The science behind the probability of extraterrestrials

[Odin]

Originally posted by Immortal Wombat
That's nads, Odin. The belief that sentience is common in the universe doesn't imply purpose, it just implies that it is a successful adaptive strategy. Given enough time, it might be the most successful strategy, because it completely removes the species into environments it has more control over.

Every species is the end result of a long line of improbable events. Ok, so sentience is not inevitable, but I think intelligence is a viable, good, strategy which evolution will take wherever there is life. On earth that led to sentience pretty quickly, and to say that that event was the unlikeliest of all is far more victorian arrogance than the suggestion that sentience is everywhere and that humanity is not special.

If we played the tape twice (moving one snail two feet to the left to satisfy Laplace) from the Cambrian, of course we probably wouldn't have humans, nor even vertebrates as they are now. But I think we would have terrestrial, air breathing animals with an organ of some kind which processes sensory data and controls behaviour. It isn't a stretch from there to intelligence, providing that the ecological conditions favour it.

If it was such a great adaptave stratagy it would of evolved long ago. I think to have evolve sentience, an organism must have this set of things:

1. Complex social structure, ecourages larger brains size. In primates, more social species have larger brains relative to body size than more solitary species.

2. Omnivorous diet. More specialized diets rely less on brain power and more on instinct

3. Dextrous appendages freed from being used for locomotion. Needed for tool making to be possible, and is why dolphins will never evolve sentience.

4. Must be a generalist

5. There must be no strucural limitations on brain expansion.





I am not saying we are unique, I am just saying we shouln't assume sentience should be common just because Sagan said so. My guess is that there is a few dozen other sentient species in our galaxy, and they definitly won't resemble the humanoid creatures in the movies.

[Immortal Wombat]

Originally posted by Odin
If it was such a great adaptave stratagy it would of evolved long ago.

I said intelligence was, not sentience. Anyway, it might well have evolved a long time ago, except that the highly intelligent velociraptors didn't need to use tools, and so left no trace or their highly complex oral tradition.

1. Complex social structure, ecourages larger brains size. In primates, more social species have larger brains relative to body size than more solitary species.

2. Omnivorous diet. More specialized diets rely less on brain power and more on instinct

3. Dextrous appendages freed from being used for locomotion. Needed for tool making to be possible, and is why dolphins will never evolve sentience.

4. Must be a generalist

5. There must be no strucural limitations on brain expansion.

I am inclined to agree with you. I think 1, 2, and 4 are probably closely related, (diet being the major limitation on niche specialisation, and an important factor in social structures as well) although becoming sentient and reliant on tools by definition immediately stops a species being a generalist. I don't think being able to use tools is necessarily the only route to intelligence, and I don't think that dextrous appendages are the only route to tools, but ok.

I think sentience is a sufficiently generalised archetype that given enough time will evolve on any planet with corporeal lifeforms. And usually only once.

[MichaeltheGreat]

Originally posted by pchang
MtG's likely sounding premise is:

The universe is really, really, really big!!!!!!!!!!!!

Billyuns and billyuns.

Still, when you're dealing with sample sizes in the range of > 10^21, it's a little odd to talk about how rare something might be.

[MichaeltheGreat]

Originally posted by Odin
5. There must be no strucural limitations on brain expansion.

We don't have that. The structural limitation is the female pelvis.

[MrFun]

Originally posted by Odin
The people who think intelligent life is common are deluding themselves. If we played the tape twice (to take a phrase from S. J. Gould) the chance that sentience would evolve again is slim. The belief that sentience is common in the universe, to me, is an rediculous extension of the arrogant victorian idea that sentience, and by extension humankind, was predestined to evolve and that we were somehow the purpose of evolution. The people who believe scentience is common tend to be physicists and astronomers who naively think that sentience will automatically emerge once you have life, obviously showing thier ignorance of biology.

We are the end result of a long line of improbable events and luck. There was a good chance that the Snowball Earth of the late Precambrian could have snuffed out animal life early on. If the Permian extiction would been just a little bit worse it would of wiped out all multicellular life. It was just dumb luck that the same reorganization of the jaw joint that happened at the transition between mammal-like reptiles and true mammals that left the lower jaw as a single sturdy bone also resulted in a change in the braincase that allowed an increase in brain size without destabilizing the jaw joint (which is why the smartest dinosaur, Troodon, was an idiot compared to the early therian mammals that it ate). If the modern ice ages had not happended, Homo would had never emerged from Australopithicus. During that worst part of the second-to last glacial advance 150,000 years ago the population of early H. sapiens was reduced to 8,000. if Africa would of became just as bit drier we would not be here.

