[kposehn]

I've always found the framework we use to search for extraterrestrial life to be too based on our own experience. It could take countless forms, most of which we could never recognize or understand, and might be present everywhere without us knowing. I'm glad that more of the science community is pushing to broaden our horizons.

[api]

I wrote a little blog about this many years ago that’s still online on my basically unupdated site:

https://adamierymenko.com/titan/

In this I’m at least speculating that Titan might be likely to host alien life in its steamy cryotropical environment. I’d love to see NASA sink a submersible in those methane seas and look for cryowhales. (Or more likely cryobacteria but cryowhales would rule.)

I’d expect life there to be wholly biochemically alien, probably based on methane or ammonia as solvents, and probably very metabolically “slow” compared to most life here. We might miss even macroscopic Titan life without time lapse photography.

To any intelligent Titanians we would look like the Balrogs from Lord of the Rings: burning lava monsters with blood of molten water.

[jcfrei]

Counterpoint: Alien life will probably look very similar to life on earth. If you look at evolution then countless species have evolved into something crab-like: https://www.youtube.com/watch?v=wvfR3XLXPvw Turns out that their form is pretty good for survival. While biology can take on a myriad of forms, the competitive nature of life will weed out a lot of them. And since the rules for biochemistry are the same across the universe similar traits that are beneficial here will probably be beneficial there.

[heavyset_go]

> Turns out that their form is pretty good for survival

Their form is pretty good for survival on Earth, we don't know if they're good forms for survival elsewhere or in general.

[cactusplant7374]

I agree with this but would the intelligent beings on other planets be the same size as humans? Could there be giant creatures that are just as intelligent as us?

[dmurray]

There are some square/cube laws that put a rough cap on how big an efficient animal can be with Earth biology. But if you change some parameters (lower gravity, energy-rich environment, stronger building materials than bone) you could get hundreds of times bigger than humans. Even on Earth, intelligent dinosaurs would have been completely possible.

[dmurray]

And I forgot to even mention whales.

[jcfrei]

There's a natural limit to size due to the square-cube law. An increase in height leads to a cubed increase in mass which means they are pretty quickly too large and require too much energy to sustain themselves.

[kevin_thibedeau]

There's no reason to believe other sentient life will be in any way relatable to us. Most significantly, there's no reason their perception of time is on the same order as ours. We could be glacially slow or impossibly fast for them to engage in any meaningful way.

[albert_e]

I am in the same boat as you.

There is also this to consider: limits of our own imagination/ comprehension.

If we are like microbes swimming inside a droplet of water, we won't be able to imagine/ comprehend / detect beings of the scale of say flies.

Our mental abilities may also be limited in similar ways. I think that puts a limit on what we can perceive / detect / understand.

[unity1001]

Even further - not only the development of biological life forms on other planets would totally depend on the circumstances on that planet and create unimaginably variable life forms, but also these very different life forms would develop very different cultures and as a result, very different technologies. So even when we look for radio signals, we are looking for something that totally depends on our own technology, which is the product of our own civilization that is in turn the product of our own culture, which is a product of our own biology that was created by the circumstances on our planet.

[zokier]

Question is how does this broadening of horizons actually help with anything? When we are heavily constrained on both our ability to collect data and analyze that data, exploding the search space seems counter-productive.

We need some way of prioritizing the search work and for that purpose looking first for life as we know it makes sense as that is where we are most likely to be able to identify life.

If searching for life as we know it does not produce results then of course it makes sense to broaden the search. But that is more relevant debate for our children than for us.

[Rury]

The thing is, people don't realize this argument fully. If you are to accept that life could take countless forms, most which we could never recognize or begin to understand, then it's quite possible rocks are lifeforms, as we don't recognize them as life now nor understand how they could be living. Since most people seemingly don't like the argument that rocks are living, then this shows that this argument (along with others) is flawed with very definition that they want "life" to have.

[cogs]

We managed to recognise stromatolites https://en.wikipedia.org/wiki/Stromatolite

[andsoitis]

> quite possible rocks are lifeforms

Humans are closer to fungi than rocks are to life.

[Rury]

This statement has nothing to do with what I am saying.

[andsoitis]

To posit that rocks are quite possibly life forms takes the meaning out of what we mean when we say “life”.

[Rury]

That's my point, and by extension, to say that life could take forms that we don't even understand, is flawed, because what life means is whatever definition we want to give it. Do we not understand our own definitions?

[andsoitis]

Right. I’m doubling down on your point. We’re singing in chorus.

[bufferoverflow]

Have you ever seen rocks do anything interesting? I don't mean outside forces acting on rocks, but rocks themselves?

