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Noclevername
2013-Feb-26, 01:40 AM
The question has arisen on this very forum, as to why we should base our searches for possible ET life around similarity to Earthlike life-- IE, made of liquid water and carbon-based compounds. Well, I've given it some thought, and here's my opinions why:

1. We know it's possible. The only kind of life we have empirical evidence for is our own type. The same cannot be said of hypothetical exotic chemistries.

2. The compounds that form our type of life are known to be formed by several natural processes, and from universally common elements. Meteorites containing various amino acids have been examined, such as the Murchison meteorite (http://en.wikipedia.org/wiki/Murchison_meteorite). Cosmic dust (http://en.wikipedia.org/wiki/Cosmic_dust) and comets (http://en.wikipedia.org/wiki/Comet#Nucleus) with complex organic compunds have been found. Interstellar ice (http://en.wikipedia.org/wiki/Interstellar_ice) has been shown to have organic components along with water ice. Hydrocarbons have been detected in space (http://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules) by spectroscopy.

3. The chemical properties of carbon and the solvent properties of liquid water make them extremely well suited for biological use.

Note that this should not be interpreted to mean that we need to limit our explorations to only looking for Earthlike life. We can and should examine as much of the Universe as possible, and gather information from many sources. But by using what we already know works as a basis, it gives us a good starting point to work from.

John Mendenhall
2013-Feb-26, 02:57 AM
Agreed. ..

Colin Robinson
2013-Feb-26, 05:43 AM
The question has arisen on this very forum, as to why we should base our searches for possible ET life around similarity to Earthlike life-- IE, made of liquid water and carbon-based compounds. Well, I've given it some thought, and here's my opinions why:

1. We know it's possible. The only kind of life we have empirical evidence for is our own type.

Yes.. but we only know it's possible on one sort of planetary body — a rocky world with enough atmosphere to retain liquid water on its surface. We don't know how likely (or even possible) life is on a world like Mars, with a much thinner atmosphere and possibly subsurface liquid aquifers. Or on (or in) worlds like Europa and Enceladus, with still less atmosphere but (probably) big reserves of liquid water subsurface.

If there was a twin of Earth conveniently nearby, then I'd agree it would be the first place to look for ET life. But there isn't.


The compounds that form our type of life are known to be formed by several natural processes, and from universally common elements. Meteorites containing various amino acids have been examined, such as the Murchison meteorite (http://en.wikipedia.org/wiki/Murchison_meteorite). Cosmic dust (http://en.wikipedia.org/wiki/Cosmic_dust) and comets (http://en.wikipedia.org/wiki/Comet#Nucleus) with complex organic compunds have been found. Interstellar ice (http://en.wikipedia.org/wiki/Interstellar_ice) has been shown to have organic components along with water ice. Hydrocarbons have been detected in space (http://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules) by spectroscopy.

Yes, there are lots of organic compounds about. Water ice is common too, as is water vapor for that matter, but how relevant are ice or vapor to life-as-we-know-it, which depends on liquid water?


The chemical properties of carbon and the solvent properties of liquid water make them extremely well suited for biological use.

I'm inclined to agree about the chemical properties of carbon. On the other hand, I am not aware of anything that would rule out complex, evolving chemical systems in liquid solvents other than water...

There are at least two places in our own solar system where liquids other than water are abundant: the clouds of Venus and the surface of Titan. In the case of Titan, we also know that organic compounds are abundant and complex.

We know this thanks to the Cassini-Huygens mission, but is one mission to Titan enough?

Selfsim
2013-Feb-26, 05:53 AM
If one sets out to test the hypothesis that: “ET life might be similar to Earthlike life, (ie: water, carbon based)”, then I would think there would be no choice other than to model those tests on Earthlike life, and to develop instruments to detect that.

If, on the other hand, one sets out to test the hypothesis that: “We think we might know of a universal model of life”, a more appropriate strategy might be to set out specifically to take note of surroundings, and look for anything unusual, (or unexpected), from amongst those surroundings. If the aim is to detect unusual things, then instrumentation to distinguish ‘Earthlike life’, from the surroundings, would not be absolutely necessary (ie: it would not be of vital importance to the mission). The priorities (in descending order of importance) would be: (i) detection of atypical things, followed by (ii) isolation, followed by (iii) identification, followed by (iv) classification, etc, etc. A large part of the specimen test equipment design would depend on the nature of what was actually detected (or noticed).

It would thus be prudent to design the test equipment for (iii) and (iv), on the basis of what is detected, which could very well end up being completely different from testing for carbon based Earthlike life, under Earthlike conditions.

By using what we already know about astrophysics, the physics of planetary atmospheres, the physics of spectroscopy, the physics of geology, inorganic and organic chemistries, molecular biology, it should give us a good starting point to work from.

Rgds

Noclevername
2013-Feb-26, 06:59 AM
If one sets out to test the hypothesis that: “ET life might be similar to Earthlike life, (ie: water, carbon based)”, then I would think there would be no choice other than to model those tests on Earthlike life, and to develop instruments to detect that.

If, on the other hand, one sets out to test the hypothesis that: “We think we might know of a universal model of life”, a more appropriate strategy might be to set out specifically to take note of surroundings, and look for anything unusual, (or unexpected), from amongst those surroundings. If the aim is to detect unusual things, then instrumentation to distinguish ‘Earthlike life’, from the surroundings, would not be absolutely necessary (ie: it would not be of vital importance to the mission). The priorities (in descending order of importance) would be: (i) detection of atypical things, followed by (ii) isolation, followed by (iii) identification, followed by (iv) classification, etc, etc. A large part of the specimen test equipment design would depend on the nature of what was actually detected (or noticed).

It would thus be prudent to design the test equipment for (iii) and (iv), on the basis of what is detected, which could very well end up being completely different from testing for carbon based Earthlike life, under Earthlike conditions.

By using what we already know about astrophysics, the physics of planetary atmospheres, the physics of spectroscopy, the physics of geology, inorganic and organic chemistries, molecular biology, it should give us a good starting point to work from.

Rgds

I don't see these as mutually exclusive.

Noclevername
2013-Feb-26, 07:04 AM
Yes.. but we only know it's possible on one sort of planetary body — a rocky world with enough atmosphere to retain liquid water on its surface. We don't know how likely (or even possible) life is on a world like Mars, with a much thinner atmosphere and possibly subsurface liquid aquifers. Or on (or in) worlds like Europa and Enceladus, with still less atmosphere but (probably) big reserves of liquid water subsurface.

If there was a twin of Earth conveniently nearby, then I'd agree it would be the first place to look for ET life. But there isn't.


There is life on Earth which does not depend on an open surface, sunlight or atmosphere.


Water ice is common too, as is water vapor for that matter, but how relevant are ice or vapor to life-as-we-know-it, which depends on liquid water?


Can't have liquid H2O without H2O. I'm just pointing out that water is a common molecule. Since many of the current theories of Earth's formation involve the majority of water coming from space, the amount of water actually in space can be given a certain prominence.

Colin Robinson
2013-Feb-26, 08:09 AM
There is life on Earth which does not depend on an open surface, sunlight or atmosphere.

True.

On the other hand, we don't know what role the atmosphere played in the origin of life on Earth. We do know that a lot of synthesis of organic compounds can take place in a reducing (hydrogen-rich) atmosphere energized by UV rays and/or lightning.


Can't have liquid H2O without H2O. I'm just pointing out that water is a common molecule. Since many of the current theories of Earth's formation involve the majority of water coming from space, the amount of water actually in space can be given a certain prominence.

Water is undoubtedly a common molecule, but so are other substances which biochemists have identified as possible alternative solvents, e.g. ammonia, methane.

Colin Robinson
2013-Feb-26, 08:13 AM
I don't see these as mutually exclusive.

I agree.

Following any single line of research to the exclusion of others would be sorta like putting all your eggs in one basket...

Selfsim
2013-Feb-26, 08:51 AM
I don't see these as mutually exclusive.I agree.

Following any single line of research to the exclusion of others would be sorta like putting all your eggs in one basket...Being clear about the different strategies resulting from the two hypotheses, ensures that you aren't putting all your eggs in the one basket.

Noclevername
2013-Feb-26, 09:56 AM
Being clear about the different strategies resulting from the two hypotheses, ensures that you aren't putting all your eggs in the one basket.

What specific strategies would you suggest?

Selfsim
2013-Feb-26, 10:08 AM
I am reminded of one of the most insightful comments I've read for a long while. Paraphrasing it somewhat, (only to draw relevance to the question posed in this thread's OP):

The empiricist says that the job of theory is to understand and predict the experiments that tell us what actually happens, whilst the rationalist says the job of experiment is to confirm the theory of what actually happens. Whilst I see physics as a continuous dialog between those world views, I point out that the experimental outcomes are as they are, and persist, whilst the theories ...

In the case we're discussing here, if one views that:
(i) the exo-planet (etc) is the laboratory where the experiments of life are played out and;
(ii) the 'theory' that predicts that the search for ET life should be based on experiments which assume a similarity with Earthlike life,
then in the light of the fact that our theory of life has no other confirming 'laboratory' other than Earth, it would behoove us to recognise that the theory is less likely to be more reliable, than whatever is found in the myriad of other 'laboratories'.

We should therefore focus our attention on detecting what those other laboratories are producing, rather than focusing on what we think they should be producing.

Rgds

Noclevername
2013-Feb-26, 10:16 AM
I am reminded of one of the most inciteful comments I've read for a long while. Paraphrasing it somewhat, (only to draw relevance to the question posed in this thread's OP):

The empiricist says that the job of theory is to understand and predict the experiments that tell us what actually happens, whilst the rationalist says the job of experiment is to confirm the theory of what actually happens. Whilst I see physics as a continuous dialog between those world views, I point out that the experimental outcomes are as they are, and persist, whilst the theories ...

In the case we're discussing here, if one views that:
(i) the exo-planet (etc) is the laboratory where the experiments of life are played out and;
(ii) the 'theory' that predicts that the search for ET life should be based on experiments which assume a similarity with Earthlike life,
then in the light of the fact that our theory of life has no other confirming 'laboratory' other than Earth, it would behoove us to recognise that the theory is less likely to be more reliable, than whatever is found in the myriad of other 'laboratories'.

We should therefore focus our attention on detecting what those other laboratories are producing, rather than focusing on what we think they should be producing.

Rgds

That sounds more like a philosophy or a point of view than a suggestion for actual strategies for data collection. As I said,
Note that this should not be interpreted to mean that we need to limit our explorations to only looking for Earthlike life. We can and should examine as much of the Universe as possible, and gather information from many sources.

It's not exclusionary. It is, as I said above, a starting point, nothing more. Begin with what we already know is possible, and work outward from there.

Selfsim
2013-Feb-26, 10:31 AM
That sounds more like a philosophy or a point of view than a suggestion for actual strategies for data collection. As I said,I was preparing my post, (which you quote), in response to a post which was prior to your post#10.
It is an attempt at trying to highlight that there is legitimate, persistent conflict within the scientific community, over these very issues.
(Ie: the disagreement is not merely limited to a clash of personalities at CQ).

