"Exo-life" or "life in the universe"?

[Selfsim]

Not quite sure what you mean by "semantic games"...

The topic I raised in the opening post of this thread was the difference between thinking in terms of "exo-life" or "life in the universe"... Are you saying that this whole topic is just a semantic game?

Frankly, the OP struck me as announcing a seemingly deliberate attempt to skirt around the major elephant in the room, which is that other instances of emerged life, are not simply 'a given'. The word-play even announces to the reader that the whole issue of exo-life existence can be avoided by selective use of language labels. I call that semantics .. pure and simple.

Your OP reference to the Copernican Principle, also sounds the warning bells and a 'call-to-arms' to all casually interested amateur astronomers that a key principle of Cosmology is threatened if Earth-life is inferred to not be ubiquitously distributed. I call this game-play.

It's true that no other life-forms have been observed by us terrestrials. Does that mean we are in a "one-life model observable universe"?

Who knows ?? Who can I consult with, who knows the 'truth' of this matter ? Paul Wally's 'Neutral' Demon, who is so far incapable of distinguishing life from non-life, and life from moons ?

Are "observed" and "observable" the same thing?

Once again ... same answer .. when it comes to life ... who knows ?

Has everything observable on the surface of Mars (for instance) already been observed? If so, why do we bother to send new devices there, such as the Curiosity rover?

Has everything observable on the surface of Earth already been observed ?
No way ! The latest predicted estimate of the number of eukaryote species on Earth is ~8.74 million, and only 1.94 million, (22%), have been described/catalogued to date ... all that after 3.2 to 4.4 million years of human evolutionary existence !
With that information, I'd say the above questions are indicative of yet more moot thinking, carrying no meaning.

In fact, an even bigger number of Earth-life species, all share the same life model ... with none displaying evidence of even one single, separate instance of independent emergence. I'd say that's some pretty good evidence that the emergence and subsequent evolution process, is pretty selective ... in spite of the attempted philosophically motivated co-option of the Copernican Principle into the life topic !

[Colin Robinson]

Then don't use it. You have agency in what you do and what you say.

Yes. But if I invent new words, or give existing words new meanings, I may diminish the chance that others will understand what I say. "Exomoon" is a term in current usage in the scientific community, and that is why I've used it, even though I find it conceptually problematic.

I'm not a fan of the term exolife either

Why are you not a fan of the term "exolife"?

A group or population are part of a single system through interaction: it's a physical organization. A category or collection is based only on similar traits: it's a logical organization. For example, The student body of a college is a group, because they all interact in some manner. However, "freshmen of colleges across the country" is a category, since they do not interact as part of a unitary system.

Life is a system. Life, so far as we can tell, starts and continues and in a manner of thinking is, what I'll call, a hyper-organism with a continuous existence going back billions of years perhaps to a single origin. Life on Mars might be part of that hyper-organism but we don't know if there is life or if it is part of the same genesis because we have reason to believe that dispersal is plausible within our solar system. Life anywhere else in the universe is likely to not be related unless and until a link can be established. Thus, exo has some sort of distinction between us and them.

OK, life on Earth is a system, a population, perhaps a hyperorganism. Life on other worlds (especially worlds in other solar systems) would presumably not be part of the same population. I agree with you about all of this.

Nonetheless, life on other worlds would logically have to possess characteristics in common with life on Earth, as otherwise it would make no sense to call it "life" at all. So the term "life in the universe" makes sense as a category. Life on Earth is a population within that category.

However, balls of matter with certain arbitrary definitions scattered throughout the observable universe is exactly that, unrelated blobs of matter that merely present similar characteristics to a definition.

The balls of matter within this solar system -- the planets and moons -- do interact gravitationally, and have a presumed common origin in an ancient cloud of dust and gases. Why can't they, too, be considered a "population" or "group"?

If the term "exolife" is defensible on the grounds that Earth life is a population, while exolife would be outside that population, can't the terms "exoplanet" and "exomoon" be defended on analogous grounds --that the planets and moons of the solar system are a dynamically interacting group, whereas exoplanets and exomoons are outside that group?

[Colin Robinson]

Frankly, the OP struck me as announcing a seemingly deliberate attempt to skirt around the major elephant in the room, which is that other instances of emerged life, are not simply 'a given'.

"Exolife", if it exists, is not an elephant in the room.

More a case of an elephant light-years away -- observable in principle, but actually observing one will take considerable effort.

Life on Earth is more like an elephant in the room -- why talk about it, we all know it is there?

But it should at least convince us that elephants do exist...

In fact, an even bigger number of Earth-life species, all share the same life model ... with none displaying evidence of even one single, separate instance of independent emergence.

Similarities between species of life on Earth are consistent with the hypothesis that abiogenesis occurred here exactly once. (It is consistent with several other hypotheses also, but the hypothesis that abiogenesis occurred exactly once is the most economical.) If this hypothesis is right, what conclusions follow about life elsewhere?

Either Earth is a typical case of a habitable planet or it isn't.

If Earth is a typical case, and if abiogenesis has occurred once on Earth, then it will have occurred once on each other typical habitable planet.

If Earth is not a typical case, then the presumed fact that abiogenesis has occurred once on Earth tells us nothing at all about whether abiogenesis on habitable planets is frequent or rare.

[Ara Pacis]

Yes. But if I invent new words, or give existing words new meanings, I may diminish the chance that others will understand what I say. "Exomoon" is a term in current usage in the scientific community, and that is why I've used it, even though I find it conceptually problematic.

If they jump off a bridge, will you too?

Why are you not a fan of the term "exolife"?

It goes back to the whole definition of a planet debate. I don't want to use similar terminology for populations and categories because that causes the types of conflations I mentioned earlier in the thread.

OK, life on Earth is a system, a population, perhaps a hyperorganism. Life on other worlds (especially worlds in other solar systems) would presumably not be part of the same population. I agree with you about all of this.

Nonetheless, life on other worlds would logically have to possess characteristics in common with life on Earth, as otherwise it would make no sense to call it "life" at all. So the term "life in the universe" makes sense as a category. Life on Earth is a population within that category.

That's premature. At present, life in the universe is identical to life on earth because it is the only category, so there is no need to differentiate.

The balls of matter within this solar system -- the planets and moons -- do interact gravitationally, and have a presumed common origin in an ancient cloud of dust and gases. Why can't they, too, be considered a "population" or "group"?

If the term "exolife" is defensible on the grounds that Earth life is a population, while exolife would be outside that population, can't the terms "exoplanet" and "exomoon" be defended on analogous grounds --that the planets and moons of the solar system are a dynamically interacting group, whereas exoplanets and exomoons are outside that group?

