Shareware Beach

Monday, 13 December 2004

Time to Uninstall SETI@Home?

Filed under: Cyberspace — Jan @ 19:40

Many people run the SETI@Home screen saver to contribute idle CPU cycles to the search for extra-terrestrial intelligence. An interesting article in Astrobiology Magazine argues that the effort is most likely to be in vain.

The SETI project uses a huge array of radar telescopes to scan signals from space for patterns (as opposed to random background noise). The article argues that signals with detectable patterns would be from aliens with limited technological skill in effectively encoding signals. The kind of alien that isn’t capable of sending signals into deep space in the first place.

Computer files are a good comparison. A simple file would be a plain text file. Even if it’s written in a language you don’t understand, there are clearly recognizable patterns in the file. Certain elements (vowels) occur far more often than others, elements appear in groups (words), some elements are used to create super-groups (punctuation), etc. It’s a very inefficient way of storing data.

A better way to store data is to compress it. A .zip file still has a certain amount of structure, since a simple layout is used to group files together in the .zip archive. But the compressed files inside the .zip look much like random bytes, with little statistical difference from random bytes. The better the compression algorithm, the closer the data will resemble a meaningless random stream of bytes. Because if there’s a pattern left, you could enhance the compression algorithm to compress the remaining pattern as well.

When sending signals through space over such distances that even the speed of light is a seriously limiting factor, you don’t have the luxury of using too many bytes. In fact, even our terrestrial communications and storage systems are using ever more sophisticated compression algorithms. Audio CDs and VHS tapes are uncompressed. MP3 songs and DVD movies use complex, patented compression methods.

Suppose you have a billion files on your PC’s hard disk, all of them containing random, meaningless bytes, except for one that contains a document written in an unknown language, compressed with a highly effective, unknown algorithm. There’s no way you can find out which file you want, let alone decipher it. Looking for a needle in a haystack is easy. Looking for a straw in a haystack is impossible.

And we haven’t even considered encryption yet.


  1. I thought SETI is supposed to search for aliens who *want* to be found, and thus are beaming out a huge ‘WE ARE HERE’ signal in an obvious format; not to pick up scattered radiowaves from another civilization that aren’t intended for easy detection.

    Comment by Mark-Jan Harte — Wednesday, 15 December 2004 @ 18:44

  2. You can’t broadcast a “we are here” signal strong enough to drown out all the other signals (regular telecommunications) that Earth is leaking into space. And those other signals are becoming less and less detectable due to compression, encryption and other advances in communication.

    Here’s another article on the subject: Radio Free Earth.

    Comment by Jan Goyvaerts — Wednesday, 2 February 2005 @ 21:42

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