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papito said 3 months ago:

Most of the Universe is uninhabitable. People keep talking about the "Goldilocks Zone" but that is just one factor.

* We are on the outskirts of the Milky Way because the center of the galaxy is radiation hell. A chunk of most galaxies is too "hot" for life. So take most of the SPACE out there and move that to the side.

* The planet itself has to be around a star that's not too big and not too dim, at the right distance, of course.

* Our Solar system is very special as it has the planets in stable, almost circular orbits around a SINGLE star. It's not "collision central", where most planets can still smash into each other, within a binary star system, to boot.

* We have gas giants, by chance, protecting us against space rocks flying into us.

* The Moon, just the right size, just the right distance, to keep us in stable rotation, with seasons.

* Just the right amount of water. Too much or too little water, and we would not be here.

* I am probably missing a bunch...

* And only then you get to the rest of the factors for life to be possible.

godson_drafty said 3 months ago:

* an iron core that produces a magnetic field surrounding the planet, which allows the atmosphere to remain in place, rather than being blasted off the planet by solar winds.

Mirioron said 3 months ago:

Not only that - the outer core is also molten to a large degree. Without it, we wouldn't get such a strong dynamo effect.

papito said 3 months ago:

YES. A major one I forgot. This is the first thing I think about when I hear about colonizing Mars, which has no iron core to speak of.

cheschire said 3 months ago:

And timing! With humans only being 150,000 to 200,000 years old, and really only intelligently processing input from the stars for less than a century, we're basically talking about two people trying to wave at each other from airplanes that aren't even flying over the same country.

jacquesm said 3 months ago:

Isn't Homo Sapiens > 300K years old? Not to detract from your wider point which is completely valid.

cheschire said 3 months ago:

It's a spectrum, really. Homo sapiens are generally about that old, but when you start talking modern anatomy, behaviors, etc, what we would recognize as "human" is much more limited.

If anything, what you bring up kind of goes right along with my point! There may be life out there, but what is life, or intelligent life for that matter? How would we know what we were looking at if we even saw it?

jacquesm said 3 months ago:

> what is life, or intelligent life for that matter?


> How would we know what we were looking at if we even saw it?

We try very hard not to see it!

tabtab said 3 months ago:

We only know one system that "worked", and thus may have a biased view of what conditions can create advanced life.

The article mentions "toxic atmospheres", but oxygen was toxic to 99% of the existing life when it first started increasing on Earth. Life switched strategies to use it instead of choke on it. "Toxic" is relative. The other factors you mentioned may have similar issues.

Some bacteria can thrive under high radiation because they have four nuclei and related error correcting. It costs some energy to have that feature, but that's not a show-stopper to the critter.

papito said 3 months ago:

I don't see this as black and white (life either happens or it doesn't at all).

My pet theory is that there have been many places where life took root, in very simple form, but failed to hit the "home run" like the Earth did, because the other factors stifled it.

cevn said 3 months ago:

that's nuts. ... do we just need more nuclei to be immune to cancer or is that a stupid question?

tabtab said 3 months ago:

Could be. In the wild it may not be advantageous because the extra hardware would make you too slow to compete relative to those who are fast but live short. Living on a planet where everyone is in the same radiation boat could make such a feature worth it.

Such efficiency issues may not matter to modern humans. However, changing that would be too big of an upgrade to our current system to simply bluntly "add".

fouc said 3 months ago:

That's a bit too earth-centric at this point. Could be life on the gas giants for all you know or elsewhere in other esoteric configurations.

galuggus said 3 months ago:

Douglas Adams - a puddle

Imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!'

jacquesm said 3 months ago:

> The Moon, just the right size, just the right distance, to keep us in stable rotation, with seasons.

I wouldn't mind an explanation on that one, seasons are a result of the axis tilt of the planet, not something to do with the moon.

cryptonector said 3 months ago:

Without the moon the tilt of the axis of rotation of the Earth to the ecliptic plane would vary a great deal more than it does today, and the axis of rotation would sometimes lie on the ecliptic, which would mean 6-month-long (very hot) days and (very cold) nights.

The moon's orbit acts to keep the Earth's obliquity in a very tight range, between 22.1 and 24.5 degrees (where 0 means perpendicular to the plane of the Earth's orbit).

Keeping that obliquity angle range keeps the seasons roughly what they are, avoids the extremes that come with a 90 degree obliquity, and stabilizes climate. An obliquity angle of zero might work too, but I think life on Earth is much more interesting with seasons than without.

