What is Gr: Definition and 952 Discussions

Decades of work are being put in trying to find a unified theory which can accommodate both General Relativity and the Standard Model. I guess that the attractive of a unified theory is more than justified, but does it really need to be the case? Is it possible that the universe works really...

http://arxiv.org/abs/1306.4035 Graviton scattering amplitudes and Pure Connection Formulation of GR Gianluca Delfino (Submitted on 17 Jun 2013) We show how the recently introduced "Pure Connection Formulation" of gravity provides a natural framework for approaching the problem of computing...

Minkowski space and deSitter space have been shown to be stable in GR under small perturbations. Perturbations do not intensify in higher frequency modes--these solutions don't go haywire and develop black holes all over the place. Piotr Bizon has shown that Anti-deSitter (AdS) space is not...

I have been puzzled by this for years, so I would welcome some enlightenment. It seems that Einstein was enamored with Mach's principle while searching for GR, but in the end GR does not seem compatible with it - or rather has nothing to say about it. What I mean is that the proverbial...

We know that the orbit of a planet and its star is a conic section. For a closed orbit, it will be an ellipse described by x^2/a+y^2/b =1, or its equivalent equation in r and θ What would be the equation of the path under GR? and how will it approximate to a conic section when r(s)/r tends to...

In the case of Komar mass, we can express the mass as an integral of ##\rho + 3P##, so we can meaningful divide the total mass (or energy) of a system into the contribution due to each part, just by integrating over that spatial part of the system. What happens if we try to do this with other...

In describing the length of a curve in spacetime it is necessary to parametrize it and in GR one comes across the notion of affine parameters. One definition of affine parameters u are parameters which are related 'affinely' to the length of the curve s trough u = as + b where a and b are...

I've seen different objects described as the field in GR: the metric, the connection (and then the metric is seen as the "potential" by analogy with EM field theory), both... Could someone comment on what object should most reasonably be considered the field of the GR theory? Could for...

Is this a simple GR explanation for how gravity moves things? In SR, the dilation effects happen in a way such that the speed of light is maintained for all observers. In GR, mass is considered denser regions of spacetime. What I was thinking: It takes longer for light to precipitate...

There seems to be an emphasis in several books on general relativity that the metric (components) in itself does not reflect anything physical, only our choice of coordinates. On the other hand it can seem like the authors, instead of being true to this, treat the metric (components) as...

Sorry guys not a physicist!Only wish to know if there is agreement between Newton laws of motion and SR/GR in particular?I know these two don't match in some cases? What are they in simple words please!? Cheers

Hi all, I have recently completed two courses in general relativity and am well versed in things like the ray chaudhuri equation, tetrads, etc. I had to give a 2hr talk on gravitational radiation to my class and so understand GWs at some relatively respectable level. What I am inquiring about...

Hello all, in most of the general relativity excerpts I've come across they vary the date Einstein published his work between 1915, 1916, 17 and 18. Can someone clear up the reason for the discrepancy and what is the actual date of its publishing?

If there was magnetic charge Maxwell's equations could be altered to accommodate the magnetic charge? For small field strength and velocities General Relativity can be put in a form similar to Maxwell's equations? If so is there something that could be introduced into General Relativity...

Hello I am having problems in GR because I do not understand how observations frames work in this theory. I have a few more specific questions. -In the schwarzschild metric, which frame is the metric written in? (The one with swarzschild coordinates) -In the non-vaccum solutions, how do we...

I understand that writing the E-H action in terms of tetrads makes evident GR is a gauge theory. IOW general covariance/diffeomorphism invariance in GR is a form of gauge invariance. However unlike other gauge theories(for instance EM dependence on Minkowski spacetime), this gauge invariance in...

I know light behaves oddly compared to normal matter, I haven't really delved into the math of GR, and that's why I'm here to ask these questions. 1) If all of our observations of the universe are based on light, what determines that the speed of light is the maximum velocity? I'm sure its...