Depends on the astronomer. but that misses the point, if you were really comparing apples to apples then exolife would not be analogous to exomoon or exoplanet but to exosolarsystem. Planet is not a system, it's a category, so comparing it to life is apples and oranges.

[Colin Robinson]

Depends on the astronomer. but that misses the point, if you were really comparing apples to apples then exolife would not be analogous to exomoon or exoplanet but to exosolarsystem. Planet is not a system, it's a category, so comparing it to life is apples and oranges.

It's just occurred to me that, in all these terms, the prefix "exo" means "remote from us". An apple or orange a few light-years away would presumably be called an "exo-apple" or "exo-orange"…

[Paul Wally]

That's premature. At present, life in the universe is identical to life on earth because it is the only category, so there is no need to differentiate.

Life in the universe, or simply 'life', is a universal. Life on Earth would then be a particular instance of the universal life. A universal has many particular instances, and although the particular instances are differentiated among themselves, they share similarities which make them instances of the same universal. So "life in the universe" is not identical to "life on Earth", simply because a universal cannot be identical to a particular. Even if "life on Earth" is the only instance of "life in the universe", it doesn't make sense to say that they are identical. It would be like saying, one particular apple is identical to the concept of "apple".

The question is then what is the concept of life i.e., the universal of life? Now this universal is something that we can define. So when we define life, we then have a universal called life. There would then be a whole space of possible instances satisfying our definition, our criteria so to speak. The question of the existence of other life is then a question of whether some of the other instances of our concept of life exist in actuality. They may or may not exist in actuality, but they are still logically possible instances of the universal life.

[Selfsim]

Maybe because I defined it as neutral. But your argument implies that neutrality is impossible, and that's why I'm asking, how can the distinction between living and non-living not be a neutral observation, i.e. how can life not be objectively recognizable as life? Is life relative? That would make the fact that we are alive relative too, which is absurd.

Why is it absurd ?
Without sentience, could a rock distinguish life from non-life ? Sentience is an emergent property of life, and it is a fundamental for distinguishing itself.
Gee, there are some things on Earth which cannot be clearly distinguished as 'life' also (viruses, etc) … is this 'absurd', too ?

And I am led to an understanding (by the proposers of Abiogenesis 'theories'), that the reference model for 'life' is 'Earth-life', (and that the exploration of the obs. universe, will lead to enmasse testing to see if that model can then be generalised into a universal theory of life). This, out of sheer necessity, makes it relative to ourselves, which you call 'absurd'.

A theory must have implications beyond the evidence, otherwise it's completely useless as a theory. Now these implications might be inconsistent with future real-world discoveries. Scientific theories are not infallible.

A hypothesis must be capable of making testable, speculative conclusions. Once these conclusions are confirmed, it might be regarded as a theory. In this particular case, at best, it is the track record of successful testable conclusions, which would generate the distinction of the theory's ability to predict.

'The existence of life on Earth, implies life elsewhere', has no basis in direct evidence. It is not a theory. It is a speculative, philosophically based hypothesis, at best.

If your 'theory' of life/abiogenesis has no track record of making successful, testable predictions of life elsewhere, then so be it .. it is useless as a theory for predicting exo-life!

As a hypothesis however .. that's different. It may be capable of making testable speculative conclusions .. so we should get on with making and testing them.

Abiogenesis within the field of Evolutionary Molecular Biology (EMB), has tremendous value.
It is the way in which a piece of research is applied, which makes all the difference .. and the way abiogenesis, (derived from EMB), is being applied as an attempt at predicting exo-life, is completely flawed because its basis for prediction is empirically absent, as well as it dealing in non-linear processes, subject to chaotic environments.

I'm not referring to "evolutionary molecular biological research". I'm saying that anything that doesn't make predictions beyond current evidence is completely useless as a scientific theory. It shouldn't even be called a scientific theory.

Agreed !
Abiogenesis 'theories', (hypotheses), as they presently stand, when used as a method of predicting exo-life, are completely useless !

The Ptolemaic system of the solar system is an example of a theory that's incapable of making novel predictions and it's not even wrong, as Wolfgang Pauli would say. The research program that you're proposing implies that we cannot proceed theoretically unless we have evidence of a second instance of life, but if we cannot proceed theoretically with one instance there's no guarantee that a second instance is going to bring us any closer to solving the problem of abiogenesis. There's no guarantee that an n-th instance is going to solve the problem. That is because the problem is theoretical, that is, to explain how abiogenesis is possible in this universe.

If you acknowledge that the application of Abiogenesis in predicting exo-life elsewhere in the obs universe, is a speculative hypothesis, and not a theory, I have no problem.

Proceeding assuming it is a theory capable of predicting exo-life, is delusional.

By the way, I am not proposing any 'research programs'. Perhaps you forget where this conversation is being conducted ? I am not aware that this board is a platform for reviewing research programs !??

The theory I'm referring to, which explains abiogenesis from established empirically based scientific theories, doesn't exist yet. Since it doesn't exist yet, you cannot know beforehand what it will be capable of predicting.

If it doesn't exist yet, then its not a theory. Its a figment of imagination.

"Fundamentally determinable" is a bit vague, therefore it is not at all clear what it is that is falsified, according to you. I proceed on the premise that the universe and life emergence is intelligible , but that's not the same as deterministic.

And yet you assume its recurrence is predictable ? That sounds like determinable to me !

Inferences drawn from other areas of science do not inevitably form a solid basis for prediction in complex systems, such as life, or complex biochemical pathways.

As I repeatedly tried to make clear: Complexity is a mathematically implicit possibility, and therefore it can follow implicitly from a system defined purely on the basis of physical and chemical laws. These have been computationally demonstrated. The point is that you don't know that these "other areas of science", combined with purely mathematical complexity theory, are insufficient for the development of a theory of abiogenesis capable of making testable predictions.

Then put these 'theories' (hypotheses) to the test ! Most have been tested many times over, and returned null or non results! So there is no evidence to support their speculated predictive capabilities in the real world.

At the moment, these synthesised 'theories' (hypotheses) aren't presented as though they are capable of making accurate predictions about emergences of exo-life, even though many folk read this into those very research papers (ie: improperly infer it from them).

Yes, your definition of hypothesis is not agreed upon. It appears to limit hypothesis to mere mechanical inductive generalization; something a computer can be taught to do. You assume that evidence leads like breadcrumbs to a comprehensive theory of phenomena. Inductive generalization leaves hardly any room for human creativity, conceptual inventiveness and originality.

Empirical science was created specifically to constrain 'human creativity, conceptual inventiveness, and originality' and direct it towards constructive, tangible progress in the real world.

By not using the tools, a story emerges which is merely sci-fi .. just take a look at the titles in this part of the forum for evidence of such !

