Don't they, now?The scientific process results in physical evidence … opinions of scientists (or anyone's), doesn't.
Where does the scientific process get its physical evidence?
It gets it from experiments and observations. Which are planned and conducted by scientists.
How do the scientists plan their experiments? They first form a view (an opinion) as to what sort of experiment has a chance of producing significant data, to support or falsify some hypothesis...
If the experiment does produce significant data, then yes, the opinions of the scientists who planned it have then resulted in physical evidence, either for or against something.
Order of Kilopi
But, then again, that would just be my mere opinion ...
i do pretty much agree with the trust of your agument, but you really need to lighten up on those poor ol exo planets.
You may be right that it could never give answers to life with any reasonable certainty, but right now thats not what it is trying to do.
I think it will be many generations of space craft before we would ever be looking at one particular world with a watery mouth.
if ever there is such a target, maybe someone will pay for a Maccone gravitational lens program.
is our study of CMB physical evidence, or is it just evidence that fits predictions.
IT will be the same with exo planets i hope. we need lots of data so we can have models and be able to make predictions, then we need to build the hardware to see if those predictions hold true.
that is of course, just my opinion
selfism, if ever you have the inclination perhaps you could think about starting a thread where you put your case for why exo planet research is interfering with the progress of more potentially lucrative local research. I may be interpreting you wrong, but that seems to be your concern. It would be an interesting topic im sure
Last edited by mutleyeng; 2012-Apr-10 at 12:24 PM. Reason: addition
I think that the wording semantics flow in both directions in this admittedly "open question".
Many often repeat the refrain, "There is still not one single shred of evidence of life outside of Earth" (or something close to that).
This statement carries with it a certain air of definitiveness as if the question has been asked and answered (or almost exhaustively answered). The reality is that we are so far away from even beginning to scratch the surface of making a dent in the "evidence" that would be required to answer the question.
It is akin to looking at a newborn adopted infant (without any genetic testing) and stating things like, "there is not one single shred of evidence that this human will ever be able to hold a job", or "there is not one single shred of evidence that this human will become a self-made billionaire". Fine, true statements. But the infant is 7 days old. And when we all die that same infant may only be 11 days old.
I'm not sure what that adds, KABOOM.
One doesn't normally apply evidence to infants like that. We know that a vast number of infants grow up to hold down jobs, and unless the infant in question is markedly different in some way (e.g. severely disabled), we'd say that, based on the life stories of similar "samples", it seems reasonably likely that the infant will one day have a job.
Where life-bearing worlds are concerned, we have a single example. We know that life in the wider universe is either non-existent, extremely common, or somewhere in between. There is no reason to choose one of these until we have more information.
i just dont think thats a proper way to look at it Kaboom.
1. There is mounting evidence for ET life sustaining enviroments in the universe
2. there is mounting evidence for ET life.
the difference between these 2 is not semantics
So why has this thread gone on so long?
Because the word "evidence" has other meanings as well. People talk of weak evidence, circumstantial evidence, indirect evidence, inconclusive evidence.
It may not be as exciting as stronger evidence (proof). But the point is, if we follow up that weak evidence it will either lead to stronger evidence, or to falsification.
E.g. The atmosphere of Mars is now known to contain a small amount of methane. If we trace that methane to its source, we will either find
* the sort of proof you'd like -- living specimens of a Martian species of methanogen (methane-producing organism).OR
* we may find that a non-living process is producing the methane. In that case, the hypothesis that Mars has a population of methanogens will have been falsified.
Last edited by Colin Robinson; 2012-Apr-10 at 09:25 PM. Reason: small clarification
No - it does notThis statement carries with it a certain air of definitiveness as if the question has been asked and answered (or almost exhaustively answered).
I agree.The reality is that we are so far away from even beginning to scratch the surface of making a dent in the "evidence" that would be required to answer the question.
Totally false analogy. with nothing to do with the matter at hand.It is akin to looking at a newborn adopted infant (without any genetic testing) and stating things like, "there is not one single shred of evidence that this human will ever be able to hold a job", or "there is not one single shred of evidence that this human will become a self-made billionaire". Fine, true statements. But the infant is 7 days old. And when we all die that same infant may only be 11 days old.
the known discoveries of large numbers of exo planets and their variations, the universe holding more stars than thought as the article suggests, increases the evidence for the existance of et life sustaining environments - earth like or non earth like.
define ET whatever way you want.
for the record, i define it as belonging to a diferent tree of life from us.
