You are thinking about the idea of gravity effecting space slightly wrong.  In General Relativity, gravity does not effect space, rather gravity IS due to the curvature of space-time, and the degree of space-time curvature is depends upon the mass-energy located at a point in space.

So in a Newtonian framework, we view gravity as a force field generated by the presence of mass.  This force field we perceive as extending through space, but not effecting space.  However, when we move to the more accurate General Relativity framework, wear space-time is "elastic", we find that the presence of mass (or more generally mass-energy since mass and energy are equivalent within a relativistic framework), warps space-time, and it is this warping or curvature of space-time is what we perceive to be the gravitational field.  This is why in Newtonian physics the bending of light around massive bodies is not predicted (i.e. Newtonian physics tells us that light will only ever move in a straight line, since a beam of light has no mass, and so is not effected by a gravitational field), but it is a consequence of general relativity, since the light is simply moving "straight" through curved space-time, and hence appears to our senses as being bent by gravity.

This is all well and good in General relativity, when objects are large and massive, but on the quantum scale general relativity breaks down (both philosophically and mathematically), which is why we have not yet a fully coherent theory of quantum gravity.  It is thought that gravity on the quantum scale is mediated by gravitons, which are the quantised particle of the gravitational field (just as photons are the quantised particle of the electromagnetic field).  Thus, since gravity is curvature of space-time, gravitons should be the quantised perturbations of curved space-time. In general relativity, the interaction of massive bodies produce gravitational waves (which again is a macroscopic perturbation, or oscillation of curved space-time), and just as electromagnetic waves  can be considered as an ensemble of very many photons, a gravity wave can be considered similarly as an ensemble of very many gravitons. 

I will point out though that I am not a Theoretical Physicist with no formal training in General relativity or quantum gravity, but the above is how I understand it, and invite more knowledgeable than myself to correct any errors I have made.

vacuum has energy...

Because Rij =0 ( Ricci curvature in empty space equals zero) but metric tensor is not constant (space is non-Euclidean).

In material word, matter is the only substance. Hence, all real entities are made of matter and gravity acts on 3D matter (bodies). Gravity does not act on mass, which is an attribute of matter. Space is not vacuum, It is filled with a medium, whose property is gravitation. Kindly see http://vixra.org/abs/1007.0042 

Nainan

Your approach to gravity is purely Newtonian. While Einstein  introduced us to another personality  of gravity, a geometric approach. In special and general relativity of  Einstein's, space and time - have a key role and unlike Newton's classical approach, not a passive object. On the other hand, quantum mechanics proved that there is no absolute vacuum i.e. space is not null. According to recent research, I think the space - time contain physical information.

Mohsen

You are thinking about the idea of gravity effecting space slightly wrong.  In General Relativity, gravity does not effect space, rather gravity IS due to the curvature of space-time, and the degree of space-time curvature is depends upon the mass-energy located at a point in space.

So in a Newtonian framework, we view gravity as a force field generated by the presence of mass.  This force field we perceive as extending through space, but not effecting space.  However, when we move to the more accurate General Relativity framework, wear space-time is "elastic", we find that the presence of mass (or more generally mass-energy since mass and energy are equivalent within a relativistic framework), warps space-time, and it is this warping or curvature of space-time is what we perceive to be the gravitational field.  This is why in Newtonian physics the bending of light around massive bodies is not predicted (i.e. Newtonian physics tells us that light will only ever move in a straight line, since a beam of light has no mass, and so is not effected by a gravitational field), but it is a consequence of general relativity, since the light is simply moving "straight" through curved space-time, and hence appears to our senses as being bent by gravity.

This is all well and good in General relativity, when objects are large and massive, but on the quantum scale general relativity breaks down (both philosophically and mathematically), which is why we have not yet a fully coherent theory of quantum gravity.  It is thought that gravity on the quantum scale is mediated by gravitons, which are the quantised particle of the gravitational field (just as photons are the quantised particle of the electromagnetic field).  Thus, since gravity is curvature of space-time, gravitons should be the quantised perturbations of curved space-time. In general relativity, the interaction of massive bodies produce gravitational waves (which again is a macroscopic perturbation, or oscillation of curved space-time), and just as electromagnetic waves  can be considered as an ensemble of very many photons, a gravity wave can be considered similarly as an ensemble of very many gravitons. 

I will point out though that I am not a Theoretical Physicist with no formal training in General relativity or quantum gravity, but the above is how I understand it, and invite more knowledgeable than myself to correct any errors I have made.

Problem with present concepts of gravity is the assumption that it is a single phenomenon. Gravitation and gravitational attraction are separate. Gravitation is enormous pressure, applied by universal medium on 3D matter-particles and gravitational (apparent) attraction is relatively a minor by-product of separate gravitational actions on participating matter-bodies. See http://vixra.org/abs/1206.0056 

Nainan

As stated by Jonny, The bending of light around (D) a massive particle (M) is an excellent example, where the Newtonian Gravity fails to explain ( so also the common sense) the precisely observed and measured phenomena. The GR predicts it to be  4GM/(c^2 D) and matches with experimental measurement (Gravitational lensing). 

http://aerorocket.com/WarpMetrics.html

To explain this observation, GR invokes a 4D world of space-time. Just like the ball shaped Earth (3D) appears to be flat (2D) to our senses, the 4D world appears to be 3D to our senses once again.  The importance of the 4th dimension (time) is that the smallest path (in time) that connects any two 3D points in this world is not a straight line around a massive object, but a curved path.  The light always takes the path of minimum time, and hence takes the curved path around a massive body, leading to gravitational lensing effect, predicted by GR.

    I am not a theoretical physicist, but a common man.  What I now understand is that Gravity does not affect the space around it, but it affects the time (4th dimension).  This  is not obviously visible to our eyes, but we experiences it every time, we uses a GPS device indirectly.

