What Is Time? Physics, Philosophy, and the Experience of Duration

Direct Answer

What is time? The simplest answer is that time is the dimension of change and succession: it is what makes it possible for events to happen one after another, for things to become other than they were, for causes to precede their effects. Every experience we have is stamped with time — past, present, future — and physics measures it with terrifying precision. Yet the moment we ask what time itself is, it slips through our fingers.

The difficulty is ancient. Augustine posed it in the Confessions: "What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know." Time seems both everywhere and nowhere — not a thing among things, yet the condition of every thing. The philosophy of time is the attempt to say what time really is: an objective dimension of the universe, a form of the mind, an illusion, or the very pulse of being.

Historical Context

Augustine offered the first great philosophical analysis: the past no longer exists, the future does not yet exist, and the present has no duration — so how can time exist at all? His answer was psychological: time exists as distension of the mind — memory of the past, attention to the present, expectation of the future. Kant radicalized this: time is not a feature of things in themselves but a form of our intuition, the framework the mind imposes on experience. We cannot experience a world without time because time is the very structure of experiencing.

The scientific revolution gave time a new face. Newton treated time as absolute — a uniform flow independent of anything. Leibniz objected that time is only the order of successive events. In the twentieth century, Einstein's relativity showed that time is not a single cosmic clock: simultaneity is relative, and space and time are woven into spacetime. Bergson had already protested, on philosophical grounds, against treating time as merely another spatial dimension: lived duration, he insisted, is qualitative and irreversible, and the physicist's time is an abstraction from it.

Key Concepts

Presentism. The view that only the present exists: past and future are not real.

Eternalism. The view that past, present, and future all exist equally; the universe is a four-dimensional block.

The B-theory of time. The view, associated with McTaggart and modern physics, that the distinction between past, present, and future is not an objective feature of reality but a feature of our perspective; "now" is like "here."

The A-theory of time. The view that the present is objectively special, and that time genuinely passes from future through present to past.

Duration (Bergson). Lived, qualitative time — the flow of consciousness — as opposed to the spatialized time of clocks and coordinates.

Philosophical Perspectives

The deepest divide in the philosophy of time is between the A-theory and the B-theory. McTaggart argued in 1908 that time requires change, that change requires the A-series (events being future, present, then past), and that the A-series is contradictory — so time is unreal. Most philosophers reject his conclusion but accept his distinction: A-theorists hold that the present is objective and time flows; B-theorists hold that time is a static dimension and "flow" is an illusion of consciousness.

Modern physics leans B-theoretic: relativity treats past, present, and future symmetrically, and the "now" of one observer is not the "now" of another. This is the block universe picture. Bergson's protest — that lived time is not the time of coordinates — has been revived by philosophers who argue that physics and experience describe different things and that neither refutes the other.

Modern Reflection

Time remains the most intimate and the most mysterious feature of our existence. Neuroscience studies the brain's clocks; psychology shows that time expands and contracts with attention and emotion; economics prices time; ecology warns that time is running out. The philosophical question — is the future already there, is the present special, does time flow? — is no longer idle: it bears on everything from the physics of cosmology to the ethics of death and the meaning of a finite life.

Heidegger, in Being and Time, argued that time is the horizon of being: we are the creatures for whom the future matters, for whom existence is a project running ahead of itself. Whether or not physics agrees, that is what time is for us — and the philosophy of time is the ongoing attempt to hold together the physicist's time, the psychologist's time, and the time in which we live and die.

Related Thinkers

• Augustine — the psychological analysis of time
• Kant — time as a form of intuition
• Henri Bergson — duration against spatialized time
• Bertrand Russell — the B-theory and the scientific view

Related Quotes

• "What then is time? If no one asks me, I know; if I wish to explain it, I do not know." — Augustine, Confessions
• "Time is the form of inner sense: the a priori condition of all appearance." — Kant, Critique of Pure Reason
• "The time of the physicist is not the time of life; duration is not a line." — Henri Bergson, Time and Free Will

Sources

• Time — Stanford Encyclopedia of Philosophy
• Time Machines — Stanford Encyclopedia of Philosophy
• McTaggart, The Unreality of Time — Mind
• Henri Bergson — Stanford Encyclopedia of Philosophy

Further Learning

• Continue with What Is the Philosophy of Time? and Is Time an Illusion?
• Explore the Understanding Reality collection
• Read about the philosophy of time and the philosophy of science