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Colin Robinson
2012-Nov-19, 11:26 PM
(An off-shoot of the thread "expert says aliens dont exist")

In what circumstances, if any, does absence of evidence amount to evidence of absence?

The analogy of cobwebs in a cellar/ spiders in a cellar is a way of thinking about this question. If you have checked a cellar for cobwebs, and found there are none, then it is reasonable to conclude that the cellar is not inhabited by web-building spiders.

It is not reasonable to conclude that the cellar never had spiders, or never will have spiders, or that other cellars (that you haven't looked at) don't have spiders right now.

The analogy I'm trying to make here is between spiders in cellars and life in the universe, be it alien (to us) extraterrestrial life or not-so-alien life on Earth.

It's true that we don't yet know whether alien life exists. We don't have conclusive evidence. We do know that not-so-alien life exists. This is like knowing that spiders exist in one cellar, but not yet knowing whether they exist in other cellars.

Why would you expect to know, until you go down into the cellars and look around for cobwebs?

Jens
2012-Nov-20, 12:26 AM
It's true that we don't yet know whether alien life exists. We don't have conclusive evidence. We do know that not-so-alien life exists. This is like knowing that spiders exist in one cellar, but not yet knowing whether they exist in other cellars.


Discussing this seriously, I would say there is a big difference, because we know that the conditions in one cellar are basically equivalent to the next, and that spiders can, in practice, live in many cellars. We also know that spiders lay eggs and can easily travel from one house to the next.

When you talk about extraterrestrial life, our knowledge is much more incomplete. We don't know under what conditions life can evolve, really. So we know it exists here, but for all we know it could be that you have to have a perfect set of coincidences for it to happen at all, and it could be it has never taken place anywhere else. So I don't think it's wrong to speculate, of course, but to assume that it is likely that life exists elsewhere (because it exists here) seems unreasonable to me, whereas with spiders it is not (because we understand how spiders arise and move and what conditions they live in).

pzkpfw
2012-Nov-20, 12:29 AM
I see no Igloos in my cellar. Is it unreasonable to say no Eskimos have ever lived in my cellar?

Jens
2012-Nov-20, 12:31 AM
By the way, in the now closed thread, you answered a question from me like this:



Yes, the point I was trying to make was along the lines of what you've written. Except that I would make the last few words "... is it unreasonable to think that somebody may have come here?"

I might or might not object, depending really on the nuance of "might". I don't think it's unreasonable to speculate, but if that "may" gets close to "it's likely" than I would object. I don't think it's unreasonable to speculate. But you don't normally start to think about whether something happened unless you have some evidence to think so. For example, I didn't wake up this morning and speculate that it might have snowed last night. Now, if the weather report had forecast it, and the temperature was below zero, and it had been cloudy when I went to bed, then yes I would consider the possibility.

Colin Robinson
2012-Nov-20, 01:17 AM
I see no Igloos in my cellar. Is it unreasonable to say no Eskimos have ever lived in my cellar?

That looks to me like a classic non sequitur. The conclusion may be perfectly true, but it hardly follows from the premise.

I mean, I can imagine an Eskimo travelling to New Zealand, and seeking accommodation in a cellar there... but I cannot see why he or she would build an igloo down in the cellar.

Colin Robinson
2012-Nov-20, 02:02 AM
Discussing this seriously, I would say there is a big difference, because we know that the conditions in one cellar are basically equivalent to the next, and that spiders can, in practice, live in many cellars. We also know that spiders lay eggs and can easily travel from one house to the next.

True.

The point I'm trying to make, is that "absence of evidence" can mean two different things.

1. We haven't found evidence of entity X in location Y, which is a location we haven't explored yet.
2. We've explored location Y, and noticed a lack of the evidence we'd expect from entity X, if it were present.

From the first sort of "absence of evidence", hardly any conclusions can reasonably be drawn. The fact that you've never seen cob-webs in the basement means very little if you have never gone down into the basement.

From the second sort of "absence of evidence", conclusions can be reasonably drawn, but it is still a fallacy to over-generalize. E.g. If a particular planet has no methane in its atmosphere then it could reasonably be concluded that methane-generating organisms don't exist there. It would over-generalizing to conclude that no organisms of any sort exists anywhere except Earth.


When you talk about extraterrestrial life, our knowledge is much more incomplete. We don't know under what conditions life can evolve, really. So we know it exists here, but for all we know it could be that you have to have a perfect set of coincidences for it to happen at all, and it could be it has never taken place anywhere else. So I don't think it's wrong to speculate, of course, but to assume that it is likely that life exists elsewhere (because it exists here) seems unreasonable to me, whereas with spiders it is not (because we understand how spiders arise and move and what conditions they live in).

Yes, it is conceivably true that Earth, as a life-bearing planet is radically exceptional – that emergence of life requires circumstances so unusual that Earth is the only place life exists.

But that's a speculation too.

Colin Robinson
2012-Nov-20, 02:56 AM
By the way, in the now closed thread, you answered a question from me like this:

I might or might not object, depending really on the nuance of "might". I don't think it's unreasonable to speculate, but if that "may" gets close to "it's likely" than I would object.

I'd probably object too, if someone said "it's likely" about extraterrestrials visiting Earth.

We earthlings may have demonstrated the feasibility of space travel within a solar system, but an interstellar space mission with a crew is another matter — maybe it has never been done, and never will be...

Paul Wally
2012-Nov-20, 03:01 AM
In what circumstances, if any, does absence of evidence amount to evidence of absence?


Absence of evidence amount to evidence of absence if the necessary investigation has been carried out. If the investigator doesn't do the necessary investigation then he/she can't say there's no evidence, because the reason for that lack of evidence would be the investigator not doing his/her job properly. In the case of extraterrestrial life we can't say there's no evidence and therefore it doesn't exist, we've hardly begun to explore the galaxy.

In the mean time, given the difficulties, I think the best approach would be to attempt to solve the problem of how life emerges through the processes of self-organizing complexity. The solution to that problem would be something applicable everywhere just like physics is applicable everywhere.

NoChoice
2012-Nov-20, 03:50 AM
I see no Igloos in my cellar. Is it unreasonable to say no Eskimos have ever lived in my cellar?

Yes, that is unreasonable - as a scientific statement. In that context you can only say "I don't know."

In the context of a "normal" human conversation it may not be unreasonable but that is not really the context of this discussion.
So-called "skeptics" tend to switch that context as they need it for their agenda.
But those are not honest modes of discussion.

The only possible honest answer to the questions "are there aliens in the universe?" or "have we ever been visited by aliens?" is "We don't know."

Jens
2012-Nov-20, 04:01 AM
The only possible honest answer to the questions "are there aliens in the universe?" or "have we ever been visited by aliens?" is "We don't know."

Of course that's true, but we can also make educated guesses. For example, on the first question, it seems to me that given the huge, huge number of planets in the universe, that it seems probable that life exists somewhere. I would be surprised if it doesn't. On the other hand, given the lack of evidence of any visit by aliens, my inclination is to doubt that it's ever happened. But neither of those is a certainty, just a guess based on what I find reasonable.

NoChoice
2012-Nov-20, 04:18 AM
Of course that's true, but we can also make educated guesses. For example, on the first question, it seems to me that given the huge, huge number of planets in the universe, that it seems probable that life exists somewhere. I would be surprised if it doesn't. On the other hand, given the lack of evidence of any visit by aliens, my inclination is to doubt that it's ever happened. But neither of those is a certainty, just a guess based on what I find reasonable.

I agree with everything you said.
It may be your (and mine) and all skeptic's inclination to arrive at that conclusion, but as such it has absolutely no scientific merit. It's personal reasoning, not a scientific conclusion.
That's why I am speaking up here. Although a skeptic myself as far as alien visitations are concerned, many skeptics seems to be confused by the distinction of a personal conclusion versus a scientific one.

We simply do not have enough or even any data to arrive at a proper scientific conclusion, hence it must be (at this point in time): "We simply do not know". End of story, really.

pzkpfw
2012-Nov-20, 04:27 AM
That looks to me like a classic non sequitur. The conclusion may be perfectly true, but it hardly follows from the premise.

I mean, I can imagine an Eskimo travelling to New Zealand, and seeking accommodation in a cellar there... but I cannot see why he or she would build an igloo down in the cellar.

My point is that spiders are well known and very common. It's reasonable to think that spiders may have or might soon, live in a cellar, even with the lack of evidence via webs.

Aliens (as in non-human beings from space), on the other hand, are about as likely (actually less) than Eskimos in my cellar.

I don't buy the "we don't know 'yes' or 'no' so have to accept 'maybe'" approach.

(I happen to think it's hugely likely that there is other life out there. My opinion is strongly that Earth is not the only place with life. However, I'm just as certain none of that other life has ever visited Earth. The distances are too great. This is a case where I need evidence in favour, and won't accept lack of evidence as leaving open the possibility. Edit: pretty much the same as Jens in post #10.)

NoChoice
2012-Nov-20, 04:35 AM
Aliens (as in non-human beings from space), on the other hand, are about as likely (actually less) than Eskimos in my cellar.

(My bold) Please show how you mathematically quantified both probabilities and based on what scientific data.

My point being: you can't because of lack of data. Hence, all you did was personal reasoning, not scientific reasoning.
The classic skeptic's mistake.

pzkpfw
2012-Nov-20, 04:42 AM
(My bold) Please show how you mathematically quantified both probabilities and based on what scientific data.

My point being: you can't because of lack of data. Hence, all you did was personal reasoning, not scientific reasoning.
The classic skeptic's mistake.

My main evidence is simply the distances required to be travelled. Until that's answered, aliens visiting Earth becomes an improbable event, especially given the lack of evidence.

There's no evidence a zebra walked down my driveway today, but it could have. You could say there's no evidence a zebra didn't, so I have to accept the possibility it might have. I'd say that's silly.

Let's flip it: what scientific reasoning do you have for your case? What is your probability for your opinion?

(I'll note I used italics to emphasise words like "opinion" in my post. I'm well aware of what I'm writing.)

Selfsim
2012-Nov-20, 05:13 AM
E.g. If a particular planet has no methane in its atmosphere then it could reasonably be concluded that methane-generating organisms don't exist there. It would over-generalizing to conclude that no organisms of any sort exists anywhere except Earth.Still, that possibility exists, and is as equally probable as any other, in the light of having no direct knowledge of how life emerged here.


Yes, it is conceivably true that Earth, as a life-bearing planet is radically exceptional – that emergence of life requires circumstances so unusual that Earth is the only place life exists.

But that's a speculation too.The intricate relationship between the planet Earth and the emergence of life, is not known at all scales which might be relevant to the emergence of life. Nor are the details retraceable in arrears via 'post-diction'.
Earth does not have to be radically exceptional for life to be present here, if we have no idea about how it got to be here in the first place. That would be jumping to a premature conclusion, also.

Jens
2012-Nov-20, 05:14 AM
It seems to me that there is a general agreement:

Alien existence: probable, but not certain
Alien visits: improbable, but not impossible

I would think the real disagreement is not in the semantics, but in translating the "probable" and "improbable" into actual figures.

NoChoice
2012-Nov-20, 06:15 AM
My main evidence is simply the distances required to be travelled. Until that's answered, aliens visiting Earth becomes an improbable event, especially given the lack of evidence.

That is not evidence by any stretch of the definition. That is simply the status quo of our (imho primitive) scientific understanding. This current understanding has huge holes in it and even mainstream physicists are speculating about possibilities to circumvent the cosmic speed limit.
Do we know for certain that such possibilities exist? No.
Do we know for certain they are impossible? Again no.

And again: no evidence. Just personal speculation and opinion.


Let's flip it: what scientific reasoning do you have for your case? What is your probability for your opinion?
Specifically, which case or opinion of mine is in need of scientific reasoning?
My statement that all we can say is "We don't know"?
That is simply (or, rather, should be) the default position of any honest scientists when approaching any new or unexplained phenomenon.


The fact of the matter is that neither the believer of alien visitation nor the skeptic has a scientific leg to stand on.
And the often (and often misguidedly) cited null-hypothesis is of course the default position: "We don't know".
Any other null-hypothesis is colored by personal preference and therefore neither scientific nor honest.

Jens
2012-Nov-20, 06:48 AM
And again: no evidence. Just personal speculation and opinion.


I find your attitude too dismissive. It's opinion, but based on what seems to be very good reasoning. There doesn't seem to be a way to travel those vast differences, and we have never seen any evidence of anybody else doing it either. We don't have regular visits by aliens, which might be expected if FTL travel was possible. So my reasoning tells me, it's improbable that FTL travel is possible, and improbable that we have been visited by aliens. Of course, as I've agreed with repeatedly, "we don't know" is correct. But I still believe it's improbable, and I think I have good reason to think so, not simply because of "personal preference" (I have no preference one way or the other), but rather by my personal reasoning, which might or might not be correct.

tnjrp
2012-Nov-20, 07:11 AM
In what circumstances, if any, does absence of evidence amount to evidence of absence?In some simple cases, it's reasonable to conclude that this is indeed the case, which makes AOE = EOA a reasonable guideline in everyday life. In more general cases, it isn't. AOE simply makes it less likely that a certain proposition is "true" as opposed to existence of (tenable) evidence, but it doesn't make for a solid case against any more than it stops falsifiably predictive enquiry (AKA science). That said, not all propositions we have AOE of are equally likely to ever become evidenced, even if the exact numbers for or against that happening cannot be calculated and we thus cannot assing the options an exact propability.

NoChoice
2012-Nov-20, 07:16 AM
I find your attitude too dismissive. It's opinion, but based on what seems to be very good reasoning. There doesn't seem to be a way to travel those vast differences, and we have never seen any evidence of anybody else doing it either. We don't have regular visits by aliens, which might be expected if FTL travel was possible. So my reasoning tells me, it's improbable that FTL travel is possible, and improbable that we have been visited by aliens. Of course, as I've agreed with repeatedly, "we don't know" is correct. But I still believe it's improbable, and I think I have good reason to think so, not simply because of "personal preference" (I have no preference one way or the other), but rather by my personal reasoning, which might or might not be correct.

Agreed. There are good reasons to be of the opinion that it is improbable that alien visitations are currently happening. Very good reasons in fact. That is why it is my personal opinion at the moment.

The reason I am dismissive of that particular reasoning as scientific (and, pzkpfw, please understand that it is not personally dismissive) is that I hold science to very high standards. And I further make a very clear distinction between a personal opinion and a scientific opinion. When a scientist publicly declares that alien visitations are humbug or nonsense or woo-woo or whatever the qualifications may be, that distinction becomes very very important. The general public, not generally trained to be very distinctive, may take that proclamation as a scientific fact.

