Evidence for ET is mounting daily, but not proven.

[astromark]

At this time I would like to summarise what we know and think of this subject... Understanding we 'Know' very little. Some speculation is required.
A fellow named Drake came up with a formula of expected civilisations across the universe... According to the drake equation we should find life forms where it can be. Where can it be ? Is a good question. I would think that recent science has shown it might be more places than we had thought.
I think it is fair to assume that Drake was thinking of Earth like environments... The goldilocks zone might be a little larger and more diverse than we had previously thought... NB. The use of the word 'might'...
I want to know more of this and have drawn conclusions of 'my own' that might have little or no place here...
I would not find argument regardless.
This subject of evidence of habitations where a ET might inhabit is the central interest to many SETI supporters.
Thinking of humanity as the first or only such life form is alien to my thinking...
but can not be completely disregarded as a possible answer to why we are still unaware of any alien life.
What could a higher life form be like... many imaginative ideas spring to mind but remain as just ideas of a imaginative mind.
I imagine a bio- technical merger as a possible reality. Advantages are to me apparent.
The most important factor in this discussion is the distance any such life forms might be from here...
Without going into a realm of faster than c. velocities. As I can not imagine a method workable.
We might simply be to far away to reach.
This is both good and bad if true... Good because the likely hood of us been eaten or conquered is diminished and bad because we remain alone and find no place to go... That the question remains unanswered for ever... wow. We might not be alone. We might just as well be...

[Bobunf]

We needn't worry about hiding our radio signals from ET lest he be hostile. For over 3 billion years we (and our ancestors) have signaled the presence on the Earth of abundant life. First methane, then oxygen and ozone out of thermal equilibrium. Obvious abundant life. Maybe ETs even able to detect the signal of chlorophyll. Over the last ten thousand years we've sent signals the result of increasing agricultural output, extensive metal working and coal burning. And for over 200 years we've been seeding the atmosphere with all kinds of interesting industrial gases and pollutants such as sulfur dioxide, chloroform, gasoline, kerosene, naphthalene, benzene, DDT and, in the last hundred years, freon and it's replacements. Signals using a 600 million square kilometer antenna.

Any ET worth worrying about should have some ability to predict the course of biological and social evolution, and the atmosphere will give him voluminous trend lines to follow. The oxygen rich world with plenty of water and land; the first signals of agriculture, metal working, coal burning and then the first evidences of the industrial revolution. Is ET advanced? Is ET smart? Then he should know life is here, intelligent life is here and that a technological civilization is emerging; even if he is several thousand light years away - a volume with about a billion stars. Even if superluminal observation, communication and travel are impossible.

Forget radio, our atmospheric gases let ET know we are here and a whole lot more.

[Bobunf]

As for whether any kind of ET life exists, there is one mathematical truth:

There are an infinite number of numbers a billion times smaller then the reciprocal of the number of stars. If the number of stars were 10^23 and the probability of life originating near any single star was 1/10^32, life elsewhere would be a virtual impossibility. The number of stars, planets or habitable planets does not eliminate the barrier of bio-genesis.

And three lines of evidence:

 First, life on Earth appeared to start quite soon after Earth formed, which suggests that life can originate fairly easily and quickly. Or that it had originated somewhere else than Earth, somewhere with lots more time. On the other hand, there is no evidence for more than one biogenesis amongst terrestrial life.

 Second, there is no credible evidence of any other life in our solar system, whether originating independently or transported to or from Earth. For decades we have analyzed atmospheric gases of all the major bodies in the solar system, as well as square kilometers of the surface of Mars and the Moon, a few bits of Martian subsurface, even bits of the surface of Venus, Titan and various asteroids and comets, and the insides of thousands of meteorites. All without result. Of course, more can, should and will be done, but to date things are looking pretty grim.

There was the claim that evidence of life was found in a Martian meteorite, but that is not widely accepted. There has been the hint of methane in the Martian atmosphere, but these hints leave two answered questions: Was there really any methane? If there was, was the methane produced biologically or non-biologically?

