What do you think is the most likely explanation for the Fermi paradox?

[Colin Robinson]

Perhaps they got caught in a nearby supernova and now consist only of presolar grains.

Yes, supernova explosions made be the factor, or one of the factors, which make galaxies difficult or impossible to tame...

[Noclevername]

Considering that all living things do drink, in the sense of taking in water, it is reasonable to ask why they haven't drunk the oceans and rivers dry...

The answer is that there's a balance between the water living things take in and the water they emit, e.g. as urine and as exhaled water vapour.

Yeah, the phrase is not usually used to mean multiple species worldwide, but a single thirsty person. I used it in that context.

But if a species wants to colonise nearby stars, and succeeds in doing so, and if its colonies then want to colonise stars which are nearby to them, doesn't that mean the species steadily spreads through more and more of the Galaxy until and unless something stops it?

The difficulty of interstellar travel means the default is not spreading, it's staying. To establish spreading between stars as a "natural" situation that just sorta happens, is to overlook the massive efforts and mind-boggling energy that must be expended each and every time.

Robin Hanson mentions that point: "Without FTL travel to mediate conformity, we would also not be surprised by a great diversity among the different parts of an explosion, and especially among different explosions... We would expect, for example, different cultures, languages, and body form details. We expect much less diversity, however, regarding choices which would put a civilization or entity at a strong competitive reproductive disadvantage."

A single star system has unimaginable room for diversity. And plenty of orbital volume for avoiding threats, too, especially if you count the Oort clouds.

[Colin Robinson]

Robin Hansen's argument is that living (evolving) species have a general tendency to expand where they can...

Under natural conditions, sure. Interstellar travel is hardly a natural occurrence.

Does what we call "natural selection" only take place under "natural" conditions?

Hanson's argument is that the logic of evolution will continue wherever there is reproduction, variation, and competition...

[Noclevername]

Does what we call "natural selection" only take place under "natural" conditions?

Hanson's argument is that the logic of evolution will continue wherever there is reproduction, variation, and competition...

But we are not talking about reproduction or evolution. We're talking about travel. You can have societies reproduce, compete, and evolve within a star system.

Added: The physics of interstellar travel are a constant. The energy needed to accelerate mass demarcates hard physical limits on what cultures can do.

[Colin Robinson]

But we are not talking about reproduction or evolution.

Robin Hanson's argument is that living (evolving) species have a general tendency to expand where they can...

We're talking about travel. You can have societies reproduce, compete, and evolve within a star system.

You can have organisms reproduce, compete, and evolve within a droplet of water. The question is whether they'll spread beyond the droplet if they get the chance?

[Noclevername]

Robin Hanson's argument is that living (evolving) species have a general tendency to expand where they can...



You can have organisms reproduce, compete, and evolve within a droplet of water. The question is whether they'll spread beyond the droplet if they get the chance?

You are comparing apples to oranges. A biological species spreading to a different niche on a single planet is fundamentally unlike intelligent beings choosing a non-trivially massive effort requiring the sacrifice of huge amounts of non-renewable energy. One is a natural process, a fundamental part of evolution. The other pushes the maximum possible limits of nature.

[Colin Robinson]

The physics of interstellar travel are a constant. The energy needed to accelerate mass demarcates hard physical limits on what cultures can do.

How does that relate to your earlier comment

I can buy that a species might want to colonize nearby stars, with great effort.

Do you think the species that wanted to do that would be blocked by hard physical limits?

[Noclevername]

How does that relate to your earlier comment



Do you think the species that wanted to do that would be blocked by hard physical limits?

I'm saying, each and every interstellar journey requires a major effort for any civilization. Either a fast (relativistic) trip or a very slow generation/sleeper ship. Either you pay in energy expenditure, or in time. A slowboat ship will take thousands of years for each star, while a fast ship needs more energy than Earth's whole economy could produce. Every single time.

Those are the hard physical limits. No getting around them. So I don't think any civilization is going to be spreading across the galaxy at the mathematical maximum rate. It just could not be sustained.