But when it comes to the topic of alien visitations, there can currently be no scientific opinion, except the default position of "we don't know". The responsible way of wording (because it is public and the scientist (although only uttering a personal opinion) may be taken as an official representative of science) would be something like, "i don't think there are alien visitations because..., but at this point we don't know this for a fact."

An idealistic notion or standard perhaps, but nonetheless I think a very important distinction to make and to be aware of.

pzkpfw
2012-Nov-20, 07:27 AM
...

Nope.

Current scientific understanding, is that c is (apart from some very specific unique situations) a hard speed limit, and those stars out there are very far away. You can cast doubt on this, with claims of holes in our understanding etc, but then you are simply adding your own level of personal opinion (you do, after all, write "IMHO") and doubt to the mix. You add little more than the hope that invisible Unicorns may fly Aliens to Earth.

Earlier you indicated you'd want "scientific reasoning" to support my case; but here you've shown you'd happily wave away science, anyway; by simply implying that since we don't "know everything" any possibility must be accepted. That's just your same argument repeated again.

I have zero evidence of any animal walking down my driveway today.
Is it likely my own kids' two cats did? Yes.
Is it likely my neighbours cats did? Well, maybe.
Is it likely Wellington Zoo's Zebra did? Well, it's technically possible, but pretty darn unlikely.
I'm not going to simply say "I don't know if a Zebra walked down my drive today".

The idea of Aliens visiting Earth is an extraordinary one, and will require good evidence in favour to be taken seriously.

To simply say "we don't know" is accurate, but in the context of this kind of discussion, it is a comment usually made by those who wish it were true, not a mere possibility.

NoChoice
2012-Nov-20, 07:40 AM
Nope.

Current scientific understanding, is that c is (apart from some very specific unique situations) a hard speed limit, and those stars out there are very far away. You can cast doubt on this, with claims of holes in our understanding etc, but then you are simply adding your own level of personal opinion (you do, after all, write "IMHO") and doubt to the mix. You add little more than the hope that invisible Unicorns may fly Aliens to Earth.

Earlier you indicated you'd want "scientific reasoning" to support my case; but here you've shown you'd happily wave away science, anyway; by simply implying that since we don't "know everything" any possibility must be accepted. That's just your same argument repeated again.

I have zero evidence of any animal walking down my driveway today.
Is it likely my own kids' two cats did? Yes.
Is it likely my neighbours cats did? Well, maybe.
Is it likely Wellington Zoo's Zebra did? Well, it's technically possible, but pretty darn unlikely.
I'm not going to simply say "I don't know if a Zebra walked down my drive today".

The idea of Aliens visiting Earth is an extraordinary one, and will require good evidence in favour to be taken seriously.

To simply say "we don't know" is accurate, but in the context of this kind of discussion, it is a comment usually made by those who wish it were true, not a mere possibility.


You are not arguing with me or responding to anything I said.
You are arguing with an abstract notion of what you think I represent.

Who said anything about unicorns?
Who was
implying that since we don't "know everything" any possibility must be accepted.?

You argue and get emotional with a position and you very falsely assume that this was my position.
The last sentence of your post made that very clear.

Selfsim
2012-Nov-20, 07:47 AM
To simply say "we don't know" is accurate, but in the context of this kind of discussion, it is a comment usually made by those who wish it were true, not a mere possibility.Hi pzkpfw;

Could you please elaborate some more on that last comment?

Are you saying that 'unknown' is an indefinite state?

Paul Beardsley
2012-Nov-20, 02:24 PM
Hi pzkpfw;

Could you please elaborate some more on that last comment?

Are you saying that 'unknown' is an indefinite state?

I think I understand what pzkpfw is saying. UFO believers often say "we don't know" not as an admission of our limitation of knowledge, but as an appeal to their listeners to join the fantasy. "We don't know" often equates to "who's to say..." which is often followed by "...the aliens haven't found a way around the lightspeed limit?"

However, this is an aside. Clearly "we don't know" is the correct answer to many questions, not least, "Is there life on other planets?" But to say "we don't know" without further qualification is misleading if it causes people to think all possibilities are equally probable - and I think that is what usually happens.

R.A.F.
2012-Nov-20, 04:12 PM
It's true that we don't yet know whether alien life exists. We don't have conclusive evidence. We do know that not-so-alien life exists. This is like knowing that spiders exist in one cellar, but not yet knowing whether they exist in other cellars.


I know for an absolute certainty that if I look through enough cellars, I will eventually find spiders...

I know for an absolute certainty that if I look through enough Solar Systems, I will eventually find...and this is where your analogy falls apart...because the only "ending" to this sentence is we don't know what we will find...


Now instead of spiders...if you had used something unproven to actually exist...like the loch Ness Monster, then your anaogy would have been fine.

Selfsim
2012-Nov-20, 08:44 PM
I think I understand what pzkpfw is saying. UFO believers often say "we don't know" not as an admission of our limitation of knowledge, but as an appeal to their listeners to join the fantasy. "We don't know" often equates to "who's to say..." which is often followed by "...the aliens haven't found a way around the lightspeed limit?"

However, this is an aside. Clearly "we don't know" is the correct answer to many questions, not least, "Is there life on other planets?" But to say "we don't know" without further qualification is misleading if it causes people to think all possibilities are equally probable - and I think that is what usually happens.Hmm .. thanks for that .. I was kind of left hanging and in need of more input. :)

I'm pretty sure I've argued quite strenuously for the 'unknown' status myself .. but I really do mean 'unknown' period … (as in end of story). Within the bounds of mainstream science speculation however, 'possibilities' from that point onwards, I think, should be approached pretty much from an equi-probable perspective unless they are constrained in some manner by prior science based observation or measurement, (eg: exo-life, isn't). From thereon, the physical science themes usually end up being centered around inference based logic which can lead to either correct, or incorrect conclusions. (Ie: The flaws of inductive reasoning).

The ATM, pseudoscience or anti-science realms are (of course) more extreme ones, and are a completely different 'kettle of fish'.

I have no problems with making use of inference based logic, so long as it is distinguished in the claim, (alongside its above implications). The use of statistical arguments, (implied by the use of the term 'probable'), in the absence of quantitative evidence, are necessarily flawed … specifically by this lack of precedent. Qualitative arguments based on the general sense usage of terms like 'probable' or 'likely', I find, are usually skewed in the direction of prior belief and opinion.

All of this constrains 'unknown' to a discrete state of its own, and is quite definitive.

Apologies if you're already aware of the above, I'm really more attempting to make use of this post to clarify in more detail where I've been coming from, (given that I seem to frequently invoke 'concerns' when I express views based on these principles … and its probably long overdue, what's more).

Cheers

Colin Robinson
2012-Nov-20, 09:56 PM
I know for an absolute certainty that if I look through enough cellars, I will eventually find spiders...

I know for an absolute certainty that if I look through enough Solar Systems, I will eventually find...and this is where your analogy falls apart...because the only "ending" to this sentence is we don't know what we will find...

I agree that we know more about cellars (even those we haven't yet looked at) than we know about other solar systems...


Now instead of spiders...if you had used something unproven to actually exist...like the loch Ness Monster, then your anaogy would have been fine.

I think the Loch Ness Monster is a misleading analogy, for the following reasons:

1.Compared to other planets, or even to ancient Earth, modern Scotland is a location we know much more about. It is like comparing a cellar you visit regularly to one you've just glimpsed through a crack in the floor.

2.The Loch Ness Monster is a specific proposition, whereas life beyond Earth is a more general one. Discussing life beyond Earth is not like looking at Loch Ness, and asking whether the Loch holds a very big vertebrate with a long neck. It's like looking at a lake that has not hitherto been examined by biologists, and asking what sort of things might live there, including any microbes, plants, small or large animals.

3.The proposition that life does not exist beyond Earth, if true, implies that Earth is radically exceptional — that there a great class of phenomena happening here which doesn't happen on any other of the billions of planets and moons in the universe. The proposition that Nessie does not exist has no such exceptionalist implication.

Selfsim
2012-Nov-20, 10:32 PM
3.The proposition that life does not exist beyond Earth, if true, implies that Earth is radically exceptional — that there a great class of phenomena happening here which doesn't happen on any other of the billions of planets and moons in the universe. The proposition that Nessie does not exist has no such exceptionalist implication.'Radically exceptional' ??? Not so! I assert that you have imposed that interpretation, yourself!

The 'class of phenomena' which could just as easily also happen everywhere, may also just happen to have generated something here, which we relate to as 'life'. There is nothing to say that the same phenomenon has to generate something we refer to as 'life', elsewhere, or even here again, if 'run' a second time around!

This business of labelling Earth as 'radically exceptional', is all assumption based clap-trap, seemingly intended to throw the Copernican Principle in as a way of winning an argument, nothing more. The Copernican Principle has never been intended to apply at sub-molecular micro-biological scales! Its use in this way, is nothing more than ATM, or pseudoscience!

PS: The relationship between pre-biotic environments (at the planetary scale) and the emergence of life is not known or understood! The inference that somehow a given environment automatically gives rise to the emergence of life, is purely made-up conjecture! Until a targetted exo-environment is discovered, which also produces 'life', the relationship is as hypothetical as the existence of aliens. A single instance of 'life' correlated with a specific, broadly defined pre-biotic environment, does not constitute evidence of causation!

swampyankee
2012-Nov-20, 11:31 PM
We know what evidence that [some] spiders leave behind -- cobwebs, sucked-out husks of their prey, etc, but the evidence of alien life, especially microscopic alien life, is likely to be much harder to find, especially as we can't be entirely sure what it's going to look like.

Paul Wally
2012-Nov-21, 12:06 AM
We know what evidence that [some] spiders leave behind -- cobwebs, sucked-out husks of their prey, etc, but the evidence of alien life, especially microscopic alien life, is likely to be much harder to find, especially as we can't be entirely sure what it's going to look like.

Alien life (if found) is going to look like life. How else are we going to identify it as life? Of course, if it doesn't look like life, and actually is life (whatever that means) then we get a false negative. And if it looks like life, but isn't life then it's a false positive. Both scenarios seem nonsensical to me, because what would something that doesn't look like life look like if it is life, and what would something that looks like life look like if it isn't life?

Selfsim
2012-Nov-21, 04:34 AM
My goodness!! .. What was that?? (re: post#30) …

Can someone explain that one .. quickly .. before I go round the twist? :)

Colin Robinson
2012-Nov-21, 08:08 AM
3.The proposition that life does not exist beyond Earth, if true, implies that Earth is radically exceptional — that there a great class of phenomena happening here which doesn't happen on any other of the billions of planets and moons in the universe. The proposition that Nessie does not exist has no such exceptionalist implication.

'Radically exceptional' ??? Not so! I assert that you have imposed that interpretation, yourself!

The 'class of phenomena' which could just as easily also happen everywhere, may also just happen to have generated something here, which we relate to as 'life'. There is nothing to say that the same phenomenon has to generate something we refer to as 'life', elsewhere, or even here again, if 'run' a second time around!

You seem to think that "class of phenomena" to which I was referring is a state of affairs which preceded life on Earth, and which (in your view) might occur elsewhere without producing life.

Actually no, the "class of phenomena" I was referring to is life itself, not a precursor to life.

If the phenomena we call life are unique to Earth out of all the planets in the universe, then Earth is radically exceptional. Even if Earth was not exceptional at all before life started to happen here.

Your personal (and speculative) theories about the origin of life would provide an explanation of how Earth's exceptional character as a living planet might have come about, if it has...

Colin Robinson
2012-Nov-21, 08:29 AM
We know what evidence that [some] spiders leave behind -- cobwebs, sucked-out husks of their prey, etc, but the evidence of alien life, especially microscopic alien life, is likely to be much harder to find, especially as we can't be entirely sure what it's going to look like.

Whatever it's going to look like, it will need a source of energy. In order to find life on a planet or moon, or to show it isn't there, a logical strategy is to follow the energy flows, and see whether or not there are complex, self-perpetuating systems with energy flowing through them... A system like that still might or might not qualify as living, depending on how life is defined...

MaDeR
2012-Nov-21, 04:42 PM
The 'class of phenomena' which could just as easily also happen everywhere, may also just happen to have generated something here, which we relate to as 'life'. There is nothing to say that the same phenomenon has to generate something we refer to as 'life', elsewhere, or even here again, if 'run' a second time around!
So in short you claim Earth could be only planet with life in entire universe for no reason at all? :rolleyes: I find lack of reason even more improbable than assumption itself - and this is something else. I'm in way impressed.


This business of labelling Earth as 'radically exceptional', is all assumption based clap-trap, seemingly intended to throw the Copernican Principle in as a way of winning an argument, nothing more. The Copernican Principle has never been intended to apply at sub-molecular micro-biological scales! Its use in this way, is nothing more than ATM, or pseudoscience!
Translation: we are not allowed to use Copernican Principle in areas that generate results that you do not like.

Selfsim
2012-Nov-21, 08:11 PM
So in short you claim Earth could be only planet with life in entire universe for no reason at all? :rolleyes: So, there is a reason for the Universe's existence? What is it?

(I didn't {claim} what you've implied ... but I get that you want me to say that).

I find lack of reason even more improbable than assumption itself - and this is something else. I'm in way impressed.So you have reasons for everything more often than not, eh?
(You must … otherwise you wouldn't find the absence of knowledge more improbable than some wild assumption).
Pick a card …!!… Any card will do ...



Translation: we are not allowed to use Copernican Principle in areas that generate results that you do not like.Inaccurate translation. Try again.

Luckmeister
2012-Nov-21, 08:27 PM
So in short you claim Earth could be only planet with life in entire universe for no reason at all? :rolleyes:

I didn't read that into what Selfsim said. Reason? That deals with thought and intent. Are you using that term as a synonym for cause? If so, there is of course a cause for life's emergence. One of the problems in these discussions is that we have yet to pin that down definitively.

So you find it impossible to think that life could be unique to Earth? That's fine as long as you realize that's your intuition speaking, not a scientific conclusion.

ETA: After rereading posts, I think you are saying that Selfsim has no reason for thinking that life could be unique to Earth. Is that correct? If so, the answer to that would be that we have no scientific evidence to conclude otherwise. At this point we can't make a conclusion either way. All we know for sure is that Earth has life.

Paul Wally
2012-Nov-21, 08:48 PM
I didn't read that into what Selfsim said. Reason? That deals with thought and intent. Are you using that term as a synonym for cause? If so, there is of course a cause for life's emergence. One of the problems in these discussions is that we have yet to pin that down definitively.

So you find it impossible to think that life could be unique to Earth? That's fine as long as you realize that's your intuition speaking, not a scientific conclusion.

I think what MaDeR means by reason is explanation. If life is unique to Earth then there must be an explanation as to why it is so. I think that is what MaDeR is saying, and I would agree with that.

