Proper Time
Invariant elapsed duration along a specified timelike path.
FOUNDATIONAL PHILOSOPHY / PHYSICS OF TIME
A New Philosophy of Time
The question “What is time?” may be underspecified because clocks, relativity, thermodynamics, quantum mechanics, information, biology, experience, and cosmology use temporal structure in different ways.
What Clocks Actually Measure
A clock is a physical system used to compare repeatable change. In relativity, an ideal clock measures proper time along its worldline. That operational result does not by itself reveal one universal substance called time.
Coordinate Time
A reference-system label used to organize distributed events; indispensable but not identical to local elapsed time.
Experienced Time
Neural, biological, memorial, and attentional organization producing felt duration and passage.
The Underspecified-Question Thesis
Before asking what time is, a serious theory must specify which temporal function is under discussion.
GEOMETRIC
How much duration accumulates?
Clocks, metric intervals, worldlines, redshift, and differential aging.
CAUSAL
Which events can influence others?
Light cones, domains of dependence, horizons, and accessibility.
DIRECTIONAL
Why does the future differ from the past?
Entropy, records, radiation, agency, and cosmological boundary conditions.
ONTOLOGICAL
What exists?
Presentism, eternalism, growing-block views, relational time, and timelessness.
Current status: the multi-layer distinction is a supported organizational synthesis. It is not yet a single experimentally established theory of temporal reality.