I will respond to you query in post #10 at a later time, (ie:when I get the chance).

swampyankee
2013-Feb-26, 10:33 AM
One advantage to searching for life-as-we-know-it is that there is probably a better chance of noticing it than of noticing life-as-we-do-not-know. Leaving aside something reasonably fast-moving and reasonably large, we'd spot anything (creatures the size of cars swimming in a liquid methane sea ...), but for something microscopic, reproducing slowly, and living in liquid ammonia-hydrogen cyanide slush, it may be a bit harder. As an analogy, we keep finding more habitats on Earth, like here (http://www.universetoday.com/851/bacteria-found-deep-underground/), and some of these prokaryotes may reproduce very slowly (one estimate I've read for some communities of deep underground life is that individuals reproduce only a few times per century). We have at least some experience with biochemical processes with long-chain carbon molecules in aqueous environments, and we have a lot more experience with chemistry in aqueous solutions than those in other solvents.

Van Rijn
2013-Feb-26, 10:44 AM
Note that this should not be interpreted to mean that we need to limit our explorations to only looking for Earthlike life. We can and should examine as much of the Universe as possible, and gather information from many sources. But by using what we already know works as a basis, it gives us a good starting point to work from.

Right. I recall some comments (I think by David Morrison, but I'm not sure) essentially saying that astrobiologists are currently focusing on something close to "Earthlike" life (carbon based using water as a solvent, something at least close to DNA, etc), because of the issues you mention, and because of the difficulties of how to test for extremely non-Earthlike biology.

For instance, as telescopes improve it will be possible to do increasingly sophisticated examinations of exoplanets with similar mass and insolation to Earth. And we can consider what we would expect to see from an exoplanet with Earthlike life, or what would exclude Earthlike life. As more and more parameters are tested (such as looking for significant oxygen, methane, spectral signatures that would fit something similar to chlorophyll, etc.), then if a significant percentage fit all or most of the life parameters, eventually it would be hard to argue for non-life alternative explanations. If no other world has a good fit of the parameters, then it would be unlikely the worlds had life as we know it.

For life significantly different from Earth life, it would be much more difficult to decide how to test, and how to exclude non-life explanations. We could imagine silicon based life using something similar to silicon PV cells . . . but it would be difficult to go from speculation to detailed tests.

Of course, that's the biology side. For a SETI search, the details of biology don't matter much. And in the solar system, it will be easier to get samples from various worlds, and easier to test for "life as we don't know it" if something strange is noticed.

Noclevername
2013-Feb-26, 11:40 AM
I was preparing my post, (which you quote), in response to a post which was prior to your post#10.
It is an attempt at trying to highlight that there is legitimate, persistent conflict within the scientific community, over these very issues.
(Ie: the disagreement is not merely limited to a clash of personalities at CQ).

True. There's a variety of motives and points of view, as is true of any endeavor. That's mostly why I prefer to focus on methods over beliefs.


I will respond to you query in post #10 at a later time, (ie:when I get the chance).

No hurry. CQ isn't going anywhere... again?

John Mendenhall
2013-Feb-26, 05:20 PM
I agree.

Following any single line of research to the exclusion of others would be sorta like putting all your eggs in one basket...

Or all your ova and sperm on one planet . . .

Zo0tie
2013-Feb-26, 06:13 PM
If the observed environment is not in chemical or physical equilibrium that would tip us off that something is causing the dis-equilibrium. The high oxygen content of our atmosphere is an example. An indicator of possible life would be the availability of an energy flux and observed organized structures that should have been eroded by that energy flux long ago. For example a sterile shale rock will show many microfossils. Life may be defined as a mechanism for complex chemical systems to preserve themselves against entropic degradation within an energy rich environment. Obviously movement or growth is an indicator but that movement and growth may be very slow and require precise measurement.

If something was found on Titan based on methane-acetylene, or on Io based on silicon-sulfur that met the above conditions only the most dogmatic scientist would refuse to consider it possible life just because it has no water or carbon content.
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20100603/

Noclevername
2013-Feb-26, 08:54 PM
If the observed environment is not in chemical or physical equilibrium that would tip us off that something is causing the dis-equilibrium. The high oxygen content of our atmosphere is an example. An indicator of possible life would be the availability of an energy flux and observed organized structures that should have been eroded by that energy flux long ago. For example a sterile shale rock will show many microfossils. Life may be defined as a mechanism for complex chemical systems to preserve themselves against entropic degradation within an energy rich environment. Obviously movement or growth is an indicator but that movement and growth may be very slow and require precise measurement.

If something was found on Titan based on methane-acetylene, or on Io based on silicon-sulfur that met the above conditions only the most dogmatic scientist would refuse to consider it possible life just because it has no water or carbon content.
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20100603/

But we don't know what the abiotic "normal" is for those worlds. We don't know what complex chemical reactions happen in the absence of life. The only true evidence for life is observing actual life.

Bad Ronald
2013-Feb-27, 02:39 AM
I agree with the OP. Plus, BEFORE all these alien solar systems were discovered we had preconceived notions, if not assumptions, that other solar systems would be like our's, & alot of them are NOT ... AT ALL! Ditto for ALIEN life. REAL alien life will probably be as unexpectedly different & bizarre from Earth life as many alien solar systems are from our solar system.

neilzero
2013-Feb-27, 04:31 AM
Chemists and biologists have hypothesized radically different chemistries, but the details have seemed very unlikely so typically the hypothesiser has concluded, "this probably won't be workable for along list of reasons." Neil

Colin Robinson
2013-Feb-27, 08:12 AM
Chemists and biologists have hypothesized radically different chemistries, but the details have seemed very unlikely so typically the hypothesiser has concluded, "this probably won't be workable for along list of reasons." Neil

That may be more-or-less true for alternatives to carbon, because carbon is both chemically very versatile and cosmically abundant, and it's hard to find anything that compares with it in those two respects.

But alternatives to water are a different matter.

It's important to separate out the two questions, because a growing and evolving system in a solvent other than water could still be based on carbon compounds. They would be different carbon compounds (because a molecule that functions in a particular way in one solvent often won't function the same way in another solvent), but carbon compounds nonetheless.

TooMany
2013-Feb-27, 08:15 PM
I know this is unscientific, but sometimes it seems as if things are just rigged to promote the kind of organic life we find on earth. After hydrogen and helium, oxygen is the most common element. So it's no surprise that water is common. Next in line are carbon and then nitrogen. That takes care of the majority of elements found in organic molecules. In fact the order of abundances of these particular elements in the Sun is the same order as in animals.

OTOH, silicon (chemically flexible like carbon) is only 1/16 as common as carbon in the Sun, but far more plentiful on earth than carbon. So if there were another possible life chemistry, I suppose it might be silicon based. Whereas CO2 is a gas SiO2 is glass. Maybe silicon life forms could exist on some of those hot planets? In any case, worrying about a type of life like this doesn't make much sense unless we have some indication that complex silicon molecules can form in some common solvent.

We find organic molecules in space, in asteroids and comets. There appears to be a bias toward these organic compounds as a foundation for the complex molecules needed to create living matter.

Noclevername
2013-Feb-27, 08:21 PM
I know this is unscientific, but sometimes it seems as if things are just rigged to promote the kind of organic life we find on earth. After hydrogen and helium, oxygen is the most common element. So it's no surprise that water is common. Next in line are carbon and then nitrogen. That takes care of the majority of elements found in organic molecules. In fact the order of abundances of these particular elements in the Sun is the same order as in animals.

There appears to be a bias toward these organic compounds as a foundation for the complex molecules needed to create living matter.

I think that's looking at it backwards. All that means is that life is made out of what's readily and conveniently present. We're "rigged" for the Universe, not the Universe for us. We had to cut our biology to fit the available molecules.

Colin Robinson
2013-Feb-27, 09:05 PM
But we don't know what the abiotic "normal" is for those worlds.

But we do know what chemical equilibrium is.


We don't know what complex chemical reactions happen in the absence of life.

But we do know that the chemical processes found in living things are a subset of the class of complex chemical reactions. If we're considering where to look for living things, I'd suggest confirmed presence of complex chemical reactions is a major factor to consider...


The only true evidence for life is observing actual life.

That is one reason for concentrating on planets and moons we can reach now with space probes -- the worlds of our own Solar System.

Even if living things elsewhere in Solar System are microscopic, and chemically different from Earth life, as long as they are within reach of space probes we can examine them and study them.

theloniusmonkey
2013-Feb-27, 09:18 PM
The question has arisen on this very forum, as to why we should base our searches for possible ET life around similarity to Earthlike life-- IE, made of liquid water and carbon-based compounds. Well, I've given it some thought, and here's my opinions why:

1. We know it's possible. The only kind of life we have empirical evidence for is our own type. The same cannot be said of hypothetical exotic chemistries.

2. The compounds that form our type of life are known to be formed by several natural processes, and from universally common elements. Meteorites containing various amino acids have been examined, such as the Murchison meteorite (http://en.wikipedia.org/wiki/Murchison_meteorite). Cosmic dust (http://en.wikipedia.org/wiki/Cosmic_dust) and comets (http://en.wikipedia.org/wiki/Comet#Nucleus) with complex organic compunds have been found. Interstellar ice (http://en.wikipedia.org/wiki/Interstellar_ice) has been shown to have organic components along with water ice. Hydrocarbons have been detected in space (http://en.wikipedia.org/wiki/List_of_interstellar_and_circumstellar_molecules) by spectroscopy.

3. The chemical properties of carbon and the solvent properties of liquid water make them extremely well suited for biological use.

Note that this should not be interpreted to mean that we need to limit our explorations to only looking for Earthlike life. We can and should examine as much of the Universe as possible, and gather information from many sources. But by using what we already know works as a basis, it gives us a good starting point to work from.

A search for life is essentially a search for intelligence. Not that we may not stumble across an E. Coli on Mars, but we are more likely to find a signal than a bug. To find the latter we need boots on the ground. At the very least robotic boots.

TooMany
2013-Feb-28, 12:52 AM
I think that's looking at it backwards. All that means is that life is made out of what's readily and conveniently present. We're "rigged" for the Universe, not the Universe for us. We had to cut our biology to fit the available molecules.

You seem to be arguing that life would arise from whatever is available. Throw any old pile of elements together and life emerges? I doubt that.

What I'm trying to say is that these elements are very special and form all sorts of complex molecules. We aren't made from these elements because they are common, but rather because of their special properties. I'm suggesting that our biology can exist only because of these properties.

I'm not a chemist, but I would like to know if there is another chemistry based on different elements that is capable of making the complex molecules needed for life.

Noclevername
2013-Feb-28, 06:25 AM
You seem to be arguing that life would arise from whatever is available. Throw any old pile of elements together and life emerges?

No, I'm absolutely NOT arguing that or anything like it. You misinterpreted my statements entirely.

I'm arguing against use of the anthropic principle as a logical basis for saying the Universe is "rigged". Our point of view towards the universe is what's biased, not the universe towards us.

Colin Robinson
2013-Feb-28, 07:51 AM
A search for life is essentially a search for intelligence. Not that we may not stumble across an E. Coli on Mars, but we are more likely to find a signal than a bug. To find the latter we need boots on the ground. At the very least robotic boots.

Are we more likely to find a signal than a bug?

