What is the logic of assuming the existence (or nonexistence) of alien life

[primummobile]

I apologize, I meant no insult. I also have trouble with understanding non-explicit statements (I have Asperger's Syndrome) and I sometimes need it pointed out to me if I am misinterpreting something.

No need to apologize. I have Asperger's too, and that's probably half the reason I am having trouble understanding this. But it makez me good at certain things, and one of those is computer programming, so, for all my faults, one of the things I am very good at is following all the "nots" in a statement. I think someone in all this is misinterpreting one of my "nots" and I am misinterpreting their reply. I too need things explicity explained. I have trouble with irony or riddles and I feel like a lot of the replies are riddles.

[primummobile]

I'm confused.
I read your opening post, and then i read the options you present us are



where was option c) assume there probably is without claiming it as knowledge
Your opening post was firmly in option c)
which is very different from assume nothing.
Because people may question the validity of your assumptions does not mean they reject an, as yet, unquantifiable possibility

Because I also said in my first post that I make a very strong distinction between belief and knowledge. To me, assumptions can only be made when you some kind of evidence to back it up. Others may equate belief with assumptions. I don't. If you or anybody else doesn't think the same way, all you have to do is tell me. To my knowledge, you are the first person to say that.

[mutleyeng]

Because I also said in my first post that I make a very strong distinction between belief and knowledge. To me, assumptions can only be made when you some kind of evidence to back it up. Others may equate belief with assumptions. I don't. If you or anybody else doesn't think the same way, all you have to do is tell me. To my knowledge, you are the first person to say that.

There are a number of threads on here about what is "evidence" for ET life. The arguments have been gone over in quite some detail in those.
I think it fairly safe to say that those you think were claiming a non existence position where actually only rejecting your evidence and assumptions.
Its fine to have assumptions, but if you use them to justify a position then you should expect to have them challenged.

[primummobile]

There are a number of threads on here about what is "evidence" fo

r ET life. The arguments have been gone over in quite some detail in those.
I think it fairly safe to say that those you think were claiming a non existence position where actually only rejecting your evidence and assumptions.
Its fine to have assumptions, but if you use them to justify a position then you should expect to have them challenged.

I accept that. But I want to make it clear that what you would call an assumption I only call a reasonable belief. If someone thinks I am being unreasonable I would expect to be told that. I guess you could say that I assume that some form of exo life is more likely than not to exist, but I think that is an oversimplification.

I lurkex around these boards for a while before joining. I was very active over on Wikipedia before joining here, and most of my time was consumed by making editors find reputable sources for what they were putting in articles. I pay a lot of attention to detail and so I guess I was just taken aback when I interpreted replies to my posts to mean that I was being unreasonable in my beliefs because I thought I was being explicit in saying that my beliefs are not assumptions. I guess it's pretty silly to start all of this over the definition of a word.

[primummobile]

There are a number of threads on here about what is "evidence" for ET life. The arguments have been gone over in quite some detail in those.
I think it fairly safe to say that those you think were claiming a non existence position where actually only rejecting your evidence and assumptions.
Its fine to have assumptions, but if you use them to justify a position then you should expect to have them challenged.

And I really only wanted to know the truth value of "not assuming aliens do not exist". Throwing what I believe into the mix probably muddied the waters, but that was not my intention. I just wanted to make clear what I believe because I think that is important to know for someone who is evaluating your statements.

[mutleyeng]

well, if you came to these boards and claimed it as knowledge that ET existed, you'd get carried away in a straight jacket.
The debates here are essentially between those with your position, who consider they have grounds for a reasonable belief - and those who do not consider your evidence leading you to that belief as legitimate.
I am entirely neutral on the question of life - that means that I neither think it likely or unlikely - its just unknown. I think thats where most you thought denied the possibility of ET life also sit.

[chrlzs]

I may have missed this point being raised earlier, if so I apologise for skimming..!

But it seems to me that the claim we have an abundance of life here on earth is VERY misleading. By definition (assuming you accept evolution), 'abundance' is what inevitably happens once you have a SINGLE outbreak of life. And as far as I am aware there is no evidence of anything but one single outbreak of life, somewhere on this planet, at some particular time, under very precise (and at this stage, unknown) conditions. In all the time before or since, no other life has sprung into existence. In all of our (perhaps crude and simplistic) experiments, not once have we managed to duplicate those conditions. In other words, rather than it being very likely that life will spring up given the right earth-like conditions, I would argue exactly the reverse...