The quantity of life in our solar system, other than on Earth, must be small since that life is not noticeably affecting its environment, and the probability that life with an independent origin exists at all declines with each succeeding new observation; essentially daily. So far the evidence seems to suggest that life in our solar system was a one-off affair and that it does not easily spread across interplanetary distances.

The decreasing probability that life originated more than once in our solar system must constrain the probability that life originated in many environments outside our solar system. The decreasing probability that life managed the distance between planets in our solar system must constrain the probability that life traveled between stars.

 Third, there is no evidence of any life beyond the solar system. To date, about the only way we can assess this would be from the effects of advanced technological civilizations.

Enrico Fermi at Los Alamos in 1950 asked, “Where are they?” That is (in more explicit and modern terminology), given the large number of stars (about 10^23) and the 13.7 billion year age of the Universe, where are, what should be, the numerous technologically advanced descendants of life that originated elsewhere? They haven’t visited or contacted us in any way, and we haven’t been able to detect any evidence of extrasolar life, such as large scale engineering projects, other artifacts, radio, optical or other emissions. There’s been more than enough time for numerous galactic empires.

So here’s what we think we know in 2011:

 There is no evidence for more than one biogenesis amongst terrestrial life.
 We have no evidence for an independent origin of life anywhere, in spite of observations in our solar system that would probably have revealed anything in the way of an extensive ecological system.
 The evidence is that there are billions of planets, moons and other bodies around stars in our galaxy, and that, at the very least, many millions of these will be possible homes for life. But, as far as we know, it could be that none have life. Especially since advanced technological civilizations appear to exist today at great rarity. As far as we know, it could be that none exist except for us.

Decreasing probability that life originated more than once in our solar system and that life travels interplanetary distances.
Increasing number of possible habitats favorable for life.
No evidence of any advanced ETs.

We really can't say much. Certainly not "Evidence for ET mounting daily."

[KABOOM]

As for whether any kind of ET life exists, there is one mathematical truth:

There are an infinite number of numbers a billion times smaller then the reciprocal of the number of stars. If the number of stars were 10^23 and the probability of life originating near any single star was 1/10^32, life elsewhere would be a virtual impossibility. The number of stars, planets or habitable planets does not eliminate the barrier of bio-genesis.

And three lines of evidence:

 First, life on Earth appeared to start quite soon after Earth formed, which suggests that life can originate fairly easily and quickly. Or that it had originated somewhere else than Earth, somewhere with lots more time. On the other hand, there is no evidence for more than one biogenesis amongst terrestrial life.

 Second, there is no credible evidence of any other life in our solar system, whether originating independently or transported to or from Earth. For decades we have analyzed atmospheric gases of all the major bodies in the solar system, as well as square kilometers of the surface of Mars and the Moon, a few bits of Martian subsurface, even bits of the surface of Venus, Titan and various asteroids and comets, and the insides of thousands of meteorites. All without result. Of course, more can, should and will be done, but to date things are looking pretty grim.

There was the claim that evidence of life was found in a Martian meteorite, but that is not widely accepted. There has been the hint of methane in the Martian atmosphere, but these hints leave two answered questions: Was there really any methane? If there was, was the methane produced biologically or non-biologically?

The quantity of life in our solar system, other than on Earth, must be small since that life is not noticeably affecting its environment, and the probability that life with an independent origin exists at all declines with each succeeding new observation; essentially daily. So far the evidence seems to suggest that life in our solar system was a one-off affair and that it does not easily spread across interplanetary distances.

The decreasing probability that life originated more than once in our solar system must constrain the probability that life originated in many environments outside our solar system. The decreasing probability that life managed the distance between planets in our solar system must constrain the probability that life traveled between stars.

 Third, there is no evidence of any life beyond the solar system. To date, about the only way we can assess this would be from the effects of advanced technological civilizations.

Enrico Fermi at Los Alamos in 1950 asked, “Where are they?” That is (in more explicit and modern terminology), given the large number of stars (about 10^23) and the 13.7 billion year age of the Universe, where are, what should be, the numerous technologically advanced descendants of life that originated elsewhere? They haven’t visited or contacted us in any way, and we haven’t been able to detect any evidence of extrasolar life, such as large scale engineering projects, other artifacts, radio, optical or other emissions. There’s been more than enough time for numerous galactic empires.