Actually, I think the prime example of supreme arrogance is to believe that sentient life is very unlikely elsewhere in the universe -- "we are soooo special -- look at ourselves -- we are the only intelligent life in the whole universe."

[Dr Strangelove]

Originally posted by Immortal Wombat

A large amount of earth's atmosphere's apparent suitableness for life was driven to balance by life itself. The photosynthetic microbes which pumped all the nasty toxic oxygen into the atmosphere probably caused a mass extinction. It was those harsh and eminently unsuitable conditions which led to the first eukaryotes' success. It is possible that a wide range of atmospheres will allow the development of the kind of life which leads to "perfect" oxygen/nitrogen/CO2 atmospheres.

True,but the elements have to be present. A number of planets in this solar system lack sufficient quantities of one or more of the basic elements necessary.

It is fortuitous that in Europa we have a reasonably good test case for many of these variables- size, atmosphere, proximity to the sun.

If that's your idea of close to the sun remind me never to take you up on an invitation to go on a summer vacation.

[Lancer]

If you sit a monkey at a keyboard sooner or later he'll type 'Henry the VIII I am, or, 'this thread is toast'.
So it is with intelegent live evolving. If you have enough monkeys and keyboards (the size of the universe) and billions of years for them to type away in, you'll get War and Peace a few times if that's the chance of intelegent life. Or, the chance might be that all that needs to be typed is 'The science behind the probability of extraterrestrials', in which case there's life everywhere.

However, shouldn't SETI have heard something by now if intellegent life was very common?

[pchang]

SETI has only been able to sample a very small portion of our galaxy. In addition, that intelligence would have had to be communicating with radio waves for us to hear it. The time when a civilization uses radio waves to communicate could be a vairly small time window. We are moving towards systems with less and less loss out to space.

[Lancer]

pchang , have we tried beaming lasers at other stars or any other type of communication? How about recieving light signals. They would travel faster than radio waves, yes?

[Dauphin]

They all travel at the speed of light.

We have directed some stuff at other planets, but I really wouldn't expect a response to such limited activities.

[Mordoch]

Originally posted by Odin
If the modern ice ages had not happended, Homo would had never emerged from Australopithicus. During that worst part of the second-to last glacial advance 150,000 years ago the population of early H. sapiens was reduced to 8,000. if Africa would of became just as bit drier we would not be here.

This last example is actually a pretty lousy one here in my view. Why H. Sapiens may have been in trouble, Neandertals were doing fine during the same period. By current definitions Neandertals would qualify as intelligent life, and created fairly sophisticated tools. At least in my view, Neandertals were also at a point where on their own they would have evolved to become more intelligent eventually. Especially once the last ice age ended, a Neandertal with more sophisticated tool usage capabilities or other aspects of intelligence would have had an evolutionary edge. While the intelligent life on this planet would have been different, it still would have existed. You can take the "exact circumstances" needed to create intelligent life too far.

[Dr Strangelove]

Originally posted by pchang
SETI has only been able to sample a very small portion of our galaxy. In addition, that intelligence would have had to be communicating with radio waves for us to hear it. The time when a civilization uses radio waves to communicate could be a vairly small time window. We are moving towards systems with less and less loss out to space.

How powerful would our signals have to be to not get lost in the background EM noise at 50 light years, 100 light years, 500 light years or 1000 light years? How powerful would their signals have to be for us to pick them out of the background at those distances? It's one thing to use signal analysis to try to pick out patterns from the noise, but that noise is being generated from the activity of stars. The signals broadcast by stars are vastly more powerful than any we could ever hope to generate. If an alien culture 100 light years away broadcast signals of approximately the same power as ours would they even register on our instruments? How powerful would those signals have to be in order to stand out from the noise of the stars.

[Dauphin]

The total radio transmissions we put out into space are about the same or more than overal radio emissions from our sun.

If you choose the right frequency, something like the Arecibo antenna can detect signals above the background noise from 100 light years, possibly up to 1,000.

[Dr Strangelove]

Originally posted by Dauphin
The total radio transmissions we put out into space are about the same or more than overal radio emissions from our sun.

I find that difficult to believe.

If you choose the right frequency, something like the Arecibo antenna can detect signals above the background noise from 100 light years, possibly up to 1,000.

The total radio transmissions from every piece of radio broadcast equipment on the planet is distributed amongst a broad range of frequencies. If you compressed all of their signals into one band you'd probably have random garbage that would be difficult to distinguish from star noise and other background cosmic radio signals. In order for someone from a distant star to distinguish the signals that we make from the background he's going to have to narrow his reception down to one source or relatively few sources in order to determine that the signal has an orderliness to it imposed by an intelligent broadcaster.

[pchang]

Actually no. Our signals are very easy to distinguish from the background noise. Of course, we know what to look for since we made the signals in the first place.