1. SETI Lecture Thirty-Two, Apr. 21, 2003

2. Assignments Text: Read chapter 17, Intelligent life in the universe, pages 276-292. Text: Read chapter 17, Intelligent life in the universe, pages 276-292. Project due Friday April 25. Project due Friday April 25.

3. Starships Suppose we find a very interesting planet around a nearby star, what then? Suppose we find a very interesting planet around a nearby star, what then? Can we go there? Can we go there? It is very, very hard! It is very, very hard! Just because stars are so far away. Just because stars are so far away. A light year (distance light travels in a year) = 3x10 8 m/s times 3 x 10 7 sec/year A light year (distance light travels in a year) = 3x10 8 m/s times 3 x 10 7 sec/year Light year = 10 16 meters! Light year = 10 16 meters!

4. What Could Justify Enormous Cost? To escape destruction. To escape destruction. To colonize the Galaxy. The return on the investment might be the entire Milky Way. To colonize the Galaxy. The return on the investment might be the entire Milky Way. Just exploring or communicating might not be worth it. Just exploring or communicating might not be worth it. Much much cheaper to just talk. Much much cheaper to just talk. Communication over interstellar distances is very feasible. Communication over interstellar distances is very feasible.

5. Message in a Cosmic Bottle How to send or receive a radio beacon? How to send or receive a radio beacon? Want signal to look “unnatural” and stand out above background of natural radio noise in Galaxy. Want signal to look “unnatural” and stand out above background of natural radio noise in Galaxy. Broad frequency region around a few GHZ (few times 10 9 cycles per second). This is in the microwave region (high frequency radio) of the spectrum. Here natural noise is relatively small. Broad frequency region around a few GHZ (few times 10 9 cycles per second). This is in the microwave region (high frequency radio) of the spectrum. Here natural noise is relatively small.

6. Send very sharp frequency signal Frequency  Signal Strenth Natural noise Try to have your signal stand out above the noise

7. Which frequency? Have large computers plus special radio receivers search millions of frequencies at once. “Mother of all police scanners” Have large computers plus special radio receivers search millions of frequencies at once. “Mother of all police scanners” One example: hydrogen atoms emit and absorb radiation at 1.4 GHZ (spectral line in microwave frequency). One example: hydrogen atoms emit and absorb radiation at 1.4 GHZ (spectral line in microwave frequency). Don’t send at 1.4 GHZ, swamped by noise. Don’t send at 1.4 GHZ, swamped by noise. Send at 1.4 times  = 4.46 GHZ (  =3.1415926) Send at 1.4 times  = 4.46 GHZ (  =3.1415926)

8. Interference Pioneer 11

9. How to send images? Encode dark pixels as zeros and bright pixels as ones. Encode dark pixels as zeros and bright pixels as ones. Send rectangular array of ones and zeros as long string. Send rectangular array of ones and zeros as long string. Example: send string 437 units long. Why 437? It can be uniquely factored into 19 x 23. Example: send string 437 units long. Why 437? It can be uniquely factored into 19 x 23. Try arranging signal into rectangular grid: either 23 x 19 or 19 x 23. Try both. Try arranging signal into rectangular grid: either 23 x 19 or 19 x 23. Try both.

10. Example: simple code seti.bas Reads a message file (for example message.dat) as a long string of ones and zeros. Reads a message file (for example message.dat) as a long string of ones and zeros. Arranges string into rectangular array. Arranges string into rectangular array. Try 19 x 23 and then 23 x 19 Try 19 x 23 and then 23 x 19 Show seti.bas, string.dat Show seti.bas, string.dat Run seti.exe Run seti.exe

11. Example of message we have sent

13. Why Send Messages? Curiosity. Curiosity. Want to help others. Want to help others. Want to learn from others (IE hope they answer our messages). Want to learn from others (IE hope they answer our messages). To arrange meeting, to share technology, to share culture/ arts … To arrange meeting, to share technology, to share culture/ arts … To have someone remember us when we are gone. To have someone remember us when we are gone.

14. Why not? Radio transmissions are cheap Radio transmissions are cheap Security risk??? Beacon may call attention to earth. Security risk??? Beacon may call attention to earth. However, knowledge and technology from ET communication may be crucial to our survival. However, knowledge and technology from ET communication may be crucial to our survival. How to learn enough about a Galactic civilization to compete and defend ourselves, while at same time maintain our cultural identity. How to learn enough about a Galactic civilization to compete and defend ourselves, while at same time maintain our cultural identity.

15. What to send? Info about us. For example our biochemistry and genetic code. Info about us. For example our biochemistry and genetic code. Info on our technology. Info on our technology. Info on the local environment. Info on the local environment. Info on our culture, arts, values… Info on our culture, arts, values…

16. Clip from Movie Contact

17. Is anyone there? Intelligence is ability to use radios. Intelligence is ability to use radios. Important differences searching for intelligent compared to primitive life! Important differences searching for intelligent compared to primitive life! How many civilizations are there in the galaxy that might try to call us? How many civilizations are there in the galaxy that might try to call us? The Drake equation is away to discuss our ignorance of this fundamental question. The Drake equation is away to discuss our ignorance of this fundamental question.

18. Next Time Text: Read chapter 17, Intelligent life in the universe, pages 276-292. Text: Read chapter 17, Intelligent life in the universe, pages 276-292. Project due Friday April 25. Happy to talk to you about it. Project due Friday April 25. Happy to talk to you about it.