The Nature of Time as a Temporal Interval

To repeat, Buddhism is not speaking about “time” as a thing that passes. Rather, it is talking about periods of time, “temporal intervals,” which are imputations on sequences of events experienced on a mental continuum.

• A temporal interval may be an imputation on a sequence of karmic experience, such as the interval between someone’s acting destructively and that same person’s experiencing unhappiness and suffering as the result that ripens from it.
• It may also be an imputation on a cognitive sequence, such as the interval between someone’s seeing a leaf falling from a tree and then that same person’s seeing that leaf on the ground.
• Further, a period of time may be an imputation on a continuum of forms of physical phenomena changing according to the physical laws of cause and effect, such as the continuum of the leaf just mentioned or the continuum of a pot of milk transforming into a pot of yoghurt.

Thus, since time is an imputation on an interval within a continuum or sequence of mental or physical events, it is clear that time is relative to and dependent on the observer. This is the case both from the point of view of the observer’s non-conceptual experience of two events and an observer’s conceptually labeling both the events and the interval between them with categories and words.

• But, please keep in mind, time is a nonstatic phenomenon that is neither a form of physical phenomenon nor a way of being aware of something.
• A period of time is not the same as a person’s subjective perception and conceptualization of a period of time, which are ways of being aware of something.
• For most people, the interval of a year, for instance, seems much shorter as they grow older. A year seems to pass more quickly at age forty than at age four. This is because one year is only 2.5 % of the life of a forty-year-old, but 25 % of the life of a four-year-old. From an objective point of view, however, since time is not a “thing” that passes, then to speak of different speeds at which time is passing, accelerating as we grow older, makes no sense. It is like speaking of different speeds at which the son of a barren woman drives his car.

Since time is an interval on a nonstatic mental or physical continuum, the units with which time is conceptually labeled and measured are merely conventions.

A “Year”

A specific interval can be labeled by one individual in many different ways, depending on the conventions he or she follows. Take, for example, the label “year.” A “year” is usually measured in terms of the spatial movement and position, either of heavenly bodies or of the persons measuring a year. This, of course, raises the topic of the relation of time and space, but let us leave that aside.

• A solar year – the temporal interval measured according to one revolution of the earth around the sun. Traditionally, this was measured from the perspective of the earth according to the passage of the sun through either twelve signs (khyim) or twenty-seven lunar constellations (zla-skar, lunar mansions) of the zodiac (‘khor-lo). These signs or lunar constellations are galaxies other than our own Milky Way. But because the sun orbits around the center of the Milky Way galaxy, while the other galaxies are moving in different ways and appear relatively stationary from our point of view on the earth, the interval between successive times a certain galaxy appears in the background behind the rising sun will differ each year. Because of this phenomenon, we have leap years and leap days. Thus, the length of solar years is variable.
• A lunar year – the temporal interval measured according to twelve cycles of phases of the moon: for instance, from new moon to new moon or full moon to full moon. This interval also varies from year to year, since new and full moons depend on the position of the sun relative to the position of the moon. When the moon is between the earth and the sun, it is new moon (zla-stong), and when the moon is on the other side of the earth, it is full moon (zla-gang). And, since the interval varies between when the sun is at the start of a specific galaxy, such as Aries (lug), two successive times, the interval will also vary between two successive times the new moon occurs when the sun is at the start of Aries. Because of this phenomenon, intercalary months (zla-bzhol, leap months) are periodically added in the Buddhist and Hindu calendars to correlate lunar and solar new years.
• Moreover, one person can label twelve cycles of phases of the moon “a year,” but that same person or someone else could also label it “less than a year” if the same period is measured with solar years. And the interval will be different depending on when the person measures it.
• From a relativistic point of view, the interval of a year is also relative to the speed at which the person is traveling on whose mental continuum it is measured, and the speed at which the person measuring it is traveling. The closer the person travels to the speed of light, the longer the duration between the person’s 29th and 30th birthdays will be, when measured by the observation of someone traveling at a slower speed. Again, recall that we are not talking here about the experiencing of the two birthdays by the two people traveling at different speeds, which is a way of being aware of a year, but about the interval between the two birthdays itself, which can be labeled “a year.”