ZunarJ5
2012-Nov-21, 10:18 PM
Alien life (if found) is going to look like life. How else are we going to identify it as life? Of course, if it doesn't look like life, and actually is life (whatever that means) then we get a false negative. And if it looks like life, but isn't life then it's a false positive. Both scenarios seem nonsensical to me, because what would something that doesn't look like life look like if it is life, and what would something that looks like life look like if it isn't life?

I see what you're saying. It makes sense.

The problem is solved when you define life. This can be complicated, I'm sure there are many proposed definitions. Once your parameters are set determining whether something qualifies as life should be procedural.

Of course, we will need to keep an open mind. As what we understand about the universe changes we will have to alter our definitions.

Selfsim
2012-Nov-21, 11:02 PM
.. As what we understand about the universe changes we will have to alter our definitions.Which would call into question just how accurate those initial definitions are, and thence, how much/little value should be assigned to the predictions made in the present, from a theory which makes use of such definitions(??)

(…None of which have clear answers in science … metaphysics, maybe ??).

Paul Wally
2012-Nov-21, 11:21 PM
Which would call into question just how accurate those initial definitions are, and thence, how much/little value should be assigned to the predictions made in the present, from a theory which makes use of such definitions(??)

(…None of which have clear answers in science … metaphysics, maybe ??).

How can a definition be inaccurate? Definitions can be changed (as ZunarJ5 correctly stated above) but that's entirely a matter of convention. How do we check whether our definition of life is accurate, there is no test or experiment or observation that we could do that would tell us that our definition of life is either right or wrong because it makes no sense to do that.

Jens
2012-Nov-22, 12:08 AM
I think what MaDeR means by reason is explanation. If life is unique to Earth then there must be an explanation as to why it is so.

I suppose, but the explanation could simply be that it's an extremely unlikely event, and it just happened coincidentally to happen here.

Selfsim
2012-Nov-22, 12:53 AM
How do we check whether our definition of life is accurate, there is no test or experiment or observation that we could do that would tell us that our definition of life is either right or wrong because it makes no sense to do that.Are you saying the definitions are untestable? (If so, the hypothesis giving rise to them, would be beyond the scientific domain, and should be reformed appropriately).

I can think of a test …it would be done on some non-Earth lifeform sample, (discovered whilst exploring), or on something 'engineered' in the lab, which is significantly dissimilar from Earth-life chemically, or in genetic code.

Paul Wally
2012-Nov-22, 12:59 AM
I suppose, but the explanation could simply be that it's an extremely unlikely event, and it just happened coincidentally to happen here.

That's a possible explanation, but it seems to border on a tautology. Life is unique to Earth because it's unlikely. Why is it unlikely?

We know that emergent self-organizing complexity is ubiquitous on all scale levels from the molecular level to the large scale structure of the universe, why wouldn't life be a certain general class of outcomes within that space of possibilities? If complex self-organization doesn't require a specific unlikely chain of events to occur then I would like to hear an explanation of why the emergence of life should be fundamentally different.

Paul Wally
2012-Nov-22, 01:31 AM
Are you saying the definitions are untestable?

I'm not even saying that. I'm saying that it doesn't make sense to speak of testing a definition. A definition is not the kind of thing that we can test empirically.

Definitions come from how we categorize things in the world. We look at a bunch of things and see that they all have some set of features in common, then we say all things that have those features belong to the same category. When we then encounter some new thing with the same features, then that new thing also belongs to the same category.

Selfsim
2012-Nov-22, 01:49 AM
We know that emergent self-organizing complexity is ubiquitous on all scale levels from the molecular level to the large scale structure of the universe, why wouldn't life be a certain general class of outcomes within that space of possibilities? Well, I'd say it could be viewed this way, for sure. But there could quite easily be other 'general class outcomes within that space of possibilities', which don't result in our familiar 'life functions' (there's that definition thing again).

The problem is that we have no feeling for the scale of distribution of the emergence process. Ie: does the same process which leads a 'self-replicating life pattern', occur at the molecular level, or is at some macro or larger scales, or is it at the smaller quantum scales? If its the latter, then randomness might play a way bigger role than we think and thus, predictability of theories is at stake. Perhaps its a time-varying process, and the length of time it stays in the 'life-conducive' phase, (which would also indicate its proximity to criticality), plays some sort of role ultimately in the establishment of self-replication(??) If it is a fractal pattern, then the scale at which our version of 'life' sits in it, might provide some kind low resolution feel for it all .. (but where/when the next instance might be … forget it).

In fractal geometry, there are many, many set outcomes which get discarded, as they merge towards infinity. This is frequently overlooked in favour of the pretty colourful patterns presented in a fractal picture. I often wonder for a given fractal (say the Mandelbrot set), for a time-limited run, how many sets end up escaping? (Ie: what proportion of blackness is there?) Its a pretty meaningless question though … just something to ponder ..


If complex self-organization doesn't require a specific unlikely chain of events to occur then I would like to hear an explanation of why the emergence of life should be fundamentally different.Well consider again a fractal image .. there is self similarity (at all scales) but just how big those scales should be translated, ('inferred'?), back into the real universe, is completely unknown until we have some data/evidence. Perhaps what happens around the 'edges' is some kind of indicator .. but that again, comes back to the level of scale applicability.

I know you might not want to hear this .. but we simply don't have anywhere near enough empirically sourced data to even start to build build a complexity model of non-Earth based life. We barely only just have enough to model our own .. and that's taken hundreds of years to accumulate that knowledge. And I think we'd have to start there, and work backwards to get a complex chemistry/abiogenesis model. …

The quickest way to model it, I think, is to discover it someplace else, and use that as the data source.

Selfsim
2012-Nov-22, 02:06 AM
A definition is not the kind of thing that we can test empirically.And yet that's exactly what we're doing when we analyse a bunch of observations (like those you mention below). We pick one critter, and then go looking for features/characteristics which match that. (That is the testing part) ... We pick another, and test its likeness again on something else, etc, etc … Ie: pattern matching is a 'test'.


Definitions come from how we categorize things in the world. We look at a bunch of things and see that they all have some set of features in common, then we say all things that have those features belong to the same category. When we then encounter some new thing with the same features, then that new thing also belongs to the same category.And everything we've done that on, is sourced from Earth-life.
We have a bunch of definitions for Earth-life which have a very substantial empirical basis.

We have zip for any other speculated non-Earth-life. Thus our definitions for 'non-Earth life', are completely unconstrained by anything for which we think they may be remotely applicable to. They are all Earth 'derived'. How does one eliminate this bias? (Make a discovery someplace else or, 'engineer' one .. or speak directly with ET via his/her/its super-dooper high powered radio/laser comms system, I guess).

Definitions contrived prior to that 'discovery' are a shot-in-the-dark, and thus should be regarded that way, as should any inferences, (speculations), built upon them .. and there's no way to separate different speculations, on the basis of 'likely'/'unlikely', without that discovery.

Jens
2012-Nov-22, 04:03 AM
That's a possible explanation, but it seems to border on a tautology. Life is unique to Earth because it's unlikely. Why is it unlikely?


Sorry, I don't see that. A tautology is something that is true by definition, like, I am my mother's son. Saying "one possible explanation could be..." can't be a tautology. It's not even a statement really, but more like a question. I was just saying that if we find that life is unique to the earth, we'd have to look for an explanation, and there could be several, with one being the possibility that life is extremely unlikely.

Colin Robinson
2012-Nov-22, 08:09 AM
Sorry, I don't see that. A tautology is something that is true by definition, like, I am my mother's son. Saying "one possible explanation could be..." can't be a tautology. It's not even a statement really, but more like a question. I was just saying that if we find that life is unique to the earth, we'd have to look for an explanation, and there could be several, with one being the possibility that life is extremely unlikely.

I think it is true by definition that a low probability event is a rare event.

E.g. If life has a extremely low probability of emerging, even on a world where conditions for its emergence are optimal, then only an extremely small proportion of worlds will have indigenous life on them.

To say that does not tell us whether the probability of life emerging is in reality extremely low, and if so why...

Another question to consider can be expressed in the four words:

If not life, what?

That is: On a world where a range of complex molecules can form in the atmosphere, dissolve in liquid water or another solvent, and interact chemically for millions of years... on such a world, what sort of systems will emerge, if not living systems?


I was just saying that if we find that life is unique to the earth, we'd have to look for an explanation, and there could be several, with one being the possibility that life is extremely unlikely.

I agree there could be other reasons than low probability for an event being rare or unique. It is conceivable that even though there is a high probability of life emerging in certain conditions, there are extremely few places in the universe where those conditions are found.

But the question then is specifically what these extremely rare planetary conditions would be?

ZunarJ5
2012-Nov-22, 12:53 PM
Which would call into question just how accurate those initial definitions are, and thence, how much/little value should be assigned to the predictions made in the present, from a theory which makes use of such definitions(??)

(…None of which have clear answers in science … metaphysics, maybe ??).

If we have to alter our definitions, um, yeah, I suppose that would put into question how accurate the original definition was. Yep, makes sense ;)

Seems to me humanity has had to do this a few times already.... whats new?

ZunarJ5
2012-Nov-22, 01:00 PM
From wikipedia - Life (cf. biota) is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not,[1][2] either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate

Seems like this is a broad enough definition to withstand the advance of understanding for quite some time.

Selfsim
2012-Nov-22, 08:06 PM
From wikipedia - Life (cf. biota) is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not,[1][2] either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate

Seems like this is a broad enough definition to withstand the advance of understanding for quite some time.Perhaps good enough for broad understanding adequate for pub conversations and Earth-based life, but in so far as being adequate for testing for the specifics of some sort of alternative chemistry or genetic model variant discovery, it may be wildly inadequate. Modifications to these definitions would be as much up for grabs as modifications of the tests themselves. (For example: what did the Viking Labelled Release experiments tell us? And were they too restrictive because of the assumed model (which included our life definitions)? Would long-cycle dormant lifeforms be classified as 'living' by a test based on such a broad definition, if the 'lifeforms' were contained within a sample of soil, that happened to be in a dormant state?)

My point is that thinking we can design tests in advance, (making use of such broad definitions), and thinking that they will return definitive results, in order to conclude some exo-environment has life, may not be as straight forward as we would like. This is particularly pertinent to the argument which challenges our abilities to predict what 'should' exist in other environments.

Given the corresponding potential for speculated diverse forms of life, (ie: the permutation space), which would correspondingly be included within the broad definition you cite, what might be the potential for false positives or false negatives from a test designed from such a definition? How could they be ruled out? (Ie: what constrains what we deliberately want to exclude from the results? I assert it all comes down to the empirical evidenced base, underpinning the original definitions used, as much as the presence/absence of some speculated lifeform).

Having highlighted the point, the interesting thing is that this definition may be just what we need for 'catching our eye', and following up with a more detailed sample test. If such a broad range of detection and analysis steps are needed in order to lead to a definitive result, then the full gamut of human perceptiveness and technologies may be needed, onsite, to diagnose the discovery. If this is so, then our search space is limited by human space travel/survival abilities.

Thinking we can remotely diagnose life, assumes an extremely specifc, and tightly focused definition of what constitutes life (eg: 'bio-gases', etc).

Basing the definitions of what we know, also includes a bias in a theoretically extreme permutation space. How can we ever remove this bias in order to objectively detect potentially diverse lifeforms? (An accidental discovery brought on by pure exploration and inquisitiveness might be optimal .. who knows??)

transreality
2012-Nov-22, 09:38 PM
Thinking we can remotely diagnose life, assumes an extremely specifc, and tightly focused definition of what constitutes life (eg: 'bio-gases', etc).

Basing the definitions of what we know, also includes a bias in a theoretically extreme permutation space. How can we ever remove this bias in order to objectively detect potentially diverse lifeforms? (An accidental discovery brought on by pure exploration and inquisitiveness might be optimal .. who knows??)

Not really. What we are familiar with is things that aren't life. Sand grains, gases, ice, minerals etc. We know basically how these behave, and how they look. They are relatively simple. When we see something that doesn't behave simply then it is of immediate interest.

If a whole lot of mineral grains align along a curved surface, that could be a morphology. It may not be, but we don't need a previous life analogue
to be searching for, in order to spot it. If we see concentrations of gases that defy a simple explanation (such as methane on mars) then we can investigate the cause without requiring an alien respiratory model.

Selfsim
2012-Nov-22, 10:18 PM
If we see concentrations of gases that defy a simple explanation (such as methane on mars) then we can investigate the cause without requiring an alien respiratory model.That's what I mean by 'exploration' .. y'know .. snooping things out, noticing what 'catches the eye' and investigating further. At a certain point in the process of narrowing the field down however, a life model will be required. The interpretation of results demands one. If the model has little prior evidence giving rise to the definitions it is designed to 'interpret', (ie: 'alternative 'lifeforms'), then ambiguity will be the end result. (How much ambiguity is related to the 'inaccuracy' of the test .. and ultimately, also the inaccuracy of the definitions in the interpretive model).

Mind you, I might yield (a little) on my 'inconclusiveness-of-remote-detection-of bio-signs' hypothesis, if chlorofluorocarbons were detected in an exo-atmosphere . (http://phys.org/news/2012-11-chlorofluorocarbons-evidence-alien-life.html). that might serve as a good falsification test … its a pretty specific thing to be looking for, mind you, perhaps on a par with looking for ET radio signals … (I'll have to have more of a think about that one …)

Paul Wally
2012-Nov-22, 11:10 PM
Well, I'd say it could be viewed this way, for sure. But there could quite easily be other 'general class outcomes within that space of possibilities', which don't result in our familiar 'life functions' (there's that definition thing again).

There are certainly other classes of emergent complex systems, but if we're looking for life then anything that's not life is not what we're looking for. So when we're looking for life we're not looking for 'other general class outcomes'. A question that might be of interest to mathematicians is how large is the life-class of outcomes within the total space of possibility and how accessible is that space from a dynamic systems point of view. Could there be something like a life-attractor?



The problem is that we have no feeling for the scale of distribution of the emergence process. Ie: does the same process which leads a 'self-replicating life pattern', occur at the molecular level, or is at some macro or larger scales, or is it at the smaller quantum scales? If its the latter, then randomness might play a way bigger role than we think and thus, predictability of theories is at stake.

From what I understand emergent complexity results from the interaction of sufficiently large ensembles of interacting parts. This is not only a phenomenon of physics but also of mathematics. We could change the rules of interaction to non-physical laws (in e.g. cellular automata) and still get emergent complexity. Randomness is actually a good thing, because it brings a certain variability into the system such that the system itself 'explores' different possibilities.



