Evidence for ET is mounting daily, but not proven.

[Colin Robinson]

Let's suppose the probability that a planet can support life if it is in the Goldilocks zone is 1. It's a certainty. Being in the zone means the plane can support life. But - and what a huge but - it says absolutely nothing about whether or not the planet does support life. That is contingent upon the emergence of life on that planet, or its transfer from another source.

On this question, there is an interesting paper by the planetary scientist Jonathan Lunine of the University of Arizona. Its title is Saturn’s Titan: A Strict Test for Life’s Cosmic Ubiquity.

Lunine writes:

From the point of view of “astrobiological Copernicanism”—
whether life itself is a common cosmic phenomenon—it is enough to consider a
“truncated Drake equation” of the first four terms only, multiplied by the duration of time
over which a planet remains habitable. This is the number of life-bearing planets in the
Galaxy.

The first four terms of the Drake equation being
1. Rate of star formation
2. Fraction of stars with planets
3. Average number of habitable worlds per planetary system
4. Fraction of habitable planets where life actually forms [or gets transferred to]

What this means... the number of habitable worlds is a factor in the equation for how much life there is in the galaxy. It is not the only factor.

And we have insufficient data, as yet, on which to make an informed decision about the odds for either of these mechanisms.

Yes, Lunine goes on to say that we still don't know a lot about the fourth factor. And he suggests a couple of strategies for finding out more...

[KABOOM]

That's a very poor analogy. If 100 people were in that metaphorical hotel...one of them MUST have committed the murder. Without any further information, there's a 1% chance that any individual was the murderer.

That's nothing like the situation regarding life elsewhere. To stretch your poor analogy - you have one convicted murderer in custody, and a hotel. You don't know if there's even been a murder in that hotel. There's people in it. You're saying that because you have one murderer in custody (the earth, in this dreadful analogy) then it's evidence that others in that hotel are murderers as well. Without even a dead body to look at, how can you infer that?

We know that this one habitable place, Earth, has life. We know of many other potential habitable places. We have, to date, no idea if those places have life or not.

We have ever mounting evidence for habitability. We do not have ever mounting evidence for life.

Habitability is not life. It's habitability. To call it evidence for life is willfully misleading.

Wrong, once again you have failed to comprehend the analogy (and probably have never been in a court of law). All of the other patrons in the hotel are irrelevant for purposes of compiling evidence against ME.
If anyone else is guilty it is "non life". My guilt is life and the fact that I was in the hotel is evidence yet not proof.

[mutleyeng]

Lunine writes:



The first four terms of the Drake equation being
1. Rate of star formation
2. Fraction of stars with planets
3. Average number of habitable worlds per planetary system
4. Fraction of habitable planets where life actually forms [or gets transferred to]

What this means... the number of habitable worlds is a factor in the equation for how much life there is in the galaxy. It is not the only factor.



Yes, Lunine goes on to say that we still don't know a lot about the fourth factor. And he suggests a couple of strategies for finding out more...

and only factor 4 has anything to do with whether life beyond earth exists in the first place. the error bars on that are still anything from zero (meaning unique) to 1, so who cares what you get from your trucated drake equation...its utterly meaningless.

[djellison]

Wrong,.

Not really. Your analogy has so little to do with the ACTUAL discussion at hand as to be moot. The mistake I made was to try and warp it into making any relevant sense.

[Colin Robinson]

and only factor 4 has anything to do with whether life beyond earth exists in the first place. the error bars on that are still anything from zero (meaning unique) to 1,

Factor 4 is defined as the fraction of habitable planets where life actually appears. This could only be zero if you consider Earth to be something other than a planet.

[Eclogite]

But it is still evidence. Indirect evidence. I was a guest at the hotel on the night of the hotel murder. That is evidence against me. Not enough evidence to prove beyond a doubt that I committed the murder.

As djellison has pointed out your analogy is flawed. If you wish to use a hotel analogy it would be this one.

You are resident in a hotel. There has been a murder in the hotel. You wonder whether murders may occur in other hotels. Indeed, you wonder whether there are other hotels. You learn that there are and that some of them seem to have bedrooms and reception and a restaurant and guests and hotel staff. None of this is evidence for a muder occuring in any of those hotels. Sure, it raises the possibility that a murder could occur in one or more of them, but there is no way in which the exitence of those hotels and there guests can be considered evidence for a murder in one or more of those hotels. All we have is the murder in our own hotel.