So here’s what we think we know in 2011:

 There is no evidence for more than one biogenesis amongst terrestrial life.
 We have no evidence for an independent origin of life anywhere, in spite of observations in our solar system that would probably have revealed anything in the way of an extensive ecological system.
 The evidence is that there are billions of planets, moons and other bodies around stars in our galaxy, and that, at the very least, many millions of these will be possible homes for life. But, as far as we know, it could be that none have life. Especially since advanced technological civilizations appear to exist today at great rarity. As far as we know, it could be that none exist except for us.

Decreasing probability that life originated more than once in our solar system and that life travels interplanetary distances.
Increasing number of possible habitats favorable for life.
No evidence of any advanced ETs.

We really can't say much. Certainly not "Evidence for ET mounting daily."

Good post but you make a lot of leaps.

It is safe to say there is currently no other "advanced" life form in our solar system at present. 99+%

There is no evidence that there has ever been multi-cellular (animal) life forms previously outside of Earth in our solar system. ~ 85%?

The above probabilities are directional, not literal.

Yes, life on Earth arose "quickly". However, it stayed in microscopic form for ~ 3 billion years before evolving into larger forms. Is this "typical"? We have no idea, but it certainly suggests within a Darwinian framework that it will take a long time to bio-genesis to spawn "large life forms".

Our solar system is ~ 4.5 billion years old. Conditions on Mars, Venus and satellites of Saturn, Jupiter were presumably very different at earlier stages than they are today. We have barely scratched the surface of being able to determine if bacterium-like life forms ever arose on our neighboring planets (Mars, Venus). Using our own timeline on Earth, microscopic life could have taken afoot on early Venus, Mars and as conditions changed it did not allow for life to sustain (much less evolve into larger forms).

We know less about the potentiality for microscopic life on satellites such as Europa, now or earlier in its history. We will likely not know the answers to these questions for several generations within our own solar system.

While less exciting, I believe that IF we do discover "evidence" of current/prior microscopic life anywhere within our Solar System (other than Earth) that the significance of such discovery would be HUGE and dramatically increase the likelihood of "larger life" elsewhere. It would suggest that bio-genesis can happen pretty frequently (twice within our solar system) and then where it goes from there is just an issue of "runway" (does the host planet/moon have the ability to sustain the conditions that allow for bio-genesis to take place and evolve from there). Then the emphasis may shift to how unique is Earth in that it has been in a Goldilocks Zone for over 3.5 billion years?

[baric]

Enrico Fermi at Los Alamos in 1950 asked, “Where are they?” That is (in more explicit and modern terminology), given the large number of stars (about 10^23) and the 13.7 billion year age of the Universe, where are, what should be, the numerous technologically advanced descendants of life that originated elsewhere? They haven’t visited or contacted us in any way, and we haven’t been able to detect any evidence of extrasolar life, such as large scale engineering projects, other artifacts, radio, optical or other emissions. There’s been more than enough time for numerous galactic empires.

This presupposes that interstellar travel is possible. Show your work before making this assumption.

What the Fermi Paradox accomplishes is assuring us that a Star Trek future is not going to happen.

[Trakar]

We needn't worry about hiding our radio signals from ET lest he be hostile. For over 3 billion years we (and our ancestors) have signaled the presence on the Earth of abundant life. First methane, then oxygen and ozone out of thermal equilibrium. Obvious abundant life. Maybe ETs even able to detect the signal of chlorophyll. Over the last ten thousand years we've sent signals the result of increasing agricultural output, extensive metal working and coal burning. And for over 200 years we've been seeding the atmosphere with all kinds of interesting industrial gases and pollutants such as sulfur dioxide, chloroform, gasoline, kerosene, naphthalene, benzene, DDT and, in the last hundred years, freon and it's replacements. Signals using a 600 million square kilometer antenna.

