In 1987, the legendary experimental composer John Cage published “ORGAN2/ASLSP (As Slow As Possible),” a piece for organ designed to be played, you guessed it, as slow as possible. It was an adaptation of a similar composition Cage wrote for piano in 1985. The premiere performance in 1987 lasted 30 minutes.

Since 2001, an organ at St. Burchardi church in Halberstadt, Germany has been playing a version of “As Slow As Possible” intended to last 639 years. The instrument, specially constructed for this purpose by a group called the John Cage Organ Project, is intended to keep going until 2640. The project’s official website explains how they settled on Halberstadt and 639 years:

Michael Praetorius, a composer and important theorist of music of the late 16th and early 17th centuries, wrote that an organ with the first modern keyboard arrangement had been built in Halberstadt’s cathedral in 1361. This organ was the first of its kind with a claviature of 12 notes, and this claviature is used on our keyboard instruments today. So one can say that the cradle of modern music was in Halberstadt. Subtract 1361 from the millennial year 2000, and the result ist 639. In the year 2000, – 639 years had passed since the “fatal day of Halberstadt” (Harry Partch) – the performance of Cage’s “as slow as possible” for the coming 639 years began.

Monday, the organ played its first chord change in exactly two years. As the BBC explains, volunteers added another pipe into the organ to create a new sound. The next chord change is scheduled for August 5, 2026. The first 21 months of the performance were a rest — that is, complete silence. That’s 163,938 performances of 4’33”!