Hi people , i am an engineering sophomore. but after my undergrad i want to move into physics lane especially theoretical physics. for which i am doing ground works and building my profile ( as a non physics student , to get into good physics grad school i would need a good profile ofcourse !)...

So apparently (wiki), the manisfestly covariant form of Maxwell's equations is dF=0 and d*F=µJ for F the Faraday 2-form and J the current 3-form. My question will probably seem silly to you but I am simply wondering how does this field affect the motion of a particle of charge q in GR? Is it...

I'm curious as to how many of you have used this book: https://www.amazon.com/dp/0521829518/?tag=pfamazon01-20 because me and Jorriss were thinking of getting it. Is it any good? Based on google and amazon previews it looks awesome especially the chapter on the field theoretic view of GR and it...

I am new to this area, so pardon me if the below question might seem... 1. What area/subject/sub-topic of physics deals with attempts at bridging GR and QM? 2. What does it say? in layman language 3. What is a quantum field? 4. is there any area of QM where some credible mathematical...

Why does \eta^{\rho \alpha}\eta_{\alpha \sigma} \partial_{\nu} \partial^{\sigma}h_{\mu \rho} = \partial_{\nu}\partial_{\alpha}h^{\alpha}_{\mu} WHY DOESN'T it equal \partial_{\nu}\partial_{\alpha}h^{\alpha}_{\mu} + \partial_{\nu}\partial^{\sigma}h_{\mu \sigma}

Fluid solutions of the EFE are very useful in GR and pervade all of the theory's applications be it cosmological (FRW dusts for matter-dominated models, radiation fluids for radiation-dominated ones...) or astrophysical (stars interior models, etc). Now, I know there is a component of...

OK, I started reading GR for mathematicians from Wu and Sachs. And I see that from the start that they look on finite dimensional linear algebra, has there been any treatment for a general setting? MP

How do we mathematically define a inertial frame in GR? Is it only a basis in some tangentspace or does it have to be induced by a coordinatechart? :/

In Wald's GR he makes use of a coordinate basis consisting of ∂/∂x^{n} where n runs over the coordinates, and I understand his argument that ∂f/∂x^{n} are tangent vectors, but I can't wrap my head around the operator ∂/x^{n} spanning a tangent space of a manifold. Any clarification on this would...

Hey there guys! So we know that in linearized GR we work with small perturbations \gamma _{ab} of the background flat minkowski metric. In deriving the linearized field equations the quantity \bar{\gamma _{ab}} = \gamma _{ab} - \frac{1}{2}\eta _{ab}\gamma is usually defined, where \gamma =...

Hi Can anyone explain why from varying a Lagrangian? \frac{\partial \mathcal{L}}{\partial (\partial_{\alpha }\phi)}(\frac{1}{2}\sqrt{-g}g^{\alpha\beta}\partial_{\alpha} \phi \partial_{\beta} \phi) = g^{\mu\nu}\partial_{\mu}\partial_{\nu}\phi +...

Can the Planck relation, and the Heisenberg and the time-energy uncertainty principles be derived, or produced, from the equations of General Relativity?

I swing an accelerometer around my head with a constant relative speed of v and a radius of r. I want the exact formula with highly relativistic effects, so v = .8 c and r = 1 meter, say. What proper acceleration will the accelerometer read?

Does putting the concept of acceleration in SR make it equivalent to GR? I see a lot of sources (including many posts in this forum) which seem to say that SR can handle acceleration fine, but not gravity. However, an acceleration IS gravity by the equivalence principle, so what's the...

Are Finkelstein/Kruskal interior black hole solutions compatible with Einstein's GR? This topic is a spin-off from a number of recent discussions: "Are "flowing space" models compatible with GR?" "Schwartzchild and Synge once again" "Oppenheimer-Snyder model of star collapse" "Notions of...

