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- "The fact that it did happen here tells us nothing more than that, and until we dig out evidence of a ‘second genesis,’ perhaps here in our own Solar System i

- "The fact that it did happen here tells us nothing more than that, and until we dig out evidence of a ‘second genesis,’ perhaps here in our own Solar System inside an icy moon, or on Mars, we can form no firm conclusions." I'm convinced the absence of evidence is, itself, valuable evidence. The (apparent) single origin of Earth life is a remarkable statistical observation hiding in plain sight.

JohnMakin 2y ago
> I'm convinced the absence of evidence is, itself, valuable evidence. That isn't how science works. We have an astounding lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space, it doesn't indicate anything but the fact that there's a lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space. It may not indicate with absolute certainty whether there is or isn't one, but you cannot say its existence is more likely based on lack of evidence for it - that is superstition.
- aradox66 2y ago
  I think science does actually offer tools beyond pure falsifiability for evaluating truth claims
- jerf 2y ago
  "Absence of evidence is not evidence of absence" is simply false, however much fun it may be to say. Let us suppose, for instance, that we had indeed scanned over the entire universe and found that there was no evidence for life. Would we then be justified in saying "the absence of evidence is not evidence of absence"? Of course not. What other evidence of absence do you expect to uncover, other than a lack of evidence for existence? Do you expect to go out into space and have some sort of space god hand you a genuine, bona-fide certificate of nonexistence of something? It is important not to overestimate the strength of the absence of evidence, but setting the strength to zero is just as wrong. If we look in many places where we expect to find life, because we have a theory that life is easy and essentially appears the cosmological instant it is possible, and we have a theory that the conditions for life are easy and abundant, yet we look out into the universe and see no evidence of this, yes, we are completely justified in adjusting our understanding of the probabilities involved. The more of the universe we see, and the more it lacks various sorts of life (all the way from the simplest, sparsest bacteria-type life up to galaxy-spanning intelligences, each to their own degree) the more we are justified in coming to conclusions about their probabilities. Another thing people have problems with in this debate is understanding the difference between justified beliefs and true beliefs. If we hypothetically examined all but one-trillionth of the observable universe and found it bereft of any other life, we would be justified in the conclusion that the most likely scenario is that there isn't any. We could end up being wrong if that remaining one-trillionth just so happened to contain other life, but we would still be justified, having collected extensive "absence of evidence". We can not claim that we have seen enough of the universe to know that it is true that there is no other life, and we have not seen enough of it to be justified in claiming there is no bacterial life, but I do feel at this point we are pretty justified in claiming that at least this galaxy and the nearest ones do not have any galaxy-spanning, multi-million-year civilizations in them, for instance. Maybe they're there and they just don't do anything visible, but that's a pretty precise claim.
  - aeve890 2y ago
    >Let us suppose, for instance, that we had indeed scanned over the entire universe and found that there was no evidence for life. Would we then be justified in saying "the absence of evidence is not evidence of absence"? Scanned how? What's the operational definition of "life" in that hypothetical scenario? Maybe there's life, but you're looking where isn't, or you're missing something you don't classify as "living". Maybe the universal definition of life is vastly broader than we think.
    - bluGill 2y ago
      It is entirely possible our definition of life is wrong. However it is what we have currently and there is currently no reason to think some other definition might be better. If we ever find something that sortof seems like life, but doesn't fit our current definition of life we can then have the debate about how and if the definition should change. However without knowing what might or might not fit in it is impossible to know how to make it better. There is no requirement that we adjust the definition of life, perhaps we need some hierarchy of some form and this new life like thing isn't life but something else that life is a subset of. It is even possible that we go through the above several times with different, contradictory results. But for now our definitions of life are good enough.
    - jerf 2y ago
      Sorry, you can't escape that way. My answer is, whatever definition of life you like. I don't care what it is. You get to choose. For the sake of the hypothetical, we have scanned over the entire universe for that sort of life, and then we use the same definition of "life" for our declaration that there is no evidence of "life", so you can't escape through equivocation between those two definitions either.
