Overview

Time is one of the most familiar yet mysterious concepts. We measure it, waste it, and run out of it, but defining what it is remains a profound philosophical and physical problem.

Core Idea

The core idea is change and duration. Time is the dimension in which change happens.

Formal Definition

In physics, time is the fourth dimension of spacetime. In metaphysics, there are two main views:

  • A-Theory (Tensed Time): Past, Present, and Future are real properties. The passage of time is real.
  • B-Theory (Tenseless Time): Time is just a coordinate like space. “Earlier than” and “Later than” are fixed relations. The “flow” of time is an illusion.

Intuition

  • A-Theory: Time is a river flowing past us. The future doesn’t exist yet; the past is gone. Only the NOW is real (Presentism).
  • B-Theory: Time is a landscape (Block Universe). The dinosaurs are “over there” in time just as New York is “over there” in space. All moments exist equally.

Examples

  • Time Dilation: Einstein showed time slows down at high speeds or in strong gravity. This supports the B-Theory (Block Universe).
  • Entropy: The arrow of time (why time moves forward) is linked to the increase of disorder (Second Law of Thermodynamics).

Common Misconceptions

  • Misconception: Time is universal and constant.
    • Correction: Relativity proved time is relative to the observer. There is no “universal clock.”
  • Misconception: We experience the present instantly.
    • Correction: Because of neural processing lag, we actually live slightly in the past (about 80ms).
  • Space: The three-dimensional extent in which objects and events have relative position and direction.
  • Eternalism: The view that past, present, and future all exist.
  • Presentism: The view that only the present exists.

Applications

  • GPS: Satellites must correct for relativistic time dilation to be accurate.
  • History: The study of events in time.

Criticism and Limitations

  • The “Now”: Physics has no explanation for the subjective experience of “Now.” It treats all moments as equal coordinates.

Further Reading

  • The Order of Time by Carlo Rovelli
  • Time and Free Will by Henri Bergson