So based on what I see (or rather DON'T see) here on Terra, I think the chance of life existing elsewhere is pretty much vanishingly small. While I don't dispute there may be some of it elsewhere, given the tyranny of distance and all the other factors of timing, self- and cosmological- destruction, the chance of it becoming intelligent/sentient let alone technological, let alone interested in 'reaching out'... I'll happily accept that we are, for all intents and purposes, currently - and likely for the duration of our race - quite alone.

And btw, that doesn't depress me at all - I find plenty of other stuff easily interesting enough to keep me occupied..

[Paul Wally]

In the case of the question of existence of alien life, the absence of evidence overwhelms the evidence of absence. We have only closely examined a vanishingly small part of even our own solar system. We don't even know how to look for extraterrestrial life. We don't know if there are microbes in the middle cloud layers of Venus, the supposed oceans of Europa, or the hydrocarbon lakes on Titan. We know so little about them that it is logically impossible to assume that life does not exist. The only thing we can do is to not assume that life does not exist. If you are not assuming something, it means that you are assuming nothing. Taking any other position with so little information available cannot be logically supported.

Why do you have to assume anything? My approach would be to make suppositions, not assumptions. Suppose X is true, what follows if X is true? Suppose X is false, what follows etc.
There's a difference between making assumptions and making suppositions. Look, I just supposed X and then I supposed not(X) (no problem), but it would be irrational to assume both X and not(X).

For me, science operates at the level of supposition (not assumption), and that's where all the interesting (original) work is going on. I think it's far more interesting to have a rational discussion around different suppositions around alien life, than to have these dead-end discussions about who assumed what, and what can be assumed, and what can be said and what cannot be said. Sometimes these type of dead-end discussions even lead to restrictions on what can be thought and what cannot be thought, and this I find quite strange, because why must lack of evidence for something prevent us from thinking about the different logical possibilities?

[Selfsim]

We also know that the entire universe, including where both of us are sitting, started in the same initial conditions. So, unless Earth is really special, it is mathematically unlikely that no other life exists.

This is the key issue -- whether Earth is special? Over the last few centuries, science has established that Earth is not special in the sense that everything else goes around it, not special in the sense of being composed of different elements, not special in the sense that its solar system is near the centre of the galaxy...

a) Colin: Why is this a key issue? I would've thought the key issue would have been whether life is special¹?
b) Initial conditions: There is theoretical evidence that the observable universe started out chaotically. Randomness and order would seem at home in the aftermath .. and it is !
c) Primummobile: 'Mathematically unlikely: Could you please demonstrate for us, the mathematics behind such a statement ? I keep seeing 'mathematics' being used to make a point, and yet there is nothing from mathematics I know of, which would suggest that such a statement is anything more than pure arm-waving and a hijack of mathematics.


Footnotes:
1. I dislike using the term 'special' .. something unique, doesn't have to be 'special'. That being said, I only used the term as a quote of what was said.

[mutleyeng]

For me, science operates at the level of supposition (not assumption),

I'm good with this - but then i was also good with a methodical sonar weep of Loch Ness too. That didnt mean i gave any of the evidence any credibility.

[Van Rijn]

And as far as I am aware there is no evidence of anything but one single outbreak of life, somewhere on this planet, at some particular time, under very precise (and at this stage, unknown) conditions. In all the time before or since, no other life has sprung into existence.

We don't know that. We wouldn't know about other abiogenesis events unless they happened to have current and distinct descendents, or if there was something very distinct left in the fossil record. It's possible there have been multiple abiogenesis events on Earth.

In all of our (perhaps crude and simplistic) experiments, not once have we managed to duplicate those conditions. In other words, rather than it being very likely that life will spring up given the right earth-like conditions, I would argue exactly the reverse...

I would argue that we can't say very much about that based on current laboratory experiments. These laboratory experiments are extremely small scale compared to the planet over geological periods. Now, if you were conducting experiments with something like the volume of the Pacific Ocean, and you couldn't get results after a few hundred million years, then you might have a significant argument.