[See: The Tibetan Calendar]

A “Day”

If we consider only one interval called a “year,” is there an objective interval that is being labeled differently here by one person or by two different persons, even if they are at the same location and traveling at the same speed relative to each other? If there were such an objective interval of time, it would have to be something labeled on parts, such as a certain number of days. The label “day,” however, can have different definitions depending on how it is measured: For example, there are three types of days discussed in Tibetan and Hindu astrology. Depending on how someone defines and measures a day, a day could be:

• A solar day (nyin-zhag) – the temporal interval from one dawn to the next dawn. This interval is relative to the persons’ position on the planet and will vary over the course of a year, as dawn occurs later each day after the summer solstice and earlier each day after the winter solstice.
• A zodiac day (khyim-zhag) – the temporal interval between the sun being located, from the perspective of the earth, at one degree and then the next degree in the course of its movement around the 360 degrees (dbyug) of the zodiac. These intervals also vary over the course of a year, since the orbit of the earth around the sun is elliptical and thus the speed of the earth varies as it orbits the sun.
• A lunar date day (tshes-zhag)– the temporal interval correlated with the phases of the moon. If we divide into thirty equal portions the distance, relative to the zodiac, between the position of the moon at one new moon and the next new moon, then a lunar date day is the temporal interval between the moon being located at one thirtieth-portion and then the next. These too vary over the course of a month and a year, due to the elliptical orbit of the moon around the earth and the elliptical orbit of the earth around the sun.
• A clock day – in the West, the temporal interval from the halfway point between one sunset and sunrise to the halfway point between the next sunset and sunrise. Sunrise and sunset, of course, are labeled in terms of the position of the sun relative to the east and west horizons of the person observing them. These halfway points do not vary over the course of a year but are relative to one’s location.

An “Hour”

Is there a certain absolute number of hours that are being measured by these different labels of days?

• The twenty-four-hour day was an Egyp­tian invention, from which it went to the Jews, the Greeks and the Romans. For all of them, however, such a day was a division of a solar day. The day and night were each divided into twelve hours, from dawn to dusk and dusk to dawn, so that the length of an hour, being one-twelfth of the day or night, varied according to the sea­son and length of daylight, whether it was an hour of the day or an hour of the night, and also according to one’s position on the planet. Hindu and Buddhist astrology divides the day and night, from dawn to dusk and dusk to dawn, each into six hours (dus-tshan, dus-sbyor). A standard-length clock hour (lag-‘khor chu-tsod), with twenty-four such hours in a day, was not adopted in Western Europe until the end of the thirteenth century CE with the invention of mechanical clocks.
• Both zodiac and lunar days in Hindu and Buddhist astrology are divided into sixty hours (dbyug-gu) of equal length.

We can apply the same type of analysis for minutes and seconds. What about atomic clocks that use as a standard of measurement the intervals in the atomic resonance frequency of cesium? This interval will also vary depending on the speed at which the cesium atoms are moving, for instance, on a star ship, and on the gravitational pull to which the atoms are subjected.

The question, then, is, “Is there a common-locus temporal interval that serves as the basis for labeling by different persons and with many different labels of temporal units?" A common locus (gzhi-mthun, common denominator) of two phenomena is something that is an example of both phenomena, such as a loaf of bread being a common locus of a food and something baked in an oven.

There are several Buddhist opinions concerning this question of a common locus. They fall within the orb of the Chittamatra and Prasangika debate concerning the existence of external phenomena (phyi-don).

