Time

Time is a concept that's difficult to think about. We divide it into manageable pieces like seconds, minutes, and years, but those divisions are man made. Time itself, as an entity, really has no divisions; it's smooth (as opposed to the percussive passing of ticking seconds in a watch) and unending. Something that time isn't, however, is constant. For understandable reasons, most people assume that a second is a second is a second and that it will never change. Time seems to be the one thing we can count on to always be the same. But it's not true.

First of all, our perception of time, as well as the importance of a given unit of time, varies depending on the system being considered. To humans, a year is significant enough that we keep track of how many of them we've experienced. Years indicate our expected development and position. Yet, babies' ages are frequently counted in months. Their development is acute enough that simply saying "She's about a year old" isn't specific enough. Six months is not the same as nine for a baby, but no one takes note of the difference between a person who is 57 years and 6 months old and their "different" age three months later.

Even then, humans assign significance to different units of time depending on their circumstances. Seconds of age mean nothing, but seconds of a race make the difference between the winner and the loser. We count months of pregnancy, semesters remaining before graduation, decades of fashion and trends (the 60s, the 70s, etc.), hours of sleep, minutes to get ready, and years of experience. Each accepts a unit of time that makes sense.

Physics works in very much the same way. In particle physics, a second may as well be an eternity for particles which exist for millionths or billionths of seconds before decaying. Waiting for a second is allowing for so much change in a sub-atomic system that it would be like examining a 90-year-old man and trying to determine how heavy and tall he was at his birth.

When the universe was a "baby", smaller units of time had significantly more meaning than they do today. We recognize five major milestones in the development of matter before the first second of the universe transpired. In the same way that a month differs in the consideration of the life of an infant, billionths of seconds mattered in the beginning of the universe because even a billionth of a second could double its life. And yet today, not even a second means anything to the universe as a whole. For that matter, days, years, and even millennia are inconsequential moments in the universal perspective. In 100,000 years, 99.9% of all of the stars in the universe will be as identical as a man turning 57 is to himself a day after his birthday (even though they burn hundreds of billions of tons of hydrogen each second). Only when we start talking in millions (and in most cases, billions) of years do we begin to notice the first inklings of significant change.

So, certain lengths of time are only important if they correspond to the length of time it takes for something to change. Even then, in a single system (like that of the universe, as explained above), the important unit of time changes with the passage of time. It depends on who is measuring, when he's measuring, and why he's measuring.

And even then, there's more to the story. Perception and importance aside, a single unit of time differs depending on the observer. With absolutely no metaphor or figure of speech employed, the length of a second (or any other unit of time) depends upon the velocity of the person observing the thing experiencing the second. The principles behind this fact are all contained in Einstein's explanation of time and space which is known generally as (trumpet fanfare) relativity and will be discussed in the next installment.