Transcript Slide 1
Is There Life Out There? It must be made very clear that none of these experiments has ever produced a single living organism, or even a single strand of DNA for that matter. However, they do demonstrate conclusively that "biological molecules" can be created by man. Miller-Urey Experiment This chemical apparatus is designed to synthesize complex biochemical molecules by energizing a mixture of simple chemicals. A mixture of gases (ammonia, methane, carbon dioxide, water vapor) is placed in the upper bulb to simulate the primordial Earth atmosphere and then energized by spark-discharge electrodes. After about a week, amino acids and other complex molecules are found in the trap at the bottom, which simulates the primordial oceans into which heavy molecules produced in the overlying atmosphere would have fallen. The Drake Equation How likely is it that life in any form—carbon-based, silicon-based, water-based, ammonia-based, or something we cannot even dream of—exists somewhere out there beyond the Earth? Let’s look at some numbers to develop statistical estimates of the probability of life elsewhere in the universe. An early approach to this statistical problem is known as the Drake equation, after Frank Drake, the U.S. astronomer who pioneered this analysis: Drake Equation Calculator Freeware Drake Equation Of all the star systems in our Milky Way Galaxy (represented by the largest box), progressively fewer and fewer have each of the qualities typical of a long-lasting technological society (represented by the smallest box at the lower right corner). Meeting Our Neighbors For definiteness, let’s assume that the average lifetime of a technological civilization is 1 million years—only 1 percent of the reign of the dinosaurs, but 100 times longer than our civilization has survived thus far, and 10,000 times longer than human society has so far been in the “technological” state. The Drake equation then tells us that there are 1 million such civilizations in the Galaxy, and we can then estimate the average distance between these civilizations to be some 30 pc, or about 100 light-years. Thus, any two-way communication with our neighbors will take at least 200 years (100 years for the message to reach the planet and another 100 years for the reply to travel back to us)—a long time by human standards, but comfortably less than the lifetime of the civilization. Might we hope to visit our neighbors by developing the capability of traveling far outside our solar system? This may never be a practical possibility. At a speed of 50 km/s, the speed of the current fastest space probes, the round-trip to even the nearest Sun-like star, Alpha Centauri, would take about 50,000 years. The journey to the nearest technological neighbor (assuming a distance of 100 pc) and back would take 1 million years—the entire lifetime of our civilization! Pioneer 10 Plaque A replica of a plaque mounted on board the Pioneer 10 spacecraft. Included are a scale drawing of the spacecraft, a man, and a woman; a diagram of the hydrogen atom undergoing a change in energy (top left); a starburst pattern representing various pulsars and the frequencies of their radio waves that can be used to estimate when the craft was launched (middle left); and a depiction of the solar system, showing that the spacecraft departed the third planet from the Sun and passed the fifth planet on its way into outer space (bottom). All the drawings have computer-coded (binary) markings from which actual sizes, distances, and times can be derived. (NASA) Water Hole SETI One of the most sensitive and comprehensive projects in the ongoing search for extraterrestrial intelligence (known to many by its acronym SETI) was Project Phoenix, carried out during the late 1990s. Large radio antennas were used to search millions of channels simultaneously in the 1–3 GHz range. Nothing resembling an extraterrestrial signal has yet been detected, except signals that we ourselves have generated. An intelligent signal!! But from our own Pioneer 10 probe leaving our solar system…