Lesson 9: Other Worlds, Other Life 9.0 Introduction and Overview "Is there other life in the Universe?" This must be one of the oldest questions of mankind. As we close in on other mysteries, such as the origin of life, this may remain one of the last great unanswered questions. Or not; the answer could come tomorrow. If we assume for a moment that there is indeed other life in the universe, then we will want to find it, if for no other reason than curiosity. As we are so young, relative to the universe, it is likely that any other intelligent beings would be older, and hopefully wiser. Search strategies can be both passive ("wait for a signal", "look and listen") and active ("send a signal", " send robots or people"). Active robot or human searches seem hardly worth the extreme expense of thousands or millions of times yearly planetary energy consumption, if we have no target in mind, so efforts have almost exclusively centered on the "passive" searches. One exception, a 3-second radio signal from Arecibo in 1974 to a galactic cluster of some 100 million stars, has been soundly criticized. Two other exceptions, plaques and records attached to Pioneer and Voyager spacecraft are unlikely to ever be seen and are redundant: the spacecraft itself is the message. We have been sending other signals inadvertently for over 90 years. Radio and TV sitcoms are bad enough; what do our immensely powerful over-the-horizon radar signals say about mankind? Figure 9.0.1 The Arecibo message. The "passive" searches are in fact not very passive: search strategies must be devised, instruments acquired, deployed and operated. Data must be acquired and analyzed. Observing plans must be coordinated to avoid needless duplication and techniques shared and published. The instruments are typically large and expensive to build and operate. The data analysis has in one case involved the cooperation of millions of computers, forming the de facto largest computer in the world, by far. Search for Extraterrestrial Intelligence (SETI) is the generic name for these passive search strategies. There have been about 80 such programs over the last 40 years, starting with Frank Drake's Project Ozma of 1960. Most have been from the U.S., but there are now also programs covering the southern skies from Australia and Argentina, to name just two. Sky and frequency coverage are far from complete. Visit http://setiathome.berkeley.edu/ for information on a large SETI search and several articles about SETI in general. This program processes data from Arecibo, the world's largest radio dish. These data are broken up into 107-second workunits. As of April, 2001, some 90 million workunits have been analyzed. Each one is sliced and diced into 131 thousand fast Fourier transforms (FFTs), searching for power spikes in various bandwidths and time resolutions. A bit less than two billion spikes have been found, 90 million varying in intensity as if from a celestial source. Not one of these has indicated the presence of extraterrestrial most significant ones are from human radio leakage interference or satellite signals. SETI and UFO reports have often been lumped together (sometimes by otherwise respected political leaders), but there are obviously great differences. Any one of these SETI spikes would probably carry more weight with scientists than any UFO report (due to lack of measurements and repeatability), yet millions and billions of them have been found to be spurious. What are we to think of a few hundred scattered UFO reports? Figure 9.0.2 A message from the people of planet Earth. A gold-plated copper disk was attached to the side of each of the two Voyager spacecraft. It carries sounds and images of our planet for any extraterrestrial civilization that might encounter the probes thousands of years from now.