A signal -- e.g. the sort of radio signal that could be produced by technology as we know it -- would be easy enough to detect with radio telescopes. However, we'll only detect it if in fact we have cosmic neighbors who can produce such a signal, and then only if they are kind enough to send us one.

I really think we're more likely to find living things beyond Earth by going to other worlds in search of them, or at least sending robotic probes in search of them. Rather than waiting for them to come to us, or expecting them to send us the radio equivalent of a postcard.

Colin Robinson
2013-Feb-28, 08:20 AM
I agree with the OP. Plus, BEFORE all these alien solar systems were discovered we had preconceived notions, if not assumptions, that other solar systems would be like our's, & alot of them are NOT ... AT ALL! Ditto for ALIEN life. REAL alien life will probably be as unexpectedly different & bizarre from Earth life as many alien solar systems are from our solar system.

I think this is a very good point. The first exo-planets we discovered weren't planets as we knew them, they were pulsar planets and hot Jupiters.

It may turn out that life beyond Earth is based on water and carbon compounds. But what sort of carbon compounds?

The very fact that carbon is so versatile (e.g. nylon and polythene are also carbon compounds) suggests that living things elsewhere could use carbon in very different ways.

For instance, are we likely to find a familiar biological catalyst, such as chlorophyl, in the spectrum of an exo-planet with plant-like life? Or is it more likely that the photo-synthesizing organisms of a different world will use something quite different as a catalyst?

Selfsim
2013-Feb-28, 09:49 AM
What specific strategies would you suggest?Mars Viking 1's biology experiments were designed assuming a global distribution of heterotrophic life exists on Mars. The end result was controversy, with very little agreement on the overall outcome of the very specific LR, PR and GEX experimental results. This is a classic example of the end result of a strategy for testing the hypothesis that: “ET life might be similar, (even similarly distributed), to Earthlike life".

Curiosity's instrument package however, is broader in scope. It is capable of not only detecting the general organic chemicals which are predicted by the hypothesis that: "We may know of a universal model for life", but also to analyse the immediate surroundings, which provides the baseline for distinguishing what is 'typical', and what is 'not typical', for the martian environment. (This also serves as the baseline data relative to the broad environmental conditions predicted to be sufficient for an instance of our universal model of life to have once evolved). Curiosity's underlying strategy is one of 'perceiving' unusual things from a backdrop of 'martian-ness'. Curiosity's design exemplifies the evolution of methodical thinking about local exo-life search strategies. A lot was learned from the mistakes of the Viking bio-experiments.

'BOLD', (Biological Oxidant and Life Detection), is another up and coming mission being planned for Mars for 2018 (? I think). It is a step in same direction as Viking but is even more aggressively specific in what is being sought. It assumes microbial cell membranes, (amongst other very particular Earthlife biologicial features ... like chirality, etc). We shall see how successful/unsuccessful this approach is (again) .. in several years time, I suppose.

So overall, I don't really need to provide any strategies of my own ... they're already out there.

Noclevername
2013-Feb-28, 10:43 AM
Mars Viking 1's biology experiments were designed assuming a global distribution of heterotrophic life exists on Mars. The end result was controversy, with very little agreement on the overall outcome of the very specific LR, PR and GEX experimental results. This is a classic example of the end result of a strategy for testing the hypothesis that: “ET life might be similar, (even similarly distributed), to Earthlike life".

Curiosity's instrument package however, is broader in scope. It is capable of not only detecting the general organic chemicals which are predicted by the hypothesis that: "We may know of a universal model for life", but also to analyse the immediate surroundings, which provides the baseline for distinguishing what is 'typical', and what is 'not typical', for the martian environment. (This also serves as the baseline data relative to the broad environmental conditions predicted to be sufficient for an instance of our universal model of life to have once evolved). Curiosity's underlying strategy is one of 'perceiving' unusual things from a backdrop of 'martian-ness'. Curiosity's design exemplifies the evolution of methodical thinking about local exo-life search strategies. A lot was learned from the mistakes of the Viking bio-experiments.

'BOLD', (Biological Oxidant and Life Detection), is another up and coming mission being planned for Mars for 2018 (? I think). It is a step in same direction as Viking but is even more aggressively specific in what is being sought. It assumes microbial cell membranes, (amongst other very particular Earthlife biologicial features ... like chirality, etc). We shall see how successful/unsuccessful this approach is (again) .. in several years time, I suppose.

So overall, I don't really need to provide any strategies of my own ... they're already out there.

Thank you, that was a well thought out answer and worth the wait.

Colin Robinson
2013-Feb-28, 10:49 AM
I'm not a chemist, but I would like to know if there is another chemistry based on different elements that is capable of making the complex molecules needed for life.

There may be.

It's a topic which biochemists and other scientists have been thinking and writing about for a long time. Of course it's true that no such life-form has been found, nor has one been created in a laboratory. But on the other hand, there doesn't seem to be any simple argument, based on known natural laws, to say that it couldn't exist. (In the sense that for instance a perpetual motion machine is ruled out by known laws of thermodynamics.)

Some literature that you can read online:

Robert A. Freitas Jnr; Xenology; Chapter 8, Exotic Biochemistries (http://www.xenology.info/Xeno/8.0.htm)

David Darling; Encyclopedia of Science; Alternative Forms of Life (a clickable list of relevant pages in the Encyclopedia) (http://www.daviddarling.info/encyclopedia/A/alternative_forms_of_life.html)

John A. Baross and others; The Limits of Organic Life in Planetary Systems (lengthy technical discussion) (http://www.nap.edu/catalog.php?record_id=11919)

Selfsim
2013-Feb-28, 10:39 PM
There may be.

It's a topic which biochemists and other scientists have been thinking and writing about for a long time. Of course it's true that no such life-form has been found, nor has one been created in a laboratory. But on the other hand, there doesn't seem to be any simple argument, based on known natural laws, to say that it couldn't exist. (In the sense that for instance a perpetual motion machine is ruled out by known laws of thermodynamics.)

Some literature that you can read online:

Robert A. Freitas Jnr; Xenology; Chapter 8, Exotic Biochemistries (http://www.xenology.info/Xeno/8.0.htm)

David Darling; Encyclopedia of Science; Alternative Forms of Life (a clickable list of relevant pages in the Encyclopedia) (http://www.daviddarling.info/encyclopedia/A/alternative_forms_of_life.html)

John A. Baross and others; The Limits of Organic Life in Planetary Systems (lengthy technical discussion) (http://www.nap.edu/catalog.php?record_id=11919)Thanks for that Colin. The Darling link gives a quick overview of the known chemical molecular structures formed by 'alternative' elements and compounds (eg: boron, ammonia, hydrogen peroxide, carbon dioxide, nitrogen, phosphorous, arsenic, etc).

Linking this back to the OP, the question then becomes how would one detect such unfamiliar 'samples of interest'?

The reasonable strategy for detection would call for making full use of human perceptions/intuitions, fed by robotic extensions of the human senses, (time sampled optical/visual, microscopic), followed by sample return to Earth, or onsite local examination by humans, or generalised onsite robotic labs. The strategy here is non-specific exploration .. ie: not looking for anything in particular, but setting out to notice the unusual things pertinent to that environment. Its a very generalised criterion, but it has also proven to be a very effective one in human exploration history.

The second phase would involve lab instrumentation designed to isolate and categorise the compounds/elements present in a 'sample of interest'. This requires broad-band mass spectrometers, gas chromatographs, x-ray flourescence/diffraction instrumentation etc. The aim would be to explore the chemistry and structures and observe the native reactions going on in that environment. Deliberate pro-active measures would be undertaken only to expose and identify those reactions .. as opposed to setting out to deliberately (or accidentally) induce an Earthlike life response (like say, the production of co-incidental metabolic-like by products).

The ultimate diagnosis of 'life', requires this gradual, cumulative build up of data. This is also the way to avoid the 'trap' of looking for a particular type of hypothesised life, finding it to be absent, and missing what may actually be present, only because we didn't know such a thing could exist, (and therefore had no specifically preconceived tests for it, in that environment).

Once again, the differences between the two initial hypotheses, (I've mentioned previously), are highlighted by the different approaches (and the different possible outcomes). One is prescriptive and specific, and the other is more generalised, and addresses the unanticipated.

Selfsim
2013-Mar-01, 10:37 PM
Just a few other observations and comments ...

There seems to be the feeling that certain chemical elements which comprise life might have special properties ultimately resulting in 'life'. (http://cosmoquest.org/forum/showthread.php?142605-Why-life-as-we-know-it&p=2112035#post2112035) There is also discussion about the prevalence and properties of those naturally occurring elements, and some of their specific compounds. There are references alluding to the possibility that 'living' things elsewhere, might 'use' those same elements 'in very different ways'. (http://cosmoquest.org/forum/showthread.php?142605-Why-life-as-we-know-it&p=2112093#post2112093)

The fundamental properties of elements and compounds we also associate with 'life', are universal, and are not just limited to life .. eg: energy content, valency, bonding affinity and electrostatic (ionic) forces.

The properties which distinguish 'life', are not by any means, 'fundamental' (either in Physics or Chemistry). Many characteristics of life are also not merely the sum of its fundamental component properties, nor are they the simple sum of its fundamental component behaviours, or even the sum of subsequent, more complex processes.

Even the distinction between organic and inorganic (http://en.wikipedia.org/wiki/Organic_compound) carbon compounds, (http://en.wikipedia.org/wiki/Organic_compound) whilst useful for modelling purposes, is somewhat arbitrary. The Laws of Biochemistry (http://en.wikipedia.org/wiki/Biochemistry) are actually distinguished by the functions and processes they happen to perform in what we call 'living things', (derived from examination of Earth-life functions). I find the leap between observations of the abundances and the properties of certain inorganic elements throughout the universe, and the inference that this somehow tell us things about the likelihood of ET life, to be an enormously huge leap of faith. This is specifically because of the non-intuitive relationships between the physics and chemistry of elements and their compounds, and how this ends up constituting a living thing.

The point I'm making here, is that mechanistic model based explanations (physics, inorganic/organic chemistry, bio-chemistry, etc) are insufficient for covering the huge gaps needed in order to draw inferences or predictions about the 'possibilities' of 'alternative lifeforms'. Moving forwards from this 'unknown', then places emphasis on testing ...

Searching for ET life is about eliminating uncertainties. The tests we perform in searching, need to be able to progressively eliminate these uncertainties in order for us to ultimately classify something as living, or non-living. The testing is very complex. At present, such task complexity demands human involvement and a stable, controlled environment. This also cannot be done at present, over light year distances, either.

TooMany
2013-Mar-02, 01:25 AM
No, I'm absolutely NOT arguing that or anything like it. You misinterpreted my statements entirely.

I'm arguing against use of the anthropic principle as a logical basis for saying the Universe is "rigged". Our point of view towards the universe is what's biased, not the universe towards us.

Do you mean the Universe we live in is an improbable universe, but it just happens to have a physics that allows life to exist and hence us? So are you referring to the "multiverse" idea? That there are countless other universes in which life is not even possible?

eburacum45
2013-Mar-02, 07:26 AM
There may be three categories into which life on other worlds could be placed;
1/ Life as we know it, which could be detected using tests we can conceive of today;
2/ Life as we don't know it, but which is sufficiently similar to life as we do know it that similar tests coul also detect it (this would include minor differences in biochemistry such as different handedness, different proteins and amino acids, different genetic systems and so on, but which produce similar biomarkers such as oxygen, methane or photosynthetic pigmentation)
3/ Life as we don't know it, which is sufficiently dissimilar to Earth life that we would have to start from scratch when devising tests for its existence. This third category is problematic, and could be difficult to distinguish from the absence of life.

