Sending Extraterrestrial Messages
Suppose astronomers wanted to send a message to an alien
civilization that is living on a planet with an atmosphere very similar
to that of Earth's. This message must travel through space, make it
through the other planet's atmosphere, and be noticeable to the residents
of that planet. What band of the electromagnetic spectrum might be best
for this message, and why?
Someone already said radio waves, more specifically FM and TV waves and
gave their reasoning. I totally agree with that persons answer. However, I
am having a hard time now coming up with an answer of my own. Is there any
other correct answers?
There is not a single simple answer to your question. An extra terrestrial
civilization capable of attempting to make contact with Earth would have
to contend with a number of problems similar to what the SETI project has
to. Atmospheric transparency probably is not very important since they (or
we) could send a message from a satellite in orbit above the atmosphere.
Our "partner in space" would need to be closer than the age of the Earth
because otherwise they would not know we even existed. This is a very
liberal distance because it does not assume that the signal is the result
of a "human intelligence", only that it is consistent with potential life.
A more restrictive limit would be only a couple of hundred light years. On
the other hand, we might not be their only target. This would mean that
the "Hello" message signal would have to be distinguishable by any
conceivable civilization, otherwise, it would not be distinguishable from
galactic "noise". What such a signal might be is an interesting question
itself. The transmission frequency would have to be in a relatively
noise-free region of the electromagnetic spectrum. It is also geo-centric
to assume that such a civilization has not found a way to harness, let us
say neutrino signals, which we Earthlings would have a difficult time
identifying with current technology. I do not think there is a single
"correct" answer to all the possibilities.
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Update: June 2012