Dr. Bergman observes and studies cosmic rays at the highest energies. These microscopic particles (atomic nuclei) have macroscopic energies (up to 50 Joules), but are very rare, with one hitting a particular square kilometer of the earth only once a century or so. Ultra-high energy cosmic rays (UHECRs) are detected in the same way that particles at LHC experiments at CERN in Switzerland are detected, except that because they are so rare, we have have to use the whole atmosphere as the detector and instrument several hundred square kilometers of desert (just to the west of Delta, UT) in order to get a measurable rate. Dr. Bergman's specialty is the optical observation and reconstruction of UHECR-induced extensive air showers, either through nitrogen fluorescence or through Cherenkov radiation. Dr. Bergman was instrumental in building the Telescope Array Low Energy (TALE) extension (pictured above), which allows for fluorescence and Cherenkov detection of air-showers at lower energies. The links to the left give additional details of his interests.