1. 28.4 The Search for Extraterrestrial Intelligence

2. For the sake of argument… (and this section) we will assume that we have intelligent, communicative neighbors.

3. Meeting Our Neighbors We assume –The average lifetime of a technological civilization is 1 million years We further assume –The average distance between civilizations is 30 parsecs (pc) or 100 light years As a result, any two-way communication will take at least 200 years

4. The fastest space probes today… Travel at 50 km/s. This means that to go to the star nearest our solar system, Alpha Centauri, it would take about 50,000 years. To our nearest assumed technological neighbor would take 600,000 years. Speeding up to light speed would help. Speeding up to light speed would help. We just can’t do it yet.

5. What have we already done? Pioneer 10, launched in the mid-1970s, is now beyond the orbit of Pluto contains a plaque with Earth info. Voyager has similar information.

7. Is it a good idea to contact ET? Any civilization that contacts us would likely be more advanced than us. From your book, “If extraterrestrials behave even remotely like human civilizations on Earth, then the most advanced aliens may naturally try to dominate all others.” Maybe not all intelligent species do this! Maybe not all intelligent species do this!

8. Radio Communication Long-wave radio radiation may be the best form of energy to use to communicate –Light and other high frequency radiation is scattered while moving through dusty interstellar space Likely we would listen for radio signals from other civilizations. This is underway for some stars.

9. Radio Communication Problems Our success is contingent upon whether or not ET is broadcasting radio signals. Some stars give off radio waves, as do some interstellar gas clouds. Even Earth gives off radio waves! Why? Because of all of the radio stations! Only FM signals leave Earth (AM broadcasts are trapped in our ionosphere).

10. Radio Communication Problems The radio waves the Earth gives off are not constant. Why? There are pockets of radio activity on Earth (eastern US, western Europe). If any sufficiently advanced civilization resides on a planet orbiting any of the thousand or so stars within 70 ly of us, we have already broadcast our presence to them!

11. The Water Hole What frequency do we aim for? At or near 20 cm. This is near the frequency of hydrogen, and the simple molecule hydroxyl (OH). These two together form water. The range of 18-21 cm is called the water hole, or oasis, where all advanced galactic civilizations would gather electromagnetically.

12. Project Phoenix Also known as “SETI” – Search for Extraterrestrial Intelligence. Began in the late 1990s. Large radio antennas are used. Computers “listen”. Humans listen only if the computer shows something interesting. No signs have been detected yet.

13. Arecibo Radio Telescope – Puerto Rico

14. Arecibo googled

15. VLA – Socorro, NM