Anti-matter has the same mass as the equivalent normal matter. The electrical charges are reversed, though. Gravity is the resuly of mass, therefore anti-matter has the same gravity as normal matter.
http://en.wikipedia.org/wiki/Antimatter
"Today's standard model shows that every particle has an antiparticle, for which each additive quantum number has the negative of the value it has for the normal matter particle. The sign reversal applies only to quantum numbers (properties) which are additive, such as charge, but not to mass, for example. The positron has the opposite charge but the same mass as the electron. An atom of antihydrogen is composed of a negatively-charged antiproton being orbited by a positively-charged positron."
I'm just copying this from an old post I made from
another thread:
All known matter is surrounded by a kind of cloud of electrons. Electrons are electrically neutral. This is why my fingers are able to push down on these keys as I type: Like charges repel each other.
What if, through some collossal blunder of physics, the atoms of my fingers were surrounded by a cloud of positively charged electrons (Called Positrons)? My fingers would then pass through the keyboard, causing a shearing effect that would seperate the matter at the atomic level, and damaging the keyboard and my fingers.
If a controllable beam of positrons were to be emitted in a preset area and stream, it would pass through all known forms of matter. In fact, the only thing that would halt such a shearing effect would be another beam of positrons.
We are already able to make electrons pretty much do what we want (stunguns, Tesla Coils, etc.). How difficult would it be to do the same with positrons?
As a lifesaving tool, it would effortlessly cut through steel, concrete and anything else the user wished. As a weapon, it would bore holes through armor thicker than anything currently known. Anything made of atoms would be influenced by a positron beam.
That's the theory. Putting it in a package the size of a chrome flashlight, however.....