I'm starting to think that given enough time and space any context in which self replicating structures can occur will give rise to some form of life (as a statistical inevitability).
(I've probably been reading too much sci-fi.)
Alien life does not need to be restricted to matter as we know it; if space itself can give rise to self replicating structures, then it too could be alive.
Beyond that, life could occur in any medium and at any scale (in either space or time).
Even regarding terrestrial life, how long did it take for us to notice microbes (as something other than a curse from god)?
There could even be macroscopic lifeforms moving so quickly that we are unable to see them.
So the answer, as far as I can tell, is really that it depends on the kind of life we're referring too.
And if it's too far outside the human context of understanding or perception, then the answer is no.
By looking at what happened in earth judging it is a normal likelihood for a cell to form within billion year and evolve to us within 4 billion years, is nuts.
Scientists thinks this way because they have no idea about what statistical possibility of this to happen in such time.
What happened and happening in Earth even if not a miracle to one then it is result of a luck statistically impossible to find anywhere in cosmos.
It is worth to mention that all living beings in earth are descendants of same cell. Even in earth there is no sign of multiple different cell formation which shows how lucky we were.
You’re confusing the odds of a specific lottery ticket hitting the jackpot with any ticket winning. Someone will win fairly regularly.
So yea, the odds of life evolving to something genetically compatible with humanity when we did might be tiny, but we aren’t the only possible form of intelligent multicellular tool using life and it could have happened +/- a few billion years. Given earth starting 5 billion years ago the odds of some intelligent civilization eventually showing up might actually be fairly high, we just don’t have enough data to know.
A chemical soup and enough porous rocks down at the bottom of the ocean to operate as reactors powering endothermic reactions.
These are spread across the entire surface of the earth.
If, by chance, some set of reactions occur forming molecules (or groups of molecules) that catalyse their own formation, then you have constrained self-replication.
Once you have this - and you only need it once, there's an exponential (s-curve really) boom in the prevalence of the chemicals in question.
Any changes to these molecules that preserve the self-replicating nature of the soup will be preserved to an extent and those changes that improve self-replication will not only be preserved but will begin to outpace the parents.
If, for example, I stick a little hydrogen on the front of a structure it'll develop the ability to trace along ion lines.
A chemical soup that hunts its own food.
Of course, these mutations can lead to divergence - which eventually leads to a pseudo-competition.
Step by step, piece by piece, complexity builds up.
Structures integrate and develop the ability to funnel 'food' to where it needs to go for transformation.
And if it is possible for this to happen, then given enough time and enough distinct reactors, it is not simply possible - it is absolutely inevitable.
> It is worth to mention that all living beings in earth are descendants of same cell. Even in earth there is no sign of multiple different cell formation which shows how lucky we were.
I don't see why this has to be the case. If unlikely conditions are correct for something unlikely to occur, then it's not longer unlikely to occur multiple times.
E.g. if you play around with chemical reactions and you hit the right conditions, it usually happens all over the place, and not just one molecule combining.
We don't even really have an agreed-upon definition of life, so the question is basically non-sensical. Alive are the things we say are alive, which is mostly stuff like us: some type of metabolism, growth, response to stimuli. By that definition we would certainly recognize it, at least up close.
If we're willing to expand the definition of life, e.g. to accept some type of self-aware computer as alive, then we'd have to tweak the definition, such as it is, and then we're no longer talking about "life" as we think of the word today.
I guess people often wonder about other biochemistries. As far as I know, from a semester of undergrad astrobiology, we don't currently consider those very likely. Silicate chemistries were speculated for decades, but the chemical dynamics just don't tend to work out. The other main idea was ammonia as solvent, but that'd be hardly exotic, and the current thinking is that biochemistry would be entirely too slow at the temperatures where ammonia is liquid.
The wilder ideas, like high energy chemistries on the surface of neutron stars only ever appear in science fiction. (Excepting the odd paper from the seventies, but that was a strange time.)
Maybe people will accuse me of a lack of imagination, but I think it's telling that these threads are almost always mainly the home of comments shouting the word "quantum" like it means something, or getting their information from Mass Effect.
I do think it's an interesting question whether we'd be able to recognize other types of intelligence, but I am pretty sure we'd be able to recognize other types of life.
