The SETI Search and Computers
From MidWest PC Review, April 1998
On November 16, 1974, a signal was sent to the stars. The Arecibo Interstellar Message was aimed precisely at a globular cluster in M13, 25,000 light years distant. To give you some idea of the distance, consider that in the intervening 24 years, the message is a mere 0.10% of the way there.
The message was arranged just as a picture is painted onto your CRT. It has a very low resolution, something you'd never consider on your PC. It's a mere 73x23 bits (the numbers were chosen partly because they're both prime numbers). This totals only 1,679 bits or just over one and a half kilobits of data. If you compare it to a single ASCII character in your cornputer's memory, the message would fill the space required by only 209 characters or less than three lines of text on your screen. It's not much. But it's all we've intentionally sent toward the stars.
Yet the message contained in that short burst has some interesting information. The top row indicates a binary counting convention and the second row the atomic numbers of the chemical elements hydrogen, carbon, nitrogen, oxygen and phosphorus. Why those? We're made of them.
Then it gets more complex: DNA (nucleotides and the sugar-phosphate backbone), the number of nucleotides in the genes of the creature shown (a crude approximation of a man), even the planetary system around our sun. Finally, at the bottom is the Arecibo radio-telescope, it's wavelength and size. There. Can you manage all that in 1,679 bits?
Computers weren't much in 1974. But sending a signal to the stars is much easier than detecting one passing our way. Yet, it may have been done. And the signal, aptly named the "Wow!" signal was received right here in Ohio. In Delaware, Ohio, is the "Big Ear" radio-telescope, operated by Ohio State. That project, now un-funded, gained a spot in the Guinness Book of World Records. The extra-terrestrial signal was never proven -- nor disproven -- and so we are, it seems, back to square one.
Last summer's blockbuster movie, "Contact", written by Carl Sagan and starring Jodie Foster, may be just what the SETI field needs. This "Search for Extra-Terrestrial Intelligence" is being carried out on a wide range of fronts. And it requires computers, fast computers, that can manipulate receivers to scan wide ranges of frequencies and scan the skies night and day. You've got to be there listening when the first "Hello" comes through. But the questions begs yet another: Is there anyone out there?
N = R* x fp x ne x fl x fi x fc x L
The now-famous "Drake Equation" makes this needle in a haystack search a little more concrete. Let's take a look. N is the number of communicating civilizations that the Milky Way has to offer. That's what we're looking for. Who's calling? The formula to get at it requires that we consider suitable stars (R*), those stars with planets (fp), those planets which are earth-like (ne), and the fraction of those planets that develop life.
B u t we're not there yet. How many of those planets with life have intelligent life (fi), how many of those have life that's able to develop a technology suitable to broadcasting into space (fc), and finally L, the lifetime of those civilizations. What good is it that a beacon was pointed our way if it was eons ago?
So, write that formula in BASIC and plug it into your PC. What do you come up with? There are plenty of scientists who think the answer is zero and there are others, probably a majority, who feel that N is somewhere in the millions. In "Cosmos", Sagan summed it up like this: "It seems fairly clear that if self-destruction is not the overwhelming preponderant fate of galactic civilizations, then the sky is softly humming with messages from the stars."
But where are they then? Since we first turned our electronic ears on the skies, we've heard nothing but static. Nowadays, computers are aiding the search, sifting through the galactic background noise. But it's like trying to locate a single grain of sand on an endless beach. And what would it sound like, where might we find it, how would we know?
They're all good questions. First, we have to narrow down the search to a suitable range of frequencies. Terrestrial radio and television pretty well jam the lowest frequencies so we'd look in the 1 to 3 Gigahertz range (the "Galactic Water Hole", it's called, where it's thought any intelligent civilization would hang out).
We'd look for a narrow-band signal because it's less likely to be of natural origin. And we'd look for some sort of modulation, the key to transmitting intelligence. A computer is our hope here. We'll have at least 2 billion "channels" to tune and just so we don't miss anything, we'd better check them about once a second.
Testing Our Ability
Can it be done? Of course. And it's been tested with the farthest known signal source designed by man: Pioneer 10. This little probe, launched in the early 1970's, transmits with about eight watts. That's just a bit more than a Citizen's Band radio. And it's beyond our solar system, having passed Neptune more than a decade ago. It's over 10,000,000,000 kilometers away. The signal takes nine hours and ten minutes to reach us. And the signal is easily detected. Galactica, here we come.
Unlike the movie "Contact", this is real. We're indeed listening. Talk about Digital Signal Processing (DSP)! The top-of-the-line Project Phoenix has a Multi-Channel Spectrum Analyzer that uses eight commercial computer motherboards. There are 72 custom circuit boards and a DSP VLSI (Very Large Scale Integration) chip. All told, there are 384 chips doing DSP alone. How fast is this computer? It blazes along at 75 GFLOPS. That's 75 billion floating point operations per second.
And there are other projects: BETA, META, Serendip. We're listening to the stars. The SETI Institute (www.seti-inst.edu) is the best source for information along these lines. The Planetary Society (www.planetary.org), partly founded by Carl Sagan is another fascinating group that delves into all kinds of space science matters, SETI being one of their primary interests. And if you'd like to read about Ohio's contribution to SETI, check out the Big Ear site (www.bigear.org [Note. You are currently within that website.]).
Someday, somewhere a scientist will be notified (probably by pager), that a computer feels that it's on to something. We won't be standing at a console waiting. The wait has already been too long. We know that the universe is not awash in signals aimed our way. But one of these days a signal may give Earth a glancing blow, as both some distant planet and Earth spin. A computer will take notice. A computer will make the page. A computer will make history. Contact!
Copyright © 1997-2005 Ohio State University Radio Observatory and North American AstroPhysical Observatory.
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