Normal matter is organized into tight little worldsatomswith positive protons in their nuclei and negative electrons revolving around them. There is also a homeless waif, the positron (positive electron), that seems to have no place in this orderly scheme. Born in atomic catastrophes, it lives only until it hits a normal electron. Then the two "annihilate" one another, turning into gamma rays.
Some physicists have reasoned that since positrons exist, there should be negative protons (anti-protons), around which positrons could revolve to form atoms of "reversed matter." Last week a group at Massachusetts...