The Truth is Out There

Hardware freaks who cant think of anything original to say

The SETI@Home Project
Many of you may have asked, just what is the SETI@Home Project?  Why do they need our help in this project? and What are we analyzing when we process a work unit?  In this episode, I will give a brief explanation on just what the SETI@Home Project is all about.  Most of this information is taken from the SETI@Home website.

Where do we look?
Many of you may have ventured out at night and looked up at a starry sky and wondered...Is there anyone else out there?  There have been many estimations on the probability of other, Extraterrestrial, life in the universe.  I wont go into the calculations, but you can find more info here.  From the calculations, though, it is thought that the number of intelligent communicating civilizations in the galaxy equals the number of years such a civilization.  The Earth has had the ability to communicate outside of our planet for about 50 years.....taking that number, there are at least 50 intelligent communicating civilizations in the universe.  If the lifetime of a communicative civilization is larger, than the number of them would be the same.......that number could be very very large.

The probability of an extraterrestrial civilization sending signal specifically meant for other civilizations to hear would be pretty small.  Most likely, any type of signal from a civilization would come from their every day communications with each other.  Here on Earth, we have a variety of signals that escape into space.  TV, radio, microwave communications, broadband/narrowband cellular, search radars, and other forms of communication escape through our atmosphere and into space every day.  The earliest communication that has leaked from Earth date back only 50 years.  The Earth's communication "bubble" would have only leaked to a sphere 50 light-years from the earth.  Not quite a large area relative to the universe, but other older civilizations would have a communication bubble the size of their communication lifetime, which may be very large. 

If we are to look for a signal from such a civilization, just where and how do we look for it?  When you look up at the night sky, you can only see the visible spectrum.  But if you cant see it, that doesn't mean that it isn't there!  The visible spectrum is a very small part of the overall electro-magnetic spectrum.  Communication can come from just about any part of the electro-magnetic spectrum.  The problem is that many of those frequencies do not travel well in space....another problem is the detection of such a signal from a ground based observatory on Earth.  

Radio waves are one of the best ways to communicate.  Radio wave transmitters are cheap to produce, information transfer is easy, and the equipment to receive that info is easy and cheap to make. Radio waves also disperse in all directions making it easy to communicate with many different people in any direction, finally these radio waves travel as fast as you can get....the speed of light.  Since it is one of the most efficient ways to communicate here on Earth, other civilizations may have came to the same conclusion.  

Radio Waves...OK....but narrow it down a bit?
Well....OK we picked radio waves....but what frequency?  Well you don't want to choose your favorite FM radio frequency.  Yes some of the music sounds strange and "other worldly" but would be bad to use in a search for ET.  You don't want to scan too large of a range of frequency, would take too long......picking a range which there is low background noise would be a bonus.

There happens to be a narrow range of frequencies that has low background noise, and are particularly significant.  In the radio portion of the electro-magnetic spectrum there is a narrow region that has quite a low background, and this is from around 1000 to 10,000 MHz.  At lower frequencies, there is a lot of noise from space itself, at higher frequencies there is a lot of noise from Earth based transmitters (and the atmosphere).  

Of particular interest within this region, there are two "universal" frequencies.  These are the frequency bands for hydrogen gas (H₂ -1420 MHz) and the hydroxyl group (-OH - 1640 MHz).  Of course a combination of the two produces water (H₂0), which many consider to be essential for life!  Other civilizations may also recognize the importance of these two frequencies, and may send signals that are around these frequencies.  There is low background noise around this area, and the chance of picking up an Earth based signal around these frequencies are low because, by international agreement, no one is allowed to produce broadcasts between 1420 MHz and 1427 MHz.

How Do We Listen?
Answer is simple.....get the biggest dish you can find (and overclock it! ;-).  Well the biggest dish on Earth is the Arecibo Radio Telescope.  The Aricebo telescope is sort of fixed, because it is fitted into a natural depression in the Earth.  I say "sort of" because the receivers are on a track platform above the dish, and can be moved.  Because of this the telescope can look at objects as far as 20 degrees away from directly overhead.  The receivers on the platform can track across the sky and follow objects as the Earth moves.  

The receiver on the telescope records ("listens") over a band of frequencies.  The receiver isn't doing any detection of signals....it just listens, and records what it is listening to.  The SETI@Home project, doesn't have a solid fixed time on the telescope, but it sort of "piggybacks" while other researchers are using the telescope.  When the telescope is being used, the SETI receiver sort of goes along for the ride, listening to what is happening while the other researchers point the telescope and goes about their business.  The receivers aren't on all the time, some experiments need extreme sensitivities, and during some of these experiments the SETI receivers are turned off, to prevent any interference from the receivers.

While the receivers do the listening for the project, it is up to us home-based SETI@Home members to do the detection for them!  In the next few episodes, I will try to explain just how we are doing that!

Information used for this episode was primarily taken from the SETI@Home website.  If you want more information take a look at these two links:
About SETI
SETI: The Radio Search

-Lamb Chop Home