The only known recordings of a brilliant physicist who predicted the existence of parallel universes have been found in the basement of his rock star son's flat.

The tapes document how Hugh Everett, a quantum physicist, developed his idea at the age of 24, while a graduate student at Princeton University in 1957. Everett's theory gave rise to the concept of a multitude of universes, or a "multiverse", where all life's possibilities play out. It means that somewhere Elvis is still rocking, the Nazis won the second world war and England qualified for Euro 2008.

The recordings are believed to have been made in 1977, after a physics conference at which Everett's parallel worlds theory was resurrected after being shunned for two decades. The tapes were thought lost after his death at the age of 51 in 1982.

They were found during the making of a TV documentary in which Mark Everett, the physicist's son and lead singer of the US band Eels, attempts to understand the work that consumed his father. The programme, Parallel Worlds, Parallel Lives, airs on BBC4 this evening.

The tapes record a conversation between Everett and Charles Misner, a physics professor at the University of Maryland. In the background, Mark can be heard playing the drums.

Everett talks of how his inspiration came after talking about the ridiculous consequences of quantum theory over a few glasses of sherry with Misner and Aage Petersen, an assistant of the Nobel prize-winning physicist Niels Bohr. Everett completed a draft paper describing the idea in 1956. On seeing it, his supervisor, John Wheeler, said: "I am frankly bashful about showing it to Bohr in its present form, valuable and important as I consider it to be, because of parts subject to mystical misinterpretations by too many unskilled readers."

Everett's work tackled one of the most puzzling mysteries to emerge from the field of quantum mechanics. One consequence of the theory is that tiny particles such as electrons can behave in a curious way that allows them to be in two places at once. As Bohr was to comment: "Anyone who is not shocked by quantum theory has not understood it."

In the 50s, the prevailing view, and one championed by Bohr, was that weird quantum behaviour vanishes as soon as the object is measured.

But Everett thought differently. His calculations showed that whenever quantum mechanics said a particle was in two places at once, the universe divides. In one universe the particle appears in one place, while in a second it appears in the other. The implications were apparently so alarmingly counter-intuitive that Everett's ideas were largely ignored, notably by Bohr.

Speaking to New Scientist magazine, Mark Everett said the rejection had had a devastating effect on his father. But recently, the theory has been accepted by many scientists as profoundly important.