I know you might not want to hear this .. but we simply don't have anywhere near enough empirically sourced data to even start to build build a complexity model of non-Earth based life. We barely only just have enough to model our own .. and that's taken hundreds of years to accumulate that knowledge. And I think we'd have to start there, and work backwards to get a complex chemistry/abiogenesis model. …

The quickest way to model it, I think, is to discover it someplace else, and use that as the data source.

To discover life someplace else will put your personal doubts to rest, but it probably won't solve the problem of abiogenesis. Instead of having one unexplained instance of life emergence we will have two unexplained instances of life emergence.


From wikipedia - Life (cf. biota) is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not,[1][2] either because such functions have ceased (death), or else because they lack such functions and are classified as inanimate

Seems like this is a broad enough definition to withstand the advance of understanding for quite some time.

If we take this definition of life just to illustrate my point. In this case "Life" is a four-letter label for "objects that have signaling and self-sustaining processes". Instead of saying " "objects that have signaling and self-sustaining processes", we replace that whole string with a four-letter word. We may just as well just use the letter L or :rofl: or we could make it an acronym OTHSASP. Or what about not labeling it at all? For example: We can look anywhere for "objects that have signaling and self-sustaining processes" and if we find "objects that have signaling and self-sustaining processes" then we call it "objects that have signaling and self-sustaining processes". But it's so much shorter to just say that we can look anywhere for life and if we find life then we call it life.

MaDeR
2012-Nov-23, 08:18 PM
So in short you claim Earth could be only planet with life in entire universe for no reason at all? So, there is a reason for the Universe's existence? What is it?
Non seqitur. I asume you confirm that is your claim.

Sooooooo... Earth just happened to have life, and rest of entire universe not, just like that. And this does not - God forbid - make Earth special at all. Nope, absolutely not. Yeah... what I am supposed to say to that? *shakes head*


I didn't read that into what Selfsim said. Reason? That deals with thought and intent. Are you using that term as a synonym for cause? If so, there is of course a cause for life's emergence.
I am not native english speaker. Explanation, justification, reason, cause... I think everyone know what I was talking about.

Anyway, if life is so insanely rare that it appeared on Earth only, it automatically make Earth special and unique on scale of entire universe for any reasonable definition of "unique" or "special", regardless of cause or lack of thereof. I find fervent Selfism's denial of Earth uniqueness in this scenario hilarious.


So you find it impossible to think that life could be unique to Earth?
Not impossible, "merely" extremely, utterly improbable. Life present only on Earth does not break any laws of physics. What I find impossibe is claim that life is exclusively and only present on Earth just because.

Selfsim
2012-Nov-24, 02:05 AM
Non seqitur. I asume you confirm that is your claim.

Sooooooo... Earth just happened to have life, and rest of entire universe not, just like that. And this does not - God forbid - make Earth special at all. Nope, absolutely not. Yeah... what I am supposed to say to that? *shakes head*Keep shakin' it ..
What I said originally was:

There is nothing to say that the same phenomenon has to generate something we refer to as 'life', elsewhere, or even here again, if 'run' a second time around!If there is nothing to say, then there are no reasons … just speculation .. (and head shaking is, serendipitously, probably the appropriate response, actually). :)
We have no idea as to the sensitivities/tolerances to initial conditions, of the life emergence process. There are many phenomena which display extreme sensitivity to initial conditions and their outcomes are not theoretically predictable at certain scales. We know from mathematical modelling, (the Lorenz equations), that certain classes of natural phenomena, when run in succession, diverge dramatically due to the tiniest variations in the initial conditions. The process might be common everywhere. The end result, may not be, on the scales relevant to what we're looking for. Ignorance of the phenomena would seem to be the very worst reason for its dismissal.

How would you propose to rule out such classes of phenomena, in order to conclude that life emergence is precisely repeatable, and predictable?

(At least I'm saying 'we don't know' ..)

Are there two precisely identical 'MaDers'? If not, then why would there be two identical 'life-types' in an arbitrary search space? I might concede in this particular aspect, on the basis of the concept of the 'Infinite Universe' .. but we're not searching in an 'Infinite Universe'. We're searching in an 'Observable Universe' for a type of life which itself, is perfectly capable of generating uniqueness at 'everyday' scales. We have no ideas as to the scales on which uniqueness might present itself, when it comes to life emergence .. it is simply not constrained by any data, synthesised, or not .. so we are unable to rule this out.

…. Explanation, justification, reason, cause... I think everyone know what I was talking about.Another assumption, eh? ..

Anyway, if life is so insanely rare that it appeared on Earth only, … (which we don't know) …
… it automatically make Earth special and unique on scale of entire universe for any reasonable definition of "unique" or "special", regardless of cause or lack of thereof.No .. why does the Earth have to be 'special and unique', if we have no idea as to how life emerges?
Anyway, to highlight the imprecision of your thinking on this, I see no reason why Earth would not be unique when viewed from some scales, perspectives or dimensions. You rule these out on the basis of what, 'reasonable definition'?? What, precisely, is that 'reason' in the face of something being 'not known'?
I find fervent Selfism's denial of Earth uniqueness in this scenario hilarious.We don't know whether Earth is unique or not, in ways that impact the emergence process … (or even whether those ways are relevant to the emergence process at all, or not!)

Not impossible, "merely" extremely, utterly improbable. Life present only on Earth does not break any laws of physics. What I find impossibe is claim that life is exclusively and only present on Earth just because.So you make up some story to satisfy your need to negate or minimise things which you only think are improbable, eh?

Colin Robinson
2012-Nov-24, 04:21 AM
There are certainly other classes of emergent complex systems, but if we're looking for life then anything that's not life is not what we're looking for. So when we're looking for life we're not looking for 'other general class outcomes'.

If we are looking only for life as such, we may miss out on phenomena that are related to life and very relevant to the study of life, even if they don't fit into the category of life itself...


A question that might be of interest to mathematicians is how large is the life-class of outcomes within the total space of possibility and how accessible is that space from a dynamic systems point of view. Could there be something like a life-attractor?

I'm glad you mentioned attractors.

As I understand it, they are a component of chaos theory antithetical to the "butterfly effect", in the sense that the butterfly effect says that small random differences in initial conditions can make a very big difference to outcomes... whereas attractors are systems which tend to hold together and grow larger, regardless of small random differences.

I would have thought living things by their very nature are attractors, and so are the auto-catalytic sets of molecules which Stuart Kauffman considers to be the precursors of life. In short, not all attractors are life, but all living things are attractors.


From what I understand emergent complexity results from the interaction of sufficiently large ensembles of interacting parts. This is not only a phenomenon of physics but also of mathematics. We could change the rules of interaction to non-physical laws (in e.g. cellular automata) and still get emergent complexity. Randomness is actually a good thing, because it brings a certain variability into the system such that the system itself 'explores' different possibilities.

An important point.


To discover life someplace else will put your personal doubts to rest,

It's not just a question of the personal doubts of someone here. The probability/improbability of life emerging on any particular planet is an unresolved scientific question. There are theories, but no certainty.

Discovering life someplace else (unless it was so similar to Earth life as to imply a single origin) would tell us abiogenesis is not especially rare on the cosmic scale — that there is a class of worlds where life has a high probability of emerging.


but it probably won't solve the problem of abiogenesis.

Instead of having one unexplained instance of life emergence we will have two unexplained instances of life emergence.

Yes, although a second instance would give us more clues to consider...

Selfsim
2012-Nov-24, 06:00 AM
I'm glad you mentioned attractors.

As I understand it, they are a component of chaos theory antithetical to the "butterfly effect", in the sense that the butterfly effect says that small random differences in initial conditions can make a very big difference to outcomes... whereas attractors are systems which tend to hold together and grow larger, regardless of small random differences.Not quite. Attractors are where a dynamic (time changing) system will end up eventually. It may not necessarily be an equilibrium point (eg: a marble rolling around inside a bowl ... in this case, the attractor would be where the marble ends up .. ie: an 'equilibrium' point, at the lowest point in the bowl). Another attractor might not necessarily be an equilibrium 'point', but could be say something like an orbit (or time-varying 'trajectory'). Yet another class is 'chaotic', where such a system never traces out the same path, (or never returns to exactly the same co-ordinates), whilst orbiting the attractor, (ie: a 'Strange' attractor). The Lorenz equations define an example of this latter class of system, and are thus said to be 'chaotic', demonstrate the butterfly effect, and yet have clearly distinguishable attractors.
One can picture the 'sensitivity to initial conditions' to be like putting a golf ball. Any small change to the initial force, direction, wind, bumps, etc, can result in the ball never taking the same path (as might be evidenced by the incredulity of missing a hole, which seemed 'so simple', the first time 'round!). A block sliding down a slope covered in sandpaper, never traces out the same path in time (this is an analogy for earthquakes over time ..).


I would have thought living things by their very nature are attractors, and so are the auto-catalytic sets of molecules which Stuart Kauffman considers to be the precursors of life. In short, not all attractors are life, but all living things are attractors.It depends on what aspects (parameters) of the system one is interested in studying. The emergence process might be the attractor. It might be a strange attractor, and thus never ends up in exactly the same 'state' (or co-ordinates) ... (it might not be, also).

The point of viewing the emergence process which led to life in this way, results in an appreciation of the multitude of different ways natural systems can evolve .. the non-inevitability is quite different from the impression which results from studying, rigorous, formulaic, inorganic chemistry 'rules' where, provided a broad set of conditions are established initially, exactly the same thing always results. (This just isn't the way complex systems 'typically' behave ... and so we wouldn't expect that).

(Complex systems encompass lots of attractor types, as well, by the way ... they're just ... well, ... more 'complex').


It's not just a question of the personal doubts of someone here. The probability/improbability of life emerging on any particular planet is an unresolved scientific question. There are theories, but no certainty. ... and with 'no certainty', comes 'no predictability' (at certain scales).

Discovering life someplace else (unless it was so similar to Earth life as to imply a single origin) would tell us abiogenesis is not especially rare on the cosmic scale — that there is a class of worlds where life has a high probability of emerging.Why 'a high pobability of emerging', if the emergence process occurs at say, a point on a phase trajectory, which never returns to the same place (ie: the strange attractor described above)? (Just as an example).

Colin Robinson
2012-Nov-24, 08:18 AM
Not quite. Attractors are where a dynamic (time changing) system will end up eventually. It may not necessarily be an equilibrium point (eg: a marble rolling around inside a bowl ... in this case, the attractor would be where the marble ends up .. ie: an 'equilibrium' point, at the lowest point in the bowl)...

You've mentioned many classes of attractors... You haven't directly said either yes or no to my assertion that living things are also a sort of attractor, as are Kauffman's autocatalytic sets.

If an attractor is where a dynamic system will end up eventually, like a rolling marble ending up in the lowest point in a bowl... then what about a dynamic system consisting of an amoeba in a Petri dish surrounded by molecules of nutrient? Wouldn't the attractor be where the nutrient ends up -- in the body of the amoeba?


The emergence process might be the attractor.

That is Stuart's Kauffman's hypothesis, as I understand it — emergence of life is an attractor, in the sense that a dynamic system with sufficient diversity of complex interacting molecules will lead to emergence of auto-catalytic sets which will then evolve into organisms; although it is not predictable which specific compounds (out of the vast number of potential catalysts) the auto-catalytic sets will contain.


Why 'a high pobability of emerging', if the emergence process occurs at say, a point on a phase trajectory, which never returns to the same place (ie: the strange attractor described above)? (Just as an example).

I only said that IF we find a 2nd instance of life (e.g. on one of the outer moons), and it is chemically different enough to imply a separate origin, THEN we could draw the conclusion that emergence of life is not a rare event in the universe.

On the other hand, I'd agree that we may conceivably find that what has emerged on another world is a different attractor: a complex chemical system that falls outside our definition of what life is: an attractor we might call "weird non-life"...

MaDeR
2012-Nov-24, 10:06 AM
I will focus on most important point of discussion.




Anyway, if life is so insanely rare that it appeared on Earth only, it automatically make Earth special and unique on scale of entire universe for any reasonable definition of "unique" or "special", regardless of cause or lack of thereof.
…No .. why does the Earth have to be 'special and unique', if we have no idea as to how life emerges?
I assumed for purpose of this discussion that life is exclusive to Earth only. This make Earth unique even if "we have no idea as to how life emerges".

Let's repeat it again as simplest I can.

1. Assume life is present on Earth and Earth only.
2. Uniqueness is defined as entity having property that other entities does not have. In this case, 'property' is life, and 'entity' is planet.
3. Fact of 'uniqueness' of Earth does not rely on reason/cause of emergence of life.
4. Conclusion: it is enough that life is present only on Earth (assumption in 1) to consider Earth as unique (2), even if we do not know why life is only on Earth (3).

Do you have problem with any of these points?

Paul Wally
2012-Nov-24, 06:08 PM
If we are looking only for life as such, we may miss out on phenomena that are related to life and very relevant to the study of life, even if they don't fit into the category of life itself...

A fair point, and certainly an important consideration. But my issue is that if we are looking for life, then we can only look for life as we have defined it. But I'm not saying that we should look only for life and not also for things roughly similar. But anything that's roughly similar or even completely different could be categorized in relation to life as we've defined it. Perhaps it's better to speak of degrees of life-likeness within fuzzy set theory, but even in such a case there is a reference of what constitutes life such that other forms become then comparable to such a reference. What I find untenable is if we formulate a definition of life and then not apply it consistently to all situations, i.e. we should use the same definition whether we are on Earth, Mars, Titan, etc.



It's not just a question of the personal doubts of someone here. The probability/improbability of life emerging on any particular planet is an unresolved scientific question. There are theories, but no certainty.

Sure, probability is an unresolved question but so are many other questions, like how life emerges. Answering the question of how life emerges makes the question of probability conditional on what the answer to the question of life-emergence is. Probabilities are derived from how abiogenesis happens, but abiogenesis cannot be derived from statistical probabilities. Even if we somehow knew what the probabilities were, we would still not understand how abiogenesis happens. This is why I consider the question of abiogenesis more pertinent than the probabilities, firstly because probabilities are derivative from a theory of abiogenesis and secondly, because we're not going to get representative statistics from empirical data any time soon, and thirdly, even if we did somehow have representative statistics the phenomenon of abiogenesis would still be unexplained.



Discovering life someplace else (unless it was so similar to Earth life as to imply a single origin) would tell us abiogenesis is not especially rare on the cosmic scale — that there is a class of worlds where life has a high probability of emerging.


Indeed, a second discovery would tell us that. But if we had no reason to believe that abiogenesis should be rare then we would only have our suspicions confirmed, but nothing new is essentially learned from that fact. If we always suspected that abiogenesis shouldn't be rare and it turns out not to be rare then what new understanding is actually gained? Actually I'm beginning to think that more useful information is gained from finding a place where we expect abiogenesis to have happened but it didn't.


