The Doomsday Argument
Created | Updated Jul 15, 2003
This argument has been discovered at least three different times. It is a logical result of Bayesian Mathematics. It is also related to the Anthropic Principle and Fermi’s Paradox. The basic argument goes like this:
Given that there are x numbers of humans that ever lived, that your number in this sequence is virtually near the end of the current sequence suggests that doomsday, through whatever means, asteroid, Grey Goo, virus, agricultural breakdown of takers and leavers society, whatever, is just around the corner.
Many people immediately think they can refute this argument easily, but not so.
History
The credit for this argument goes to Brandon Carter. He was the first, but did not publish. Other unrelated co-discoverers were H. B. Nielsen and Richard Gott. Frank Tippler told John Leslie
About it and Leslie was the first to publish a clear explanation of the argument, The End of the World (Routledge, 1996).
As Mark Twain once remarked “There are lies, damn lies, and statistics.” This seems to fall into the realm of statistics and probability. Lets look at an analogy that may help.
An Analogy
There are two buildings with 100 rooms in each, numbered 1-100 as well as 110 people. There are 10 rooms on each floor. A coin flip decides which building you go to. Heads go to building A, tails to building B. The room numbers are covered up so you cannot see what number room you are placed in. When the first ten rooms in building A are filled, the remaining people are sent to building B regardless of the coin flip outcome. The people in either building do not know which building they are sent to. The building with just ten people in rooms 1-10 are then asked to guess if they are in a building with 10 people or 100 people. The process of selection and movement are unobserved by all. The numbers are uncovered. You go out of your room and see that your room number is 7. You decide that you are in the building with 10 people. Working this out mathematically you see that there is 91% probability that you are in building A. Similarly, finding that you were in room 97 would give you a 100% certainity that you were in the building with 100 people.
Doom Soon and Doom Later
This relates directly to the scenarios for the survival of the human race. There are two scenarios, Doom Soon and Doom Later. Doom Soon means that there is going to be less than 100 billion humans that ever existed. Doom Later means humans will expand and grow old as a race and that humans will number in the 100’s of trillions, or higher, rather than billions. Being in Building A relates to Doom Soon, you are the 70 billionth person who ever lived and therfore near the limit of the human race at Doom Soon, or approximately 100 billion. Nature seems to like the number 100 billion. Approximate number of neurons in a human brain, number of stars in a normal sized galaxy, number of people who ever lived on earth?
What Next?
If the doomsday argument is correct does this mean we should just give up? No, it means we should try harder. For example, spending money on observing near earth asteriods and determining successful strageties for deflecting them rather than waiting for one to drop on our heads. The doomsday argument can be seen as the salvation of the human race rather then the end.
