Why does the presence of mass cause space-time to bend?
@grahamshort asked the Naked Scientists: Why does the presence of mass cause space-time to bend? What do you think? @grahamshort, Wed, 20th Apr 2011
Ah! Good, an easy one.
In ordinary (Euclidean) space, gravity bends the path of light. In Minkowski space-time, the path of light is the definition of a straight line. Straightening the path of light by definition changes the rules of geometry. The internal angles of a triangle no longer add up to 180°, and two straight lines may cross more than once. If you divide space-time into 4D hypercubes, you will find that they don't fit together perfectly in any 3D slice of space-time, holding one dimension constant. To make the hypercubes fit perfectly, you must view the whole 4D continuum. Computers do this easily; human minds need to be reprogrammed at a fundamental level to do so. This is what we call the warp of space-time.
Another excuse to post the Feynman video!
The answer is frame-dragging effect
It is clear that currently, no one knows the answer to this question with accuracy. The following observations, however, may be relevant. Quantum mechanical theory indicates that zero is not a possible value of electromagnetic energy, and this is supported by the discovery of the Casimir Effect, which is interpreted as detecting wavelike energy in empty space. Quantum mechanics tells us that matter is composed of wavelike energy. It is not a great leap of logic to conclude that empty space and matter are the same thing, differing only in their energy states. (We could generalize by saying that space-time and matter-energy are the same thing.) If that is so, the phenomena that are known to exist in matter when it changes its energy could also apply to the transition between empty space and matter. One such phenomenon is expansion. The transition between "empty space" and matter could involve some sort of expansion or contraction of the underlying phenomenon of matter-energy-space-time by reason of the laws governing its existence, which, of course, remain imperfectly understood. We might be able to say with some confidence that gravity is the evidence that those laws, whatever they are, are not strictly linear, and that this nonlinearity is the basis for the expansion. But if so, that raises other questions (as usual), such as, is G constant? G, the universal gravitational constant that links mass and the curvature of space-time, if it is an expression in nonlinearity in quantum effects (probably at the string level), then field theory, as concieved as the basis for the existence of electromagnetism, may have to be rethought because the photons, being integer-spin particles, are capable of unlimited superpositions; but the formulation in which their superimnposability is ordinarily expressed are linear, which is not consistent with the notion that the difference between the presence and absence of a photon would have gravitational effects. (It is here assumed that, just as the difference between the presence or absence of an electron is known to have gravitational effects based on the particle's mass, so must it be so also for the photon, because the photon, although having no proper mass, nonetheless has momentum and should therefore some type of gravitating effect just as any other particle). But if the photon exerts a gravitational effect, and does so because of nonlinearity acting on the difference between the field energy state corresponding to no photon and the state corresponding to one photon, then , because photons are superimposable, adding more photons should result in further nonlinear effects, which of course would translate into increased gravity, exactly as expected so long as the degree of nonlinearity between states remained constant. Whether that can be assumed is unclear, which brings into question the constancy of G. Viewing the quantized electromagnetic field as something compatible with photons exerting gravity therefore results in a description of the quantized electromagnetic field which, being nonlinear, is somewhat different than what one normally thinks of.
Please read the last paragraph in the following link.
On reading the said reference, it appears that it is speaking only of the effect caused by rotating bodies. A stationary body does not "drag" a frame. Frame-dragging, of course, would be an outgrowth of the more general law as to how energy and momentum in a given location distort space-time there, and by extension, in its neighborhood also. All of which is probably the macroscopic description of the way everything is constructed at the quantum level, which of course is a major question in physics today, and which may be answerable, in rough terms, by saying that empty space-time and space-time occupied by one or another type of recognizable matter or energy are simply different quantum states, but that this difference is not simply one of energy, but also geometry, which could be the manifestation of a weak nonlinearity in the states resulting in a slight incompatibility of fit between portions of space-time in different states. Or perhaps some other effect we don't yet understand. That is the case argued in general terms. At some point, science has to get more specific, dealing with many issues such as the hypothetical existence of the graviton, which allegedly would be the carrier particle accounting for the gravitational attraction in the way that the photon accounts for electromagnetic force. But of course, that means that the picture of gravity being propagated via a particle would have to be reconciled with the picture of it being the consequence of a distorted medium (space-time), and at first, those pictures seem to be highly incompatible, inasmuch as there is no particular reason why particles being exchanged between objects and creating a force between them implies anything at all about the space and time around them. But we have been here before: the picture of sound being a form of quantized energy existing as a result of various energy levels of phonons (which has been verified in the context of thermodynamics etc.) and the picture of sound as a change in the density of chaotically moving other particles also seems fundamentally irreconcilable, but it turns out that because these other particles are subject to quantum laws, their exists with respect to their motions descrete energy states that are equivalent to phonons. Science may someday likewise be able to reconcile the two descriptions of gravity, and doing so appears as a major objective of string theory. Atomic-S, Sun, 12th Apr 2015
I was curious, we always look at space as vast emptiness (not accounting for light rays and all the other energy waves, just talking about pure space), where once we thought it was an aether. Since we have so much secondary evidence (as in, we have not perceived space per se, but we see the affect it has on matter), do we have any theories that support space being itself a medium of some sort? It can be warped, it provides enough drag as to keep all but photons from going light speed. Light can be bent through it just as light can be bent through water or glass. It seems to me that space could be the "aether" past scientists thought it was, only it is a substance so inert that only matter attempting to travel at relativistic speeds are even affected by it. Again, I am no scientist, but I was curious as to what you guys and the community think and to maybe gain some better understanding of the universe.
Here is the best answer available I think: