Rgb says
First of all, please use the paragraph structure.
Sure, sorry bout that.
Rgb continues
While it is true that these estimates came from the best data we have, which isn't very much, you have to understand that we still only have ONE single data point to work from when we're dealing with planets that have life. As far as we know, there aren't any other like Earth.
I'm pretty sure this dealt with the capailty for life not the fact itself. If we're only dealing in planets which have life then at one point in history, we'd have to say that no life was possible.
Mars could possibly have supported life in the past, and possibly could again. That's enough to show that Earth isn't unique.
Cavedigger says
If only one universe, then questions of design creep in.
Then doesn't the "if" have to be answered before we can move on?
..and continues
I think it's still wide open... I can certainly envisage the earth being the only life-abundant planet in the Galaxy.
Why? The vast majority of the values needed are common to the entire galaxy. If all that's neccesary after this is to be within a certain range of proximty to a sun, and water, how likely is it that there's only one planet with these two values?
Mars seems to have, or have had, both.
If the question is how many life bearing planets at any one specific time, then sure, it's posssible there's only one, but across all time?
The BBC did a Horizon special about this recently, with computer simulations varying the strength and existence of physical laws, and almost none of the universes failed, most were just different.
I can't find a link atm, but will continue looking
Sidelined says
The AP seems to be applicable only when we focus on the Earth and our intelligent life, otherwise it seems a moot point.
And I agree.