[Colin Robinson]

it seems to me that the claim we have an abundance of life here on earth is VERY misleading. By definition (assuming you accept evolution), 'abundance' is what inevitably happens once you have a SINGLE outbreak of life. And as far as I am aware there is no evidence of anything but one single outbreak of life, somewhere on this planet, at some particular time, under very precise (and at this stage, unknown) conditions. In all the time before or since, no other life has sprung into existence. In all of our (perhaps crude and simplistic) experiments, not once have we managed to duplicate those conditions. In other words, rather than it being very likely that life will spring up given the right earth-like conditions, I would argue exactly the reverse...

Perhaps it depends whether you think of the origin of life as an single event or a process —

Was it a sudden, perhaps fortuitous, emergence of a replicating molecule out of a random soup of organic chemicals?

Or did relatively simple catalytic cycles, favored by the principles of thermodynamics, gradually become more efficient and more complex -- cycles along the lines of the reductive Krebs process, where carboxylic acids are formed out of an energy-rich mixture of hydrogen and carbon dioxide?

If we think of it as a single event, it may seem very significant that such an event happened only once.

If we think of it a process, I'm not sure whether you would expect it to happen a second time on a planet where it has already happened -- a planet where the energy from those energy-rich chemical mixtures already has channels to flow thru.

Here are links to two articles in which abiogenesis is understood more as a process than a single event:

Christian de Duve The Beginnings of Life on Earth

James Trefil, Harold Morowitz, Eric Smith The Origin of Life

[Colin Robinson]

Why do you have to assume anything? My approach would be to make suppositions, not assumptions. Suppose X is true, what follows if X is true? Suppose X is false, what follows etc.
There's a difference between making assumptions and making suppositions. Look, I just supposed X and then I supposed not(X) (no problem), but it would be irrational to assume both X and not(X).

For me, science operates at the level of supposition (not assumption), and that's where all the interesting (original) work is going on. I think it's far more interesting to have a rational discussion around different suppositions around alien life, than to have these dead-end discussions about who assumed what, and what can be assumed, and what can be said and what cannot be said. Sometimes these type of dead-end discussions even lead to restrictions on what can be thought and what cannot be thought, and this I find quite strange, because why must lack of evidence for something prevent us from thinking about the different logical possibilities?

Yes, I think this is a very important point!

It's an important part of science to look at suppositions (not yet established as facts), and ask: If this were true, what would follow?

I'm reminded of the distinction which Karl Popper made between a "bucket" theory of knowledge and a "searchlight" theory. Whether science is like lowering a bucket into water, or more is it like aiming a searchlight? In "the searchlight" model, you have to think about where and how the searchlight is to be directed -- it isn't just a matter of letting data pour in, like water into a bucket...

[Selfsim]

Why do you have to assume anything? My approach would be to make suppositions, not assumptions.
...
For me, science operates at the level of supposition (not assumption), and that's where all the interesting (original) work is going on. I think it's far more interesting to have a rational discussion around different suppositions around alien life, than to have these dead-end discussions
...
why must lack of evidence for something prevent us from thinking about the different logical possibilities?

Thinking about logical possibilities is fine ... but no progress will be made in the real world, (about the existence or otherwise of life elsewhere), unless such 'thinking' returns useful real-world data. I see the discussion of exolife, as not falling into any category of productive reasoning (deductive, inductive or abductive). The problem is there is no data that allows a conclusion to be formed, or allows the construction of a premise.

(Similarly, the lack of data cannot in itself, be considered as a valid basis for formulation of the premise that exo-life doesn't exist either, as this leads to the logical fallacy of 'argumentum ad ignorantium').

Cheers

[Paul Beardsley]

No, you did not ask WHO said it. You asked for QUOTES. I gave you the quotes leading up to it. In the last quote, I asked "why you woukd you not assume that life does not exist?" and the reply was "why not assume that?" That's the thrust of this entire thread. I want to understand that statement.

You said It was just my opinion that the views being taken by some was too minimalist. i.e. "extraterrestrial life does not exist because we have seen no evidence of it."

I said I read the thread in question - I must have missed the bit where somebody said that. Can you provide the quotation?

Obviously, I meant the quotation that supported your claim that some were being too minimalist.

