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Comment by sktrdie | Hacker News Reader

I really think that the great filter (of the fermi paradox) is behind us. Meaning, some stupefying rare event happened either when (i) life began in the first place, or when (ii) we evolved into advanced technological species.

For (i) I remember watching a documentary by Brian Cox which explained it quite well (can't find the video anymore). Essentially it was about how all species branch from DNA. The fact that there's only DNA, and not other types of life constructs spread around our earth (heck not even 1), would make the beginning of life (abiogenesis) a very rare event.

For (ii) it is an obvious rare event because out of the billions of species that ever existed on earth, we're the only ones to have developed technological intelligence. This "characteristic" evolved only once on earth - where life is prolific -, hence by no means a certain development of evolution.

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That DNA gains dominance proves very little. It stands to reason that in the primordial soup, once one self-replicating molecular biology came into existence it pretty quickly consumed all the elements any others would need.

Moreover, life on Earth proves little about the nature of life anywhere else - for example what type of self-replicating biology might exist in the high pressure environment of a gas giant? We don't know, but all the components are there and there's plenty of energy so why not?

The reason Earth-like's are interesting is because we know what we're looking for when we go looking for life on them. They're a sure thing to expend limited resources on.

- FTL is not possible.

- Technological life exists for a few thousand years. They are a small blip so basically nothing in terms of cosmic timelines.

- Even if it sends out probes, those probes generally fall into the gravity wells of the planets they are sent to over the millions of years.

- Hence why intelligent life is common, but not often seen.

One thing to do, and we should do it fast... is to make self replicating robotic probes that spread throughout the galaxy. I guess it should collect samples of life once it finds it and find ways to seed the universe with it. Or create some sort of Ark of Life to carry DNA from intelligent life forms to other places where they could perhaps be cloned.

We should not focus on our own survival, but increasing the chances of intelligent life in general to survive in the universe and find each other. We are probably doomed as a species, but we can do that for the universe.

- Even if it sends out probes, those probes generally fall into the gravity wells of the planets they are sent to over the millions of years.

But then wouldn't we have possibly observed these probes? Maybe they have visited our planet, just so long ago such that any evidence of their arrival has decayed...

Metal decays fast enough, but not only that the Earth's crust moves and most of the planet is water. It's like looking for a small piece of metal that was here say 10 million years ago, is very rusted and probably at the bottom of the ocean. And even if they send probes, it's not as if they or we send a million of them. We send a few, and they are expensive, and they are easily lost.

Why would any self-respecting interstellar civilisation build probes out of metal? It's expensive, heavy, doesn't breed very well, and doesn't last.

A true interstellar self-replicating probe is going to look like a fat molecule. Hell, they could be here already; panspermia is still a totally valid theory.

> One thing to do, and we should do it fast... is to make self replicating robotic probes that spread throughout the galaxy. I guess it should collect samples of life once it finds it and find ways to seed the universe with it.

This looks like a bad idea because is a planet has life and the probe seeds it with the life of the other planet, you may kill all the native population.

Anyway, the probes we send will have a few bacteria as free riders, so we will seed them with Earth bacterial life anyway.

There are some protocols to clean the probes that go to Mars (and other planets), so if find life there it will be Mars' life. (But this is very difficult, I think that bacteria are very sneaky and they probably will win.)

> - Even if it sends out probes, those probes generally fall into the gravity wells of the planets they are sent to over the millions of years.

[citation needed]; a civilization wouldn't just shotgun these things and wave farewell, it would have instrumentation, guidance and engines on board.

it might have all these things, but if you don't have ftl then they take a very long time to get to their destination. tens of thousands to millions of years. There are a few planets between 4 and 42 light years from here. At 4 light years using a Nuclear pulse propulsion it would take 100 years. At 40 it would take 10x that, so 1,000 years. That's nuclear which requires a immense amount of fuel which probably does not make sense for satellites. Other mechanisms for prop. are much slower. By the time any of these get to their destination, people who built them will be dead and possibly the civilizations which have launched them will have gone extinct.

The problem is we don't know a lot about the probabilities of abiogenesis. We do know the basic components for life, such as complex hydrocarbons and amino acids, do occur in non-biological nature. The question is how likely they are to combine into something self-replicating.

> Essentially it was about how all species branch from DNA

That is not correct. Most models consider RNA as a precursor to DNA. Over time, RNA has come to fulfill more narrow intra-cellular roles, but at some point in time it was probably the dominant gene format. By the same token, it's likely that RNA as an information carrier was preceded by other molecules, and very early proto-organisms might not even have had a unified gene carrier system - they might have been just "running systems" that split in two every once in a while.

> (ii) we evolved into advanced technological species.

This is also doubtful. Humans do combine several fortunate intellectual capabilities, but the components making up our neuronal structure are not unique to us. What's more, we do find advanced capabilities in organisms that developed after we split from a common ancestor, suggesting that the building blocks of general intelligence might arise readily under different circumstances and using different biological implementations (albeit with the caveat that we share a common biochemical machinery, the details of which may or may not make general intelligence more likely).

