As time goes by


When the ball drops tonight, time will be on our collective mind.

Astronomers can measure such temporal milestones with incredible accuracy, of course. Time aficionados will probably note that the ball will drop a second or two too late or too early. It always does.

On one level, time is inextricably woven into the fabric of the universe. To exist, a thing must have height, width, and breadth, but it must also possess duration. It must continue to exist in time. Hence, astronomers don’t call space “space.” They call it “spacetime.”

The way we measure time is another matter entirely. Most of us assume that God lowered a calendar and clock down from heaven on a string, but that assumption is far from the truth.

In fact, astronomers invented time, or at least our way of measuring its passage. Time and astronomy are thus inextricably intertwined, much to the detriment of time, I am sorry to say. A single orbit of the Earth around the sun, for example, determines the year, about 365.25 days.

The “moonth, ” or “month” as you Earthlings call it, was originally measured by the orbit of the moon around the Earth. A set of lunar phases, the ancient way of determining a month, takes about 29.5305882 days. The trouble comes because 29.5305882 days doesn’t divide evenly into the 365.25-day year. We simply can’t have months of equal days. Also, what do we do with that pesky .25 of a day when we measure out the year on a calendar?

We thus arbitrarily add a day to the calendar every four years.

Adding to the mind-numbing complexity, Earth’s orbit is a seamless path. There are no convenient tick marks to tell us when the new year begins. Why then do we begin the year in the middle of the blessed winter?

The logical time to begin the calendar year is when the world begins to come alive again after its winter dormancy, that is, on the first day of spring. In fact, the ancient Romans, from whom we get our basic calendar, began the year in March.

The Roman calendar was only 355 days long, i.e., 12 months of, on average, 29.58 days each — pretty close if all you care about is the length of the month. Unfortunately, that left the problem of that 365-day solar year.

Thus, the priest-astronomers who were in charge of the calendar periodically added an extra month after Feb. 23. The trouble was that they often did so arbitrarily (mostly if some powerful bureaucrat wanted to lengthen his term in office by a month).

By 46 BCE, the calendar year was a couple of months out of sync with the solar year. Their month of March was happening during the dead of winter in the month we call January.

At the advice of astronomers, Julius Caesar, the Roman dictator at the time, added 67 days to November that year, essentially stopping the motion of the calendar for two months. Voila! The year now began in January, but at least spring began in March again.

To eliminate future problems, the wise Julius standardized the year at 365.25 days, adding a leap day every four years. But there was another problem. The solar year is actually 365.242199 days. Julius’s year was 11 minutes and 14 seconds too long.

The extra 11 minutes may not seem like much, but they add up over the centuries. By 1582, the first day of spring was 10 days removed from the traditional date of March 21.

So in 1582 Gregory, the Pope at the time, decreed that years that begin centuries, like 1900, would not be leap years. Exceptions would be made for years divisible by 400. Thus, the year 2000 WAS a leap year.

In addition, Gregory removed 10 days from October 1582 to bring the calendar back into sync with the seasons, a decision that caused considerable consternation, especially among folks who had to pay a full month’s rent on their land for an October that lasted only 21 days.

Sadly, only a few Catholic countries accepted the reform. Centuries passed before Protestant nations were fully in line. By 1752, when Britain finally accepted the convention, 11 days had to be removed from the calendar. The farmers who paid rent on their land were not happy about the change. According to an old painting by William Hogarth, they rioted. “Give us our 11 days,” they chanted.

But even the Byzantine complexities of the Julian calendar didn’t do the trick entirely, at least so far as the length of a day is concerned.

Earth’s rotation is slowly lengthening because of tidal forces caused by the dragging effect of Earth’s moon. Thus, our current Time Lords at the US Naval Observatory must add a leap second to the calendar every few years.

Recall, our temporal problems happened because Earth doesn’t take an even number of days to orbit the sun, and the moon takes an uneven number of days to orbit the Earth. The way we measure time is a constant reminder that we live on a planet in space orbiting a star.

Furthermore, all of our calendar manipulations depend on the notion that time is a ticking clock. An absolute and unchanging tick of some cosmic timepiece second marks each second.

However, even the cosmic tick is an illusion. The passage of time is dependent on our peculiar position in spacetime.

In his Special Theory of Relativity, Albert Einstein demonstrated mathematically that for an object in motion, time slows down. That effect has been verified many times over the years with careful experimentation. It’s real.

Spacetime bends and stretches depending on the velocity that we are traveling through the void. We experience the slow-velocity version of temporal reality. At high velocities, clocks slow down and time stretches out.

Even at low speeds, nothing much seems to happen, but something does. If you hop into your car and drive to visit your Aunt Earline in Albuquerque, you are traveling at a very low velocity of only, say, 65 miles per hour. Both you and she will think you took exactly the same amount of time to get there. However, although neither she nor you can detect it, from her point of view, you took a tiny fraction of a second longer to get there than you thought you did.

On Earth, we are moving very slowly with respect to, say, the International Space Station in orbit around Earth. Our clocks tick off the seconds at what we think of as a fixed rate. But the clocks on the International Space Station, which is moving more rapidly than we are, tick more slowly. In fact, the astronauts aboard the Space Station age 0.014 seconds more slowly for every year they are aboard the ISS. Their internal clocks are ticking more slowly as well.

As an astronaut approaches the speed of light, the effect intensifies dramatically. If she is moving rapidly enough with respect to Earth, her clock would seem to slow down to a crawl if an observer on Earth had a camera pointed at it. To the astronaut, the clock would tick normally.

If the astronaut could observe events on Earth, she would see those events happening in rapid motion as if the video of those events had been dramatically speeded up.

Thus, when and if that astronaut returned to Earth after what for her was a lifetime of travel, she would have aged normally from her point of view, but all her relatives would have long since passed away. She, the legendary space traveler, would perhaps be greeted by her great-great-grandchildren as some latter-day Rip Van Winkle, a quaint representative of an earlier, more primitive age.

Despite the malleability of time, we still tend to perceive it in absolute terms. No temporal concept exemplifies that notion more than the word “now.”

“Now,” my friends, is an illusion. Information takes time to get from one place to another.

Look up from this newspaper. Whatever you see is the result of light bouncing off that object and traveling to your eyes. That process takes time.

Even the touch of a hand on yours is not experienced now. The information must travel from the nerve endings in your hand up to your brain, and that takes time.

The problem is exacerbated when we observe objects at great distances. If we had a telescope powerful enough to see alien civilizations on other planets, we would be seeing them in the past. For a planet 1,000 light-years away, that civilization would have progressed 1,000 years beyond the time that we see them “now.”

In a very real sense, there is no absolute moment in time that corresponds to “now” for us and that alien civilization. We are forever separated not just by an ocean of space but also by an unconquerable ocean of time.

Still, the main problem with time is that there never seems to be enough of it. As our new year begins at midnight, I hope that you will use what time you have left on the planet to do some good for yourself and for the world.

By Tom Burns


Tom Burns is the former director of the Perkins Observatory in Delaware.

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