You never get over the moment you realize that you're definitely going to die. You're usually a small child when the insight hits, and you usually have a vague idea of what death is, but the first-person epiphany — the "Wait, that's going to happen to me?" experience — changes everything. Your sense of time and its fleeting passage can never go back to what it was before you discovered that you too are on the clock.
It's no wonder we spend our whole lives after that trying to add as many rollover minutes as we can, and in the developed world, at least, we've done a pretty good job of it. In 1900, U.S. life expectancy was just 47.3 years. Now — thanks to better medicine, cleaner food and a whole host of health and safety regulations — it's up to 78.1. That's not the best in the world — other healthy, wealthy countries like Japan and Iceland crack the 80-year mark — but it's not bad.
Suppose, however, we could do even better. Suppose we could suddenly add another five or 10 or 20 years to American life expectancy. That would be a good thing, right? Maybe — or maybe not. We'd all like the extra time, but could our economy handle it? Our environment? What about our food and water supply? What about the millions of extreme oldsters themselves, not to mention their families? For every George H.W. Bush, who goes parachuting at 85, or George Burns, who performed his stand-up act at 95, there are many more sickly, bedridden nonagenarians who draw no joy from their added time, piling up medical bills and misery but not much more. Would extra years of life for all mean extra years of decay for most?
We can't know the answer for sure, but science loves to run experiments, particularly thought experiments — intellectual exercises that require nothing but imagination, computer models and a lot of statistics. One of the best tools around for life-expectancy studies is a handy algorithm called the Future Elderly Model (FEM), developed by researchers at the nonprofit Rand Corp. As its name suggests, the FEM starts with today's not-yet-old population, then manipulates variables such as health, income, employment status and more to predict how they'll fare in their senior years.
For TIME, Rand conducted one such FEM simulation. "We imagined that a pill emerged in 2012 that could increase life expectancy for every 50-plus American by 10 years," says Dana Goldman, a former Rand director and the current director of the Schaeffer Center for Health Policy at USC. "Then we ran the numbers to see what would happen."
The data going in suggested that the results would be dramatic. The U.S. is now home to 39 million people over 65, or nearly 13% of the population. That's a big patch of gray, and it's getting bigger fast. In 2011, the leading edge of the 76-million-strong baby-boom generation — born from 1946 to '64 — will cross the line to 65, and they'll keep coming until 2029. Already the government spends $600 billion per year in Social Security payments for people 51 or older, and a staggering $1.3 trillion when you include Medicare, Medicaid and disability benefits.
According to the FEM model, the very year the imaginary long-life pill appeared, the over-65 population would jump 7% more than it otherwise would have, reaching 44 million. In 2014, it would be up 13%, to 49 million. By 2030, after the last boomer arrived in the senior set, the aged population would have swelled by almost a third more than it would have without the pill, hitting 85 million. The growth rate would not be quite as dizzying after that, but by 2080, the final year of the simulation, there would be 151 million 65-plussers in the U.S., or more than 43 million extra people, all of them old. That difference is nearly equivalent to the entire population of Spain.