Suppose: on some planet untouched by man, there was a species identical to a species on earth, would you say they share the same ancestor?
Suppose: I generated an organism (that already exists) starting from raw chemistry, would that share the same ancestor as the one that already exists?
Disclaimer: I'm bad at maths and good at dreaming.
The bare simplest genomes are viral genomes about 1000 bases long. These can only operate in environments created by more complex genomes. But even taking them, the theoretical diversity in a genome 1000 bases long, using the 4 canonical nucleic acids, is 4^1000. The number of atoms in the entire universe is around 10^80 (https://educationblog.oup.com/secondary/maths/numbers-of-ato... ).
There's a lot of complexity here: other life may use other nucleotides; those atoms and bases are constantly being rearranged; many base changes are relatively silent - they don't materially matter; etcetera.
I don't know how to calculate all of the rest of these factors, but I think the odds are more than astronomical.
OK, let's do this then. Here we will approximate the ratio 4^1000/10^80:
x = 4^1000 / 10^80
ln(x) = 1000 * ln(4) - 80 * ln(10) // You know your logarithm calculation rules, right? Right?!
ln(x) = 1386 - 184 // Who needs decimal places anyways? ;)
ln(x) = 1202
x = 10^522
Eh, at one point I did. I'll take your word for it. It seems familiar.
Now factor in number of rearrangements since the universe started. Or heck, let's keep it simple to the last 4.5 billion years.
I count about 30 atoms in a nucleotide, so X is a bit more than 10^523.
Let's say 2 rearrangements per day (this will vary dramatically, but I have to pull some number out of a hat). Over 4.5 billion years that's on the order of a bit more than 10^12. so X is around 10^511.
Yep, still more than astronomical.
And I'm very sad to (re?)learn this finite number of atoms in the universe, that's quite underwhelming for something expanding all the time.
Most combinations of nucleotides aren't functional, or even capable of being synthesized by natural processes. This limits what can be created quite a bit. The true odds are still extremely high, but not nearly as high as these calculations guess.
This is incorrect. It's an unsolved question in modern physics if the universe is finite or infinite. Even if it's finite most theoretical physicists believe that visible universe (94 billion light years across) is only a small piece of a far larger universe - so there are probably far more atoms.
If the universe is infinite it may be that there are infinite number of copies of every living organism on Earth out there.
2. Seems like you're broadly stretching the definition of a biological ancestor.
It's like saying a standard opener move in a boardgame is unlikely because there's a lot of other moves available. It's standard move because the game have an optimal set of opener move to achieve victory.
So if another planet with similar environment exist, the range of solutions for self preservation goal might be a tiny subset out of the hundreds of millions of bits of genetic information.
It's trivial to apply my hypotheticals to models in which life didn't all descend from a common ancestor.
We don't have such a thing to our knowledge so it's not trivial. If you still feel it is, do the application yourself - it's trivial after all.
I'm finding it very difficult to understand what you mean by "models of life". Actually I have no idea. What does this phrase even mean?
2) There are thoughts that life on Earth, presuming it started on Earth and wasn't seeded from meteorites, may have started from multiple populations. But it's presumed that if it did so those multiple populations were either out-competed by one population, or sufficiently alike that they effectively merged in their descendants.
At any rate, at this point, all life that we have so far detected shares similar enough features to presume a common origin. This includes incredibly separate lineages such as the bacteria and archaea.
Would you consider modern computers to be descended from IBM mainframes? Someone building a duplicate lifeform from parts based on existing knowledge and existing lifeforms does not negate that those existing lifeforms evolved into form since the beginning of terrestrial life. Your work is standing on preexisting evolutionary knowledge, processes, and a chain of life, even if it technically replaces biological reproduction with a human engineer.
From a dialectical point of view you're effectively invoking god to nitpick. If you believe you aren't you're going to have to spell it out for me.