I have no problems with speculation, so long as it is recognised as speculation. Those who cannot recognise reality when it presents itself, seem to also have lost the desire and/or skills needed to operate the toolset.

[Selfsim]

Life in the universe, or simply 'life', is a universal. Life on Earth would then be a particular instance of the universal life. A universal has many particular instances, and although the particular instances are differentiated among themselves, they share similarities which make them instances of the same universal. So "life in the universe" is not identical to "life on Earth", simply because a universal cannot be identical to a particular. Even if "life on Earth" is the only instance of "life in the universe", it doesn't make sense to say that they are identical. It would be like saying, one particular apple is identical to the concept of "apple".

The question is then what is the concept of life i.e., the universal of life? Now this universal is something that we can define. So when we define life, we then have a universal called life. There would then be a whole space of possible instances satisfying our definition, our criteria so to speak. The question of the existence of other life is then a question of whether some of the other instances of our concept of life exist in actuality. They may or may not exist in actuality, but they are still logically possible instances of the universal life.

The search for exo-life (and subsequent biological testing of samples), IS the test of a speculative version of a universal theory of life.

Until such tests are carried out on a large number of samples sourced from other 'worlds', the theory' (hypothesis), is purely speculative and carries zero significance.

Your opening statement in the above has zero empirical evidence supporting it beyond Earth-life, and has highly questionable theoretical reasoning. At best, it is a philosophically based assertion only and I take exception to the assertion that it represents reality.

Prove it !

[Ara Pacis]

Life in the universe, or simply 'life', is a universal. Life on Earth would then be a particular instance of the universal life. A universal has many particular instances, and although the particular instances are differentiated among themselves, they share similarities which make them instances of the same universal. So "life in the universe" is not identical to "life on Earth", simply because a universal cannot be identical to a particular. Even if "life on Earth" is the only instance of "life in the universe", it doesn't make sense to say that they are identical. It would be like saying, one particular apple is identical to the concept of "apple".

Observation suggests otherwise. If there is one apple, then all apples are the one.

The question is then what is the concept of life i.e., the universal of life? Now this universal is something that we can define. So when we define life, we then have a universal called life. There would then be a whole space of possible instances satisfying our definition, our criteria so to speak. The question of the existence of other life is then a question of whether some of the other instances of our concept of life exist in actuality. They may or may not exist in actuality, but they are still logically possible instances of the universal life.

I thought that archtypes as a serious concept in empiricism went out of fashion with Plato.

[Colin Robinson]

'The existence of life on Earth, implies life elsewhere', has no basis in direct evidence. It is not a theory. It is a speculative, philosophically based hypothesis, at best.

I would put it this way...

The existence of life on Earth, when combined with the notion that Earth is a planet, raises questions like:

* Do other planets have life on them, or is Earth the only planet with life?

* How common or uncommon is it for a planet to have life on it?

* If other planets do have life, what sorts of life do they have? Are the chemistries and morphologies similar or different to those seen here?

* If other planets do not have life, why not? Is it simply because they differ from Earth in ways that mean nothing could live there? Is it because even on a habitable planet, emergence of life is a low-probability thing?

* If life hasn't happened on other Earth-like and chemically-active planets, what has happened? Are there self-perpetuating chemical systems which are not living organisms?

Questions like these have been considered by scientists and non-scientists even since Copernicus presented his argument that Earth is, in fact a planet.

"We don't know" is not an answer that satisfies our curiosity.

All substantial answers (positive or negative) are speculations...

The all-important further question is:

* What sort of research, if any, may answer questions like these?

[Selfsim]

"We don't know" is not an answer that satisfies our curiosity.

So why should curiosity distort the reality of the situation .. that being "unknown" ?
Geee, I thought most humans learned to keep their wants and desires separate from reality around the pre-adolescence years !? (Apparently not !)

All substantial answers (positive or negative) are speculations…

So … ??
Why should that result in the reality of our situation being deliberately distorted by the same process of collective consensus about which speculative 'answer' is correct, or not ?

Sure, follow a line of enquiry .. but don't lose track of the reality of the situation .. which is simply and demonstrably, ... "unknown" !

The all-important further question is:
* What sort of research, if any, may answer questions like these?

Certainly not amateurs reading their philosophically based wants-and-desires into research reports, journals, magazines, biased mass media publications, etc, etc.

"The existence of life on Earth, does not imply life exists elsewhere" .. and;

"We know of extant life on one planet only";

… are statements based in demonstrable reality and theory ... they are supportable by all currently available verifiable, independently observational evidence, and they are falsifiable.

Live with it.

[Colin Robinson]

"We know of extant life on one planet only";

We've attempted a scientific search for life on two planets only...

Certainly not amateurs reading their philosophically based wants-and-desires into research reports, journals, magazines, biased mass media publications, etc, etc.

In that case, we'd better rely on professionals, who combine specialist knowledge of planetary astronomy and biology. The astrobiologists.

Mind you, not all astrobiologists consider philosophy irrelevant to what they are doing.

[Paul Wally]

Why is it absurd ?
Without sentience, could a rock distinguish life from non-life ? Sentience is an emergent property of life, and it is a fundamental for distinguishing itself.

What does sentience have to do with whether something is alive or not? A tree is a form of life, and there were living trees on Earth long before sentient humans were there to see it as alive. What is your definition of "life" then?

A hypothesis must be capable of making testable, speculative conclusions.

The purpose of an hypothesis is usually to explain some unexplained phenomenon, e.g. the emergence of life. The speculative part is the hypothesis, and the conclusions (consequences) are implied by the hypothesis for different test conditions.

Once these conclusions are confirmed, it might be regarded as a theory.

No, there is no "once". The number of conclusions depend on the number of possible test conditions, and we cannot know beforehand whether some test is going to refute the hypothesis. An hypothesis is regarded as a theory when it's well confirmed, i.e. when it has already made several successful predictions. But the difference between hypothesis and theory is just a matter of degree of confirmation, so it's not clear when an hypothesis becomes a theory. I don't think it's really important anyway. Both hypotheses and theories are fallible.

In this particular case, at best, it is the track record of successful testable conclusions, which would generate the distinction of the theory's ability to predict.

"Ability to predict" and "ability to make correct predictions" are two different things. A universal theory based on fundamental principles will have the ability to predict consequences for a wide range of possible test conditions. That such a theory will make correct predictions is not something that can be known beforehand.

'The existence of life on Earth, implies life elsewhere', has no basis in direct evidence. It is not a theory. It is a speculative, philosophically based hypothesis, at best.

And I didn't say that, nor did anyone else in this thread say that. So why bring it up?

If your 'theory' of life/abiogenesis has no track record of making successful, testable predictions of life elsewhere, then so be it .. it is useless as a theory for predicting exo-life!