At least one thing I'm optimistic about is that by observing other semi-intelligent species, we can see that social behavior and cooperation is one of the driving forces of intelligence. There are different moralities, cruel to ours, but overall this implies to me a common ability to cooperate and explore, among any evolved civilizations.

> we can see that social behavior and cooperation is one of the driving forces of intelligence.

Most octopuses are solitary animals, yet probably qualify as semi-intelligent.

Interesting argument I saw recently: assume, as many physicists think, that inflation/string theory is correct and there are a very large number of universes, which vary in their physical parameters.

Not all universes will be suitable for life. Of those that are, a large majority will be just barely suitable, so life is just probable enough that it arises once in the universe. A much smaller number of universes will make life so probable that it arises lots of times.

Therefore it's very likely that our little planet has the only life in our universe.

Well, for (i), we wouldn't necessarily see any of the other life systems if DNA life outcompeted it. Bear in mind that we've only really explored a handful of Earth's ecosystems --- it's known that the microbial biosphere extends way into the lithosphere, for example. I'd be totally unsurprised (although thrilled) to learn of a discovery of an alternate life system there.

For (ii), remember that we can't observe any other Earth-like planets in enough detail to know whether there's human-like technological life there or not; all we really know is that we haven't observed any here, and there are plenty of simple explanations why not, one of the most plausible being that transporting human-like creatures from one star system to another in a reasonable time is almost inconceivably hard.

In fact, life like ours is so unsuited for living in space that it's probably reasonable to assume that any successful space-based civilisation isn't going to be using life like ours.

That assumption leads to some interesting corrolaries: for example, once you're adapted to living way out in the dark, the inner solar system is going to be horribly inhospitable. And you're likely to be quite slow, because everything's going to take a long time.

So if such a civilisation existed on the outskirts of Sol system, it would be entirely plausible that they wouldn't come and visit --- coming here is too dangerous, and besides, if we're going to be interesting to talk to we'll be rebuilding ourselves to be like them and be out there soon...

Isn't it technically twice... the Neanderthals? whom possibly would have gone onto further technological advancements had we not out competed them for resources?

These observations don't discount the possibility that life is incredibly pervasive throughout the universe, yet on each planet that harbours life it is natural that just one species reaches dominances to make observation about Life, The Universe, and Everything, such as we are making... but are still ultimately prevented from becoming Type III civilisations by physical constraints (i.e. interstellar flight is impossible) and therefore the Great Filter lies before us.

Neanderthals are our cousins. Meaning it's essentially a species in the same genus tree (very closely related to us). Characteristics which are "not rare" are found across species in various branches in the tree - think of vision or smell, etc. I do agree however that we might be the first - hell there was a first species that developed vision so why not think we might be the first who have developed tech. intelligence.

There is evidence of tool use dating back 2 million+ years. Those species are grouped under genus Homo and would likely have been ancestors of both modern humans and Neanderthals.

That the current thinking and evidence on abiogenesis says that this all happened very very early in the earths history would lead me to believe that abiogenesis is probably quite common. The existence of only DNA based life forms, given we now have good evidence that other chemical elements could have become the bases of dna (as opted to g c t and a) would also tend to indicate that it was probably just the 'winner' of that early evolutionary arms race, i.e. What chemical formula can reproduce the fastest under those early conditions

I think it's likely that higher intelligence could evolve more often were it not a "first past the post" race where whichever species gets there first prevents the others from doing so by squeezing them out with regard to the necessary natural resources.

Thus, I'm inclined to think that if there are many planets with the required ingredients for life, there could likewise be many examples where intelligent life has arisen, but like on Earth, limited to one advanced species per planet.

I tend to believe that molecular technology and AI are the great filter. Just picture the situation we find ourselves in: We are stuff made from the rules of the pattern generating system that we call our universe. We are figuring out the rules and we are continuously improving our tools to manipulate stuff at an ever lower level. Once we can easily manipulate the building blocks our existence is based on, it opens the door to such a tremendously large number of ways how things can go wrong that the probability of self-destruction comes very close to 1. It would require an extremely high intelligence to deal with all these failure modes, something that an biochemistry-based evolutionary process is highly unlikely to bring forth. The problem is basically that figuring the rules out is much easier than using them safely. The invention of AI makes our tools to manipulate matter vastly more dangerous, for example, intelligent gray goo would be smart enough to not immediately eat away its basis for existence and to plan ahead instead of just executing a simple rule set.

We are so special, the only intelligent species in the galaxy etc reminds me of the sun revolves around earth statement a few hundred years ago, the fact is we don't have the technology to explore even the closest stars, even our own solar system is unexplored, think europa, so making statements about life in the universe based only on one planet is science fiction.

I agree completely. While we are definitely making progress, it is early days yet and we're still taking baby steps around the playpen of Earth. We haven't even toddled next door to our neighbor, Mars.

That said, it means there are lots and lots of exciting missions to look forward to as our technological abilities grow.

Beautiful read on the Fermi Paradox http://waitbutwhy.com/2014/05/fermi-paradox.html

A good start in answering these question is to look for life in our own solar system. Maybe it is not as rare as we think.

Intelligent life is rare on Earth. Out of tens of millions of species on our planet that exist or have existed, only one is intelligent enough to make a civilization.

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