Tuesday, July 29, 2008

Time and the Secret of Life

Now the thing about time
Is that time isn't really real
It's all on your point of view
How does it feel for you?
Einstein said that he could never understand it all
Planets spinning through space
The smile upon your face
Welcome to the human race
Isn't that a lovely ride?

-James Taylor
“The Secret of Life” (excerpt)

I’ve always liked James Taylor’s song “The Secret of Life,” the first line of which is “the secret of life is enjoying the passage of time.” That sounds desirable, and maybe even plausible, though it’s one of those easier-said-than-done things. But it’s the verse quoted above that got me thinking about the nature of time and how we experience it, compared to how we think about it in the context of science and history.

Our subjective experience of time must have evolved just like every other aspect of our physical and mental characteristics, and it seems to be related to consciousness (whatever that is!). In hunter-gatherer and even basic agricultural cultures, there are a few basic time scales, and not much need for precision. Your body needs to be able to sense and react in fractions of a second to detect and properly respond to movement associated with predators and prey, and to be able to throw things accurately. Without artificial light sources and timekeeping devices, you also need a sense of the day/night cycle to plan and accomplish those things you need to do in daylight, and to seek safe shelter for night time. This scale comes pretty naturally from the apparent movements of the sun and the stars.

You also need a sense of the seasonal/annual cycle to judge the likely availability of food sources, and for planting and harvesting. There are environmental cues for this scale too – the changing length of the day, changes in weather, the location of the rising and setting sun, and the patterns of stars that change with the seasons. Early humans spent a lot of time outdoors and certainly would notice these things more than most people do these days.

The longest time scale for most basic human activities would be essentially your lifetime, say 20-100 years. Children grow and change noticeably on scales of months to years, and our faces and bodies change through adulthood. Beyond a lifetime, you need some sort of artifact to keep track of time. Before writing, there were oral traditions, stories memorized and passed on to children to help preserve traditions and know-how and to provide some sense of continuity. This might be counted in generations, but here is where it starts to get somewhat abstract, when you think about what happened before your life and what might happen after you die.

These seem to be the natural and easily understandable human time scales, and anything outside of this range is going to require something beyond your own senses. Writing allows records to extend beyond a lifetime more reliably than oral storytelling. Calendars and simple timekeeping devices like an hourglass or sundial make it possible to measure time and to compare ideas of time with other people. Subjective time starts to have some objective milestones.

Where this all breaks down is when science and history start to tell us about events and phenomena that fall outside these individual human time scales. I know about all sorts of events with all sorts of time scales – e.g., different events in a computer take place in nanoseconds to microseconds (CPU and memory operations) or milliseconds (disk operations), different by factors of thousands to millions, but all too short for me to comprehend in any direct sense.

At the other end, we have geological and cosmological events happening over scales of many thousands to millions to billions of years. While I can use analogies like the cosmic calendar (here's Carl Sagan explaining it) to understand these time scales in some sort of abstract way, I can’t directly or emotionally comprehend how long even 500 years is, let alone ten million or thirteen billion years.

I accept the reality of these time scales, and since I have read and studied a lot of science over the years, I perhaps have more familiarity with “scientific time” than the average person. But even when the scientific evidence is clear, these enormous time scales are still literally mind boggling to me. So I can understand how it can be hard for some people to "get their head around" concepts like “continental drift” (plate tectonics) and evolution that require time scales so far beyond anything an individual human can experience or even imagine.

I don’t know if the secret of life really is enjoying the passage of time. I’m not even sure whether time is really real (I do know that my 13 hour flight from San Francisco to Taiwan really seemed more like 30 hours). Or as somebody undoubtedly said before, maybe time is just nature’s way of keeping everything from happening at once.

P.S. I'm re-reading Bill Bryson's A Short History of Almost Everything, which is great (more later I suppose). In chapter 21, he talks about how difficult it is for anything to get fossilized, and about trilobytes and other odd creatures of the "Cambrian explosion," referring to the geological period when complex life-forms somewhat suddenly appear in the fossil record, around 540 million years ago. To try to convey this distant age, he suggests you imagine that you can travel backwards into time at the rate of one year per second. At this rate, you reach the first century CE in about half an hour (2008 seconds), and the beginnings of human life in just over 3 weeks. But you would have to fly for almost 20 years to get to the start of the Cambrian period!

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