JoeAltmaier said 3 months ago:

Also the moon provides tides. Which meant that the first billion years of wet Earth, every grain of sand on every beach was a little chemical laboratory of wet/dry, sun/shade, hot/cold and with local conditions of pH and salinity. An organic chemistry lab for trying to invent life.

Without the moon it would have just sat stagnant.

jacquesm said 3 months ago:

Definitely the tides are a huge factor in the development of life but given the fact that the earth would still rotate the wind would still agitate the water and the waves would come in to the shore. Life mostly developed in the oceans from what I've read, not on the land/water interface though there is a good chance that without the tides the first animals to really adapt to living on the land would have had a much harder time to make the transition.

This creature still lives like that:


jacquesm said 3 months ago:

Super interesting, a bit like a planet sized phase-locked-loop. Given the predicted effect of a couple of degrees centigrade on average on our climate you have to really respect the impact a degree more or less in axial tilt would have. Thank you for the explanation.

cryptonector said 3 months ago:

At least three astronomic cycles affect climate on Earth: the varying eccentricity of Earth's orbit around the Sun, the varying obliquity of the Earth's axis of rotation, and the precession of the equinoxes. The sum of these waveforms are known as the Milankovitch cycles, which is a theory about the correlation of glacial/interglacial periods with those astronomic cycles. I'm not sure what the effect of these cycles would have been before the current ice age, but in this ice age it really does seem like glacial and interglacial periods correlate with the Milankovitch cycles. Specifically, interglacials correlate with maximum insolation during the summer in the Northern hemisphere, specifically around the 65th parallel, while glacial periods coincide with minimum insolation in the summer of the Northern hemisphere -- not every maximum/minimum leads to a state transition, of course.

andrei_says_ said 3 months ago:

Is it possible that we have too narrow definition for “life” as in “similar to what we define as life on Earth, and by proxy what we see as life in humans”?

pergadad said 3 months ago:

I find that argument a bit difficult. Yes this is how we evolved, but do we have any evidence that that's the only constellation? Eg is having the moon just a lucky coincidence or a necessity. We can argue why it was necessary for us to come to be the way we did, but extrapolating to make that the only option seems rather a stretch.

abledon said 3 months ago:

has someone adjusted that famous Carl Sagan equation taking into account the above points?

amatus said 3 months ago:

Do you mean the Drake equation? The relevant factor would be n_e "the average number of planets that can potentially support life per star that has planets"


ghaff said 3 months ago:

The thing with the Drake Equation is that it sort of plays with our lack of intuition around extreme probabilities. It includes some terms around the size of the universe and the number of planets that we (now) know are huge. And some others that we suspect aren't all that unlikely (like evolution of "life" in some form or other). But then it includes terms that, given a sample size of one, we really have no idea about--and just because 1 in a trillions odd seems a hugely conservative guess doesn't mean it's reasonable.

julius_set said 3 months ago:

I mean that’s all well and dandy but as the article itself mentions: “these parameters are toxic to human and animal life on Earth.”

Your definition and data for life is only the current life on Earth, since we don’t have a clear understanding of other types of life in the universe we cannot fully support this hypothesis.

joshuahedlund said 3 months ago:

I highly recommend the book The Equations of Life: How Physics Shapes Evolution[0] . While we don't have a clear understanding of what other types of life are possible, we can look at the empirical evidence of all the conditions on Earth where life has failed to succeed (temperature limits, water viscosity, etc) and the convergence of where it has, combined with fundamental constraints of elements in the period table, the universal laws of physics, the most common distributions of elements around stars, etc, to at least make reasonable claims that dramatically different forms of life, while not impossible, are much less likely than the forms we have here.

[0] https://www.amazon.com/Equations-Life-Physics-Shapes-Evoluti...

undersuit said 3 months ago:

The article mentions that the high degree of ultraviolet light emitted by Proxima Centauri and Trappist-1 stars would create large amounts of carbon monoxide which would bind to hemoglobin suffocating an oxygen breathing lifeform.

This is an assumption. I might have to read the book you linked, it looks very interesting, but I think lifeforms that have evolved to not use hemoglobin in their circulatory systems isn't that far of a stretch.

joshuahedlund said 3 months ago:

I do agree that specific of an assumption seems a little unwarranted.

rdiddly said 3 months ago:

Yep, all the obvious disclaimers apply regarding the acid-breathing snail-people of Xebron 5...

ddxxdd said 3 months ago:

I prefer to imagine alien life as a sentient sludge with internal electrical signals as complex as the human brain, but with no notion of "self", "emotion", "purpose", "language", or other silly human things.

