All of us are sensitive to the passing of time and can’t help but notice the time-induced savaging of our reflected features (usually long after everyone else has noticed). From the instant we are conceived until the second we take our last gasp, our lives are governed by a measure of the velocity of our planet’s rotation on its axis. As physicians we are all vitally interested in time. There are pressures in our hospitals to place a relative value on individual lives according to the number of ticks on the biological clock. We measure things constantly with a “t” value, monitor developmental progress over time, and regularly make life-and-death decisions based on the passage of time. But what is this thing that we place so much professional, personal, and social value on?

For me, the “simple” concept of time has begun to develop some very fuzzy edges for a number of different reasons. From a purely medical standpoint, there are some interesting paradoxes. Just one example of this, and one we can all relate to, is my memory of an amazingly fit and intellectually bright 86-year-old patient telling me several years ago that she couldn’t believe she was old because her mind seemed as young and active as it was when she was in her twenties. She just didn’t recognize that old person staring back at her in the bathroom mirror and wondered why her body was so much older that her brain.

Lately I have been experiencing thoughts similar to my patient’s (who is still as bright at 99 years of age) and wonder why most of us end up with pretty active brains but have bodies in advanced stages of decrepitude. Oh, I know dementia affects fairly large numbers of our more senior citizens, but many of the remaining majority are fully sentient. So why does time wreak havoc on our corpus while leaving our computer alone? I’m sure anthropologists will have a theory that includes the passing down of verbal histories and the usefulness of age-determined wisdom in the survival equation, and I’m fully aware of the theories of unused cellular reservoirs, but the answer, for me at least, still remains enigmatic. Does “time,” in fact, treat some biological tissues differently for some reason?

Stephen Hawking continues to write about time and how it is probably not the way we have always imagined it to be. His latest book, The Universe in a Nutshell, is a delight and poses a whole new set of theoretical constructs of time. It’s not easy reading, but it’s well worth the effort. I had previously liked the “big bang” theory of the origin of the universe because it seemed to explain why time runs in only one direction. The big bang itself has a time-zero, which nicely provides us with a temporal concept that’s easy to grasp. However, what happens when expansion ends and contraction begins? Does time now start to go the other way? According to modern theoretical physicists like Hawking, the big bang theory no longer works, perhaps for the above reason, so the new thinking involves something called membrane (brane) theories that posit multiple dimensions of time. These theories, at least for now, seem to satisfy the unidirectional requirement of time in our universe.

I’m still perplexed (my usual mental state it seems) by what actually happens to ensure time progresses in one direction. Is there an instant-to-instant alteration in matter/antimatter or an instant-to-instant energy exchange between pions and anti-pions in order for there to be a quantifiable change? I know we can record the visible progress of time as the earth rotates on its axis, but what is actually happening to the building blocks of the universe to determine a linear progression? In other words, what changes from one instant to the next? What is the smallest increment of time and what measureable characteristics determine the physical nature of the smallest increment?

These are all terribly interesting questions and I’m sure I’ve articulated what most readers were contemplating during their summer vacations. If anyone has any answers to these questions of time I would appreciate a quick call—after looking in the mirror this morning I don’t think I have much of the stuff left.

—JAW