What is Gr: Definition and 952 Discussions

"Hidden variable" in SR and GR Relativity??.. My question is, since we live in a 3-D world, what would happen for an "alien" living on a 4-D world??..if we suppose that space-time has only 4 dimension, and that after a Wick rotation then X_{0} =it then what we think is just a time component...

Homework Statement The acidic waste from a student's experiment needs to be disposed of, but pouring it down the sink would increase the impact of acid rain on the local water supply. Explain how you could determine the amount of limestone needed to neutralize the environmental impact of the...

Sorry if you have already covered this subject. Is it possible to apply the formula F = -GMm/R^2 for a relativistic particle substituting m with its relativistic mass?

the "future" in GR In GR, is all of time already contained in ST and we're just moving through it? this seems to be the only way to explain the fact that for different observers time passes at different speeds. is this correct? (this isn't a philisofic question)

From my very limited knowledge of General Relativity, i have the impression that mass is just considered as 'other' in this theory. By that i mean, GR assumes matter to be made of something other than space-time, and only deals with the effect that matter has on the geometry of space-time. Is...

I'm just curious as to how GR doesn't allow this. --thanks.

When I first read about accelerated expansion in 1999 I immediatelly thought of gravitational repulsion between matter and antimatter. I know it is an old idea, and very much out of the mainstream, but when you read reviews about the arguments against it, it really makes you think. It is a case...

Aboslute time in GR?? :shy: although for Einstein fans this post could be a "blasphemy" .. my question is if under some assumptions we could derive (or at least an approximation to ) GR in a way so there is some kind of "absolute time-frame" of reference for every observer in the universe of...

In the 3+1 formulation of GR we have the following basic variables: g_{ij} = \textrm{metric on a spatial surface} \pi^{ij} = \textrm{momentum conjugate to }g_{ij} N^i = \textrm{shift vector} N = \textrm{lapse function} Both N and N^i are purely gauge variables, so are essentially unimportant...

What are the incompatibilities between GR and QM?? appart from the fact that GR is NOn-renormalizable (perturbatively :rolleyes: ) since there are almos infinite types of UV divergences \int_{0}^{\infty}dxx^{n} n=-1,0,1,2,3,4,... What other incompatibilities are there?..if space weren't...

The Rindler geometry and its horizon can be obtained by a simple succession of Poincaré transformations to match the frame of an accelerated observer. By combining this SR result and the equivalence principle it follows that a uniform gravitational field is represented by the Rindler metric and...

I understand why it is so desirable to be able to write all the laws of physics by the same rule in any system of coordinates. I also nearly understand that the equivalence principle leads to the need of curved spacetime. But how to make that as obvious as possible? Thanks, Michel

If we apply the Bohr-Sommerfeld quantization to GR (semiclassical) \oint_{S} \pi _{ab} dg_{ab}=\hbar (n+1/2) :confused: :confused: In this case if "Energies" (or whatever you call energy since in Quantum GR H=0 for the "Hamiltonian constraint" ) then using Einstein equation we see that...

I think that in Special Relativity, the drift of the perihelion can be calculated by cumulating elementary Lorentz transformations along the (Newtonian, unperturbed) trajectory. I read that the result of this calculation is much smaller than the experimental value. It is also well known that...

If you have the metric g_{ab} , \pi _{ab} as the metric and "generalized momenta", my question is if you can define GR using Poisson Bracet: \dot g_{ab} =[g_{ab},H] \dot \pi _{ab}=[\pi _{ab},H] and hence use these equations to obtain and solve the metric.:shy:

This weekend I played the game of the perihelion precession in GR. I started with the Schwarzschild geometry and used the hamilton-jacobi method. It was quite interresting to compare the integral with the classical counterpart. The full two-body problem may be more complicated to handle...

Can someone help me to calculate the difference between accelerations due to Newton’s law of gravitation and Einstein’s general relativity? Let’s assume the gravitating mass M equals to 1kg and the distance r equals to 1m than the acceleration due to Newton is: a = G * M / r^2 = 6,6742...

In SR, relativitic mass, momentum and energy is conserved but what is conserved in GR since the frames in GR are noninertial.

I've done college courses on both & it's not clear yet how they conflict. I'm looking for a more technical account. Have I done enough to understand it, or do I have to do wait till QFT?

http://www.physorg.com/news12054.html "It demonstrates that a superconductive gyroscope is capable of generating a powerful gravitomagnetic field, and is therefore the gravitational counterpart of the magnetic coil. Depending on further confirmation, this effect could form the basis for a new...

A. Einstein states in The Principle of Relativity, pp 111 - 112: "The modification to which the special theory of relativity has subjected the theory of space and time is indeed far-reaching, but one important point has remained unaffected. For the laws of geometry, even according to the...

Hi I don't know where to start in this question can someone please help me out. Diethylene glycol, although toxic, has occasionally, and illegally, been added to wines to enhance the sweet flavour. Propose an experimental design, including the procedure and the equipment that you would use, to...

I am attempting to learn GR (for fun) using Sean Carroll's text. I have made it ALL the way to . . . . page 9 I don't understand the equation on the bottom of page 9; (1.16) (namely, why there are TWO delta x ^u and delta x^y; but to type out my question I will need to know how you guys...

In words, how would a path of an object moving in a straight line with a constant velocity differ from the path of an accelerating object moving in a straight line according to Einstein's picture of curved space-time?

Is it possible to define linear momentum in any curved space? According to wikipedia, it's not: http://en.wikipedia.org/wiki/Linear_momentum Why? Which is an example of space-time asymptotically Minkowski?