You then gave me a load of quotations, none of which support your claim that some were being too minimalist, none of which stated or implied "extraterrestrial life does not exist because we have seen no evidence of it." So perhaps you can withdraw the claim now.

[Selfsim]

Yes, I think this is a very important point!

It's an important part of science to look at suppositions (not yet established as facts), and ask: If this were true, what would follow?

I'm reminded of the distinction which Karl Popper made between a "bucket" theory of knowledge and a "searchlight" theory. Whether science is like lowering a bucket into water, or more is it like aiming a searchlight? In "the searchlight" model, you have to think about where and how the searchlight is to be directed -- it isn't just a matter of letting data pour in, like water into a bucket...

Important ?? I don't think so !

Due to the paucity of data, one has to go wherever the data leads. And the data comes from exploration of the real-universe.
What's more, it is just as likely to be completely unanticipated, as it is expected from purely philosophically motivated speculation.
Our best attempts at directed searches, in the light of having no data-based premises, are basically akin to searching in near infinite space, in darkness, for something we know we can only just barely detect in our local neighbourhood, in full light, right under our noses !

With such little understanding, focussing too heavily on logical reasoning as a basis for prioritising the search space, is nothing more than being led by philosophy, metaphysics, politics and delusion.

Where is the scientific importance in that ?

[Colin Robinson]

a) Colin: Why is this a key issue? I would've thought the key issue would have been whether life is special¹? Footnotes:
1. I dislike using the term 'special' .. something unique, doesn't have to be 'special'. That being said, I only used the term as a quote of what was said.

Well, if life is special/unique, and if Earth is the only place that has it, out of the astronomical number of planets in the universe... then I would have thought that made Earth a special/unique place? Wouldn't it?

[Colin Robinson]

Important ?? I don't think so !

Due to the paucity of data, one has to go wherever the data leads. And the data comes from exploration of the real-universe.
What's more, it is just as likely to be completely unanticipated, as it is expected from purely philosophically motivated speculation.

I agree that data comes from exploration, and that what's found may be unanticipated. Still... scientists have debated whether to look for life beyond Earth via a "follow the water" strategy or a "follow the carbon" strategy, or what... One thing that is understood by all sides in such a debate is that there needs to be a strategy of some sort, there needs to be a program of research. This means having some conception (or "supposition", as Paul Wally says) of what the possibilities are...

[Selfsim]

This is the key issue -- whether Earth is special? Over the last few centuries, science has established that Earth is not special in the sense that everything else goes around it, not special in the sense of being composed of different elements, not special in the sense that its solar system is near the centre of the galaxy...

a) Colin: Why is this a key issue? I would've thought the key issue would have been whether life is special?

Well, if life is special/unique, and if Earth is the only place that has it, out of the astronomical number of planets in the universe... then I would have thought that made Earth a special/unique place? Wouldn't it?

Hmm .. yet another speculative response with a bunch of 'ifs' (or leading assumptions).

Here's one that's not speculative: The existence of life on Earth, does not imply life exists elsewhere.

Earth may not be unique at the scales of, and in the attributes you mention ... and that implies nothing about life.

[Selfsim]

I agree that data comes from exploration, and that what's found may be unanticipated. Still... scientists have debated whether to look for life beyond Earth via a "follow the water" strategy or a "follow the carbon" strategy, or what... One thing that is understood by all sides in such a debate is that there needs to be a strategy of some sort, there needs to be a program of research. This means having some conception (or "supposition", as Paul Wally says) of what the possibilities are...

The strategy of feasible exploration, suffices.
Suppositions are superfluous.

[Colin Robinson]

Hmm .. yet another speculative response with a bunch of 'ifs' (or leading assumptions).

Here's one that's not speculative: The existence of life on Earth, does not imply life exists elsewhere.

Earth may not be unique at the scales of, and in the attributes you mention ... and that implies nothing about life.

??? But the scale I mentioned was the planets of the universe, and the only attribute I mentioned was presence of life...

Logically, non uniqueness of Earth at that scale, and in that attribute, must surely imply presence of life somewhere else?

[Colin Robinson]

The strategy of feasible exploration, suffices.

