charliebigspuds":uau80gjr said:
If matter is affected by gravity, is it not plausable that antimatter be affected by antigravity? This is what I am suggesting that dark matter / energy is.
If there was 1 part per billion of anti matter and 1 part per billion of matter left after they destroyed each other. Assuming that gravity / antigravity have the same strenth, then could gravity / anti gravity keep the matters apart and be pushing them further apart, which would explain why things are speeding up?
To start I don't know of any "antigravity" (and dark energy is somewhat different than any AG would be). An antimatter (AM) atom has the same mass as a regular atom, it's only the charges that are reversed. An anti-electron has a + charge instead of a - charge and an anti-proton has a - charge vs a + charge. Something made up entirely of anti-iron atoms (for an example) would have the same mass and warp spacetime (have the same gravity) as the same thing made up of regular iron. In turn gravity would affect both in exactly the same way. You wouldn't know the difference until/unless the AM iron came into contact with any normal matter. Then the + AM electron shell would "touch" the normal - shell and the fun would begin.
As for dark matter (DM) ... we don't know what it is. When we look at the rotation of solar systems about their galactic center(s), the velocities are not what would be expected from estimating the masses of the shining/luminous solar systems. So it seems there's other stuff in these galaxies that
isn't giving off light, hence the name
dark matter. It doesn't seem possible for it to be the rocky stuff, of any of the other stuff, akin to the planets, asteroids, comets, etc in our solar system. When you look at the mass of our solar system, the vast majority of it is the Sun. The rest is a pittance and we think most solar systems are similar. So there's a mystery as to what the DM is made of.
As for dark energy ... as you noted the universe is expanding, indeed it appears as is this expansion is getting faster and faster (accelerating) every year. We have no idea of what's causing this other than to call the cause "dark energy". It's different from any sort of anti-gravity because it's happening in the vast intergalactic spaces where, so far as we can tell, there isn't any stuff, matter or AM, at all. So without any mass, there can't be any gravity or anti-gravity, at least as we define gravity. I would add that the universe's expansion is not galaxies moving through space but rather that space itself is expanding (pulling the galaxies along in it, like leaves in a moving stream) and that it's this expansion that accelerating. Again a different thing from any sort of gravitational (normal or hypothetical AG) effect which would cause galaxies to move
through space.