Sunday, January 28, 2007

It's About Time

What time is it? How old are you? How long will the movie last? What is your ETA? When was the War of 1812 fought? What is the current life expectancy?

All those questions have one thing in common; they all ask about some measure of time. Time is one thing that is almost always on our minds, that we all possess but most of us have too little of, and that we can measure but have no good definition as to what it really is.

We can’t see it, feel it, touch it, taste it, or smell it. We can sense it, to some degree, but few of us can agree on how.

What is time?

Even Webster has a difficult time with that question. It is defined as the interval between two events. But look up interval and you’ll find its definition includes the word time, the time that has elapsed between two events.

Albert Einstein proved mathematically that time is a dimension and it is only one-dimensional in that it always flows forward. We call it the arrow of time. So there are three dimensions of space – length, width, and height – and one dimension of time.

We measure length, width, and height with such things as rulers, yardsticks, odometers, and micrometers. We measure time with clocks. The standard unit of time is the second.

A second is one thirty-one-million-five-hundred-seventy-seven-thousand-six-hundredth of a year. And a year is defined as the length of time it takes the earth to orbit once around the sun.

But we have discovered that the earth doesn’t really keep good time. The orbit is not perfect. It was more than sufficient enough through all of history until the twentieth century. Then we needed a little more precision.

We now define a second in terms of the oscillation rate of a certain kind of cesium atom. And it takes something called an atomic clock to keep track of those oscillations. Atomic clocks are incredibly accurate, losing or gaining less than a billionth of a second per day.

Why would anyone need to measure time that accurately? It’s not as though the boss is going to dock you’re wages for a billionth of a second.

Somewhat ironically, one of the most important reasons we need to measure time so precisely is because we need to know precise distances. And the most common example of that is the Global Positioning System, or GPS devices that many of us have in our cars or take with us on wilderness hikes.

The speed of light is a constant. No matter how the observer is moving, light is always measured as traveling at exactly the same speed. And radio waves are basically just light waves that are too large to be seen.

So when at least three of the GPS satellites, all of which have atomic clocks, send a radio cue to your GPS unit, the unit deciphers the difference in arrival time of each signal and calculates the distance to each. Its software then identifies that calculated location on a map and displays it on the screen. It is accurate to within just a few feet.

Atomic clocks have also allowed us to prove beyond doubt what a guy named Alfred Wegener inferred in 1914, that the continents we live on are moving. North America is moving away from Europe at the breakneck speed of about two inches every year.

Even though we can measure it precisely, and use it in everyday conversations with ease, time is still an enigma. It continues to elude an easy description. And we may never master it.

But at least we can use it to organize our lives. We keep schedules, mark calendars, and meet deadlines. Speaking of which, mine draws near, so it’s time to send this one to my editor.

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