Noclevername
2013-Mar-02, 07:29 AM
Do you mean the Universe we live in is an improbable universe, but it just happens to have a physics that allows life to exist and hence us? So are you referring to the "multiverse" idea? That there are countless other universes in which life is not even possible?

Stop putting words in my mouth. I meant exactly what I said, and nothing more.

Selfsim
2013-Mar-02, 09:41 AM
There may be three categories into which life on other worlds could be placed;
1/ Life as we know it, which could conceivably be detected using tests we can conceive of today;
2/ Life as we don't know it, but which is sufficiently similar to life as we do know it that similar tests coul also detect it (this would include minor differences in biochemistry such as different handedness, different proteins and amino acids, different genetic systems and so on, but which produce similar biomarkers such as oxygen, methane or photosynthetic pigmentation)
3/ Life as we don't know it, which is sufficiently dissimilar to Earth life that we would have to start from scratch when devising tests for its existence. This third category is problematic, and could be difficult to distinguish from the absence of life.See, this is an example of the type of thinking which I find difficult to justify during empirical testing. Each category, whilst initially seeming to be quite logical and rational, assumes clearcut (but hypothetical) outcomes prior to the actual testing of some 'sample of interest', (which might be discovered somewhere other than Earth).

Let me explain.

There have been several recent cases I'm aware of, where 'samples of interest' were exhaustively tested to determine life/no life, which resulted in highly 'controversial' results. These were classified as: Nanobacteria, (http://en.wikipedia.org/wiki/Nanobacterium) Nanobes, (http://en.wikipedia.org/wiki/Nanobe) Nanons (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2242841/) and Protobionts (http://en.wikipedia.org/wiki/Protobiont). Various aspects of these samples were tested, all of which resulted in partial matches for what we'd expect from certain aspects of something we'd call 'living'. They all also produced results consistent with 'no life'.

So, where do these 'samples of interest' fit into the categories (1) to (3) above? It would seem to vary, depending on which test result one is considering (staining, morphological analysis, and antigenicity, amplicon counts, growth on axenic media, susceptibility to chemical and physical agents, etc, etc).

See, I can see no reason to exclude the possibility that our own definitions of 'life' might have to be re-written upon some, (or even all), future discoveries, just as the examples given, seem to be doing. If one follows this line of thinking, it is quite possible that our present tests for 'life' might be radically different in the future, simply because of what we don't presently know about 'universal' life. Perhaps this fascination we all have for finding other life in the universe might all turn out to be a complete non-event once we get sufficient mileage under our belts, that humans will look back with the benefit of hindsight, and see just how naive we really were about what we had in mind, when we initially set out on this quest(?)

We need to allow the data/testing to do the leading on this one. We need to follow those results ... as opposed to allowing logical, rationalist speculative thinking to tell us what must/must not exist (and to allow it to overly influence the testing methodologies of future samples).

(IMO).

Colin Robinson
2013-Mar-02, 10:27 AM
There may be three categories into which life on other worlds could be placed;
1/ Life as we know it, which could be detected using tests we can conceive of today;
2/ Life as we don't know it, but which is sufficiently similar to life as we do know it that similar tests coul also detect it (this would include minor differences in biochemistry such as different handedness, different proteins and amino acids, different genetic systems and so on, but which produce similar biomarkers such as oxygen, methane or photosynthetic pigmentation)
3/ Life as we don't know it, which is sufficiently dissimilar to Earth life that we would have to start from scratch when devising tests for its existence. This third category is problematic, and could be difficult to distinguish from the absence of life.

I think looking for oxygen and/or methane is more likely to work than looking for a photosynthetic pigment like chlorophyl.

My reason is that oxygen and methane are simple substances that can indicate energy flows associated with life. Laws of thermodynamics imply that a growing and self-repairing system (whatever its chemical composition) does need an energy flow, and the possible strategies are not unlimited, in terms of basic inputs and outputs. This doesn't mean either oxygen or methane is a sure sign of life, just that they may be important clues.

When we consider the far more complex molecules that living thing use to catalyze chemical reactions, the number of possibilities may be much greater. There is clearly an astronomical number of possible carbon compounds (even before you start thinking of compounds of silicon etc), and who knows how many of the compounds many have catalytic properties which living things could use? Even here on Earth, different bio-molecules get used for essentially the same job, e.g. some living things use haemoglobin for transport of oxygen, while others use haemocyanin.

So I'm inclined to think that finding chlorophyl in the spectrum of an earth-like exo-planet is only slightly more likely than finding an alien space craft on the White House lawn. The sorts of clues we're more likely to find are

* combinations of simple molecules that imply flows of chemical energy.
* along with complex molecules vaguely similar (at most) to those we're familiar with; i.e. the sort of stuff that gets described as "unknown organic compound".

In the case of Titan, we've already found both of the above. That is why I think Titan should be given a closer look.

eburacum45
2013-Mar-02, 05:31 PM
There have been several recent cases I'm aware of, where 'samples of interest' were exhaustively tested to determine life/no life, which resulted in highly 'controversial' results. These were classified as: Nanobacteria, (http://en.wikipedia.org/wiki/Nanobacterium) Nanobes, (http://en.wikipedia.org/wiki/Nanobe) Nanons (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2242841/) and Protobionts (http://en.wikipedia.org/wiki/Protobiont). Various aspects of these samples were tested, all of which resulted in partial matches for what we'd expect from certain aspects of something we'd call 'living'. They all also produced results consistent with 'no life'.

So, where do these 'samples of interest' fit into the categories (1) to (3) above? It would seem to vary, depending on which test result one is considering (staining, morphological analysis, and antigenicity, amplicon counts, growth on axenic media, susceptibility to chemical and physical agents, etc, etc).

Interesting point. The 'nanobacteria' described above seem to have been a false alarm, but it may be the case that false alarms of this sort are much more common in the extraterrestrial environment than true positives. And there might be many different kinds of 'protobiont' on other worlds; they could be far more common than life as we recognise it. So any set of tests for extraterrestrial life would need to take into account the possiblity of false positives as well as protobiont-like structures that don't conform to our current ideas of life.

Our own planet might have been covered in protobionts for millions, or hundreds of millions of years, although it's a bit tricky to determine what exactly they were like after all this time. We may never know.

TooMany
2013-Mar-02, 06:14 PM
Stop putting words in my mouth. I meant exactly what I said, and nothing more.

Hey, take it easy. It's not always so easy to know what someone else is getting at. I'm not putting words in your mouth, I'm trying to ask you what your point is because it's not clear to me. I thought maybe that was it the multiverse. Please notice that my sentence started with "Do you mean".

TooMany
2013-Mar-02, 06:20 PM
There may be.

It's a topic which biochemists and other scientists have been thinking and writing about for a long time. Of course it's true that no such life-form has been found, nor has one been created in a laboratory. But on the other hand, there doesn't seem to be any simple argument, based on known natural laws, to say that it couldn't exist. (In the sense that for instance a perpetual motion machine is ruled out by known laws of thermodynamics.)

Some literature that you can read online:

Robert A. Freitas Jnr; Xenology; Chapter 8, Exotic Biochemistries (http://www.xenology.info/Xeno/8.0.htm)

David Darling; Encyclopedia of Science; Alternative Forms of Life (a clickable list of relevant pages in the Encyclopedia) (http://www.daviddarling.info/encyclopedia/A/alternative_forms_of_life.html)

John A. Baross and others; The Limits of Organic Life in Planetary Systems (lengthy technical discussion) (http://www.nap.edu/catalog.php?record_id=11919)

Those were interesting. While ammonia seems like a possible solvent, apparently there are potentially some issues with that. It would be very interesting if there are multiple very different chemical pathways to life. It would imply that life is perhaps even a more universal and robust process than we have assumed.

I read the executive summary of the last reference and found this quote that backs up my contention about complexity:


The canonical characteristics of life are inherent capacities to adapt to changing environmental conditions and to increase in complexity by multiple mechanisms, particularly by interactions with other living organisms.

Noclevername
2013-Mar-02, 06:50 PM
Hey, take it easy. It's not always so easy to know what someone else is getting at. I'm not putting words in your mouth, I'm trying to ask you what your point is because it's not clear to me. I thought maybe that was it the multiverse. Please notice that my sentence started with "Do you mean".

Sorry, didn't mean to snap at you.

All I was trying to get at was that the way that you worded your statement...

... sometimes it seems as if things are just rigged to promote the kind of organic life we find on earth.

...is something I've heard a lot from Creationist and Intelligent Design proponents. It's a big red flag to me. The idea that the Universe is rigged for life rather than life being rigged for the Universe is, IMO, flawed logic. The universe seems to be "set up" for life because life follows the laws of physics. It's like seeing a puddle and thinking that the ground is shaped to fit the water, instead of the water conforming to the shape of the ground.

ADDED: http://en.wikipedia.org/wiki/Anthropic_principle

TooMany
2013-Mar-03, 01:13 AM
Sorry, didn't mean to snap at you.

All I was trying to get at was that the way that you worded your statement...


...is something I've heard a lot from Creationist and Intelligent Design proponents. It's a big red flag to me. The idea that the Universe is rigged for life rather than life being rigged for the Universe is, IMO, flawed logic. The universe seems to be "set up" for life because life follows the laws of physics. It's like seeing a puddle and thinking that the ground is shaped to fit the water, instead of the water conforming to the shape of the ground.

ADDED: http://en.wikipedia.org/wiki/Anthropic_principle

No harm done. No I'm long way from that point of view. Religious ideas aside, there are real scientific questions here. You suggest that life is simply molded to the physics; that's true. However, not all possible physics are going to make life possible. Are there chemistries very different from our terrestrial example that will support life within our physics? We don't know yet.

We don't know yet how sensitive life (even as we know it) is to the details of the physics. What if stellar fusion worked differently and the abundances of elements was quite different? What if chemical bonding didn't work exactly as it does? Would it still be possible for life to emerge? We don't know, but maybe one day we will.

It seems that a popular solution these days to the problem of why is the universe suitable for life is that it is only one of countless universes. So life always finds itself in a seemingly "rigged" universe, but it is not really rigged. It is simply a random and rare case among a vast multiverse of different physics that happens to form life. That explanation avoids "Intelligent Design" entirely. On the other hand, I don't think you can avoid the "design" concept by arguing that life will always evolve regardless of the details of the physics, but will fit whatever physics there is. That seems quite unlikely.

In any case, intelligent design is a self-defeating solution. It fails to answer what designed the designer. Thus it makes no actual progress in explaining our existence. Instead it pretends to make the problem go away (which is satisfactory for some people).

Noclevername
2013-Mar-03, 01:33 AM
On the other hand, I don't think you can avoid the "design" concept by arguing that life will always evolve regardless of the details of the physics, but will fit whatever physics there is. That seems quite unlikely.


