I read the book "Alone in the Universe" by John Gribbin recently.  He argues that the conditions that produced intelligent (sort of) life on earth are incredibly rare, so this explains the "Fermi paradox":  if there are aliens out there, why don't we see them?   (assuming as seems reasonable, that we don't). 

He gives a lot of plausible reasons for why the rareness of life.  Like, only a certain part of the Milky Way is a good home for life.  Our planet has a magnetic field that shields it from the solar wind - charged particles that stream out of the sun.  Continental drift may not be common, and it's crucial for regulating the concentration of carbon dioxide in the atmosphere, which is a kind of natural thermostat for Earth.  He thinks there were serendipitous mass extinctions of life forms that were unlikely to become intelligent, like the Ediacarans.  They were a weird kind of multicellular life that were around before the Cambrian.  Strangely shaped things.  And so on. 

Some of it is very questionable to me.  Like, he thinks that land life is much more likely to become technological, and that the reasons are obvious.  I'm not sure what the obvious reasons are and I looked online and didn't find them.  I wondered if part of the reason was that aquatic creatures would be less likely to develop hands, but then I found that octopi can manipulate objects with their tentacles.   A lot of technology wouldn't work underwater, but being underwater would make some things easier, too.  Aquatic intelligent creatures might be very good at spatial thinking since they live in 3 dimensions.  He mentions the idea of an advanced civilization putting self-replicating machines out into the universe that would colonize everything in time, and report back what they found to the home planet.  So why aren't there self-replicating alien machines on Earth, if there are alien civilizations?  But I'm not convinced that an advanced civilization would necessarily want to do this, or that it would be at all practical or feasible. 

He talks about a dinosaur called Troodon, which lived right before a 6-mile wide rock (probably) smashed into the earth, causing the end-Cretaceous extinction.  He says based on its brain size, Troodon was about as smart as a small baboon.  So the dinosaurs were on their way to evolving intelligence when they were wiped out. 

It would be interesting to speculate what an intelligent creature that Troodon could have evolved into, would have been like.  They might have been more warlike than us (NOT a happy thought) since they were carnivorous and we evolved as omnivores.  Carnivores generally seem to be rather aggressive towards others of the same species.

There are obviously a lot of pitfalls with arguing that life is rare, based on lucky accidents that produced us.  Evolution is very creative, and examples of convergent evolution show how the same solution to a problem that life is faced with, are found over and over.  Why shouldn't intelligence be a solution that convergent evolution finds over and over, on different planets, even?  And, different solutions to different problems posed by different circumstances, could be found by alien life, and the limitations of our imagination are no argument against this. 

To me, the slow speed of light compared to the size of the cosmos seems a good reason why we'd be left alone by Them.  The Milky Way galaxy is about 100,000 light years in diameter.  One could perhaps make a good argument that other intelligent life would exist on a roughly similar time scale to us, so that 100,000 years would look like a long time to Them, too. 

If it's true that conscious life is very rare, then it returns the specialness to us that science took away so much, by discovering the hugeness of the universe, that the sun and stars don't revolve around us, etc.  The wonderful nature of our world is partly explained by the fact that we are here to see its wonders - which is made possible by the enormous size of the universe. 

For me, thinking about this kind of spacey thing is a mind-refreshing relief from the humdrum forced on me by health problems.  And you can enjoy exploring the cosmos too in your imagination.

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In order to have technology -- anything from making a crude stone tool to building a space shuttle -- requires brains. Brains require a constant supply of oxygen, which requires a heavly vascularized brain and a large heart, and large lungs to efficiently oxygenate the blood. Fish are highly specialized and occupy a fairly restricted niche dependent on saline or fresh water, temperature, depth, etc,. They are streamlined swimmers with no apendages . They obtain oxygen through their gills by diffusion, cerainly not efficiently enough to supply a large brain and incapable manipulating their environment and making anything. The only large brained aquatic animals are the land mammals that returned to the sea.

The other denizens of the deep are primarily invertebrates, which have a highly specialized way of life and are also gill-breathers which, of course, would restrict their brain size. Yes, the octopus has a significantly larger brain, has memory and can solve problems. It can manipulate things with its tentacles and perhaps pile small rocks together, but it can't build anything substantive. It can't get enough leverage to move large objects because it has no skeleton. It can't use a hammer because there is too much resistance from the water. It can't use wood because it floats and rots; can't smelt metal; metal rusts and corrodes; and can't build glass palaces at the bottom of the sea.

So what kind of a intelligent aquatic creature would you devise to create a technological world under those circumstances ? Imagination is not enough. You are creating a world with a lot of wishfull thinking and not a lot of science. And that is not someplace I want to go. I have said about all I can say about this topic. Thanks for the mental exercise.

I think, for the most part, that a technological civilization would not evolve from an obligate aquatic animal. The largest limitation would be the inability to use fire or create metallurgy. That is not to say there couldn't be an intelligent aquatic “animal” and a culture just not a technological one.
Harry Harrison wrote a SF trilogy – West of Eden – an alternate history in which he describes a technological society of evolved semi-aquatic dinosaurs. However, humans have also evolved but only to the level of the stone age. The two critters are mostly separated by climate – the dinos can't handle the colder regions and the humans have no desire to get anywhere close to the dinos in the tropic and sub-tropic environments.

I agree that that there is life - of one kind or another - on other planets, not just because of the large number of planets that have been discovered but because the nebulae in our galaxy, like the Orion nebula, are producing an enormous amount of prebiotic molecules ( water, formaldehyde, cyanide sulfur dioxide and many more). This has been going on long before the earth was formed, and it's inevitable that this raw material of life was here during the formation of the planet and was incorporated during its accretion period. For me, the question of where life came from, the earth or space, is moot. The earth is space stuff. So, the answer is yes to both questions.