(By the way, the article seems to be mostly about whether we'd recognize alien life seen through a telescope, but that hasn't deterred speculation about other kinds of life in the thread.)
Source: I actually studied this in college, for a bit.
> We don't even really have an agreed-upon definition of life, so the question is basically non-sensical.
...
> I am pretty sure we'd be able to recognize other types of life.
...
> Source: I actually studied this in college, for a bit.
So, let me summarize. You find the question non-sensical, then you are sure you know the answer, and finally you appeal to authority (your own) to elevate your opinion over those of us mere common-sense mortals.
Sorry, I'd have liked to give more weight to your angle, but you kinda made that hard.
Yeah, I didn't express myself very clearly, sorry.
Let me try again: I think our various definitions of life are not the actual definition that most astronomers have in their head. I think the actual definition people believe is "I know it when I see it." Two illustrative examples:
Let's say we find a system of chemical reactions going on somewhere that meets most definitions: self-regulating, initial chemical seeds as a basis for heredity, some chain of triggers that causes it to look like it's responding to a stimulus.... This is isn't far-fetched, reactions like this exist in a lab. I don't think we'd call that thing alive - we don't currently. There would be arguments, but most people would probably agree it's a technicality.
Now let's say we find something totally way out there crazy from a science fiction book, like a naturally occurring "computer" running an alien civilization on it. It doesn't have homeostasis - would we call it alive? Most people probably would.
I guess I am prposing that the prevailing actual definition of life that lives in our heads is probably closer to "would I feel bad about killing it?" By both this and the more technical definition, we'd almost certainly recognize it, at least when studied up close. (But probably not through a telescope.)
Is that more sensible?
> you appeal to authority (your own) to elevate your opinion over those of us mere common-sense mortals.
I mean, I'm actually kind of arguing in favor of a common-sense definition, and it's a comment on the internet, which would take me three times as long to type if I sourced it. I would do that for a blog post, but I don't even know if anyone is going to read this :)
But, in fact, this is all so abstract that I wouldn't know what to cite. I still think having an idea of biochemistries, the energy scales, etc. makes someone in the field more qualified to speculate than completely uninformed internet comments.
>We don't even really have an agreed-upon definition of life, so the question is basically non-sensical.
I disagree. The most common definition used by working astrobiologists goes along the line of "chemical system that can self-sustain and can undergo darwinian evolution". Our definition of life is intricately tied with our theories about life's origins, and the counter-examples to that definition are fictional and their premise falls apart on closer examination.
Let's take the self-aware computer you mentioned. How would such a computer come to being, exactly? It could have been built by something that does satisfy the above definition (in which case you could consider the computer not alive, but a biosignature). Or it could have been built through some darwinian process, and you're still firmly within the above definition.
Steve Benner has a nice paper about this. DOI: 10.1089/ast.2010.0524
The article doesn't actually address the problems with the 'evolutionary definition', probably because it would mean trying to chip away at a theory that a lot of people spent a lot of time trying to disprove.
> Alive are the things we say are alive, which is mostly stuff like us: some type of metabolism, growth, response to stimuli. By that definition we would certainly recognize it, at least up close.
I don't think I expressed myself very clearly, but I actually agree with you on most counts. The definition you listed is also the one I mentioned + evolution.
> What about fire?
I actually rambled about fire, and then deleted the paragraph because the comment was already all over the place. Fire, to me, is a good example of the "good definition" problem I mentioned. I guess we'd all agree it doesn't respond to stimuli, and a necessary property of having a metabolism would be some kind of homeostasis. It also doesn't undergo evolution.
But rejecting it on those grounds doesn't feel complete. Let's say we find some chemical reaction that does self-regulate. This exists in a lab or computer modeling (e.g. https://doi.org/10.1073/pnas.2022987118). Let's say its properties are determined by some initial chemical markers: a basis for heredity. Would we now call it alive?
I don't think we would. I think our definition of life is "I know it when I see it" and the more formal definitions we've tried on in astrobiology are basically just retrofitted to the examples we know or can think of.
> we don't even really have an agreed-upon definition of life
Regulated metabolism. Homeostasis. I think that's close to capturing the idea we're after. A self-aware computer still has to store its bits somewhere, and get energy and material to do that, presuming it wants to stay alive. That process might as well be called metabolism. Unless it is just totally alien (heh) physics, there would be some kind of metabolism, and localized regions which create an environment suitable for that metabolism to place. That would, if nothing else, produce heat and unusual compounds.