No, it won't.Originally Posted by Colin Robinson
What if there are non-carbon based life forms on Mars, producing biogenic methane, but it gets consumed by some other unknown process, and the methane originally detected, is from a non-biogenic source ? (Your conlusion would be erroneous)... Or there exist carbon based ones, that produce a, hitherto, unknown form of non-biogenic methane ?
Or if the 'marginally biogenic' methane has been transported from its production area to another zone, by some unknown process ? (Ie: the notorious 'we didn't look in the right place' problem).
My point is, there is a major issue of being unable to distinguish between a null result and a non result … which can lead to an invalid conclusion. This problem also points to a possibly flawed hypothesis*, (because of a lack of definition of what ET is). A random chance discovery is still, nonetheless, entirely possible.
(I might add, for no real reason, human exploration may also help to minimise the possibility of erroneous conclusions, as humans are well suited to the complex task of detection, under such circumstances ..)
As described above, it may also lead to a non-result .. and if we can't distinguish this from a null result, the hypothesis may be flawed.It may not be as exciting as stronger evidence (proof). But the point is, if we follow up that weak evidence it will either lead to stronger evidence, or to falsification.
* (But at least it has been cited this time .. thanks for doing so ).
That particular definition might also satisfy only one particular individual …Originally Posted by mutleyeng
Does that form necessary and sufficient grounds for constituting scientific evidence ?
If life is found on Mars, it is pretty insignificant for me if we cant isolate it as of unique origin. For others they will be happy with that as being ET.
By my definition, you could also find ET on earth, of earth...thats still good enough for me because we have answered the extra terrestrial aspect through probability. I win either way.
Noted that 'happiness', is also subjective (ie: individual reality).Originally Posted by mutleyeng
I think we'd need another term, other than 'ET', eh …?Originally Posted by mutleyengIt is highly 'improbable', hence 'implausible' (I really do object to having to use those terms), that such a finding will be made, because of the vast amount of hard scientific evidence presently supporting the theory of a common origin of terrestrial life.Originally Posted by mutleyeng
i dont really know how plausible it is.
they tell me most life on earth lives under the surface, we havnt checked out all that much of it.
plate tectonics may limit really ancient life...i dont know. At least it gives astrobiologists an excuse for field trips to Yellowstone.
Defining ET or Alien dosnt bother me.
You find something - either it satisfys me or it dosnt
Last time I checked this out, I found this interesting article, about a study which figured out that 86% of all species on land, and 91% of those in the sea, have yet to be discovered and catalogued.
The most precise prediction so far, comes up with a total of 8.74 million eukaryote species on Earth. (Micro-organisms and viruses are not included in this figure). 2.2 million (~25%) of these, are expected to be marine dwelling.
So far, about 1.25 million species, (14% of the predicted number), have actually been described and catalogued, and another ~700,000 have been described, but not catalogued, (as at the end of 2011).
As far as I know1 however, with only a handful of minor exceptions2, of all of the catalogued species so far, all have nucleic acid based genomes, and align with the standard genetic code3. All known species have the same 3 polymer types, have the same chirality in the DNA/RNA proteins, and work in accordance with either Glycolysis, Citric Acid or Oxidative Phosphorylation metabolic processes. In all known eukaryotes and the majority of prokaryotes, glycolysis is performed in the same ten steps, in the same order, with the same ten enzymes. All use the ATP molecule as transport for chemical energy within cells.
On its own, the 1.25 million number may not sound very convincing, however, when one considers the full range of statistically possible variations just within what we understand to be the 'Standard Earth-Life Genetic Code', it is quite overwhelming that the same commonality exists amongst all known species here on Earth. Whilst other variants may be possible in pure theory4, it would be extremely exceptional to find something radically different from this model, on Earth5.
Once again, there is no evidence to suggest that any variant of this model, would result in viable 'life', anywhere else.
1. Happy to be corrected on any of this, (if its in error) … base reference source is a summarised version of 'The Phylogenic Tree'.
2. Which are close standard genetic code derivatives, anyway.
3. There are 1.4 x 1070 informationally equivalent genetic codes, and all known life aligns with just one of 'em !
4. They may be theoretically possible, in number (ie: the maths), but whether these other models result in viable lifeforms, is totally unknown.
5. There is much, much more evidence than just the genetics bit mentioned in this post. That's just the beginnings of it, and excludes anatomical, morphological, DNA, molecular and genetic inheritance evidence.
Try this one: The hypothesis that measurable amounts of methane in the Martian atmosphere are being produced by a population of methanogenic organisms (Hypothesis A) will be falsified, if and when a non-living process that produces methane is found on Mars, and if the scale of the non-biological methane production is consistent with the measured level of Martian atmospheric methane.