What do you mean by a "strategy of feasible exploration"? Does it mean sending robotic probes, or humans, here and there at random thru the solar system, with no idea what they are looking for? That would be "feasible", and it would be "exploration" of a sort... Would that "suffice"? If so, what would it suffice for?

Suppositions are superfluous.

I have to disagree.

[Parallel Universes]

I find it tragic that every discussion gets derailed by this discussion. The factions who want to argue about whether aliens exist are destroying the possibility of fresh discussion. How can we ever philosophise about the possible nature of otherworldly beings when the same nay sayers keep popping their heads up and shouting "HOGWASH!"

We get it. Ok. A minority of you simply can't get past this stumbling block. You would rather raise this same tired debate over and over rather than let a discussion unfold based on an assumption.

We once thought our individual nations were the centre of the world and all of creation. Clearly many of us still do.

[Selfsim]

I find it tragic that every discussion gets derailed by this discussion. The factions who want to argue about whether aliens exist are destroying the possibility of fresh discussion. How can we ever philosophise about the possible nature of otherworldly beings when the same nay sayers keep popping their heads up and shouting "HOGWASH!"

We get it. Ok. A minority of you simply can't get past this stumbling block. You would rather raise this same tired debate over and over rather than let a discussion unfold based on an assumption.

We once thought our individual nations were the centre of the world and all of creation. Clearly many of us still do.

Huh ?
If ever there was a thread to hammer this out .. its this one !

Your desire to "philosophise about the possible nature of otherworldly beings" would be the "derail" ... sorry to leave you in a 'tragic' state ... and all at your own calliing, I might add !

[Paul Beardsley]

I find it tragic that every discussion gets derailed by this discussion. The factions who want to argue about whether aliens exist are destroying the possibility of fresh discussion. How can we ever philosophise about the possible nature of otherworldly beings when the same nay sayers keep popping their heads up and shouting "HOGWASH!"

We get it. Ok. A minority of you simply can't get past this stumbling block. You would rather raise this same tired debate over and over rather than let a discussion unfold based on an assumption.

We once thought our individual nations were the centre of the world and all of creation. Clearly many of us still do.

What Selfsim said, 100%. Parallel Universes, I suspect you might have got confused about which thread you were replying to.

Here on BAUT (as it was) we've had all manner of speculative discussion about possible extraterrestrial life. There was even one about whether other civilisations would listen to music. And whereas one or two people did indeed fail to "get it" (i.e. that the discussion was purely speculative) they did not derail the thread.

[profloater]

This thread started about logic and assumptions. In fiction we can examine weird starting assumptions using logic and imagination. Usually fiction writers who then claim the details are factual are disapproved.

It is important to separate what we regard as evidence from extrapolation and imagination when using the mantle of logic to arrive at conclusions.

If we are separated by too many light years, the mathematical possibility of life on distant planets surely remains a subject for fiction, we cannot expect to find evidence.

[Van Rijn]

Thinking about logical possibilities is fine ... but no progress will be made in the real world, (about the existence or otherwise of life elsewhere), unless such 'thinking' returns useful real-world data. I see the discussion of exolife, as not falling into any category of productive reasoning (deductive, inductive or abductive). The problem is there is no data that allows a conclusion to be formed, or allows the construction of a premise.

Are you referring to this thread, or all discussions about exolife?

When we study the universe, we make hypotheses based on known physics. Sometimes we've found things that didn't fit known physics, but a lot of it has. It has certainly been something to build on.

Similarly, if we're going to look for exolife (as I think everyone here agrees with the possibility of exolife and that it is a possibility that should be investigated, correct?) it would seem reasonable to make hypotheses based on known life. That doesn't stop anyone from considering other possibilities, but it would be a reasonable place to start.

[chrlzs]

We don't know that.

Which is why I prefaced those comments with the 'as far as I am aware' bit..

We wouldn't know about other abiogenesis events unless they happened to have current and distinct descendents, or if there was something very distinct left in the fossil record. It's possible there have been multiple abiogenesis events on Earth.

But that is sorta my point - either:
1. There is/was one very precise, extremely unlikely set of conditions and chemicals from which life can appear - which is the one I'm betting on...
or
2. There is a range of conditions and chemicals, or if they are precise, those conditions were (even briefly) widespread - in which case we *would* very likely see distinct descendants (in a regional sense) / differing biochemistry / fossil records

Do we? AFAIK, we don't, and I think we probably should. I'll happily admit I'm not widely read on this aspect of abiogenesis, but I've never seen any references to multiple 'beginnings'. Perhaps the books that were cited give some clues, but it would be nice if this aspect got a bit of coverage here..