Are viruses alive? They aren't commonly considered to be. They don't have a regulated metabolism without parasitising on the cells of other organisms.
But then again, I doubt humans would have homeostasis for long without their microflora. How is that different? Isn't a virus just a more extreme case of symbiosis? What about less extreme obligate parasites?
Life defies categorization. At best you can find common markers (in addition to the ones you've mentioned, the traits required for natural selection to occur - i.e. reproduction, variation in trait, and variance in offspring - may also be of interest), but in the end it boils down to the anthropocentric notion of "things like us", which isn't very useful outside earth.
This was a good write up as it contained criteria and points for "defining life", it was nice to have a refresher on the meaning of "entropic" life as well.
I've often thought if complex extraterrestrial beings were discovered they may not "look" much different than anything found on earth, since the spectrum is so vast on this planet (bacteria, plants, mammals, cephalopods, etc.) - considering the universal confines of physics and locomotion.
Isn't there something special about crab/spider anatomy as well and it being very "evolutionarily stable" or something? Cannot recall any papers or information on specifics here at the moment.
Meanwhile, I always laugh watching old Twilight Zone episodes and how they have regular humans playing aliens - they don't even bother to differentiate them as a species (likely because of available technology) but think this can work well in a way.
He talks about why certain things simply make sense. Like how wings evolved six times, why communication via sound is simple and communication via some sort of telepathy is not, and why it makes sense for a large animal to be symmetric. From that he reasons why alien life probably wouldn't look all that different.
Communication through sound is just vibrating your inner organs at a pattern of frequencies, causing the air to vibrate at the same frequency, and resulting in someone else's ear drums vibrating at the same frequency. This causes thoughts to spontaneously appear in your partner's head. How is this different from telepathy?
Who is to say that is a universal phenomenon? May have something to do with our level of gravity, life cycle of the blastocyst, metabolic requirements from respiration, other fauna competition, etc. Which is not to say there is a better alternative on the table, but I would hesitate to say that we should expect crabs on other planets.
Edit: Kicking myself over the missed opportunity to say "space crabs" or a Zoidberg reference
The spectrum on this planet really isn't all that vast. Sure, to you looking at an organism's morphology it looks vastly different, but so do dog breeds from eachother yet they are all dogs. You have a lot in common with all forms of life in terms of how your cell biology works, because we all share a common ancestor.
Life on another planet might originate from an ancestor that functions dramatically different than the last common ancestor for all life on Earth, and that might have huge implications for what a potential multicellular organism with this evolutionary trajectory would look like (if such life even utilized multicellularity, or cells at all)
Remember when most of the known exoplanets were hot Jupiter-like worlds, so it looked for a moment that perhaps those were the dominant type of planet, but then it became clear that this type of planet was commonly detected just because they were the only type of planet our techniques were capable of detecting?
Same, but for life. We’re probably only going to find the kind of life that has the characteristics and behaviors that we currently recognize as life, and is in a place we think of pointing our telescopes at, and our telescopes are a fine enough sieve to see.
At some point, if you stretch the definition of life too far, what's the point? Like, what's the point of saying a rock is alive? We've got them everywhere, we know they exist everywhere but we can't really do anything with that info.
Knowing something is alive gives us a basis for interacting with it. Saying we found life on Mars isn't important because we found life there. It's important because it challenges or confirms our expectations about so many other things.
It's kind of like shooting hoops. The hoop stays in the same place and we try and throw the ball into it from different angles. Each angle we can throw it in from teaches us something new. If you took that hoop and just decided that you get a point by moving the hoop to the ball instead, what does that actually help us with?
Another way of saying it. If everyone is a superhero, then nobody is.
Disappointed to see there is no mention of Lem's Solaris, whose devoted large paragraphs to this very question.
For a very enlightening, very poetic short story from a little known author, I would encourage sci-fi fans to search for "La porcelaine de l'univers" from Bruno Vizerie.
One interesting research group tackling this question is ex-computer engineer, currently biologist Prof. Micahel Levine's group.
They built xenobots (biological robots) from frog cells which are not evolutionarily programmed to do tasks which they accomplished. Their research in part deals with emergence of agency at multi-cellular level. And they want to get at the fundamental signatures of what makes some collection of agents into a new single agent at an higher level.
