On 03-Dec-08 21:02, Orchid XP v8 wrote:
> andrel wrote:
> 
>> What I sometimes do is point out that there probably have been born 
>> less than 12 billion people in total. 6 of them are still alive, hence 
>> the statistical support for the idea that everybody dies is rather weak.
>>
>> It is a nice examples to show that most people don't understand 
>> exponential growth.
> 
> Hmm. How the **** do people compute numbers like this?
You know approximately how many people lived in a certain age and how 
old they got. From then on it is a simple mathematical sum.

Say that we have 1000 people in year x and 1010 in year x+1. Assume also 
that the average age in year x is 50 (and ignore second order effects 
and wars) then 20 people will have died of that 1000 hence 30 were born 
that year. There is a lot of room for improvement, but something like 
that is the basic idea.

There is a table on http://en.wikipedia.org/wiki/World_population. Why 
don't you write a program to compute it in Haskell? (my 12 billion was 
computed by someone else and I only checked that it was roughly in that 
order of magnitude. Would be nice to have an estimate and knowing how it 
was computed)

If you go back longer, you are less certain, but OTOH the number of 
people is so much less than are living now that it does not make much 
difference. Remember that homo sapiens has only lived for about 
2500-3000 generations. The tail backwards is not so long.

>  I mean, how can 
> you *possibly* know how many people are alive right now? Obviously it's 
> an estimate, but how do we tell if it's even remotely correct? It's not 
> like you can *check* it!
Oh yes you can. It is called a census. They have even done that in 
china, which is of course the major contributor. I am sure they also do 
that in the UK IIRC they also ask you for your religion and recognize it 
if enough people answer it. Resulting in klingon and jedi and some other 
strange ones to be official religions now.

> 
> I still like Warp's "grains of rice" example. (If only I could remember 
> who the hell it was about...)

Is that the one where you put one gain of rice in a corner of a 
chessboard and double it on the next square? until you have 2^63 at the 
last one?

>> And indeed most people look surprised.
> 
> Try this: Walk up to somebody, and quietly tell them "you're going to 
> die". Watch the look on their face. Seriously, they act like this is 
> *news* or something...

Most people know they are going to die (or at least assume so, see 
above). This line is mostly used in films and books meaning something 
like 'you are going to die very very soon and I don't mean that on a 
cosmic timescale'.

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