
#1
Apr1204, 02:10 PM

PF Gold
P: 3,669

in quantum gravity theories, can a quanta of gravity exist in isolation
or would it need other interacting quanta to perpetuate? 



#2
Apr1204, 04:04 PM

Astronomy
Sci Advisor
PF Gold
P: 22,801

could produce a shower of divergent opinion, almost a "full spectrum" of views I think in asking it you probably want to elicit a wide spectrum. I shall give one very focused view I dont think of gravity as a substance that you can have quanta of. I think of gravity as revealing geometry the shape of space I think that the correct name for "quantum gravity" is really Quantum Geometry. the quantum theory of how space is shaped (because the shape determines how matter flows around, how planets orbit etc) I think that one should ask not about quanta of gravity but about the quanta of geometry and these are things like quanta of area and quanta of volume distance and curvature might come in discrete amounts too anyway it is geometrical entities that should out to be quantized in a quantum theory of geometry I think that a "graviton" is a fictional entity that is convenient in analyzing the behavior of the gravitational field in certain restricted (approximately flat) situations. it is a ripple in the fabric of geometry but in highly curved dynamic situations analyzing in terms of "gravitons" wouldnt work very wellthey dont really exist it is just handy sometimes to pretend they do. The real quanta of geometry are quanta of area and volume and suchlike geometrical things, and if you know the volumes of enough regions and the areas of enough surfaces you have a handle on the geometry of space. In quantum gravity one of the landmark results is that areas and volumes of things are in fact quantized and are somewhat like the energy levels of an atom. That's what I look for from a quantum theory of spacetime geometry, that is, a quantized version of GR. other people doubtless have different perspectives on this 



#3
Apr1304, 11:34 AM

PF Gold
P: 3,669

i will be quite happy now, if i can relate how an inspiraling body
gives of geometry, or how mass is converted to geometry, thanks for your patience. 



#4
Apr1304, 11:45 AM

Astronomy
Sci Advisor
PF Gold
P: 22,801

tyro questionright as usual, very hardtounderstand stuff here how does mass effect the curvature of space? when two neutron stars spiral in towards each other they radiate energy (carried away by ripples in the gravitational field) and the system loses mass as it loses energy how can this possibly be? there are equations to describe what happens but I have no inkling of the mechanisms that make those equations work and why they fit maybe someone else can add insight here 



#5
Apr1304, 03:34 PM

PF Gold
P: 3,669

if i considered that the destruction of mass initiated a shock wave that perturbed the quanta of geometry akin to the pixels on an oscilloscope, and the continuum of quanta transfered this shock energy to new born mass perterbances of geometry would this be a conservation of mass, geometry?
or am i thinking utter ***P 



#6
Apr1404, 12:42 AM

Astronomy
Sci Advisor
PF Gold
P: 22,801

there was one of them here a couple of months ago, I will try to find a link I imagine these people think like that (maybe similar to how you are thinking) and they relate gravity to how shocks and defects propagate thru a crystal lattice someday, if they havent already done it, they might make computergenerated animated films of these "solidstate" gravity ideas it's way out of my ken all I can do is try to remember who that guy was that came to PF and try to dig up some keywords for a search IIRC the guy was unhappy. from his point of view so much attention is given to string and LQG that there is not enough attention left over for "condensed matter" models of gravity one thing you can say for those people is they have some different ways of visualizing gravity  incredibly, wolram, the lady and I went scubadiving today it had been several years since I had a tank on my back speaking of gravity, it is a very different experience in neutral buoyancy the difference between up and down becomes more subtle one rolls over or drifts heels over head rather easily but it doesnt make much difference drawing a deep breath (of air from the tank) makes you more buoyant and you start to rise, letting out a breath (as a cloud of bubbles) makes you less buoyant and you stop rising and slowly settle back down I admit this is irrelevant, but it was a nice way to spend the afternoon  you are venturing ahead of the crowd, if you want to speculate what makes gravity work talk about pushing to the ragged edge! What I see going on today is they're mainly just trying to get a satisfactory quantum description of GRable to match the usual GR effectsno easy matter in itself I'd guess they wont try to imagine actual mechanisms until after GR is quantized. progress on gravity is like tunneling through a mountain of solid rock a few inches a day, and they forgot to bring the dynamite 


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