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Astronaut: 'Single-Planet Species Don't Last'
An anonymous reader writes "Gemini, Apollo and Space Shuttle astronaut John Young, due to retire in two weeks, says that the human species is in danger of becoming extinct: 'The statistical risk of humans getting wiped out in the next 100 years due to a super volcano or asteroid or comet impact is 1 in 455. How does that relate? You're 10 times more likely to get wiped out by a civilization-ending event in the next 100 years than you are getting killed in a commercial airline crash.' He says that the technologies needed to colonize the solar system will help people survive through disasters on Earth. Young has written about this topic before in an essay called 'The Big Picture'." In related news, the Shuttle overhaul program is on track for a May 2005 launch.
Lets think about the stats for a bit to see why your statement doesn't logically imply anything.
Consider that the number of people involved in any particular crash is quite low compared to the number of people on the planet. Thus, while there may be multiple crashes in any given period, the chances of *you* being killed in that crash are quite low.
On the other hand, if you have a single civilization-ending event, by definition the chances of it affecting you are quite high.
So to estimate the impact on *you* in particular, you need to compare
(number of people killed in plane crashes)/(total number of people on earth)*(chance of a plane crashing)
vs
(number of people affected by civilization-ending event)/(total number of people on earch) * (chance of civilization-ending event)
Maybe you should learn some statistics...
The probability is not 100% it is in fact 20%.
Chance of no event in a 455 year period: 454/455 = 99.8%
Chance of no event in 100 such periods: (454/455)^100 = 80.3%
Hence chance of an event in 100 such periods: 19.7%
Using your whacked out mathematics I guess in 100000 years the probability of at least one event is 200%?!?
Not quite how it works.
In fact, a 1 in 455 chance of humanity being wiped out in each successive 100 year block gives us a 454 in 455 chance of surviving that 100 year block.
Our odds of surviving 200 years is the odds of us surviving the first block (454 in 455) times the odds of us surviving the second (another 454 in 455) - about 99.5%
In other words, the odds of us surviving 100n years is (454/455) ^ n. The odds of us making it through the next millennium, then, is (454/455) ^ 10; that equates to about 44 in 45, or a one in 45 chance of our species being wiped out before we see the next millennium bug.
The odds at 10000 years (n=100) diminish to about one in five that we'll all have been wiped out - that is, four in five that we're still here.
Around the 30 000 year mark, the chances we're wiped out are pretty much even. That would mean we'd tend to expect mass extinction events about once every 60000 years, on average. you could consider that as a kind of indicator as to the validity of the original statistic.
Beyond that point, it becomes easier to quote the odds we're still here than that we're not.
After 100 000 years, we get down to about a one in ten chance of still existing. In other words, out of all the possible ways the next 100 millennia could go, only one in ten of them finish with us still existing.
In other words, the number predicts survival is unlikely, but it's not impossible, and the odds keep dropping, but they don't reach zero.
Whether the 1 in 455 number is right or not is open to question, of course, but just because we've been around more than 45500 years is no reason to dismiss it completely.