When I got my teaching credential, I had to take a biology class because I hadn’t taken any biology as an undergrad (I also had to take government and P.E. as well for the same reason—having aced the AP American History exam 17 years earlier in high school spared me from having to take an American History class). One of the things that sticks with me still is the somewhat inevitability about the formation of cell membranes given the characteristics of the atoms that compose the molecules that compose the membrane. I was left thinking that life like as we know it on earth might, in fact, be very much a likely outcome of any planet of suitable size, location and composition.
Nowhere in nature (that we know of) does any organism make a membrane from scratch. All membranes are extended from an existing membrane, and then pinched off. Possibly, all life and all its existing membranes were extended from a primordial membrane.
Arguably, DNA, RNA, and the proteinome are just the universal membrane's way of making more membrane more efficiently.
I’m surprised there isn’t more discussion of life as a kind of information processing. This would put life on a spectrum from viruses (very little or arguably no intrinsic information processing) to humans, which can process even abstract information. But it would also include the kind of life we might potentially find in Jupiter’s clouds, or in the layers of the sun.
Discussing life in terms of Darwinian evolution or chemical complexity seems to miss the point. I’d be happy to consider an AI or a cloud “alive”, even if (like a virus) it requires help to replicate.
But we are... the product of code, read by machines, processing input to produce decisions.
How are not information processors ? Do you think computers are not a natural extension of us ?
There is absolutely discussion of life as information processing, for instance Stanislas Dehaene is super interesting but I ve heard conferences in biochemistry explaining why all amino acid would work to code information, but the 4 DNA uses have chemical properties that help persist and clone it better and the like.
Sorry, I meant that the article doesn’t talk about life as information processing. Perhaps I should have said, “I’m surprised there wasn’t”. Although I got about ¾ of the way through it so maybe I missed it. But at the time of posting, nothing in these threads either.
Readit News
(I've probably been reading too much sci-fi.)
Alien life does not need to be restricted to matter as we know it; if space itself can give rise to self replicating structures, then it too could be alive.
Beyond that, life could occur in any medium and at any scale (in either space or time).
Even regarding terrestrial life, how long did it take for us to notice microbes (as something other than a curse from god)?
There could even be macroscopic lifeforms moving so quickly that we are unable to see them.
So the answer, as far as I can tell, is really that it depends on the kind of life we're referring too.
And if it's too far outside the human context of understanding or perception, then the answer is no.
So yea, the odds of life evolving to something genetically compatible with humanity when we did might be tiny, but we aren’t the only possible form of intelligent multicellular tool using life and it could have happened +/- a few billion years. Given earth starting 5 billion years ago the odds of some intelligent civilization eventually showing up might actually be fairly high, we just don’t have enough data to know.
A chemical soup and enough porous rocks down at the bottom of the ocean to operate as reactors powering endothermic reactions.
These are spread across the entire surface of the earth.
If, by chance, some set of reactions occur forming molecules (or groups of molecules) that catalyse their own formation, then you have constrained self-replication.
Once you have this - and you only need it once, there's an exponential (s-curve really) boom in the prevalence of the chemicals in question.
Any changes to these molecules that preserve the self-replicating nature of the soup will be preserved to an extent and those changes that improve self-replication will not only be preserved but will begin to outpace the parents.
If, for example, I stick a little hydrogen on the front of a structure it'll develop the ability to trace along ion lines.
A chemical soup that hunts its own food.
Of course, these mutations can lead to divergence - which eventually leads to a pseudo-competition.
Step by step, piece by piece, complexity builds up.
Structures integrate and develop the ability to funnel 'food' to where it needs to go for transformation.
And if it is possible for this to happen, then given enough time and enough distinct reactors, it is not simply possible - it is absolutely inevitable.
I don't see why this has to be the case. If unlikely conditions are correct for something unlikely to occur, then it's not longer unlikely to occur multiple times.
E.g. if you play around with chemical reactions and you hit the right conditions, it usually happens all over the place, and not just one molecule combining.
If we're willing to expand the definition of life, e.g. to accept some type of self-aware computer as alive, then we'd have to tweak the definition, such as it is, and then we're no longer talking about "life" as we think of the word today.
