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SETI
- Allen Telescope Array
- Optical SETI
- Interstellar Message Construction
- Project Phoenix 1995-2004
- Background Science
- History of SETI
- Center for SETI Research Team
- Other people doing SETI
- Hollywood's View of SETI
Signals and Noise
by Mark Langston, Senior Unix Systems Administrator
In the late 1930's, Claude Shannon formalized the distinction between signal and noise with his mathematical theory of communication, developed at Bell Labs to optimize telephone transmissions. Some days, I think quite a bit about signal and noise as it often seems my work has me oscillating between the two extremes, trying to tease a signal from an overwhelming abundance of noise.
The hidden signal might be that one salient bit of debugging information I need to resurrect a failed system, seemingly lost amid myriad unrelated but confusingly similar pieces of information. Other days, the signal may be our network traffic, and I find myself struggling to keep our connection alive against overwhelming odds (last weeks unprecedented rain brought out construction crews with several backhoes, the fiber-optic cable's only natural enemy). Each day, I must avoid or ignore the interfering noise as I quickly and accurately seek out the signals I need to perform my job tasks.
It's no surprise that signal-to-noise comparisons dominate my thinking about the work day. Shannons theory exactly defines our SETI efforts; we attempt to separate signals from both terrestrial and interstellar noise. Being so intimately involved with this effort underscores for me the relativity of the terms "signal" and "noise". Things that we take for granted, and often actively seek out, become obstacles in the search for extraterrestrial intelligence.
Shipping companies and cruise lines depend upon ship-to-shore radio links. We all seem to place a great deal of value on the convenience and utility of cell phones, microwave ovens, and wireless networks. In our day-to-day lives, these are highly desirable signals. When listening with the world's biggest ear for signals originating from distant solar systems however, the helpful devices become obtrusive noise-emitters, obscuring the potential signals SETI seeks.
But when conditions are right--when such noise sources are quiet or masked off, and the equipment hums along (silently)--the radio-frequency hush is matched by our silence in the control room as we monitor the screens for hints of those elusive signals. In the wee hours of the morning, you can almost sense the soft susurration of the background noise, the cosmic canvas across which a signal might be painted.
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