[willis936]

It is a fun thought, but chemistry is not infinitely complex. Much like the Fermi paradox, once you start applying real world qualifiers on chemistry of complex life the search space becomes quite small.

https://youtu.be/469chceiiUQ

Life inside of stars does enable different options.

[nwallin]

I used to think that too. Life could be anything; crystals, pure energy, eddies in the superfluid cores of neutron stars, swimming in seas of metallic hydrogen in Jupiter's core, living clouds floating in Venus' upper atmosphere.

The trouble is that when you start asking yourself about what the fundamental nature of life is, all the fun stuff starts to fall out.

For life to be life, it needs to do work. You need a metabolism. You need to "do stuff". The only way to do work ("work" in the physics sense) is to leverage an energy gradient; you need to have hot/cold, high/low pressure, bright/dark, high/low salt concentrations, high/low energy chemicals, positive/negative charge, etc. And you need to extract work from the differences between them. Therefore, you need to have a physical barrier between your high/low energy states; if you didn't, the system would reach equilibrium without you. So you need a physical barrier, it has to be a solid or liquid: you've eliminated your beings of pure energy, superfluid eddies, living clouds.

It's all well and good to use whatever weird energy gradient you want, but most energy gradients are simply too inconvenient; if you want to get energy, chemistry is ultimately going to be the only one that works. It's fine for plants to break water molecules with relatively high energy photons, but you can't build complicated structures with light. You need chemistry. And for chemistry you need to be in the liquid phase. So you've eliminated your crystal based life.

So everything is chemicals with complex structures in a liquid. It doesn't have to be proteins constructed with amino acids, it doesn't have to be ribosomes constructed from RNA, but you need some sort of 'interesting' chemical. How do you build interesting chemicals? Well you have to use carbon. You have to use carbon, no other element fits the bill. The metals are right out; they only form metallic bonds and ionic bonds which are non-structural. The noble gases are out because they don't do chemistry. The halogens are out because they can form just the one covalent bond. The chalcogens (oxygen, sulfur, etc) are also out for the same reason; with only two covalent bonding points you can form chains and rings, but not a branching structure. Nitrogen is too happy to form a triple bond with itself, producing a gas, so basically all molecules with lots of nitrogen atoms are explosive. Phosphorus is a decent candidate, but its chemistry is very finicky. Carbon is great, because it forms 4 covalent bonds that are not too strong and not too weak. Silicon is ... ok? But it cannot form double bonds, it tends to form weak bonds, and is unstable in most chemistries.

So life has to be carbon based. This puts an upper limit on temperatures, because interesting carbon chemistry breaks down at high temperatures. Venus is out, the depths of Jupiter are out.

So we're looking at other solvents besides water. Methane is a great candidate, and as a result lots of people are clamoring to get a Titan mission going. Ammonia is something people talk about, but it's unlikely to be able to form ponds or oceans on a world; it's probably going to break down into methane and molecular nitrogen, because again, carbon rules. But if we detected a large amount of ammonia in the spectra of a planet that could maintain temperatures consistent with liquid ammonia, you could bet that everyone is going to clamoring to study it in detail.

So what are we looking at? Carbon based life on planets with liquid oceans. Which is basically the same as us. We haven't gotten here because we're biased towards what we're like, we've gotten here by starting from first principals, considered everything, and eliminated the things which are impossible.

[don_esteban]

I don't see how your argument refutes living clouds. Hurricanes, after all, are self-organized heat engines, a proto-life that is hampered on Earth by very marginal conditions and that pesky dry land.

On gas giants, the conditions are much better for sustainable 'life' of long-lived cyclones, you can see huge amounts of them on Jupiter an Saturn, even very long-lived ones (hello The Great Red Spot). Instances of these cyclones merging with ('eating') each other are well-documented.

Yes, they work on very different scales (both space- and time-) then us, and might have problems reaching high-intelligence in reasonable time, but I see no reason a long-lived giant cyclonic storm can't match the complexity of small bacteria. In the environment they 'live' they would interact with similar 'life' on a continuous basis and the more successful ones would survive and might even 'evolve' in a Darwinian fashion.

This shows that the chemistry-based arguments are way too limiting.

Of course, stars themselves are a prime example of self-sustaining energy-extraction 'life', again, absolutely without the need for chemistry - there the problem is that the meaningful interaction with the outside environment is rather limited (on the star's scale) so it would be more difficult to 'evolve'. I would still like to see self-sustaining solitons of magnetic energy thriving in/on the stars, competeing with each other (and their interactions/fights ending up in solar flares), but I am not sure such things can work (unlike hurricanes, that definitely work).

[otabdeveloper4]

This isn't true, because information complexity and structure are measurable physical quantities.

(In the same way we recognize language vs random noise even if we can't understand it.)

[nitwit005]

There is no agreed upon definition for life, and certainly no information complexity requirements.