[See: No External Phenomena: Gelug Chittamatra]

The Chittamatra Position According to Tsongkhapa’s Earlier View

In the Chittamatra tenet system of Indian Buddhism, according to Tsongkhapa’s interpretation of it during the earlier part of his life, there is conventionally a common-locus clay pot involved when several people all validly see a clay pot at the same time, but each from a different angle and distance. The same would be true of two different people traveling at different speeds and observing a temporal interval, such as the year 2006. Each would experience a year 2006 and, conventionally, it would be the year 2006 for both of them. Ultimately, however, there is no common-locus clay pot or year 2006 coming from a different natal source (rdzas) than someone’s cognition of it. A common-locus clay pot or year 2006 could not be an object cognized by an arya’s total absorption (mnyam-bzhag, meditative equipoise).

The Chittamatra Position According to Tsongkhapa’s Later View

In his later writings on Chittamatra, Tsongkhapa reinterprets Chittamatra as asserting that there is no common-locus clay pot or year 2006 even conventionally existent. This is the generally accepted Gelug Chittamatra view. When two people validly see a clay pot at the same time or experience the interval they label the year 2006, each person is experiencing the ripening of tendencies (sa-bon, seeds) of shared or collective karma (thun-mong-gi las) on his or her own mental continuum. It is not that each person is validly seeing a common-locus clay pot or experiencing a common-locus year 2006.

Nevertheless, according to Chittamatra, the clay pot or year 2006 is findable – both persons can point to a clay pot, in terms of what each person validly sees. In fact, when both of them are asked to point to a clay pot that they see on a table, for instance, each will validly see the other pointing to the same clay pot that he or she validly sees there. Similarly, both persons traveling at different speeds can point to the change in their bodies due to aging that occurred over the year 2006, and which they validly experience, and both can validly label that the change occurred in the interval called “year 2006.” And if the person who was traveling near the speed of light and who experienced the change in his body over the year 2006 were to meet the person who experienced the year 2006 while traveling at a much slower speed and who somehow was still alive, the slower speed person could also point to the change that occurred on the faster speed person’s body and correctly label that change as having occurred in the interval called “year 2006” of the faster speed person. He wouldn’t label it, however, as the interval called “year 2006” measured in terms of the changes of his own body.

The Gelug Prasangika Position

Gelug Prasangika agrees with Tsongkhapa’s later interpretation of Chittamatra concerning there being no common-locus clay pot or year 2006, either from the viewpoint of superficial truth or deepest truth, experienced by two different persons, either at different locations or traveling at different speeds. However, the understanding of this is different.

Prasangika agrees with Chittamatra that the appearance of something, such as a “clay pot” or “ year 2006,” cannot be established from the side of that validly knowable object but depends on the mind that cognizes the appearance. But, for Prasangika, this is because there is no findable referent “thing” (btags-don) on the side of a validly knowable object that corresponds to the names or labels for it. Thus, the year 2006 experienced by the person traveling at faster speed and the year 2006 experienced by the slower speed person are neither the same nor different – neither one nor many. This is because there is no such thing as a truly existent findable “year 2006.” However, unlike Chittamatra, Prasangika asserts that there are external objects – validly knowable objects, such as a clay pot and the year 2006, that have a different natal sources and different essential natures from those of the cognitions of them.

Gelug Prasangika also asserts that the existence of a clay pot or the year 2006 cannot be established by a common-locus defining characteristic mark (mtshan-nyid) on the side of the clay pot or the year 2006. This is because there is no such thing as a findable common-locus defining characteristic that has the power from its own side to establish the existence of anything as what it conventionally is. Thus, there is no such thing as one or more bases having or sharing a findable defining characteristic mark (mtshan-gzhi) on their own sides that establishes or makes them what they conventionally are. The existence of an “interval of time,” such as the year 2006, is established only in terms of what a valid mental label for it refers to – whether there is just one valid mental label or many valid labels, and whether the many valid labels are labeled by one individual or many different ones. Remember, according to Chandrakirti’s explanation, a valid label is one that is:

• Established by a convention (tha-snyad)
• Not contradicted by others validly measuring and labeling the same label in terms of superficial truth
• Not contradicted by others validly measuring and labeling the same label in terms of deepest truth.

[See: Applying Emptiness When Stuck in Traffic]