Spaceborne Life Forms

[CorporalCaptain]

Drawing conclusions from a sample of size one is pretty foolish.

If Earth is the only world on which life will ever arise, then of course all life is carbon-based.

Otherwise, we need to actually observe life from other worlds, before generalizing about what chemistry is required for naturally occurring life.

 

[YellowSubmarine]

Actually, when it comes to a biospheres, it's a sample of zero, because we have not observed any other biospheres, and ours constitutes an observational bias – we didn't find ourselves randomly. So from statistical point of view we know absolutely nothing about life. You could have life that doesn't require complex molecules because it works on submolecular or supermolecular level, you could have complex molecules that whose existence we have never suspected because we have never observed them in the right conditions, you could have life that's not based on chemistry at all. Our knowledge of physics and chemistry says that all of those are unlikely, but that's about all that we have. From chemistry/physics we can assume that most life contains carbon as a main constituent, but I don't think we could say anything more.

On the other hand, when it comes to organisms, we have observed way more than one evolutionary possibilities, and among them we have seen evidence in convergent evolution for traits, so limbs, wings, eyes and fins would have to be very common in the universe. And in similar biochemistry and environment we might find very Earth-like lifeforms. I'd bet we could find species that are strikingly similar to some of ours.

 

[CorporalCaptain]

Actually, when it comes to a biospheres, it's a sample of zero, because we have not observed any other biospheres, and ours constitutes an observational bias. So from statistical point of view we know absolutely nothing about life.

This doesn't make any sense.

As one of the samples, we will count for something. In fact, we will count as much as any other individual sample.

 

[YellowSubmarine]

Why?

As one of the samples, we will count for something. In fact, we will count as much as any other individual sample.

The other observations would be random, we aren't.

Will we count for something? On some questions – maybe, on some questions – not at all, and on some questions any data from other samples would be million times more significant than anything that we concluded from ourselves.

Try to estimate the abundance of life in the universe.
- If you have one sample: 1/number of worlds explored, with a certain statistical significance
- If you have only yourself: brain explodes

Try to guess which is the most common type of biochemistry.
- If you have one sample: the one you observe, with great uncertainty
- If you have only yourself: you are sentient, most lifeforms aren't, so you're not representative of life... uncertainty jumps so high that any other observation immediately dwarfs any conclusion you've drawn from yourself

We could, however, use ourselves as a good representative for intelligent life... Possibly. The bias won't be so great.

 

[CorporalCaptain]

Why must we count for something? Because it's completely contrary to all known experience to suppose that there will ever come a time when there are more than a finite number of known sample biospheres. As one of the known samples, we will therefore always count for something, even if progressively mounting evidence suggests it's just a corner case.

 

[CorporalCaptain]

The other observations would be random, we aren't.

Will we count for something? On some questions – maybe, on some questions – not at all, and on some questions any data from other samples would be million times more significant than anything that we concluded from ourselves.

Your assertions here are definitely false if the known samples end up being in proximity to us. You could also just as easily argue that it is definitely false if the known samples end up being in our own galaxy.

You are rejecting observational knowledge for its not meeting a standard that is impossible to meet in practice. We cannot randomly sample stars in randomly sampled galaxies of the universe. For the foreseeable future, we are going to have to make do with evidence from within our cosmic neighborhood. All our observations will be nonrandom in that sense.

 

[YellowSubmarine]

Assuming that panspermia is extremely unlikely to happen, we are independent random samples. Even if panspermia is likely, we would be able to distinguish which samples evolved independently. Yes, we are all dependent on the conditions in our corner of the galaxy, so even that won't be enough to judge all life with certainty, but that's unimportant since we know that the universe is filled with places with similar conditions. Observing life on Alpha Centauri and observing life on the other side of the universe at the same conditions should be the same thing as long as we can conclude that we aren't branches of the same evolutionary tree.

 

[CorporalCaptain]

Assuming that panspermia is extremely unlikely to happen, we are independent random samples.

So you are conceding that data from our biosphere is significant, and very possibly statistically significant, under the proper care to make sure the context is properly considered? If so, good. If not, I don't know what else to say. I've already cautioned against drawing any generalizations until we have at least one more sample. I don't know how much more cautious I can be and still remain reasonable.

 

[YellowSubmarine]

I meant that the rest are random samples. But yeah, I do concede that for many of the questions with the proper care we would be a good example, so what I said was a bit extreme, especially given that I used us to draw some examples in my very first post. I had given too much thought on the issue of abundance of life, so I carelessly assumed that the same applies for the other questions, especially those raised here. But still, when unsure, we should exclude ourselves for safety.

 

[CorporalCaptain]

^ I can accept that as a fair cautionary remark.