As 'Tomorrow Never Knows' is the last track on Revolver, and the clearest signpost of things to come, it's often assumed that it was the last track recorded. In fact, it was the first track laid down for Revolver. Certainly the weirdest and most experimental track to appear under the Beatles' name at the time, this was John's attempt to capture something of the LSD experience in words and sounds.

The words were borrowed, adapted and embellished from Timothy Leary's 1964 book The Psychedelic Experience, which was itself a poetic reinterpretation of the ancient Tibetan Book Of The Dead. John had been sent the book by Barry Miles, who ran Indica Books in Southampton Row and was an influential figure on the British underground scene in the Sixties. He had an arrangement with the Beatles to send them significant books, magazines and newspapers to keep them up-to-date.

Leary, known as the High Priest of LSD, had spent seven months in the Himalayas studying Tibetan Buddhism under Lama Govinda. The psychedelic Experience was a direct result of this period of study. "I would ask Lama Govinda questions," says Leary, "and then I tried to translate what he said into something useful for people. Book Of The Dead really means 'Book Of The Dying' but it's your ego rather than your body which is dying. The book is a classic. It's the bible of the Tibetan Buddhism. The concept of Buddhism is of the void and of reaching the void - that is what John captured in the song."

The working title of the track was in fact 'The Void', taken from Leary's line "Beyond the restless flowing electricity of Life is the ultimate reality - the void." Its eventual title was a Ringoism which John snatched at because it added some deceptive levity to what to what otherwise might have sounded like a bleak journey into nothingness. The actual sound of the piece, which consists of 16 tape loops made by each of the Beatles fading in and out, grew out of Paul's home experimentation on his tape recorder. "He had this little Grundig," says George Martin. "He found by moving the erase head and putting a loop on he could actually saturate the tape with a single noise. It would go round and round and eventually the tape couldn't absorb any more and he'd bring it in and play it."