Yes, although a second instance would give us more clues to consider...

I suppose it would give us some clues, I'm just not a big fan of this approach. For instance, if we do find another instance of life then abiogenesis already happened there, perhaps billions of years ago, and then we're really in the same problematic situation as we are here on Earth and that is the problem of how it got started, unless we find a planet or moon where abiogenesis is in the process of happening, but how likely is that?

Colin Robinson
2012-Nov-25, 01:48 AM
A fair point, and certainly an important consideration. But my issue is that if we are looking for life, then we can only look for life as we have defined it. But I'm not saying that we should look only for life and not also for things roughly similar. But anything that's roughly similar or even completely different could be categorized in relation to life as we've defined it. Perhaps it's better to speak of degrees of life-likeness within fuzzy set theory, but even in such a case there is a reference of what constitutes life such that other forms become then comparable to such a reference. What I find untenable is if we formulate a definition of life and then not apply it consistently to all situations, i.e. we should use the same definition whether we are on Earth, Mars, Titan, etc.

Agree that we should use terms like "life" as consistently as we can.

Speaking in terms of degrees of life-likeness does have advantages, I think, for instance when discussing things like viruses and prions here on Earth. Also in relation to Titan — there's a tendency to think in either/or, yes/no terms, but reality may be more fuzzy, in the sense that Saturn's big moon may turn out to have systems that function like living things in certain respects but don't qualify in others.

For instance, what if there is a catalytic agent on Titan that is chemically quite complex, yet simpler than any bacterium, and it does things like promote decomposition of organics, and it also reproduces, in the sense of causing the formation of more little things rather like itself, however it doesn't pass on variations accurately enough for darwinian evolution to work?


Indeed, a second discovery would tell us that. But if we had no reason to believe that abiogenesis should be rare then we would only have our suspicions confirmed, but nothing new is essentially learned from that fact. If we always suspected that abiogenesis shouldn't be rare and it turns out not to be rare then what new understanding is actually gained?

I think there's an important distinction between suspecting and knowing.

For instance, exo-planets have been suspected to exist on theoretical grounds since the days of Giordano Bruno. There have also been eminent scientists, like James Jeans, who suspected that planets of other stars either didn't exist, or were extremely rare. The argument was settled by actual discovery of the first exo-planets, which was a historical breakthrough.

Probability of abiogenesis — whether it is cosmically rare or cosmically frequent — has likewise been a topic of theoretical argument. Quite a few biochemists, including Oparin and Christian de Duve, have suspected that it is a high-probability event, occurring throughout the cosmos on planets with favorable conditions. Other biochemists, such as Jacques Monod and Norman Horowitz, have suspected that abiogenesis is a low probability, cosmically rare event.

So, yes, I think we will have learned something important if we find that Mars or Titan has microbial life unrelated to life here on Earth.


Actually I'm beginning to think that more useful information is gained from finding a place where we expect abiogenesis to have happened but it didn't.

I'd agree that would scientifically interesting too.


I suppose it would give us some clues, I'm just not a big fan of this approach.

Is this because you think that we're likely to learn more about abiogenesis from lab work and/or theoretical modeling here on Earth, than by studying other worlds?


For instance, if we do find another instance of life then abiogenesis already happened there, perhaps billions of years ago, and then we're really in the same problematic situation as we are here on Earth and that is the problem of how it got started, unless we find a planet or moon where abiogenesis is in the process of happening, but how likely is that?

Not sure how likely, but in the case of Titan, I think it is quite conceivable. Have you heard of the hypothesis that it got its present, thick atmosphere quite recently, in terms of the history of the solar system? If that hypothesis is true, maybe an abiogenesis process has had time to start but not to finish...

Selfsim
2012-Nov-25, 04:27 AM
You've mentioned many classes of attractors... You haven't directly said either yes or no to my assertion that living things are also a sort of attractor, as are Kauffman's autocatalytic sets.It is not clear to me whether you are attempting (i) to establish an analogous model, (by hypothesising life to be some particular type of attractor), or (ii) whether you are asserting that life is an attractor in the emergence phase space in the physical universe?

All I've done is distinguish the different classes of attractors and describe how they are classified (by their behaviours). We have no idea about life's behaviours beyond Earth, or own emergence process, so why would you expect me to provide you with an answer to such a question?

Kauffman is working on creating a model from which we may learn something or, which might lead to some kind of test .. but so what? That doesn't make life an attractor in the physical universe.
His idea that autocatalytic sets might emerge from complex chemistry is clearly one of the leading contenders as far as hypotheses are concerned but again, that doesn't 'make it so', in the physical universe! (A detailed theoretical description of the mechanism and lab evidence might 'elevate' his hypothesis, however).

If an attractor is where a dynamic system will end up eventually, like a rolling marble ending up in the lowest point in a bowl... then what about a dynamic system consisting of an amoeba in a Petri dish surrounded by molecules of nutrient? Wouldn't the attractor be where the nutrient ends up -- in the body of the amoeba?The analogy may be valid .. but I wouldn't have the foggiest as to whether it meets the formal criteria for being described as an attractor. There is a formal mathematical definition of an attractor also, you know … we're not only talking about what might be an aesthetically pleasing learning aid, when it comes to what is, and isn't, an attractor.

That is Stuart's Kauffman's hypothesis, as I understand it — emergence of life is an attractor, in the sense that a dynamic system with sufficient diversity of complex interacting molecules will lead to emergence of auto-catalytic sets which will then evolve into organisms; although it is not predictable which specific compounds (out of the vast number of potential catalysts) the auto-catalytic sets will contain. So?
He has a hypothesis .. good on him .. so do many others …

I only said that IF we find a 2nd instance of life (e.g. on one of the outer moons), and it is chemically different enough to imply a separate origin, THEN we could draw the conclusion that emergence of life is not a rare event in the universe.I don't see how two data points can be used as a valid sample, indicative of what might happen elsewhere in the universe. Thus, 'rare' is still speculative, and without any particular evidence justification.

Selfsim
2012-Nov-25, 04:43 AM
I will focus on most important point of discussion.


I assumed for purpose of this discussion that life is exclusive to Earth only. This make Earth unique even if "we have no idea as to how life emerges".

Let's repeat it again as simplest I can.

1. Assume life is present on Earth and Earth only.
2. Uniqueness is defined as entity having property that other entities does not have. In this case, 'property' is life, and 'entity' is planet.
3. Fact of 'uniqueness' of Earth does not rely on reason/cause of emergence of life.
4. Conclusion: it is enough that life is present only on Earth (assumption in 1) to consider Earth as unique (2), even if we do not know why life is only on Earth (3).

Do you have problem with any of these points?You know, I could swear there's a logical fallacy in this argument somewhere … let's see …
i) assert the conclusion (out of thin air .. ie: step (1)) and then;
ii) proceed to use the assertion as the basis for ruling out other contending 'possibilities' (step (3));
iii) conclude that the eliminated possibilities are inconsequential to the uniqueness (step 4)!

I also notice your deletion of the term 'special' as in 'special and unique'.

I have no problems with the definition of unique.
The argument (if that's what it is supposed to be) presented in steps (1) to (4) is complete nonsense!

I could go on .. (but I've lost interest, I'm afraid).

Colin Robinson
2012-Nov-25, 06:02 AM
You know, I could swear there's a logical fallacy in this argument somewhere … let's see …
i) assert the conclusion (out of thin air .. ie: step (1))

I think you may have forgotten what this strand in the discussion was about: Whether the proposition that there is no life beyond Earth, if true, implies that Earth is exceptional/unique?

Was MaDeR's step one asserting a conclusion out of thin air, or was it simply a reminder of the proposition whose implications we've been discussing?

Paul Wally
2012-Nov-25, 04:23 PM
I think there's an important distinction between suspecting and knowing.

For instance, exo-planets have been suspected to exist on theoretical grounds since the days of Giordano Bruno. There have also been eminent scientists, like James Jeans, who suspected that planets of other stars either didn't exist, or were extremely rare. The argument was settled by actual discovery of the first exo-planets, which was a historical breakthrough.

Probability of abiogenesis — whether it is cosmically rare or cosmically frequent — has likewise been a topic of theoretical argument. Quite a few biochemists, including Oparin and Christian de Duve, have suspected that it is a high-probability event, occurring throughout the cosmos on planets with favorable conditions. Other biochemists, such as Jacques Monod and Norman Horowitz, have suspected that abiogenesis is a low probability, cosmically rare event.

So, yes, I think we will have learned something important if we find that Mars or Titan has microbial life unrelated to life here on Earth.

This really makes me wonder what it means to learn something new, i.e. to make scientific progress. I should give this some more thought, but currently I think an increase in knowledge is theory-relative. For instance if we have a theory of gravity predicting that everything with mass causes gravity, then we are not surprised when we find that there's gravity on Mars also and that things fall there just as they fall here. So no new information is added by, for example, writing in my scientific notebook that there is gravity on Mars, because that information is already contained in the theory of gravity.

Take for instance the organic soup hypothesis, which basically says that life will evolve in any sufficiently large and complex chemical solution in a liquid solvent given enough time and usable source of energy. I.e. the processes of self-organizing complexity will eventually lead to a type of organization that we call life. If we then find a planet where there is a liquid solvent, complex chemistry, energy source plus life, as the hypothesis predicts, then that would be a fact already contained in the hypothesis and no new information is therefore added by asserting that fact. It is only when some information is discovered not predicted by the hypothesis that we actually gain new information.



Is this because you think that we're likely to learn more about abiogenesis from lab work and/or theoretical modeling here on Earth, than by studying other worlds?

I would rather say that currently it's better to use experimental research and theoretical modeling for theory building and to use space exploration for theory testing. That's not to say we shouldn't use planetary data in addition whenever we can, it's just that at the moment it's a very inadequate empirical base to build a theory of abiogenesis on.



Not sure how likely, but in the case of Titan, I think it is quite conceivable. Have you heard of the hypothesis that it got its present, thick atmosphere quite recently, in terms of the history of the solar system? If that hypothesis is true, maybe an abiogenesis process has had time to start but not to finish...

That would be interesting. However, even in that case I don't think we will be able to observe the whole abiogenesis process but rather something like a snapshot of that process. I think this kind of empirical base (planetary and space exploration) is too sparse in space and time to build a theory on, but it's excellent for testing of theories.

MaDeR
2012-Nov-25, 05:50 PM
First let's remind what was in step 1 and 3:


1. Assume life is present on Earth and Earth only.
3. Fact of 'uniqueness' of Earth does not rely on reason/cause of emergence of life.



You know, I could swear there's a logical fallacy in this argument somewhere … let's see …
i) assert the conclusion (out of thin air .. ie: step (1))
Bzzt, error. This is NOT conclusion. Point 4 is conclusion.

Point 1 is assumption. They by their nature are from thin air. They are axioms in the way - you can take them or leave them. We are indeed, as Colin said, exploring consequences of certain scenario: "what if Earth is only place to have life in entire universe?". For this scenario to work, assumption shown in point 1 is neccessary.


ii) proceed to use the assertion as the basis for ruling out other contending 'possibilities' (step (3));
As expected, you contested this point. What is your justification? Why uniqueness of Earth would depend on some particular cause (or lack of thereof) for life being only on Earth?
Let's use some examples:
1. Cause: God said so and created universe last Thursday with this in mind. So, only Earth have life. Is Earth unique? Yes.
2. Cause: % of probablity of abiogenesis happening is insanely, extremely low on scale of universe. So, only Earth have life. Is Earth unique? Yes.
3. Cause: we did not found any life whastoever despite searching enitre universe for bilion years. So, only Earth have life. Is Earth unique? Yes.
4. Cause: omnicidal maniacal civilization of eldrith abominations killed everything and everyone, indcluding itself, but somehow overlooking our planet. So, only Earth have life. Is Earth unique? Yes.

What is difference? None. Regardless of cause, Earth is unique in any case, always. Therefore, knowledge of cause is not neccessary to determine "life is only on Earth, so Earth is unique".


I also notice your deletion of the term 'special' as in 'special and unique'.
What is difference? I remind that I am not native english speaker. I just shortened to "unique" in my steps as it is enough.


(but I've lost interest, I'm afraid).
What a shame.

Colin Robinson
2012-Nov-25, 06:58 PM
This really makes me wonder what it means to learn something new, i.e. to make scientific progress. I should give this some more thought, but currently I think an increase in knowledge is theory-relative. For instance if we have a theory of gravity predicting that everything with mass causes gravity, then we are not surprised when we find that there's gravity on Mars also and that things fall there just as they fall here. So no new information is added by, for example, writing in my scientific notebook that there is gravity on Mars, because that information is already contained in the theory of gravity.

Take for instance the organic soup hypothesis, which basically says that life will evolve in any sufficiently large and complex chemical solution in a liquid solvent given enough time and usable source of energy. I.e. the processes of self-organizing complexity will eventually lead to a type of organization that we call life. If we then find a planet where there is a liquid solvent, complex chemistry, energy source plus life, as the hypothesis predicts, then that would be a fact already contained in the hypothesis and no new information is therefore added by asserting that fact. It is only when some information is discovered not predicted by the hypothesis that we actually gain new information.

Perhaps the difference is this... Before any space probes got to Mars, the proposition that everything with mass has gravity was already very well established by means of Earth-based observations of trajectories of planets and moons. For instance, if Mars did not have gravity, why would Phobos and Deimos remain in orbit around Mars?

The hypothesis you've mentioned about the origin of life is not so well established... The view that life has a high probability of emerging in the conditions you've described is based on a conceptual model, and a generalization from a sample size of one...


I would rather say that currently it's better to use experimental research and theoretical modeling for theory building and to use space exploration for theory testing. That's not to say we shouldn't use planetary data in addition whenever we can, it's just that at the moment it's a very inadequate empirical base to build a theory of abiogenesis on.

That would be interesting. However, even in that case I don't think we will be able to observe the whole abiogenesis process but rather something like a snapshot of that process. I think this kind of empirical base (planetary and space exploration) is too sparse in space and time to build a theory on, but it's excellent for testing of theories.

Yes, "testing" is the key word here, I think.

tnjrp
2012-Nov-26, 06:28 AM
What is difference? None. Regardless of cause, Earth is unique in any case, always. Therefore, knowledge of cause is not neccessary to determine "life is only on Earth, so Earth is unique"It would indeed seem odd to argue against considering the possibility of exolife while not admiting to the possibility that Earth is indeed unique. OTOH Rare Earthers for example fairly celebrate the possibility of if-not-unque-then-at-least-exceedingly-special Earth.