[mutleyeng]

im easy if you either call it zero to mean unique, or if you put a positive number in there provided you update that positive number to be relative to the numbers of worlds you arrived at from steps 1,2 and 3.
unless you do that, the equation is useless while you have still to determ whether the spark of life follows predictable repeatable patterns.
Im with you all the way in that i think it does...but i dont know that it does, and thats the problem.

[Colin Robinson]

As djellison has pointed out your analogy is flawed. If you wish to use a hotel analogy it would be this one.

You are resident in a hotel. There has been a murder in the hotel. You wonder whether murders may occur in other hotels. Indeed, you wonder whether there are other hotels. You learn that there are and that some of them seem to have bedrooms and reception and a restaurant and guests and hotel staff. None of this is evidence for a muder occuring in any of those hotels. Sure, it raises the possibility that a murder could occur in one or more of them, but there is no way in which the exitence of those hotels and there guests can be considered evidence for a murder in one or more of those hotels. All we have is the murder in our own hotel.

If you accept that abiogenesis happened on Earth, then the relation between this planet and its living things is not really comparable to a hotel and a murderer who happens to be staying there. Nor to a house with an open door and a green dog who just might walk in...

How about this for a metaphor? Nature has been compared to a blind watchmaker. Earth is a workshop where this artisan operates. And in this workshop, the artisan, though blind, has indeed produced watches -- quite how it was done, we don't quite know.

Right now, we know that nature has other buildings which look like they could serve as workshops. We also know that the basic materials to build watches are present in at least some of these places. We've heard sounds from one or two buildings that reminded us of the tick of a watch, but might be something else.

Some of the buildings are far away, but others are close enough to visit. The doors are open. Are we going to look inside and see if there are watches there?

[Jeff Root]

KABOOM did not intend the bit about being in a hotel at
the time of a murder as an analogy. It is NOT an analogy.
It is an illustration of what is or is not evidence. Trying
to make an analogy out of it was the mistake. It worked
fine as an illustration. If KABOOM was in the hotel at the
time of the murder, then he is a suspect. Being in the
hotel at the time of the murder is an important piece of
evidence.

This is elementary.

-- Jeff, in Minneapolis

[Paul Beardsley]

I was going to come up with a new "clever" analogy, then realised this thread is looping and looping again and looping some more, and (some) people are not reading each other's messages properly, and so on...

Then it suddenly occurred to me that the title of the thread is backward.

In fact, evidence against ET is being eroded daily.

We still have zero evidence for ET, but many objections (such as the once-widely-held view that extrasolar planets must be vanishingly rare) are disappearing.

[KABOOM]

KABOOM did not intend the bit about being in a hotel at
the time of a murder as an analogy. It is NOT an analogy.
It is an illustration of what is or is not evidence. Trying
to make an analogy out of it was the mistake. It worked
fine as an illustration. If KABOOM was in the hotel at the
time of the murder, then he is a suspect. Being in the
hotel at the time of the murder is an important piece of
evidence.

This is elementary.

-- Jeff, in Minneapolis

Thank you Jeff. It was a simple point that it typically takes many individual pieces of "evidence" to prove something beyond a resaonable doubt. Hence, I accept the premise that there continues to be additional "evidence" found in the case to prove that life exists elsewhere. I also acknowledge that it is a long journey and much more is needed, well beyond the lifetimes of any posters on this forum.

If recent Kepler and other exo-planetary searches were coming back "near empty" or exclusively showing only gas giants then the probability of life elsewhere would be decreasing due to such "evidence".

[djellison]

KABOOM did not intend the bit about being in a hotel at
the time of a murder as an analogy. It is NOT an analogy.
It is an illustration of what is or is not evidence. Trying
to make an analogy out of it was the mistake. It worked
fine as an illustration. If KABOOM was in the hotel at the
time of the murder, then he is a suspect. Being in the
hotel at the time of the murder is an important piece of
evidence.

This is elementary.

-- Jeff, in Minneapolis

For those of us just too stupid to understand the elementary - please explain what that 'illustration' has to do with this thread.