Any ET worth worrying about should have some ability to predict the course of biological and social evolution, and the atmosphere will give him voluminous trend lines to follow. The oxygen rich world with plenty of water and land; the first signals of agriculture, metal working, coal burning and then the first evidences of the industrial revolution. Is ET advanced? Is ET smart? Then he should know life is here, intelligent life is here and that a technological civilization is emerging; even if he is several thousand light years away - a volume with about a billion stars. Even if superluminal observation, communication and travel are impossible.

Forget radio, our atmospheric gases let ET know we are here and a whole lot more.

The difference being, EM emissions don't necessarily require you to know that the Earth exists to detect them. To detect the gases in our atmosphere requires focussing quite narrowly upon our planet from interstellar distances. Unless life as we know it is so bizarrely rare and specific to particular types of stars, there is little about our Sun that would seem to require the closer inspection of our system by alien SETI astronomers necessary to detect the Earth and the composition of our atmosphere.

[Trakar]

As for whether any kind of ET life exists, there is one mathematical truth:

There are an infinite number of numbers a billion times smaller then the reciprocal of the number of stars. If the number of stars were 10^23 and the probability of life originating near any single star was 1/10^32, life elsewhere would be a virtual impossibility. The number of stars, planets or habitable planets does not eliminate the barrier of bio-genesis.

And three lines of evidence:

 First, life on Earth appeared to start quite soon after Earth formed, which suggests that life can originate fairly easily and quickly. Or that it had originated somewhere else than Earth, somewhere with lots more time. On the other hand, there is no evidence for more than one biogenesis amongst terrestrial life.

more in line with the Goldilocks theme, it may just be that the particular and specific conditions of Early Earth were highly "just right" for the formation (abiogenesis) of life. It may well be not a matter of life being easy to form anywhere, but rather being easy to form in certain rare and largely unusual situations, that just happened to come about early in our planet's history.

The rest, I agree with without significant exception or further stipulation.

[Trakar]

Good post but you make a lot of leaps.

It is safe to say there is currently no other "advanced" life form in our solar system at present. 99+%

There is no evidence that there has ever been multi-cellular (animal) life forms previously outside of Earth in our solar system. ~ 85%?...

I would put the current understandings for both at 100%, at least until there is compelling empiric evidences indicating otherwise.

[Trakar]

This presupposes that interstellar travel is possible. Show your work before making this assumption.

What the Fermi Paradox accomplishes is assuring us that a Star Trek future is not going to happen.

You don't need warp drives to undertake interstellar travel. And a massively engineered and populated stellar system (even if it did not engage in any interstellar transport) should be detectable across a good chunk of the galaxy.

[Bobunf]

This presupposes that interstellar travel is possible. Show your work before making this assumption.

I think you misinterpreted my post. I do not assume that interstellar travel is possible. Visits are clearly only one way in which we would detect extrasolar ETs. Large scale engineering projects like Dyson spheres and various types of emissions, intentional and not, would also inform us of ETs existence.

[baric]

You don't need warp drives to undertake interstellar travel. And a massively engineered and populated stellar system (even if it did not engage in any interstellar transport) should be detectable across a good chunk of the galaxy.

Interstellar travel remains a fantastic claim, so show your work.

Calculate the energy required to move a enough mass to support a ship crew across an interstellar distance along with the mass required for fuel and sustenance during the voyage.

Don't forget fuel for deceleration and then double all of that so that a two-way trip is possible.

My money is on Fermi's Paradox.

[Bobunf]

Good post but you make a lot of leaps.

There were quite a few leaps, but I don’t see where you addressed any of my leaps.

it will take a long time to bio-genesis to spawn "large life forms".

But that does not mean that such life does not produce very large effects. More than 3 billion years ago the Earth’s atmosphere contained an amount of methane out of thermal equilibrium – a phenomenon almost within our reach to detect in planets within a few dozen light years of Earth, perhaps even in this decade. It should be easy for a 22nd century type technological civilization even thousands of light years distant. It would be easy for us to detect any world in our solar system with an atmosphere substantially out of thermal equilibrium.

