Friday, August 19, 2005

Fermi Paradox

Why have we not yet received communication from outer space?
There are two main theories - one is the rare earth theory - one that in its more extreme forms uses the anthropological principle combined potentially with the concept of multiple universes.

The second theory is "phase transition" which argues there has not been enough time for aliens to reach us. The problem with this theory is that if there is anyone else in the galaxy it is likely they are only about 50 million light years from us. BUT it is hard to argue that if lets say mammals not dinosaurs had taken off 265 million years ago we could not - all things going right - have had 65 million years of mammal evolution and be 200 million years ahead of where we are now.
Furthermore humans will be visible to all other aliens in the galaxy of similar technology if not now then in a few hundred years and we will be able to see them also. It won’t be long after that that we can detect planets that have life in the solar system.

This means that if there are aliens that are more advanced than us they are already on their way sending either a message or a ship. But even this underestimates the aliens.

If you were an alien race exploring space you would probably not wait for the light signal - you would probably send a space ship to every plausible planet and investigate it for resources, colonization, communication or other purposes. This would mean there would be a wave heading out from any race more than 1000 odd years ahead of current humans going not too far from the speed of light investigating planets sending back signals etc. there would be little point hiding from a more primitive species so you would probably notice these ships besides the concern would be meeting a more advanced and dangerous species - one where you would want warning and a "buffer zone" where the speed of light limitation would give you time to devise a strategy.

The fact we have not noticed anything like this indicates there is nothing we will be able to see in space that is more advanced than us (there could be a lag of lets say 1000 years plus some function of the distance of course but in the big scheme of things this is not much).

The Phase transition theory is supported by the Carter-Rees arguments in that In temporal terms, it is the interval 9.3* 10^9 years ago to 1000 x 10^9 in the future that is a valid time in which life can evolve - this means we are quite near the beginning of this period and could have out run the other species in fact the Carter-Rees argument implies we have indeed done that. or more weakly the principle of mediocraty implies we should not assume we are specially lucky.


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