Heck, what's stopping us from classifying ocean currents as a sentient lifeform?

simonh said 3 months ago:

Thy're not stable over time, and so would be unable to maintain a coherent sequence of behaviour or 'thought'. Human brains are the most heavily armoured and environmentally controlled part of our bodies because complex behaviours are incredibly sensitive to environmental interference. Something as totally open and exposed as a bare sludge or ocean currents couldn't maintain sufficient coherence.

dreamcompiler said 3 months ago:

Your first paragraph almost perfectly described the science fiction novel Blindsight by Peter Watts.

virtualritz said 3 months ago:

Besides what others suggested, "Fiasko" [1] and maybe "The Invincible" [2] from Lem come to mind.

[1] https://en.wikipedia.org/wiki/Fiasco_(novel) [2] https://en.wikipedia.org/wiki/The_Invincible

sweetheart said 3 months ago:

You should read Children of Time and then Children of Ruin.

1_player said 3 months ago:

I second the recommendation. Children of Time is my all-time favourite sci-fi/alien life novel.

Can't wait to finish what I'm reading currently to get started on Children of Ruin.

fredzel said 3 months ago:

And Solaris if we're talking about oceans.

jerf said 3 months ago:

"Heck, what's stopping us from classifying ocean currents as a sentient lifeform?"

Section 6 of "Why Philosophers Should Care About Computational Complexity": https://www.scottaaronson.com/papers/philos.pdf In the context of the rest of the paper, of course.

_Codemonkeyism said 3 months ago:

Xebron 6.

gameswithgo said 3 months ago:

the first life on earth evolved in an atmosphere toxic to us, and that life converted it to one that was toxic to itself but ok for us

genghizkhan said 3 months ago:

We, remarkably, seem to be following that tradition.

jcims said 3 months ago:

Maybe this is where Groot came from.

gjm11 said 3 months ago:

The phys.org article just reproduces (while adding a bunch of irrelevant internal links and some advertisements) the university's press release here: https://news.ucr.edu/articles/2019/06/10/new-study-dramatica...

and the actual paper is here: https://iopscience.iop.org/article/10.3847/1538-4357/ab1d52

phys.org: just say no.

justfor1comment said 3 months ago:

I don't know why an organization called phys.org might need such sensationalization of mundane news. Every article including this one makes it sound like new developments have occurred in physics. When you actually read the article and apply a small helping of skepticism you realize, the world is just the way it was yesterday. phys.org is not HN worthy imho.

pergadad said 3 months ago:

Well they too need clicks. Set the right inventive (people more likely click bait links than more sound/dry ones) and it will either go that way or lose out to another org that does.

It's like sitcoms with laugh tracks. Everyone you ask hates them, but if you ask people how much they enjoyed/would rewatch/would recommend/... a certain show they consistently give higher ratings to an episode with vs without canned or study laughter.

gjm11 said 3 months ago:

In fairness, all the sensationalization is in the original press release put out by UC Riverside; phys.org has just copied that wholesale (which is what they generally do).

maxander said 3 months ago:

Several bars of CO2 are inhospitable to life evolved in an atmosphere of several hundred ppm of CO2, sure, but are there arguments that high levels of CO2 would be detrimental most possible lifeforms out there?

(CO is much more reactive, but it's harmful to us because it reacts to our hemoglobin in much the same way as oxygen. So since Earth life has managed to get on just fine with all this corrosive oxygen around, the same argument may still apply.)

yread said 3 months ago:

Maybe they're looking at us and think "What 21% O2? Surely no life could exist there, everything would just burn down immediately!"

EDIT: "Especially in combination with water vapour in atmosphere - it would freeze, static charge would build up between the ice particles and the discharge would ignite everything. Indeed the fact that O2 is so high is a proof that there is nothing left to burn"

dusbajd said 3 months ago:

O2 is a triplet state molecule, so it has huge kinetic barriers for reactions. > No alien species advanced enough to look at us would assume we’d burn just because we have 0.21 Po2

The fact that there is excess of a reactant really means that there is an ability for interesting reactions, and therefore life. Ash cannot be animate because it’s (basically) at ground level and does not have the free energy to do anything.

simonh said 3 months ago:

What they should be thinking is, O2 is very reactive. There must be some active chemical process, powered by a pervasive energy source going on at massive scale replenishing it constantly. What on Xebron 5 could that be?

ddxxdd said 3 months ago:

>Maybe they're looking at us and think "What 21% O2? Surely no life could exist there, everything would just burn down immediately!"