If Hypothesis A does get falsified, there might (as you've pointed out) still be methanogens on Mars that do not produce measurable amounts of methane (Hypothesis B).
One difference between Hypothesis A and Hypothesis B, is that Hypothesis A can be tested, although doing so will take a lot of work. But how would you test Hypothesis B?
As I'm sure you know, the scientific community is more interested in hypotheses it can test, than in those that it can't...
Etymologically, I think you'll find "extraterrestrial" means "beyond Earth". Thus "extraterrestrial life" means "life beyond Earth". However, I don't think anyone would call the residents of the International Space Station "extraterrestrials", even though they are living beyond Earth right now.This problem also points to a possibly flawed hypothesis*, (because of a lack of definition of what ET is).
I've seen "extraterrestrial" defined as life which originated beyond Earth. If we are going to define it like that, then logically we should define "terrestrial" life as life which originated here. The trouble with definitions like that, is how do you prove a particular family of organisms originated on one planet rather than another? If "terrestrial" and "extraterrestrial" are defined in terms of origin, it would be difficult to prove that "terrestrial" life exists! To do so, you would need to rule out the possibility that the organisms on Earth have descended from an extraterrestrial ancestor.
So it probably makes more sense to define "terrestrial" and "extraterrestrial" not in terms of where the first ancestors of an organism appeared, but in terms of its more recent ancestry...
E.g. If a living organism is found on Mars and turns out to be adapted to Martian conditions to an extent consistent with millions or billions of years of evolution there, then in my opinion it should count as a Martian organism, and as an extraterrestrial one...
In any case, finding such a thing, when and if it happens, will be a breakthrough.
thanks for post 738 selfism.
It was interesting and certainly puts things into context well.
What would be interesting addition to the data would be to establish reasonable hypothesis as to how you could explain the existance of two surviving trees of life, where one is abundant and the other limited to very small geological/geographical areas. Then run the numbers again for just those the hypothesised environments*.
Basically that limits it to extremophiles and microbial life.
when i say hypothesised environments, the environments are real enough, the hypothetical is that they could hide undiscovered tree of life.
So, straight from the horse's mouth (NASA/JPL's site) …From this it is clear that it has been determined that measurements of the characteristics of the environment surrounding any discoveries, have to be taken, in order to interpret that discovery (especially if we can't specifically characterise what it is we're looking for in advance). This is also what I mean about gathering direct evidence for that database which aims at correlating environmental conditions with anything 'suspect' (meaning 'life' of some sort). The discovery could potentially be meaningless without the habitat data.The MSL mission has four primary science objectives to meet the overall habitability assessment goal:
1) The first is to assess the biological potential of at least one target environment by determining the nature and inventory of organic carbon compounds, searching for the chemical building blocks of life, and identifying features that may record the actions of biologically relevant processes.
2) The second objective is to characterize the geology of the landing region at all appropriate spatial scales by investigating the chemical, isotopic, and mineralogical composition of surface and near-surface materials, and interpreting the processes that have formed rocks and soils.
3) The third objective is to investigate planetary processes of relevance to past habitability (including the role of water) by assessing the long timescale atmospheric evolution and determining the present state, distribution, and cycling of water and carbon dioxide.
4) The fourth objective is to characterize the broad spectrum of surface radiation, including galactic cosmic radiation, solar proton events, and secondary neutrons.
and then .. more detail ..
So, my big point in all this is that IF one commences the search NOT from a biased assumption of 'life exists' ... but from a the cold, hard reality of the known facts .. ie: THERE IS NOTHING AT ALL KNOWN ABOUT 'ET LIFE', the test design will end up being scoped, so as to maximise the chances of finding the UNKNOWN. This is such an important point, I can't emphasise it enough !! This was the lesson learned from the Viking Lander ! All the speculation in the world amounts to zip, if one starts to believe any of it ! Exploring demands as unbiased approach as is humanly possible. The only way to achieve this, is by staying focused on physical reality. Forget all this 'opinion' stuff .. all it does is bog down progress ! (That's one huge opinion, I might add, .. but at least I can back it up !)MSL will investigate a site that shows clear evidence for ancient aqueous processes based on orbital data and undertake the search for past and present habitable environments. Assessment of present habitability requires an evaluation of the characteristics of the environment and the processes that influence it from microscopic to regional scales and a comparison of those characteristics with what is known about the capacity of life, as we know it, to exist in such environments. Determination of past habitability has the added requirement of inferring environments and processes in the past from observation in the present. Such assessments require the integration of a wide variety of chemical, physical, and geological observations.
