizon and unification with QM, what other phenomena cannot be explained by GR?

GR is invariant under general coordinate transformations. If I understand correctly, this is basically devoid of any physical content. It just means that relabelling points does not change anything physical. So it's devoid fo physical content, right? On the other hand, in special...