Search for Extraterrestrial Religion

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Extraterrestrial Civilizations

When for a message that may be received by SETI an important consideration is the type of civilization that is likely to be communicating. I approach this question by estimating the number of civilizations that might be out there and the distances between them. This tells us if they are close enough to communicate. If they can communicate with us, what does this tell us about them?

It turns out that only long-lived civilizations can communicate. At present, our experience tells us that religion has provided the stability required for a civilization to achieve a long lifetime. Unless some alternative source of stability has been found, we should expect that extraterrestrial religion will strongly influence the type of extraterrestrial communications we might receive And it is possible that science will provide the basis for a stable extraterrestrial religion.

The probability of planetary civilizations forming can be calculated and the average number existing at any one time will depend on their average lifetime. An optimistic set of assumptions for the Milky Way gives the following estimates:

    Civilization Lifetime, years    Number of Civilizations  

    300                                    30

       10,000                                 1,000

  1,000,000                              100,000

10,000,000                            1,000,000

  In turn, if the civilizations are distributed uniformly in the Galaxy, further calculation shows that their average separation in light-years will be as follows:

    Number of Civilizations           Average Separation, L-y

                    30                             16,180

               1,000                               2,802  

           100,000                                  438

1,000,000                                  199

To communicate, civilizations must be no further from another civilization than twice their lifetime, otherwise signals will still be on their way after the civilization has expired. Civilizations with lifetimes of 300 years are not going to be able to communicate. They cannot wait 12,000 years for a reply. I don't think even lifetimes of 10,000 years are much help. There is a wait of 3,600 years for a reply, and time for just two calls. Communication is improbable, but it is possible.

Only for lifetimes above 1 million years do round-trip times make sense, and then patient waiting for a reply is needed.

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