We humans have this uncanny ability to tell time and create schemes to measure its passage.
Time is our greatest ally and our greatest enemy.
We exist in it, are bound by it. We all have a story, with a beginning, a middle, and an end. The beginning, we haven't much of a choice about; it just happens, thanks to our parents. The middle, well, that's the challenge, what to do with the decades we have allocated to us; how to live a life of meaning, given the many compromises, disputes and limitations of existence. And the end, the unspoken, the terrible finality of life, the elephant in everyone's closet, the ultimate demonstration of our powerlessness against nature's unrelenting force. That one we speak little of, naively believing silence equates with oblivion.
No wonder people feel time is hurrying up as they age. I hear this often, people asking whether there is some kind of astronomical phenomenon going on that's speeding up time. This time is, essentially, the duration of a day, the precise ticks and tocks of clocks. And it turns out that, at least astronomically, the very opposite is happening. Existential time, of course, is another story.
A day is defined in different ways and it has different names. As a unit of time, we define a solar day as having 24 hours or, better, 86,400.002 seconds — what we use in our clocks. There are 365.242 solar days in one mean tropical year. (And a tropical year is the time it takes for the sun to return to the same position in the sky as seen from the Earth.) Now, because the Earth is tilted by 23.5 degrees with respect to the vertical as it orbits the sun, and it wobbles like a spinning top (the precession of the equinoxes), the tropical year is about 20 minutes shorter than the time it takes for the Earth to complete a full orbit around the sun as measured with respect to the fixed stars (called the sidereal year).
Confusing? Perhaps a bit. But what's really interesting is that the moon plays a key role in the duration of a day defined as the time it takes for the Earth to spin once around its axis. The gravitational pull from the moon (and from the sun with one-fifth of the force) acts harder on the side of the Earth facing it. This causes the planet (and, more effectively, the oceans) to bulge. Since the Earth rotates around itself faster than the moon orbits it, this watery bulge travels ahead of the moon. The net result is that the extra mass from the tidal bulge tugs at the moon, giving it an orbital boost, while the friction on the ocean floor acts to brake Earth's rotation ever so slightly.
In the end, Earth's spinning slows down by about 1.7 milliseconds per century, while the moon slowly drifts away from us. In other words, if we think of a day as the time for Earth to complete a turn around its axis, days are getting longer, not shorter. For example, fossil records indicate that some 620 million years ago, a day lasted 21.9 hours, and a year 400 days.
Clearly, the widespread perception of shorter days and faster time is not coming from astronomy. What then? Well, for one thing, there is an age-related perception of time. We rarely hear children complaining that time is passing too fast for them to get things done. (Unless they are having a blast somewhere and want more.) In fact, this perception seems to get worse with age as many studies seem to corroborate. William James blamed it on the lack of novelty in old age: the less memorable events in our lives, the faster time passes. Compound that with stress: If we have more "time pressure" to complete work-related or personal tasks, time seems to accelerate.
Of course, as you grow older time passed also becomes a smaller fraction of your age. For a 10-year-old, a year is 10 percent of his life, while for a 60-year-old, it's about 1.67 percent. It seems that to slow down the passage of time, you need to find your own ways to slow down and create diversity in your life. Bring in novelty to your days, release yourself from overstressed activities, carve in a bit of time to just be. These seem to be the antidotes to the anguish of not having enough time to live.
It's simple enough, really: To feel more in control of time, live a little.
Marcelo Gleiser is a theoretical physicist and writer — and a professor of natural philosophy, physics and astronomy at Dartmouth College. He is the director of the Institute for Cross-Disciplinary Engagement at Dartmouth, co-founder of 13.7 and an active promoter of science to the general public. His latest book is The Simple Beauty of the Unexpected: A Natural Philosopher's Quest for Trout and the Meaning of Everything. You can keep up with Marcelo on Facebook and Twitter: @mgleiser
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