- feoren 2y ago
  Science is ultimately rooted in logic, and I'm not sure why so many people forget this. We seem to pretend that we can evaluate every possible claim in a complete vacuum, and that it's somehow pure to ignore any sort of logic or prior knowledge when we do so. But this has never been "how science works", nor how humans work. Science operates on top of the logic and knowledge that we already have about the universe. So if I claim that there is a Flying Spaghetti Monster roaming around our solar system, and it is 1000x larger than our sun, emitting a divine brightness so intense that it would burn the eyes of all who gaze upon it, you're 100% justified to say "no there isn't. We would have seen it." "Aha!" I say, "but absence of evidence is not evidence of absence! Therefore you can't say anything at all about whether there's a supermassive superluminal Giant Spaghetti Monster!". That is absolute nonsense. > you cannot say its existence is more likely based on lack of evidence for it If its existence would imply evidence, then you absolutely can judge its likelihood based on whether that evidence exists or not. And you can also judge its likelihood based on a reasonable extrapolation from prior knowledge, by the way. Yes, it is more likely that there is a 10 kg rock orbiting Neptune than a 10^20 kg Spaghetti Monster, even though we have not directly observed either one. We understand the mechanisms by which a small rock comes to orbit a planet. We see that kind of thing all the time. It may be difficult to formalize some of these priors, but that's a failure of our formalisms, not a mandate that we must not use that knowledge when doing science.
  - JohnMakin 2y ago
    > "Aha!" I say, "but absence of evidence is not evidence of absence! Therefore you can't say anything at all about whether there's a supermassive superluminal Giant Spaghetti Monster!". That is absolute nonsense. Note that the comment you are replying to said nor implied anything of the sort.
    - feoren 2y ago
      >> Note that the comment you are replying to said nor implied anything of the sort. That's literally the exact claim being made: > We have an astounding lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space, it doesn't indicate anything but the fact that there's a lack of evidence A lack of evidence indicates nothing but a lack of evidence. No! That's not true! It's a widely held misconception and it's worth debunking.
close04 2y ago
If I read 98% of your comment I might draw a pretty accurate conclusion based on the absence of something in it. But if I read just 2% any conclusion I draw is whatever I want to read in the tea leaves. Do you think we investigated closer to 98% or to 2% for possible evidence?
bluGill 2y ago
Not in this case. the amount of the universe we can really observe is tiny. Sure we can see a lot of stars, but that is about it. We cannot directly see any planets outside our solar system (this might not be completely true, I'm not sure what the limits are), except by how they change the light of the star. Basically we can't even detect earth sized planets around most stars, as they are too small. If we cannot detect planet sized objects that means there is no hope of seeing lifeforms on the planet. The limits are not just our technology levels. Many of the signs you want to life for of life are things that we know by laws of physics could not possibly reach us no matter how good the detection equipment is. That is why SETI looks for radio waves - they are one of the few signals we can detect that could signal life. However we would never detect earth technology levels of just 120 years ago (there is some debate about what we could first detect). There are not many stars within 100 lightyears of earth, so the vast majority of our galaxy (must less the universe) still has no idea we are here. Even radio signals degrade with distance, so there is a limit to how far we can detect them or they can detect us. In short, while there is absence of evidence, there is reason believe that we don't have enough evidence to declare anything. If we find life that will be conclusive, but the we don't before our sun dies there still won't be enough evidence to state there is none.
- happosai 2y ago
  > We cannot directly see any planets outside our solar system (this might not be completely true, I'm not sure what the limits are) Glad you expressed uncertainity. Indeed We can see some exoplanets directly. I also only learned this very recently. https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...
  - andrewflnr 2y ago
    It only happened recently, relative to SETI efforts overall.
  - bluGill 2y ago
    Thanks for the correction. Note that all those planets are very large (none of significantly smaller than Jupiter, and most are much larger). Also all are very close to earth, and the "smaller" it is the closer it is". Physics provides limits to what we will ever be able to directly observe from earth (though I'm not an astrophysicist, find one if you want to know more details, I'm confident in that statement anyway but do understand my expertise isn't here)

