Continuing from above.
Time is an enigma. On the one hand, nothing is more familiar to us than time. We feel its passing, we measure it precisely with clocks, and we know one day we shall run out of it. On the other hand, if we are pressed to say what time is, to try to define it, we find it surprisingly difficult. And that goes not just for the proverbial man in the street, but also for the brightest philosophers and scientists.
St. Augustine, in his Confessions, book XI, wrote, “What, then, is time? I know well enough what it is, provided no one asks me. But if I am asked what it is and try to explain, I do not know.”
Centuries later, William James in his Principles of Psychology could do little better with time, admitting “Its meaning we know so long as no one asks us to define it, but to give an accurate account of it is the most difficult of philosophic tasks.”
Time is deeply puzzling, and that puzzlement is reflected in the diversity of theories that have been proposed (see, e.g., Bardon 2013; Maudlin 2012a). Parmenides and Zeno, Greek philosophers from the town of Elea roughly 500 years BCE, held that time is an illusion of the human mind, and that reality itself is timeless. Heraclitus, their contemporary from the town of Ephesus, disagreed, claiming that time and change are fundamental realities and, as his view was famously described by Plato, that “No man ever steps in the same river twice.” Plato himself, talking via his character Timaeus, proposed that time arises from the motion of the sun, moon and planets, and that if these ceased to move then time itself would stop. Aristotle disagreed, proposing that even if these heavenly bodies stopped moving other objects would continue to change, and time is simply our accounting device to keep track of such changes. St. Augustine returned to a view similar to that of Parmenides and Zeno, arguing that time exists only in the human mind.
Newton (1687/1934) proposed that time and space are aspects of objective reality, independent of the human mind, and claimed “Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year.”
Locke (1690) in An Essay Concerning Human Understanding agreed with Newton about the reality of time, and tried to bootstrap our conception of time from pure experience: “Tis evident to anyone who will but observe what passes in his own mind, that there is a train of ideas, which constantly succeed one another in his understanding, as long as he is awake. Reflection on these appearances of several ideas one after another in our minds, is that which furnishes us with the idea of succession; and the distance between any parts of that succession, or between the appearance of any two ideas in our mind, is that we call duration.”
Kant (1787) in his Critique of Pure Reason disagreed with Locke’s claim that our conception of time can be bootstrapped from experience, and claimed to the contrary that time is not an aspect of objective reality but is an innate a priori concept that we impose upon our experiences.
Einstein (1921) in The Meaning of Relativity disagreed strongly with Kant, arguing: “The only justification for our concepts and system of concepts is that they serve to represent the complex of our experiences; beyond that they have no legitimacy. I am convinced that the philosophers have had a harmful effect upon the progress of scientific thinking in removing certain fundamental concepts from the domain of empiricism, where they are under our control, to the intangible heights of the a priori. For even if it should appear that the universe of ideas cannot be deduced from experience by logical means, but is, in a sense, a creation of the human mind, without which no science is possible, nevertheless this universe of ideas is just as little independent of the nature of our experiences as clothes are of the form of the human body. This is particularly true of our concepts of time and space…”
From the Introduction: The Origin of Time In Conscious Agents – Donald D. Hoffman click to open and read more.
Donald Hoffman is a Professor of Cognitive Science at University of California.
Read earlier short articles in the series.