Matter........Antimatter Gravity.........Antigravity?

[claymore]

Just as there is antimatter, are there any grounds for suggesting there is such a thing as Antigravity . And could it be the force that keeps the universe expanding ?

[jake-the-peg]

Anti-matter has positive mass so not in that way anti-particles are affected by gravity.

The graviton if it exists is most likely to be it's own anti-particle in the same way that a photon is.

The accelerating expansion of the Universe is most commonly believed to be a result of the energy density of the vacuum

Nice little piece on that here:
http://www.math.ucr.edu/home/baez/vacuum.html

[Robb Phoenix]

To understand this topic you must first understand gravity.Gravity is not a force. The Newtonian theory of gravity is wrong. this is because if one move one of the objects the force on the others change instantly.This means gravitational effects travel with infinite velocity which is impossible.(it must travel equal or less than light speed).
Einstein made a suggestion that bodies are not made move on curved orbits called gravity, as the mass of a body distorts space time, other objects around it feel the effects of this distortion which we know as gravity.Particles travel the nearest thing to a straight path in curved space but because spaace time is bent their paths appear bent.Thus it is always attractive.
The expansion of the universe is like Jake said is due to DarkEnergy.

[jake-the-peg]

Gravity not a force?

Hmmmm

Don't want to hold off on that in case they find the Graviton Rob?

Might be a little early to go that far

[Teddio]

No one knows what mass is but it only comes in one "flavour". (including antimatter) The force between two masses is attractive.
Compare that with electric charge. no one knows what that it either but it comes in two "flavours", positive and negative, giving the possibility of attractive and repulsive forces between two charged bodies.

[Robb Phoenix]

Hey what i said was what Einstein said.
If scientists found out the graviton, then as gravitational effects are instantaneous, they must travel faster than light hah and that would throw Einsteins work on relativity to the dead.

[Robb Phoenix]

i remember reading about an experiment proving Einstein's predicton given above. it involved studying microscopic effects on three perfect spheresby earths gravitational field. it showed deviation from the Newtonian theory but was consistent with Einstein.