I would argue that we can't say very much about that based on current laboratory experiments. These laboratory experiments are extremely small scale compared to the planet over geological periods. Now, if you were conducting experiments with something like the volume of the Pacific Ocean, and you couldn't get results after a few hundred million years, then you might have a significant argument.

I'm not sure I agree. If we had no idea of what we are after, then yes, but we DO know what we are after! We have examples of the primitive starting points of life all around us - they are chemically analysable, we understand the basic processes, the chemical structures... It's a pretty good example of reverse engineering where you not only have the blueprints, you also have as many samples as you need to dissect / analyse..

Of course we can't quantify it meaningfully in mathematical terms, but I think it's fair to say it is really, really difficult to get life started. Maybe even a few more reallys...

So I stand by my point - saying that life is 'abundant' on Earth is misleading, in this context.

[Selfsim]

Thinking about logical possibilities is fine ... but no progress will be made in the real world, (about the existence or otherwise of life elsewhere), unless such 'thinking' returns useful real-world data. I see the discussion of exolife, as not falling into any category of productive reasoning (deductive, inductive or abductive). The problem is there is no data that allows a conclusion to be formed, or allows the construction of a premise.

Are you referring to this thread, or all discussions about exolife?

I cannot speak of all discussions on exo-life (some are carefully worded to denote the speculative bases of what is being discussed), but I was referring generally to forum discussions involving speculations which presume the existence of exo-life, as a given.

When we study the universe, we make hypotheses based on known physics. Sometimes we've found things that didn't fit known physics, but a lot of it has. It has certainly been something to build on.

Similarly, if we're going to look for exolife (as I think everyone here agrees with the possibility of exolife and that it is a possibility that should be investigated, correct?) it would seem reasonable to make hypotheses based on known life. That doesn't stop anyone from considering other possibilities, but it would be a reasonable place to start.

Sure, but don't forget the testability part of a proper hypothesis. In isolation, I don't challenge the 'reasonableness' of the general idea of looking for Earth-life, if one chooses to pursue the search for exo-life ... after all, there is no other choice once one embarks on such a quest. Carbon based biological life tests have to be conducted locally (or via return sample ... oh, SETI signals or ET poking faces at a robotic camera might suffice as well). This limits the practicality of the testing. Such tests cannot be applied over light year distances. This means that the hypothesis is severely constrained by practical testing limitations which ultimately limits the ability to gather the data, and form conclusions. No amount of 'reasonableness' (or logical reasoning) will overcome this practicality imposed limitation. Also, we simply don't have any data to make the firm connection between what we can measure these scales, and the presence/absence of life (whist excluding other unknown non-biological processes).

Using Physical theories to make exo-life hypotheses: the raw fundamental laws of physics dominate at astronomical scales, (and on astronomical objects), but in complex systems, their complex interactions can have entirely unexpected and unpredictable results. In the absence of any data on exo-life, it is also reasonable to say that deterministic physical theories can only be used to infer where exo-life may exist elsewhere (at best). Using Earth-life as a substitute for Physical Law as you have suggested, comes with all the limitations outlined above.

Regards

[primummobile]

Why do you have to assume anything? My approach would be to make suppositions, not assumptions. Suppose X is true, what follows if X is true? Suppose X is false, what follows etc.
There's a difference between making assumptions and making suppositions. Look, I just supposed X and then I supposed not(X) (no problem), but it would be irrational to assume both X and not(X).

For me, science operates at the level of supposition (not assumption), and that's where all the interesting (original) work is going on. I think it's far more interesting to have a rational discussion around different suppositions around alien life, than to have these dead-end discussions about who assumed what, and what can be assumed, and what can be said and what cannot be said. Sometimes these type of dead-end discussions even lead to restrictions on what can be thought and what cannot be thought, and this I find quite strange, because why must lack of evidence for something prevent us from thinking about the different logical possibilities?

That's my whole point. That I am NOT assuming. I started this thread based upon the belief that others were assuming no life exists.