Is there life beyond us? (version 2.0)

[Bob B.]

Inspired by Apollo@Pluto's question about extraterrestrial life, I've expanded the poll to include more options.  I'd like to hear your opinion.  By "complex life" I mean life forms similar to those appearing during Earth's Cambrian explosion.  By "intelligent life" I mean human-like intelligence.

[LunarOrbit]

I'm certainly no expert, but I suspect that anything more complex/intelligent than a fish is going to be pretty uncommon. But with the constant battle between predators and prey I think the evolution of intelligence (at least to the level of dogs) is almost inevitable, if given enough time.

Looking at the huge variety of life on Earth I think it's certainly possible for intelligent life to spring up more than once on a planet. We have a few species that are as intelligent as human children (certain breeds of dogs and monkeys, dolphins, etc.) I wouldn't bet against the possibility of intelligent life happening more than once in this universe.

Life with human-like intelligence is going to be extremely rare.

[Bob B.]

I tend to agree with your assessment, LO.  How common life is, I think, depends on what sparks its initial creation.  If microbial life springs up easily, which I think it might, then I believe more complex life forms are likely to evolve in favorable habitats.  Complex life may be common on Earthlike planets, however the number of planets that combine the favorable characteristics of Earth may be rare.  Even still, there are so many stars in the Universe that it is hard to image there not being millions of potential “Earths”.

Although I believe animal-like intelligence may have occurred millions of times over throughout the Universe, I think the emergence of human-like intelligence is probably very rare.  Nonetheless, I believe there may be other intelligent beings out there somewhere, though I doubt we’ll ever know about them.

[Homo bibiens]

I've got my opinion just like everyone else, but given the extremely limited data available to us, there's necessarily a great deal of speculation here.  Some random thoughts.


Reasons life ought to be rare:

Even on earth, the level of biodiversity seems pretty sensitive to conditions.  There is life in Antarctica, but not nearly as much as in Brasil.  Walk up a tall mountain, and you can see trees and the like give way to moss and lichens, and eventually bare rock, if the mountain is tall enough.  So even on earth, life seems to be pretty sensitive to conditions such as temperature.  Go to the moon, and, unless there is some form of "life" so radically different from anything we know that we can stare right at it and not recognize it, there is nothing.

Intelligent life, of the human level, hasn't existed for very long, a blink of the eye on the time scale of the earth.  We don't really know how long humans are likely to stick around, and whether they will give way to more advanced life forms, or if they (and other highly intelligent life forms, such as orangutans and chimpanzees) will disappear, leaving behind an earth populated by insects and slugs or such things.  It is true that humans are an extremely adaptable species, but the track record for the lifespan of advanced species isn't real good.  So even if intelligent life does develop frequently, it is possible it might not last real long.  (Aside - this is one reason I have trouble getting worked up about the possibility that a giant asteroid will wipe out humanity.  What are the odds that humanity will survive long enough for that to happen?)


Reasons life ought to be common:

Huge number of star systems, unless there is some reason for scarcity of planets we don't know about, there ought to be lots of those, with incredibly varied conditions.

Diversity of conditions within a planet - for life to exist on a planet, it need exist only in one place, it doesn't have to blanket the entire planet.  So even if the conditions for life are pretty strict, within a single planet, there is considerable variation in conditions, so maybe the odds that somewhere on the planet, the conditions are right, is not so bad.  But reference moon comments above - an entire planet/moon/whatever you want to call it, and as far as I know, we got nothing.

I guess we can estimate the number of planets out there a lot and possibly also speculate about what types of conditions they are likely to have.  But what is the probability that a planet with a given set of conditions will develop life?  I don't think we can do a whole lot better than make up numbers.  One in a thousand?  One in a million?  A billion?  A trillion trillion trillion?  I don't even know how to go about estimating such a thing, and yet the answer is hugely sensitive to this number.

[spacecat27]

I remember a discussion I had some years back with the quite brilliant Chinese grad student who used to post on Orstio's board.... Does an infinite universe assure infinite possibilities?  That is, not only possibilities for life, but every conceivable permutation... a planet governed by intelligent possums...etc.

The upshot: could be.  (Though they'd have to be giant possums to have the brain capacity   )    When you consider the size of an 'average' galaxy- and then the billions...trillions... of galaxies out there- I wouldn't doubt life- even intelligent life- has cropped up elsewhere; but the distances are so incredibly vast that I doubt there could ever be contact in any way.