As far as I'm concerned, there is no theory of abiogenesis yet. I'm proposing the possibility of such a theory, and I see no reason why such a theory should be impossible.

Abiogenesis within the field of Evolutionary Molecular Biology (EMB), has tremendous value.
It is the way in which a piece of research is applied, which makes all the difference .. and the way abiogenesis, (derived from EMB), is being applied as an attempt at predicting exo-life, is completely flawed because its basis for prediction is empirically absent, as well as it dealing in non-linear processes, subject to chaotic environments.

I don't know who you're talking about here. I'm sure there's a wide variety of different ideas out there on how to approach the problem.

Abiogenesis 'theories', (hypotheses), as they presently stand, when used as a method of predicting exo-life, are completely useless !
If you acknowledge that the application of Abiogenesis in predicting exo-life elsewhere in the obs universe, is a speculative hypothesis, and not a theory, I have no problem.

I cannot comment because I don't know what you are talking about specifically. Do you have any specific examples of such attempts at predicting exo-life?

If it doesn't exist yet, then its not a theory. Its a figment of imagination.

The important question is of course whether such a theory can exist, which is what I was talking about this whole time. In my view: I don't see why such a theory should be impossible.

And yet you assume its recurrence is predictable ? That sounds like determinable to me !

"Recurrence" means that the same thing happens again. So that word is not applicable here. If exo-life exists, then it exists independently from Earth-life. Maybe it has existed even before Earth-life. In that case we would be the "recurrence". If we had a theoretical explanation of how life in the universe is possible, we should be able to derive the necessary conditions for the likely emergence of life from such a theory. If such a theory is impossible then the emergence of life is unintelligible. If the theory makes wrong predictions then we revise our basic assumptions.

Then put these 'theories' (hypotheses) to the test ! Most have been tested many times over, and returned null or non results! So there is no evidence to support their speculated predictive capabilities in the real world.

Which theories?

At the moment, these synthesised 'theories' (hypotheses) aren't presented as though they are capable of making accurate predictions about emergences of exo-life, even though many folk read this into those very research papers (ie: improperly infer it from them).

Looks like the normal trial-and-error process of science, but this is all very general so I don't know what these theories are that you're referring to.

Empirical science was created specifically to constrain 'human creativity, conceptual inventiveness, and originality' and direct it towards constructive, tangible progress in the real world.

No, empirical science is about testing our ideas against empirical findings.

I have no problems with speculation, so long as it is recognised as speculation. Those who cannot recognise reality when it presents itself, seem to also have lost the desire and/or skills needed to operate the toolset.

Yet it seems that you don't believe that reality presents itself to us. Is a tree alive when nobody's looking?

The search for exo-life (and subsequent biological testing of samples), IS the test of a speculative version of a universal theory of life.

Until such tests are carried out on a large number of samples sourced from other 'worlds', the theory' (hypothesis), is purely speculative and carries zero significance.

Since we don't yet have this universal theory of life, I don't know what it is that you want to test. I'm curious as to exactly what these samples are supposed to test in absence of any theory.

Your opening statement in the above has zero empirical evidence supporting it beyond Earth-life, and has highly questionable theoretical reasoning. At best, it is a philosophically based assertion only and I take exception to the assertion that it represents reality.

The fact that the concept of life is a universal doesn't require empirical evidence. "Life" is definable as a general concept, and that makes it a universally applicable concept. What this means is that it makes sense to ask the empirical question: "Is there life elsewhere in the universe?". If life was not a universally applicable concept, the question would have no meaning.

Observation suggests otherwise. If there is one apple, then all apples are the one.

No, it's not about observation. If the last apple was eaten , we would still have the concept of "apple".

I thought that archtypes as a serious concept in empiricism went out of fashion with Plato.

Well, it's not about what's the latest fashion but about whether you understand what I'm talking about. My point is that if we have a definition of something, that definition applies universally. That's the nature of definition. If we define the concept of life then that concept applies universally.

Sure, follow a line of enquiry .. but don't lose track of the reality of the situation .. which is simply and demonstrably, ... "unknown" !

"Unknown" is not the reality of the situation. The reality of the situation exists whether we know about it or not. I think you should try to get this distinction between "reality" and "knowledge" sorted out.

[Ara Pacis]

No, it's not about observation. If the last apple was eaten , we would still have the concept of "apple".

we have apples on earth and nowhere else, that is the observation. If there are no more apples and no more us along with them, then there is no concept.

Well, it's not about what's the latest fashion but about whether you understand what I'm talking about. My point is that if we have a definition of something, that definition applies universally. That's the nature of definition. If we define the concept of life then that concept applies universally.

Fashion, in this sense, implies consensus. There is no consensus in modern empiricism, the scientific method and epistemology that archetypes have any meaning.

And what makes you think a hypothesis is separated from theory only by degree? A hypothesis is a logical conjecture based on observation that is, of course, falsifiable. A theory adds accompanying hypotheses, experimentation, repeatability/predictability, etc. And then there's laws that are something else entirely. Again, you're confusing system and category.

"We don't know" is not an answer that satisfies our curiosity.

That has little to do with empiricism.

All substantial answers (positive or negative) are speculations...

No, explanatory answers that have evidence and are suggestive highly reliable probability estimates are not speculations.

[Colin Robinson]

All substantial answers (positive or negative) are speculations...

No, explanatory answers that have evidence and are suggestive highly reliable probability estimates are not speculations.

The posting you've quoted began with a list of questions about life in the universe. When I said that all substantial answers are speculations, I meant current suggested answers to those questions.

I'd agree that, even in relation to these questions, some suggested answers are more speculative that others.

For instance, compare:

1. the proposition that abiogenesis may have occurred not only on Earth, but also on other worlds with similar compositions, temperatures, etc.

2. the proposition (mentioned by Selfsim in the thread "Is Life Inevitable") that the sorts of chaotic chemistries whose outcome on Earth was abiogenesis, might on other planets lead to self-perpetuating but non-living chemical systems which remain non-living over billions of years.

Proposition 1 (as we keep being reminded) is a generalization from a single example.

Proposition 2, however, is a generalization from no examples at all. There is (as yet) no known case of a planet where the described scenario has occurred.

Proposition 2 is an interesting conjecture, all the same. I'm not sure how much it has been studied... but if it hasn't been, probably it should be. It may turn out to work mathematically. It may even, conceivably, turn out to be true.

[Paul Wally]

we have apples on earth and nowhere else, that is the observation. If there are no more apples and no more us along with them, then there is no concept.

Now I didn't say there would be no more us along with apples. We have concepts of many extinct life-forms, we even have concepts of fictitious life-forms. To have a clearly defined concept of something does not require its existence in actuality.

Fashion, in this sense, implies consensus. There is no consensus in modern empiricism, the scientific method and epistemology that archetypes have any meaning.

