Physicists at Northwestern University have successfully trapped a single positron for an entire month , allowing researchers to study its quantum properties with unprecedented precision. "Further investigations using the trap might reveal the secret of why the world around us is made of matter and not antimatter, when things could have presumably gone either way," reports Scientific American. From the report: Every normal particle of matter has an antimatter counterpart with equal mass but opposite charge. To build their trap, physicists started with atoms of sodium 22, a radioactive isotope with a half-life of about two and a half years. When one of these atoms decays, it emits a positron -- the antimatter counterpart of the electron. "The big challenge is to persuade these positrons to slow down and then capture them," says Gerald Gabrielse, a physicist at Northwestern University, who oversaw the project.…