"Any sufficiently advanced technology," wrote science fiction giant Arthur C. Clarke some years ago, "is virtually indistinguishable from magic." This acknowledgment of our own technological immaturity has subsequently become known as Clarke's Law, and is one basis for Shklovskii's and Sagan's Assumption of Mediocrity which underlies so much SETI research. SETI League President Richard Factor has proposed an interesting corollary to Clarke's Law: "Any sufficiently advanced modulation scheme is virtually indistinguishable from noise."
At the recent Central States VHF Conference, NASA geophysicist Dr. Thomas A. Clark alluded to Factor's corollary in expressing a healthy skepticism as to the viability of SETI in general, and amateur SETI in particular. "How can we hope to detect them," Tom asked, "if we don't even know what form their signals might take?" He points to the primary use of the Water Hole frequencies by human civilization, spread-spectrum Global Positioning Satellites, and wonders whether technology such as ours could even detect such signals at a distance, let alone recognize them as being of intelligent origin.
Over the past few years Kent Britain of the North Texas Microwave Society has done quite a bit of analysis of spread-spectrum signals, especially with respect to their growing presence in the shared 33 cm amateur band. Proponents of wireless LANs in this part of the spectrum tout their inherent security. Kent questions these claims, and with good reason. He has demonstrated how, with simple components (filters, amplifiers and double-balanced mixers), the spreading signal can be canceled, effectively decoding spread-spectrum without the key. This being the case, what's the problem with detecting SETI signals?
The problem is that the signals with which Kent has been working are a known entity. They are unmistakably strong, and their general format is known to us a priori. None of this is true of the interstellar communications we hope to intercept. Perhaps Tom Clark is right -- there are just too many variables.
Might digital signal processing help? The primary DSP tool employed in SETI and elsewhere is the Fast Fourier Transform. It can dig coherent signals out of the noise, offering tens of dB of processing advantage. But to implement FFT in our computers, we must make some a priori assumptions about the nature of the signals being detected. Are these assumptions valid for SETI?
At Ohio State University, Professors Chuck Klein and Robert Dixon are working with an alternative to the Fourier Transform, the Karhunen-Loeve. An adaptive transform, the KLT makes no assumptions whatever about the nature of the signal being detected. In computer simulations, it appears to work well with all types of signals, particularly complex ones. Klein's work is yet another example of the type of breakthrough thinking which can not only make SETI viable, but which can spin off to practical applications we cannot begin to imagine. And that, after all, is a major justification for SETI, magic notwithstanding.
entire website copyright © The SETI League, Inc.
this page last updated 4 January 2003
Top of Page