Over the last 200 years, the progress of medicine and public health has caused a dramatic increase in human life expectancy. In 1820, the global average human lifespan was just 26 years; in 1950, it was 49 years; today it is 72.9 years — and in Japan, 84.7 years. Most people believe that this is a good thing. Except in dire and unusual circumstances, most people want to live longer rather than shorter lives.

But where does this end?

The Irish playwright George Bernard Shaw speculated about this in the final act of his play Back to Methuselah. (In the Book of Genesis, Methuselah was the longest-lived Biblical patriarch, living to the age of 969.) In this work, Shaw imagined that 29,000 years from now, disease will have been completely eradicated, and after reaching adulthood, humans will cease to age. Nonetheless, in this future, it’s regarded as statistically certain that everyone will eventually die in a fatal accident. They say things like: “I wonder whether my accident will occur in 100 or 1,000,000 years’ time.”

I suggest Shaw was right to imagine a future in which aging ends and death only comes by chance — and that this is the future that we should aim for. It is not realistic to expect true immortality. We are embodied biological beings, and given enough time it is inevitable that an accident will end our lives — we may just fall and break our necks or be struck by lightning. Even if we can make our lives safer, the risk of fatal accidents can only be reduced and never completely eliminated.

Still, other things being equal, longer lives are better lives.

As the ancient Greek physician Hippocrates said, “Life is short, but knowledge of a craft is long.” If we all had thousands of years to live, we could acquire much more knowledge and skill than is possible in a mere 85 years. The philosopher John Stuart Mill listed all the inexhaustibly interesting things that we can learn about: “the objects of nature, the achievements of art, the imaginations of poetry, the incidents of history, the ways of mankind, past and present, and their prospects in the future.” How wonderful it would be to have thousands of years to learn about them!

Other things being equal, longer lives are better lives! On this point, Professor Wedgwood and I agree. But of course, other things are not always equal.

In fact, we know that when it comes to lifespan, Shaw’s Methuselan future will be far from equal. Because we can still die from accidents, each of us will still face some small risk of dying each year of our lives — say, one in a thousand. If this risk is equally distributed, then every child can expect to live, on average, for a thousand years. But expecting to live for a thousand years is not the same as actually living for a thousand. At an attrition of one-thousandth each year, half will be gone before they’re 693, and fewer than two in five will see their thousandth birthday.

Six hundred and ninety-three years is not nothing. It is in fact more than long enough to be imagined by writers as diverse as Jonathan Swift (Gulliver’s Travels), Karel Čapek (The Makropulos Affair), Jorge Luis Borges (The Immortals), J.R.R. Tolkien (The Silmarillion) and Michael Schur (The Good Place) as — in one way or another — depressingly bleak. But it is also much less than 1,000. A minority, however, will live longer — much longer. Just 16 or so of today’s 8.2 billion people would still be alive after 20,000 years, each of whom could still expect to live another thousand years. This is roughly the current number of people in the world worth more than $100 billion.

Now, there is nothing wrong with inequality per se — variety is, as they say, the spice of life. But vast inequalities can easily be used to wield incredible power. And the 20,000-year-olds will not only live longer — they will also hold vast wealth. For time is money. Just a $1 investment in their youth in an S&P 500 index fund yielding a real return of 5% per year could easily result in 6×10⁴²³ dollars by their 20,000th year. Elon Musk could only drool at so many zeros.

The prospect of having an 11/12 chance of living longer than 78 years sounds great — as Professor Wedgwood says, “other things being equal.” But the absolute certainty of living in a world dominated by a tiny few whose sheer luck at avoiding accidents allowed them to accumulate power over the rest of us can’t be worth it.

Thanks, but no thanks, Methuselah.