Ask Dr. SETI ®
by Erick Sherman
For half a century now, SETI scientists have been searching the electromagnetic spectrum, in hopes of uncovering Encyclopaedia Galactica. It is my considered opinion that they are looking in the wrong library. There is likely only a very brief period in the development of each intelligent civilization in which its society will be broadcasting electromagnetic radiation sufficiently strong to be identifiable by us, or by them, as a transmission containing discernible information.
I recently read "Space Contact The Day After" By Tim Folger (Scientific American, January 2011, pages 40 - 45). A thought I have actually considered, from childhood in the fifties, is that I don't believe any of the potentially tens or hundreds of thousands of possible civilizations would be transmitting strong, omnidirectional radio signals for a period significantly exceeding 200 Earth years.
Our first radio signals left this planet only about 100 years ago. The really strong signals (100,000 watts or more) began, at the earliest, around 40 years later. Yes, there are stronger signals transmitted by various radar systems. But these contain no "language," and so would not lend themselves to translation or interpretation. Radar signals should indeed be identifiable as being of intelligent origin, but would not convey easily recognized intelligence. Many of our other transmissions are highly directional, such as those we use to control satellites or the rovers on Mars, but these are considerably weaker and would not be as easy to detect. In addition, being directional, detection becomes less likely the more the receiver is displaced from the original line of transmission. Further, these mechanical controllers would not contain much usable "language" to interpret. We Earthlings have had functionally advanced civilizations for in excess of 4000 years, yet we have been broadcasting for less than 100.
In addition to our high powered broadcast television and radio signals, we emit various cell telephone and other microwave signals. Away from this planet, these signals would form an intense cacophony. Much as the effective averaging described in the Scientific American article would obscure specific intelligence, these signals are already an extensive average of multiple communication streams. However, these are much weaker than the older broadcast signals. As newer generations of cell signals are developed, ever more intelligence is spread across the electromagnetic spectrum, using incrementally less power. In the near future, this wireless form of communication will become ubiquitous, using lower and lower power signals from less and less expensive connectivity devices. Using more connect points allows more connections, and allows more bandwidth to be shared by each of these connections. But, it diminishes the signals' detectability over interstellar distances.
There are a number of factors that prompt reducing the dependence on electromagnetic radiation as a means of communication. First, the basic broadcast concept is very limited in its overall ability to conduct communication. Interactive capability is inordinately more effective. However, as interactivity involves bidirectional communication, the distances are restricted. In addition to distance, the number of interactive connections is finite for a given concentration point. This second condition further restricts the distance, simply because of the number of connections. Further, on our planet, the ability to move large amounts of data (intelligence, or content) to and from our communications devices seems to be a very important to us. Larger amounts of data require more bandwidth, further restricting the number of connections at a particular concentrator and therefore further reducing the distance from concentrator to interacting connection. Economics drives our choice to operate each concentrator at lower and lower power. I personally believe we on this planet will functionally eliminate high power broadcasting except for special circumstances, such as radar.
While we may eventually intercept transmissions from other worldly civilizations, we may never be lucky enough to catch one during its "active transmissions" period that might allow interpretation of language or intelligence. If we do actually catch one of these, it would suggest that there are considerably more intelligent life forms in the Universe than even SETI optimists suppose. Since signal strengths are likely too low to detect over intergalactic distancs, we would have to interpret data from our own galaxy in inferring possible numbers for our immediate Universe.
SETI observers, if they are extremely lucky, may some day receive the existence proof they seek. But they should not expect it to be information-rich electromagnetic communication. The best they should expect would be a repetitive and relatively coherent narrow band signal. If they're looking for Encyclopaedia Galactica, they'll have to try some other library.
Disclaimer: The opinions expressed in editorials are those of the individual authors, and do not necessarily reflect the position of The SETI League, Inc., its Trustees, officers, Advisory Board, members, donors, or commercial sponsors.
entire website copyright © The SETI League, Inc.; Maintained by Microcomm
this page last updated 5 February 2011
Top of Page