This also brings to mind a Sci-Am article from some years ago where a mathematician had theoretically calculated that at some point the 'possibilities' would run out... and begin to repeat.  Thus, out there somewhere is another 'you'... doing what you are doing.

At any rate- I think there is other life out there.  Since we are kind of 'out in the sticks' of our galaxy, and our galaxy is kind of 'out in the sticks' of the universe, and the distances are so vast-- I doubt we will ever become aware of any, let alone be visited by any.

Even if some inconceivably advanced civilization developed a way to 'warp' space and time and actually travel such distances, there would be no reason for them to come here.  We are not in a 'traffic area' or 'on the way' to anything else particularly interesting.  Contact would be purely accidental- and if "they" have that kind of technology, they're not going to make little navigational errors! 

[DonPMitchell]

I think there are critical steps in our evolution, any one of which might have been fantastically improbable.  The appearance of muscle protein that allowed complex cells to move around, the appearence of photosynthesis, the Cambrian explosion when basic animal forms appeared, etc.

We only know one thing for sure -- it happened once.

[Johno]

I would suggest that the appearance of MOST proteins is highly improbable.  Generally speaking if you remove, replace or duplicate a single base-pair of the DNA responsible for a protein's synthesis, you get either a highly disfunctional version of the protein or more often plain gibberish.

So for life to arise even once, you need at least one of the following:

* A big universe
* Vast tracts of time
* A creator or motive force.

Personally I believe all three are factors, but YMMV.

[Bob B.]

I think there are critical steps in our evolution, any one of which might have been fantastically improbable.

Given the immensity of the Universe, even something fantastically improbable can produce multiple examples.  By some modern estimates, there may be as many as 10²³ stars in the observable universe.  Suppose one out of ten of those are of the right stellar class, and one out of ten of those have a terrestrial planet (or moon) in its habitable zone.  Say one out of a million of those planets develop life, one out of a million of those develop complex life, and one out of a million of those develop intelligent life, then, even with such long odds, we still get about 1,000 intelligent species in the observable Universe.

Something else to consider is how long does an intelligent species survive before becoming extinct?  Let's say one million intelligent species have come and gone over the last 5 billion years.  If each of those survives for one million years, then there are only about 200 in existence at any one time.  When it comes to determining the odds of contacting other intelligence, how long intelligence survives is almost as important as how often it emerges.

[ijuin]

I expect that the majority of planets that are at least as hospitable as Mars will have microbes, and more advanced life may be found on some of the more hospitable of those. However, I think that civilization of any sort (especially the starfaring sort) is quite rare--rare enough that no alien explorers would have come to our solar system since before the Cambrian.

If aliens think in any way comprehensible to humans, then if they found a hospitable planet that they had the means to colonize, then they almost certainly would do so in the long run. It is pretty implausible that a "hands off" policy could stay in force, never breached by even one person, for millions of years--it takes only one person willing to flaunt the rules, after all. Thus, if aliens had come to Earth and found it to be desirable real estate, then they would have set up shop. The fact that early humans found valuable minerals lying around on and near the Earth's surface is pretty good evidence that there has been no advanced civilization on Earth for several million years before humans came around--any civilization would have mined all that stuff and spread it across their cities rather than modern humans finding it in rich, concentrated veins.

[DonPMitchell]

Evolutionary psychology suggests that high intelligence emerges out of sexual/political competion.  That is certainly true for all the social species we know of on Earth.

If an alien species was advanced enough to come to Earth, I am pretty sure that would be bad news for us.

[DonPMitchell]

This reminds me, I think H.G. Wells "The War of the Worlds" is one of the most brilliant science fiction stories.

Wells thought that the two hallmarks of human evolution were the brain and the hand.  He supposed that the Martians had evolved to the point where they were little more than a giant hand with a brain.  They had no organs of digestion, but instead sucked the blood out of lesser animals and circulated it in their bodies.  Apparently they also thought people were yummy.

In "The Time Machine", he proposed the remarkable idea that the working class and the wealthy class might evolve into two different species (the Morlocks and the Eloi).

[LunarOrbit]

The War of the Worlds and The Time Machine are two of my favorite books.

[DonPMitchell]

They keep making movies based on War of the Worlds and The Time Machine, and they always mess it up and miss the interesting points that H.G. Wells was trying to make.