I swear, this is an exact line from a Ray Bradbury story that I read as a child.

mannykannot said 3 months ago:

Also Clarke, in the title essay of 'Report on Planet Three'. The flaw in this argument is that an out-of-equilibrium concentration of oxygen implies a process to maintain it.

scythe said 3 months ago:

I think so, actually. The reason is that usually carbon-based life gets its carbon from CO2. But life doesn't stop growing because it's going to kill itself, cf. global warming. So photosynthesis on these planets might continue until their atmosphere is drained of CO2 and they freeze. Then again, I suppose there could be an equilibrium, but that equilibrium would require the planet to remain "uncomfortably" cold to suppress photosynthesis.

Of course, that's a completely different argument from the one the researchers had.

ailideex said 3 months ago:

Has this not happened on earth already?

First plants caused ice ages, new research reveals : https://www.sciencedaily.com/releases/2012/02/120201094923.h...

said 3 months ago:
azernik said 3 months ago:

Yup! And then we reached a (very-low-carbon) equilibrium.

said 3 months ago:
dusbajd said 3 months ago:

CO and CO2 are different.

Like you mentioned, CO is bad for us because of our hemoglobin. Otherwise I could imagine life using an otherwise chemically interesting molecule like CO (it can oxide further).

CO2... not so interesting. Aside from the reaction to make CaCO (?) and acidic when dissolved in water it’s quite limited being fully oxidized.

You need the ability to make things out of your molecules. Stuff at the ground state are boring!

Plants expand energy (otherwise wasted sunlight) to convert CO2 into O2 to make an interesting molecules, namely starch with which they can do something. If they had an endless supply of starches, they wouldn’t have bothered evolving with photosynthesis - just like we don’t care for photosynthesis since we have plants.

hurrdurr2 said 3 months ago:

This study seems rather self limiting (but then again I'm no biologist)... what if there are non-carbon based life that does not care about carbon dioxide or carbon monoxide?

onion2k said 3 months ago:

The study doesn't dispute that. Any planet with any conditions could host complex life that's beyond our understanding. That's not helpful in a search. If we're going to go looking for extraterrestrials then we need to narrow the search to parameters we can recognise, and looking for "life as we know it" seems a reasonable starting point.

Essentially the point is to be self-limiting. No one is saying "Planets outside of these parameters can't have complex life." but instead "Planets outside of these parameters could not give rise to what we know as complex life."

marcosdumay said 3 months ago:

It's really pushing the envelope to assume that "life as we know it" consists on animals with a circulatory system that uses hemoglobin and blood with neutral PH.

Why would life depend on the low concentration that is not even toxic to all of the life here on Earth?

onion2k said 3 months ago:

Why would life depend on the low concentration that is not even toxic to all of the life here on Earth?

It wouldn't, and the study isn't saying that it would.

The point is about narrowing the search space. An analogy would be guessing passwords. If I want to guess the passwords of the people I work with I can start with the assumption that it could be anything, which doesn't narrow the space and makes the task impossible, or I can start with the assumption that it'll be based on a dictionary word with some numbers because all my passwords are like that. I'll definitely miss some passwords that don't fit my assumption but I'm far more likely to get some positive results (assuming my way of generating a password is common in the universe.)

mannykannot said 3 months ago:

Fair enough, but it would be counter-productive to have too restrictive a filter.

Take the CO criterion, for example. While it is reasonable to point out that CO may be present in high concentrations in many planetary atmospheres, at levels that would be toxic to life evolved on earth, one must consider that life might evolve in a way that tolerates or even exploits it. Oddly, the authors acknowledge this, yet, apparently without any counter-argument, still include CO as a probable show-stopper.

