Time According to Sir Issac Newton

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The English philosopher Sir Issac Newton made his greatest contribution to the study of space, time and motion in his work Philosophae Naturalis Principia Mathematica. In the section entitled "Scholium," Newton theorized that that mathematical time passed by independently without disruption by other forces in the universe. Additionally, he stated time that was a dimension of the universe in which events occur in sequence.  This is known as the realist view of time. Essentially, Newton believed that time was as real as the objects that it contains and it could be measured.

"Absolute, true, and mathematical time, in and of itself and of its own nature, without reference to anything external, flows uniformly and by another name is called duration. Relative, apparent, and common time is any sensible and external measure (precise or imprecise) of duration by means of motion; such a measure - for example, an hour, a day, a month, a year - is commonly used instead of true time." -Principia

Prior to the late seventeenth and the early eighteenth centuries, Newton's era, a number of views on time refuted the idea that time could be measured, instead arguing that time could not occur without a change occuring somewhere in the universe. In this view, time is the measure of the intervals between or cycles of changes in the universe. This is contrary to Newton's point that time can continue regardless of the rest of the universe. The pre-Newtonian and many post-Newtonian theories considered relative time; Newton wanted to seperate that from absolute time. As mentioned in the above quote from Principia, Newton considered traditional measurements of time to be units of relative time, whereas absolute time could not be measured in such a manner.

An Arguement for Absolute Time
Newton's "Scholium" provides a number of arguments for absolute time. Distinguishing between relative and absolute time allowed for the corrections of inequalities in the solar day, the amount of time it takes for the sun to return to its zenith, which was originally thought to be uniform throughout. Whereas the Ptolemaic astronomy of antiquity considered the sideral day--the amount of needed for a fixed star to return to its zenith--to be constant, emerging theories during the scientific revolution began to doubt that the rotation of the Earth remained constant over a year (a constant rotation was crucial to the uniformity of the sideral day). With Newton's theory of time, absolute time could remain constant even as relative time was liable to change due to changes in the Earth's rotation.

The Newtonian theory does consider time as a dimension to be the fourth dimension of motion. While Newton didn't fully explore the effects of relative motion on time, his theory did set some precedent for Einstein's theory of relativity, at least giving him material to vastly expand on.

William Charleston's Theory:
Many of the core aspects of Newton's theory can be found in William Charleston's Physiologia Epicuro-Gassendo-Charltoniana (1654), which was published twelve years before Newton was born. Charleston stated that time is a real entity, that it is constant regardless of other forces, and that it is distinct from any measure of it. In fact, Newton became familiar with this text while he was an undergraduate, and it clearly influenced his later theories; however, thanks to Newton's combined success, particularily with his Principia, Newton's theory on time is far more well known than that of Charleston.

Interestingly, when Newton considered time to be a real entity, he did not regard it as a true, worldly substance. Instead, he believed that time had a special existence akin the ubiquity of God. Here we can see the influence of religion, especially deism--the belief that God can exist while allowing natural laws to govern the universe without a supernatural element)--on Newton at the beginning of the Enlightenment.

Indeed, Newton theory of time not only provided part of the basis for classical physics as far as the early twentieth century (not coincidentally, Einstein's time), but also became a crucial element of the Newtonian system of philosophy and theology.

Aristotle's View of Time

According to the Classical Greek philosopher Aristotle, time is the measure of motion. Motion for Aristotle was both quantatitve and qualitative. He used astronomy to define the idea that time there were equal intervals for time; that is, time has uniformity. He correlated the rate of motion of the stars with the uniformity of motion and thus the uniformity of time. Aristotle believed that there was a fifth element beyond earth, air, fire, and water known as aether, which rotatoes around the center of the universe (in Aristotle's time, the center of the Earth). If the motion of aether is the measure of time, then the stars rotate uniformly as well. With the advent of the Scientific Revolution in the sixteenth century, Aristotle's theory came under significant revision with the work of astronomers Nicholaus Copernicus and Galileo Galilei. These developments eventually became a subject of interest to Newton.