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## What's being curved, when mass bends the "spacetime continuum?"

 Quote by Kraflyn I hope this explains it a bit. Please do not hesitate to ask about anything related to this topic. I do sometimes mention something one might be unfamiliar with, worth explaining some more. Cheers.
Ah ok, that makes more sense. To me a "vacuum" is simply an area devoid of matter.

 Hi. No problem. Do ask if You are interested in any particular detail here. For instance, I briefly mention supernovae teams and accelerated expansion of universe. This topic of supernovae suggesting acceleration deserves a thread on its own. However, if one is interested in it in order to clear some points connected to the current topic - why not explaining it, then. A good answer starts with a good question! Cheers.
 Space is made up of magnetism. That's what holds the universe together. Magnetic forces bend and warp due to the constant motion of the objects in the universe. The whole universe pulsates back and forth, expanding and contracting, bound all together by magnetism. Its that simple, or complicated, how ever you want to look at it.

Space is made up of something, it's called magnetism. Everything in space is moving back and forth, bending and warping, pulsating like a beating heart,
The universe expands and contracts, albeit bound together by magnetic force. It's that simple, or complicated, however you want to make it.

 Hi. There are some prominent theories on the electric universe, true. There's even a movie about those theories on electric universe. This might be true in the end, I guess. Cheers.
 Hi. Philspazer, this is exactly what happens in Casimir effect: http://en.wikipedia.org/wiki/Casimir_effect. Your X = quantum vacuum. Cheers.

 Quote by Muphrid Interesting perspective. This is rather close to the interpretation of "Gauge Theory Gravity", where the metric and other objects are just fields on a Minkowski background and the relations between these fields give rise to particular geodesics. The predictions are in great agreement with GR for what's in our capabilities to test, and it gives a very clean and obvious footing for doing QM in a gravitational background.
What is the difference of those perspectives (if any) with Einstein's GR?
'According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration' and ' The existence of the gravitational field is inseparably bound up with the existence of space'. (A.E.1920)

 Hi. No impact on GR whatsoever. The question asked about the causal physical theoretical origin and foundation of GR. Cheers.
 I'll let you guys in on a little secret...the aether actually does exist. Long live the aether!

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 Quote by buzzdiamond Space is made up of magnetism. That's what holds the universe together. Magnetic forces bend and warp due to the constant motion of the objects in the universe. The whole universe pulsates back and forth, expanding and contracting, bound all together by magnetism. Its that simple, or complicated, how ever you want to look at it.
 Quote by buzzdiamond Space is made up of something, it's called magnetism. Everything in space is moving back and forth, bending and warping, pulsating like a beating heart, The universe expands and contracts, albeit bound together by magnetic force. It's that simple, or complicated, however you want to make it.
No, this is not true. Magnetism is but one aspect of electromagnetism and it is NOT what spacetime is "made of", nor does the universe work the way you think it does.

 Quote by StationZero I'll let you guys in on a little secret...the aether actually does exist. Long live the aether!
I'll show you an aether! *shakes a fist*

 Hi. Well, according to quantum field theory, all fields are quantized in the end and collapsed into particles. There are no electromagnetic fields there; there are only photons. But this kind of thinking takes us into realm of quantum gravity once we try to embed a photon into curved metric. There is no standard description of quantum gravity yet, and the question "what is curved exactly" still remains there... If we say: "metric is curved", the question becomes: "what is metric physically?" If we say: "magnetism is curving", the question becomes: "what is magnetism physically?" If we say: "XYZ is curving", the question becomes: "what is XYZ physically?" ... If we say "my fist is curving space" ... It's a tricky little question... Cheers.
 I suppose what constitutes a geometric explanation has come a long way since Leibniz wrote: "If the mechanical laws depended upon Geometry alone without metaphysical influences, the phenomena would be very different from what they are." XXI Discours de métaphysique - Baron Gottfried Wilhelm von Leibniz, 1686. These influences he described as "preserving always the same force and the same total direction". I suppose we call these metaphysical influences conservation of energy and momentum now and hold them to be subsumed into geometry as the manifestation of certain mathematical symmetries.
 Hi. Yes, indeed. Hm... There are issues with general theory of relativity regarding conservation... There are actually 3 issues: A) Changing potential energy reference level changes physics of objects immersed in geometry. Namely, the constant term that changes referent potential energy level acts as a cosmological constant $\Lambda g_{\mu \nu}$. And we all know what this does to expanding universe. B) impulse-flow-density tensor of graviton, $t_{\mu \nu}$ is not conserved, energy is not conserved under co-ordinate transformations... which is maybe a consequence of A)... C) Both A) and B) might prove to be just consequences of general theory of relativity being non-linear. Namely, in relativity, the energy of a system is not simply sum of energy of constituents. Just consider special theory of relativity: $E^2-p^2 =m^2$. Not quite linear, is it... On the other hand, in Hamilton-Lagrange formalism, everything is linear. If constituent have well defined actions and lagrangians and hamiltonians, the action or lagrangian or hamiltonian of a system is simply sum of actions of lagrangians or hamiltonians of constituents. And yet, general theory of relativity uses action principle... For instance, if matter and radiation and vacuum field are all present, we just add impulse-flow-density tensors, linearly, and it's all good. Just like quantum theory too: however, quantum theory is linear theory through and through! No wonder we can't really make relativistic extension of linear theories in an acceptable manner. For instance, there are virtual particles in a theory of relativistic quantum fields. My point is simply: there is something wrong with current geometric description known as general theory of relativity. It's not a secret. So yes, use of geometry has gone a long way since Leibniz. A discussion on issues regarding general theory of relativity are most welcome on my part, of course. Cheers.
 Holy balls, I just looked up Casimir effect, then quantum vacuum, then http://www.newscientist.com/article/...ctuations.html then LHC, and further and further... I gotta tell ya, I'm just a musician who watches discovery and history channel and I'm feelin really good about myself for figuring out some of this stuff. Thanks for putting science to my imagination and theories Kraflyn, you rock.

 Quote by harrylin What is the difference of those perspectives (if any) with Einstein's GR? 'According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration' and ' The existence of the gravitational field is inseparably bound up with the existence of space'. (A.E.1920)
GR is a general theory of curved manifolds, and it allows for geometries that aren't topologically flat--stuff with wormholes, for instance.

Theories in which gravity can be accounted for by a field on a flat spacetime background fundamentally can't reproduce any geometry that isn't topologically flat like the background. You can consider other backgrounds, but these have to be entered in "by hand."

The difference in picture is clear, though. Where GR attributes the effects of gravity to an actual curving of spacetime, a field theory will say that spacetime is still flat but the motions of particles and objects are affected by some sort of ever-present field.

 Quote by Muphrid [..] The difference in picture is clear, though. Where GR attributes the effects of gravity to an actual curving of spacetime, a field theory will say that spacetime is still flat but the motions of particles and objects are affected by some sort of ever-present field.
That sounds to me as a mere difference in phrasing (except that one allows more than the other, if I correctly understand you). Einstein's GR even has both, as I cited. According to his GR the motions of particles and objects are affected by an ever-present gravitational field and he accounted for that field by means of a "conditioning" of space-time by matter.

 I disagree. To me, GR suggests there is no gravitational field--there is simply the geometry of spacetime, which is warped and curved and which, in turn, affects the motions of test particles. Gravity as a field theory on a flat background doesn't require the conceptual middle man that is the spacetime geometry--there is a gravitational field, and it affects trajectories directly.