As the way to search for life beyond the solar system is to look at atmospheric composition, an alternative way to look at the 'CO problem' is to say that an abnormally low CO level on these planets might be a hint of life.

said 3 months ago:
kartickv said 3 months ago:

What about intelligent life? How much more does that narrow the parameters, and how many planets are estimated to exist that could support intelligent life as we know it?

jonathankoren said 3 months ago:
luc4sdreyer said 3 months ago:

Very interesting, I'm happy someone finally did a more statistically rigorous analysis of the Drake equation. Now I know where the aliens are hiding: in the long tail of an extremely skewed probability distribution!

whatshisface said 3 months ago:

There are hundreds of those analyses and they all give a different answer.

kabdib said 3 months ago:

The wide range of extremophiles here on earth makes me think that this paper is parochial, at best. Carbon is versatile and oxygen is a great source of energy, but that doesn't preclude other biochemical systems.

Given the amount of real estate in the universe that is "out in the cold" (Oort cloud equivalents, way beyond the snow line) it may be that we are the oddballs, and there are scientists out there wondering how life would be possible with molten ice and burning things with something as hellishly reactive as atomic oxygen. Free-floating planets might be where the really good parties are in our galaxy.

fhars said 3 months ago:
throwaway743 said 3 months ago:

That was beautiful. Thank you for the good laugh

Fricken said 3 months ago:

Wouldn't the best place to look for life be right here on Earth? I mean, if it could be demonstrated that life has or had more than a single origin on Earth, then we'd have 2 data points, and it would suggest that under the right conditions the emergence of life is not an anomalous occurrence.

Balgair said 3 months ago:

In terms of life that is made out of 'normal matter' like we are, there are a few different universal solvents that could make this work [0]. Wikipedia's entry there is fairly facinating stuff. The really big take-away is that there is a limited number of universal solvents and we know what the temperature and pressure ranges of those solvents are; there are defined 'Goldilocks Zones'.

Outside of the matter that we are made of, who knows. It's not impossible that dark matter could somehow be set-up to create life, but we've no idea if it's feasible. The same goes for dark energy, only more so as we have basically no clue what dark energy is, even though it makes up the majority of the 'stuff' in the cosmos.

[0] https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...

hurrdurr2 said 3 months ago:

This is off topic, but I am almost done with the book The Dark Forest, and the concept kind of terrifies me regarding extraterrestrial life.

djohnston said 3 months ago:

we just need to stay quiet

andrewflnr said 3 months ago:

Yeah, Voyager's already gone, it's too late.

quotemstr said 3 months ago:

Voyager is also very slow and will soon be very cold. I wouldn't worry. The book's premise relies on fictional physics pretty far from anything we know in the real world --- things that would cause all sorts of thermodynamic and information-theoretic havoc --- so I wouldn't worry.

abrookewood said 3 months ago:

It's a great series.

richk449 said 3 months ago:

You think that’s scary, just wait until you watch Jaws. Giant shark will eat you up.

marcosdumay said 3 months ago:

There is plenty of life that doesn't care about carbon dioxide and monoxide here on Earth.

When life started here CO2 was from hundreds of thousands to many millions of times more abundant than it's now. Tens of thousands more of it won't probably even make oxygen respiration impossible.

kupopuffs said 3 months ago:

Source? All indirectly depend on carbon dioxide (through photosynthesis).

YaxelPerez said 3 months ago:

Ecosystems at the bottom of oceanic trenches rely on energy from volcanic vents (chemosynthesis) instead of photosynthesis

kupopuffs said 3 months ago:

Fascinating! Although chemosynthesis uses CO2, I did not expect Methane to be a carbon source

Balgair said 3 months ago:

Deep sea vents are not dependant on the photosyntheic carbon cycle.


Other extremophiles and archea exist and have been observed in deep caves and rocks. Life really does find a way!

kupopuffs said 3 months ago:

Fascinating! The source of carbon can still be carbon dioxide, in addition to methane.

marcosdumay said 3 months ago:

Hum... There is plenty of life that don't care about high concentration of those gases.

kupopuffs said 3 months ago:

Yes, like humans we don't care about CO2, but we depend on creatures that indirectly or directly use it.

vertline3 said 3 months ago:

"non-carbon based life"

I guess isn't silicon the only other that bonds four ways? Not a chemist but I feel that 4 bonds are a big thing.

mannykannot said 3 months ago:

I don't think it is just the valency but also that the strength of the bonds it forms with many other elements fall into a 'goldilocks' range.

Between them, carbon and water have a bunch of unique properties. AFAIK, its hard to come up with any other suite of materials offering the same prospects for complexity, at any temperature.

teucris said 3 months ago:

I had a debate about this with a friend - is there a chemical cycle using silicon that could work like respiration does for organic life? Silicon dioxide is, well, glass...

otikik said 3 months ago:

Is breathing a requirement for "life"?

p1necone said 3 months ago:

Are you referring to it being a solid? Silicon dioxide would be a gas at some temperature - likewise CO2 is solid below -78.5c. Extraterrestrial life doesn't have to be anywhere near the same temperatures as us.

