[g__day (Matthew)]

You have a number of competing theories for this one, from SuSy to super gravity to relativity. We can not answer for sure is gravity quantised yet (dip into Loop Quantum Gravity vs the Higgs Field and Higgs Bosun). We are pretty sure that Gravity can radiate in any Realtivistically dominated volume of spacetime within 97% - 100% of the speed of light (based on the theory of relativity and experiements in 2003 involving quasars and Jupiter. But we don't yet have a framework for gravity that works well at extremes of interstellar distances (just look at MOND) or microscopic distances (for that matter none of the four forces work sensibly at these down to quantum levels.

Under GR spacetime itself can expand faster than lightspeed without voilating any rules. Because its the framework or topology of spacetime, not the matter nor the energy within it, doing the streching. In laymans terms outside or between two gravitationally held volumes of space (where relativity definitely applies) say the rather large and empty void of spacetime between two super clusters, spacetime itself can expand at, equal or above lightspeed without violating General Relativity.

Too GR and its rules break down in any of the following situations:

1. Quantum level - as you approach a Planck level of space, time or distance - you are ruled by quantum mechanics not relativity, which follows a totally different and wierd set of rules

2. The really energetic places - once you the heat to the level where energy densities approach 10^15 GeV (think above 10 ^ 24 Kelvin - much, much hotter than a super nova) you are getting into the realms of the heirarchy problem. At this point the fours forces (gravity, electromagnetism, strong nuclear and weak nuclear forces) are predicted to re-combine one by one (like a backwards Big Bang cycle) until you have three, then two and finally only quantum gravity remains to control such a reality. Once strong, weak and electomagnetism merge you are nowhere near the domain of GR and the rules of gravity can be kissed away.

3. Extremely dense objects, think grav stars and black holes, again within their event horizon scenario 2 above may play. Outside the event horizon gravity is certainly the dominant force and relativity again holds sway.

The Higgs field interacting on the Higgs bosun is an interesting model, show that gravity is really just a side effect of a deeper underlying reality.

Finally here's an interesting aside for you. If all the matter and energy of the Universe was once again localised you'd have a black hole with an event horizon how big? Well about 20% bigger than the best estimate for the volume spacetime is believed to occupy today! So how did the big bang every manage to outrace its own crushing gravitational shell - that should have imploded it back into oblivion before it got past a trillionith, trillionith, trillionith of a second?

Answer - likely gravity didn't exist as a seperate force until the Universe had cooled and expanded and inflation finished - at around 10^-34 seconds after the big bang. Prior to that quantum gravity held sway. Once inflation kicked in the Universe was travelling maybe 50,000 times faster than lightspeed until it had expanded form a point in space up to the size of a orange. By this stage it cooled enough for gravity to phase into dominance. But the Universe by this stage had become casually disconnected into clumps (Hubble Spheres) expanding away from each other faster than lightspeed. So gravity could not travel from one lump to the next fast enough for the expanding peices of the Universe to catch the fleeing pieces and pull it all back together!

To this day our reality is our Hubble Sphere - a light cone 14.8 +/- 0.1 billion light years, in a Universe that may exceed 200 billion light years diammeter. Beyond this distance things are too far away and receding too faster to every influence us under GR. Perhaps this is what Dark Energy really is, our reality passing where other Hubble Spheres have come and gone and their residual gravity wells expanding our Universe!