I guess people often wonder about other biochemistries. As far as I know, from a semester of undergrad astrobiology, we don't currently consider those very likely. Silicate chemistries were speculated for decades, but the chemical dynamics just don't tend to work out. The other main idea was ammonia as solvent, but that'd be hardly exotic, and the current thinking is that biochemistry would be entirely too slow at the temperatures where ammonia is liquid.
The wilder ideas, like high energy chemistries on the surface of neutron stars only ever appear in science fiction. (Excepting the odd paper from the seventies, but that was a strange time.)
Maybe people will accuse me of a lack of imagination, but I think it's telling that these threads are almost always mainly the home of comments shouting the word "quantum" like it means something, or getting their information from Mass Effect.
I do think it's an interesting question whether we'd be able to recognize other types of intelligence, but I am pretty sure we'd be able to recognize other types of life.
(By the way, the article seems to be mostly about whether we'd recognize alien life seen through a telescope, but that hasn't deterred speculation about other kinds of life in the thread.)
Source: I actually studied this in college, for a bit.
...
> I am pretty sure we'd be able to recognize other types of life.
...
> Source: I actually studied this in college, for a bit.
So, let me summarize. You find the question non-sensical, then you are sure you know the answer, and finally you appeal to authority (your own) to elevate your opinion over those of us mere common-sense mortals.
Sorry, I'd have liked to give more weight to your angle, but you kinda made that hard.
Let me try again: I think our various definitions of life are not the actual definition that most astronomers have in their head. I think the actual definition people believe is "I know it when I see it." Two illustrative examples:
Let's say we find a system of chemical reactions going on somewhere that meets most definitions: self-regulating, initial chemical seeds as a basis for heredity, some chain of triggers that causes it to look like it's responding to a stimulus.... This is isn't far-fetched, reactions like this exist in a lab. I don't think we'd call that thing alive - we don't currently. There would be arguments, but most people would probably agree it's a technicality.
Now let's say we find something totally way out there crazy from a science fiction book, like a naturally occurring "computer" running an alien civilization on it. It doesn't have homeostasis - would we call it alive? Most people probably would.
I guess I am prposing that the prevailing actual definition of life that lives in our heads is probably closer to "would I feel bad about killing it?" By both this and the more technical definition, we'd almost certainly recognize it, at least when studied up close. (But probably not through a telescope.)
Is that more sensible?
> you appeal to authority (your own) to elevate your opinion over those of us mere common-sense mortals.
I mean, I'm actually kind of arguing in favor of a common-sense definition, and it's a comment on the internet, which would take me three times as long to type if I sourced it. I would do that for a blog post, but I don't even know if anyone is going to read this :)
But, in fact, this is all so abstract that I wouldn't know what to cite. I still think having an idea of biochemistries, the energy scales, etc. makes someone in the field more qualified to speculate than completely uninformed internet comments.
I disagree. The most common definition used by working astrobiologists goes along the line of "chemical system that can self-sustain and can undergo darwinian evolution". Our definition of life is intricately tied with our theories about life's origins, and the counter-examples to that definition are fictional and their premise falls apart on closer examination.
Let's take the self-aware computer you mentioned. How would such a computer come to being, exactly? It could have been built by something that does satisfy the above definition (in which case you could consider the computer not alive, but a biosignature). Or it could have been built through some darwinian process, and you're still firmly within the above definition.
Steve Benner has a nice paper about this. DOI: 10.1089/ast.2010.0524
The article doesn't actually address the problems with the 'evolutionary definition', probably because it would mean trying to chip away at a theory that a lot of people spent a lot of time trying to disprove.
> Alive are the things we say are alive, which is mostly stuff like us: some type of metabolism, growth, response to stimuli. By that definition we would certainly recognize it, at least up close.
What about fire?
> What about fire?
I actually rambled about fire, and then deleted the paragraph because the comment was already all over the place. Fire, to me, is a good example of the "good definition" problem I mentioned. I guess we'd all agree it doesn't respond to stimuli, and a necessary property of having a metabolism would be some kind of homeostasis. It also doesn't undergo evolution.
But rejecting it on those grounds doesn't feel complete. Let's say we find some chemical reaction that does self-regulate. This exists in a lab or computer modeling (e.g. https://doi.org/10.1073/pnas.2022987118). Let's say its properties are determined by some initial chemical markers: a basis for heredity. Would we now call it alive?
