In geological time, an instant can be 10 million years because that amount of time is just 1⁄450 of the Earth's history. A thousand years is an interval so short that it has little meaning to geologists and is only a passing moment. Geology breaks down the time-frame on earth based on principle physical and biological features. The four eras, which are the largest spans of time, covering hundreds of millions of years, are as follows:
In traditional Chinese medicine, energy flows in the body through channels called organ meridians, related to 12 specific organs in the body. These meridians are the ones used in acupuncture and acupressure to release tension and stress, as well as to keep the body healthy. They have peaks of time when they flow according to the 24 hour clock—each one having a 2-hour time period. It's not that one stops and the other begins to flow, they're flowing all the time, but one takes the lead for that 2-hour period. It is similar to how birds fly in a V-formation so that the lead bird is supported by the rest of the flock and can relinquish the lead when it gets tired. Often, acupuncturists will put needle points on these meridians at their peak time to ensure the best routing of energy to the body and its related organ.
Each of these eras is broken down into periods or systems, and each period is further divided into epochs or series. The divisions are based on changes in the Earth, formation of landmasses, glaciations, and the development of different species and the extinction of others. It's not that dissimilar from biology in the way that everything is classified and categorized according to certain chief features.
You may have heard some women refer to their biological clock ticking away. This usually means that they are ready to have children or that time is running out to have children. This analogy can be applied to other things in nature, too. (I'm sure nature doesn't have that on its mind.) There are all kinds of biological clocks. All living things need to tell time to survive, to coordinate their internal functions with the clocks of the outside world, to know when to hibernate, fly south, sprout, shed, or grow a winter coat. Our hearts need to know when to pump blood and our lungs when to breathe. Different organs in the same body may keep different times to different kinds of clocks, releasing chemicals in concert with communications from a central brain. Stomachs, livers, and sleep centers, may all tick to different, yet coordinated, times.
The limits of our ability to perceive time intervals even determine how we see the world. If we could sense intervals shorter than 1/24 of a second, which we can't, you would see the dark gaps between the frames of a movie. If we could perceive much longer intervals of time, on the other hand, we could actually be able to watch plants or children grow.
The hour is actually a recent addition to keeping track of time. Until the fourteenth century, days were divided into much less regular intervals of morningtide, noontide, and eventide. The first hours were flexible, they varied from summer to winter, and from daylight to darkness. Each day (dawn to dusk) and night (dusk to dawn) was divided into twelve equal parts. This meant that the hours of a summer day lasted longer than the hours of the same summer night. Winter daylight hours were correspondingly shorter and winter night hours correspondingly shorter. But even regular hours wouldn't work when the Industrial Revolution made it necessary for the trains to run on time and the workers to arrive for the five o'clock shift. Minute hands were needed to provide a more precise time interval, thereby introducing the need to be more accountable for one's time.
Our experience of time definitely seems to change as we grow older. Some people think that this quickening sense of time depends upon the diminishing percentage of a lifetime that each hour or year takes up. To a year-old baby, a year is a lifetime—an eternity. To a 10-year-old, a year is but a tenth of his or her lifetime, and each hour is proportionately shorter. When we reach 50, time is passing five times faster still, and a year is only 2 percent of our lives. And if we reach 100, a year is only 1 percent. (If someone could come up with a pill to slow down time, it would probably outsell Viagra.)
The time interval we call a year is marked by a single revolution of the Earth around the Sun. Our day is a single spin of the Earth around its axis and, long before we showed up on Earth, the month was very likely matched by the orbit of the Moon around the Earth. It doesn't any longer because the Moon's orbit is continually changing as the Moon moves further away. None of these astronomical measures could be considered absolute because they are constantly changing. Some 500 million years ago, our day was only 20 and a half hours long.
Let's leave our earth perspective for a moment and consider the concept of time on the planet Mercury. There the day is longer than the year. In other words, it takes Mercury longer to revolve on its axis than it takes for it to orbit once around the Sun. Talk about a confusing birthday party! We get so accustomed to thinking of days as the natural division of years into 365 parts that it's easy to forget that the day, like the year, just happens to define time relative to our planet's unique position in relationship to the Sun.
An important point to discuss before I finish this section on astronomical time is the concept of distance. In mathematics, there is a formula that defines the relationship between distance, speed (or rate), and time. Distance equals rate times time (d = r × t). Anytime you move from one place to another, a certain amount of time expires. For example, I can walk from my house to the library. If I walk at three miles per hour and it takes me two hours to get there, I've covered a distance of six miles. So distance is the product of my rate, or the speed at which I travel, times the duration of time it takes for me to get from one place to another. This is all directly related to space and time through the absolute speed of light. Let me explain.
In order for us to locate ourselves in the universe in relation to all of the other billions of celestial bodies around us, we need to know how far away they are. Powerful astronomical telescopes and radio telescopes can locate planets, stars, black holes, quasars, and other galaxies. By locating their point of origin, or source of light, and other electromagnetic radiation, the distance can be calculated by how long it takes for the light to reach us. The speed of light is the measuring tool used to find out how far away these celestial bodies are. For example, it takes the light from the sun approximately eight minutes to reach us on earth. The light from some of our neighboring planets can take weeks and months to get to us. After that, distances and time are measured in light years or the distance that light travels in one of our earth years. That's pretty far away. Our closest star, Proxima Centauri, is four light years away, or 24,000,000,000,000 (twenty-four trillion) miles.
Time gets lost in the vast distance of space and, before we get lost in time, let's finally look at special relativity.
Excerpted from The Complete Idiot's Guide to Theories of the Universe © 2001 by Gary F. Moring. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.