Are we all clear on this now?
Err, since the demotion of Pluto there are now only 8 planets in total in our solar system, and currently only one earth like planet (the Earth!), although Venus and Mars may have been earth like for a period of time earlier in the solar system's history.....the 40 billion is based off research I found from 2013 saying there is 40 billion earth like planets in our solar system, the 1 out of a thousand is purely an estimate.
I'm not such an expert but if that is true, this means that we are expecial in the Universe. Anyways the Universe is big, really big, for this reason 23 sounds stange in my opinion...Meaning there are (more or less) 23 intelligent species in the universe, and due to how many of those that could be advanced enough to use or understand space travel, is possibly 1 out of 23, maybe 2 or 3 out of 23, and the reason why we haven't discovered them yet.
You're right after all...This is the question to be answered:
'In my opinion, such equations are a total waste of space. Most, if not all, the factors are the subject of pure imagination or sheer guesswork.
Any one factor is enough to render any "result" invalid. '