JohnMakin 2y ago

> I'm convinced the absence of evidence is, itself, valuable evidence. That isn't how science works. We have an astounding lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space, it doesn't indicate anything but the fact that there's a lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space. It may not indicate with absolute certainty whether there is or isn't one, but you cannot say its existence is more likely based on lack of evidence for it - that is superstition.

aradox66 2y ago
I think science does actually offer tools beyond pure falsifiability for evaluating truth claims
jerf 2y ago
"Absence of evidence is not evidence of absence" is simply false, however much fun it may be to say. Let us suppose, for instance, that we had indeed scanned over the entire universe and found that there was no evidence for life. Would we then be justified in saying "the absence of evidence is not evidence of absence"? Of course not. What other evidence of absence do you expect to uncover, other than a lack of evidence for existence? Do you expect to go out into space and have some sort of space god hand you a genuine, bona-fide certificate of nonexistence of something? It is important not to overestimate the strength of the absence of evidence, but setting the strength to zero is just as wrong. If we look in many places where we expect to find life, because we have a theory that life is easy and essentially appears the cosmological instant it is possible, and we have a theory that the conditions for life are easy and abundant, yet we look out into the universe and see no evidence of this, yes, we are completely justified in adjusting our understanding of the probabilities involved. The more of the universe we see, and the more it lacks various sorts of life (all the way from the simplest, sparsest bacteria-type life up to galaxy-spanning intelligences, each to their own degree) the more we are justified in coming to conclusions about their probabilities. Another thing people have problems with in this debate is understanding the difference between justified beliefs and true beliefs. If we hypothetically examined all but one-trillionth of the observable universe and found it bereft of any other life, we would be justified in the conclusion that the most likely scenario is that there isn't any. We could end up being wrong if that remaining one-trillionth just so happened to contain other life, but we would still be justified, having collected extensive "absence of evidence". We can not claim that we have seen enough of the universe to know that it is true that there is no other life, and we have not seen enough of it to be justified in claiming there is no bacterial life, but I do feel at this point we are pretty justified in claiming that at least this galaxy and the nearest ones do not have any galaxy-spanning, multi-million-year civilizations in them, for instance. Maybe they're there and they just don't do anything visible, but that's a pretty precise claim.
- aeve890 2y ago
  >Let us suppose, for instance, that we had indeed scanned over the entire universe and found that there was no evidence for life. Would we then be justified in saying "the absence of evidence is not evidence of absence"? Scanned how? What's the operational definition of "life" in that hypothetical scenario? Maybe there's life, but you're looking where isn't, or you're missing something you don't classify as "living". Maybe the universal definition of life is vastly broader than we think.
  - bluGill 2y ago
    It is entirely possible our definition of life is wrong. However it is what we have currently and there is currently no reason to think some other definition might be better. If we ever find something that sortof seems like life, but doesn't fit our current definition of life we can then have the debate about how and if the definition should change. However without knowing what might or might not fit in it is impossible to know how to make it better. There is no requirement that we adjust the definition of life, perhaps we need some hierarchy of some form and this new life like thing isn't life but something else that life is a subset of. It is even possible that we go through the above several times with different, contradictory results. But for now our definitions of life are good enough.
  - jerf 2y ago
    Sorry, you can't escape that way. My answer is, whatever definition of life you like. I don't care what it is. You get to choose. For the sake of the hypothetical, we have scanned over the entire universe for that sort of life, and then we use the same definition of "life" for our declaration that there is no evidence of "life", so you can't escape through equivocation between those two definitions either.
feoren 2y ago
Science is ultimately rooted in logic, and I'm not sure why so many people forget this. We seem to pretend that we can evaluate every possible claim in a complete vacuum, and that it's somehow pure to ignore any sort of logic or prior knowledge when we do so. But this has never been "how science works", nor how humans work. Science operates on top of the logic and knowledge that we already have about the universe. So if I claim that there is a Flying Spaghetti Monster roaming around our solar system, and it is 1000x larger than our sun, emitting a divine brightness so intense that it would burn the eyes of all who gaze upon it, you're 100% justified to say "no there isn't. We would have seen it." "Aha!" I say, "but absence of evidence is not evidence of absence! Therefore you can't say anything at all about whether there's a supermassive superluminal Giant Spaghetti Monster!". That is absolute nonsense. > you cannot say its existence is more likely based on lack of evidence for it If its existence would imply evidence, then you absolutely can judge its likelihood based on whether that evidence exists or not. And you can also judge its likelihood based on a reasonable extrapolation from prior knowledge, by the way. Yes, it is more likely that there is a 10 kg rock orbiting Neptune than a 10^20 kg Spaghetti Monster, even though we have not directly observed either one. We understand the mechanisms by which a small rock comes to orbit a planet. We see that kind of thing all the time. It may be difficult to formalize some of these priors, but that's a failure of our formalisms, not a mandate that we must not use that knowledge when doing science.
- JohnMakin 2y ago
  > "Aha!" I say, "but absence of evidence is not evidence of absence! Therefore you can't say anything at all about whether there's a supermassive superluminal Giant Spaghetti Monster!". That is absolute nonsense. Note that the comment you are replying to said nor implied anything of the sort.
  - feoren 2y ago
    >> Note that the comment you are replying to said nor implied anything of the sort. That's literally the exact claim being made: > We have an astounding lack of evidence that there is a Flying Spaghetti Monster roaming around the deepest reaches of space, it doesn't indicate anything but the fact that there's a lack of evidence A lack of evidence indicates nothing but a lack of evidence. No! That's not true! It's a widely held misconception and it's worth debunking.

