Media playback is unsupported on your device Media caption The BBC's David Sillito speaks to composer Philip Glass and director Robert Wilson

Composer Philip Glass and director Robert Wilson have revived their opera Einstein on the Beach, which is being performed in Britain for the first time as part of the London 2012 Festival.

In a rare interview with the BBC's arts correspondent David Sillito, Glass tells how he was inspired by listening to the sounds of trains going over tracks, why Einstein on the Beach has no plot and that it is perfectly acceptable to fall asleep when you go to watch it.

So why has it come back?

The reason we rebuilt the piece…both Bob (director Robert Wilson) and I are in our 70s now - this maybe our last time to do it.

What has also happened is that there's several generations of theatre-goers who haven't seen the piece

It's the kind of piece that everyone's talked about but not enough people have seen. (Although) if everyone who said they were at (the performances) in the 1960s and 70s were actually there, well they wouldn't have been able to all fit in.

It's the kind of thing that everyone in retrospect wished they had been there.

It was a very avant-garde tradition-breaking piece when it happened in 1976. The odd thing is that theatre's not changed that much since then - if anything most theatre has become more conventional, probably because of the influence of television and film

In terms of experimental work this is still cutting edge - not because we were so far ahead but because everyone else stayed so far behind.

It's got worse though over the last few years then, you're saying?

I think so. I think that we've taught our audiences bad viewing habits. Short attention spans and stories that are very recognisable. However, I think that's going to change now. I think that the younger generation - people in their 20s - are getting fed up with it again.

Younger workers have the kind of appetite for innovation that Bob and I had when were in our 20s and 30s.

Do you think you'll learn anything of Einstein from this?

You always do. Someone asked me 'what's changed?' The piece hasn't really changed but we've changed, so the way we look at it is different. A couple of things are really different. For the first time we have really state-of-the-art lighting.

We now have 37 years of experience of playing that music. The difference is that we can actually play it now! Philip Glass

A few months ago we were in Michigan and we saw (Einstein) in a theatre. I walked in into a scene that was being done but for the first time the lighting was so dramatic, it looked like it was pumping off the stage.

We know that the technology is there and we can use it and so now we're in a different place than we were, that's one thing.

The second thing is that the performers are better trained than they were in '76, simply because the people who did experimental theatre didn't necessarily have balletic training as dancers or really conservatory training as singers.

We were working with people who were interested in new work and experimental work but didn't have the kind of training that the young people have today.

Did the people in the 70s know what they were embarking on?

No, but neither did we. We managed to teach it to them and I recently saw the film that was done in '84. It's actually not bad at all. In '76 it was much rougher.

There's a performance practice that goes with the work - it goes with the period actually and it does change. For a new work to be really new it means the way you perform it has to be new too.

If you think about it, it can't be any other way. If you use the same performance techniques to do a work then in which way would it be new?

With this work, the performance practice didn't exist when we began it. We learnt it, we continued to learn from it in '76, in '84, in '92.

We now have 37 years of experience of playing that music. The difference is that we can actually play it now!

Not only do we play it, we do more than that, we perform it, that's the difference. It's one thing to play something - anyone can play the piano - but to actually perform a piece, you have to get beyond it, you have to get beyond the technical problems of playing, and the piece is well beyond that now.

From Bob's point of view we're looking at an amazing image which I'd like to think we never saw before.

If you look back on your career, what part does Einstein on the Beach play in it?

It's curious because at the time most people experienced it as the beginning of something, but for me it was the end. It was the end of a period that had gone on for 10 years and it was a summation of a way of thinking about the musical language, in terms of rhythm and harmony and melody.

Media playback is unsupported on your device Media caption Philip Glass: "If you fall asleep... that's ok"

And Einstein was the culmination of that. The very next piece was Satyagraha - many people may know it because it's been around London a lot at the English National Opera (ENO).

When you see Satyagraha and you think about Einstein, it's very, very different. In fact it was so different that when I did that in 1980-81 - which was only four or five years after Einstein - many people were deeply disappointed. They thought that I had abandoned something.

Actually I was starting a new body of work, I was starting something new. It took a while for people to [accept that]. Now that's been forgotten but I think they thought I'd do the Son of Einstein or the Return of Einstein - I didn't do that.

You mentioned the people saying they'd been there in 1976 who couldn't possibly have been there - why do you think people say 'I was there'?

Well you notice people don't say that they were on the Titanic. That you probably couldn't survive, but even an avant-garde work like Einstein on the Beach, people said it was life-transforming for them.

Why does it have this reputation?

I think the reason was that Bob and I were not beginners by any means, we brought real maturity and a sense of style to what we did and we treated each other as equals, which we were and we continue to be. It wasn't just one person, two streams came together.

Well, you know, if you fall asleep, when you wake up it'll still be going on Philip Glass

I had been working in theatre a long time, Bob had also been working but I think what happened is that we brought a very accomplished technique each of us had in our work, and by good luck and good fortune we were able to communicate very easily together. We actually understood each other very well.

Four-and-a-half hours, no plot, very few words?