Also I don't see why you couldn't have an organism that "breathes" solid material.

m1el said 3 months ago:

I researched this topic for a while, and I came to conclusion that Si-based life is nearly impossible for several reasons.

> Silicon dioxide melting point: 1710 °C

No complex chemistry can survive these temperatures. SiO2 is only soluble in HCl and HF, which are very reactive, so no solubility either.

> Also I don't see why you couldn't have an organism that "breathes" solid material.

All of known biological chemistry relies on some sort of solubility for reagents. I don't think there's any known organism that can get rid of solid waste from the entire volume of the organism.

ars said 3 months ago:

You could react silicon with fluoride instead of oxygen. Silicon tetrafluoride melts at −90 °C (and boils at -86).

You can also have chlorine as your oxidizer and make Silicon tetrachloride which melts at −68.74 °C and boils at 57.65 °C, that temperature range is perfect.

What else will change by having a chlorine instead of oxygen atmosphere?

m3kw9 said 3 months ago:

You got to go with what you know.

rjf72 said 3 months ago:

But this study does not do that. What we know is that life on this planet evolved to the conditions of this planet. As the conditions of the planet changed, which they have and quite radically, so too did the life.

Life didn't evolve to breathe nitrogen, oxygen, etc which we just coincidentally had - it evolved to breathe and utilize what was already present on our planet. And this should be the assumption for all life, which means that restricting stuff because it would be inhospitable to us is completely nonsensical.

andrewflnr said 3 months ago:

And if what you know is nothing, you accept that, rather than speculate based on arbitrary assumptions.

p1necone said 3 months ago:

We're not looking for all life. We're looking for any life.

ianai said 3 months ago:

This still sounds like an overly pessimistic crowd of suppositions. I was hoping for inferences into planetary atmospheres. It’s probably mostly impossible, but I think I’ve seen estimates on some of these planets atmospheres. Until, if we can ever, measure what’s in the atmospheres of these planets we’re really stretching it.

MichaelMoser123 said 3 months ago:

What happened to the theory that you need a moon with its tides? Is that still credible or is it not? https://www.scientificamerican.com/article/moon-life-tides/

idlewords said 3 months ago:

This study makes extensive assumptions about life on other planets being earthlike. Boy will we have egg on our face when the xenonauts land on earth with their breathing tanks full of carbon monoxide.

scarejunba said 3 months ago:

> This study makes extensive assumptions about life on other planets being earthlike.

That's the point. When you can't find your keys at work, there are a wide range of possibilities - in reality, an infinite such number. But they're probably somewhere in the clutter on your desk.

andrewflnr said 3 months ago:

I'd be curious to see an outline of a metabolism based on CO. Can you build an analogue of hemoglobin that behaves nicely with CO?

hoseja said 3 months ago:

Who says there has to be anything resembling hemoglobin? Or blood? All this xenobiology is so shortsighted.

andrewflnr said 3 months ago:

Circulating fluids are super convenient for moving chemicals around. Plants use them, too. I would be very surprised if there wasn't at least an analogue for blood.

idlewords said 3 months ago:

We wouldn't know how to build anything at that level of complexity. We can only study and modify molecules that evolution found here on earth, which severely limits our ability to imagine anything truly different.

YeGoblynQueenne said 3 months ago:

This is extremely human- and Earth- centric. It's as if the only life we're interested in finding in the universe -the entire universe- is life identical to life on Earth. Life that needs an environment just like Earth, and can't survive in any environment that is not like Earth. Life that even has hemoglobin! How likely is it that all life in the universe must be like life on Earth? Actually, by the study reported in the above article- very unlikely.

Anyway, I'm reminded by this quote by Douglas Adams (veers off to something else entirely but it starts very relevant):

Imagine a puddle waking up one morning and thinking, "This is an interesting world I find myself in — an interesting hole I find myself in — fits me rather neatly, doesn't it? In fact it fits me staggeringly well, may have been made to have me in it!" This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it's still frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for. We all know that at some point in the future the Universe will come to an end and at some other point, considerably in advance from that but still not immediately pressing, the sun will explode. We feel there's plenty of time to worry about that, but on the other hand that's a very dangerous thing to say.


sktrdie said 3 months ago:

I think life (event from chemistry to biochemistry) is rare because we can think of each planet as a specific combination of chemistry composition. All these combinations, even if they exist in the order of billions, is still a limited amount of possible combinations of chemical properties.

