Theoretical Limits to Human Lifespan

Theoretical Limits to Human Lifespan

Advances in technology — particularly medicine and sanitation — have increased average human lifespan beyond that of our ancestors. What if this process were to continue indefinitely — even to the point of the elimination of all natural causes of death? How long could human beings potentially live?

One might be tempted to say, “forever.” But of course that would overlook non-natural, i.e. accidental causes of death. In a given year, there is around a 0.068% chance of dying accidentally. For the average human lifespan, those are comfortable odds — but if natural human lifespans are extended indefinitely, those numbers are going to catch up with us sooner or later.

In general, if $p$ is the chance of something happening, then $1-p$ will be our given chance of it not happening in any given year. If we want to generalize that across many possible years, we can find that with $(1-p)^n$. So if $n$ is the number of years in question, $f(x) = 1-(1-p)^n$ will be a function plotting our chances of death as the years increase. Now,

$1-(1-0.00068)^{1000} = 0.493$ So that, after a thousand years, our chances of survival would have dropped to a mere 50%. At 10,000, it drops to essentially zero. So even if all natural causes of death could be done away with, we’d have only even odds of making it to a thousand, and nobody would live ten thousand years.

Now of course, this is assuming a constant chance of accidental death. Perhaps it would be possible to reduce risks of accidental death in the same way causes of natural death can be eliminated over time. In fact, if human lifespans could be extended indefinitely, perhaps it would become a higher priority to eliminate and minimize chances of accidental death.

Still, it seems that the chances of accidental death will always be nonzero, hence that the indefinite extension of human lifespan is improbable, even given medical breakthroughs far beyond those currently contemplated.