Antihydrogen Makes a Fleeting Debut

Like a high‐profile wedding of movie stars, the recent mating of positrons with antiprotons at CERN commanded worldwide attention. But even by Hollywood standards the marriage was short‐lived: The antihydrogen lasted a mere 37 nanoseconds before the positrons were annihilated by collisions with electrons in the detector. That time was too short and the number of antiatoms formed was too few for researchers to conduct high‐precision comparisons between hydrogen and its antimatter counterpart. Such studies would tell us whether nature obeys CPTinvariance, that is, whether phenomena remain invariant under the simultaneous operations of charge conjugation, parity inversion and time reversal, and whether matter and antimatter feel the same pull of gravity. The recent experiment at CERN fired imaginations by demonstrating the reality of antihydrogen, but antiatoms must be produced nearly at rest, rather than in flight as in the CERN experiment, before they can be studied in detail.