[Spacedude]

Quote Originally Posted by Grant Hatch :
"One thing is for sure.... we are relative late comers to the scene and it seems that life arose almost as soon as the planet was no longer molten. Then wiped out and arose again as the planet went through the late heavy bombardment. At least according to paleo geology..... This would seem to indicate that life is a natural part of our universe... at least "locally". We may find that it's CROWDED out there. Intelligence would also "seem" to be a natural consequence of evolution, though we only have a sample of one to extrapolate from."

There may be a simple explanation but why didn't the dinosaurs develop intelligence? They had 150 million years to evolve "better" brains but apparently they did not. Meanwhile, after their demise we humans evolved intelligence in less than 66 million years.....and basically from impact surviving "rats" at that.

[Noclevername]

Intelligence of the rocket-building sort, is one of trillions of possible consequences of evolution. There is no guaranteed path! It has no endpoint, it is non-deterministic.

[Colin Robinson]

Quote Originally Posted by Grant Hatch :
"One thing is for sure.... we are relative late comers to the scene and it seems that life arose almost as soon as the planet was no longer molten. Then wiped out and arose again as the planet went through the late heavy bombardment. At least according to paleo geology..... This would seem to indicate that life is a natural part of our universe... at least "locally". We may find that it's CROWDED out there. Intelligence would also "seem" to be a natural consequence of evolution, though we only have a sample of one to extrapolate from."

There may be a simple explanation but why didn't the dinosaurs develop intelligence? They had 150 million years to evolve "better" brains but apparently they did not. Meanwhile, after their demise we humans evolved intelligence in less than 66 million years.....and basically from impact surviving "rats" at that.

I don't think there's a very simple explanation. The way evolution works is actually a pretty complex question...

But dinosaurs developed a range of intelligence levels, as mammals have. Birds belong to the dinosaur clade, and the corvids (crow family) are comparatively smart...

It may seem self-evident that it's better to have a larger, more intelligent brain. But it's not actually that simple. One downside of a large brain is that brain tissue requires a serious investment of energy.

Whether or not a larger brain provides an evolutionary advantage depends on factors like the environment an animal lives in and the sorts of things it can eat.

The primate brain, along with the primate hand, are adaptations for fast movement in forest canopies, and a varied, omnivorous diet — including things which move quickly and are challenging to catch, such as insects...

[Noclevername]

Not to mention, the vast majority of evolutionary lines and branches did not and do not lead to brains of any kind. So if one pre-Cambrian ancestor had zigged instead of zagged, intelligence of any degree might not have ever been.

ADDED: And perhaps THAT is the solution to the Fermi "paradox".

[Van Rijn]

There may be a simple explanation but why didn't the dinosaurs develop intelligence? They had 150 million years to evolve "better" brains but apparently they did not. Meanwhile, after their demise we humans evolved intelligence in less than 66 million years.....and basically from impact surviving "rats" at that.

This gets into speculation, but there has been an argument that, given the length of time and limitations of the fossil record, there could have been a large brained, tool using, and technological dinosaur species without it being found by us. So we can’t make an absolute assumption about brain size or ability of possible dinosaur species.

There was even a short story based on this written by a scientist, but I forgot the story title.

*spoiler* I’m going to lay out the plot below. Consider yourself warned:

In the story, some scientists find small amounts of chemicals that don’t break down easily in a layer laid down in the ~60 million year range. There is no known natural process to produce them but they are commonly produced in modern chemical industry. There were a few more hints, but the characters realize that almost all explicit signs of technology similar to ours would have been worn down by geological processes over that time, and few bodies would fossilize properly even for a common species. Then, the main character happens to read a recent article finding an anomalous uranium isotope in the same layer, with a half-life of millions of years, so it couldn’t have existed as long as the Earth, but is produced by fission explosions and a detectable amount could have lasted for 60 million years. They realize the ancients probably had a war, not necessarily killing them all directly, but something they could never properly recover from, leading to eventual extinction. Naturally, while the main character reads this science article, he hears news of a growing world crisis involving North Korea.

