Like the musical Woodstock, the legend of the “Woodstock of Physics” grows year after year.

Twenty years ago this month, nearly 2,000 physicists crammed into a New York Hilton ballroom to hear about a breakthrough class of materials called high-temperature superconductors, which promised amazing new technologies like magnetically levitated trains.

“It was an electrifying event,” said Philip F. Schewe, a science writer at the American Institute of Physics who runs the news conferences at the physics meetings, then and now. “You wished you were there.”

Many of the participants from the 1987 session reconvened yesterday at an American Physical Society meeting in Denver, partly to reminisce and partly to take stock of what has happened since then and what has not.

Superconductors, discovered in 1911, carry electricity with no resistance. Most work at temperatures below minus-420 degrees Fahrenheit, and by the 1970s, physicists had generally concluded that that was just a chilly limit of how nature works.