MSL is not a life detection mission and is not designed to detect extant vital processes that would betray present-day microbial metabolism. Nor does it have the ability to image microorganisms or their fossil equivalents. MSL does have, however, the capability to detect complex organic molecules in rocks and soils.
If present, these might be of biological origin, but could also reflect the influx of carbonaceous meteorites. More indirectly, MSL will have the analytical capability to probe other less unique biosignatures, specifically, the isotopic composition of inorganic and organic carbon in rocks and soils, particular elemental and mineralogical concentrations and abundances, and the attributes of unusual rock textures. The main challenge in establishment of a biosignature is finding patterns, either chemical or textural, that are not easily explained by physical processes.
MSL will also be able to evaluate the concentration and isotopic composition of potentially biogenic atmospheric gases such as methane, which has recently been detected in the modern atmosphere. But compared to the current and past missions that have all been targeted to find evidence for past or present water, the task of searching for habitable environments is significantly more challenging (e.g., Grotzinger, Nature Geoscience, 2009).
Primarily, this is because the degree to which organic carbon would be preserved on the Martian surface–even if it were produced in abundance–is unknown.
MSL's job is to snoop out as much as it can .. and just maybe, it might find something which catches the watchful eyes of the human minds pouring through the data. The only better alternative to this I can think of, (along with the extra risks and costs), is to actually send 'fully armed', (technologically), humans to snoop it out directly !
Last edited by Selfsim; 2012-Apr-11 at 11:06 AM. Reason: Deleted last paragraph .. it appears earlier on.
The major paper, (book actually), authored by the 'Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council' is called: "The Limits of Organic Life in Planetary Systems; The National Academies Press, 2007".
Its purpose was primarily to provide guidance for NASA on the search for exo-life. The table of contents is here.
Of particular interest is the Chapter on "Strategies to Mitigate Anthropocentricity".
Here's a quote from that Chapter:
After a hundred pages or so, and eight Chapters, the final conclusions/recommendations are here.Finally, the committee considered more exotic solutions to problems that must be solved to create the emergent properties that we agree characterize life. It considered a hierarchy of “weirdness”:
- Is the linear dimensionality of biological molecules essential? Or can a monomer collection or two-dimensional molecules support Darwinian evolution?
- Must a standard liquid of some kind serve as the matrix for life? Can a supercritical fluid serve as well? Can life exist in the gas phase? In solid bodies, including ice?
- Must the information content of a living system be held in a polymer? If so, must it be a standard biopolymer? Or can the information to support life be placed in a mineral form or in a matrix that is not molecularly related to Darwinian processes?
- Are Darwinian processes and their inherent struggle to the death essential for living systems? Can altruistic processes that do not require death and extinctions and their associated molecular structures support the development of complex life?
The MSL/Curiosity Rover technologies, are a direct flow-on from these recommendations.
This is a great example of how local exploration and the technologies being built into robotic probes aligns with a sound, well though out strategy, which, after much review of what IS known, ends up concluding basically that 'We don't know what's out there.' ... no word-play, no biased beliefs about the presence or absence of exo-life, no vested interests other than pure exploration out of nothing more than: 'Curiosity' !
Speculation ??? Nahh .. forget it .. leave that for Sci-fi movies .. keep it well and truly clear of real Science by swamping it with real, physical, well considered evidence, brought to bear, courtesy of the scientific process, I say.
(Yep .. yet another big opinion .. must be time for me to stop posting ! )
Actually, you know, the very title of this thread "Evidence for ET is mounting daily, but not proven", is based on a public statement by one of the top smart people -- Carl Pilcher, the current director of NASA's Astrobiology Institute. Here is what Pilcher said
The opening post of this thread has a link to the article where this quote appears.The evidence is just getting stronger and stronger... I think anybody looking at this evidence is going to say, 'There's got to be life out there.'
"There's got to be life out there"
does not equal
"There is life out there"
Look at the OPERA debacle for instance and Ereditato's story (and ultimate fate).
I have mentioned my issues with the field of Astrobiology:
I am yet to find evidence that preconceived belief isn't the prime motivator for most of what what they say.Originally Posted by Selfsim
Pitcher would seem to be attempting to make serious in-roads by working on public perceptions, (concensus reality), rather than science (physical reality).
I really wish that the public could develop more of a sense of the distinctions between the two, so as to be able to recognise the two distinct motivations behind such messages.
well, as a member of the public, i found Pilchers quote in the article to be overzealous, particularly in relation to the arsenic eating microbe, which dosnt seem to have gone down too well outside of NASA.
I think it is unfair to OPERA to compare
The quote from Chris McKay in the same article read like a much more realistic (responcible) thing to say.
I am of course assuming that Pilcher wasnt quote mined