What is Gr: Definition and 952 Discussions

I have some question that might be hard for me to phrase clearly, but I'm going to give it a try. So, as far as I understand it, according to GR gravity is a side effect of the way mass (or mass energy, or whatever) curves space-time. So that when an object "falls" to the Earth, it isn't...

Regular readers to GA&C here in PF will know only too well that some of our prolific posters feel the mainstream work is rather too heavily model-laden for their taste ... and others that this characterisation quite unfair. Wrt those who are comfortable with the redshifts of galaxies (and SN)...

I'm a gr 11 physics student at Ashbury College (Ottawa, Canada) and our class (in multiple teams) has been entered in a roller coaster contest, held by Wonderland. (A theme park in Ontario, Canada). My friends and I are determined to win this contest, and I am sure that the ideas of those in...

If the higgs field is responsible for giving particles their mass, isn't it then the higgs field that is responsible for the effects of GR? Is this assesment true and, if so, does it have any implecations? Could the higgs field (which has been described as an ether) and spacetime be in some way...

It has been years since I have thought of relativity, but I came across a book by Jerome Drexler in which he attempts to support his view that ultra high energy protons (cosmic rays) are what dark matter is all about in the galactic halos. In spite of the fact that it seems to me these protons...

can anyone well versed in both GR and quantum explain to me the very underlying problems with these to theories, and if time was not a factor ie... time was not as GR explains, would that solve any problems. To my knowledge time is the result of the geometry of the universe, as in theory, what...

Gen Rel is highly visual---as well as being formulated abstractly. I don't want to seem to be claiming that a successful quantization will need to be visual as well. If it has a clear rigorous abstract formulation and it works, makes testable predictions etc., that should be enough. But...

Many physicists agree that GR implies, under certain conditions, that gravity has a component, which if gravity is viewed as the analog of the electric force, is analogous to the magnetic force under a set of equations similar to Maxwell's equations. See e.g. http://arxiv.org/abs/gr-qc/0207065...

I've been trying to work out the meaning of the metric in General relativity. I have a few ideas, but nothing's really come together. These are what I think is right, from SR: the space-time distance is a quantity which is agreed upon by all observers, a fundamental property of the interval...

What natural terrestrial phenomena are significantly influenced by general relativity?

The question is whether I am naive to suppose that either GR or LQG predicts new universes. I have also posted essentialy the same question (and post) in the Steller Astrophysics forum. Martin Bojowald has removed the singularities from GR using LQG. See...

I got this from Wikipedia (under the definition of centrifugal force): I need some clarification here. I had understood that the "ficticious forces" of centrifugal and coriolis were "inertial effects," and that with GR the gravitational force was also an inertial effect. The Wikipedia...

From MSNBC: GR confirmed again as gravity measurements reflect the predicted space-time dragging effect caused by spinning objects. A research team analyzed millions of laser signals bounced off two satellites, called LAGEOS and LAGEOS 2. Both are highly reflective spheres not designed to do...

Does anyone know why I end up with the wrong answer? I went delta q is equal to m c delta t, the derived the equation delta t is equal to delta q divded by mc. I therefore did the math as 232 kJ divided by (10 kg times 4.2 x 10 ^3 j/kg C) and got 9.7 x 10 ^4, when the answer was supposed to...

Does anyone know why I end up with the wrong answer? The question is:

This paper does a lot of testing of different kinds, and concludes that the string theorists assertion that the graviton reproduces the physics of GR in flat spacetime is a myth.

in the sticky above about wrong claims, chris hillman attempts to debunk the idea that "GR is an aether theory". however, his argument seems a bit disingenuous when compared to einstein's own writing on the topic. einstein stated, in "Ether and the Theory of Relativity", an address...

OK Physics Help Plz 1st question A person, resting in a boat, notices that 16 waves pass the boat every 38 s. How many waves wouldf pass the boat in 55 s. 2nd question If 180 waves wash up ona shore in 1.00 h, what is the time between waves, in seconds? 3rd...

Plz give me some help like i know like frequency = cycles/seconds and period=seconds/cycles but how do i answer a snwer like If 180 waves wash up on a shore in 1.00 h. what is the time between waves, in seconds? lol help me guys .. my dad always said i have to try hard to get the education i...

Please take a look at http://xxx.lanl.gov/abs/physics/0204044 and post your comments/opinions.

Please take a look at http://xxx.lanl.gov/abs/physics/0204044 and post your comments/opinions.

a)Can we add extra terms with covariant derivative equal to 0 so the coupling constant in relativity is dimensionless?. b)for a metric gab that is time independent,can we define an "energy" term E so dE/dt is conserved?... c)from the Wheller-De Witt equation can we construct a linear...

Another one of the physics teacher working at the college I attended (see my previous post) wrote a book on basic http://universite.deboeck.com/Resources/Titles/28011100266200/Images/28011100266200L.gif . In this book it says that the expansion of the Universe is due to the expansion of space...

Experiment shows that many physical quantities are conserved and that the associated conservation laws can be linked to symmetries. However it seems strange that general relativity is a theory built from principles of symmetry and yet energy might not be conserved in general relativity.Surely...

selfAdjoint has given a link to a really enlightening post by Steve Carlip Here is the Carlip post https://www.physicsforums.com/showthread.php?p=227804&posted=1#post227804 Carlip is tops. A major reliable authority in General Relativity and Quantum Gravity. Good idea to listen to what he...

