My sons were not Einsteins in school, but apparently Einstein wasn't either. But they quickly learned, as Albert had calculated, time is relative. This ticking one-way arrow of minutes and hours is not constant. The speed of light is always the same, not the speed of time.

My boys figured it out even without the physics. When we were in a hurry and time needed to speed up, they would go so slowly. When we wanted the minutes to stop, their internal clocks seemed to rev up. If there was a task to be done, the time to finish was relative to whether they wanted to do something else. If they desired to go with friends, the lawn was mowed in record time. If they had other work around the house, the lawn mower and minutes never moved so slowly. The one exception to Einstein's calculation that time slowed down as speed increased was when they were late for curfew and — in spite of their racing to get home — the seconds just flew along with their driving.

Time particularly dragged when our sons didn't like doing something. It was always, "This is taking too long," "Aren't we done yet?" Sometimes it was, "We had to wait a million years." Thinking about it, they were no different than the rest of us and our perception of time. Time is relative, perhaps, not to the velocity of our bodies but to the speed of our minds. Time does fly when you are having fun. Or the corollary, "Time dies when you are not having fun."

It is interesting to imagine why nature slows down time when we do painful things, and experiencing fun seems to accelerate it. One would have hoped it would be just the opposite. It is probably related to the relative tension more than relative time. With increased focus and attention, the time seems to slow, permitting the execution of difficult tasks faster. It is like hitting a ball in slow motion, or more appropriately, it is being able to calculate escape routes while being chased by a bear.

The trick is to either make hard tasks more pleasant so they are done quicker, or to teach ourselves and our children the real speed of time. For example, if children knew that picking up their room only takes them two minutes in real time and not the seven hours of "pain time," perhaps the job would get done. Counting in seconds, one thousand one, one thousand two, slows down their whining and speeds up the work.

The biology of time is pretty complex. We have our circadian rhythm that turns out not to be truly daily but a 25-hour cycle. This odd disconnect between our body's time and the clocks of the Earth is usually corrected or reset by the light-dark cycle. No wonder our children ask if we have arrived yet even as we back out of the garage, arrive home at 1 a.m. when curfew was midnight or they turn in their homework a week late. Their biorhythms are out of sync with the clocks of grown-ups. Kids have their own jet lag.

Time also seems to have been sped up by our modern world. TV shows — 30 minutes broken by hundreds of different views and camera shots and thousands of commercials. (Adrenaline exaggerates more than just time.)

Instantaneous is not fast enough. In contrast, the ancients thought in terms of growing seasons; children today think in selling seconds. When time speeds up, children grow up faster. Racing through childhood causes life to pass too quickly, making babies adults before their time.

Time is relative. We know that from science. We feel it from our senses.

My sons taught me so.

Maybe they were Einsteins after all.

Joseph Cramer, M.D., is a fellow of the American Academy of Pediatrics, practicing pediatrician for more than 25 years and an adjunct professor of pediatrics at the University of Utah. He can be reached at [email protected].