time

Table of Contents

Introduction
Time and its role in the history of thought and action
- Nature and definition of time
- Prescientific conceptions of time and their influence
  - The individual’s experience and observation of time
  - Cyclic view of time in the philosophy of history
    - Environmental recurrences and religion
    - The cyclic view in various cultures
  - One-way view of time in the philosophy of history
- Early modern and 19th-century scientific philosophies of time
Contemporary philosophies of time
- Time in 20th-century philosophy of physics
  - Time in the special theory of relativity
  - Time in general relativity and cosmology
  - Time in microphysics
    - Quantum mechanical aspects of time
    - Time in particle interactions
  - Time in molar physics
- Time in 20th-century philosophy of biology and philosophy of mind
Time as systematized in modern scientific society
- Time measurement: general concepts
  - Principal scales
  - Relativistic effects
  - Clocks
  - Time units and calendar divisions
    - Lengths of years and months
    - Astronomical years and dates
- Rotational time
  - Standard time
  - Universal Time
  - Variations in the Earth’s rotation rate
  - Coordinated Universal Time; leap seconds
  - Time determination
- Dynamical time
  - Ephemeris Time
  - Ephemeris second
  - TDB and TDT
- Atomic time
  - Basic principles
  - Atomic clocks
    - Cesium clocks
    - Other atomic clocks
  - SI second
  - Atomic time scales
  - Time and frequency dissemination
  - Relativistic effects
- Pulsar time
- Radiometric time
- Problems of cosmology and uniform time

References & Edit History Related Topics

Images & Videos

Alfred North Whitehead

Ajanta Caves: reclining Buddha

relativity of simultaneity

Listen to physicist Sean Carroll explaining the connection between entropy and the second law of thermodynamics

How do atomic clocks work?

For Students

Alfred North Whitehead

Read Next

Calendar marking march 15th

22 Questions About Time and Timekeeping Answered

Moonrise over Tucson, Arizona

Why Doesn’t Arizona Observe Daylight Saving Time?

Discover

World Data Locator Map: Australia

Is Australia an Island?

Flags of the countries of the world (flagpoles).

How Many Countries Are There in the World?

"Landing of Columbus" by John Vanderlyn, oil on canvas; commissioned 1836/1837, placed 1847. In the rotunda of the U.S. Capitol, Washington, D.C. 12' x 18' ft. (3.66 m. x 5.49 m.) Christopher Columbus and members of his crew are shown on a beach

5 Unbelievable Facts About Christopher Columbus

The Colosseum, Rome, Italy. Giant amphitheatre built in Rome under the Flavian emperors. (ancient architecture; architectural ruins)

New Seven Wonders of the World

Russian grand duchess Anastasia; undated photograph. (Anastasiya Nikolayevna, Tsar Nicholas II)

Did Duchess Anastasia Survive Her Family’s Execution?

NBA Lakers Celtics Finals Kevin Garnett shooting.

10 Great Sports Rivalries

Ahura Mazda - relief of the Zoroastrian god Ahura Mazda at the ancient ruins of Persepolis in Iran. Also known as Ormazd Zoroastrianism,

Which Religion Is the Oldest?

time: Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

News •

America will 'lead the pack' in strike on Iran if no deal is reached, Trump tells 'Time' • Apr. 27, 2025, 11:37 PM ET (Jerusalem Post)

Photos and Videos

Alfred North Whitehead

Ajanta Caves: reclining Buddha

relativity of simultaneity

Listen to physicist Sean Carroll explaining the connection between entropy and the second law of thermodynamics

How do atomic clocks work?

Explore three simple ways and three complicated ways of time traveling

See All Videos and Images →

Topics

time perception dynamical time time dilation solar time twin paradox anachronism time reversal geologic time atomic time sidereal time light electromagnetism gravity relativity chemical reaction antimatter molecular beam physical constant force energy

Dig Deeper: More Articles That Discuss This Topic

Key People

Henri Bergson

Henri Bergson

French philosopher

Ferdinand Berthoud

French horologist

Quiz

Italian physicist Guglielmo Marconi at work in the wireless room of his yacht Electra, c. 1920.

All About Physics Quiz

Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.

Physics and Natural Law

List

Calendar marking march 15th

22 Questions About Time and Timekeeping Answered