[Luckmeister]

The proper definition and usage of the term evidence is critical to forming conclusions by application of the scientific method. Evidence of possible habitability is not evidence of ET life. Sure, it may bolster one's belief that ET exists but it is only evidence for one of the factors that can then be explored as a possible place where actual evidence of life may be found. To call it evidence of life is premature.

That's why the Drake Equation is not evidence, per se. It is only the very rough calculation of odds that there may be evidence for ET life.

[Colin Robinson]

The proper definition and usage of the term evidence is critical to forming conclusions by application of the scientific method.

Discussing the question of possible life on Titan, Phil Plait offered the following definition of evidence...

... evidence is not proof. Evidence just means an observation was made that is consistent with life...

Source: No, we haven't found life on Titan

I wonder what you think of this definition, Luckmeister?

[mutleyeng]

The context of the article has to be taken into account.
He wasnt trying to define what is evidence in the scientific method.
He was writing a responce to questions he was getting about a specific issue which wasnt phrased in any kind of scientific way.
and the actual question he was answering was "Have we found evidence that there might be life on Titan?"

That dosnt look very scientific to me

[Luckmeister]

Here's another quote from the same article:

"Have we found evidence that there might be life on Titan? Sorta."

Evidence that there "might" be life on Titan is like saying that there is evidence that a planet might be habitable for life, which I already said I have no problem with. It is saying that it is direct evidence of existing life that I have a problem with.

ETA: People writing press releases are not immune from the temptation to misuse the word "evidence" when trying to attract readers. They often don't even realize they are taking liberties with the word.

With what they have observed at Titan, you'd have a hard time finding a credible planetary scientist or biologist who wouldn't say that life on Titan is still an extremely unlikely longshot.

[Jeff Root]

KABOOM did not intend the bit about being in a hotel at
the time of a murder as an analogy. It is NOT an analogy.
It is an illustration of what is or is not evidence. Trying
to make an analogy out of it was the mistake. It worked
fine as an illustration. If KABOOM was in the hotel at the
time of the murder, then he is a suspect. Being in the
hotel at the time of the murder is an important piece of
evidence.

This is elementary.

For those of us just too stupid to understand the elementary -
please explain what that 'illustration' has to do with this thread.

The first word in the title of the thread is "Evidence". A great
deal of the misunderstanding and argument in the thread has
been about the meaning of the word "evidence". Understanding
its meaning is critical to understanding the assertion made in
the title. So far, you haven't got it. You don't understand what
"evidence" is.

The illustration shows -- in a very minimalist way -- how evidence
works, in the hope that you will get it.

-- Jeff, in Minneapolis

[Jeff Root]

The proper definition and usage of the term evidence is
critical to forming conclusions by application of the scientific
method. Evidence of possible habitability is not evidence of
ET life.

Which is why NOBODY has said that it is evidence of ET life.

On the other hand, it IS evidence FOR ET life. That is, it is
evidence which supports the expectation of ET life.

If you know of a place where life might be, but the evidence
is that there are no stars or planets or significant amounts of
matter there, then that is evidence AGAINST life in that place.
If you find that there is a star in that place, that is evidence
FOR life there. If you find a planet there, it is evidence FOR
life in that place. If you find that the planet is in the "habitable
zone", it is evidence FOR life there. If you find that the planet
has an oxygen-rich atmosphere, it is evidence FOR life there.

Maybe that oxygen was generated by life. If it was generated
by life, then the oxygen is evidence OF life there. If it was not
generated by life, then the oxygen is NOT evidence OF life there.
But whether the oxygen was generated by life or not, until we
know whether life exists there or not, the oxygen IS evidence
FOR life in that place.

Sure, it may bolster one's belief that ET exists but it is
only evidence for one of the factors that can then be explored
as a possible place where actual evidence of life may be
found. To call it evidence of life is premature.

Which is why NOBODY HAS DONE SO.

That's why the Drake Equation is not evidence, per se. It is only
the very rough calculation of odds that there may be evidence
for ET life.

The Drake equation does not calculate odds. It never has and
never will. It is not useful for calculating odds, even roughly.
It is a tool for thinking about the possibilities and analyzing the
requirements for life in the Universe.

