What if the probability was 1x10^-80 ?
> Lets assume for simplicity, there is only one habitable planet in the entire Milkyway galaxy, Earth. And there are 'y' number of planets in Milkyway in total.
Okay...
> Then, the probability of finding a habitable planet (Earth) in such a galaxy is 1/y.
This does not follow. I'm going to quote Feynmann here:
"You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won’t believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!"
If I put tarantula behind your sofa, then we can say the probability of there being a tarantula behind your sofa is pretty much 1. If you have 5 sofas in your house, then the probability of there being a tarantula behind a random sofa in your house is 1/5.
However, it doesn't follow that the probability of finding a tarantula behind any sofa is 1/5. All we can say about that is that it's non-zero.