Good thing I'm not arguing that, then. :)

Selfsim
2013-Mar-03, 04:20 AM
Ok, so as an attempt at bringing the conversation back to the constraints reviewed and agreed by the various NRC Committees, they say (Executive Summary, Page 2, bottom (http://www.nap.edu/openbook.php?record_id=11919&page=2)):


The survey made clear that most locales in the solar system are at thermodynamic disequilibrium, an absolute requirement for chemical life, and that many locales at thermodynamic disequilibrium also have solvents in liquid form and environments where the covalent bonds between carbon and other lighter elements are stable. Those are weaker requirements for life, but the three together appear, perhaps simplistically, to be sufficient for life.So, three broadly distinguishing sufficient characteristics (no new physics or alternate universes).
Further …

The committee found that using thermal and chemical energy to maintain thermodynamic disequilibria, covalent bonds between carbon atoms, water as the liquid, and DNA as a molecular system to support Darwinian evolution is not the only way to create phenomena that would be recognized as life. Indeed, the emerging field of synthetic biology has already provided laboratory examples of alternative chemical structures that support genetics, catalysis, and Darwinian evolution. Organic chemistry offers many examples of useful chemical reactivity in nonwater liquids. Macromolecular structures reminiscent of those found in terran biology can be formed with silicon and other elements.(My underlines).
So, the key characteristic according to them is thermodynamic equilibrium.
The problem with this is (from Wiki (http://en.wikipedia.org/wiki/Non-equilibrium_thermodynamics)):

Most systems found in nature are not in thermodynamic equilibrium; for they are changing or can be triggered to change over time, and are continuously and discontinuously subject to flux of matter and energy to and from other systems and to chemical reactions. Non-equilibrium thermodynamics is concerned with transport processes and with the rates of chemical reactions. Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods.Note the bit in bold.
They have distinguished a minimum 'sufficient' characteristic, (which is everywhere), and yet such a characteristic "is beyond the scope of currently known macroscopic thermodynamic methods".

I think that distinguishes the detection problem .. in a nutshell.

Further ..
The thermodynamic study of non-equilibrium systems requires more general concepts than are dealt with by equilibrium thermodynamics.All of which leads onto analysis of auto-catalytic systems, (which we've spoken at length about previously, in this forum). Such dynamic systems can be stable, can oscillate, can be damped, underdamped, critically damped, can have attractors (of all different types), etc.

Careful, generalised observations of the environments in which samples of interest reside, would be the first step in the process. Going in looking for details like, for eg: chirality of DNA molecules, just seems to be way, way too prescriptive to me., given this definition of the fundamental 'search' problem.

Noclevername
2013-Mar-07, 02:02 PM
So we can't actually draw conclusions about ET life unless and until we actually find some. Leaving us with nothing to do now but speculate on possibilities, using known data. ;)

Selfsim
2013-Mar-07, 10:40 PM
Well, even more than that, no knowledge of how it evolves can be claimed, either ...

You might not know, but I do.… (etc). :)

The speculation is a matter of choice ..

Accumulated volumes of undistinguished speculation however, (as exemplified by the 'typical' quote above), are of great community concern. Mass delusions are often started that way.

TooMany
2013-Mar-08, 12:47 AM
Mass delusions are often started that way.

Well I'm certainly not worried about scientific speculation based on what we know resulting in mass delusions, possibly mistakes but that's how science works.

You're thinking of War of Worlds which is something else entirely.

ASTRO BOY
2013-Mar-08, 12:55 AM
Well, even more than that, no knowledge of how it evolves can be claimed, either ...
… (etc). :)

The speculation is a matter of choice ..




Speculation and/or Imagination are part and parcel of science and the scientific method. Always has been and probably always will be.
In general we speculate, hypothesis with an educated guess on some probability...eg: Most scientists, including Astro-Biologists and Cosmologists hypothesis that ET would/should exist elsewhere.
That hypothesis is based on what observational data we already have.
In fact some see it more as a valid scientific assumption.

Why search for life as we know it?
Because it would be easier for us to recognise as such.....because we are logically more familiar with that type of life...We are here, so why shouldn't some similar form of life be elsewhere under similar conditions?

It in no way disputes any suggestion that "life as we don't know it" may also exist....It's just a necessary step we use, similar to that used in the scientific method.
At any rate, as it generally always does, time will certainly tell.

Selfsim
2013-Mar-08, 02:02 AM
Well I'm certainly not worried about scientific speculation based on what we know resulting in mass delusions, possibly mistakes but that's how science works.

You're thinking of War of Worlds which is something else entirely.Scientific speculation is distinguished by test results. I've never seen any as a result of what goes on here .. have you?

I can only conclude that the accumulated volumes of undistinguished speculation evident here, is thus not scientific speculation at all. It is actually more like 'War of the Worlds' … so I guess we're in agreement about that, eh?

danscope
2013-Mar-08, 04:12 AM
" .....but speculate on possibilities, using known data ." I wonder, just exactly what data he's refering to?
The scientific community has 0.00000000000000000000000% data Zip, cypher, nada, goose egg.
You have dreams and fantasies. Nothing to quantify in the least.

Selfsim
2013-Mar-08, 06:03 AM
" .....but speculate on possibilities, using known data ." I wonder, just exactly what data he's refering to?
The scientific community has 0.00000000000000000000000% data Zip, cypher, nada, goose egg.
You have dreams and fantasies. Nothing to quantify in the least.Well paradoxically (for those citing supporting 'evidence') there actually appears to be 'data' .. and your point is also right on the mark, and highly valid!?!!

But how can that be? ..

Paraphrasing (a little), the relevance of 'the data' is subject to the speculative hypothesis being true, (which it isn't). Which means that the relevance of the data is subject to adoption of the philosophical perspective of logical positivism .. which isn't science .. its pure philosophy .. as is the idea that what is presently 'unknown', is also real .. which is also the subject of the same philosophical standpoint.

The NASA Astrobiological (https://astrobiology.nasa.gov/roadmap/) definition of 'life' is also highly culpable in this debate …

… Although this discipline will benefit from an understanding of the origins and limits of terrestrial life, it also requires that we define the environmental conditions and the chemical structures and processes that could support life on other habitable planets. Thus we need to exploit universal laws of physics and chemistry to understand polymer formation, self-organization processes, energy utilization, information transfer, and Darwinian evolution that might lead to the emergence of life in planetary environments other than Earth. See, by defining 'life' to be capable of 'Darwinian Evolution' from the outset, we get all this so-called "evidence" (from Earth's history) being cited. But the point is, (as you infer), the relevance of Earth's evolutionary record to speculated exo-'life', is subject to the affirmative outcome of the very tests derived from the initial speculative 'exo-life exists' hypothesis ... which have never been properly executed .. (certainly not to the extent of eliminating any of the uncertainties). Any results so far obtained, cannot be argued to be a valid empirical result as far as the exo-life hypothesis is concerned, and thus the relevance of Earth-life's historical development, has thus never been empirically established, (even in the slightest).

Ie: the existence of 'data' from Earth life's historical development is a completely separate and moot point. Hence:

.. Zip, cypher, nada, goose egg .. is a completely empirically valid, scientifically founded viewpoint.

Noclevername
2013-Mar-08, 07:07 AM
Scientific speculation is distinguished by test results. I've never seen any as a result of what goes on here .. have you?


Scientific experimentation is distinguished by test results. Scientific calculation is distinguished by test results. Speculation is a thought experiment.


" .....but speculate on possibilities, using known data ." I wonder, just exactly what data he's refering to?

Yeah, don't bother to actually ASK me what data I mean. It's more fun to make up your own answers.

The data I was referring to is the known laws of physics and chemistry, which apply to life and are as far as we have observed, the same across the Universe.


Well paradoxically (for those citing supporting 'evidence') there actually appears to be 'data' .. and your point is also right on the mark, and highly valid!?!!

To clarify, I'm not one of those claiming evidence of anything and vigorously oppose those who do. You are conflating two separate arguments.



Paraphrasing (a little), the relevance of 'the data' is subject to the speculative hypothesis being true, (which it isn't).
If by "paraphrasing" you mean "distortion".
An untested hypothesis by definition cannot be ruled true or untrue by science.


Which means that the relevance of the data is subject to adoption of the philosophical perspective of logical positivism .. which isn't science .. its pure philosophy .. as is the idea that what is presently 'unknown', is also real .. which is also the subject of the same philosophical standpoint.

The NASA Astrobiological (https://astrobiology.nasa.gov/roadmap/) definition of 'life' is also highly culpable in this debate …
See, by defining 'life' to be capable of 'Darwinian Evolution' from the outset, we get all this so-called "evidence" (from Earth's history) being cited.

See, there's that "E" word again. Not what I was talking about in the post danscope was replying to. The NASA definition also fails to use the term. In fact in the quote you provided the word MIGHT is specified.


But the point is, (as you infer), the relevance of Earth's evolutionary record to speculated exo-'life', is subject to the affirmative outcome of the very tests derived from the initial speculative 'exo-life exists' hypothesis ... which have never been properly executed .. (certainly not to the extent of eliminating any of the uncertainties). Any results so far obtained, cannot be argued to be a valid empirical result as far as the exo-life hypothesis is concerned, and thus the relevance of Earth-life's historical development, has thus never been empirically established, (even in the slightest).
Thus my use of the word possibilities. Not to be confused with evidence, of which I readily acknowledge we have zero. And have stated so repeatedly.


Ie: the existence of 'data' from Earth life's historical development is a completely separate and moot point. Hence:
is a completely empirically valid, scientifically founded viewpoint.

Moot point? You are essentially arguing for Earth exceptionalism, which is not supported by anything known. And you call that science?

ASTRO BOY
2013-Mar-08, 08:26 AM
Science is full of logical scientific assumptions, the probability of ET life being one of them.......

extract from " http://en.wikipedia.org/wiki/Extraterrestrial_life " as follows sums up my views on what data there is available to make such assumptions........


Alien life, such as bacteria, has been hypothesized to exist in the Solar System and throughout the universe. This hypothesis relies on the vast size and consistent physical laws of the observable universe. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere other than Earth.[2][3] This argument is embodied in the Copernican principle, which states that the Earth does not occupy a unique position in the Universe, and the mediocrity principle, which holds that there is nothing special about life on Earth.[4] Life may have emerged independently at many places throughout the Universe. Alternatively life may form less frequently, then spread between habitable planets through panspermia or exogenesis.[5] In any case, complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth based on computer model studies.[6] According to these studies, this same process may also occur around other stars that acquire planets.[6] (Also see Extraterrestrial organic molecules.) Suggested locations at which life might have developed include the planets Venus[7] and Mars, Jupiter's moon Europa,[8] and Saturn's moons Titan and Enceladus.[9] In May 2011, NASA scientists reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".[10][11] Life may appear on extrasolar planets, such as Gliese 581 c, g and d, recently discovered to be near Earth mass and apparently located in their star's habitable zone, with the potential to have liquid water.[12] In December 2011, scientists working with NASA’s Kepler space telescope announced the discovery of Kepler-22b, an exoplanet that appears to be orbiting a sun-like star within the habitable zone.[13]

ASTRO BOY
2013-Mar-08, 08:30 AM
I would imagine that if Panspermia was found to be valid, the ETL we eventually find evidence of, would probably be "Life as we know it".