-- Jeff, in Minneapolis

[Jeff Root]

The context of the article has to be taken into account.
He wasnt trying to define what is evidence in the scientific method.
He was writing a responce to questions he was getting about a
specific issue which wasnt phrased in any kind of scientific way.
and the actual question he was answering was "Have we found
evidence that there might be life on Titan?"

That dosnt look very scientific to me

It isn't an instance of science, but there is nothing unscientific
about it. It is not worded badly. It is a reasonable question as
is, without modification. One usually needs to answer such
questions with more than just "yes" or "no", though, and I'm
sure someone asking Phil would have been disappointed if
that were all he had said.

-- Jeff, in Minneapolis

.

[Colin Robinson]

People writing press releases are not immune from the temptation to misuse the word "evidence" when trying to attract readers. They often don't even realize they are taking liberties with the word.

To see whether someone is taking liberties with the word "evidence", we need a definition of that word. I asked what you thought of Phil's statement that evidence is "an observation... consistent with". You haven't answered. If you disagree with what Phil wrote about what "evidence" means, fine. Please just tell us why you disagree, and what your definition of "evidence" is. On the other hand, if you agree that evidence does or can mean "an observation... consistent with", why hesitate to say so?

[eburacum45]

Which is why NOBODY has said that it is evidence of ET life.

On the other hand, it IS evidence FOR ET life. That is, it is
evidence which supports the expectation of ET life.

I'm not disagreeing with you, but this is analogous to saying that the ownership of guns is evidence for murder. If people own guns then there is a good chance that murder will occur; but if no-one uses the guns then there will be no murder.

If life does not occur on any of these potentially habitable worlds then the expectation of life is a false one.

[Paul Beardsley]

"An observation consistent with something" is not a definition of evidence. It simply means there is no contradiction between the two.

To count as evidence, the observation has to actively support the hypothesis.

Last night, Matilda's Cake Shop was robbed. Police want a speedy result, so they've arrested local man Michael Jenkins.

If Jenkins was staying with friends 100 miles away at the time of the robbery, that would be evidence that he did not rob the shop. It's not proof, but it is evidence.

But if Jenkins was at home at the time of the robbery, would this be evidence that he did rob the shop? Of course not! It's merely consistent with the police's belief, not supportive of it.

There's a lot of fruitless quibbling over prepositions going on in this thread - "for" and "of". A more important matter is being overlooked - that there is a neutral ground where things are neither evidence for nor against a hypothesis.

An Earth-sized planet found in a star's habitable zone occupies this neutral ground. Its existence is consistent with a universe teeming with life; its existence is equally consistent with a universe in which no life exists beyond Earth's atmosphere. That's what I call "not evidence".

[mutleyeng]

goodness me,
we do totally get what you can, if you have a mind to, consider is evidence for something.

ok, sheesh, those might be dragons footprints in the yard...youve convinced me.
excuse me, must just call my homeopath, my astrologer told me i will be under the weather this month.

[Colin Robinson]

I was going to come up with a new "clever" analogy, then realised this thread is looping and looping again and looping some more, and (some) people are not reading each other's messages properly, and so on...

Then it suddenly occurred to me that the title of the thread is backward.

In fact, evidence against ET is being eroded daily.

We still have zero evidence for ET, but many objections (such as the once-widely-held view that extrasolar planets must be vanishingly rare) are disappearing.

What you're saying here is not in that "loop" category, anyway!

Another view that used be held by prominent scientists was that even extra-solar planets existed, human technology wasn't going to be able to detect them in the foreseeable future. If I remember correctly, that was one of the arguments used by G. Gaylord Simpson in his 1964 paper "The Nonprevalence of Humanoids".

[Strange]

If there is a problem with my logic, I would love to see it.

Modus ponens gives a deduction from definite premises:

If P, then Q.
P.
Therefore, Q.

But you are saying:
If P, then Q.
P.
Therefore, R.

where:
Q=possibility of life
R = life exists

Or to put it another way
If P, then maybe Q.
P.
Therefore, Q.

Your last line should be: Therefore, maybe Q.

[Jeff Root]

Strange,

Can you show me where I said it?

-- Jeff, in Minneapolis

[chrlzs]

"An observation consistent with something" is not a definition of evidence. It simply means there is no contradiction between the two.
...
There's a lot of fruitless quibbling over prepositions going on in this thread - "for" and "of". A more important matter is being overlooked - that there is a neutral ground where things are neither evidence for nor against a hypothesis.