Microscopic life could have originated on Venus, Mars, Europa, etc., but there’s no significant evidence that it has or is producing any effect on its environment. So far, the waste products of any purported microscopic life on Mars, Europa, etc. display no significant effect on the surfaces or in the atmospheres of their worlds. Also, there’s no evidence of non-terrestrial life transported to Earth, nor of an independent abiogenesis on Earth.

We’ll know more as the decade progresses with:
 maybe ten more missions to Mars including two arriving next year and the ExoMars Trace Gas Orbiter and lander in 2016
 several samples returned to Earth from the Moon, Mars, Phobos, asteroids and comets
 at least one mission arriving at Jupiter
 and continued detailed analysis of the atmospheric gases of all of the significant solar system worlds.

But, if there is other life in our solar system, it must not be doing too well. And the absence of evidence isn’t evidence of presence. I don’t think an assessment, at this point, that things are looking pretty grim for other life in our solar system is too wide of the mark.

[Bobunf]

Baric, nobody, especially including me, is making any claims about interstellar travel. Quit asking already.

[Bobunf]

The difference being, EM emissions don't necessarily require you to know that the Earth exists to detect them. To detect the gases in our atmosphere requires focussing quite narrowly upon our planet from interstellar distances. Unless life as we know it is so bizarrely rare and specific to particular types of stars, there is little about our Sun that would seem to require the closer inspection of our system by alien SETI astronomers necessary to detect the Earth and the composition of our atmosphere.

I don’t think the focus is really all that narrow. First ET inventories the planets in the interstellar neighborhood, identifying those planets orbiting stars of appropriate age and characteristics, in appropriate orbits, of appropriate size. Just like we’re doing now.

This is not close inspection, nor very expensive. With another hundred years of technology we’ll probably have a pretty expansive notion of what our interstellar neighborhood is; and the inventorying will cost less and be far more capable.

Only then look for planets with atmospheric gases out of thermal equilibrium. Just like we’ll be doing in a decade or so.

All of this is relatively easy, cheap and very reliable. You don’t have to wait for atmospheres to turn on or turn in the right direction. They’re always on.

Once ET finds a planet with probable life, it’s hard to imagine they would not focus strongly on that planet. Unless life is so bizarrely ubiquitous that they just add it to their list of three million life bearing planets. Not likely, I think.

[baric]

Baric, nobody, especially including me, is making any claims about interstellar travel. Quit asking already.

Hello.

If you want to use Fermi's Paradox as one point of evidence against ET life, invoking "galactic empires" along the way, then you are clearly suggesting that interstellar travel is possible.

If it is not, then there is no Paradox and it is irrelevant to the chances for ET life.

[Trakar]

I don’t think the focus is really all that narrow. First ET inventories the planets in the interstellar neighborhood, identifying those planets orbiting stars of appropriate age and characteristics, in appropriate orbits, of appropriate size. Just like we’re doing now.

This is not close inspection, nor very expensive. With another hundred years of technology we’ll probably have a pretty expansive notion of what our interstellar neighborhood is; and the inventorying will cost less and be far more capable.

Only then look for planets with atmospheric gases out of thermal equilibrium. Just like we’ll be doing in a decade or so.

All of this is relatively easy, cheap and very reliable. You don’t have to wait for atmospheres to turn on or turn in the right direction. They’re always on.

Once ET finds a planet with probable life, it’s hard to imagine they would not focus strongly on that planet. Unless life is so bizarrely ubiquitous that they just add it to their list of three million life bearing planets. Not likely, I think.

This, in itself, presumes that life is common enough that we have a really good idea of exactly what constitutes "...planets orbiting stars of appropriate age and characteristics, in appropriate orbits, of appropriate size..." If they have already found ET life, or have a better understanding of the processes of abiogenesis, they may well have a much more limited search criteria (one that we may or may not fit within - nothing says that our example of life is typical or exemplifies the most likely situation for life to arise). My point was simply that EM emissions are much more simple to detect than detailed planetary atmospheric composition, and that there are reasonable arguments that tech civs may continue to emit detectable EM and in fact become somewhat more detectable as they develop to the point of expanding into and exploiting their stellar neighborhood. It is not that there is anything wrong with checking detected planet's atmospheres, merely that it is a slower and more laborious process, and mostly limited to utility in the nearer interstellar neighborhood.

