The apples on the boughs over our heads look almost ready to drop. A century ago, these fruit-laden trees at the back of Michael Frayn and Claire Tomalin's large walled garden near the Thames could have prompted reflections on Newton's mythical revelation. They might have summoned up the reassuring laws that governed the earth below, the skies above, and the thoughts within the minds of the creatures who made sense of this tangible world. Now, after Einstein, after quantum physics, and after a harvest of revolutions in our grasp of the cosmos and consciousness alike, all that is solid seems to have melted into air. How can we really know that ripe apple will ever hit the turf?
From our table, the famously angular, quizically alert writer gestures over a smooth tract of Surrey lawn to his substantial-looking house. "I think it is striking, when you think about it, how little contact we have at any one instance with the world," he muses. "The eye has to keep moving continuously to have any picture of what's immediately in front of it at the moment. Just looking at this house - that doesn't exist for us at any one instant in time. That is constructed over a period." Blink, and there goes the neighbourhood... and I envisage a Michael Frayn sketch in which new theories of perception wreck the property market in Richmond-upon-Thames overnight.
In English literature, the terrain of philosophical comedy has often been a cramped one. Frayn's work has managed, over four decades, both to command and to extend it. In plays from Alphabetical Order to Copenhagen and Democracy, in novels from The Trick of It to Headlong and Spies, he has blown gales of laughter, intrigue and human perplexity over the shifting landscapes of science and philosophy. Order and chaos, perspective and relativity, randomness and causality: Frayn doesn't so much present versions of such ideas as enact them. Because, in the end, only the perfomance can ever test their worth. As he writes, "there are no rules without the game".
You might even connect the play-within-a-play farce of his global smash Noises Off - a laugh-machine from Sicily to Saskatchewan - to the interest in framing and viewpoint that flows through his career. "Everything is relativistic," he affirms. "There is no general frame of reference. There are particular frames of reference we use for particular purposes." Switch from one to another and the rep disaster in Noises Off becomes a side-splitting pastiche, or the suburban home of Spies an outpost of Nazi espionage.
Around 30 years ago, the former journalist and 1950s Cambridge graduate in philosophy published a synthesis of the ideas that inspired or engaged him in Constructions. Now he returns to the battleground (or chessboard) of high-level speculation with The Human Touch: Our part in the creation of a universe (Faber, £20). For Frayn, that human touch - our frame, our perspective - in effect creates a world that does exist without us, but not in a form we could grasp.
"There is this paradox that lies behind philosophy and science and everything else," he explains, quiet, precise and remarkably sure of his vast intellectual ground. "On the one hand, human beings are plainly very peripheral phenomena in the universe, both in time and space - an unimportant bubble on the surface of the ocean. But on the other hand, without human beings to perceive it from a particular point of view, and to talk and think about it, I don't see what substance the universe has. To me it's a tautology that, if there's no one there to talk about it, there's nothing that can be said. And at the same time one has to be bear in mind that it has this completely objective existence, independent of us."
With lashings of wit to leaven his erudition, a host of funny anecdotes and some exuberantly Fraynian digressions, The Human Touch develops its vision of a world spun from human stories. It bounds across topics that range from the origin of numbers to the nature of scientific "laws", from grammar to dreams. In one of the many glinting images that stud the book like jewels, Frayn describes human consciousness lurking "like an outlaw on the boundary between philosophy and science", one that "slips away across the frontier to elude capture by the forces of law and order from either side". He canters bandit-style over the same borderlands, sneaking into the territory of physicists, linguists or psychologists to rustle prime intellectual steers, leave a mocking message on the fence-post, and ride off chuckling into the sunset.
You might imagine that a playwright and novelist who writes a 500-page volume grappling with the toughest questions in modern thought would sound anxious about its reception from the specialists. True, Frayn does says that he worries that "serious philosophers and serious scientists" will judge his lay enthusiast's knowledge to be "completely inadequate to do what I'm trying to do".
But in Frayn World nothing, and nobody, stays at rest for long. "We think and act on the move. On the move ourselves, in a world that moves around us," as he puts it. Forget the problem of stepping into the same river twice; he wonders if you can even do that once. This is a philosophy of events, not of entities. "People get obsessed with ontology - with what exists and doesn't exist," he says. "And the basic question is: What happens?"
In Frayn's life, rather a lot happens. In this ever-mobile universe, his six-year-old granddaughter Emmy is now on a cinema screen near you. She's offering a bunch of flowers to Helen Mirren's miserable monarch in Stephen Frears's The Queen - a film co-produced by Granada's Andy Harries, who is married to director and writer (and Michael's daughter, the eldest of three) Rebecca Frayn. So "I'm more interested in reviews of that than in knowing what my own reviews are going to be like," admits the proud grandfather, as he prepares for a sudden switch of perspective from our bucolic outdoor seminar to a meeting about finance for Rebecca's film of Spies. "All life," as he writes, "is process, traffic, trade."
The Queen has opened to a sheaf of utter raves. The Human Touch, which treads lightly but sharply on so many academic toes, may well bring more of a mixed bag. In a pre-emptive strike, Frayn quotes the opinion of his old tutor and ongoing mentor, Jonathan Bennett, that the idea of a story-shaped world is "anthropocentrism run amok". And in the London Review of Books, the philosopher Jerry Fodor has already been reduced to grammar-free expostulation by Frayn's insistence on the primacy of coherent fiction over verifiable fact: "Piffle". But then The Human Touch is a creative writer's book about philosophy, one that privileges narrative skills and sensitivities. And, as Frayn says, philosophers' books about writing tend to be dismal efforts. They "have always assumed that the factual use of language was the fundamental use of language". But, in historical terms, "I suspect it's a specialised version of narrative". For him, fiction precedes fact.
You might, from one perspective, read Frayn's book as an apologia for its author's writing life, which soars into challenging abstraction but then swoops down into touching, comic intimacy. For example, it often enlists metaphors taken from the theatre, right up to the idea that we relate to our personality as "an actor in a Mike Leigh play" does to his part. All Frayn's world's a stage. Towards the end, he even refers to the project as a kind of valedictory curtain-call: "Soon I shall close my eyes not temporarily and experimentally, but permanently and in earnest". Yet there's nothing in his manner as we talk to prompt hints of lachrymosity. Instead, he likens the book's birth from years of note-taking not to a testament but to a cold: "You feel this tickling at the back of your throat and at the start you can't think what it is. Then you know, ominously, it's the first symptoms of a cold. It's a bit like that with a book."
The full-blown intellectual sneeze of The Human Touch conveys, at many points, the virus of laughter. On top of its other virtues, it offers an anthology of vintage humorous Frayn. "There's something slightly comic about our entire situation in the world," says its author, before racing off in a headlong dash to make the meeting for which this interview will no doubt make him late. "There is a comic disparity between the scale on which we live and the scale on which the universe lives - and something comic about our pretensions to understand this universe. But that's not to dismiss them."
Born in 1933, Michael Frayn was brought up in Ewell, south London, attended Kingston grammar school and read philosophy at Cambridge. After studying Russian on National Service, he worked for the Manchester Guardian and Observer. His first novel, The Tin Men (1965), was followed by nine others including Sweet Dreams, The Trick of It, the Booker-shortlised Headlong and Spies, winner of both Commonwealth and Whitbread awards. His plays include Alphabetical Order, Clouds, Donkey's Years (currently revived in the West End), Noises Off, the multi-award winning Copenhagen and Democracy, as well as acclaimed translations of Chekhov. The Human Touch is published by Faber this week. Michael Frayn lives with his second wife, the biographer Claire Tomalin, in Petersham, Surrey