Selfsim
2013-Mar-08, 08:53 AM
Alien life, such as bacteria, has been hypothesized to exist in the Solar System and throughout the universe. This hypothesis relies on the vast size and consistent physical laws of the observable universe. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere other than Earth.[2][3] This argument is embodied in the Copernican principle, which states that the Earth does not occupy a unique position in the Universe, and the mediocrity principle, which holds that there is nothing special about life on Earth ...
Invalid because of reasoning based on a circular argument. (As explained in "The Copernican Fallacy and Numbers" (http://cosmoquest.org/forum/showthread.php?140478-Copernican-Fallacy-amp-Numbers&p=2091377#post2091377)).

ASTRO BOY
2013-Mar-08, 11:08 AM
Invalid because of reasoning based on a circular argument. (As explained in "The Copernican Fallacy and Numbers" (http://cosmoquest.org/forum/showthread.php?140478-Copernican-Fallacy-amp-Numbers&p=2091377#post2091377)).

No. not at all....Just a difference of opinions and interpretations of a vague philosophical concept.
We all should be prepared to acknowledge and accept that fact and the validity history has accorded it.
I remain aligned with Carl, Stephen and many more authoritive experts on this matter for the reasons stated many times.

danscope
2013-Mar-08, 08:38 PM
There is the philosophical argument . But it is not a scientific one. You only have Earth for your data set. Idle speculation is the domain of casual philosophy. When you find evidence of ET life, you can begin your science. And it will be on the
evening news. Of that, you may be certain.

Noclevername
2013-Mar-08, 08:45 PM
There is the philosophical argument . But it is not a scientific one. You only have Earth for your data set. Idle speculation is the domain of casual philosophy. When you find evidence of ET life, you can begin your science. And it will be on the
evening news. Of that, you may be certain.

Not only not idle, but very useful. And the data we have is not limited to observing life itself. Since life is a process that works according to chemical and physical laws, those laws and their applications are also relevant data.

danscope
2013-Mar-08, 11:01 PM
You have no data concerning life elsewhere. You can dream all you want. That is not data

Noclevername
2013-Mar-08, 11:15 PM
You have no data concerning life elsewhere.
The data I mentioned concerns the POSSIBILITY of life elsewhere. We can't rule it out.

I'm getting tired of having to distinguish the difference for you.


You can dream all you want. That is not data


You can repeat that all you want, but that does not make it fact.

Selfsim
2013-Mar-09, 12:58 AM
The thing I see going on here,* is that for those motivated by the thought that 'exo-life exists', theory is all important. Theories require evidence (or data), otherwise they remain hypothetical. This would be why the: 'data exists .. in support of the possibility' claim, is viewed as 'important' .. but this is only 'important' if one is attempting to build a theory which explains why (or how) life could exist elsewhere. Such a theory is only 'important', if the idea that life does exist elsewhere, is viewed as being 'important' from the outset. Nothing (or no-one) in science says that I have to believe that. I therefore choose not to. (Note: this does not mean that I don't believe exo-life exists .. what it does mean is that the belief about this, is unimportant to me, in resolving this question).

However, the other way of looking at this, is that the only way we can establish the reality of the existence of life elsewhere, is to develop a test for it, which eliminates uncertainties to the point of leaving little/no room for other reasonable interpretations. It is a purely empirical testing process which must be followed. The main purpose a theory of exo-life has in such an empirical test, doesn't go much beyond defining the nature of the test to be applied. The issue is that we already have tests for diagnosing 'life'. No more tests are needed, therefore there is no purpose for additional theory (or 'supporting data', as the existence of the laws of Physics and Chemistry are not exclusively for justifying the existence of 'life' .. they go way beyond that, (clearly) ).

On a slightly different tack, I find Noclevername's point about speculation here being all about 'thought experimentation', intriguing. However, throughout scientific history, thought experiments only really become useful in science when they result in something tangible ..From Wiki: (http://en.wikipedia.org/wiki/Thought_experiment#In_science)

Scientists also use thought experiments when particular physical experiments are impossible to conduct (Carl Gustav Hempel labeled these sorts of experiment "theoretical experiments-in-imagination"), such as Einstein's thought experiment of chasing a light beam, leading to Special Relativity. This is a unique use of a scientific thought experiment, in that it was never carried out, but led to a successful theory, proven by other empirical means.
The point being the last emboldened part.

The truly important aspect of 'thought experiments' encompassing exo-life speculation, hypothesis, theory, or whatever ... is the empirical part (ie: "proven by other empirical means"). Without the latter, a 'thought experiment' about exo-life remains in thought only ... which is not physical reality, or physical existence.

I hope this post aids in clarifying the perspectives. Needless to say, my leaning is towards the empirical interpretation, because test results persist, but theories change to suit the results. The search for life is the test for a universal theory of life. The search for Earth-like life elsewhere, is not big enough to encompass all the 'possible' unknowns (such as Life as we don't know it).


Footnote:
* This is not intended as an attack, so please don't take it that way .. I'm trying to bridge dissimilar perspectives in this post ..

Grant Hatch
2013-Mar-09, 07:16 AM
Ok, so as an attempt at bringing the conversation back to the constraints reviewed and agreed by the various NRC Committees, they say (Executive Summary, Page 2, bottom (http://www.nap.edu/openbook.php?record_id=11919&page=2)):

So, three broadly distinguishing sufficient characteristics (no new physics or alternate universes).
Further …
(My underlines).
So, the key characteristic according to them is thermodynamic equilibrium.
The problem with this is (from Wiki (http://en.wikipedia.org/wiki/Non-equilibrium_thermodynamics)):
Note the bit in bold.
They have distinguished a minimum 'sufficient' characteristic, (which is everywhere), and yet such a characteristic "is beyond the scope of currently known macroscopic thermodynamic methods".

I think that distinguishes the detection problem .. in a nutshell.

Further ..All of which leads onto analysis of auto-catalytic systems, (which we've spoken at length about previously, in this forum). Such dynamic systems can be stable, can oscillate, can be damped, underdamped, critically damped, can have attractors (of all different types), etc.

Careful, generalised observations of the environments in which samples of interest reside, would be the first step in the process. Going in looking for details like, for eg: chirality of DNA molecules, just seems to be way, way too prescriptive to me., given this definition of the fundamental 'search' problem.

:confused:
Forgive my comment if I misunderstand...... BUT...., I was following the discussion with interest and reading the links along the way when I came to the above.... Hmmmm, unfortunately the quoted material within the quote above does not appear to be included.... however all of it IS in post #47. The operative word in the NRC committee was "thermodynamic DISequilibrium" (caps mine) not "thermodynamic equilibrium" as stated by Selfism. Am I missing something here? There would be no inconsistancy with the wikipedia source in that case.....

Noclevername
2013-Mar-09, 07:44 AM
The thing I see going on here,* is that for those motivated by the thought that 'exo-life exists',
Let me just point out again that I am not one of those people. My own motivation here is regarding discussion on the the LIS subforum.


[for them] ...theory is all important.
I can't answer for them.


Theories require evidence (or data), otherwise they remain hypothetical.
Absolutely true.


This would be why the: 'data exists .. in support of the possibility' claim, is viewed as 'important' ..
Again, I didn't intend for that statement to be taken as support of any claims about exolife.

but this is only 'important' if one is attempting to build a theory which explains why (or how) life could exist elsewhere. Such a theory is only 'important', if the idea that life does exist elsewhere, is viewed as being 'important' from the outset.

I disagree entirely. It is relevant here because the threads are continually being derailed by "well we don't have evidence of ET life so there's no point in talking about it". (At least that's how it comes across.)


Nothing (or no-one) in science says that I have to believe that. I therefore choose not to. (Note: this does not mean that I don't believe exo-life exists .. what it does mean is that the belief about this, is unimportant to me, in resolving this question).
Belief is unimportant to science, yes. How we define belief is absolutely important to both science and to this board.


However, the other way of looking at this, is that the only way we can establish the reality of the existence of life elsewhere, is to develop a test for it, which eliminates uncertainties to the point of leaving little/no room for other reasonable interpretations. It is a purely empirical testing process which must be followed. The main purpose a theory of exo-life has in such an empirical test, doesn't go much beyond defining the nature of the test to be applied. The issue is that we already have tests for diagnosing 'life'.
Absolutely true.


No more tests are needed, therefore there is no purpose for additional theory (or 'supporting data', as the existence of the laws of Physics and Chemistry are not exclusively for justifying the existence of 'life' .. they go way beyond that, (clearly) ).

Again, theory is not a word I used. "Supporting" data is not a phrase I used. Justifying life is not a motivation I used. Once again you are conflating what I was saying with the opinions of others.

And purpose is a personal motivation. Many people have different purposes, good and bad, in discussing exolife concepts here.


On a slightly different tack, I find Noclevername's point about speculation here being all about 'thought experimentation', intriguing. However, throughout scientific history, thought experiments only really become useful in science when they result in something tangible ..From Wiki: (http://en.wikipedia.org/wiki/Thought_experiment#In_science)

The point being the last emboldened part.

Agreed.

The truly important aspect of 'thought experiments' encompassing exo-life speculation, hypothesis, theory, or whatever ...

And here's the crux of our problem. The three things you named are not the same. You are lumping together disparate factors. The one LIS is concerned with is only the first.

I also disagree with thge "truly important" part of that sentence; what one gives importance is a matter of personal opinion, or motive.


...is the empirical part (ie: "proven by other empirical means"). Without the latter, a 'thought experiment' about exo-life remains in thought only ... which is not physical reality, or physical existence.
Never said it was. I said on several occasions that it wasn't.

But since the whole point of this thread is speculating about exolife, thought experiments are what we're limited to here right now.


I hope this post aids in clarifying the perspectives.

Unfortunately not. You have, however, clarified the reasons why there is so much misunderstanding in this thread and elsewhere.


The search for Earth-like life elsewhere, is not big enough to encompass all the 'possible' unknowns (such as Life as we don't know it).

Just as I said in the OP.

I pointed out that it's a useful starting point, and went to some pains to make that clear. Obviously I should have tried harder.


Footnote:
* This is not intended as an attack, so please don't take it that way .. I'm trying to bridge dissimilar perspectives in this post ..

Thank you for trying. However, your understanding of my perspective was inaccurate; I hope this response clarifies some of what I'm really thinking.

Grant Hatch
2013-Mar-09, 08:55 AM
Hmmm, I still havn't figured out how to quote bits and pieces of another post properly....

"The main purpose a theory of exo-life has in such an empirical test, doesn't go much beyond defining the nature of the test to be applied. The issue is that we already have tests for diagnosing 'life'. No more tests are needed, therefore there is no purpose for additional theory (or 'supporting data', as the existence of the laws of Physics and Chemistry are not exclusively for justifying the existence of 'life' .. they go way beyond that, (clearly) )."

"The search for Earth-like life elsewhere, is not big enough to encompass all the 'possible' unknowns (such as Life as we don't know it)."

Not sure if you were serious but if you were this would be my response. (Respectfully)
Surely, as our understanding of the universe increases so does our ability to theorize. Could we have even begun to have a "valid" (to our understanding today) discussion of this subject not so long ago? Yet you say there is no purpose for additional theory, that we have tests sufficient to the endeavor. (Perhaps for life as we know it) Yet that presupposes that our present understanding/paradigm is up to the task.... The purpose of theorizing is to incorporate everything we know (and adapt and change as we learn more and incorporate it into the "nature" of the test) into a theory we hope IS empirically testable, ESPECIALLY for the detection of life as we DON'T know it. Since most of the rest of our Solar system would be in that category I find it an extremely interesting subject.

