There is some fish or something that change its colors to exactly match its surroundings. It can do this in some small amount of time? Even current days computers would not have the power to process that information as quick as this fish. Does that make it intelligent? Albiet in a different way than we are used to thinking of intelligence. I find it hard to discuss to define what intelligence is or isnt.

Also what defines life? ET life will be absolutely nothing like life as we know it. I doubt it would have intelligence as we currently imagine it ( I dont think they could pass a high school SAT test that was translated into their language )

One thing is that in movies you always see weird ETs that have two eyes a nose and a mouth. ETs will NOT have 2 eyes a nose and a mouth. That is the signature of life on earth and of evolution here.

Life on Earth is comprised of the most abundant elements in the universe (as a matter of fact they are more abundant off planet than on).

So why would ET life be "absolutely nothing like life as we know it?"

To me, it stands to reason that ET life would be similar to life life as we know it, perhaps even in form.

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"Where the telescope ends, the microscope begins. Which of the two has the greater view?" - Hugo

"Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." - Churchill

Life on Earth is made of hydrogen and helium?

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Octopi.. Squid... are very good at that.
Processing power is what enables it- the same as you catching or throwing a ball. Imagine calculating the trajectories.
But processing power that lacks the ability to think about its processing power lacks intelligence. The most powerful processor ever to exist would be useless for intellectual thought if it could not think about anything, even if it could process information quickly.

This is speculation- true. But you say doubt... why?
There are certain things that are mostly constant. A rock on a planet ten billion light years away will be hard. Water would be wet if the atmosphere and pressure were similar to here.

Convergent evolution is out then?

You're speculating, but you have no way of knowing that convergent evolution on another planet will end up with the same successful traits as some of the traits that we have.

I disagree; I think it's likely that there are billions of species of beings who resemble humans to some degree and who we would recognize as intelligent. The vastness of the universe makes this almost a necessity IMO.

We have two eyes because that's the minimum number needed for depth perception; certainly a highly desirable trait regardless which planet you evolved on. A nose is also extremely valuable for sensing danger. And all animals here on Earth have some sort of a mouth; for creatures that don't absorb nutrients through roots or something similar, or directly through their cell walls, it's pretty much a necessity.

In other words, the basic physiological structures that are common to most animals here on earth evolved for a reason. For other species that evolved elsewhere, there will almost certainly be enough environmental conditions that are sufficiently similar to our own that they will evolve similar structures.

That's not to say that there may not be a lot of planets with intelligent creatures that somewhat resemble our insects, or even plants - or they may be so bizarre that we have nothing to compare them to. But there will also be a whole bunch with species that are no more different from us than, say, an octopus or a bat, and probably many species that resemble sci-fi aliens, and I think it's likely that there are some species, somewhere, who look no more different from one race of humans than does another.

And I think that, in a lot of cases, we wouldn't be able to pass their SAT's.

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"Scientific progress goes 'boink'?"

Let me clarify: The most abundant elements in the universe are Hydrgoen, Helium, Carbon and Oxygen. Helium is inert. So the three most abundant, and chemically active, ingredients are the top three with which life on earth is comprised.

I would've thought you knew this?
Indeed, I'm rather certain we've had this discussion before.

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"Where the telescope ends, the microscope begins. Which of the two has the greater view?" - Hugo

"Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." - Churchill

Of course intelligence is a difficult thing to pin a single one sentence definition on but we can identify a number of characteristics that seem to have been necessary for it to develop on earth and many of these will be needed by any life form that is to be regarded at intelligent. Especially if it is ever to develop two critical by-products that human intelligence has spawned Technology & Culture.

The examples of marine life offered earlier were explained that adapting colour and shape to the local environment was primarily a matter of pure processing power. Assuming the animal has the appropriate body features that allow it to change it's physical appearance rapidly then the control mechanism simply needs to read inputs from the surrounding environment telling it what that looks like and then send instructions to all the necessary organs to bring about the shape and colour shift. In programming terms this is not actually such a complex process, It can be almost a reflex and could even be performed by distributed processors. For example an animal could have a hundred processing nodes each connected to 100 sections of its body and each node connected to its own light sense organ (eye). Each of the 100 (eyes) passes information to its parent node about what the environmental colours and textures are and the node sends standard sets of signals to the cells it controls to change to match that. Once such a mechanism evolves it can be passed down genetically hard wired with little need to change over many generations.

