What is Gr: Definition and 952 Discussions

http://arxiv.org/pdf/1101.5974 The Link between General Relativity and Shape Dynamics Henrique Gomes, Tim Koslowski 14 pages (Submitted on 31 Jan 2011) "We show that one can construct two equivalent gauge theories from a linking theory and give a general construction principle for linking...

In another thread, it's considered a generally accepted fact that the WEP is not valid anymore the way it was initially postulated: I find this surprising, because such a change in the principles of the theory should be more stressed in introductory GR textbooks, and kind of disturbing...

Whenever I read about or listen to things GR related, physicists always say "with incredible accuracy" or other words that imply GR isn't 100% accurate, i.e. they never use the words 100% accurate How innaccurate are they talking? A popular one always seems to be the planet Mercury's orbit

Total angular momentum is not conserved due to lack of spacetime spherical symmetry, it is precisely this fact that causes the angular momentum of the quadrupole moment to have to be radiated away as gravitational radiation. (see Schutz, chapter 9: exercises 39,40 and 47). In this context...

Mentz was kind enough to give me this explanation for co-frame basis for a specific metric that I specified. However, I was wondering if there is a general procedure for finding the co-frame basis vectors for a general Einstein metric. I see the procedure involves the tensor product of the...

Can someone please explain to me why general relativity is not renormalizable? Because from how I understand it, the lagrangian density is just R/G, where R is some complex function that contains 2,3, and 4 point terms of the metric g (which is the quantized field). Since R has mass dimension...

I would like to understand the reason why GR is commonly believed to be the best therory of gravity we have. As far as I know there are many theories of gravity some of which is quite similar to GR. Do we really know that GR is the best theory (it describes the observed phenomena better then...

I have a question regarding how you choose courses to take in graduate school, and the amount of freedom you have in choosing courses. I'm tentatively planning on applying for admissions to PhD programs for 2012, and I'm planning on applying to a mix of biophysics, medical physics, and high...

I want to find a good reference in GR about the application of tetrad. Is there any good suggestions?

A very important idea in General Relativity is, same laws in all reference frames. How does that work in rotating reference frames? Jonny

I've been studying GR for 2 semesters now and am about to dive into quantum mechanics and so I thought it appropriate to ask this question. Why is it that Quantum theory and GR don't interlap at quantum scales? More generally, why doesn't QED fit into GR? fundamental concepts as well as specific...

Does anyone know of any website that has animations of what this Diffeomorphism Invariance in General Relativity can do? I read a lot of articles about it but can't seem to get the essence or visualize how it actually occurs exactly. Thanks.

Hi, I am doing question A2/15 B2/23 (specifically part (ii)) at the top of page 50 here: http://www.maths.cam.ac.uk/undergrad/pastpapers/2001/Part_2/list_II.pdf I have done everything up to and including showing the impact parameter is given by b=h/E, but I am having trouble doing parts (a)...

So I am stuck on another question I've been looking at Ina brake test on dry concrete a Porsche Boxter traveling with an initial speed of 33.2 m/s can stop w/o skidding after moving 62.8 m . The mass of the Boxter including driver is 1340kg. Determine the magnitude of the average...

A cart on a surface with a coefficient of friction of 0.20 is attached to an overhanging weight. THe cart has a mass of 2.5 kg while the overhanging weight has a mass of 1.0 kg. Determine the Acceleration Hanger Fg = 9.8 N Cart Fg = 24.5 N Fk = 4.9 N A = Fnet/m = 4.9 N/2.5...

Prof Hagen Kleinert suggested that the action (3) \[A = \int_{{t_a}}^{{t_b}} {dt\frac{M}{2}{g_{\mu \nu }}(q){{\dot q}^\mu }{{\dot q}^\nu }} \] can lead to GR. He writes, "Einstein's equivalence principle amounts to the postulate that the transformed action (3) describes directly the...

He who calls himself "Nabeshin" stated: "It seems to me the distinction can be best seen in the following: Differential geometry is mathematics, and this will tell us what the geodesics on a given manifold are. So if we're just finding geodesics on manifolds, maybe it's the manifold...