MaDeR
2012-Nov-26, 01:58 PM
It would indeed seem odd to argue against considering the possibility of exolife while not admiting to the possibility that Earth is indeed unique. OTOH Rare Earthers for example fairly celebrate the possibility of if-not-unque-then-at-least-exceedingly-special Earth.
I suspect Selfism do not want to admit that in this scenario Earth is special and unique, because usually these kind of things are inevitably evisecrated and utterly destroyed by scientific progress. Earth was supposed to be in center of solar system/galaxy/universe/whatever and most important thing in entire universe, after all.
Copernican Principle is deadly thing for someone that do not agree with certain logical consequences of CP, yet agree and admit that so far CP was succesful in prediction of our role in universe, or rather lack of thereof.

Selfsim
2012-Nov-27, 02:08 AM
Its against my better judgement …
First let's remind what was in step 1 and 3:

Bzzt, error. This is NOT conclusion. Point 4 is conclusion.

Point 1 is assumption. They by their nature are from thin air. They are axioms in the way - you can take them or leave them. Axioms????
An axiom is something accepted as true without controversy .. they are so obvious, they are deemed to be self-evident!
So you think that assuming "life is present on Earth and Earth only", is a self-evident truth, eh?


We are indeed, as Colin said, exploring consequences of certain scenario: "what if Earth is only place to have life in entire universe?". For this scenario to work, assumption shown in point 1 is neccessary.… whatever …
It beats me why you're so fascinated with defining 'uniqueness'(?)
I've already stated I have no problems with the concept … but, 'to each his own', I suppose ...


ii) proceed to use the assertion as the basis for ruling out other contending 'possibilities' (step (3));As expected, you contested this point. What is your justification? Why uniqueness of Earth would depend on some particular cause (or lack of thereof) for life being only on Earth?
...
What is difference? None. Regardless of cause, Earth is unique in any case, always. Therefore, knowledge of cause is not neccessary to determine "life is only on Earth".Oh yeah?
Did I hear someone mention panspermia, lithopanspermia, exogenesis, or the PAH world hypotheses, (just to mention a few hypotheses which infer the possibility that life might not be unique to 'Earth and Earth only' …). I find this assumption to be so fatally flawed, specifically because it excludes other 'possibilities', that the follow-up, doesn't really justify further expenditure of time or electrons.


2. Cause: % of probablity of abiogenesis happening is insanely, extremely low on scale of universe. So, only Earth have life. Is Earth unique? Yes.No … even a likely outcome is not a dead certainty … therefore not 'unique' by necessity.

]3. Cause: we did not found any life whastoever despite searching enitre universe for bilion years. So, only Earth have life. Is Earth unique? Yes.No .. 'the entire universe' cannot be searched 'in a billion years' ...

Coming back to Colin's reminder of what this sub-discussion is all about ..
Whether the proposition that there is no life beyond Earth, if true, implies that Earth is exceptional/unique? The problem I have is with the proposition .. not the general point attempting to be (poorly) made, nor with the CP (at its level of applicability). The initial proposition cannot be verified in practice, and only qualifies in theory, when considered along with the antithesis that life exists elsewhere. The 'argument' in isolation, is pure pseudoscience, expressed in scientific and rational language (only). Thus follow-on consideration, is a waste of time.

TooMany
2012-Nov-27, 02:09 AM
So you find it impossible to think that life could be unique to Earth? That's fine as long as you realize that's your intuition speaking, not a scientific conclusion.


I strongly disagree that this is not science. In science we do use our intuition; we speculate (often with near certainty) and then verify. For example, seeing erosion channels on Mars we speculate that water once existed and we expect that minerals that form in water on earth would also form on Mars and then we actually find them (no big surprise).

Life is similar. It is almost absurd to seriously consider that it occurs no where else but on earth. Organic chemicals are found throughout the solar system and even floating around in interstellar space. We know that these chemicals spontaneous from more complex molecules found in life. Planets are now known to be common. What could possibly be so unique about earth that it would be the only place that life forms out of the 100s of billions of systems in the galaxy not to mention the millions of galaxies we can detect?

Selfsim
2012-Nov-27, 02:16 AM
Ok;

The reasons for my not wishing to continue in this discussion, have nothing to do with the points I’ve raised being shown to have any particular flaws. My reason for not wishing to continue, is that MaDer seems to hold the generalised Copernican Principle (CP) to be so all-important, at all scales, that it approximates a religious belief.

The language shortfalls also make it very difficult for me to follow MaDer’s ‘arguments’.

The CP is a guiding principle for astronomical research. It is continually under test. It was never intended to be applied as a working principle at all scales. It is irrelevant at the quantum level, which is currently thought to impact many biological processes. It has never been shown to be relevant at scales essential to the development of complex biology either.

The relationship between the Earth’s micro-scale environment, around the time thought to be applicable to abiogenesis, if it happened here, is unknown, and un-retraceable (in retrospect). As a consequence, there are thus also no ‘black and white’ definable characteristics at this scale, which would enable the ruling out of other classes of micro-factors, typically cited when presenting the case for uniqueness of life, (or its non-uniqueness). In this regard, our fixation with a single characteristic, (ie: the macro-scale Terran environment), which Earth possessed at the time, as being the predominating enabling ‘cause’ for abiogenesis repeating, is really without sufficient foundation -ie: certainly to the extent of ruling out the other possible influences known to impact complex system dynamics (perturbations). For example: (by way of a closely associated analogy): can we rule out uniqueness occurring across phenotypes, or evolving genotype variations, if eukaryotic life moves into space, or onto Mars, Europa, in vitrio? Clearly not, if the mechanism for it is a combination of the complexity of signalling and expression, the sheer size of the permutation/recombination space of gene structures, and is largely not dependent on broad-ranging environmental factors.

The point is: uniqueness or similarity, is not solely the product of a specific environment. There is nothing ‘unusual’ or ‘special’ about an environment, which makes this characteristic necessarily so, (or otherwise).

Word-play also comes into this. ‘Earth’ and whatever defines it, in the sense in which MaDer uses it, may quite easily be irrelevant, partially relevant, or fully relevant also, and so, the CP survives on this basis, (and appropriately so), yet again ....

Uniqueness is apparent at certain scales of the Universe, (ie: within a given search space). MaDer has never once acknowledged the point. The Lorenz formulae are a model for non-linear processes, which generate uniqueness within the combined phase space for a system, (spatially and temporally). This is a theoretical explanation for the short-term unpredictability of the weather, (a familiar, ‘everyday scale’ phenomenon). There are no constraints which would exclude the abiogenesis process from being critically influenced by considerations of this aspect, or even being a similar process, within this class of phenomenon. (His unsupportable initial ‘assumption’ (1), automatically rules out such possibilities, along with others such as panspermia hypotheses etc., and results in an apparent contradiction of the CP at astronomical scales. It is the initial ‘assumption’ which is flawed .. not the CP).

I have already stated that I have no problems with uniqueness at certain scales, within a given search space. I have already stated in this thread, the theoretical grounds upon which I would yield the argument (ie: the Infinite Universe). If MaDer was interested in a proper debate, he would have recognised these aspects, and moved on.

The field of Astrobiology cannot progress on the sole basis of Astronomical ‘principles’, (at astronomical scales) and I’m clearly not alone in stating this.

My overall perspective remains. The recognition of the validity of the state of being ‘unknown’, whilst taking full cogniscence of ‘working principles’ for Astronomical research, is important when exploring that unknown space. MaDer’s proposition rules that out, unjustifiably so, from the outset.

The usage of the CP to rule out ‘unknown’ aspects, which may/may not only be loosely associated with it, in this case, is entirely inappropriate, (for all the reasons stated).

Selfsim
2012-Nov-27, 02:41 AM
What could possibly be so unique about earth that it would be the only place that life forms out of the 100s of billions of systems in the galaxy not to mention the millions of galaxies we can detect?Try asking the question:

"What could possibly be so complex about the abiogenesis process, that it would generate a single life form, (ie: a LUCA), out of the 100s of billions of systems in the galaxy, not to mention the millions of galaxies we can detect in our observable universe, that it may not generate another instance of an exo-LUCA, which we'd relate to as 'life', within that same finite observable universe?"

Take a look at the permutation space in DNA. It is, numerically, 'astronomical' and yet, there is only one standard genetic code which is known to result in 'life'.

So, from that, it can be said that there is yet another instance of a known complex system, which numerically rivals the quantities you mention and yet, selects for only one common outcome, right under our noses!

Why would one think there are only two of 'em?

(Ah dunno … :shoulder-shrug: :) )

Cheers

Selfsim
2012-Nov-27, 06:22 AM
I strongly disagree that this is not science. In science we do use our intuition; we speculate (often with near certainty) and then verify.
PS: Oh, I forgot to add that useful scientific speculation should end up as a testable hypothesis.

A statement of what it would take to be falsified, also signals a properly formed hypothesis.

It is a common misconception to think that hypotheses end up undergoing 'verification' ... hypotheses are tested, and the results compared with pre-defined verification and falsification criteria, before forming conclusions. Sometimes, the motivation is actually from the negative perspective (falsification) of the hypothesis. Mathematicians, occasionally deliberately set out to disprove conjectures, also.

TooMany
2012-Nov-27, 04:17 PM
Take a look at the permutation space in DNA. It is, numerically, 'astronomical' and yet, there is only one standard genetic code which is known to result in 'life'.

Cheers

I have no idea what your point is. If you are referring to the possible sequences of amino acids in DNA molecules, yep that's vast, but what does this mean: "there is only one standard genetic code which is known to result in 'life'." The variation of genetic code in living things on the earth is vast also. What is this "one standard genetic code"?

Selfsim
2012-Nov-27, 08:28 PM
I have no idea what your point is. If you are referring to the possible sequences of amino acids in DNA molecules, yep that's vast, but what does this mean: "there is only one standard genetic code which is known to result in 'life'." The variation of genetic code in living things on the earth is vast also. What is this "one standard genetic code"?All known organisms, with extremely rare exceptions, use the same genetic code (http://en.wikipedia.org/wiki/Standard_genetic_code#RNA_codon_table) for for transmitting information from the genetic material to catalytic material. The few known exceptions are simple and minor variations from this standard genetic code.
All known organisms use highly (in the extreme) similar, (or 'the same'), metabolic pathways and enzymes, to process energy bearing molecules. In all eukaryotes, the process is performed in the same 10 steps, in the same order, using the same 10 enzymes, in spite of other 'possible' alternatives'.

The energy storage molecule is the same in all known species, (ie: ATP), even though there are others functionally capable of performing the role.

The structures to perform replication, heritability, catalysis and metabolism are all similar, (in spite of 'the odds' against it). They all use the same 4 polymers to perform these functions, (out of hundreds known). Chirality is common, (in spite of the alternatives).

DNA is synthesised from only four nucleosides out of the hundred or so known. Protein catalysis uses the same 22 amino acids out of the 400 (or so known).

Hepatitus B is one of the smallest known viruses with 3200 base pairs. This results in ~ 1.075x101924possible ordered sequences for this virus, and yet there is only one which defines Hepatitus B. (This number pretty much dwarfs the ~ 9 x 1021 stars in the observable universe).

The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Why would we be surprised about any of this?

Paul Wally
2012-Nov-27, 09:26 PM
All known organisms, with extremely rare exceptions, use the same genetic code (http://en.wikipedia.org/wiki/Standard_genetic_code#RNA_codon_table) for for transmitting information from the genetic material to catalytic material. The few known exceptions are simple and minor variations from this standard genetic code.
All known organisms use highly (in the extreme) similar, (or 'the same'), metabolic pathways and enzymes, to process energy bearing molecules. In all eukaryotes, the process is performed in the same 10 steps, in the same order, using the same 10 enzymes, in spite of other 'possible' alternatives'.

The energy storage molecule is the same in all known species, (ie: ATP), even though there are others functionally capable of performing the role.

The structures to perform replication, heritability, catalysis and metabolism are all similar, (in spite of 'the odds' against it). They all use the same 4 polymers to perform these functions, (out of hundreds known). Chirality is common, (in spite of the alternatives).

DNA is synthesised from only four nucleosides out of the hundred or so known. Protein catalysis uses the same 22 amino acids out of the 400 (or so known).

Hepatitus B is one of the smallest known viruses with 3200 base pairs. This results in ~ 1.075x101924possible ordered sequences for this virus, and yet there is only one which defines Hepatitus B. (This number pretty much dwarfs the ~ 9 x 1021 stars in the observable universe).

The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Why would we be surprised about any of this?

So we have a LUCA. How is that relevant to the question of abundance or rarity of life in the universe? Correct me if I'm wrong but your argument goes that something very specific happened on Earth which lead to the formation of life on Earth, and that makes it a very unlikely event. Therefore the chances that this same specific event happening somewhere else is unlikely.

That reasoning is fundamentally flawed because we don't know whether the specific event that happened on Earth is the only event leading to life.
The other specifics you're mentioning ATP, DNA nucleotides , Hepatitus B etc. are completely irrelevant to the issue of abundance/rarity of life in the universe, because they follow from natural selection in biological evolution, and were specifically selected because they work so well here.

Selfsim
2012-Nov-27, 10:22 PM
So we have a LUCA. How is that relevant to the question of abundance or rarity of life in the universe? Correct me if I'm wrong but your argument goes that something very specific happened on Earth which lead to the formation of life on Earth, and that makes it a very unlikely event. Therefore the chances that this same specific event happening somewhere else is unlikely. Incorrect. I have not made this 'claim'. My only claim is that: 'we don't know'.

The point I'm raising, (on the other hand) is, as I said:

The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Why would we be surprised about any of this?

Focusing on 'planetary environments', is only one way to view abiogenesis. A dynamic systems (or process) perspective is yet another way .. and it leads to considerations of the broader spectrum of possible influences. I am not using the perspective to assert anything about how it necessarily occurred … we don't know how it occurred.

Colin Robinson
2012-Nov-27, 11:45 PM
Its against my better judgement … Axioms????
An axiom is something accepted as true without controversy .. they are so obvious, they are deemed to be self-evident!
So you think that assuming "life is present on Earth and Earth only", is a self-evident truth, eh?

The word "axiom" is used somewhat differently in classical Greek thought and in modern logic. Its classical meaning is a self-evident truth. Its meaning in modern logic is a proposition used as the starting point of an argument. (See the WP page Axiom (http://en.wikipedia.org/wiki/Axiom).)

MaDeR was using the word axiom in the modern sense, not the classical sense, I think.


hypotheses are tested, and the results compared with pre-defined verification and falsification criteria, before forming conclusions. Sometimes, the motivation is actually from the negative perspective (falsification) of the hypothesis. Mathematicians, occasionally deliberately set out to disprove conjectures, also.

Yes, scientific and mathematic arguments often begin with a proposition (or axiom) whose truth or falsity is unknown. In order to consider the question: If this proposition were true, what would the implications be?