Definition of abstract concepts are widely used in both science and mathematics. It has nothing to do with consensus. If life is defined as a certain kind of structural and functional organization, then that mathematical structure defines a space of possibilities all satisfying the definition of the structure. Earth-life forms would then be a particular subset of the entire space of possibilities implied by the definition.

A hypothesis is a logical conjecture based on observation that is, of course, falsifiable.

An hypothesis is a tentative explanation, and explanation usually requires more ingenuity than "logical conjecture based on observation". Sometimes it requires going beyond the evidence to some original principle explaining a wide range of seemingly unrelated phenomena. This way of thinking is called abduction and it's completely different from induction, which seldom if ever explains anything.

[Ara Pacis]

2. the proposition (mentioned by Selfsim in the thread "Is Life Inevitable") that the sorts of chaotic chemistries whose outcome on Earth was abiogenesis, might on other planets lead to self-perpetuating but non-living chemical systems which remain non-living over billions of years.

Proposition 2, however, is a generalization from no examples at all. There is (as yet) no known case of a planet where the described scenario has occurred.

Proposition 2 is an interesting conjecture, all the same. I'm not sure how much it has been studied... but if it hasn't been, probably it should be. It may turn out to work mathematically. It may even, conceivably, turn out to be true.

Would weather/geology count?

[Ara Pacis]

Now I didn't say there would be no more us along with apples. We have concepts of many extinct life-forms, we even have concepts of fictitious life-forms. To have a clearly defined concept of something does not require its existence in actuality.

It was an analogy. We are the apple.

Definition of abstract concepts are widely used in both science and mathematics. It has nothing to do with consensus. If life is defined as a certain kind of structural and functional organization, then that mathematical structure defines a space of possibilities all satisfying the definition of the structure. Earth-life forms would then be a particular subset of the entire space of possibilities implied by the definition.

Abstraction =/= Archetype.

And as a matter of epistemology, how can a categorization scheme nest multiple varieties of something of which only one exists in a universe of possibilities in which none can be empirically predicted to exist? Until you know how life originated here, you have no basis for predicting that such a confluence of events could have happened elsewhere in time and space. Anything else is wishful thinking.

An hypothesis is a tentative explanation, and explanation usually requires more ingenuity than "logical conjecture based on observation". Sometimes it requires going beyond the evidence to some original principle explaining a wide range of seemingly unrelated phenomena. This way of thinking is called abduction and it's completely different from induction, which seldom if ever explains anything.

And you still insist it's the same as a theory, only differing by degree?

[Colin Robinson]

Would weather/geology count?

We're discussing whether the process whose outcome on Earth was abiogenesis, could have a different outcome on another planet.

While there are different theories about the process that led to emergence of life here, all theories (as far as I know) involve a range of organic compounds – amino-acids, for example – reacting chemically with one another in the presence of liquid water. I don't know whether or not the long-term result of such a chemical chaos, on another Earth-like planet, can be a chemical system other than life. But if it can, it would presumably be global chemistry very different from geology as we know it, or weather as we know it.

We might in fact need another word ending in -ology, if such a planet is every discovered.

[Paul Wally]

We're discussing whether the process whose outcome on Earth was abiogenesis, could have a different outcome on another planet.

While there are different theories about the process that led to emergence of life here, all theories (as far as I know) involve a range of organic compounds – amino-acids, for example – reacting chemically with one another in the presence of liquid water. I don't know whether or not the long-term result of such a chemical chaos, on another Earth-like planet, can be a chemical system other than life. But if it can, it would presumably be global chemistry very different from geology as we know it, or weather as we know it.

We might in fact need another word ending in -ology, if such a planet is every discovered.

Yes, there is chemistry wherever there is matter. Perhaps we should use the term 'chemical complexity', then we can ask what the level of chemical complexity is on other planets and moons. We wouldn't make the distinction of Earth chemical complexity and exo-chemical complexity, just the class of phenomena called chemical complexity, and Earth biochemistry is an example of chemical complexity in the universe.

[Gomar]

my opinions:
A)There are no alien, space, other-dimensional, non-human tourists, inhabitants, captains and their 1st mates with pointed ears walking around planet Earth. Thus, there are no aliens capable of doing so in the entire galaxy.

B)no alien artifacts, monoliths, probes, ships, signals, housing, structures, etc. exists on planet Earth. If the Egyptian pyramids had been made of steel, or diamonds, or there were elevators, lights, plumbing, high tech tools, alien machinery etc. then anyone would have no doubt that aliens made them.

C)No artificial placement, terra-forming, movements, of stars has ever been observed. Thus, no aliens exist capable of moving stars as easy as we place flowers, homes, roads, etc.

D)No explosions, or unusual activity, or sudden disappearance of stars or galaxies has been detected. Thus, proving, aliens do not wage war, nor blow up each other's worlds.

E)Humans are not caught and sold as slaves by aliens, as Africans were 500 years ago, proving no human slave market exists.

I could go on with many examples as to why aliens have never been, and never will be, on Earth, but I have to feed my dog, and my goldfish
which are my pets... proving I am more intelligent, because I am not their pet.

[Ara Pacis]

Yes, there is chemistry wherever there is matter. Perhaps we should use the term 'chemical complexity', then we can ask what the level of chemical complexity is on other planets and moons. We wouldn't make the distinction of Earth chemical complexity and exo-chemical complexity, just the class of phenomena called chemical complexity, and Earth biochemistry is an example of chemical complexity in the universe.

Now this I can agree with. Congratulations, you won the thread.

[Selfsim]

Yes, there is chemistry wherever there is matter. Perhaps we should use the term 'chemical complexity', then we can ask what the level of chemical complexity is on other planets and moons. We wouldn't make the distinction of Earth chemical complexity and exo-chemical complexity, just the class of phenomena called chemical complexity, and Earth biochemistry is an example of chemical complexity in the universe.

There is chemical complexity on Titan (& Venus, etc). But it seems reasonable to conclude that there are no sentient beings revealing themselves to us by, for example: sending us probes and signals or leaving evidence of past structures where they modified their environments to suit their needs. The complex chemistry there has produced different results from Earth's, (in spite of the same chemicals laws being followed), but under this idea, this would just be another variant instance of chemical complexity in the universe.

Should we then call this 'Titan-complex-chemistry' (TCC) and, perhaps Earth's should be 'Earth-complex-chemistry' (ECC)? Mars has chemical complexity too .. 'Mars-chemical-complexity' (MCC), perhaps? So does Saturn (SCC), Neptune (NCC), Uranus (UCC), Europa (ECC), Enceladeus (EnCC), and so on … they all exhibit environmental dissimilarity from eachother ...