Selfsim
2013-Mar-09, 09:00 AM
:confused:
Forgive my comment if I misunderstand...... BUT...., I was following the discussion with interest and reading the links along the way when I came to the above.... Hmmmm, unfortunately the quoted material within the quote above does not appear to be included.... however all of it IS in post #47. The operative word in the NRC committee was "thermodynamic DISequilibrium" (caps mine) not "thermodynamic equilibrium" as stated by Selfism. Am I missing something here? There would be no inconsistancy with the wikipedia source in that case.....Hi Grant;
Yep a little ambiguous (apologies for that). You can replace my 'equilibirum' with 'disequilibirum' if you like, as what the NRC singles out as an "absolute requirement for chemical life". (I was using the term "Thermodynamic Equilibrium" in the sense of it being the name of the field of study in which 'disequilibrium' then has meaning). The point remains however that determination of thermodynamic disequilibrium is not necessarily a straight forward matter, especially if one has to go down to the scale of the specific habitat in which chemical life might exist. Just because a planet's global environment may appear from our vantage point, as being in thermodynamic disequilibrium, doesn't necessarily mean that the habitat of relevance (say on the surface, etc) is in the same state. If this remains uncertain, then so does the 'likely existence' of the 'absolute requirement' for chemical life. (Eg: on Mars, the hunt for chemical life seems to be heading underground .. so just how reliable is the remote determination of global thermodynamic equilibrium/disequilibrium?)

The Wiki reference points out that thermodynamic equilibrium throughout natural systems is mostly a temporary state anyway, (and thus, so is disequilibrium), so I'm starting to wonder whether this overall 'bio-sign' (or absolute requirement for life), means anything much at all from our remote vantage point, as far as the existence or otherwise of life ..(??)

Hope this makes where I was coming from a little clearer(??)

Cheers

Grant Hatch
2013-Mar-09, 04:16 PM
Hi Grant;
Yep a little ambiguous (apologies for that). You can replace my 'equilibirum' with 'disequilibirum' if you like, as what the NRC singles out as an "absolute requirement for chemical life". (I was using the term "Thermodynamic Equilibrium" in the sense of it being the name of the field of study in which 'disequilibrium' then has meaning). The point remains however that determination of thermodynamic disequilibrium is not necessarily a straight forward matter, especially if one has to go down to the scale of the specific habitat in which chemical life might exist. Just because a planet's global environment may appear from our vantage point, as being in thermodynamic disequilibrium, doesn't necessarily mean that the habitat of relevance (say on the surface, etc) is in the same state. If this remains uncertain, then so does the 'likely existence' of the 'absolute requirement' for chemical life. (Eg: on Mars, the hunt for chemical life seems to be heading underground .. so just how reliable is the remote determination of global thermodynamic equilibrium/disequilibrium?)

The Wiki reference points out that thermodynamic equilibrium throughout natural systems is mostly a temporary state anyway, (and thus, so is disequilibrium), so I'm starting to wonder whether this overall 'bio-sign' (or absolute requirement for life), means anything much at all from our remote vantage point, as far as the existence or otherwise of life ..(??)

Hope this makes where I was coming from a little clearer(??)

Cheers

Hi Selfism,

Thanks for clearing that up. I appreciate your interest and knowlege on the subject as I am just a neophyte attempting to learn more about the subject. I am in total agreement with you on the difficulties and validity of a remote, from a distance, determination or "discovery of life" using the thermodynamic disequilibrium "test" model. I believe there are much better ways to look for life from a distance. The problem seems to be discriminating between signatures that can ONLY be ascribed to life versus those due to purely natural processes. That is why I think theories incorporating the latest (and future) advances in our understanding of the possible signatures of life forms and ways to detect it is an on going and possibly never ending process.... I do not believe we now have (and may never have) definitive "tests" for the detection of all possible life forms....

Noclevername
2013-Mar-09, 04:35 PM
I do not believe we now have (and may never have) definitive "tests" for the detection of all possible life forms....

I couldn't help but key on this statement, which I agree with. It's one of the reasons I think we need to continually explore possibilities with an eye towards potential life, from individual speculation to computer simulation, incorporating all the information about the Universe that we can gather. It will give us a broader idea of what might be out there, and what might not; what might be alive, and what might not. It will help us to refine our definitions of life.

Paul Wally
2013-Mar-09, 05:05 PM
My take on this is that "life as we know it"/"life as we don't know it" dichotomy is once again one of those rather artificial problems discussed in this forum. I don't really see what the big issue is here, maybe that is because it is really not at all clear what is meant by "life as we know it". Maybe we should very clearly define "life as we know it", then we will understand by how much something must differ from it to qualify as "life as we don't know it".

Take for instance a hypothetical carbon based microbial life, living in a water environment, absorbing nutrients from it's environment, metabolising, reproducing, it even respirates with oxygen and releases carbon dioxide into the environment. The only difference is that this organism doesn't have something that we would call nucleic acid. It uses a completely different chemical mechanism to store genetic information. Now is this organism "life as we don't know it" or would something more different qualify? Silicon based life perhaps? What about carbon based life that uses a different solvent than water, say liquid ammonia. Where do we draw the line?

Noclevername
2013-Mar-09, 05:15 PM
My take on this is that "life as we know it"/"life as we don't know it" dichotomy is once again one of those rather artificial problems discussed in this forum. I don't really see what the big issue is here, maybe that is because it is really not at all clear what is meant by "life as we know it". Maybe we should very clearly define "life as we know it", then we will understand by how much something must differ from it to qualify as "life as we don't know it".

Take for instance a hypothetical carbon based microbial life, living in a water environment, absorbing nutrients from it's environment, metabolising, reproducing, it even respirates with oxygen and releases carbon dioxide into the environment. The only difference is that this organism doesn't have something that we would call nucleic acid. It uses a completely different chemical mechanism to store genetic information. Now is this organism "life as we don't know it" or would something more different qualify? Silicon based life perhaps? What about carbon based life that uses a different solvent than water, say liquid ammonia. Where do we draw the line?

Technically only Earth life is "life as we know it", because at present it's the only one we actually know. The main point of this thread at least, is that it's the only type we can say with 100% surety is possible. Could other types exist? Could they be different from us, and if so by how much? Those are the interesting questions, and the reason why we have an LIS section.

ASTRO BOY
2013-Mar-09, 08:47 PM
That is why I think theories incorporating the latest (and future) advances in our understanding of the possible signatures of life forms and ways to detect it is an on going and possibly never ending process.... I do not believe we now have (and may never have) definitive "tests" for the detection of all possible life forms....

Yep, like all things in general.....we build/discover/research and improve on through experience and being Innovative and Imaginative.
I call it inevitable progress.

Selfsim
2013-Mar-10, 01:06 AM
I couldn't help but key on this statement, which I agree with. It's one of the reasons I think we need to continually explore possibilities with an eye towards potential life, from individual speculation to computer simulation, incorporating all the information about the Universe that we can gather. It will give us a broader idea of what might be out there, and what might not; what might be alive, and what might not. It will help us to refine our definitions of life.If we're genuinely looking for 'a broader idea of what might/might not be out there', then why bother constraining that 'idea' with stories made up about what may/may not constitute 'life'?

The universe makes this stuff, and it doesn't really matter how we think it might make it .. at the end of the day, the universe will do what it does, regardless of what we think it does, (ie: make 'potential' life).

All that remains, is for us to go out there and see what it has actually made.

This type of 'speculation' does nothing to forward knowledge of what the universe has done, unless we can somehow synthesise life from non-living things, or we can demonstrate its existence by some measurement, which we know, rules out 'potential' uncertainties.

For example, I can produce a crayon drawing of an alien (and even animate it on the computer). How is that different from the approach you suggest (which incorporates 'individual speculation')? I mean after all, the animation of my crayon alien, also incorporates a lot of known information about the Universe too, doesn't it? The real physical information, (ie: sourced not from my imagination), that it may be missing, could quite easily make all the difference between it actually living, or not living too.

The speculation I used in drawing it however, will not change this physical status.

ASTRO BOY
2013-Mar-10, 02:01 AM
All that remains, is for us to go out there and see what it has actually made.



That will be done in time along with knowledge gained by Speculating and Imagination and logical assumptions.





For example, I can produce a crayon drawing of an alien (and even animate it on the computer). How is that different from the approach you suggest (which incorporates 'individual speculation')? I mean after all, the animation of my crayon alien, also incorporates a lot of known information about the Universe too, doesn't it? The real physical information, (ie: sourced not from my imagination), that it may be missing, could quite easily make all the difference between it actually living, or not living too.

The speculation I used in drawing it however, will not change this physical status.

I for one cannot see any logical analogy there.

While all agree we have no definitive proof of life elsewhere as yet, the most unlikely scenario we could possibly discover is that we are it.
I could see the Church/s jumping on that bandwagon and declaring it as the evidence for a miracle quick smart.

That is because of the numbers and extent argument, along with the potential of the stuff of life and the chemical and physical possibilities in a near infinite Universe.
To press that point once again....It is a reasonablel scientific assumption based on the data available.

Paul Wally
2013-Mar-10, 11:13 AM
Technically only Earth life is "life as we know it", because at present it's the only one we actually know. The main point of this thread at least, is that it's the only type we can say with 100% surety is possible. Could other types exist? Could they be different from us, and if so by how much? Those are the interesting questions, and the reason why we have an LIS section.

With Earth-life do you mean life from Earth or Earth-like life? If the former, then of course we can never look for Earth-life other than from Earth itself but if it is Earth-like then of course we again have to define what it is that distinguishes Earth-like life from non-Earth like life. Since these terms are not clearly defined I don't find much use for it as far as the search for life is concerned.

This is what I think better represents the situation:
We don't search for "life as we know it" nor do we search for "life as we don't know it". We search for life, period. Life is simply what we currently understand by life, i.e. the search for life is the search for life as we understand it and not life as we know it. What we currently understand by life is
the definition of life. Here's an extract from Wikipedia: Life: (http://en.wikipedia.org/wiki/Life)


Wikipedia

Since there is no unequivocal definition of life, the current understanding is descriptive. Life is considered a characteristic of organisms that exhibit all or most of the following:[26][28]

1. Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.
2. Organization: Being structurally composed of one or more cells — the basic units of life.
3. Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
4. Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
5. Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity, diet, and external factors.
6. Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
7. Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.


My point is then that if we search for the above characteristics then we search for life as we currently understand it but that is not the same as searching for life as we know it. That is because it is possible, in principle at least, that the above characteristics can be realized in a variety of different ways such that life as we understand it also includes life as we don't know it.





For example, I can produce a crayon drawing of an alien (and even animate it on the computer). How is that different from the approach you suggest (which incorporates 'individual speculation')? I mean after all, the animation of my crayon alien, also incorporates a lot of known information about the Universe too, doesn't it? The real physical information, (ie: sourced not from my imagination), that it may be missing, could quite easily make all the difference between it actually living, or not living too.



