There’s an air of electricity and anticipation in the foyer of the Barbican theatre. Expensive hair and fur coats mingle with edgy hipsters and intellectual corduroy. This is a big night: Robert Wilson and Philip Glass' Einstein on the Beach was first staged in France in 1976 and brought them to the notice of the world. Since that unveiling, it’s been called one of the most important works of the 20th century. Two decades have passed since its last production and it has never been staged in this country… until now. It's exciting.

"It's autodidactic. You learn how to see it by seeing it. The piece teaches you how to see it. The piece teaches you how to hear it," says Robert Wilson in the programme. As a member of the audience, you're definitely starting from scratch. Usual short-hand is removed or skewed and the brain is challenged to give up trying to fit this experience into the usual slots in its search for meaning. Sense is removed. Either you leave (some did), or you hand yourself over for retraining, which takes time. And there is plenty of time… five hours to be precise.

Time is a motif, as is space, relativity and atomic bombs, but it's not that easy. Einstein is there at the front of the stage as the epic absurdity rolls out over his shoulder, but he doesn't help either, though he does play a mean violin. Dancing, stylised walks, singing, lights, huge props and mumbled dialogue are all aspects of the performance. Some things slow down, while others speed up or stand still. The music doesn't go where your brain wants it to and there’s so much unrelated business going on that it’s impossible to keep track of everything. It’s about experiencing, rather than analysing.

Interaction between characters is minimal and everyone seems to be going through their own motions (operating invisible keyboards and high tech machinery or writing equations over and over on an invisible blackboard) as part of a huge impersonal machine with everyone playing their part without wondering why, occasionally turning to the audience and making a face or grinning as though that were part of their programme whose meaning is now lost; one character repeatedly appears on stage holding a book in front of its face and shaking its head; moving through the action but not interacting.

The overall feeling is of a nostalgic future described by Dada, designed by Max Ernst and influenced by ‘Metropolis’. There's also a strong aura of 1970s’ avant garde - a couple of hours in, a huge slab of fluorescent light does a solo turn on stage, moving at an imperceptible speed from horizontal to vertical. It’s excruciating. Especially, when once perpendicular, it ascends into the heavens at a similar 'speed' to the accompaniment of a female soloist. The hand-made, jerky movement of big pieces of the set and cheap-looking props suspended by string shuddering into and out of view also makes it feel old-fashioned. That's fine too. The whole thing looks stunning and the lighting is complex and electrifying.

Philip Glass' music sounds like modern classical/opera at times, but often veers towards the challenging, difficult end of the spectrum which is not always easy on the ear. Snatches of uncomfortable melody and unusual, sharp 'harmonies' are repeated… repeated… repeated, and the words being sung are often lists of numbers. There’s nothing familiar to satisfy the thirst for a conventional beat or melody, but it does inspire unfamiliar emotions, some of them exhilarating. Recurring spoken dialogue with unrelated action is a consistent theme. One of my favourite sections performed by the compelling Kate Moran as she lay on her back, ended with the line, "I wasn't tempted to buy one but I was reminded of the fact that I had been avoiding the beach."

The absurdity thrilled me, as did the bravery of the production in general. Despite the impersonal, robotic aspects, when the end finally came, it was intensely emotional. The standing ovation was powerfully moving - not only were we congratulating the cast and crew, we were applauding each other: Together, we got through it. Not only that, some of us, in the words of Robert Wilson, learned how to see it by seeing it.

- Denise Flower