They're all part of the same Solar System … should we call that 'Solar System Chemical Complexity' (SSCC) …?... there are other planetary systems too … should we call them 'Other Planetary Systems' complex chemistry (OPSCC) …?… hmm .. this is getting complicated … We could start by grouping all these by similar broad characteristics of complex chemistry .. and the physical characteristics, which allow for specific complex chemistries capable/not capable of supporting human-like life emergence … now the only planets for which we have any inklings about, when it comes to the presence/absence of Earth-like life, are the local group … should we then model our categories on these, and give them labels like …. Mercurians, Subterrans, Terrans, Superterrans, Neptunians, Jovians, etc, etc ?

This is starting to sound too much like 'planet vs the exo-planets' again … hmmm .. perhaps we could group them by something more generic .. Class M (Mesoplanet), Class T (Thermoplanet), Class P (Psychroplanet), Class hP (HypoPsychroplanet), etc, etc ?…. anything but planet/exo-planet because that non-Copernican perception theme keeps creeping back in again ! (Even though they might all be different in the chemical complexity detail .. which could make all the difference to the end products they produce (ala Titan, Venus, Earth, Kepler xyz etc) … problem is .. we just don't know enough about what level of initial detail distinguishes 'the necessary conditions', in terms of chemical complexity and end-process life products, (from our generalised abiogenesis theory), viewed from astronomical scales .. but we know that the laws of simple chemistry are universal and are fundamental. There is then the concern that we have no idea about how these map into a self-replicating complex cellular lifeform .. we speculate that process must also be universal, (and its end products), in order for our theory to be able to predict, (otherwise it wouldn't be any use). A formulaic approach almost declares that we should choose parameters for our model we know result in consistent, predictable outcomes .. otherwise the theory might become unstable !!

… We know that there exists a class of natural phenomena, where tiny differences in the initial conditions of many of these sub-chemical complex reactions, imposed by perhaps unpredictably changing environments over arbitrary abiogenesis timeframes, could tip the balance, so as to inhibit the progress towards 'life' (which is defined as being Earth life anyway) … and that this might well be the rule, rather than the exception … who knows ?

Regards

[Selfsim]

As an example of how a particular hypothesised abiogenesis reaction may not go along a clearly predictable pathway, check out what Wiki has to say .. (Mind you, admittedly, they do point out that citations are required for some of the following, but it does serve as a reminder that there are things not so straightforward about one of the apparent 'basics'):

The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not at all a straightforward process. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were formed in high concentration during the Miller–Urey and Oró experiments. The Miller experiment, for example, produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain.
...
More fundamentally, it can be argued that the most crucial challenge unanswered by this theory is how the relatively simple organic building blocks polymerise and form more complex structures, interacting in consistent ways to form a protocell. For example, in an aqueous environment hydrolysis of oligomers/polymers into their constituent monomers would be favored over the condensation of individual monomers into polymers.

Ok.. in spite of these 'doubts' about the viability of this particular process being a good explanation of abiogenesis, (which is not my point), the point I'd like to make is that some chemical variables, like the concentration of inhibiting compounds, are also easily perturbed by micro-environmental fluctuations .. so how many more of such variables exist? If an exo-planet looks like Earth, (when viewed from Earth), does this necessarily imply the same result as what may have happened on Earth, once, billions of years ago? How does one go about developing a theory which could predict those micro-changes which might actually inhibit the abiogenesis ?

syzygy42 has mentioned several other examples of how flux along metabolic pathways, or along signalling pathways in feedback/regulatory networks in present-day biology, can be highly variable. He mentioned that there was a strong argument for a certain amount of noise being required, in order for a biological system to function properly.

How many analogous mechanisms might be involved in the abiogenesis process also, and how sensitive might these be to environmental fluctuations ? What happens when they are perturbed during the process ? Does the end result meet the thresholds for successful input into the next, (perhaps), nested step in the process ?

How can we go about developing a theory which could predict a successful 'exo-outcome', based on things observable from Earth? (Which is Copernically not privileged). Especially when the process might be subject to the same or different dynamicaly unpredictable local weather fluctuations as Earth's ? And how do we make the prediction if these factors are capable of inhibiting the 'expected' outcome ? What really are 'the necessary conditions' .?. and at what scales are they 'the necessary conditions' ?

Does the Copenican Principle have anything to say about why such unpredictable fluctuations can't arise?

Regards

[Colin Robinson]

How many analogous mechanisms might be involved in the abiogenesis process also, and how sensitive might these be to environmental fluctuations ? What happens when they are perturbed during the process ? Does the end result meet the thresholds for successful input into the next, (perhaps), nested step in the process ?

How can we go about developing a theory which could predict a successful 'exo-outcome', based on things observable from Earth? (Which is Copernically not privileged). Especially when the process might be subject to the same or different dynamicaly unpredictable local weather fluctuations as Earth's ? And how do we make the prediction if these factors are capable of inhibiting the 'expected' outcome ? What really are 'the necessary conditions' .?. and at what scales are they 'the necessary conditions' ?

Does the Copenican Principle have anything to say about why such unpredictable fluctuations can't arise?

Could environmental fluctuations result in the chemistry of another Earth-like planet being less complex than the chemistry here? And perhaps stop anything emerging that could undergo darwinian evolution? Maybe yes...

Could environmental fluctuations result in the chemistry of yet another Earth-like planet being more complex than the chemistry here? And perhaps able to undergo a faster and/or more diverse darwinian evolution?

As I understand it, the principle of mediocrity (or Copernican principle) doesn't rule out differences between planets. It just says we may not assume that the differences will necessarily result in our own planet having the most of something.

Regards

[Selfsim]

Could environmental fluctuations result in the chemistry of another Earth-like planet being less complex than the chemistry here? And perhaps stop anything emerging that could undergo darwinian evolution? Maybe yes...

Could environmental fluctuations result in the chemistry of yet another Earth-like planet being more complex than the chemistry here? And perhaps able to undergo a faster and/or more diverse darwinian evolution?

As I understand it, the principle of mediocrity (or Copernican principle) doesn't rule out differences between planets. It just says we may not assume that the differences will necessarily result in our own planet having the most of something.

Regards

Well ya know, Colin ... even though these conversations have been difficult, if one looks back over some of the issues raised, I do find a semblance of a basis for looking at this whole matter, in a different way.

Paul's point has been that he can't see why a generalised theory could not be developed. I have never actually thought that it couldn't. (As usual, we are addressing different matters ... beats me why this always seems to be the case ... ??). Anyway, my only issue is that if one attempts to do this, one should be deliberately cautious not to impose, (even accidentally), a deterministic philosophical view in order to have the outcome predictable ... This way of doing things actually breaks the traditional process by which classical science is normally done. (I'd have to come up with another post/thread to explain where I'm coming from, on this point).

