Longer periods away from home - just over two weeks in Japan and Korea in this case - always make me think about time and our experience of it. On the larger scale, one experiences the elasticity of time complicated by homesickness, jet-lag, work schedule and the personal, emotional shape of absence (the last couple of days always fly by as far as I am concerned). On the smaller scale, trips away are almost the only periods in which I experience regular, abstract exercise, usually swimming. If I swim 20 minutes a day for a week or more, the weirdness of time very quickly becomes apparent: the subjectivity of the time I experience, weaving in and out of my thoughts, is totally at odds with the stop-clock ahead of me, ticking away the seconds, and the ordinary clock to my left or right, converting time elapsed into portions of a circle, slices of a pie.

This is, it might seem, pretty banal stuff. The subjectivity of our experience of time is widely acknowledged. As we get older, time seems to go faster - or is it that we seem to move faster in time? The spatial metaphors we use are confused and confusing. The theories to explain this change range from the physiological (the body cools as we age) to the arithmetical (each moment is a smaller proportion of a lengthening lifespan).

If time is so mutable, so much a matter of the ebb and flow of consciousness, is it in fact illusory? The commonsense view has long been that of classical science. Isaac Newton contrasted "absolute, true, and mathematical time" which "in and of itself and of its own nature, without reference to anything external, flows uniformly and by another name is called duration" with what he called "relative, apparent and common time". This is the view he bequeathed to the industrial age, the world of clocks, measurement and effective time management, but one which was exploded in its metaphysical aspects by Einstein's musings on relative motion and the speed of light, by the space-time continuum, and the uncertainties of quantum mechanics.

Time is the stuff of music: music manipulates our experience of time; it plays with the rhythm of experience; it stretches and complicates our relationship to the passing of time. If the world of physics is a space-time continuum, music is a pitch-time continuum. We use spatial metaphors to express our experience of frequency - notes are higher and lower, something expressed formally in staff notation, and deeply inscribed in our experience of music as performers and listeners. A large interval between two notes is a gulf to be stretched over. The quintessential musical form, melody, as it moves up and down in pitch space, over time, is a sort of quasi-miraculous bridging of the gap between the abandoned past, the ungraspable present and the as-yet-to-be-achieved, utterly unreal future. We grasp it and, as we do so, time is attended to and made palpable and affective.

It's no coincidence that the great age of music as metaphysics - Schopenhauer above all - coincided with the construction of larger and more complex forms in classical music. These brought a specialised form of rationality, musical rationality, to the subjective experience of time, through both the eked out, endless melody of Wagner, and the great symphonic structures of Bruckner and Mahler. Nineteenth-century music's ambitions for itself were in many ways as cosmic as the Pythagorean vision of an art form in tune with the construction of the universe itself, the music of the spheres. It wanted to mirror the ebb and flow of being itself.

While this all seems impossibly grandiose in a postmodern age, classical music still has the capacity to generate visions of the sublime. Here is Daniel Barenboim, recently quoted in the International Herald Tribune: "Since every note produced by a human being has a human quality, there is a feeling of death with the end of each one, and through that experience there is a transcendence of all the emotions that these notes can have in their short lives; in a way, one is in direct contact with timelessness."

There does seem a sort of affinity here between musical ambitions and the kind of metaphysics disdained by Anglo-American analytic philosophers. Karl Jaspers (1883-1969), for example, wrote of the possibility of certain experiences as "instants of eternity in time", of a human capacity to be transported to an eternal present. Surely music is one of these routes to epiphany?

The problem in Barenboim's analyis though, is the very humanity of the musical experience he identifies. Because surely, when we get metaphysical about music, what we are looking for is an escape from ourselves, a direct glimpse of something transcendental, something objective if inchoate, a grappling with time and timelessness, with being and not-being, which goes beyond the messy subjectivity of our day to day perceptions and our all too limited language. We still long to grant musical discourse a special relationship with the world, we hanker after the music of the spheres. "Such harmony", Lorenzo says to Jessica in The Merchant of Venice, "is in immortal souls;/But whilst this muddy vesture of decay/Doth grossly close it in, we cannot hear it." Romanticism's claim for our musical tradition is that in it, we hear some echo of the cosmos.

In the baldest sense this is pretentious nonsense. Music is a language, with a syntax which, whether generated by culture or embedded in our genetic make-up - or, most likely, a combination of both - is just as bound to us, to our humanity and our limited cognition, as ordinary language. There is no magical escape from the bounds of the human, from the veil of unknowing, the bonds of time.

And yet: In the same way that the metaphysicians - Schopenhauer, Heidegger, Jaspers - try to approach the unsayable and the unknowable, to break out of the limits of language and give at least an inkling, however illegitimate an inkling, of the nature of being and time (and I have to say that their attempts have never persuaded me, not that I'm a philosopher), music grapples with the sublime and the transcendent. In doing so it uses a language which, in its very lack of a proper semantics, its lack of definition, its continual striving to speak without actually speaking (or in the case of vocal music, saying so much more than is actually said), reaches outside itself more credibly than the jargon of the philosophers.