However for an animal to look up at the night sky and observe the movement of the points of light it sees, then for it to go further and observe that over time they do not all move in the same way - that some appear to change direction and that these motions also correspond to patterns across the cycle of the seasons is a very different matter. For a creature to do that it must have a powerful memory. It must have a sense of time and be able to think about where things were in the past and where they will be in the future. Humans had achieved all of that long before they even learned how to make metal tools. If you want to look for intelligence then it seems that you cannot escape from the need to have a powerful memory. Memory allows thoughts to be retained over time - it allows the animal to have a sense of its own existence through time and memory allows a method of communication which will allow ideas in one animal to be passed on to others down through the generations. I would suggest that without that kind of massive storage and retrieval capacity, combined with an ability to run comparisons between sets of stored information no animal will have intelligence and certainly not problem solving intelligence.

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Maybe so, but I doubt that there are any such species within the visible universe, so we are unlikely to ever meet them.

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I think that even the visible universe is sufficiently large that I would still be satisfied that my assertion is reasonable - that is, if I may be allowed to modify my original statement by redefining "are" to mean "have been, now are, or will be." (The thing that I find most striking about the Drake equation is the effect of varying the length of time that ET's exist.)

Atlasoftheuniverse.com puts the number of large galaxies in the visible universe at 350 billion. There is an article on space.com in which Dr. Charles Lineweaver (research astronomer) guesses that there may be a billion Earth-like planets in our galaxy. Using these numbers, and assuming that there is nothing special about the Milky Way, if only one-billionth of Earth-like planets in the visible universe contain sentient life, and only one-billionth of these creatures closely resemble us, that still leaves 350 species.

However, I agree completely that the chance that a human will ever encounter one of them is vanishingly small.

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"Scientific progress goes 'boink'?"

Ah, now you've added "chemically active." Yes, I think we have had this discussion before, which is why I was surprised by your comment. Hydrogen and helium account for 98% of the total in the universe, but the human body is about 10% hydrogen, and the helium contribution is essentially zero. As has been discussed before, abundance is not nearly so much of an issue as the elements that can make complex molecules.

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I say there is an invisible elf in my backyard. How do you prove that I am wrong?

Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser

[quote=3rdvogon;1216132]Of course intelligence is a difficult thing to pin a single one sentence definition on but we can identify a number of characteristics that seem to have been necessary for it to develop on earth and many of these will be needed by any life form that is to be regarded at intelligent. Especially if it is ever to develop two critical by-products that human intelligence has spawned Technology & Culture.

The examples of marine life offered earlier were explained that adapting colour and shape to the local environment was primarily a matter of pure processing power. Assuming the animal has the appropriate body features that allow it to change it's physical appearance rapidly then the control mechanism simply needs to read inputs from the surrounding environment telling it what that looks like and then send instructions to all the necessary organs to bring about the shape and colour shift. In programming terms this is not actually such a complex process, It can be almost a reflex and could even be performed by distributed processors. For example an animal could have a hundred processing nodes each connected to 100 sections of its body and each node connected to its own light sense organ (eye). Each of the 100 (eyes) passes information to its parent node about what the environmental colours and textures are and the node sends standard sets of signals to the cells it controls to change to match that. Once such a mechanism evolves it can be passed down genetically hard wired with little need to change over many generations.

agreed

intelligence , memory or memory , intelligence go hand in hand

Astronomers seem to have many different definitions of Earth-like. Some consider that any terrestrial planet within a certain range of masses and a certain distance of the local star to be Earth-like, no matter what conditions pertain on those worlds. By some definitions Venus and Mars would count as Earth-like. Other authorities, such as Ward and Brownlee, have a much more restrictive view of what an Earth-like planet is.

Our Galaxy contains maybe 200 to 400 billion stars; for there to be 100 billion Earth-like planets, Lineweaver must be adopting an inclusive definition of Earth-like, which includes tidally locked terrestrials in red dwarf systems and many other world quite different to our own. I think it is possible that life, even intelligent life, might evolve on such very different worlds, but each instance of life will have many differences to the life on our planet.

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Going back to the original post, however, two eyes, a mouth and some kind of olfactory organs do seem to be a reasonable configuration for an anterior cluster of organs. They may even be placed on some kind of independently mobile head, as they so often are on our world.

However, considering the wide range of eyes, mouths and olfactory organs which can be found on our planet alone, the chances are that even with such an assemblage an intelligent alien won't look very much like a human.