Just a quick comment on your question about: "another Earth-like planet being more complex than the chemistry here? And perhaps able to undergo a faster and/or more diverse darwinian evolution?" ... In a very general sense, if a system gets 'too' complex, I think it it might completely shut down dynamically, as it clogs up with too much complexity .. which interestingly, hints at some optimal value, (and constraints), in order for the dynamics to be sustained. This value should also be tracked in such a generalised model.

I'm sure there are others .. like 'attractors', which would tend to 'rope in' certain 'preferred' behaviours. All of these are generalised parameters one could track (and maybe even simulate) ... its all been considered before, and has many man-years worth of theoretical development effort already poured into it all ... (mainly from the biological sciences stream .. and 'no' .. this hasn't come from anyone who particularly calls themselves an 'Astrobiologist' ).

Randomness is still a very big player in it all, and it is for this reason predictability has to be 'suspended' ... (at least for the time being).

Regards

[Paul Wally]

There is chemical complexity on Titan (& Venus, etc). But it seems reasonable to conclude that there are no sentient beings revealing themselves to us by, for example: sending us probes and signals or leaving evidence of past structures where they modified their environments to suit their needs. The complex chemistry there has produced different results from Earth's, (in spite of the same chemicals laws being followed), but under this idea, this would just be another variant instance of chemical complexity in the universe.

I'm glad we can at least agree on the universality of the concept of chemical complexity.

Should we then call this 'Titan-complex-chemistry' (TCC) and, perhaps Earth's should be 'Earth-complex-chemistry' (ECC)? Mars has chemical complexity too .. 'Mars-chemical-complexity' (MCC), perhaps? So does Saturn (SCC), Neptune (NCC), Uranus (UCC), Europa (ECC), Enceladeus (EnCC), and so on … they all exhibit environmental dissimilarity from eachother ...

Well no. I'm sure you will agree that the name of a planet has nothing to do with the kind of chemistry going on there. So the question is then how we can compare the chemistries of different planets. This is not a difficult problem. Complexity is something measurable in terms of the structural complexity of molecules as well as the dynamic complexity of the chemical processes. These are measurable criteria, and based on such criteria, the chemistries on different planets can be classified. We could go further and compare chemical processes on different planets in terms of their structural similarities, i.e. are there processes structurally similar to Earth biochemical processes?

They're all part of the same Solar System … should we call that 'Solar System Chemical Complexity' (SSCC) …?... there are other planetary systems too … should we call them 'Other Planetary Systems' complex chemistry (OPSCC) …?… hmm .. this is getting complicated … We could start by grouping all these by similar broad characteristics of complex chemistry .. and the physical characteristics, which allow for specific complex chemistries capable/not capable of supporting human-like life emergence … now the only planets for which we have any inklings about, when it comes to the presence/absence of Earth-like life, are the local group … should we then model our categories on these, and give them labels like …. Mercurians, Subterrans, Terrans, Superterrans, Neptunians, Jovians, etc, etc ?

See above.

This is starting to sound too much like 'planet vs the exo-planets' again … hmmm .. perhaps we could group them by something more generic .. Class M (Mesoplanet), Class T (Thermoplanet), Class P (Psychroplanet), Class hP (HypoPsychroplanet), etc, etc ?…. anything but planet/exo-planet because that non-Copernican perception theme keeps creeping back in again ! (Even though they might all be different in the chemical complexity detail .. which could make all the difference to the end products they produce (ala Titan, Venus, Earth, Kepler xyz etc) … problem is .. we just don't know enough about what level of initial detail distinguishes 'the necessary conditions', in terms of chemical complexity and end-process life products, (from our generalised abiogenesis theory), viewed from astronomical scales .. but we know that the laws of simple chemistry are universal and are fundamental. There is then the concern that we have no idea about how these map into a self-replicating complex cellular lifeform .. we speculate that process must also be universal, (and its end products), in order for our theory to be able to predict, (otherwise it wouldn't be any use). A formulaic approach almost declares that we should choose parameters for our model we know result in consistent, predictable outcomes .. otherwise the theory might become unstable !!

As I said, this is about structural comparison between different chemistries, which has nothing to do with the prefix "exo" nor with any planetary classification system that doesn't involve structural comparison between chemistries. As far as I know you are correct that we don't know how the "universal laws of simple chemistry map into self-replicating complex cellular lifeforms", but we can start with simple virtual or artificial chemistry models to see whether something structurally similar to self-replicating units emerge from that. We can then play around with such a model, for example, by randomizing some of variables to see how sensitive the self-replicating outcome is to random variations.

If an exo-planet looks like Earth, (when viewed from Earth), does this necessarily imply the same result as what may have happened on Earth, once, billions of years ago?

It probably doesn't imply the same result, but it might possibly imply a structurally similar (life-like) result, which followed a completely different pathway.

syzygy42 has mentioned several other examples of how flux along metabolic pathways, or along signalling pathways in feedback/regulatory networks in present-day biology, can be highly variable. He mentioned that there was a strong argument for a certain amount of noise being required, in order for a biological system to function properly.

Yes, but life has structure, if it was just noise there would be no biology and no "us" to talk about it. The structure is that which is invariant with respect to random perturbations (noise).

How many analogous mechanisms might be involved in the abiogenesis process also, and how sensitive might these be to environmental fluctuations ? What happens when they are perturbed during the process ? Does the end result meet the thresholds for successful input into the next, (perhaps), nested step in the process ?

Good question, and we don't know yet. That's why we must develop testable models.

[Selfsim]

There is chemical complexity on Titan (& Venus, etc). But it seems reasonable to conclude that there are no sentient beings revealing themselves to us by, for example: sending us probes and signals or leaving evidence of past structures where they modified their environments to suit their needs. The complex chemistry there has produced different results from Earth's, (in spite of the same chemicals laws being followed), but under this idea, this would just be another variant instance of chemical complexity in the universe.

I'm glad we can at least agree on the universality of the concept of chemical complexity.

Hmm … 'gladness' may be a little premature here, Paul. I was 'trying the concept on' … my previous post was intended to contain a degree of parody of the current way 'exo-life' matters are interpreted by the 'custodians' of all things 'exo-life' (ie: the notorious 'Astrobiologists' ..).

Even universality of chemical complexity (CC), when taken as an assumption for attempting to predict abiogenesis events throughout the universe, is not a 'given'. Such 'universality', may simply tun out to be an indicator of the state of temporal evolution of abiogenetic chemistry, which may, or may not, ultimately evolve into life. I was watching a lecture the other day on the molecular behaviours of solutes/solvents within the vicinity of hydrophilic/hydrophobic surfaces, (liquid water being the solvent). This would not seem to fall into the category of 'complex chemistry' and yet, it was speculated that it may be a fundamental cause of cellular structure evolution.