The problem is that your crayon drawing doesn't represent anything of scientific value. And the animation is just pixels moving around on a computer screen. You haven't defined the the rules by which this hypothetical organism functions. The way computers are used to solve real scientific problems is through simulations of mathematical models, and the mathematical models are not arbitrary speculations but based on things we currently know, like the laws of physics and chemistry. In the case of research in theoretical biology computers are widely used to model complex biological systems or aspects of biological systems like metabolism, reproduction, growth, evolution .. etc. And these are abstract concepts, which makes them multiply realizable meaning that we can model life as we don't know it.

eburacum45
2013-Mar-10, 04:28 PM
Even life that is remarkably similar to Earth-life but which originates from another world should be easy to distinguish from Earth-life; it will share no genetic relationship with Earth-life, unless somehow it is descended from it. Any organism that is the product of a different abiogenesis event will have a genetic heritage that is entirely different to life on Earth. Such an organism could have different genetic coding for various proteins and enzymes and so on, and might even have organic molecules of different handedness (or a mixture of more than one handedness), yet still resemble Earth-life superficially.

Extraterrestrial life that would conform very closely to our ideas of biology could be easily distinguished at a molecular level, unless there has been a panspermia event or deliberate translocation at some time in the past (and even then, if the translocation occurred long enough ago, divergence should make it easy to determine that the organism has been separate from Earth's biosphere for a long time).

Noclevername
2013-Mar-10, 04:41 PM
With Earth-life do you mean life from Earth or Earth-like life?

I meant Earth life, the life we can observe. We can look for things that we know are necessary for known life, like liquid water and certain compounds. We know those things exist off Earth, and we know that they are conducive to at least one form of life, so they make a useful starting point.

Paul Wally
2013-Mar-10, 07:38 PM
We can look for things that we know are necessary for known life, like liquid water and certain compounds.

Yes, I agree completely. It's just that some people interpret looking for things necessary for known life as looking for known life, which is of course nonsense. Say for instance if we decide to look for life in Europa's subsurface ocean, then that doesn't mean we're looking for Earth life. You get my point?

Noclevername
2013-Mar-10, 07:46 PM
You get my point?

That looking for Earth life off Earth makes no sense? Do you know of anyone doing so?

Paul Wally
2013-Mar-10, 07:51 PM
That looking for Earth life off Earth makes no sense? Do you know of anyone doing so?

Sorry, I really mean Earth-like life.

Noclevername
2013-Mar-10, 07:54 PM
Sorry, I really mean Earth-like life.

Oh. Then I guess I don't get your point.

Paul Wally
2013-Mar-10, 08:05 PM
Oh. Then I guess I don't get your point.

Looking for life in Europa's subsurface ocean doesn't mean we're looking for Earth-like life. We have to be open to the possibility that life there, if it exists, will be completely different. So why look specifically for Earth-like life if we don't know what we're going to find.

Noclevername
2013-Mar-10, 10:59 PM
Looking for life in Europa's subsurface ocean doesn't mean we're looking for Earth-like life. We have to be open to the possibility that life there, if it exists, will be completely different.

Of course we do. Never said otherwise.

But the reason Europa is so interesting is because of the liquid water. That's why it recieves more focus from astrobiologists than, say, our own Moon. We know the Moon has little of what is necessary for life from Earth.


So why look specifically for Earth-like life if we don't know what we're going to find.



"Specifically" is not the term I would use. In fact it goes against what I advised in the OP about only using similarity as a starting point. If it seems like life is possible there, we look, period. If it's similar enough for us to recognize as life, we'll see it. But the reason so many think life might be there is the water, because Earth life uses water.

Similarity is a matter of degree, not a binary dividing line.

Colin Robinson
2013-Mar-26, 11:25 PM
Of course we do. Never said otherwise.

But the reason Europa is so interesting is because of the liquid water. That's why it recieves more focus from astrobiologists than, say, our own Moon. We know the Moon has little of what is necessary for life from Earth.

"Specifically" is not the term I would use. In fact it goes against what I advised in the OP about only using similarity as a starting point. If it seems like life is possible there, we look, period. If it's similar enough for us to recognize as life, we'll see it. But the reason so many think life might be there is the water, because Earth life uses water.

Similarity is a matter of degree, not a binary dividing line.

I agree that similarity is a matter of degree, not a binary dividing line.

It is true that Earth life uses liquid water. It's also true that Earth life involves complex active chemistry. Both these statements apply to all known species, when they are actually doing stuff characteristic of life like metabolism and reproduction. Microbes in dormant mode, as spores, are another topic; but no species stays in dormant mode forever.

The question is whether astrobiology should concentrate on environments with liquid water, or on environments with complex, active chemistry, or both?

From either point of view, Earth's Moon is a non-starter — it has neither liquid water, nor complex, active chemistry.

If we are going to concentrate on following the liquid water, then Europa gets high priority -- there is strong evidence of a subsurface ocean, and being a moon of Jupiter, it is less far to go than some of the other outer moons.

On the other hand, if we want to follow the complex, active chemistry, then Titan should get a high priority, because the chemistry of its atmosphere is already known to be very complex and very active.

Hlafordlaes
2013-Mar-27, 12:04 AM
....What I'm trying to say is that these elements are very special and form all sorts of complex molecules. We aren't made from these elements because they are common, but rather because of their special properties. I'm suggesting that our biology can exist only because of these properties.

I'm not a chemist, but I would like to know if there is another chemistry based on different elements that is capable of making the complex molecules needed for life.


.... It may turn out that life beyond Earth is based on water and carbon compounds. But what sort of carbon compounds?

The very fact that carbon is so versatile (e.g. nylon and polythene are also carbon compounds) suggests that living things elsewhere could use carbon in very different ways.

For instance, are we likely to find a familiar biological catalyst, such as chlorophyl, in the spectrum of an exo-planet with plant-like life? Or is it more likely that the photo-synthesizing organisms of a different world will use something quite different as a catalyst?

When I wonder along these lines, also as a non-chemist, I think of discrete combinatorial systems. Given my (seriously outdated) linguist's bent, in theory there ought to be multiple combinations of elements in a discrete combinatorial system that encode differently yet "mean" similarly. Like 2+2=4 and 1+3=4. The beauty of these systems is that finite elements governed by laws can generate near-infinite combinatorial output.

In language, of course, there are many ways of encoding the same or similar information, although some ways are meaningless and/or forbidden by the syntax (as in chemistry?). (After all, most of what you or I wrote as undergraduates was a restatement of what others had said, in the form of a test.) Could chemistry be similar to language, or otoh, is the syntax so strict that very few meaningful combinations are possible?

I pose the question of life as one of a natural system able to pass information from one chemical state to another, and among discrete individual "reaction centers" over time. Does this lead to a DNA-analog in an observed system? Does information complexity increase?

Man, I wish I knew chemistry... and a whole lot of other stuff.:o

Colin Robinson
2013-Mar-30, 04:35 AM
It's all very well to say that "life as we know it" (based on water as well as carbon) would be easier to recognize.

But what if it turns out that the nearest second instance of "life as we know it" is several light-years away, while the nearest life as we don't know it is on a planet which comes within 50 million kilometers of Earth?

This could (conceivably) be the case,

* if life does require an Earth-like temperature;
* if life also requires a polar liquid for a solvent,
* if the polar liquid doesn't always have to be water.

I'm talking here about Venus — not its torrid surface, but its cloud layer, where the temperature is Earth-like and there is abundant liquid in the form of droplets of sulphuric acid: a strongly polar substance, which can interact chemically with organic molecules in a range of ways.

Please note: I'm not saying that this scenario (microbial life in the atmosphere of Venus, and nowhere else in the Solar System besides Earth) is the most plausible.

I am saying it's conceivable.

And if it is the case, we could spend decades or even centuries looking in vain for "life as we know it" in the outer Solar System, and by straining our telescopes at exo-planets, while overlooking something that, in cosmic terms, is almost in our own back-yard.

Noclevername
2013-Mar-30, 01:23 PM
It's all very well to say that "life as we know it" (based on water as well as carbon) would be easier to recognize.
Again, degrees. Think "More Earthlike" and "Less Earthlike", not "this is the definition of Earthlike".


* if life does require an Earth-like temperature;
* if life also requires a polar liquid for a solvent,
* if the polar liquid doesn't always have to be water.


That would be fairly Earthlike.


And if it is the case, we could spend decades or even centuries looking in vain for "life as we know it" in the outer Solar System, and by straining our telescopes at exo-planets, while overlooking something that, in cosmic terms, is almost in our own back-yard.

Do you really think we'd go centuries without examining our nearest planetary neighbor? Concepts for Venus balloon probes within the near future are already on several drawing boards. Don't assume exclusivity. Humanity can look at more than one thing at once.

Colin Robinson
2013-Mar-31, 02:13 AM
Again, degrees. Think "More Earthlike" and "Less Earthlike", not "this is the definition of Earthlike".



That would be fairly Earthlike.



Do you really think we'd go centuries without examining our nearest planetary neighbor? Concepts for Venus balloon probes within the near future are already on several drawing boards. Don't assume exclusivity. Humanity can look at more than one thing at once.

Yes, I know projects like that are on the drawing boards. There has also been some work done on what sort of biochemistry might work in an environment where the most abundant liquid is H2SO4 rather than H20.

But when will the projects get off the drawing boards and onto the launch pads? One obstacle to this happening may be perception of Venus as a "hell" planet. It started to be described that way back in the sixties, when we discovered that the clouds there are not made of water, and that the surface is not a jungle or a sea. Still today, a web-search with words like "Venus, hell" will generate many hits.

It's been half a century already since the first space probes reached our nearest planetary neighbor. Probably by now we should have got used to the idea of a Venus with a high-temperature surface and a sulphuric acid cloud belt. But have we?

Hlafordlaes
2013-Apr-05, 02:03 AM
Here's a bit of news (http://www.rdmag.com/news/2013/04/power-behind-primordial-soup-discovered) regarding the role of phosphorus re early life, perhaps a small step toward understanding abiogenesis.

As for someday communicating with alien life, I was reminded the other day of the fact that the most common form of communication on Earth is bioluminescence. Might make the Starfleet sport of flashing Vulcans more respectable some day.

Grant Hatch
2013-Apr-14, 08:26 AM
Here's a bit of news (http://www.rdmag.com/news/2013/04/power-behind-primordial-soup-discovered) regarding the role of phosphorus re early life, perhaps a small step toward understanding abiogenesis.

As for someday communicating with alien life, I was reminded the other day of the fact that the most common form of communication on Earth is bioluminescence. Might make the Starfleet sport of flashing Vulcans more respectable some day.

Nice find. The linked article describes a connection between known geological/chemical processes following cometary and astroidal bombardment of the early earth and the systemic creation of key chemical precursors neccessary/leading to...., the molecules required/used by the genesis/creation of "life as we know it". If these initial "stellar/planetary genesis" conditions are "non unique" in the sense that they have occurredwithin a more or less homogenous (at least locally) interstellar medium (% of heavy elements) during the creation of other nearby stellar systems.....we may indeed encounter (more or less) "life as we know it" due to the make up of the local environment ...... Still, Many other possibilities exist and life is not (I believe) limited to any particular chemistry ........."