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The number he gave was one billion. This is a guess, of course, but at least it's an educated one, so we can probably say with a reasonable degree of certainty that the number is quite large. And I intentionally used what I believe to be an extremely conservative estimate (one in a billion) for both the number of planets with sentient life and the number of these planets with species that closely resemble humans. I think that this more than compensates for the possibility that Lineweaver's definition of "Earth-like" may include some planets on which life forms even remotely similar to those on Earth are unlikely to evolve.

My point is that the universe is unimaginably vast, so it does not seem unreasonable to assume that life has or will take every possible form more than once. Put another way, I think that it's a surer bet that a particular life form - especially one of those that we know for certain is possible - will evolve, than that it won't.

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"Scientific progress goes 'boink'?"

Oh yes; sorry; Lineweaver did say 1 billion, and that implies that one star in every 200-400 has an Earth-like planet. I suspect that number would include worlds which are quite earth-like but have never evolved a complex biosphere. It is quite an optimistic estimate, and means that there could be several Earth-like worlds within 50 light years (more, since the Earth-like worlds might be expected to congregate within the Galactic Habitable zone).

But the emergence of a complex biosphere, even on a planet which is quite Earthlike, may be a rare event; and every single instance of the emergence of life will follow its own evolutionary path (unless there are any cases of local panspermia, which may be rare but perhaps not vanishingly so).

We might expect some of those worlds to develop intelligent life; some instances of intelligent life would probably be bipedal, and some would have two arms and a head; some would have two eyes and a mouth. There may be billions of such races in the visible universe; even hundreds of billions. But how many of them would have human-like noses? But how many of them would have human-like jaws? But how many of them would have human-like skin? How many of them would have human-like backbones? How many of them would have human-like hands, feet, internal organs? It seems very unlikely that any alien species out of the billions we are considering would be similar enough to human to pass as such.

Parallel, or convergent, evoloution produces similar creatures on our world mostly because the creatures concerned are all closely related. Parallels between marsupials and placentals occur within the single class Mammalia; parallels between sharks and dolphins within the subphylum Vertebrata.

There are no Vertebrata on any other planets outside the Earth, no mammals anywhere else in the universe. Any phyla that may be found out there on extrasolar planets that resemble vertebrates or other terrestrial biota will surely be given a separate classification to indicate that they have evolved separately; they will not share any genetic material with Earthly organisms (once again, barring panspermia of some sort) so they will be accurately described as separate taxa.

Strictly speakiing there wont even be any animals,plants, fungi, archaea or eubacteria out there either, although some of the simplest forms may resemble our own simplest forms superficially. The more complex an extraterrestrial organism gets, the less likely it is to have an Earthly analogue.

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It doesn't strike me as overly optimistic, given the increasing evidence that planets may be quite common. But even if the number is high by a factor of 2, or 5, or even 10, I don't think that it would change things significantly. Our estimate of the number of planets on which sentient life would evolve could be pessimistic by several orders of magnitude.

It's interesting that you mentioned the GHZ, since Lineweaver coauthored one of the few papers that I've been able to find on the subject. [Charles H. Lineweaver, Yeshe Fenner and Brad K. Gibson (January 2004). "The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way". Science 303 (5654): 59–62.] I believe the full text of the paper is still available online. I used it as a reference for a Wikipedia article on the GHZ, which has since been merged into the Habitable Zone article.

I agree that species may evolve along quite a different path than that which occurred on Earth, although I still maintain that the necessity of adapting to the environment will require many physiological structures that we might find familiar.

I'm probably even less optimistic than you regarding the possibility of panspermia resulting in similar life forms, at least further up the evolutionary ladder; I'm not a huge fan of the idea to start with, and it seems to me that even if planets were seeded with the same simple organisms, the resulting creatures may still look quite different in a couple of billion years.

I agree that the odds of another species very similar to ours evolving elsewhere are remote, but the reasons that I think it's possible are that a) we already know that creatures resembling humans can evolve, and b) we're talking about a huge number of planets - 3.5 x 10^20, using our original numbers.

Let's look at it another way - out of billions or hundreds of billions of sentient life forms, what are the chances that no two would be strikingly similar? Of those that would be similar, how likely is it that one of them would be human?

While all of that is true, I still believe that, given a huge number of similar environments, we can expect to see at least a few similar life forms evolve, even at the top of the food chain.

It may be that I'm stretching the principle of plenitude past its breaking point. And I'm certain that we will never know for sure. But I can't help thinking that, given the immense number of opportunities, if it happened once it could happen again.

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"Scientific progress goes 'boink'?"