Published in ScienceExpress this week (the full citation when it appears in Science will be in our Noteworthy Physics Papers thread in the General Physics forum): M. Kramer et al. Tests of General Relativity from Timing the Double Pulsar, ScienceExpress 14 Sept. 2006 Abstract: The double...

http://arxiv.org/abs/astro-ph/0609417 Tests of general relativity from timing the double pulsar M. Kramer, I.H. Stairs, R.N. Manchester, M.A. McLaughlin, A.G. Lyne, R.D. Ferdman, M. Burgay, D.R. Lorimer, A. Possenti, N. D'Amico, J.M. Sarkissian, G.B. Hobbs, J.E. Reynolds, P.C.C. Freire, F...

What book(s) would you all recommend for learning about these two theories? I have limited math knowledge; most of the equations I see look like a greek sentence to me. Is it even possible to really comprehend relativity without the math? I keep asking questions that turn out to be rather...

Which came first Quantum Mechanics or General Relativity? Or to rephase it another way, Which came first Hawking radiation or the Big Bang. Why did the singularity or black hole, which we assume caused the big bang, not simply evaporate instead of exploding, as currently accepted...

From SR to GR in an "easy" math (and physical) way Hello..i know that for example to go from Newtonian to SR you take: \frac{du}{ds}=0 \rightarrow \nabla _{u} u=0 My question is ¿is there an "easy" form to go from SR to GR in the form: \nabla _{u} u=0 \rightarrow \nabla R_{ab} =0...

Some say that the reason Einstein developed the GR is because he wanted to avoid the spooky "action at a distance," since two massive bodies exerting forces on each other at a large distance with no "mediator" seems rather odd. Therefore Einstein invented the concept of spacetime and gravity...

Hi guys, I am trying to study GR on my own. You got any good books in mind?

Hi I have a great inerest in SR and GR.As I am in quite learning stage I have started reading docs regarding this from internet. Presently I am reading a book 'Introduction to special relativity' by Robert Resnik. Is there any FREE book available on net on this subject or tell me the way I...

Hello could someone give some info about the "Numerical solution" to GR...is this a field of "Computational Physics"?.. - What i know is that you take the Hyper-surface, and you " split " it into triangles..and use the ¿angles? of every triangle as finite-coordinates..then you get a problem...

Local coordinate system in GR observed. If one considers coordinate systems in General Relativity. I think, if I understand it well enough, that in GR space & time and or in space-time a coordinate system depends on locality, e.g. on an average distance between galaxies an the total amount...

In GR, can a spinning object be traveling on a geodesic?

Is it justified to state that GR is "just" a geometrical theory to calculate the paths of objects in spacetime? Just because GR states that "gravity is a property of spacetime itself" doesn't necessary mean that spacetime is curved; just that the paths of objects in spacetime are curved in a...

May as well announce my Java applet that simulates Newton's law of gravitation. The initial conditions are set to give a demonstration of conservation of angular momentum. That is, 8 test masses are launched, all with the same angular momentum, and their orbits cross on the other side of the...

The Reader is invited to help this thread become rigorous. If any links should not fubction, inform me, I will try to correct them. Currently this thread is an analogous interpretation of circumstantial evidence and incomplete information. The writer has attempted to crudely use the...

REF: Smolin; Perimeter Institute; -- “The case for background independence” What does background independence mean. Are statistical probabilities needed to compare separated events. If the background that physics works on varies relative to distant locations in GR does that mean GR is...

Hi All, I was hoping someone could help point me in the right direction. I'm interested in simulations of General Relativity with generic mass distributions that are self gravitating, i.e. that the metric of the space-time being considered is dynamically altered by the distribution of mass whose...

Are superstrings (and related M-theory) the only option for a theory of everything? Wikipedia states: "The only mainstream candidate for a theory of everything at the moment is superstring theory / M-theory; current research on loop quantum gravity may eventually play a fundamental role in a...

I hope someone else finds this interesting, since it through me for a loop for a while. Ok, so time dilation occures in gravitational fields. I used the solution for the time coordinate transformation between "free" space and the space under gravitational influence: t_g =...

:confused: Some papers say that Palatini Formalism still works if the frame variables e^i_a is not an isomorphism (from tangent bundle to frame bundle), this generalizes GR to include the cases of degenerate metric. But one could not derive the Einstein's Equation if e^i_a is not an...

http://www.physorg.com/news12054.html "It demonstrates that a superconductive gyroscope is capable of generating a powerful gravitomagnetic field, and is therefore the gravitational counterpart of the magnetic coil. Depending on further confirmation, this effect could form the basis for a new...

Over in https://www.physicsforums.com/showthread.php?t=115295 on the forum they are talking about this research being hailed as a test for GR...BUT...could someone tell me if the "gravitomagnetic" field in http://www.physorg.com/news12054.html was what Heim was talking about. I think it's...

http://www.physorg.com/news12054.html Scientists funded by the European Space Agency have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. Under certain special conditions the effect is much larger than expected from general relativity and could...

I like simple physical setups to articulate and generate good thought experiments. Setup: Consider a hole cut in a flat sheet of material with these conditiond; Bottom portion is perfectly circular with 150 degrees of arc. End points are represented by x=+n, y=0 and x=-n, y=0. x=0, y=0...

Here is a thought experiment that doesn't seem to add up. Suppose you have a unit of mass at rest on the surface of Earth that spontaneously transforms to photos all moving radially outward into space. At some distance (say 1Km) the photons revert back to the original mass but are now 1Km...

The other day, I was trying to explain what SR & GR were for some non-science friends of mine. I started speaking of motion with constant speed, the postulates of SR, the spaceship and the ball, time dilatition, twin paradox and so on. Needless to say, they didn't understand what I was talking...