History of Time in Timeline

By Popular Timelines Editorial Team · Updated: July 13, 2026

Time is a fundamental dimension used to sequence events, measure the duration of occurrences, and determine the intervals between them. From a physical perspective, it is defined as the progression of existence from the past through the present into the future. Sir Isaac Newton viewed time as an absolute, universal constant, whereas Albert Einstein’s theory of relativity revolutionized this understanding by demonstrating that time is relative, flexible, and inextricably linked to space—forming the four-dimensional fabric known as spacetime. Subjectively, time is experienced through the human perception of change and memory, while objectively, it is measured using precise atomic standards. In thermodynamics, the 'arrow of time' is associated with entropy, explaining why processes move toward disorder and why time appears to flow in only one direction. Ultimately, time serves as the essential framework for both the scientific study of the universe and the structure of human civilization.

1907: Einstein's Reinterpretation of Spacetime

In 1907, Albert Einstein challenged the Newtonian consensus that time was universal and absolute, establishing a new conceptual framework for time and space that served as a foundation for his special theory of relativity.

1908: The Unreality of Time

In 1908, J. M. E. McTaggart published an article titled The Unreality of Time, in which he asserted that the concept of time is inherently self-contradictory because events possess the paradoxical characteristic of being both present and not present simultaneously.

1955: Invention of the Caesium Atomic Clock

In 1955, the caesium atomic clock was invented, marking a revolutionary shift in timekeeping. This development led to the gradual replacement of traditional astronomical time standards, such as sidereal and ephemeris time, with more precise standards based on the SI second.

1967: Redefinition of the Second

In 1967, the International System of Measurements officially established the second based on the physical properties of caesium-133 atoms, defining it as 9,192,631,770 cycles of radiation corresponding to specific electron spin energy transitions.

May 2010: Record for Smallest Time Interval Uncertainty

As of May 2010, researchers achieved the smallest time interval uncertainty in direct measurements, reaching approximately 12 attoseconds. This milestone was established by analyzing the delay caused by the interference patterns of out-of-sync electron waves.

2026: Absence of a Unified Quantum General Relativity Theory

As of 2026, scientific consensus has yet to produce a generally accepted theory of quantum general relativity, which remains a central challenge in physics due to the fundamental differences in how time is treated in quantum mechanics versus general relativity.