close04 2y ago

If I read 98% of your comment I might draw a pretty accurate conclusion based on the absence of something in it. But if I read just 2% any conclusion I draw is whatever I want to read in the tea leaves. Do you think we investigated closer to 98% or to 2% for possible evidence?

bluGill 2y ago

Not in this case. the amount of the universe we can really observe is tiny. Sure we can see a lot of stars, but that is about it. We cannot directly see any planets outside our solar system (this might not be completely true, I'm not sure what the limits are), except by how they change the light of the star. Basically we can't even detect earth sized planets around most stars, as they are too small. If we cannot detect planet sized objects that means there is no hope of seeing lifeforms on the planet. The limits are not just our technology levels. Many of the signs you want to life for of life are things that we know by laws of physics could not possibly reach us no matter how good the detection equipment is. That is why SETI looks for radio waves - they are one of the few signals we can detect that could signal life. However we would never detect earth technology levels of just 120 years ago (there is some debate about what we could first detect). There are not many stars within 100 lightyears of earth, so the vast majority of our galaxy (must less the universe) still has no idea we are here. Even radio signals degrade with distance, so there is a limit to how far we can detect them or they can detect us. In short, while there is absence of evidence, there is reason believe that we don't have enough evidence to declare anything. If we find life that will be conclusive, but the we don't before our sun dies there still won't be enough evidence to state there is none.

happosai 2y ago
> We cannot directly see any planets outside our solar system (this might not be completely true, I'm not sure what the limits are) Glad you expressed uncertainity. Indeed We can see some exoplanets directly. I also only learned this very recently. https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...
- andrewflnr 2y ago
  It only happened recently, relative to SETI efforts overall.
- bluGill 2y ago
  Thanks for the correction. Note that all those planets are very large (none of significantly smaller than Jupiter, and most are much larger). Also all are very close to earth, and the "smaller" it is the closer it is". Physics provides limits to what we will ever be able to directly observe from earth (though I'm not an astrophysicist, find one if you want to know more details, I'm confident in that statement anyway but do understand my expertise isn't here)