I posted this question in great debates, (I’m new ok?), but got a theology lesson instead. If no one ever died from day one, how many people would there be living on earth now? There must be an educated guess out there somewhere.
[note: I edited the thread title, since it broke off at the word “if.” Or maybe “be.” I forget. -manhattan]
[Edited by manhattan on 03-22-2001 at 06:17 PM]
Uncle Cecil himself took a stab at that question in this column right here.
Cecil’s column answers the question of how many people have lived, which may be a little different from the OP, depending on what assumptions are made.
If the reproductive lives of these immortals were the same as our own (fertile only from about 15-50 years of age), then Cecil’s answer would still apply, since the 10,000 year-olds wouldn’t be producing any new kids.
If people stayed fertile throughout their lives and reproduced at the current world population growth rate (1.3%, according to the CIA World Factbook), then the current population (using Cecil’s 40,000-year figure) would be, uh, about 2.3 x 10^224. That’s a lotta people.
This of course ignores the effects of crowding and resource usage.
Feel free to contest these numbers.
–sublight.
Contest them I shall. 
The growth rate may be 1.3%, but that represents births (22 per thousand) + deaths (9 per thousand) [source]. If you assume no one ever dies, you have to use only the birth figure, so it’s actually 2.2%. Doing the same math as Sublight, that ends up being 1.1 x 10[sup]378[/sup] people over 40,000 years. Exponential growth is a powerful thing. And immortality is bad news because of it.
Well, yes, if you assume that the growth rate is immutable. I’d tend to think that it would go down as things became more crowded.
For one thing, there’s just not enough mass on earth to make that many people. For another, it would probably influence the decision to have a kid if you’re already living in standing room only.
Ah, yes. Smackfu is right. I missed that.
As for crowding, since we’re already assuming immortality, I figured we could take some liberties with the rest of the universe (at 1 person/cubic meter, 10^378 would take up more than the volume of the observable universe).
–sublight.