[Bobunf]

Hello.
If you want to use Fermi's Paradox as one point of evidence against ET life, invoking "galactic empires" along the way, then you are clearly suggesting that interstellar travel is possible.
If it is not, then there is no Paradox and it is irrelevant to the chances for ET life.

As I pointed out before, "Visits are clearly only one way in which we would detect extrasolar ETs. Large scale engineering projects like Dyson spheres and various types of emissions, intentional and not, would also inform us of ETs existence."

I don't understand what is so hard about that. I suppose I could say: Since there is some possibility that interstellar travel is practical, the lack of visits is another indication of a bit of evidence for a paucity of currently active, technologically advanced extrasolar civilizations.

Note, interstellar travel - only a possibility. I don't say one way or the other. You do accept that it's a possibility? Perhaps a very remote possibility, but I don't know of any scientific principle that would rule out any possibility that interstellar travel could ever occur. Do you?

If I say, "Tomorrow we may receive light and heat from the sun," do you want me to "show my work?" How do I know the sun may rise tomorrow? Again, assuredly you would agree that it is at least a possibility. Perhaps a very remote possibility, but I don't know of anything that would rule it out. Do you?

[baric]

As I pointed out before, "Visits are clearly only one way in which we would detect extrasolar ETs. Large scale engineering projects like Dyson spheres and various types of emissions, intentional and not, would also inform us of ETs existence."

ok, so if they are not traveling around building galactic empires, then maybe they are building Dyson spheres?

I apologize if the phrase "show your work" rubbed you the wrong way. It was just my way of pointing out the implausibility of many of these fictional engineering projects that ETs are supposedly capable of. A lot of people toss around science fictional constructs like interstellar travel and Dyson spheres as if there is an element of reality to them, while at the same time acting as if abiogenesis is an absurd impossibility.

[Trakar]

As I pointed out before, "Visits are clearly only one way in which we would detect extrasolar ETs. Large scale engineering projects like Dyson spheres and various types of emissions, intentional and not, would also inform us of ETs existence."

I don't understand what is so hard about that. I suppose I could say: Since there is some possibility that interstellar travel is practical, the lack of visits is another indication of a bit of evidence for a paucity of currently active, technologically advanced extrasolar civilizations.

Note, interstellar travel - only a possibility. I don't say one way or the other. You do accept that it's a possibility? Perhaps a very remote possibility, but I don't know of any scientific principle that would rule out any possibility that interstellar travel could ever occur. Do you?

If I say, "Tomorrow we may receive light and heat from the sun," do you want me to "show my work?" How do I know the sun may rise tomorrow? Again, assuredly you would agree that it is at least a possibility. Perhaps a very remote possibility, but I don't know of anything that would rule it out. Do you?

Technological civilizations that exist long enough, eventually engage in interstellar travel,...in my considered opinion. This doesn't necessary mean FTL or even relativistic travel, but there are a lot of more sedate means of traversing the voids between planetary systems.

[Trakar]

ok, so if they are not traveling around building galactic empires, then maybe they are building Dyson spheres?

I apologize if the phrase "show your work" rubbed you the wrong way. It was just my way of pointing out the implausibility of many of these fictional engineering projects that ETs are supposedly capable of. A lot of people toss around science fictional constructs like interstellar travel and Dyson spheres as if there is an element of reality to them, while at the same time acting as if abiogenesis is an absurd impossibility.

Something more akin to Dyson clouds/swarms are probably more likely, IMO

[Bobunf]

Technological civilizations that exist long enough, eventually engage in interstellar travel,...in my considered opinion. This doesn't necessary mean FTL or even relativistic travel, but there are a lot of more sedate means of traversing the voids between planetary systems.

I agree with that, and, if so, it would make the absence of ET to date more of a problem. But to satisfy Baric, one of us should show their work.

