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The Fermi Paradox

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Re: The Fermi Paradox

#121

Post by rjsw »

DavidSJ wrote: post #28
keithnoizu wrote: post #25

Earlier quoted context omitted.

There is actually a pretty good explanation for it in my opinion, that it takes about this long since the big bang for life forms of our complexity to exist. (meaning our planet was seeded at some point with some primitive life forms that than continued on their evolutionary tracks towards this point in time). So you have many planets starting to get to the point where space exploration on a wide scale is feasible. M…

There is actually a pretty good explanation for it in my opinion, that it takes about this long since the big bang for life forms of our complexity to exist. (meaning our planet was seeded at some point with some primitive life forms that than continued on their evolutionary tracks towards this point in time). Interstellar seeding is not required to believe that complex life becomes possible at approximately the same…

Frequency of big meteorite impacts probably becomes less over time too.

Re: The Fermi Paradox

#122

Post by SideburnsOfDoom »

darkmighty wrote: post #95
kijin wrote: post #86

Earlier quoted context omitted.

That depends on the average lifespan of the species in question, as well as the stability of their civilization. If you only live 100 years and your society will be unrecognizable after 500 years, it's obviously foolish to embark on a project that will turn a profit 1000 years later. If you can live 1M years and your civilization has been more or less stable for 10M years, you can probably afford to wait 10K years fo…

Wow, that redwood 100+ years investment sounds interesting. Do you have a link? I have to show that to my economist friend... or save it to win an argument some time from now :)

Given a large payoff in 100 (or more) years time for a small investment now, it doesn't seem that hard to create a financial instrument that pays out a potion of the projected profits adjusted for risk, for each year that you hold it.

Re: The Fermi Paradox

#123

Post by rwallace »

XorNot wrote: post #39
nhaehnle wrote: post #29

Earlier quoted context omitted.

I often wonder this as well. The speed of light isn't really a physical limit to expansion - generation ships are theoretically possible. It may just be that the Great Filter takes the form of relatively benign[1] economic and/or sociological obstacles. At least, if you take a diff between typical beliefs at the time the Fermi Paradox was formulated vs. typical beliefs now, I would say the experience of the shutting…

If you consider the declining birth rates of modern nations as the standard of living goes up, then it stands to reason that once a civilization reaches the point where it might be able to engage in large scale space exploration, the population that can do so has become relatively stable. So you simply never (or rarely) get exponential cosmic expansion. There might be a few billions of that race roaming the stars, bu…

But declining birth rates don't lead to stable populations, they lead to shrinking populations. So if we don't manage to restore birth rates, this would be an example of 'Great Filter ahead of us'.

Re: The Fermi Paradox

#124

Post by rwallace »

Lrigikithumer wrote: post #97
ScottBurson wrote: post #17

How about this possibility: the Great Filter is now! We entered it, perhaps, when we developed sufficient collective nuclear weapons capability to wipe out most or all human life; we won't be out of it until the major threats our civilization poses to the biosphere have been resolved.

A lot of people consider nuclear annihilation a big threat but I'm not too worried about tbh. I mean if you think about it, every major player has got a trigger to end all life at any given point, doesn't it seem reasonable that at some point you invest a lot of money into systems that can safeguard and prevent this type of catastrophe. I know a lot of people may consider the governments dangerous and selfish but the…

I would like to share your optimism. But then I read about things like the US nuclear launch codes being set to 00000000 for quite a few years, or an incident when survival versus Armageddon depended on the judgment of one man [1], and I have to conclude that human governments should not be in possession of nuclear weapons.

[1] http://en.wikipedia.org/wiki/Stanislav_Petrov

Re: The Fermi Paradox

#125

Post by sampo »

maaku wrote: post #110
sampo wrote: post #20

Earlier quoted context omitted.

The chemical composition of Earth's atmosphere (21% O2) is so far away from a long term chemical equilibrium, that any current astrobiologist would interpret it as a sign of planetary scale life. (And correctly so: the oxygen was produced by life.) So life on Earth is pretty visible from the other planets in our solar system. And spectroscopy to observe the composition of atmospheres of planets orbiting the nearest s…

Meh, it's a long way from saying that "we don't know how the O2 could have been produced except by life" to "the O2 was produced by life." Just look at the current debate about methane on Mars.