   The time undergoes dilation when it is measured close to a massive particle , such as the Earth.  A Cesium clock that counts 1 s in outer space measures 38 us (microseconds) more when it is measured on the surface of the earth (Please bear in mind that 7 us correction due to movement at high velocity is deducted to get this  value).  Or, in other words, if we count 1s in our Laboratory, the corresponding clock on the geosynchronous satellite 36,000 km away measures 38 us faster time interval.  This has to be corrected to locate our position accurately down to few meters on the surface of the Earth. These corrections are routinely done using GPS software as part of the computation involved. (see the blog site below for calculations)

http://physics.stackexchange.com/questions/1061/why-does-gps-depend-on-relativity

So, let me conclude:

Ans: Gravity does not affect the space (3D), and does not lead to curvature of the space, instead, it affects the time(4D) and lead to curvature of the same through time dilation effect.

Kindly correct me, if I am wrong.

Jogy, your conclusion is a bit confusing...I guess because of some confusion in the spacetime concept. Let me try to stress some points:

Since the introduction of Special Relativity (SR, not GR) we know that the spatial and temporal coordinates are not so independent each other as common sense suggests. The fact that the speed of light is the same in all the reference frames (that is it does not depend on the observer's velocity) yet produces the effect of time dilation (and length contraction) you mentioned. Masses are not considered in SR and these effects only depend on relative velocity among reference frames (e.g. the famous twin paradox). This is also why the concept of spacetime was introduced: spatial and temporal coordinates are strictly mixed and we cannot talk separately about them.

Coming to gravitation, as stated above by Jonny, the GR introduced the concept of a curvature of this spacetime. Gravity as a interaction among bodies is no more present in a GR universe, but mass and energy affect this curvature and are of course affected by it.

Both SR and GR predict a different time flow for example in the case of orbital clocks you mentioned. However, SR can produce only time dilation, while GR can produce both dilation and contraction, depending on mass distribution around the clock. The time lag of 38microsec for GPS system is in fact explained by a combination of both effects.

So: in the newtonian framework gravity does not affect space nor time which are though as absolute constants; in the SR time and space mix them up and change depending on reference frame but gravity is still a force which does not affect them; in the GR gravity is no more a force but is interpreted as a curvature of spacetime.

Jogy,  So far no one has been able to offer a plausible explanation of how mass causes curved spacetime.  I have just had an article accepted for publication as a chapter in the Springer book series "Progress in Theoretical Chemistry and Physics". This article derives the weak gravity curvature of spacetime produced by a single fundamental particle.  It also derives from first principles the gravitational force between two particles and the electrostatic force if the particles had Planck charge rather than elementary charge "e".  I must warn you that these results are derived from the unconventional assumption that the universe is only spacetime. This implies that all particles, fields and forces are obtained from the single building block of 4 dimensional spacetime.  The model of spacetime used is a combination of the quantum mechanical properties of vacuum (zero point energy, etc.)  on the microscopic scale and the standard properties of spacetime obtained from general relativity on the macroscopic scale.  A preprint of the article is available at

 http://onlyspacetime.com/QM-Foundation.pdf

Dear Dr. John Macken, it is my pleasure that you introduced me to your concept of  "universe is only a space-time " (linked PDF). Very impressive and   re-defines the basics of every thing we know from a simple assumption of space-time.

   As stated in Page-6 of the article, gravity (ie mass)  can lead to time dilation as well as length contraction, since dt/dTau =dr/dR =1 + Gm/(r c^2). The effect of gravity on time dilation is an accurately known effect in GPS technology.  Is there any direct and measurable evidence for length contraction? Is the gravitational lensing due to length contraction? If so, kindly explain in simple words, how the light bends around the stars?

Hello Jogr, Thank you for the compliment. Much of the information you ask about is in the second chapter of my book available at: http://onlyspacetime.com/

I recommend that you also read the first chapter since it sets the stage for the second chapter. You asked the questions: “Is there any direct and measurable evidence for length contraction? Is the gravitational lensing due to length contraction?” There are several different conceptual ways at looking at the effect of gravity on spacetime but they all give the same mathematical answer to a given problem. In the book I discuss the Shapiro experiment and the different physical interpretations of this experiment. My preferred interpretation is that gravity expands the volume of space plus slows the “coordinate speed of light”. These two effects are shown to each account for half of the bending angle of light passing a massive body. I show that gravitational acceleration is directly related to a gradient in the rate of time. For example, an acceleration of 1 m/s^2 is produced by a gradient of 1.11x10^-17 seconds/second per meter. It follows that it is impossible to have gravitational acceleration in flat spacetime where there is no temporal gradient. This has implications for cosmology as discussed in the book.

Jogy: Better that we ask how matter affects the active vacuum to present to us as gravitational forces surrounding the matter particles rather than look for particles emanating from the matter. If the binding energy (B.E.) of the vacuum continuum is weakened by the presence of matter then we might find that  B.E. as Joules /m3 = N/m2 = Pa pressure?  Matter particles are then pushed toward their common centre of gravity, not pulled together and space density is real enough to apply to provide 'curvature' by its own internal forces.

Jogy your question is perfectly valid one. I tend to think that space time are imaginary concepts and does not have physical existence. Human mind superimposes the idea of space and time on oscillating energy and falls into delusion. For example, if a particle wave is presented to a physicist he superimposes his idea of wavelength and period on the wave and imagines the existence of space and time. The real physical existence is of energy in oscillation. This is the reason you cannot measure time without some kind of an oscillator and you cannot conceive of space where there is no energy. So the idea of distortion of space due to gravity is a figment of imagination. More details in the attached article.

Article Periodic relativity: Basic framework of the theory