 by Preston MacDougall May 26, 2005
Time travel, on the other hand, happens all the time. Even when standing still, we are time travelers. But always forward, and one moment at a time.
Occasionally though, time travel is less pedestrian. For instance if you are driving West on I-24 from Chattanooga to Monteagle, in Tennessee, even if your car has trouble going the speed limit on the steeper parts of the climb, you'll probably get there before you leave. That's because, while they are separated by only 45 miles, few of them straight or horizontal, Chattanooga is at the western edge of the Eastern Standard Time zone, and Monteagle is at the eastern edge of the Central Standard Time zone. Or consider my time traveling today. According to my flight itinerary I left Los Angeles just before midnight last night and I will arrive in Melbourne, Australia, at 8 am tomorrow morning. The weird part is that the flight only takes fifteen hours. What happened was that somewhere over the Pacific Ocean I crossed the International Date Line, and, for me, five o'clock Friday morning was followed by six o'clock Saturday morning. This artificial seam in the world's standardized time zones ultimately arises from the fact that clocks and calendars keep track of two very different things. Clocks keep track of time, which is most accurately kept by so-called atomic clocks. By international agreement,
the second is defined as the time it takes a cesium-133 atom,
at absolute zero temperature, to oscillate between its two lowest
electronic states nine billion, one hundred and ninety-two million,
six-hundred and thirty-one thousand, seven-hundred and seventy
times. Exactly. A minute is exactly 60 seconds, and an hour is exactly 60 minutes. But, believe it or not, a day is not exactly 24 hours. Leap seconds are given or taken away in the wee hours, depending on the date. Again, this is because clocks and calendars keep track of different things. So what does a calendar keep track of? You might think seasons, but that isn't right because it was spring when I left Los Angeles, and fall when I arrived in Melbourne. No, I think it is most accurate to say that the calendar keeps track of position - the position of the Earth in its annual trip around the sun, as witnessed by the stars in the heavens. (Even this is not perfectly accurate because of the so-called precession of the Earth's axis every twenty thousand years or so. But we will fast-forward though that astronomy lesson.) Compared to the orbital motions of the planets in our solar systems, the positions of the stars, including our sun, seem fixed relative to one another. While the myths that they inspired have taken many forms, the stars in the constellations are set. They are actually moving, but it is not noticeable, even on a geological timescale. Also, on extremely rare occasions one will explode in a supernova. Star-gazing is one of the reasons that my first visit south of the equator will be such a trip. The stars that I have seen in the heavens have been the same ones my entire life. There were some changes around the horizon, depending on season and latitude, but the Big and Little Dippers have always been there on a clear night, whether I was in Toronto, Milan or Beijing. And I could always determine which way was North by finding Polaris, or the North Star. Polaris has never been seen in Australia, or anywhere else in the Southern hemisphere. And the Southern Cross is prominent year-round in their night sky, as are the Magellan clouds. I look forward to seeing what else is different. Hopefully the weather will cooperate, because on a cloudy night there aren't any stars twinkling, no matter where you are. On the way back, as the alien visitors sing in the Rocky Horror Picture Show, it will be time to "do the time warp again." Only this time I will be crossing the International Date Line in the reverse direction. As a result, I will leave Sydney around 11 o'clock in the morning, and I will arrive in Los Angeles at 7 o'clock in the morning on the same day, even though I will have watched a sunset, followed by a sunrise, from the plane. Talk about déjà vu!
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