Thougths about the nature of time

Time is a commodity so taken for granted that we scarcely think about it.  When we do, however, we find it to be very ephemeral in nature and frustratingly difficult to pin down. 

Time is defined to us primarily by two phenomena:  the rotation of the earth about its own axis, which defines a day for us, and the rotation of the earth about the sun, which defines a year.  A secondary demarcation of time is provided by the monthly waxing and waning of the moon, which defines a month.

The passage of a day is of course defined by the cycle of day light and darkness

.  This applies everywhere on earth, although in the higher latitudes, this distinction becomes poorly defined during summer and winter solstice.  The passage of a year, on the other hand, is very clearly defined at these latitudes due to the pronounced difference in the daylight hours and the commensurate clearly defined change in seasons.  A year's passage near the equator, however would be hardly noticed were it not for annual changes in weather patterns, such as rainy and dry seasons.  The moon's changing appearance to us is observable everywhere and serves as a convenient, if not very accurate, intermediate unit of time.

Relative to the evolution of life on earth, these celestial phenomena have been present forever, and flora, fauna and mankind itself have evolved with these time parameters as constant companions.  This local, earth centered, definition of time has therefore left a profound imprint on how we function biologically.  Indeed, time is so part of our evolutionary heritage that we pay little heed to it except to bemoan its all too rapid passage.

Modern scientist have their own definition of time, which superficially is tied to the hour, minute, second demarcation, but in reality is tied to the oscillation of some esoteric atom.  This highly technical definition of time is only of passing interest here since it is not part of the human experience or evolution.

In trying to come to a more general understanding of time, I have tried to visualize it outside the context of our tried and true references, year, month, and day as defined by the interplay among sun, earth and moon.   I found it a daunting task.

One interesting attempt at such a understanding is to speculate on how life might transpire without these well established reference marks.  This is not as hypothetical as it might appear at first glance.  Given a slightly different configuration of the solar system, we could live on an earth that has no moon, rotates once about its own axis every time it orbits the sun, and has a circular orbit with a radius more or less the same as the major/minor axis of the slightly elliptical orbit that our real earth exhibits.  The orbital relationship of the earth to the sun in this scenario, incidentally, is identical to that of the real moon about the real earth.

Such a hypothetical earth would always present the same face to the sun.  Consequently, there would be no interchange between day and night.  Furthermore, because the distance to the sun is constant, weather patterns, if any, would be random and thus yield no clue as to the passage of time.  Unless life on such an earth evolved very differently from ours, the only zone that could support life would be a strip just on the sunny side of the terminator.  Beyond the terminator would reign permanent weather of extreme cold and most of the sunny side of the earth would be dominated by permanent and lethal heat.

Assuming human like creatures lived on such an earth.  What would be their conception of time?  They would have no way of keeping track of their age in any quantitative way.  They would however be aware of the passage of time by relating events to one another, i.e. I was born before ABC became village chief.  Or I am older than XYZ because I remember his birth.  Some approximate quantification of time might evolve, based on events that via repeated observations are perceived to be constant, such as the gestation period of humans. 
 
As these hypothetical humans gained in intelligence , they would eventually be able to define a year as one passage around the sun by venturing beyond the terminator and observing the night sky and the changing  pattern of stars.  This might even yield subsidiary time marks defined by the passage of planets and constellations.  Eventually some form of clock could be invented, that could provide time increments roughly analogous to our day, hour, minute, and second.

To us the sun, earth and moon are in effect a giant clock with which we evolved.  To the denizens of this other world, time as we know it would not be part of their intrinsic make up, rather it would be a belated discovery.

A different speculation on the nature of time is to view it in the context of change.  In a constant unvarying environment, hypothetical as that may be, time really has no meaning.  But introduce change, and time all of a sudden becomes pertinent.  Specifically, motion cannot be defined without time.  Even the denizens of our hypothetical earth, would be aware of at least a local notion of time.  When two people race one another, and one comes in ahead of the other, then clearly it took that person less time to arrive at the finish line.  In this instance time becomes a localized, relative parameter, and with the addition of clocks motion can even be quantified. 

What makes our perception of time so unique, is that we have a continuum of time capable of measuring everything from very short intervals, such as a 100 meter race to the evolution of the solar system and indeed the formation of the universe itself.   It is interesting that we apply our earthly time units to some of these events, where they appear out of place.  

This brings up another aspect of time as we experience it.  We can mathematically and scientifically define and quantitise time from the tiniest increment to the most colossal, but we have great difficulty gaining an intuitive understanding of time quantities that fall outside of our everyday experience.  A second, even a tenth of a second are units of time that we can relate to because we can observe them.  A thousands of a second we can accept in the abstract, but we have little intuitive sense for it.   This is even more exaggerated  when we consider large time spans.  We rarely think of future time intervals that exceed our expected life span or our current planning horizon, whichever is smaller.  However, when looking backwards in time, we can relate to events hundreds, even thousands of years in the past and have some sense of these time parameters.  But when we read that modern humans go back about 200.000 years, it becomes difficult to really grasp the meaning of that time span.  A million years in the past becomes just a number that we can’t really get our mind around, and when we are told that the world is about four and a half billion years old, we just nod our heads in wonder without any understanding of the enormous amount of time that this encompasses.

This inability to really understand these huge time increments may be the reason for some of the doubts about evolutionary theory.  Biological systems, even elemental ones such as single cell organisms, are highly complex and it is byond intuative understanding how they could have evolved from random events and mutations.  The first rudimentary single cells came into being about one billion years after the earth was created.  The more complex cells of which we and most other living things are constituted took about another billion years to evolve.  If we somehow could really understand just how long a billion years is, we might feel more comfortable with early evolutionary events.

Future time is an even more enigmatic concept to us.  Whereas we are accustomed to contemplating events that happened decades or centuries ago,  we spend very little time and effort thinking about the future except as it relates to our lives or lives of those close to us.  Yet time exists in the future as much as it does in the past, but it is like a scroll of paper that has not yet been unrolled before us and is still unwritten upon.  But we can make  conjectures and predictions about the future with reasonable accuracy.  For example we know with reasonable certainty that the life to the earth is finite and will end in another few billion of years.  Clearly not anything that we need to worry about for us or our immediate descendents, but it is a reminder that the fate of humanity is frought with danger and very likely eventual annihilation.