Here are two seemingly unrelated arguments to explain why GR is a nonlinear theory: (1) By the equivalence principle, any form of mass-energy should cause gravitational fields. Since gravitational fields carry energy, they should cause gravitational fields. (2) GR doesn't care what...

Uncapable of working through the tensors of the EFE's or visualizing the concepts upon which they are based as expressed in that manner, I have begun reverse engineering GR in an attempt to determine the basic concepts upon which it is based to find the foundation of its mathematical logic and...

Einstein, for his GR theory he made a last important effort to make it valid also for rotating objects. So consider the following thought experiment. There is an observer A standing at the North Pole and another observer B sitting on a platform, turning clockwise once every 24 hours, both with...

I just watched a video whereby the man says that you could accelerate at a constant one g for 10 years and not reach the speed of light due to GR effects. I did a non-GR calculation and found that you would hit c at about one year. Could someone tell me specifically how GR affects this rate...

Hello, I've been doing some relativity self-study and have what may be a silly question but one that has me scratching my head. I understand conceptually that under GR, gravity is not a force but rather the effect of objects following the straightest possible path (a geodesic) over curved...

This is a fork off the locked thread here: https://www.physicsforums.com/showthread.php?t=648423, and is further a response to a recent blog entry 'Does Gravity Gravitate?' (not sure of the PF rules on blogs re threads so won't post a link to it here). The blog presents well what is doubtless a...

Hello, Can somebody tell me what are the different branches of mathematics required as building block of GR?

Are "flowing space" models compatible with GR? Recently papers have been published with new "flowing space" models for GR. In particular a "flowing river" model by Hamilton: http://ajp.aapt.org/resource/1/ajpias/v76/i6/p519_s1? http://arxiv.org/abs/gr-qc/0411060 "In this model, space flows...

Hi, Are there any free online reliable resources to learn SR and GR? Thanks.

In several places I've seen a derivation of the radius of a black hole by simply determining when the Newtonian escape velocity will reach c. Similar analogies are commonly used to explain light being bent by a gravitational field. So will treating light as a particle traveling at speed c in...

As I understand it from what I have read the gravitational time dilation concept was arrived at through the equivalence principle. That the differential dilation at different locations in an accelerating system were derived from SR and included in GR by EP. But I have never encountered the...

Question 1: How does the metric relate to the light cone at a particular point? Obviously, the metric should determine the shape of the light cone, but is the converse true? Does the orientation and width of the light cone tell you everything about the metric? I'm guessing not due to the...

In reviewing some basic GR (just to keep my old brain sharp), i was looking at the Einstein notation cinvention and was a bit confused. I see how you do the dot product of say: ei.ej = δij (i.e. 1 or 0) But then the book I'm reading talks about ei.ej or ei.ej. Isn't that just the...

Hi I have recently started GR and have found the mathematics to be quite easy (have encountered differential manifolds and tensor calculus in other subjects), but the physics is troubling me, allow me to elaborate. In special relativity, we have a very intuitive idea of how observations work...

Drawing on a number of threads in this forum, and my very limited understanding of relativity, I am intrigued by the following thoughts: If I have understood correctly, in GR, c is supposed to be only a 'local global constant', and not exactly a Universal constant. Meaning that, two distant...

consider a following situation,where a person A is on Earth and another one B far from Earth where his proper time is not influenced by Earth's gravity field.now what's time flow felt by A wrt A and wrt to B.? I get the answer for it but i need a explicit explanation..Is there any link where I...

Did anybody else hear the news? A recent paper examines the derivation of Einstein's field equations and proposes that the original assumption of a divergence-free energy-momentum tensor may not be valid anymore due to the discovery of dark matter and dark energy. The authors derive new field...

Hey all, GR has just been explained to me in a lecture and I'm a little confused about a few things. I've been running through a few scenarios in my head and I don't see how they can occur without a paradox. One scenario is if you have two spaceships traveling parallel to each other at...