I'm reading in on the subject of General Relativity and came across a few things I don't understand. First of all I'm not sure where the following rule comes from, and maybe someone can explain or derive it for me: \eta^{\mu \beta} h_{\nu \sigma,\beta} = h_{\nu \sigma}^{,\mu} And I also...

I'm not sure what forum I am suppose to post GR questions so I am sorry if this is in the wrong spot. Ok my question is this. In classic phys. Newton required mass to have gravity. I read that in GR einstein required stress energy. If light has not mass or should I say a photon but EM waves...

I understand that the Black Hole and the worm hole are solutions to Einstein's Field Equations. However, what does it mean by solution? I want to understand what it means by solution to the Field Equations. Can the solution be anything that forms a gravitational field? Can a solution in...

I just flipped through a book on GR today called: A First Course in General Relativity by Bernard Schutz, and was instantly fascinated. I was blown away by the physical and mathematical richness of the subject. I always had the impression that learning it would be far down the road in my...

Self Adjoint very nicely gave me an example when QM doesn't work with GR using something called Spinors which define quantum mechanical particles. i was wondering how exactly is spinors pronounced Is it like spinners umm like the rims lol :) ? Sorry for the odd question, I just don't...

Steve Carlip, on sci.physics.research has asserted that energy is not well defined. Paraphrasing him, if you want to have a concept of energy, you need to include gravitational potential energy, right? But you can always switch to a freely falling coordinate system in which gravitational...

If light experiences gravitational redshift as said by GR, then, where did the difference between the initial and final energy, E = \frac {hc}{\lambda} go? From Hubble expansion, there is also redshift. Where did the energy difference go?

any comment on an approach to quantum gravity tried by Stephen Hawking, I think in the 1980s and 1990s, but apparently abandoned? It was called "euclidean quantum gravity" and involved a sum over spacetimes somewhat analogous to a feynmann path integral---a spacetime being like a path. In...

I would like to create (with everyone's help) a list of experiments etc that support SR and GR. These should be reproducable experiments, or profound predictions that have been upheld, as well as objects/systems that use SR/GR calculations on an everyday basis. I would predict that such a...

I was reading Michio Kaku's book Hyperspace when I came across his statement that black holes have to have another side to be consistent. I'm curious, since Godel showed that a given energy-momentum tensor does not nessecarily produce a unique metric, why must the kerr-newman solution be the...

Hi guys, Just wanted to know how GR or Sr can determine the answer to this question? How fast does the universe change?

What Maths subjects should I study to understand Quantum Mechanics and General Relativity?

If you think that ether theory is crackpot nonsense, look at gr-qc/0205035. A quite classical ether in Newtonian framework of absolute space and time, with continuity and Euler equations as conservation laws, gives an effective metric theory of gravity with exact Einstein equivalence principle...

In trying to get my head round GR and quantum gravity, I'm puzzled about the following questions: Is the gauge group for gravity defined as the set of all possible Weyl tensors on a general 4D Riemann manifold? Which abstract group maps onto this set? Is it GL(4) or a subgroup of GL(4)? How...

In trying to get my head round GR and quantum gravity, I'm puzzled about the following questions: Is the gauge group for gravity defined as the group of all possible Weyl tensors on a general 4D Riemann manifold? Is it a subgroup of GL(4)? How do you derive the number of gravitational...

In trying to get my head round GR and quantum gravity, I'm puzzled about the following questions: Is the gauge group for gravity defined as the group of all possible Weyl tensors on a general 4D Riemann manifold? How is this group defined in matrix algebra? Is it a subgroup of GL(4). How do...

Greetings, In some discussions about GR, I heard the term "covariance" and covariant form (eg, covariant form of Maxwell's equations) pop up often. I've been wondering for a while why the notion of covariance in GR is so important. I have some background in mathematical physics, so I know...

I have a question concerning the treatment of black holes in General Relativity. As I understand it, the force of gravity is replaced in GR by distortion of space, and the distortion may be dynamic, a function of time. In particular, space may be sucked into black holes. Now without the force...

hey all , Why do most physicists always team up with one set of rules when it comes to their understanding of science? on one side you have the General Relativity group. they use real experiments to calculate the world into one equation (due to calculatable Mathematics) on the other...

1. The time distortion due to relative velocity does not cause any "real" loss if time in itself,loss of time only happens with acceleration, right? How can I predict the amount of time that has been lost relative to an inertial point of view(if I know the value for the other variables)? 2...

do string theories need gravitational radiation as in GR?

Does Loop Quantum Gravity support the existence of graviton? I can't imagine how is it possible that graviton can exist if it is to agree with GR, since GR says that gravity is merely a curvature of spacetime and is isn't a force. GR => SR => time dilation & length contraction =>> how does...

maybe someone else can clarify; these recent papers suggest a surprising turnaround in the quantization of General Relativity, contrary to some earlier papers by other people, they predict no quantum gravity dispersion in longrange transmission of light: On low energy quantum gravity induced...

In 2002, the Cassini spaceprobe, on its way to Saturn, passed close to the Sun as seen from the Earth (it was actually a long way from the Sun). Using the radio communications with Cassini, a stringent test of General Relativity was performed (a similar test had been done using the Viking...

What kind of experimental predictions does String theory make that differs from the predictions that past theories (QT, SR, GR)make? Paden Roder