At a certain age, you may feel as if you’re still at life’s beginning yet also disturbingly close to the end.

You feel acutely that there’s much left to do. You were going to win an Oscar, pick up a Nobel Prize in physics and get elected president, but you haven’t even gotten around to auditioning for a film, taking a university physics course or running for dogcatcher. Simultaneously, you’re filled with longing for the many things you once did but never will again. You’ll never feel the first caress of a new love, never run another marathon.

It’s almost enough to make you want to live forever. Actually, for many people it’s precisely enough — but not for me. If I were immortal, I know these feelings — nagging anxiety that I have barely got started coupled with deep nostalgia for the past — would simply grow as the centuries piled up, and that would be excruciating.

Philosopher Martha Nussbaum says she’d like to live forever because she can imagine any number of appealing careers for herself — “a cantor, an actress, a psychoanalyst, a novelist.” But then isn’t the real goal in life hugely increased not so much in length as in width? A life during which it’s possible to pursue every one of a wide range of concurrent possibilities?

It’s true, if you were immortal, that you might eventually get to be a philosopher and a cantor and an actor and a psychoanalyst and a novelist. But don’t forget: Over that vastly extended period, life would certainly not cease exposing you to still further choices. When you finally entered psychoanalytic training in 2100, you’d have to forgo any number of other new possibilities that might at that instant present themselves, such as joining an expedition to Alpha Centauri, or taking a seat on the newly created World Supreme Court, or learning to create art with the previously unimaginable colors recently made visible on the spectrum. You might have crossed one possibility off our list, but you’d have added three more.

For each new path you took, there would be several others that you’d have to leave for later. And then the overwhelming feeling that there are ever more careers worth pursuing, ever more books worth reading, ever more virtual worlds worth exploring, ever more romantic partners worth experiencing — would intensify over endless time. Hundreds of years in, you’d still feel as though you’d barely moved beyond the opening stages of what life has to offer.

Advanced-stage longing would likewise intensify. Nearing 70 in the course of a normal mortal life, you might look back fondly at that moment of electric connection you felt decades ago at the high school prom and regret that it’s way too late to realize a long married life with that special date.

If life were unlimited, it wouldn’t be too late at all — you’d have plenty of time. But immortality wouldn’t make the possibility of mutual enchantment extend any longer than it does now. As the poet Shelley said, love itself would continue to perish even if you no longer did. Sooner or later, as decade upon decade passed, the spark would dissipate. Later still, there would come a time when you would look back on that second-chance marriage to your high school date and sigh with bittersweet wistfulness.

Many activities you once loved, meanwhile, would fall out of fashion or out of reach. As an aging mortal, your knees might make it tough to run a marathon, causing you to envy all the healthy racers from San Francisco to Sydney. As permanently youthful immortal, by contrast, you might remain fit to run marathons over the centuries. But perhaps the beloved urban races of your youth would have long since disappeared, banned because of impossibly hot global temperatures and the fact that future civilizations find interplanetary relays far more exciting. (I joke, but you get the gist.) All of the things you once did have shelf lives. The longer you live, the more of them die, increasing the weight of the time that has flowed through your fingers.

Many of us 50-, 60- and 70-somethings will remember George Burns’ quip: Old age isn’t great but it sure beats the alternative. There’s also truth to the reverse. Death isn’t great, but it sure beats the alternative.

By Andrew Stark

Andrew Stark is a professor at the University of Toronto and author of “The Consolations of Mortality: Making Sense of Death.” –Ed.

(Tribune Content Agency/Los Angeles Times)