An Earth-sized planet found in a star's habitable zone occupies this neutral ground. Its existence is consistent with a universe teeming with life; its existence is equally consistent with a universe in which no life exists beyond Earth's atmosphere. That's what I call "not evidence".

Hurrah. +1, etc..

Every time that 'of/for' reference was made I groaned. Reducing the debate to a one liner of such 'simple' black and white-ness is a misrepresentation.

Finding a 'habitable' planet means we have just found somewhere else where our kind of life might conceivably survive. It is most certainly not evidence of or for ET, as ET has not yet been proven to exist, *let alone* enjoy the same sort of conditions we happen to like...

And if you like woeful analogies, it's *exactly the same* logic as those who say that ET must exist because of all them UFO reports...

[Strange]

Strange,

Can you show me where I said it?

-- Jeff, in Minneapolis

Maybe it would be more accurate to say that is what you are.perceived to be saying. And hence the continuing discussion that is getting nowhere.

[Paul Beardsley]

Which is why NOBODY has said that it is evidence of ET life.

On the other hand, it IS evidence FOR ET life. That is, it is
evidence which supports the expectation of ET life.

This is the point of the green dog joke. We have no evidence that green dogs exist, but if they do, they are more likely to enter a house with an open door than a house with a closed door. Similarly we have no evidence that ET life exists, but if it is to be found, it seems most likely that it will be found on Earthlike worlds.

Open doors are not evidence for or of green dogs. As I said before, the preposition thing is a fruitless quibble - and I'm speaking as someone who teaches grammar for a living.

Evidence for/of ET should be restricted to phenomena that is best explained by ET, not by things that could possibly maybe at a stretch be ET, and not by things that would make for a fairly comfortable environment for life as we know it.

If you know of a place where life might be, but the evidence is that there are no stars or planets or significant amounts of matter there, then that is evidence AGAINST life in that place.

Yes.

If you find that there is a star in that place, that is evidence FOR life there.

No it is not. Absence of evidence against something does not translate to evidence for something.

The 1960s cry of, "If you're not for us, you're against us!" doesn't work in science. I'm not entirely sure it works in other fields either.

If you find a planet there, it is evidence FOR life in that place.

Ditto.

If you find that the planet is in the "habitable zone", it is evidence FOR life there.

Ditto. I see the house with the open door; I do not see the green dog.

If you find that the planet has an oxygen-rich atmosphere, it is evidence FOR life there.

Now that is a horse of an entirely different breed, because it is unlikely that a lifeless planet would have an oxygen-rich atmosphere. (This is based on my reading of James Lovelock. Others here may be more informed of this subject than I am.)

Maybe that oxygen was generated by life. If it was generated by life, then the oxygen is evidence OF life there. If it was not generated by life, then the oxygen is NOT evidence OF life there. But whether the oxygen was generated by life or not, until we know whether life exists there or not, the oxygen IS evidence FOR life in that place.

More backward logic. (Or something else is backwards.) The observer can only say if there is oxygen; he cannot say if it was generated by life (and therefore evidence of life) or not generated by life (and therefore not evidence of life).

Which is why NOBODY HAS DONE SO.

Done what? If we found free oxygen in a planet's atmosphere, I think we would consider it evidence, unless there was good reason not to. (I think this is the case with Osiris - perhaps someone else can clarify?)

[djellison]

The illustration shows -- in a very minimalist way -- how evidence
works, in the hope that you will get it.

You've still not explained what it has to do with this thread. Which is nothing.

The Drake equation does not calculate odds. It never has and
never will. It is not useful for calculating odds, even roughly.
It is a tool for thinking about the possibilities and analyzing the
requirements for life in the Universe.

Odds and possibilities are the same thing. 'Is it possible....yes....well how posible is it....let's use this equation'

The very point of drakes equation is to show the range of potentially intelligent species in the galaxy. That's why it exists. Not calculate odds? That's it's very modus operandi.

I'll repeat it yet again.

Evidence of habitability is evidence of habitability

It's not evidence for life.

We can not infer life from habitability based on a sample of 1. It's unscientific and untenable to do so. It's also dishonest and misleading.