Well no. I'm sure you will agree that the name of a planet has nothing to do with the kind of chemistry going on there.

Well, one of the points I made, was that certain planet classifications are made on the basis of the system environment that planet finds itself located in. Such system environments influence the nature of the chemistry (courtesy of energy contributions, impacts, etc).

So the question is then how we can compare the chemistries of different planets. This is not a difficult problem. Complexity is something measurable in terms of the structural complexity of molecules as well as the dynamic complexity of the chemical processes. These are measurable criteria, and based on such criteria, the chemistries on different planets can be classified. We could go further and compare chemical processes on different planets in terms of their structural similarities, i.e. are there processes structurally similar to Earth biochemical processes?

I'm not yet convinced that quantified measures of molecular complexity, necessarily lead to explanations of anything about why, (for eg), a chemical system of say, 50 compounds, differs from another of the same, or even smaller size (??) (For eg: recall the Belousov/Zhabotinsky experiments where the addition of some simple elements and compounds, produced non-linear oscillations, exhibiting a visibly fractal result).

Also, even in the simplest systems, quantification of structural, dynamic, and process simularities (structural) can become extremely cumbersome very quickly, and mathematics/algorithms can easily become overloaded when 3 dimensionality of molecules is considered. When one starts zooming in at different scales, the problem escalates if a fractal structure is encountered .. (eg at the levels of: molecule, cluster of molecules, micro-environment (liquid solvent ?), macro-environment (solids ?), etc). Any of these levels of detail, could make all the difference we might be looking for.

As I said, this is about structural comparison between different chemistries, which has nothing to do with the prefix "exo" nor with any planetary classification system that doesn't involve structural comparison between chemistries. As far as I know you are correct that we don't know how the "universal laws of simple chemistry map into self-replicating complex cellular lifeforms", but we can start with simple virtual or artificial chemistry models to see whether something structurally similar to self-replicating units emerge from that. We can then play around with such a model, for example, by randomizing some of variables to see how sensitive the self-replicating outcome is to random variations.

Ok ... so if its to be a generalised model, I suggest we start a new thread.
As a starter, one way of looking at this is from the basics of Complexity Theory ... start out considering the different dynamics we're likely to encounter in our chemical complexity model: static, dynamic, evolving, self-organising. All parameters would have to be variables, which change over time, at different rates.
Global measures would need to apply in all fields (as an assumption), along with others covering unpredictability, non-equilibria, causal loops, and openness.
Some objectives wouldn't go astray either. Eg: explanations of the structures, relative complexity, control methods, constraints, chemistry and physics laws, and they have to be computable (quantified).

Throw all that into an iterative algorithm all at once, and see what pops out, eh ?

[Paul Wally]

I was watching a lecture the other day on the molecular behaviours of solutes/solvents within the vicinity of hydrophilic/hydrophobic surfaces, (liquid water being the solvent). This would not seem to fall into the category of 'complex chemistry' and yet, it was speculated that it may be a fundamental cause of cellular structure evolution.

Chemical complexity is one form of measurable comparison, but certainly not the only one. I think what makes comparison easy in the case of chemistry is it's discrete nature. There is a finite number of chemical elements and they can combine in different possible ways, depending on physical conditions. Of course, chemistry cannot be divorced from physical conditions, but when we focus on measurable and comparable complexity then chemical complexity is one such measure. Surely you must agree that the chemical process of, for example, photosynthesis is much more complex than any chemical processes we've observed on Mars or Titan up till now.

Well, one of the points I made, was that certain planet classifications are made on the basis of the system environment that planet finds itself located in. Such system environments influence the nature of the chemistry (courtesy of energy contributions, impacts, etc).

But a classification system based on general physical characteristics of planets will be completely different from a classification based on chemical complexity. Planets belonging to the same category in the one classification will not necessarily belong to the same category in the other classification system.

I'm not yet convinced that quantified measures of molecular complexity, necessarily lead to explanations of anything about why, (for eg), a chemical system of say, 50 compounds, differs from another of the same, or even smaller size (??)

I think such a measure should depend on some clear quantifiable definition. For instance it wouldn't just be about number of compounds but also about the complexity of the chemical networks wherein these compounds interact within some structurally invariant whole; a system of some sort. You may now ask, but how do we distinguish a complex system from pure random chaos? See Complexity, specifically the part on "Disorganized complexity vs. organized complexity".

(For eg: recall the Belousov/Zhabotinsky experiments where the addition of some simple elements and compounds, produced non-linear oscillations, exhibiting a visibly fractal result).

No problem. Studying such processes may also be useful in understanding life-emergence. Fractal geometry is after all quite common in biological systems too.

Also, even in the simplest systems, quantification of structural, dynamic, and process simularities (structural) can become extremely cumbersome very quickly, and mathematics/algorithms can easily become overloaded when 3 dimensionality of molecules is considered. When one starts zooming in at different scales, the problem escalates if a fractal structure is encountered .. (eg at the levels of: molecule, cluster of molecules, micro-environment (liquid solvent ?), macro-environment (solids ?), etc). Any of these levels of detail, could make all the difference we might be looking for.

Yes, as I said we start with a simple model, preferably something we (and our computers) can handle.

Ok ... so if its to be a generalised model, I suggest we start a new thread.
As a starter, one way of looking at this is from the basics of Complexity Theory ... start out considering the different dynamics we're likely to encounter in our chemical complexity model: static, dynamic, evolving, self-organising. All parameters would have to be variables, which change over time, at different rates.
Global measures would need to apply in all fields (as an assumption), along with others covering unpredictability, non-equilibria, causal loops, and openness.
Some objectives wouldn't go astray either. Eg: explanations of the structures, relative complexity, control methods, constraints, chemistry and physics laws, and they have to be computable (quantified).

Throw all that into an iterative algorithm all at once, and see what pops out, eh ?

Roughly, my approach would be to maybe define some interaction rules between idealized "molecules" (units) to see whether self-replication and evolvability results from that. If it doesn't then invent different generic models until it works. A lot of prerequisite thought needs to go into this though. I think the emergence of self-replication and evolvability is the key theoretical (mathematical) problem. If such an algorithm could be discovered (if it wasn't already) then that would mean the possibility of a general abstract mathematical theory of self-replication and evolvability. Since it would be purely mathematical, it must be applicable wherever a structurally similar situation exists.

[willstaruss22]

I believe we cant even imagine what life in the universe is like, they may thrive in ways that would seem amazing to us. Creatures that have rock bodies, water body, diamond skeleton and very adaptable creatures who can fly then dive into a liquid and breath in that enviromnent. The movies? please we should be thinking way out the box!