[astromark]

So we study the components of life and deduce that most likely a second generation star is required in order for the heavy elements to be available.
We study and know much of Sol... and have deduced it's a middle aged second generation star... One of many that fit that description...
That we can NOT rule out life dwelling on the planets of our nearest neighbourly Alpha Cent., a or b. That little fact suggests it could be right under our nose... yet we still can not see it. We have much yet to learn... I agree. We can not yet say that life is abundant or common... We do not know those things. We can think, believe, but still not prove... Having a 'faith' in a scientific probability is not in its self any proof at all. Is it ?
We talk this subject on many levels and its the same outcome as yet... Waiting, waiting, waiting....

[baric]

I agree with that, and, if so, it would make the absence of ET to date more of a problem. But to satisfy Baric, one of us should show their work.

That is correct.

[IsaacKuo]

What the Fermi Paradox accomplishes is assuring us that a Star Trek future is not going to happen.

The Fermi Paradox is compatible with a "Star Trek future". Star Trek includes its own solution to the Fermi Paradox--the "Prime Directive". Basically, Earth lies within Federation territory, and the Federation has a policy of non-interference.

It's a "zoo hypothesis" solution.

[baric]

The Fermi Paradox is compatible with a "Star Trek future". Star Trek includes its own solution to the Fermi Paradox--the "Prime Directive". Basically, Earth lies within Federation territory, and the Federation has a policy of non-interference.

It's a "zoo hypothesis" solution.

I understand, but even you would agree that the "Prime Directive" was a fictional plot device that was discarded whenever the storyline required.

The Zoo Hypothesis doesn't really make any sense when you examine it, especially when you look at geological timescales. I guess if you want to suppose that some galactic empire stumbled across Earth only in the past 20,000 years or so out of the 4+ billion that it's been around, then it seems like a possibility.

[IsaacKuo]

Technological civilizations that exist long enough, eventually engage in interstellar travel,...in my considered opinion. This doesn't necessary mean FTL or even relativistic travel, but there are a lot of more sedate means of traversing the voids between planetary systems.

I agree with that, and, if so, it would make the absence of ET to date more of a problem.

It makes it a different problem, but I think it's not more of a problem. On the one hand, the practicality of interstellar travel introduces the possibility that aliens could be here in person. On the other hand, the practicality of interstellar travel makes it plausible for one civilization to dominate our region of the galaxy.

A couple examples:

1) If interstellar travel is impossible, then there could be billions of civilizations out there which might beam radio communications at us and no reason to fear interstellar communications. So the question is--where are the signals? (Obvious answer--most or all of them could be so far away that it would be expensive and seemingly pointless to send signals at us. So maybe there are only a hundred civilizations in range, and it just so happens that none of them feel like doing it.)

2) If interstellar travel is possible, then there could be one civilization which has dominated our region of the galaxy. So the question is--why is this one civilization not obvious to us? (Obvious answer--it's just one civilization, so maybe they just didn't care to colonize our star system.)

So, the question of whether interstellar travel is possible changes the problem, but either way there are easy answers to the Fermi Paradox.

But to satisfy Baric, one of us should show their work.

I have done the work to show how practical interstellar travel could work, but it's a lot of work and I frankly don't feel like repeating it here.

I know that's not good enough. I've seen plenty of harebrained interstellar propulsion schemes which honestly wouldn't work at all, or are only sufficiently workable to be usable in science fiction (as in, it could maybe work if we apply enough WSOD on it). So if I just say, "Hey, I've done the work and I know my proposed interstellar propulsion scheme would work"...yeah, I know that's not good enough.

[IsaacKuo]

I understand, but even you would agree that the "Prime Directive" was a fictional plot device that was discarded whenever the storyline required.

I agree that it was applied inconsistently in the Star Trek stories. That's just the fault of the writers. On the one hand, violations of the Prime Directive were supposedly extremely rare, and the consequences of those rare violations by anyone other than the main characters are shown to be severe. On the other hand, the main characters flaunt this sacred rule all the time, apparently without serious consequences.

The Zoo Hypothesis doesn't really make any sense when you examine it, especially when you look at geological timescales.

Why not?

I guess if you want to suppose that some galactic empire stumbled across Earth only in the past 20,000 years or so out of the 4+ billion that it's been around, then it seems like a possibility.