I have recently been studying GR to find out if you really can find out how fast an apple will fall on the surface of the Earth in GR. Its simple with Newtonian mechanics, just use F = GMM / R^2 A = GM / R^2 I started to with the geodesic equation. Which Christoffel symbols should I...

I understand how non-euclidean space curvature can cause a change in direction of inertial motion but I don't understand how it can cause acceleration. I guess the reason will be that not only space is curved but also time and that the time curvature somehow will provide the energy needed...

Hi, My question is the following. In special relativity, the Lorentz transformations correspond to a physical situation in which two frames of reference move with uniform rectilinear motion one with respect to the other. In general relativity, given the physical situation in which one frame...

I always hear that these two things are incompatible but I never really hear why. The most I know is that QM assumes a quantized spacetime whereas GR assumes a dynamic one, but I don't really understand if this is correct (nor do I get what that really means). I don't see how GR would fail...

I have a technical question that puzzles me. Let T_{\mu\nu} be a conserved energy-momentum tensor in curved spacetime \nabla^{\mu}T_{\mu\nu}=0. Let \Sigma be a curved spacelike hypersurface with the unit vector n^{\mu} normal to \Sigma. Define energy H on \Sigma as H \equiv...

I think I need a detailed GR book especially in Mathematics, since that is too unfamiliar to me. I want to see examples on how to calculate Christoffel Symbols via metric, how to calculate Riemann Curvature Tensor with coordinate component and tetrads. And even more, the detailed...

if newten was wrong about gravity, and einstein is right (general Relativity) does it mean that gravity is not a force.

GR predict that a photon climbing in the Earth's gravitational field will lose energy and will consequently be redshifted. A test was done by Pound and Snider in 1965 using the Mossbauer effect They measured the redshift experienced by a 14.4 Kev rays from the decay of Fe in climbing up...

Based on the wiki article: http://en.wikipedia.org/wiki/Einstein%E2%80%93Cartan_theory Cartan gravity is not just “possible extension” of GR, but it is absolutely necessary and unavoidable (search for “proof” in the article). As wiki is not a 100% trusted source, I wanted to ask: How...

Have looked on the forum but can't find this query so hope I am not repeating something that might be here already. Also hope this is the right forum for the post. Homework Statement I am working through a paper on particle motion in GR (Cohen PhysRevD 19,8,p2273) but am running into a few...

I'm an undergraduate student who is trying to decide whether to focus on mathematics or physics. I'd like to know how much Differential Geometry is applicable to GR? If I were to take rigorous courses in Differentiable Manifolds and Differential Geometry, will these courses allow a deeper...

Why do singularities mean that GR "breaks down?" The existence of singularities in the form of black holes as predicted by GR is universally accepted at this point. The fact that GR calculations don't work inside a black hole means only that we are incapable of penetrating the event horizon...

I'm reading this: ==quote== Einstein's theory of gravity, General Relativity, and our theory which governs the sub-atomic world, Quantum Theory, give seemingly inconsistent accounts of the nature of time. According to General Relativity, each observer will have a separate notion of time...

Homework Statement Starting from a general axisymmetric metric ds^2=g_tt dt^2 + 2g_tφ dtdφ +g_φφ dφ^2 + g_rr dr^2+g_θθ dθ^2 ...(0) where the metric components are functions of the coordinates r and θ only. I've managed to show (via Euler-Lagrange equations) that g_tt dt/dτ + g_tφ...

Hi, Sean Carroll talks about energy conditions in ch4 of his GR book. From what I understand we want to impose co-ordinate invariant restrictions so we need to form a scalar from the energy momentum tensor, which is done by just arbitrarily contracting with timelike/null vectors (why not...

How is Lorentz invariance handled in GR? I know that there is no global Lorentz invariance in GR, instead it only holds locally, meaning that it is obeyed in the limit at infinity:when r goes to infinity by considering infinite distance or infinitely small point mathematical objects. But when...

