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03 May 2009

While I like SETI@Home...

I have to say that I have always been a fan of SETI@Home. So much so that my wife is constantly giving me shit for running it. Of course, if I sit and analyze what it is that SETI@Home is doing, I have to be totally honest. It's a LONGSHOT to say the least. I know a lot of people will say that we have been broadcasting for over 60 years now. However, something very simple seems to escape a lot of folks: The Inverse Square Law. It applies to any omnidirectional radiation. Our crude radio and TV counts in that.

The longshot of course is that there may be intentional high power transmissions. Of course, the fact that we as a human race have only made a total of 5 transmissions ourselves doesn't speak for there being that great a chance of us finding too much. And those transmissions were all of limited length. They would probably be like a "Wow! signal" to anyone out there that just happened to pick it up.

It is very unlikely that alien civilizations are going to pick up television transmissions according to the table from this site: http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html

Note the range for UHF television (2.5 AU) and the range for the UHF carrier (0.3 LY). Neither estimate is enough to make it out to the nearest star. They don't list a range for VHF television but FM radio is in the middle of the VHF television band and the estimated range for that is 5.4 AU. Again no where near enough to make it to the first star. Let alone out of our own SOLAR SYSTEM!

The optimistic ranges for detecting a nearby planet are based on either massively powerful transmitters or highly focused outputs from large transmitters.

The calculations that I made suggested that one would need an Arecibo sized antennae with a 250,000 watt transmitter to be able to send a detectable signal to a planet as far away as 150 light years.

This is easily with the capability of earth's technology. The Arecibo antennae has only limited steering capability. I think it is mostly constrained by the direction it is pointing as it rotates with the earth so there are lots of potential targets it couldn't be aimed at. The 250,000 watts could be pulsed so that no where near 250,000 watt of continuous power would be required. But will the powers that be that control enough of earth's resources ever feel like funding a major effort to transmit to unknown alien civilizations?

I have wondered about the feasibility of a laser transmitter to reach stars. If the powers that be wanted to dedicate some resources to this idea the authors suggest that we might hit a 1000 light years with a currently feasible optical laser. I think that bumps the stars for which a signal might be detected from about a 1000 that lie within 100 light years to about a 100,000 that lie within a 1000 light years.

The article on the possibility of optical SETI: http://seti.harvard.edu/oseti/tech.pdf

And keep in mind, so far, everything about SETI is privately funded! So don't go on some tangent about wasteful government spending, this is not the place to look.

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