Historic Sites: Muon Time Dilation Experiment

Credit: Mount Washington Observatory

In the early 1960s, David H. Frisch and James H. Smith measured the rate of detection of muons at the observatory on top of Mount Washington in New Hampshire (elevation 6289 feet) and again at sea level, obtaining agreement with the time-dilation prediction of special relativity. They published their results and made an educational movie. In commemoration of this combined research/outreach event, on September 6, 2014, APS President Malcolm Beasley presented a plaque (above), as part of the APS Historic Sites Initiative, to Mount Washington Observatory Executive Director Scot Henley and Director of Summit Operations Cyrena-Marie Briedé.