[JumpCrisscross]

> Can someone remind me how it comes to pass that there are people in the scientific community who believe we are the only "intelligent" life form?

Sure. I’m a strong-form rare Earther.

Interstellar pan-spermia is possible but unlikely across large distances. Independent seeding is the only way a 14bn-year-old expanding universe 93 Gly in diameter proliferates with life.

We don’t understand abiogenesis. All indications suggest it’s a difficult problem. The abundance of elements is set by the nuclear physics of stellar fusion and neutron star collision. Solvency further restricts biological chemistry. Given this, it seems likely that life in any form is quite rare.

Then we have multicellular life. On Earth, this is a product of the fusion of mitochondria and bilipid-barrier cells. Consider the number of cells in Earth’s history. The eucharyotic union occurred once. That is improbable.

I believe we will find scattered archae beyond our Solar System. (We may find single-celled life within it.) But complex multicellular life—let alone intelligence—takes so many variables perfectly aligning that it strikes me as vanishingly improbable.

We must as a species confront the moral implications of possibly being the sole light of life in this universe. That’s an uncomfortable burden. I understand why we shy from it.

[hariguleria]

It is an echo of the ‘centrist’ mindset. It was as difficult to understand that earth was not the center of the universe. Then our sun was not the center of the universe. Now that the human soul is not the center of all living things on earth. If life is a possibility then intelligence isn’t simply a matter of time. However, the bigger question is whether intelligence is the curse of life. Is intelligence self destructive by its very arrogance and nature. Just published an article ‘Beyond Drake- Earth 2.0’ as the foundation for this very question. You can google and find it. It’s the start of a journey and a path to this question.

[saiya-jin]

Its not about being the centre of anything... more like we had so much luck its unbelievable (stable sun, big planets cleaning asteroids, moon, magnetosphere etc.), and other life out there would quite a few more billions of years to get where we are. At least in this part of Milky way.

And its entirely possible light speed is the limiting factor that can't be crossed. Hence the civilizations of distant galaxies will remain unknown to us, same as we to them.

[YeGoblynQueenne]

>> The eucharyotic union occurred once.

Once that we know of. I generally agree with the gist of your comment but we can't know what we can't know.

For me it makes more sense to admit we have insufficient data for a meaningful answer and leave it at that, until the situation changes. Science can't answer every question at any time.

[tsimionescu]

They meant, it occurred once on Earth, or at the very least it has stopped occurring for a few billion years now. That is still staggeringly low odds of a living planet seeing this event.

The same is true of abiogenesis - here we have a planet teeming with life absolutely everywhere we've looked, and yet 0 abiogenesis to be seen anywhere today. So, in general, when seeing a planet like the Earth today, we should expect to find NO life on it, as we already know teh Earth today can't sustain abiogenesis.

[YeGoblynQueenne]

I'm out of my depth here (I know a few things about computers but - biology? Not so much) but I suspect that once life gets going it kind of hogs all of the resources necessary for life to begin again.

So perhaps abiogenesis hasn't happened again on Earth because it's already happened and there's no space for it to happen again until the current batch of living things has been extinguished.

If that holds any water, then life could have started any nymber of times in the past and ended soon after, without leaving any trace we can detect.

[SturgeonsLaw]

> insufficient data for a meaningful answer

Well I can't very well see that phrase and not post it

https://templatetraining.princeton.edu/sites/training/files/...

[YeGoblynQueenne]

Cheers :)

[Kim_Bruning]

I thought your argument was well reasoned; but I would like to make a point about Life: because once life exists, things get interesting.

Life as we know it is based on genetics, which -as we know- is a kind of natural optimizer. A lot of people play with optimizers these days in AI and ML. Of course life does not optimize for click-through nor for paperclips. Instead it optimizes for "survival".

So if it is known that certain optimal points (niches) exist on the optimization landscape (fitness landscape), then one can assume they will be occupied sooner or later.

Or, in normal English: If something is at all reasonably possible, then once life exists, "Life Will Find A Way".

So once you get to the point where Life exists, the likelihood of life-related-things actually happening would actually seem to be quite high.

Of course with just life on a planet; history still moves at a slower scale than if there are planet were have actual sapients or even civilisation. Those are much faster optimizers, of course.

[T-A]

https://www.sciencealert.com/scientists-have-witnessed-in-re...

https://www.nature.com/articles/s41598-019-39558-8

[morsch]

> The eucharyotic union occurred once.

How do we know that?

[lordnacho]

That's what I thought as well. How do we know that it isn't a first-one-wins game, ie where a bunch of candidates have a reasonable chance of developing multicellular life, but whoever gets there first uses the advantage to out compete all the others?

[NineStarPoint]

We don’t, but we do know that there over the about 4 billion years of life, the first 1 to 1.5 billion years were purely prokaryotic. If it was a common thing to have work out, you wouldn’t expect such a massive amount of time before it occurred.

What I’m less confident on is that it’s the only path to complex multicellular life. It’s the step our history took, but it’s possible there are multiple rare pathways to the next step (or possibly different initial conditions could make the eucharyotic union or other options more probable? Just because it was unlikely here doesn’t mean that’s true on all planets).

[morsch]

> We don’t, but we do know that there over the about 4 billion years of life, the first 1 to 1.5 billion years were purely prokaryotic. If it was a common thing to have work out, you wouldn’t expect such a massive amount of time before it occurred.

Based on that evidence you could also conclude that it was impossible for it to happen for 1 to 1.5 billion years (because it didn't) and then it was suddenly very likely (because it did).