My conundrum is this: The DNA/RNA molecule is the "life" molecule for all living things on earth. If we expect to find earth-like life on other planets, it would have to have DNA/RNA. Although I am convinced that this is the only molecule possible for life, I find it difficult to believe that it can be easily replicated. The other problem is the presence of the mitochondrion in all true cells. It is believed to have been a symbiotic bacterium which became incorporated into the cell and serves as a power house with its own genetic material, and has made it possible for more diversity. If ths process is not duplicated on other planets, what sort of life will we get then?

These factors make me wonder whether life will be as prolific as we think, and that intelligence on par with ours will be very, very rare, much less superior to ours.

To my knowledge, there is no self replicating molecule that exists other than DNA/RNA; however, the pre-biotic chemistry for it exists. I assume the chemical precursors are pretty much consistent throughout the universe as is chemical reactivity. Oxidation/reduction is the same here as well as in the most distant galaxy. As such, any rocky planet with a reducing atmosphere would be a potential life forming stage. There are, of course, many other factors necessary for successful life genesis and survival to the point of intelligence.

Intelligence may be rare but, IMO, life is probably ubiquitous throughout the universe.

Jim, I can't quibble about what you've said (although I'd like to) but keep in mind that only one planet out of eight in our solar has has life on it. As to life on the other plants, and moons, it's pure speculation.


He's not speaking of life on other planets within our solar system.  None of the other planets in our solar system fit the necessary criteria for DNA-based life.  He's speaking of chemically-similar life on planets within similar orbits of other stars.

There are a couple hundred billion stars within our galaxy alone.  Some of them must have suitable planets at orbits that are the appropriate distance to contain liquid water.

Thanks. The "Goldilocks Zone". The point I was making was that the total number of planets is meaningless. Additionally, Mars may have had life, but no longer seems to, even though it has ice at the caps. Might it have fallen into that zone?  It's all a matter of degrees.

The point I was making was that the total number of planets is meaningless.

Umm, no, it's not meaningless.  When we're talking about a statistical likelihood of there being life on other planets, the planetary density of the galaxy and the universe is very much at issue.

Additionally, Mars may have had life, but no longer seems to, even though it has ice at the caps. Might it have fallen into that zone?  It's all a matter of degrees.

Mars is a little outside of that zone.  It is too far away from the sun for the energy from the sun to maintain its temperature within the necessary range for a long enough period of time.  Obviously, it passed through the necessary temperature range, at some point in its life-cycle, going from molten, after formation, to its current, relatively inert stage.  There was quite possibly very simple life, at some point, but the window of time was too short for that life to evolve very much.

Mars might heat up significantly, after the sun goes into the red giant phase, in another 5 or 6 billion years, but that phase will be far too short of life to reform and evolve any amount worth speaking of.  Plus, Mars and the outer plants might escape, during that period, in which case, it won't be warming, as it goes hurtling off into interstellar space.

Thanks. How do you determine the odds of life being on any one planet? We do not have any sampling data. If your talking total mass of life, that's one thing, if you're talking odds, that's another.

From our perspectve it's easy to determine that Mars is not quite in the Zone. How easy is it to ascertain from 20 lightyears distance. We have not explored the ice cap(s) on mars yet, neither have we drilled a deep core sample.  On earth we have life forms living miles beneath the surface. So, there is much more to learn. 

How do I determine the odds of any given extrasolar-planet evolving life?  I don't.  I have no freaking clue.

The only real statements that I can make are that there are a huge number of planets out there with life on them, because of the sheer numbers involved.  I made a lot of approximations, based upon other people's numbers, to explain why I reject the Fermi Paradox, back on page one of this discussion.  I can only make the most general sorts of conclusions, with my knowledge of the field.

I agree with you that there must be abundant life out there, but I think Fermi was speaking of life that was superior in intelligence and technology. On this point I agree with him that it probably doesn't exist. If life is DNA-based, then evolution would operate under the same principles as it does on earth. Since we now live in societies in which survival is no longer a life-and-death struggle, there is no selective pressure for us to get any smarter. The same would go for an alien life form.

Once they reached a comfortable, secure technological point there would be nothing requiring them to get  larger brains than they have now. So, they would probably be just like us -- wondering why they haven't been visited by a technologically superior culture.




... but I think Fermi was speaking of life that was superior in intelligence and technology.


He was speaking about intelligent species that have achieved interstellar travel, as we could possibly do, in another couple hundred years or so, if we don't wipe ourselves out, before then.

On this point I agree with him that it probably doesn't exist. If life is DNA-based, then evolution would operate under the same principles as it does on earth. Since we now live in societies in which survival is no longer a life-and-death struggle, there is no selective pressure for us to get any smarter. The same would go for an alien life form.

What you're missing is that genetic evolution doesn't matter anymore (or at least matters very little), in our evolution as a species.  Our memetic evolution is what will eventually lead us to an interstellar culture or cause us to wipe ourselves out.

Also, he's not saying that other intelligent life doesn't exist in the galaxy.  He's saying that if other intelligent life exists in the galaxy, the estimates (such as the Drake equation) have problems. That's why it's a paradox.

Personally, I think most of the problems with the estimates have to do with underestimating the difficulties of interstellar travel and overestimating the effective age of the universe, in terms of how long interstellar civilizations would have been around, and how freely they would be able to move throughout the galaxy.

Part of the problem is that he assumes an effectively limitless time for colonial expansion, relative to the age of the universe.  I don't think that the relative differences in time are quite as exponential as he assumes.

I went through most of that back on page one.

I think that at the more pessimistic end of the estimates, with the limitations of space travel factored in, it's not so hard to believe that we haven't had anyone probing us yet.


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