[Grant Hatch]

It's a long article. Can you please tell me which are the relevant passages and citations?

Really.,..? I read it in a few minutes...

[Colin Robinson]

This gets into speculation, but there has been an argument that, given the length of time and limitations of the fossil record, there could have been a large brained, tool using, and technological dinosaur species without it being found by us. So we can’t make an absolute assumption about brain size or ability of possible dinosaur species.

There was even a short story based on this written by a scientist, but I forgot the story title.

*spoiler* I’m going to lay out the plot below. Consider yourself warned:

In the story, some scientists find small amounts of chemicals that don’t break down easily in a layer laid down in the ~60 million year range. There is no known natural process to produce them but they are commonly produced in modern chemical industry. There were a few more hints, but the characters realize that almost all explicit signs of technology similar to ours would have been worn down by geological processes over that time, and few bodies would fossilize properly even for a common species. Then, the main character happens to read a recent article finding an anomalous uranium isotope in the same layer, with a half-life of millions of years, so it couldn’t have existed as long as the Earth, but is produced by fission explosions and a detectable amount could have lasted for 60 million years. They realize the ancients probably had a war, not necessarily killing them all directly, but something they could never properly recover from, leading to eventual extinction. Naturally, while the main character reads this science article, he hears news of a growing world crisis involving North Korea.

That line of speculation is sometimes called the "Silurian hypothesis", which Wikipedia has a page about.

[Noclevername]

Really.,..? I read it in a few minutes...

Could you, please, tell me anyway? What part of the linked page is the relevant part. A simple quote or short description would be fine.

[Grant Hatch]

Who's to say that dinosaurs did not have a species that became intelligent before their demise? We are working from a very small sample if we're talking bones. If dino became intelligent in the last 100 thousand years of its existence it would be a vanishingly small percentage of the geologic record of dino's.

[Colin Robinson]

Not to mention, the vast majority of evolutionary lines and branches did not and do not lead to brains of any kind. So if one pre-Cambrian ancestor had zigged instead of zagged, intelligence of any degree might not have ever been.

Yes, brains are only found in the metazoans, the multi-celled animals. Then again, it's hard to see what use a brain would be to something without muscles and a digestive tract, such as a plant or a fungus.

ADDED: And perhaps THAT is the solution to the Fermi "paradox".

It's a possible solution. One of many...

Judging by the fossil record (admittedly incomplete), the emergence of multi-celled animals is seems to have happened exactly once here on Earth. Interstellar colonisation (either from Earth or to Earth), appears to have happened here exactly zero times.

Comparing those numbers, I think a more likely resolution of the Fermi paradox is that interstellar colonisation is extremely difficult to do. Even for the brainiest of multi-celled animals.

This could either be because of the difficulty of interstellar travel, as you mentioned earlier today; or because interstellar colonies (if and when attempted) typically fail to take root in a to-them exotic environment.

[Grant Hatch]

Could you, please, tell me anyway? What part of the linked page is the relevant part. A simple quote or short description would be fine.

NO... I don't think the article's are able to be reduced too a "quote", or fully understood in such a shortened manner.... sorry

[Noclevername]

Mammals and dinosaurs are both vertebrates from the same root lines of development. We both started out with brains already installed and built on that, we inherited them. But there's plenty of life that doesn't.

Evolution throws anything at the proverbial wall to see what sticks, and most of it doesn't. The majority of random mutations are useless, limiting, or dangerous to their hosts, and are not successfully passed on. Basically, filtered chaos. The patterns that result are not necessarily going to lead to intelligence all the time. Run life over again and it may take a totally different direction.

Again, we can't extrapolate from a sample of one. We literally don't have any basis to determine the frequency that life becomes complex and smart. There's no other living worlds to compare ourselves to.

