Human life expectancy has doubled in just over 100 years. But while much of that increase has come due to lower child mortality (which skewed the average), more recently, new medical technology is allowing us to extend the “back end” of our lives. It’s certainly conceivable that in the future, you could have a say in not just when you die, but whether you will die.

Recently, Uri Lifshin at the University of Arizona ran a study asking people about their feelings about extending life indefinitely. As described by Mark Travers in Psychology Today:

[R]researchers showed that attitudes toward both science and religion were implicated in defining participants’ attitudes toward indefinite life extension; more favorable attitudes towards science enhanced support for life extension while strong religious attitudes diminished it.

We can understand why some people might want to extend their lives. Death is scary, and unknown, and feels very, very final. Religion—especially through rituals or belief systems—helps us accept earthly mortality. But science is now helping push back against the day we will die.

But do we really want to live “forever”? While we might respond with an immediate, “Of course!”, the truth is, we simply don’t emotionally or intellectually understand the size of ideas like “infinity,” “forever,” or “eternity.” While it might be reasonable to want to extend our lives, when you really think about “living forever,” you probably don’t actually want that.

Why? Because the concept of time that our brains can handle is (roughly) human-scale. We can’t truly comprehend the size and age of the universe, how many stars and planets there are, and just how long “13.8 billion years” is. We can’t really grasp that about two-thirds of the universe’s existence came before the earth was formed, that the Cambrian explosion happened after about 90 percent of earth’s existence had already elapsed, and that there was less time between Tyrannosaurus rex and us than there was between a T. rex and a Stegosaurus.

And if we have that much trouble distinguishing among “thousands,” “millions,” and “billions” of years, we would have even more difficulty in realizing that “really big” isn’t actually “infinite.”

Understanding ginormous numbers

A few years ago, blogger Tim Urban, in his blog Wait But Why, wrote a two-part series to help people understand big numbers—not just intellectually, but emotionally, using visuals. Part one starts with 1, and goes to 1,000,000. But in part two, he goes up from one million to one billion to a googol to a googolplex to Graham’s Number.

I can’t go into the details of what Graham’s number is here, but as he describes it, it makes “a googolplex to the googolplexth power sound like a kid saying ‘100 plus 100!’ when asked to say the biggest number he could think of.” To truly get a grasp of this, it’s worth reading the post—or watching one of these videos, which tells you that trying to understand Graham’s number would quite literally make your brain collapse, since it would turn your head into a black hole.

And that’s why I was so taken by Urban’s philosophical conclusion about this insanely huge number, and how it helps him accept mortality:

Thinking about Graham’s number has actually made me feel a little bit calmer about death, because it’s a reminder that I don’t actually want to live forever—I do want to die at some point, because remaining conscious for eternity is even scarier. Yes, death comes way, way too quickly, but the thought “I do want to die at some point” is a very novel concept to me and actually makes me more relaxed than usual about my mortality.

So when we think about “eternity,” we think about an infinite amount of time, and yet we can’t really comprehend “forever.” And that’s why these words from Herbert Louis Samuel, used in a prayerbook during a Yom Kippur memorial service, ring so true:

If some messenger were to come to us with the offer that death should be overthrown, but with the one inseparable condition that birth should also cease; if the existing generation were given the chance to live forever, but on the clear understanding that never again would there be a child, or youth, or first love, never again with new persons with new hopes, new ideas, new achievements; ourselves for always and never any others—could the answer be in doubt? (Gates of Repentance, 484)

We may want to add an extra ten or twenty or even a hundred years to our earthly lives. Science may even allow us to do that someday.

But we also need to realize that, in truth, we wouldn’t want to live forever on earth, since we can’t comprehend “forever.” And knowing that our earthly bodies will die—and knowing that fact not just intellectually, but emotionally, as well—can help us strive to fill our lives here and now with meaning, purpose and joy.

(This post first appeared on Orbiter).