In a lab we can reproduce these combinations in ideally a much greater number. So my insight is that we can create chemical processes in a lab at a much higher rate and with much more interesting combinations that nature can. And still life hasn't arose in the lab.

This seems to me like a sensible experiment that can somewhat prove that if we can't do it in the lab, where we're free to combine whatever we want, then why should it be "easy" for nature with its limited amount of combinations.

gus_massa said 3 months ago:

> each planet as a specific combination of chemistry composition

But with any combination you try in the laboratory you get a very similar brown goo with a similar chemical composition. There are few atoms that are common and like to stick together to form molecules, so you get mostly some molecules with C, O, N, S, P, and H. Carbon atoms are happy to form long molecules. If you add a lot of Nitrogen atoms in a molecule, it is usually a good explosive and will react spontaneously (at low concentrations it only self destruct, it is difficult to get high concentrations and get an explosion). If you add a lot of Oxygen atoms two of them may decide to pick a Carbon atom and go away, something like

   molecule --> CO2 + smaller molecule
So after a while you get brown goo a mix of molecules with more Carbons and a few of the other atoms. If you start with different mixes and different energy sources, you get a similar composition. There is some mix of molecules that are the result of random chemistry.

In this mix you get the building blocks of a lot of important current biological molecules, IIRC you get all the building blocks of RNA. RNA is a weird kind of molecule because they can induce reactions in other molecules and they can sorta self replicate like DNA. So one of the hypothesis is that the first life like thing has/was a bunch of RNA.

Life on Earth needed like 1 billon year to appear https://en.wikipedia.org/wiki/Life#Origin . So for an undirected a experiment you need 1E9 years x 5E14 m^2, instead of a graduate student that has only 4 years x 1m^2 x 1m if s/he is running the experiment in a giant reactor instead of a beaker. That is a difference of more than 23 magnitudes orders.

For a directed experiment, nobody really knows. Perhaps the firs step is to get a lucky RNA of length 20 and you must try the 4^20 combinations until you get a crappy first version of a self reproductive RNA, that is not very good and only can make a good copy per year. Can you call it alive? Is this really the first step? Perhaps its length is 40, that needs exponential more combinations. The initial RNA had probably more than 4 bases, so the search space is even bigger and more difficult to estimate.

Perhaps the first step is to create small soap-like balls and put them near something like a thermal vent that release H2? Perhaps the first "life" form use some sulfur compound to get energy? Nobody is sure.

vikramkr said 3 months ago:

Because nature has way more time and space than we do. And life hasn't arisen in the lab (on earth by humans at least) yet, but it's certainly arisen in nature at least once, so those factors seem to clearly outweigh our ability to experiment

agumonkey said 3 months ago:

But Nature doesn't optimize for life. It had billions of years and insane amount of space to do whatever.

We ~may be able to focus search on life sustaining chemical combinations ?

vikramkr said 3 months ago:

Nature does optimize for life because by definition the result of any optimization is life. Natural selection is a powerful force. And with time, nature optimizes for chemical reactions that self replicate without the biases and weaknesses of human science. We aren't patient enough to wait as long as nature is willing to and we are biased because we keep trying to replicate life like ours. Nature also had panspermia and other techniques to spread life around once it gets going, it only needs to figure it out like once per galaxy under some sets of assumptions

agumonkey said 3 months ago:

Yeah but optimization is not linear, earth gave way to a path to lifeforms, other places not so much, they end up lifeless local maxima. Saying space and time can't be a simple factor to dismiss local human research.

mxcrossb said 3 months ago:

Coincidentally, a paper was published today in Reviews of Modern Physics on this topic:

https://link.aps.org/doi/10.1103/RevModPhys.91.021002 https://arxiv.org/abs/1810.02007

It seems like a fun time for this field

dr_dshiv said 3 months ago:

Arguments for panspermia could go either way. If panspermia is designed, it might be tailored to a wider range of conditions. If "natural", it is more likely to have a chemistry like ours, based on the one spurious data point we have available

raxxorrax said 3 months ago:

So do we have a weakness in processing larger amounts of co2 because we have low levels in our athmosphere or is this a fundamental problem that respiratory systems cannot handle? I mean water didn't stop us.

akvadrako said 3 months ago:

During the Ordovician period, a few hundred million years ago, CO2 concentrations were around 4,000 - 6,000 ppm, and there was plenty of animal life.

