SETI SETI

Lecture Thirty-Two, Apr. 21, Lecture Thirty-Two, Apr. 21, 20032003

AssignmentsAssignments

• Text: Read chapter 17, Intelligent life Text: Read chapter 17, Intelligent life in the universe, pages 276-292. in the universe, pages 276-292.

• Project due Friday April 25.Project due Friday April 25.

StarshipsStarships

• Suppose we find a very interesting Suppose we find a very interesting planet around a nearby star, what then?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 A light year (distance light travels in a

year) = 3x10year) = 3x1088 m/s times 3 x 10 m/s times 3 x 1077 sec/yearsec/year

• Light year = 10Light year = 101616 meters! meters!

What Could Justify Enormous What Could Justify Enormous Cost?Cost?

• To escape destruction.To escape destruction.• To colonize the Galaxy. The return on To colonize the Galaxy. The return on

the investment might be the entire the investment might be the entire Milky Way.Milky Way.

• Just exploring or communicating might Just exploring or communicating might not be worth it.not be worth it.

• Much much cheaper to just talk.Much much cheaper to just talk.• Communication over interstellar Communication over interstellar

distances is very feasible.distances is very feasible.

Message in a Cosmic BottleMessage 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 Want signal to look “unnatural” and stand out above background of natural radio out above background of natural radio noise in Galaxy.noise in Galaxy.

• Broad frequency region around a few GHZ Broad frequency region around a few GHZ (few times 10(few times 1099 cycles per second). This is cycles per second). This is in the microwave region (high frequency in the microwave region (high frequency radio) of the spectrum. Here natural noise radio) of the spectrum. Here natural noise is relatively small.is relatively small.

Send very sharp frequency Send very sharp frequency signalsignal

Frequency Frequency

Signal Signal StrenthStrenth

Natural noiseNatural noise

Try to have your Try to have your signal stand out signal stand out above the noiseabove the noise

Which frequency?Which frequency?

• Have large computers plus special radio Have large computers plus special radio receivers search millions of frequencies at receivers search millions of frequencies at once. “Mother of all police scanners”once. “Mother of all police scanners”

• One example: hydrogen atoms emit and One example: hydrogen atoms emit and absorb radiation at 1.4 GHZ (spectral line absorb radiation at 1.4 GHZ (spectral line in microwave frequency).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 Send at 1.4 times = 4.46 GHZ = 4.46 GHZ ((=3.1415926)=3.1415926)

InterferenceInterference

Pioneer Pioneer 1111

How to send images?How to send images?

• Encode dark pixels as zeros and bright Encode dark pixels as zeros and bright pixels as ones.pixels as ones.

• Send rectangular array of ones and zeros Send rectangular array of ones and zeros as long string.as long string.

• Example: send string 437 units long. Why Example: send string 437 units long. Why 437? It can be uniquely factored into 19 x 437? It can be uniquely factored into 19 x 23.23.

• Try arranging signal into rectangular grid: Try arranging signal into rectangular grid: either 23 x 19 or 19 x 23. Try both.either 23 x 19 or 19 x 23. Try both.

Example: simple code Example: simple code seti.basseti.bas• Reads a message file (for example Reads a message file (for example

message.dat) as a long string of ones message.dat) as a long string of ones and zeros.and zeros.

• Arranges string into rectangular array.Arranges string into rectangular array.

• Try 19 x 23 and then 23 x 19Try 19 x 23 and then 23 x 19

• Show seti.bas, string.datShow seti.bas, string.dat

• Run seti.exeRun seti.exe

Example of message we have Example of message we have sentsent

Why Send Messages?Why Send Messages?

• Curiosity.Curiosity.• Want to help others.Want to help others.• Want to learn from others (IE hope Want to learn from others (IE hope

they answer our messages).they answer our messages).• To arrange meeting, to share To arrange meeting, to share

technology, to share culture/ arts …technology, to share culture/ arts …• To have someone remember us To have someone remember us

when we are gone.when we are gone.

Why not?Why not?

• Radio transmissions are cheapRadio transmissions are cheap

• Security risk??? Beacon may call attention to Security risk??? Beacon may call attention to earth.earth.

• However, knowledge and technology from ET However, knowledge and technology from ET communication may be crucial to our survival.communication may be crucial to our survival.

• How to learn enough about a Galactic How to learn enough about a Galactic civilization to compete and defend ourselves, civilization to compete and defend ourselves, while at same time maintain our cultural while at same time maintain our cultural identity.identity.

What to send?What to send?

• Info about us. For example our Info about us. For example our biochemistry and genetic code.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…

Clip from Movie ContactClip from Movie Contact

Is anyone there?Is anyone there?

• Intelligence is ability to use radios.Intelligence is ability to use radios.

• Important differences searching for Important differences searching for intelligent compared to primitive life!intelligent compared to primitive life!

• How many civilizations are there in How many civilizations are there in the galaxy that might try to call us?the galaxy that might try to call us?

• The Drake equation is away to discuss The Drake equation is away to discuss our ignorance of this fundamental our ignorance of this fundamental question.question.

Next TimeNext Time

• Text: Read chapter 17, Intelligent life Text: Read chapter 17, Intelligent life in the universe, pages 276-292. in the universe, pages 276-292.

• Project due Friday April 25. Happy to Project due Friday April 25. Happy to talk to you about it.talk to you about it.