In a 1993 article, Carl Sagan considered the atmospheric oxygen content "at least suggestive of biology" (Conclusions, 3rd paragraph).

http://www-pw.physics.uiowa.edu/~dag/publications/1993_ASear...

Re: The Fermi Paradox

#126

Post by sampo »

dennisgorelik wrote: post #117
danieltillett wrote: post #74

Earlier quoted context omitted.

I did explain it in my post, but maybe it was too short. Earth has been kept in the habitable temperature zone over the last 3.5 billion years through falling CO2 levels. Around 3.5 billion years ago the sun provided ~25% less energy than now and the CO2 levels were much higher. This is the green house effect. As the sun got brighter over time the level of CO2 in the atmosphere has fallen. For more on this see the sl…

So some CO2 is needed for plants. It does not make certain CO2 levels a requirement for intelligent life. Change in temperature does not necessarily kill intelligent life either.

At least for the foreseeable future, we still need plants and natural ecosystems to survive on Earth.

Re: The Fermi Paradox

#127

Post by sampo »

danieltillett wrote: post #74
dennisgorelik wrote: post #70

Earlier quoted context omitted.

Why do you think that current CO2 concentration levels are important for intelligent life? Slight adjustment in how body works can easily adapt organism to new CO2 levels.

I did explain it in my post, but maybe it was too short. Earth has been kept in the habitable temperature zone over the last 3.5 billion years through falling CO2 levels. Around 3.5 billion years ago the sun provided ~25% less energy than now and the CO2 levels were much higher. This is the green house effect. As the sun got brighter over time the level of CO2 in the atmosphere has fallen. For more on this see the sl…

C4 photosynthesis is an adaptation to higher temperatures and lower atmospheric CO2. And C4 is a very recent innovation (25 to 32 million years ago, says Wikipedia).

But yeah, I don't know if even the C4 plants could handle 0.01% ambient CO2.

Re: The Fermi Paradox

#128

Post by pilaf »

kowdermeister wrote: post #118

I'm a bit surprised nobody mentioned AI-s taking over as the Great Filter. I'm sure every technical civilization attempts to do that because it's very tempting to accelerate your intelligence by computation. I've also read an interesting article that why probably machine life is more abundant than biological: http://www.popularmechanics.com/how-to/blog/robot-universe-d...

If AIs were taking over left and right we'd still expect to see some kind of evidence of their existence. Since they'd only be replacing biological civilizations I don't think it would count as the Great Filter, not in the context of Fermi's Paradox at least, as you'd end up with roughly the same number of technologically capable civilizations after the filter.

Re: The Fermi Paradox

#129

Post by darkmighty »

danieltillett wrote: post #56
maaku wrote: post #10

The "we are the first" argument seemed less convincing than it could have been. A better argument from that perspective is the observation that Type III civilizations expand at an alarming rate. Whatever the motivation for expansion[1], basic simulations and back of the envelope calculations show that even with technology we could imagine building in the not so distant future, humans could expand into the cosmos at >…

I actually posted about this very topic a few days ago here. Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interest…

Interesting. Just a note: it probably wouldn't seem as if a chunk of the galaxies was removed; in fact, I believe the luminosity (after some settling time) of a start with a Dyson sphere or the like would emit about the same light a regular star does -- the difference would be the temperature. The apparent temperature of the star should increase(?) (i.e. it emits(?) higher entropy radiation): by simple energy conservation, we wouldn't expect the energy to build up indefinitely inside the sphere. Presumable the energy would be used for computation -- so the end result is that the Star's energy is used to compensate Landauer's Principle[1], essentially cooling the computer. So instead maybe we should look for galaxies that are hotter than expected for their brightness/age?

[1] http://en.wikipedia.org/wiki/Landauer%27s_principle

Re: The Fermi Paradox

#130

Post by unoti »

dmix wrote: post #31
bdamm wrote: post #30

Earlier quoted context omitted.

This model assumes that interstellar travel is profitable. There is no evidence that this is the case, even if we had Star Trek technology. If it isn't profitable, then it turns into a drain on the home planet. That isn't sustainable.

Curious: What would make interstellar travel not possible? Do you mean for humans or machines as well?

An interesting analysis on this topic of the feasibility of human space travel was written by Charlie Stross here: http://www.antipope.org/charlie/blog-static/2007/06/the_high...
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