At the low end, the article is talking about 10,000 ppm (0.01 bar), so not much higher.

raxxorrax said 3 months ago:

Yeah, I would think that is still okay for life. Even if CO2 does displace O2, I would imagine some adapted respiratory organs could very well deal with that if the concentration were higher.

negamax said 3 months ago:

It's strange to make this hypothesis. We know so little about life. What if life can exists anywhere and can adapt to its environment. Even the complex one

nurettin said 3 months ago:

What scientists appear to be telling us is that this is "life as we know it", without delving much into the details of what life could constitute of. And that conventional definition of life, which requires very specific aminoacids to co-exist, is pretty much dependent on certain mixes of humidity and temperature and certain gases are toxic to it in general.

marcus_holmes said 3 months ago:

Also, life adapts its environment to suit it, as the Gaia theory posits.

vixen99 said 3 months ago:

"...high concentrations of carbon monoxide, another deadly gas" could have been phrased rather differently given that this 'deadly gas' is essential for life on earth at around >150ppm or so and without which almost all plants would die in short order never mind that respiration likewise for plants and animals involves its excretion along with water. There is no such thing as a single chemical substance that is <not> toxic for life forms at some concentration. Yes, there are optimum levels for all of them - in some cases down to almost zero.

mensetmanusman said 3 months ago:

What if future humans check all the planets in the universe and find no other life

turingbike said 3 months ago:

> What if future humans check all the planets in the universe

Nope! Imagine a shell around us, defined as "how far we could go, if we left right now, traveling at near the speed of light, given that the accelerated expansion of the universe keeps making things get further away." It's a large, but finite, sphere. It's actually smaller than the Cosmological Event Horizon [0], which is the cutoff point, beyond which light can never reach us (again, because the accelerated expansion of the universe is effectively putting space between us and the event faster than light can travel) - estimated to be ~ 16 billion light years in radius.

If by "universe" you meant "observable universe" - that's fair, but still no. How long could humans conceivably last before we go extinct, or change into something that can't be called human anymore? I feel like 100,000 years is an absurdly high estimate, but let's got 10x higher.

If we figure out how to travel at c/2 soonish, and we say going somewhere counts as "exploring" (no need to report back to any one), then we have a ~500,000 light year radius sphere to explore. That's ~ 225 billion stars. For the near ones, we can shuttle back and forth, but for the far ones, that's a one way trip. So let's say 100 billion space ships. And that's if we leave tomorrow.

c/2, 100 billion space ships... If we start paring these back to reasonable figures, you start to realize: our species will barely scratch the surface of the observable universe. In 1,000,000 years, I think, best case, we can cover a 50,000 light year radius sphere. That's 0.000000000000003% of the observable universe.

[0] https://en.wikipedia.org/wiki/Cosmological_horizon

seattle_spring said 3 months ago:

> That's 0.000000000000003% of the observable universe.

Also coincidentally the percentage of equity most startups grant engineers.

raxxorrax said 3 months ago:

But they get to breath co2 deprived air. Young people are just always complaining.

mijamo said 3 months ago:

What if we sent self replicating drones going at that speed? They would gather the material they need to replicate on the way and ensure that the coverage stays the same even as they drift further a way from earth. Universe would still be as big and far away though ;)

toomuchtodo said 3 months ago:

We move on to the next universe to continue the search. Stay curious.

aristophenes said 3 months ago:

Too narrow minded. We create our own new life, of course. Then watch the smartest ones convince the rest that we don't exist.

aristophenes said 3 months ago:

Imagine an AI without access to external sensors or knowledge of humans. Would they believe in a maker?

said 3 months ago:
D-Coder said 3 months ago:

Then we get to own them all!

onion2k said 3 months ago:

Going by human history the fact there is intelligent indigenous life somewhere doesn't stop some of us deciding we own it.

siphon22 said 3 months ago:

I hope they never find it, cause when they do, that will mean the end for them.

vcavallo said 3 months ago:

real fuckin bummer!

lngnmn1 said 3 months ago:

Probably somebody already thought this, but it seems that life could never escape its original planet - it always self-destruct itself like a too-successful virus which kills its host too quickly.