And this can sometimes lead to the initial proposition being shown to be false, or at least less plausible than it appeared at first glance.


Hepatitus B is one of the smallest known viruses with 3200 base pairs. This results in ~ 1.075x101924possible ordered sequences for this virus, and yet there is only one which defines Hepatitus B. (This number pretty much dwarfs the ~ 9 x 1021 stars in the observable universe).

The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Why would we be surprised about any of this?

I don't think anyone expects a particular Earth species (e.g. the hepatitis B virus) to be exactly duplicated on another world with an independent line of evolution. In this sense, yes, each species is unique.

The question is whether life on Earth is radically exceptional, in the sense that there are no systems elsewhere which have energy flowing through them as they metabolize and reproduce?

Paul Wally
2012-Nov-28, 12:24 AM
The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Focusing on 'planetary environments', is only one way to view abiogenesis. A dynamic systems (or process) perspective is yet another way .. and it leads to considerations of the broader spectrum of possible influences. I am not using the perspective to assert anything about how it necessarily occurred … we don't know how it occurred.

In that case I don't know what you're saying or implying. "Uniqueness" becomes a kind of wooly concept. Everything is unique, except maybe elementary particles like electrons.

Selfsim
2012-Nov-28, 02:51 AM
"Uniqueness" becomes a kind of wooly concept. Everything is unique, except maybe elementary particles like electrons.And in the light of seeing nothing but absurdity when seriously considering the possibility that life might not occur elsewhere, (for reasons based flawed (woolly) statistical arguments which lead to conclusions of 'likely' or 'unlikely'), that's just the place to be.

TooMany
2012-Nov-28, 07:49 PM
All known organisms, with extremely rare exceptions, use the same genetic code for for transmitting information from the genetic material to catalytic material. The few known exceptions are simple and minor variations from this standard genetic code.
All known organisms use highly (in the extreme) similar, (or 'the same'), metabolic pathways and enzymes, to process energy bearing molecules. In all eukaryotes, the process is performed in the same 10 steps, in the same order, using the same 10 enzymes, in spite of other 'possible' alternatives'.

The energy storage molecule is the same in all known species, (ie: ATP), even though there are others functionally capable of performing the role.


I accept what you say, about the deep similarities among the life forms that we know about, as correct. The idea that we "know" that alternative processes are equally capable requires some evidence. We don't really know the exact reasons for this consistency. One likely possibility is common origin that has simply been replicated. Another possibility is that there actually are (for example) subtle differences among these amino acids that make the particular ones we find DNA more successful.

There is both divergence and convergence evident in the evolution of life forms on earth. Obvious macro examples of convergence are the independent emergence of flight in insects, birds and mammals (and even fish). Bats and birds have a great deal in common, but you cannot argue for a common (inherited) origin of their ability to fly. Another example is the similarity between the structure of the eye in an octopus (an invertebrate) and our own eyes. Sometimes similar things happen just because they work (have advantages). Other times there are happenstance "choices" made by evolution that favor a particular scheme where many others would succeed as well.

What are you suggesting that this commonality of biochemical processes implies?



Hepatitus B is one of the smallest known viruses with 3200 base pairs. This results in ~ 1.075x101924possible ordered sequences for this virus, and yet there is only one which defines Hepatitus B. (This number pretty much dwarfs the ~ 9 x 1021 stars in the observable universe).


This is a fallacious argument for "uniqueness" in the sense of something "special", "specific" or "having only one possible form". You might also argue that after I shuffle a deck of cards, the order of the cards presents some sort of important "uniqueness". Only a very few of the permutations you suggest will result in a viable HB virus. On the other hand, we know that virus evolve quite quickly. This is something we observe from year to year in the flu virus. May I suggest that the Hepatitis B virus (as an identifiable entity through its effects, manner of reproduction and so on) is far from unique. There are doubtless millions of possible variations of this viral DNA that will function in a similar manner.
[/QUOTE]



The point of all this, is simply that 'uniqueness' (and similarity) defined within 'natural systems', is commonplace, in spite of 'the odds' against it (or the odds for it). 'Near uniqueness', is simply a variant of the system definition.

Why would we be surprised about any of this?

I don't think anyone expects a particular Earth species (e.g. the hepatitis B virus) to be exactly duplicated on another world with an independent line of evolution. In this sense, yes, each species is unique.

The question is whether life on Earth is radically exceptional, in the sense that there are no systems elsewhere which have energy flowing through them as they metabolize and reproduce?


I don't think the use of "unique" is all that useful in this discussion. I doubt that any exobiologist expects that life in another system will be exactly like life on earth, but there are arguments that can be made in support of the probability of similarities.

For me, it is foolish to propose that earth is radically exceptional because there is no basis for such an expectation. The fact that we have not yet contacted aliens or discovered alien lifeforms is nearly irrelevant, since we have barely begun to look. It is in fact the very expectation that life can arise elsewhere that largely funds our Mars exploration. If we fail to find evidence of life on Mars, that is hardly proof of a universal negative or of some uniqueness of earth. However, if we do find life on Mars, then there will be increased acceptance of the possibility that life is common in the universe and more interest in finding alien life will follow.

Colin Robinson
2012-Nov-29, 11:39 AM
TooMany, a couple of sentences you've quoted as Selfsim's were actually not his.

I was the one who wrote (in posting #80 of this thread).


I don't think anyone expects a particular Earth species (e.g. the hepatitis B virus) to be exactly duplicated on another world with an independent line of evolution. In this sense, yes, each species is unique.

The question is whether life on Earth is radically exceptional, in the sense that there are no systems elsewhere which have energy flowing through them as they metabolize and reproduce?

I agree with your answer to the question I raised. We have no basis for expecting Earth to be radically exceptional.

TooMany
2012-Nov-29, 07:05 PM
TooMany, a couple of sentences you've quoted as Selfsim's were actually not his.

I was the one who wrote (in posting #80 of this thread).



I agree with your answer to the question I raised. We have no basis for expecting Earth to be radically exceptional.

Sorry about that error. I'm puzzled by these apparently negative attitudes toward using our brains to conjecture what might be and then pursuing evidence thereof. As if speculation should be outlawed for some unspecified reason or that it has no value.

Colin Robinson
2012-Nov-29, 09:08 PM
Sorry about that error. I'm puzzled by these apparently negative attitudes toward using our brains to conjecture what might be and then pursuing evidence thereof. As if speculation should be outlawed for some unspecified reason or that it has no value.

I agree that forming conjectures and looking for evidence (either for or against the conjecture) is an important part of science.

The scientists I respect most are those who can take seriously two or more very different conjectures about the same topic.

A couple of quotations for the current NASA Astrobiology Roadmap (2008) (https://astrobiology.nasa.gov/roadmap/).

"The existence of lakes of liquid hydrocarbons on Titan opens up the possibility for solvents and energy sources that are alternatives to those of our biosphere and that might support novel life forms altogether different from those on Earth." (p 718)

On the other hand...

"If life never developed elsewhere in our Solar System, is there a prebiotic record preserved in ancient rocks that might contain clues about how life began on Earth?" (p 719)

TooMany
2012-Nov-29, 11:05 PM
"The existence of lakes of liquid hydrocarbons on Titan opens up the possibility for solvents and energy sources that are alternatives to those of our biosphere and that might support novel life forms altogether different from those on Earth." (p 718)


Yep, that's a cool thing to check out (and even more speculative than earth-like life since we have no example). Is nature biased toward one type of chemical environment for life?

There is also the possibility of more conventional (water-based) organic life in Europa (for example) to explore.

Even if we do eventually find some evidence of life on Mars, a debate about whether it arose separately may arise. So some may still suggest that life is fantastically unlikely to emerge.

whimsyfree
2012-Nov-30, 01:53 AM
The question is whether life on Earth is radically exceptional
...
We have no basis for expecting Earth to be radically exceptional.

That's a different question. Many writers have suggested that Earth is exceptional. It has variously been suggested that the existence or properties of the following features of the Earth and Solar System are (1) likely unusual based on our observations of exoplanets and our hypotheses concerning their formation, and (2) necessary for the development of intelligent life. (cf Rare Earth hypothesis)


large moon
"moderate" rotation
asteroid belt
Jupiter
Kuiper belt
lack of large planets in the inner solar system
circular orbits
water in the inner solar system


I don't entirely buy it.

Selfsim
2012-Nov-30, 03:02 AM
I agree that forming conjectures and looking for evidence (either for or against the conjecture) is an important part of science.And don't kid yourself that science is what's going on here!

MaDeR
2012-Nov-30, 08:15 PM
Axioms????
Yep. I even checked and it happens I used this word properly. Whew, life of non-native english speaker is hard.


So you think that assuming "life is present on Earth and Earth only", is a self-evident truth, eh?
Nope. I assumed that for needs of this discussion. "Premise or starting point for reasoning" indeed.




What is difference? None. Regardless of cause, Earth is unique in any case, always. Therefore, knowledge of cause is not neccessary to determine "life is only on Earth".
Did I hear someone mention panspermia, lithopanspermia, exogenesis, or the PAH world hypotheses, (just to mention a few hypotheses which infer the possibility that life might not be unique to 'Earth and Earth only' …). I find this assumption to be so fatally flawed, specifically because it excludes other 'possibilities', that the follow-up, doesn't really justify further expenditure of time or electrons.
Now you are challenging assumption? This is red herring, distraction. I do not discuss if life is only on Earth now. In fact, you should know that I hold completely opposite view.

I claimed that if only Earth have life, then Earth is special/unique. You dissagreed with it vehemently before, now you are strangely silent about it and sidestep this issue as much as you can.

Instead of explaining why having life only on Earth do not make Earth unique/special, you dispute assumption that only Earth have life. My original claim is left uncontested.

TooMany
2012-Nov-30, 08:41 PM
I don't entirely buy it.

Neither do I. Take the large moon one. It seems remote to me that life cannot form, adapt and thrive just because there are no tides. Just look at all the strange conditions under which life thrives on earth! Life is a robust thing. So what if there's no Jupiter to clear out the Kuiper or asteroid belt? Maybe without such a major perturbation of orbits the bombardment would be much less. Have to admit though that I not familiar with the detailed analysis.

Of course we will never know for sure without continuing to explore other stellar systems. I sure wish that NASA would spend more money on this stuff than on putting people in orbit at 1.4 billion a shot to study what happens to worms in micro-G.

TooMany
2012-Nov-30, 08:46 PM
And don't kid yourself that science is what's going on here!

I think you confuse science with mathematics. (But even in mathematics we have speculations which are a driving force.)

Selfsim
2012-Dec-01, 03:26 AM
I think you confuse science with mathematics. (But even in mathematics we have speculations which are a driving force.)How do you come that conclusion?

Please explain … (I'm curious).

whimsyfree
2012-Dec-01, 03:52 AM
Neither do I. Take the large moon one. It seems remote to me that life cannot form, adapt and thrive just because there are no tides.


Tides and a stable obliquity is the supposed other essential benefit.


Just look at all the strange conditions under which life thrives on earth! Life is a robust thing.


True. I don't think intelligent life is common but I think it might turn up somewhere we don't expect. Some people seem to think it can happen only on an Earth-clone in a Solar System-clone.


So what if there's no Jupiter to clear out the Kuiper or asteroid belt? Maybe without such a major perturbation of orbits the bombardment would be much less. Have to admit though that I not familiar with the detailed analysis.


Jupiter is supposed to have provided just the right perturbations to bring water-rich planetesimals in from the Kuiper belt to provide Earth's oceans. At one time it was thought to be a comet shield, but that doesn't seem to work. I'm not sure what use the asteroid belt is supposed to be, but a recent preprint suggested that asteroid belts like ours are rare and this was somehow connected to the rarity of life. Maybe you need just the right rate and scale of bolide impacts to kick evolution along.


Of course we will never know for sure without continuing to explore other stellar systems. I sure wish that NASA would spend more money on this stuff than on putting people in orbit at 1.4 billion a shot to study what happens to worms in micro-G.

Yes but I think we will be observing other stellar systems rather than exploring them for the next few centuries.

Selfsim
2012-Dec-01, 04:03 AM
Yep. I even checked and it happens I used this word properly. Whew, life of non-native english speaker is hard.

Nope. I assumed that for needs of this discussion. "Premise or starting point for reasoning" indeed.

Now you are challenging assumption? This is red herring, distraction. I do not discuss if life is only on Earth now. In fact, you should know that I hold completely opposite view.



I claimed that if only Earth have life, then Earth is special/unique. You dissagreed with it vehemently before, now you are strangely silent about it and sidestep this issue as much as you can. Instead of explaining why having life only on Earth do not make Earth unique/special, you dispute assumption that only Earth have life. My original claim is left uncontested.Post #64:
I have no problems with the definition of unique.Post #71:
It beats me why you're so fascinated with defining 'uniqueness'(?)
I've already stated I have no problems with the concept … but, 'to each his own', I suppose …Post#73:
I have already stated that I have no problems with uniqueness at certain scales, within a given search space. I have already stated in this thread, the theoretical grounds upon which I would yield the argument (ie: the Infinite Universe). If MaDer was interested in a proper debate, he would have recognised these aspects, and moved on.As already stated three times over (above), I have no problems with defining uniqueness, which is all you're doing.

The rest is meaningless nonsense. Move on.

Colin Robinson
2012-Dec-01, 06:35 AM
As already stated three times over (above), I have no problems with defining uniqueness, which is all you're doing.

The rest is meaningless nonsense.

Selfsim, if it seems like nonsense to you, perhaps that is because you've forgotten how this part of the discussion began.

In Post #27 of this thread, I wrote:


I think the Loch Ness Monster is a misleading analogy, for the following reasons...

3.The proposition that life does not exist beyond Earth, if true, implies that Earth is radically exceptional — that there a great class of phenomena happening here which doesn't happen on any other of the billions of planets and moons in the universe. The proposition that Nessie does not exist has no such exceptionalist implication.

When you say that you "have no problems with defining uniqueness", do you mean that you now agree with the point I made in Post #27?

Selfsim
2012-Dec-01, 08:30 PM
I think the Loch Ness Monster is a misleading analogy, for the following reasons…

3.The proposition that life does not exist beyond Earth, if true, implies that Earth is radically exceptional — that there a great class of phenomena happening here which doesn't happen on any other of the billions of planets and moons in the universe. The proposition that Nessie does not exist has no such exceptionalist implication.When you say that you "have no problems with defining uniqueness", do you mean that you now agree with the point I made in Post #27?As I have already stated elsewhere, with all things being equal. I, personally, try to deliberately refrain from passing judgement between 'competing' speculations. Such a judgement would be mostly as meaningless as the speculations themselves.

