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We deduce that life requires certain conditions e.g. life supporting chemicals and a habitable zone. However, the existence of those chemicals and a habitable zone do not necessarily imply life will originate there.
In reality, we know nothing about the probability of life forming anywhere else in the Universe. We have no confirmed life data from any exo-planet.
Sure there may be 100 billion galaxies, each with 100 billion stars. That's 10^22 stars. So you think that's big!
The smallest known DNA viruses have 32000 base pairs. A single chain of DNA is composed of a sequence of 4 nitrogenous bases. Assuming they all occur in equal amounts i.e. 8000 of each, then the number of possible ordered sequences of a single chain of DNA are 32000!/(8000!)^4. Don't try using your calculator, the value is too large.
32000! ~ 1.07 x 10^130270 and 8000! ~ 5.2 x 10^27752.
32000!/(8000!)^4 ~ 1.5 x 10^19259
That pretty much dwarfs the 10^22 stars in the Universe!!
Before the biologists come looking for blood, I haven't said anything about the probability of the organism forming. However, the chances of life forming may be significantly lower than any estimate we have in mind.
On the other hand, if by fluke an alien neighbour exists and communicates with us, we can at least say we are not unique.
Regards, Rob.
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