Statistics, our Future, and Space Colonization

Interesting statistical method of calculating durations when only one piece of information is available: how long it has already existed.

Suppose you want to forecast the political longevity of the leader of a foreign country, and you know nothing about her country except that she has just finished her 39th week in power. What are the odds that she’ll leave office in her 40th week? According to the Copernican Principle, there’s nothing special about this week, so there’s only a 1-in-40 chance, or 2.5 percent, that she’s now in the final week of her tenure.

It’s equally unlikely that she’s still at the very beginning of her tenure. If she were just completing the first 2.5 percent of her time in power, that would mean her remaining time would be 39 times as long as the period she’s already served — 1,521 more weeks (a little more than 29 years).

So you can now confidently forecast that she will stay in power at least one more week but not as long as 1,521 weeks. The odds of your being wrong are 2.5 percent on the short end and 2.5 percent on the long end — a total of just 5 percent, which means that your forecast has an expected accuracy of 95 percent, the scientific standard for statistical significance.

Now how does this apply to human civilization surviving or space colonization?

The Copernican formula predicts, based solely on our 200,000-year track record, that the human race is likely to survive at least 5,100 more years but not longer than 7.8 million — roughly the same prediction you’d make based on the longevity of past mammals on Earth, Dr. Gott says.

That upper limit is a disappointment to those of us who imagine humans multiplying across the universe for billions of years. Dr. Gott doesn’t rule out that possibility, but the Copernican Principle makes him conclude it is unlikely.

And

It might seem hard to imagine that humans would invent rockets and then never use them to settle other worlds, but Dr. Gott notes that past civilizations, notably China, abandoned exploration. He also notes that humans have been going into space for only 46 years — a worrisomely low number when using Copernican logic to forecast the human spaceflight program’s longevity.

Since there’s a 50 percent chance that we’re already in the second half of the space program’s total lifespan, Dr. Gott figures there is a 50 percent chance it will not last more than another 46 years. Maybe the reason civilizations don’t get around to colonizing other planets is that there’s a narrow window when they have the tools, population and will to do so, and the window usually closes on them. “In 1970 everyone figured we’d have humans on Mars by now, but we haven’t taken the opportunity,” Dr. Gott says. “We should it do soon, because colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species. Sooner or later something will get us if we stay on one planet. By the time we’re in trouble and wish we had that colony on Mars, it may be too late.”

You could argue that he’s being too pessimistic about space exploration. The space program may be only 46 years old, but humans have been exploring new territory for tens of thousands of years, so by Copernican logic perhaps they’ll keep it doing it far into the future. But given recent trends — after going to the Moon, we now barely send humans into orbit — he’s right to be worried.

I'm beginning to think we may not leave Earth permanently.