A Poll

Gold Barz

Oh crap, two of the smartest voted for 0 and 5-10, and here I am saying at least 50.

Chronos, are you saying that the average galaxy will produce about 100 alien civilizations in total?, really man the number seems really really small to me.

GerdankenDonuts

While it is correctly classified as speculation, it is reasonable and informed speculation that lies behind the "rare earth" hypothesis. Although I would really very much like to be wrong, I would have to put my money on zero technological civilizations (besides us) in the Milky Way.

To quote one review (The Library Journal) of the text by Peter Ward and David Brownlee:

"Ward and Brownlee attribute Earth's evolutionary achievements to the following critical factors: our optimal distance from the sun, the positive effects of the moon's gravity on our climate, plate tectonics and continental drift, the right types of metals and elements, ample liquid water, maintainance of the correct amount of internal heat to keep surface temperatures within a habitable range, and a gaseous planet the size of Jupiter to shield Earth from catastrophic meteoric bombardment."

Gold Barz

I think Rare Earth is too pessimistic, I heard one of the authors was a creationist?, I dont think intelligent life is abundant but I also dont think its just us though.

GerdankenDonuts

Hi GB,

No neither author is a creationist, they are in fact two very respected scientists as I have gathered. Ward is a paleontologist and Brownlee an astronomer (errata: it is not David but Donald Brownlee that I was referring to). One of their arguments was informed by conversations with Guillermo Gonzalez, an assistant professor of astronomy at Iowa State. Ward and Brownlee were unaware of his role as a strong advocate of ID at the time of those conversations, as I recall. Nonetheless, their discussions incuded a large range of legitimate and well known scientists from many fields related to astrobiology.

I agree that it is pessimistic but there is nothing unreasonable, at least in my opinion, in the things that they point to that are probably important for complex organisms to develop ... and if you agree that all these factors are important then it is quite possible that the product of their associated probabilities could be much much smaller than the number of solar systems in our galactic habitable zone.

Gold Barz

Doesnt that book Life Everywhere by David Darling debunks or at least minimizes some of their points.

Anyways, I think it would be somewhere in between Rare Earth and Life Everywhere.

Here is the link about one of the authors being a creationist.

http://www.findarticles.com/p/articl...25/ai_79794362

GerdankenDonuts

I think I read a critique of rare earth in an article by Darling but don't recall the specifics, I will have to pick up his book and take a look. His main critique seems to be based on guilt by association. I don't recall them crediting Gonzalez (the blatant ID'er) with the seemingly overwhelming influence on their treatise that is claimed by Darling though it is something that can probably be checked relatively easily. Granted that the conclusions give support to Gonzalez's theistic viewpoint but I think despite that (actually it should be irrelevant if examined objectively, right?) the arguments made by W and B are not unreasonable.

Also, I'm not sure that I agree that they are using circular reasoning ... they are picking factors that appear to be important in the development of complex life for reasons based on the historical record of life on this planet and current biochemistry and physics. Of course it is wrong to argue from ignorance -that since we cannot think of another way complex organisms can develop there probably isn't another way- but I think that W and B try to make the case that it is likely that there are certain hurdles in the evolution of animals that, no matter how they are overcome, would be common to all histories based on what we think must be available to such organisms.

Finally, I think that it really is a testable hypothesis in principle, maybe to some extent even within our lifetimes if we can find enough potentially habitable earthlike planets and can take enough spectra of their atmospheres. Of course SETI can falsify the RE position quite quickly if they are out there and we are lucky enough to detect them.

Anyway, I am glad you mentioned Darling's book and I look forward to checking it out. As I have said before, I would love for the RE hypothesis to be wrong and I run SETI@home on a couple of machines due to a glimmer of hope that Darling's position is closer to reality.