The mere fact that if Protons were negative and Electrons were positive would lead to no changes in the universe, shows us that anti-matter is not the place to look for anti-gravity. As if you were to invert the charges on a single atom and keep the quarks the same, you'd have matter with anti-matter traits, something which becomes null if a universal charge flip were to take place. Positive or Negative are mainly just conventions, the main point being they have opposite charges.
CONTACT
Atraills Knight Sanderson
Head Astrophysicist/Scientist
