If extraterrestrial aliens are common, why aren't they obvious?

klaatu · 12-10-2009, 01:22 AM

This is the

and is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations.

If

Rare_Earth_hypothesis

is to be taken in account then there are very few planets in the Universe with same complex factors occurring making life possible.

The

Mediocrity_principle

is saying the opposite. Earth is nothing special as we are nothing special. (as an antithesis to Rare Earth theory)

Lets be pessimistic and say Rare Earth Theory is valid and the factors making life possible are so many that even if known Universe is so big (numbers of planets is so big) still remains few chances for life to occur.

But this is based on an assumption from the beginning. That life on other planets is similar to ours!

So in pessimistic scenario there are few chances in Universe for planets with life similar to ours but there are many chances for planets with life different than ours, life that obviously needs other parameters to occur than in our case.
So we again come to a reasonable good number.

Here we might run into some problem. Time can separate us more than the space is doing (or in the same time depends how you look). Many civilizations could exist but in different times than ours thus no chance in meeting them.

But this needs to be completed with another crucial factor: does alien extraterrestrial beings want to contact us?
Looking on how we are doing I might think they will expect for us to "grow up" a little and then to knock on the door.

12-10-2009, 01:22 AM	#1
klaatu Vox Moderator Human Join Date: Feb 2009 Posts: 199 Time Online: 3 h 22 m Thanks: 8 Thx 18 Times in 18 Posts	If extraterrestrial aliens are common, why aren't they obvious? This is the Wikipedia (Links) Fermi_paradox and is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. If Rare Earth hypothesis - Wikipedia, the free encyclopedia Rare_Earth_hypothesis is to be taken in account then there are very few planets in the Universe with same complex factors occurring making life possible. The Mediocrity principle - Wikipedia, the free encyclopedia Mediocrity_principle is saying the opposite. Earth is nothing special as we are nothing special. (as an antithesis to Rare Earth theory) Lets be pessimistic and say Rare Earth Theory is valid and the factors making life possible are so many that even if known Universe is so big (numbers of planets is so big) still remains few chances for life to occur. But this is based on an assumption from the beginning. That life on other planets is similar to ours! So in pessimistic scenario there are few chances in Universe for planets with life similar to ours but there are many chances for planets with life different than ours, life that obviously needs other parameters to occur than in our case. So we again come to a reasonable good number. Here we might run into some problem. Time can separate us more than the space is doing (or in the same time depends how you look). Many civilizations could exist but in different times than ours thus no chance in meeting them. But this needs to be completed with another crucial factor: does alien extraterrestrial beings want to contact us? Looking on how we are doing I might think they will expect for us to "grow up" a little and then to knock on the door. __________________ "Unless we have come to know what is correct, we cannot perceive what is incorrect." Words processed in a facility that contains nuts. Last edited by klaatu; 12-10-2009 at 01:26 AM.