I don't think we would. I think our definition of life is "I know it when I see it" and the more formal definitions we've tried on in astrobiology are basically just retrofitted to the examples we know or can think of.
Is not also some kind of metabolism also assumed?
Regulated metabolism. Homeostasis. I think that's close to capturing the idea we're after. A self-aware computer still has to store its bits somewhere, and get energy and material to do that, presuming it wants to stay alive. That process might as well be called metabolism. Unless it is just totally alien (heh) physics, there would be some kind of metabolism, and localized regions which create an environment suitable for that metabolism to place. That would, if nothing else, produce heat and unusual compounds.
But then again, I doubt humans would have homeostasis for long without their microflora. How is that different? Isn't a virus just a more extreme case of symbiosis? What about less extreme obligate parasites?
Life defies categorization. At best you can find common markers (in addition to the ones you've mentioned, the traits required for natural selection to occur - i.e. reproduction, variation in trait, and variance in offspring - may also be of interest), but in the end it boils down to the anthropocentric notion of "things like us", which isn't very useful outside earth.
I've often thought if complex extraterrestrial beings were discovered they may not "look" much different than anything found on earth, since the spectrum is so vast on this planet (bacteria, plants, mammals, cephalopods, etc.) - considering the universal confines of physics and locomotion. Isn't there something special about crab/spider anatomy as well and it being very "evolutionarily stable" or something? Cannot recall any papers or information on specifics here at the moment.
Meanwhile, I always laugh watching old Twilight Zone episodes and how they have regular humans playing aliens - they don't even bother to differentiate them as a species (likely because of available technology) but think this can work well in a way.
edit word
He talks about why certain things simply make sense. Like how wings evolved six times, why communication via sound is simple and communication via some sort of telepathy is not, and why it makes sense for a large animal to be symmetric. From that he reasons why alien life probably wouldn't look all that different.
Edit: Kicking myself over the missed opportunity to say "space crabs" or a Zoidberg reference
Life on another planet might originate from an ancestor that functions dramatically different than the last common ancestor for all life on Earth, and that might have huge implications for what a potential multicellular organism with this evolutionary trajectory would look like (if such life even utilized multicellularity, or cells at all)
[1] https://eukaryotewritesblog.com/2021/05/02/theres-no-such-th...
Carcinization?
https://xkcd.com/2314/
Same, but for life. We’re probably only going to find the kind of life that has the characteristics and behaviors that we currently recognize as life, and is in a place we think of pointing our telescopes at, and our telescopes are a fine enough sieve to see.
Knowing something is alive gives us a basis for interacting with it. Saying we found life on Mars isn't important because we found life there. It's important because it challenges or confirms our expectations about so many other things.
It's kind of like shooting hoops. The hoop stays in the same place and we try and throw the ball into it from different angles. Each angle we can throw it in from teaches us something new. If you took that hoop and just decided that you get a point by moving the hoop to the ball instead, what does that actually help us with?
Another way of saying it. If everyone is a superhero, then nobody is.
For a very enlightening, very poetic short story from a little known author, I would encourage sci-fi fans to search for "La porcelaine de l'univers" from Bruno Vizerie.
They built xenobots (biological robots) from frog cells which are not evolutionarily programmed to do tasks which they accomplished. Their research in part deals with emergence of agency at multi-cellular level. And they want to get at the fundamental signatures of what makes some collection of agents into a new single agent at an higher level.
Checkout, https://youtu.be/XheAMrS8Q1c
And a new research paper (inhavent had the time to read yet) on this question of how coherent higher order agents emerge from underlying sub-agents.
https://www.frontiersin.org/articles/10.3389/fpsyg.2019.0268...
Arguably, DNA, RNA, and the proteinome are just the universal membrane's way of making more membrane more efficiently.
Discussing life in terms of Darwinian evolution or chemical complexity seems to miss the point. I’d be happy to consider an AI or a cloud “alive”, even if (like a virus) it requires help to replicate.
How are not information processors ? Do you think computers are not a natural extension of us ?
There is absolutely discussion of life as information processing, for instance Stanislas Dehaene is super interesting but I ve heard conferences in biochemistry explaining why all amino acid would work to code information, but the 4 DNA uses have chemical properties that help persist and clone it better and the like.