A galactic empire could have stumbled across Earth billions of years ago when it first formed. And maybe some billions of years after that, they noticed a significant biosphere worthy of "zookeeping" (or whatever you want to call it). Why not?

Do you simply find it utterly implausible for there to be no "zookeeping" violations in four billion years? Well...so what if there were some violations? What sort of evidence would we have of those violations? If some prankster aliens decided to drop by in a starship and abduct some dinosaurs, would we have any evidence of it today?

[baric]

1) If interstellar travel is impossible, then there could be billions of civilizations out there which might beam radio communications at us and no reason to fear interstellar communications. So the question is--where are the signals? (Obvious answer--most or all of them could be so far away that it would be expensive and seemingly pointless to send signals at us. So maybe there are only a hundred civilizations in range, and it just so happens that none of them feel like doing it.)

There are several answers to this shortcoming:

1) There are too few civilizations out there to notice (life and/or intelligence is rare)

2) The lifespan of a technological civilization is brief. There are a lot, but they don't broadcast for very long. (Drake's final parameter)

3) They are long-lived and broadcasting, but we are not looking in the right places (location or frequency)

4) They are long-lived and broadcasting, but we do not have the technology to spot the signals

Now, we know with some certainty that #4 is still true. Until we have confidence in our ability to actually spot ET signals as opposed to just stumbling across a needle in a haystack, then the other 3 possibilities are moot.

There's no need to invoke science-fiction to explain this, no matter how appealing it may seem.

Abiogenesis, the evolution of multicellular life, intelligence, and the possibility of technology to communicate across interstellar distances are established scientific facts.

Dyson spheres, warp drives, etc remain in the realm of science fiction. It makes no sense to me to use science fiction to discount known science.

[KABOOM]

There were quite a few leaps, but I don’t see where you addressed any of my leaps.



But that does not mean that such life does not produce very large effects. More than 3 billion years ago the Earth’s atmosphere contained an amount of methane out of thermal equilibrium – a phenomenon almost within our reach to detect in planets within a few dozen light years of Earth, perhaps even in this decade. It should be easy for a 22nd century type technological civilization even thousands of light years distant. It would be easy for us to detect any world in our solar system with an atmosphere substantially out of thermal equilibrium.

Microscopic life could have originated on Venus, Mars, Europa, etc., but there’s no significant evidence that it has or is producing any effect on its environment. So far, the waste products of any purported microscopic life on Mars, Europa, etc. display no significant effect on the surfaces or in the atmospheres of their worlds. Also, there’s no evidence of non-terrestrial life transported to Earth, nor of an independent abiogenesis on Earth.

We’ll know more as the decade progresses with:
 maybe ten more missions to Mars including two arriving next year and the ExoMars Trace Gas Orbiter and lander in 2016
 several samples returned to Earth from the Moon, Mars, Phobos, asteroids and comets
 at least one mission arriving at Jupiter
 and continued detailed analysis of the atmospheric gases of all of the significant solar system worlds.

But, if there is other life in our solar system, it must not be doing too well. And the absence of evidence isn’t evidence of presence. I don’t think an assessment, at this point, that things are looking pretty grim for other life in our solar system is too wide of the mark.

Could you please elaborate on the significance of "thermal equilibrium"? A planet out of thermal equilibrium is more apt to have life? What generated the excess methane in the Earth's atmosphere 3 billion years ago, bacteria emissions?

[KABOOM]

So we study the components of life and deduce that most likely a second generation star is required in order for the heavy elements to be available.
We study and know much of Sol... and have deduced it's a middle aged second generation star... One of many that fit that description...
That we can NOT rule out life dwelling on the planets of our nearest neighbourly Alpha Cent., a or b. That little fact suggests it could be right under our nose... yet we still can not see it. We have much yet to learn... I agree. We can not yet say that life is abundant or common... We do not know those things. We can think, believe, but still not prove... Having a 'faith' in a scientific probability is not in its self any proof at all. Is it ?
We talk this subject on many levels and its the same outcome as yet... Waiting, waiting, waiting....

Is it a known fact that Sol is a 2nd generation star (vs a 3rd or 4th generation)?