[Noclevername]

NO... I don't think the article's are able to be reduced too a "quote", or fully understood in such a shortened manner.... sorry

Then how is it a useful citation?

OK, never mind. Then could you give me the source material and I'll research it myself.

[Noclevername]

It's a possible solution. One of many...

That's the trouble. We have an infinite number of solutions in search of a problem.

Judging by the fossil record (admittedly incomplete), the emergence of multi-celled animals is seems to have happened exactly once here on Earth. Interstellar colonisation (either from Earth or to Earth), appears to have happened here exactly zero times.

Comparing those numbers, I think a more likely resolution of the Fermi paradox is that interstellar colonisation is extremely difficult to do. Even for the brainiest of multi-celled animals.

This could either be because of the difficulty of interstellar travel, as you mentioned earlier today; or because interstellar colonies (if and when attempted) typically fail to take root in a to-them exotic environment.

I think regarding environments, a society that builds starships will almost certainly have developed the capacity to live in artificial ecologies, with planets being optional.

[Grant Hatch]

Many in the field now believe that life is a natural consequence of star formation...... arising in the hinterlands, the "debris" cloud that orbits the newly formed star. If it has the water and chems and energy, life would seem to follow.... unless we have an anomalous solar system which is unique in the galaxy.

[Grant Hatch]

Then how is it a useful citation?

OK, never mind. Then could you give me the source material and I'll research it myself.

Are you kidding me? Click on the shortcuts and start reading if you like.... Sorry.... I may not understand you

[Colin Robinson]

That's the trouble. We have an infinite number of solutions in search of a problem.




I think regarding environments, a society that builds starships will almost certainly have developed the capacity to live in artificial ecologies, with planets being optional.

Why do you think that's almost certain?

Do you think artificial ecologies would have a life-expectancy, a use-by date? Or would they be immortal?

[Noclevername]

Many in the field now believe that life is a natural consequence of star formation...... arising in the hinterlands, the "debris" cloud that orbits the newly formed star. If it has the water and chems and energy, life would seem to follow.... unless we have an anomalous solar system which is unique in the galaxy.

The building blocks of life aren't life. Complex organic molecules form in space, but they only came together to self replicate in a liquid-water environment.

[Noclevername]

Why do you think that's almost certain?

If they have built and fueled starships repeatedly for colonies, they have to have a more-than-one-planet economy and well developed space infrastructure. Added to that, they're travelers, so there's reason to think they'd also have spread through the resulting potential habitats in space. Plus at minimum, the ecosystem needed to keep the would-be colonists alive during the mission.

Do you think artificial ecologies would have a life-expectancy, a use-by date? Or would they be immortal?

All artificial environments are a gamble. So they need multiple redundancy to avoid a single point of failure. A city doesn't just consist of one building. Collectively, with the proper established infrastructure of replacement, space habitats may have a potentially indefinite continuity of population.

[Colin Robinson]

If they have built and fueled starships repeatedly for colonies, they have to have a more-than-one-planet economy and well developed space infrastructure. Added to that, they're travelers, so there's reason to think they'd also have spread through the resulting potential habitats in space. Plus at minimum, the ecosystem needed to keep the would-be colonists alive during the mission.




All artificial environments are a gamble. So they need multiple redundancy to avoid a single point of failure. A city doesn't just consist of one building. Collectively, with the proper established infrastructure of replacement, space habitats may have a potentially indefinite continuity of population.

It's one thing to say that, but it's another thing to demonstrate its feasibility in practice. That hasn't happened. Has it?

[Grant Hatch]

I would like to respond...though the question was directed at NoClev.... perhaps he is referring to the innumerable artificial enclosed environments which a tech race would neccessarily produced Before a starship....

[Colin Robinson]

I would like to respond...though the question was directed at NoClev.... perhaps he is referring to the innumerable artificial enclosed environments which a tech race would neccessarily produced Before a starship....

What if the stability of natural eco-systems is due to their diversity? Millions of species interacting... Can a smarter-than-average ape create an artificial enclosed environment with similar stability?