my cousin from guam swears he saw one once dude he's like an archer and he's got a hella good eye.
on topic: so what exactly are these things? particles that constitute gravity?
Well think of electro magnetism, we see colours because photons of particular wave lengths are absorbed and re-emitted from certain materials according to there atomic structure.
In other words the mediating particle for the force of electro magnetism is the photon.
There are four forces
EM, weak, strong, gravity
EM
Electron
photon
Light,magnetism, radio waves etc.
Weak
Neutrons/protons
W and Z bosons
Radioactive beta minus and positive decay, or beta radiation
Strong
quarks
gluons
The force required to seperate a proton for example into it's discrete quarks is so large it has never been done, although high energy colisions come close. The high energy reactions can spontaneously produce short lived quarks.
Gravity
Higg's Boson(theoretical/hypothetical)
Graviton(theoretical/hypothetical)
You sitting on a chair without floating upwards and other things obviously
what exactly could we do if we knew more about these?
and could we use them?
We would be one step closer to unifying all the forces, or a theory of everything as Einstein put it.
So far Electricity and Magnetism and weak have been unified. Weak quite recently, the two professors won the Nobel prize for it.
Theory states that the forces at certain energy levels become equivalent thus at the start of the universe, they became discrete as the energy levels fractions of a second after the big bang began to fall.
There is some speculation and it is just that, that electrons could be converted to gravitons and thus you could use it as a means of propulsion, but this is pretty fringe science. Google Heim theory if your interested.