Four-and-a-half hours is the short version! It's not much more than five, but let's call it four and a half - I don't want to make it too scary.

Five hours, then. How should you watch it if there's no plot, no words - how should you prepare yourself?

I heard Bob talk to someone about that recently and he said 'Well, you know, if you fall asleep, when you wake up it'll still be going on'.

I was in South India, visiting the kathakali, the traditional music dance theatre. It began at seven o'clock at night and went on until seven o'clock in the morning - something which Bob was also capable of doing.

When I got tired, I just got up, went into the bushes and went to sleep. Then I got up, came back and continued [watching]. I probably took several naps during the course of the night.

Einstein was not going to be a three-hour play. The first thing you do when you do a Shakespeare play these days, you get together with the actors and the directors and you cut the play. Does anyone see a four-and-a-half hour Shakespeare play? But that's what they would be.

You're a believer that not less is more but more is more?

More's definitely more - that's why it's more!

I have to confess that I have used your music in pieces of television.

I'm glad you came clean with this, David!

And the reason is you hear it and it sounds like modern life. It works with cities, it works with these sounds. Is that what you were thinking?

It wasn't always like that. I mean we went out with a piece called Dance in 1979 which is now considered a masterpiece. [But back then]people would throw things at us and scream at us.

People have said to me 'your music is the language of modern music today' but it wasn't always like that. When it first appeared it was very threatening and very dumbfounding and it took [some] getting used to.

It was actually a language which was based on global music, on music that grew up in Africa and India. I was in that generation of people who could look beyond the borders of Europe and North America and South America.

I was watching this film the other day about the making of Einstein in 1984 and one of the actors said 'the way we can learn the music is by listening for the changes' and that's true. We play it because of the changes, not because it doesn't change but because it does change.

But that sound, that rhythm, it's almost the rhythm of everyday life.

I think I heard it the first time when as a boy I was taking a train to Chicago. It was an overnight train and in those days we had no Walkmans or games or iPods or whatever. So you stayed up all night.

They turned the lights off and you listened to the train, the clickety-clack of the tracks, and it went on for hours. Think about it, that kind of sound. I could listen to it for hours, and I did - it was an eight-hour ride to Chicago from Baltimore.

Is it a different piece you're hearing from 1976?

In one way, of course, it's the same. In another way, what I'm enjoying about it is the ease with which the performers have entered into it, especially the dance company. They bring to it a kind of an ease and a grace that is reflected in what the actors and singers can do.

The show won't help you understand but what it does do is it makes Einstein a person, someone that you can see Philip Glass

This is a young company where many [of the performers] weren't even born when we first did it. They can step into this piece and it becomes theirs and that's what makes it more than anything else.

Is there a plot?

No, there's no plot - there, you made me say it. But there's something else. One of the problems of post-modern theatre, or writing, or music, is what do we do about the narrative, because we've been trying to get rid of it.

[Samuel] Beckett was a great master at getting rid of it. He confounded us with his. It's been going on, this whole exercise of changing the way we look at theatre.

The story of Einstein…we'd say well we don't have to tell the story because everybody knows who Einstein is. So we took something that was an icon in its own right.

And you get to see him too, In Bob's earlier work you didn't see Stalin or Freud, they never appeared. In this piece Einstein plays the violin, He's unmistakeable, he has a wig and even if it doesn't look like him, you know it's Einstein. We have a woman playing Einstein also. She puts on a wig and the same clothes and guess what, she looks like Einstein.

The point is that this iconic figure leads us through a series of images and movements that are reflective of Einstein's world.

Will it help me understand the theory of relativity?

I doubt it. When I was a boy I used to read all about Einstein. I was born in 1937, so when Nagasaki and Hiroshima happened, everybody wanted to know what this atomic energy was and what the theory of relativity was.

Einstein wrote a book himself about relativity and in one description…someone said 'How did you get the idea?' and he said 'I imagine myself sitting on a beam of light and travelling through space and I said now what will I see?'

Now he knew he'd be travelling at the speed of light and yet he correctly surmised that he would see everything else rushing past him and he would feel like he was standing still. And then he said the rest of his job was working out the mathematics to describe this event. That tells you a lot, doesn't it?

The show won't help you understand but what it does do is it makes Einstein a person, someone that you can see.

What you will recognise is that this is from the ordinary world. If you look at it that way, through the text we're referencing the world that everybody lives in. Through the images you're referencing the world that Einstein envisioned.

I think through the culmination of that and the movement and the music, it holds it together into a kind of bizarre but very intriguing package.

Is it the work you're proudest of?

No, there are two other works I'm equally fond of. One is Satyagraha and the other's Koyaanisqatsi.

Koyaanisqatsi is coming to London this coming year and Satyagraha has found a home here. So three of my favourite pieces will have found homes in London.

People always say 'what was the piece that made your career?' Well it's not one piece, it's usually about eight or 10 of them in a row, One piece is easily forgotten.

If you keep turning up with something else to do, or something else to see or listen to, there's a chance that you can make a living at this.

Einstein On the Beach is being performed at the Barbican from 4- 13 May.