We consider an spacelike infinitesimal separation {ds}^{2}<0 ds=+ or -ib [an imaginary quantity] Now I integrate ds along some path from A to B. What happens if the imaginary parts cancel out on integration[if we can manage to cancel them out]?I mean, is it physically significant in any way...

In another forum that I frequent, I have been having a discussion where the state of quantum gravity research came up. Another poster claimed that one of the first thing that any gravity scientist checks for the theory is the theory's prediction for the precession of Mercury's perihelion. Now...

Over the years there have been many alternative theories of gravity: Brans-Dicke, quadratic Lagrangians, F(R) &ct. Do any of these share the nice property of GR that the equations of motion are a consequence of the field equations and do not have to be seperately postulated? Thanks, skippy

I just want to ask a simple question: Is it true that Newtonian/Classical Mechanics does not hold true for all coordinate systems, while General Relativity does?

I asked this in one of my previous topics, but I just cannot find where I asked it, so here I am asking it again. Can someone give me a link to a web version of Einstein's GR. I want the one with Einstein's OWN WORDS, not reworded (other than simple language translation, if he did not write...

A few weeks back I posted about a test by C. Alley in the 1970's of Einstein's famous goof in predicting that a clock would run at a different rate at the poles than at the equator. Alley apparently was never big on publishing his results in journals, but I requested a conference proceedings via...

In hamiltonian formulation of GR there appears some constraints (it may be found e.g. in "Modern canonical quantum GR" by Theimann, ch. 1.2). I would like to find a Dirac algebra of the constraints (i.e. compute Poisson bracket between constraints), but my results are not consistent with...

1) where i got more atoms in 20 gr H2SO3 or in 20 mol of HCl ? 2) tell me if i Right: the mass (in gr) of 100 Molecules Of SO2(g) is: the mass of O2=31.998, the mass of S=32.065. so Together the mass is about 31.998+32.065*100=6406.3 but i don't sure how to Change it to (gr) unit...

Homework Statement This question is from a correspondence course I'm taking: Two spacecraft from different nations have linked in space and are coasting with their engines off, heading directly toward Mars. The spacecraft s are thrust apart by large springs. Spacecraft 1, with a mass of...

While the title may suggest this thread belongs in cosmology, my questions are orientated towards a better understanding of general relativity. Basically, there seems to be an assumption that after the Big Bang, the initial expansion of the universe was slowed by gravity. Many sources appear to...

Hello everyone...can anyone tell me what is the modified expression for the gravitational potential in GR which takes into account the fact that the speed of gravity is finite (c, to be precise)...In fact, it may be a non-sense question as I haven't started to read GR yet...Is there any...

Hi everyone, have a question about covariant, coordinate independent quantities in GR. Reading Kolb and Turner's book The Early Universe one can find the Boltzmann equation in a GR setting. Now, one of the terms in that equation is - \Gamma_{\alpha \beta}^\gamma p^\alpha p^\beta...

Homework Statement This is from a book for a correspondence course I'm taking. I don't have access to teachers, so hopefully some of you can fill that role :) A parent is pulling a wagon. The child and the wagon have a combined mass of 50kg and the adult does 2.2 x 10^3 J of work...

Hi all! I am still a GR noob and this example has been puzzling me for a while, so I need some help that's hopfully. Let's imagine that there are stars A and B at 10 LY from Earth (at point C) each and 10 LY from each other. A signal is sent every year from Earth (C) indicating the...

In a gravitational field time slows this is fact,the area around the gravitational field is affected ,is the space around an accelerating field also effected or only the object itself ,what I really want to ask if you place a clock so it would be in close but not contacting a accelerating mass...

I have recently notice that I the book General Relativity by R. Wald has quite strange cover. Do you have any idea what's the relation of apple and canopy with GR?

"Proper distance" in GR I am aware of two meanings of the term "proper distance" in GR. The first is when you have points in flat space-time, or space-time that's locally "flat enough", in which case it is defined as it is in SR, as the Lorentz interval between the two points. This usage of...