None-the-less, as an expression of 'good faith', I offer the below incremental views:

For starters, the analogy and question are too sloppy for me to give you a straight answer. So I'll do my best to rephrase what I think are the fundamental questions ...

i) If there are hypothetical things for which we have no direct physical evidence of, can these have implications for us?
Answer: depends on the substance forming the hypothesis. (Eg: the Oort cloud has implications for us, Strings have implications for us, Dark Matter has implications for us, etc). In some cases, the answer could also be 'unknown'. In other cases, the answer might be an outright: 'No'. In others: 'maybe'.

ii) If there are completely mythical fantasy things, (exceptional to the laws of science), for which we have no physical evidence for, nor means of detection or testing, can these have implications for us? (Eg: Undetectable non-interacting unicorns, beings who dwell beyond our particle horizon, etc)
Answer: Nope.

iii) If there are instances of theoretically possible things, for which we have no direct physical evidence of, can these have implications for us? (Eg: cells which use UTP instead of ATP as their primary energy extraction mechanism, Lorentz symmetry violation, etc)
Answer: Possibly. Depends on the theory.

iv) If there are instances of detectable living things classifiable as a 'type' of biological category for which we already have physical evidence of, in a location other than (near) Earth, can these have implications for us? (Eg: carbon-based life dwelling on Gliese 667Cc).
Answer: Maybe. That would depend on what information their existence returns to us. To a large degree, the ensuing implications might range from hypothetical, to theoretical, to philosophical, right down to personal taste and opinion.

Colin Robinson
2012-Dec-01, 09:10 PM
the analogy and question are too sloppy for me to give you a straight answer.

Not sure what you mean by "sloppy"...

Selfsim
2012-Dec-01, 09:22 PM
Not sure what you mean by "sloppy"...Respectfully, I'm not too surprised about that either.
Our thinking seems to live in separate domains … there may be overlap however … (I'm trying to find it). :)

TooMany
2012-Dec-01, 10:20 PM
Tides and a stable obliquity is the supposed other essential benefit.


Are Mars, Venice and Mercury doing flip-flops because they don't have a large moon? (Strange coincidence about the Martian day and tilt.) I just read that they think that Mars' axis has changed dramatically in the distant past. But I don't understand why the spin axis would be unstable unless it was affected by major impacts. Doesn't a substantial change in the axis require a substantial change in angular momentum? Impacts of that magnitude would probably be sterilizing events.



True. I don't think intelligent life is common but I think it might turn up somewhere we don't expect. Some people seem to think it can happen only on an Earth-clone in a Solar System-clone.


It seems quite reasonable to suspect that intelligent life is much rarer than life in general because it takes so long to evolve.



Jupiter is supposed to have provided just the right perturbations to bring water-rich planetesimals in from the Kuiper belt to provide Earth's oceans. At one time it was thought to be a comet shield, but that doesn't seem to work. I'm not sure what use the asteroid belt is supposed to be, but a recent preprint suggested that asteroid belts like ours are rare and this was somehow connected to the rarity of life. Maybe you need just the right rate and scale of bolide impacts to kick evolution along.


Well, they can't have it both ways, both shield and bringer of water-bearing comets. Maybe I'm biased, but I cannot put much stock in these "earth is so special" theories until we know a lot more from observations.



Yes but I think we will be observing other stellar systems rather than exploring them for the next few centuries.

Probably. It will be far more practical to observe than to travel there. We may need the enticement of finding a nearby world that has signs of life before there would be enough motivation to launch an interstellar probe.

I'd be interested to know whether anyone has given thought to the practical limitations of observation from afar. For example could it be practical in theory to observe a planet several light years away with the degree of resolution that we get from our earth satellites?

TooMany
2012-Dec-01, 10:34 PM
How do you come that conclusion?

Please explain … (I'm curious).

Well first let me admit that I have only the vaguest idea what point or points you are trying to make in this thread. But to answer the question, it seems like you arguing that science consists of only absolutely provable things (in an almost mathematical sense). You seem to be saying that if QED is not written at the bottom then it's not science and should be completely disregarded. I believe you even suggested that a punitive tax should be levied on those who make scientific speculations. So my thinking was that you are confusing abstract mathematics in which we prove everything step by step, with science in which we observe, speculate (hypothesize) and observe some more.

Selfsim
2012-Dec-02, 03:14 AM
... But to answer the question, it seems like you arguing that science consists of only absolutely provable things (in an almost mathematical sense).I'm quite clear that science doesn't attempt proofs. People do, as does the Judicial process. Mathematics does. I am not arguing that science consists of any proofs, whatsoever.

You seem to be saying that if QED is not written at the bottom then it's not science and should be completely disregarded.You think things written here constitute science??!!?
I believe you even suggested that a punitive tax should be levied on those who make scientific speculations.Punitive? No … electrons are multi-purpose, and thus have more useful roles to play. A tax would help to bring home that fact, don't you think?
I'm yet to see any statements made here, which I'd call productive scientific speculation. (I'm hangin' out in hope of spotting one).
So my thinking was that you are confusing abstract mathematics in which we prove everything step by step, with science in which we observe, speculate (hypothesize) and observe some more.Well I'm quite clear on the distinctions of theoretical axiomatic proof structures and the structures of reality. Proofs of theorems comprise pure logic and do not rely on evidence at all. If there are 10 causes for something and you prove a conjecture for 9 of them, you still haven't completed a mathematical proof. So which is it to be here? Use of mathematical grounds, (eg: statistical arguments), to support claims of 'likely' 'unlikely', 'probable', 'improbable' or, ... testable hypotheses capable of generating physical evidence?

Either way, when it comes to the topic of this thread, neither approach has resulted in anything of value in support of the inference-based case for, or against, the existence of alien lifeforms in the physical universe, (drawing upon data taken from our own instance).

(Bring on that tax, I say .. (just as an exclamation point) … we can afford it, y'know ... we're up to post #102!).

Hornblower
2012-Dec-02, 10:54 AM
Are Mars, Venice and Mercury doing flip-flops because they don't have a large moon? (Strange coincidence about the Martian day and tilt.) I just read that they think that Mars' axis has changed dramatically in the distant past. But I don't understand why the spin axis would be unstable unless it was affected by major impacts. Doesn't a substantial change in the axis require a substantial change in angular momentum? Impacts of that magnitude would probably be sterilizing events.
The reputed change in spin axis obliquity is a gradual drift over many millions of years as a result of gravitational perturbations from the other planets, not an abrupt change from a large impact. Such a drift could destabilize the climate during the long time that may be required for the evolution of advanced, complex life forms and perhaps preclude them. The change in the spin component of the planet's angular momentum would be balanced by a proportionately slight change in its orbit, as I think I understand it.

Supercomputer simulations show that our large Moon can prevent similar drift of Earth's spin axis obliquity.





It seems quite reasonable to suspect that intelligent life is much rarer than life in general because it takes so long to evolve.



Well, they can't have it both ways, both shield and bringer of water-bearing comets. Maybe I'm biased, but I cannot put much stock in these "earth is so special" theories until we know a lot more from observations.



Probably. It will be far more practical to observe than to travel there. We may need the enticement of finding a nearby world that has signs of life before there would be enough motivation to launch an interstellar probe.

I'd be interested to know whether anyone has given thought to the practical limitations of observation from afar. For example could it be practical in theory to observe a planet several light years away with the degree of resolution that we get from our earth satellites?

Hornblower
2012-Dec-02, 11:47 AM
Addendum: I have read that given the apparent abundance of planets, many biologists believe that life at the microbe level is commonplace, but that advanced forms comparable to ourselves may be exceedingly rare. In other words, Planet Earth, with its combination of abundant water, geological activity and stable spin axis over billions of years, might be a freak.

Unfortunately I have only my memory here, with no references at my fingertips. I welcome any input in finding references.

TooMany
2012-Dec-02, 06:15 PM
Addendum: I have read that given the apparent abundance of planets, many biologists believe that life at the microbe level is commonplace, but that advanced forms comparable to ourselves may be exceedingly rare. In other words, Planet Earth, with its combination of abundant water, geological activity and stable spin axis over billions of years, might be a freak.

Unfortunately I have only my memory here, with no references at my fingertips. I welcome any input in finding references.

Quite possibly evolution of intelligent life is very rare, but what if it evolved somewhere in the galaxy a billion years ago?

Thanks for the info about Mars' axis. My understanding of dynamics is very immature. It seems intuitive but apparently incorrect, that influences of even large planets like Jupiter would be extremely small on a spinning planet with spherical symmetry. I mean how do perturbations from say Jupiter "get a grip" on Mars to change it's angular momentum? I'll do some googling.

Hornblower
2012-Dec-02, 10:28 PM
Quite possibly evolution of intelligent life is very rare, but what if it evolved somewhere in the galaxy a billion years ago?Perhaps it is thriving to this day, but is isolated from any contact with us by the inherent barriers imposed by the vast distance.


Thanks for the info about Mars' axis. My understanding of dynamics is very immature. It seems intuitive but apparently incorrect, that influences of even large planets like Jupiter would be extremely small on a spinning planet with spherical symmetry. I mean how do perturbations from say Jupiter "get a grip" on Mars to change it's angular momentum? I'll do some googling.

The same way the Sun's gravity "gets a grip" on Mars. The gravity gradient causes a torque on the tilted equatorial bulge of the planet and results in precession, just as with Earth. The magnitude as well as the direction of the tilt changes in ways that are hard to calculate in multibody problems. It is not physics-101 neat and clean the way the action of a laboratory gyro is. Of course the contribution from Jupiter or any other planet is tiny, but nevertheless capable of significant effects over many millions of years.

whimsyfree
2012-Dec-03, 01:24 AM
Are Mars, Venice and Mercury doing flip-flops because they don't have a large moon?


The solar tide keeps the axes of Venus and Mercury stable. According to wikipedia, Mars wobbles about considerably (up to about 60o). Venice is slowly sinking into the Adriatic.


(Strange coincidence about the Martian day and tilt.)


Yes. Pity the mass wasn't included in the coincidence.


I just read that they think that Mars' axis has changed dramatically in the distant past. But I don't understand why the spin axis would be unstable unless it was affected by major impacts.


Small torques induced mainly by Jupiter are responsible.


I'd be interested to know whether anyone has given thought to the practical limitations of observation from afar. For example could it be practical in theory to observe a planet several light years away with the degree of resolution that we get from our earth satellites?

Its been discussed here before. The answer is yes if you are prepared to spend the money required to send large fleets of satellites into the outer solar system.


Addendum: I have read that given the apparent abundance of planets, many biologists believe that life at the microbe level is commonplace, but that advanced forms comparable to ourselves may be exceedingly rare. In other words, Planet Earth, with its combination of abundant water, geological activity and stable spin axis over billions of years, might be a freak.

Unfortunately I have only my memory here, with no references at my fingertips. I welcome any input in finding references.

It's not something that anyone really knows anything about, so references mainly serve to stimulate the imagination rather than inform.

It may be that Earth is simply lucky. It may have been dodging bullets for four billion years.

Hornblower
2012-Dec-03, 01:55 AM
The solar tide keeps the axes of Venus and Mercury stable. According to wikipedia, Mars wobbles about considerably (up to about 60o). Venice is slowly sinking into the Adriatic.



Yes. Pity the mass wasn't included in the coincidence.



Small torques induced mainly by Jupiter are responsible.



Its been discussed here before. The answer is yes if you are prepared to spend the money required to send large fleets of satellites into the outer solar system.



It's not something that anyone really knows anything about, so references mainly serve to stimulate the imagination rather than inform.

It may be that Earth is simply lucky. It may have been dodging bullets for four billion years.

My bold. No, references would confirm that what I quoted really was in print, and not merely in my imagination. I think I saw it in Sky and Telescope years ago. I have the complete Sky and Telescope on CDs, but the rudimentary search function is useless for this.

There are not many bullets to dodge compared to what could have been. I agree that the occurrence of large planets over a large expanse of our system has contributed to making Earth relatively safe from catastrophic impacts for several billion years.

swampyankee
2012-Dec-03, 01:30 PM
I believe the reason the spin axis is unstable for some combinations of spin axis and rate of rotation is because of perturbations from other bodies in the Solar System. A large moon may stabilize the axial tilt, restricting it to some small range.

I question, however, the conclusion that an unstable axial tilt is inimical to life, as ecosystems built up around black (or white) smokers would be largely immune to the climatic disturbances from an unstable axial tilt. Also, instability at either sufficiently long -- tens of millions of years -- or sufficiently short -- weeks -- time scales are not likely to be inimical to life.

TooMany
2012-Dec-04, 12:38 AM
The gravity gradient causes a torque on the tilted equatorial bulge of the planet and results in precession, just as with Earth. The magnitude as well as the direction of the tilt changes in ways that are hard to calculate in multibody problems. It is not physics-101 neat and clean the way the action of a laboratory gyro is. Of course the contribution from Jupiter or any other planet is tiny, but nevertheless capable of significant effects over many millions of years.

The bold is what I was wondering about when I asked how it "gets a grip". These problems are too complex to solve analytically (I'm guessing) so we use supercomputer simulations. I wonder if we also know how stable the simulations themselves are, given that the accuracy is finite. I suppose the math whizzes figure that out in order to trust their simulations. I noticed that there are apparently some people with opposing views who claim that tidal interactions with the sun or with the viscous material in planetary cores are sufficient to dampen perturbations and stabilize rotation. Of course I have no idea who is correct.

All the various orbital resonances that we see in the solar system are clear evidence that these interactions are important in the long run. Permanent chaos seems to be somehow avoided.

TooMany
2012-Dec-04, 12:42 AM
(Strange coincidence about the Martian day and tilt.)


Yes. Pity the mass wasn't included in the coincidence.


Be careful what you wish for. ;)

TooMany
2012-Dec-04, 12:53 AM
I believe the reason the spin axis is unstable for some combinations of spin axis and rate of rotation is because of perturbations from other bodies in the Solar System. A large moon may stabilize the axial tilt, restricting it to some small range.

I question, however, the conclusion that an unstable axial tilt is inimical to life, as ecosystems built up around black (or white) smokers would be largely immune to the climatic disturbances from an unstable axial tilt. Also, instability at either sufficiently long -- tens of millions of years -- or sufficiently short -- weeks -- time scales are not likely to be inimical to life.

Good point. We have plenty of animals on land, in the air and in the sea that make very long migrations annually; 10 million years would not be a problem. However I suppose an argument might be that a world with it's spin axis in the orbital plane would have a climate too drastic to support large life forms?

TooMany
2012-Dec-04, 12:59 AM
Either way, when it comes to the topic of this thread, neither approach has resulted in anything of value in support of the inference-based case for, or against, the existence of alien lifeforms in the physical universe, (drawing upon data taken from our own instance).


So why are you involved in this thread? Just to keep saying over and over "we don't know and there no support for or against"?