NSCI 314

LIFE IN THE COSMOS

16 - INTERSTELLAR COMMUNICATION (CONTINUED)

Dr. Karen KolehmainenDepartment of Physics, CSUSB

http://physics.csusb.edu/~karen/

RADIO WAVES FOR SIGNALS ADVANTAGES:

– NOT ABSORBED BY INTERSTELLAR DUST (UNLIKE VISIBLE LIGHT AND OTHER KINDS OF ELECTROMAGNETIC WAVES)

– LOW ENERGY REQUIREMENTS, THUS CHEAP

– TRAVEL AT THE SPEED OF LIGHT (LIKE OTHER ELECTROMAGNETIC WAVES, BUT FASTER THAN ANY SPACESHIP)

– CAN CARRY A LOT OF INFORMATION (LIKE OTHER ELECTROMAGNETIC WAVES)

SEARCH STRATEGIES

TARGETED SEARCH

POINT RADIO TELESCOPE IN THE DIRECTION OF SUITABLE STARS AND LOOK FOR A SIGNAL.

SKY SURVEY

SEARCH WHEREVER THE RADIO TELESCOPE (WHILE IN USE FOR OTHER PURPOSES) HAPPENS TO BE POINTING.

NUMBER OF SUITABLE STARS

LIMITATIONS ON SEARCH TIMES:(TARGETED SEARCH OF SUITABLE STARS)

OUT TO 100 LY: OUT TO 1,000 LY:

20,000 SUITABLE STARS 20 MILLION SUITABLE STARS

200,000 STARS 200 MILLION STARS

SEARCH RATE:

1 PER DAY

1 PER HOUR

1 PER MINUTE

1 PER SECOND

OUT TO 100 LY:

55 YEARS

2.3 YEARS

14 DAYS

6 HOURS

OUT TO 1000 LY:

55,000 YEARS

2,300 YEARS

38 YEARS

230 DAYS

DELIBERATE VS. ACCIDENTAL SIGNALS

ACCIDENTAL SIGNALS ARE NOT DESIGNED TO ATTRACT THE ATTENTION OF ALIEN CIVILIZATIONS. THEY ARE USED FOR OTHER PURPOSES, BUT ESCAPE INTO SPACE AND COULD BE PICKED UP BY AN ALIEN CIVILIZATION.– EXAMPLES: OUR TV AND FM RADIO

BROADCASTS, PLUS MILITARY RADAR SIGNALS

DELIBERATE SIGNALS ARE DESIGNED TO ATTRACT THE ATTENTION OF ALIEN CIVILIZATIONS.

DELIBERATE VS. ACCIDENTAL SIGNALS HOW STRONG ARE THE SIGNALS WE CAN SEND? A SIGNAL GETS WEAKER AS IT TRAVELS FARTHER

FROM ITS SOURCE. ASSUMING THAT THE HYPOTHETICAL ALIENS WHO

ARE DETECTING OUR SIGNALS HAVE THE SAME LEVEL OF TECHNOLOGY WE HAVE:– THEY COULD DETECT OUR TV AND FM RADIO BROADCASTS

IF THEY WERE UP TO 1 LY AWAY (NO STARS THAT CLOSE).– THEY COULD DETECT OUR MILITARY RADAR SIGNALS IF

THEY WERE WITHIN 30 OR 40 LY.– THEY COULD DETECT OUR DELIBERATE SIGNALS (IF SENT

WITH ARECIBO RADIO TELESCOPE) IF THEY WERE ANYWHERE WITHIN THE MW GALAXY.

IF THE ALIENS ARE MORE ADVANCED THAN WE ARE TECHNOLOGICALLY, THEY COULD DETECT OUR SIGNALS FROM FARTHER AWAY.

DELIBERATE VS. ACCIDENTAL SIGNALS BUT WOULD THEY BE ABLE TO

UNDERSTAND OUR SIGNALS?– IT WOULDN'T BE EASY IN THE CASE OF OUR

ACCIDENTAL SIGNALS. WE HAVE AGREED ON CERTAIN WAYS OF ENCODING INFORMATION IN THESE SIGNALS THAT MAY NOT BE OBVIOUS TO SOMEONE ELSE (EVEN OTHER HUMANS). EVEN IF THEY COULD FIGURE THIS OUT, THEY WOULDN'T UNDERSTAND ANY HUMAN LANGUAGES OR UNDERSTAND HUMAN CULTURAL REFERENCES.

– IN THE CASE OF DELIBERATE SIGNALS, WE WOULD HAVE TO TRY TO MAKE THE SIGNALS EASY TO UNDERSTAND.

WHAT WILL A SIGNAL CONSIST OF?

A WAVE THAT DOESN’T CHANGE WITH TIME CARRIES NO INFORMATION.

INFORMATION CAN BE CARRIED BY CHANGING EITHER THE AMPLITUDE (OR INTENSITY) OR WAVELENGTH (OR FREQUENCY) OF A WAVE WITH TIME.•IN AN “AMPLITUDE MODULATED” (AM) SIGNAL, THE AMPLITUDE CHANGES WITH TIME.•IN A “FREQUENCY MODULATED” (FM) SIGNAL, THE FREQUENCY CHANGES WITH TIME.

BUT WHAT CONTENT DO WE WANT TO PUT INTO THE MESSAGE, AND HOW DO WE PUT IT THERE?

HOW CAN WE INCREASE THE LIFELIHOOD THAT THE ALIENS WILL UNDERSTAND WHAT WE ARE TRYING TO SAY?

WHAT WILL A SIGNAL CONSIST OF?

WHAT CONTENT DO WE WANT TO PUT INTO THE MESSAGE, AND HOW DO WE PUT IT THERE?

THEY WOULDN'T UNDERSTAND ANY HUMAN LANGUAGE. PICTURES?

– HOW DO WE TRANSMIT A PICTURE USING RADIO WAVES OR LASERS?

MATHEMATICS?– MATHEMATICS PROVIDES A UNIVERSAL LANGUAGE

THAT ANY TECHNOLOGICAL CIVILIZATION WILL UNDERSTAND.

– WE CAN USE MATH TO TRANSMIT A PICTURE.– BUT WHAT KIND OF MATHEMATICS?

COUNTING IN BINARY AND DECIMAL

0+0=0 1+0=1 1+1=2 2+1=3 3+1=44+1=5 5+1=6 6+1=7 7+1=8 8+1=9

NOTICE THAT A NEW SYMBOL IS CREATED FOR EACH NEW NUMBER.

UNTIL… 9+1=10, WHICH IS “NINE PLUS ONE IS TEN, BUT WRITE ZERO AND CARRY THE ONE.” A NEW SYMBOL IS NOT CREATED TO REPRESENT THE NUMBER TEN. IN THE DECIMAL (OR BASE TEN) SYSTEM, THERE ARE ONLY TEN DIFFERENT SYMBOLS (0, 1, 2, 3, 4, 5, 6, 7, 8, AND 9) USED.

IN BINARY (BASE TWO), THERE ARE ONLY TWO SYMBOLS (0 AND 1):

0 + 0 = 0 1 + 0 = 1 1 + 1 = 10

(10 = THE NUMBER TWO WRITTEN IN BINARY)

10 + 1 = 11 (THREE) 11 + 1 = 100 (FOUR)…

DECIMAL

0

1

2

3

4

5

6

7

8

BINARY

0

1

10

11

100

101

110

111

1000

DECIMAL vs. BINARY

•IN DECIMAL, AN EXAMPLE IS 7205 •7205 = (7 x 1000) + (2 x 100) + (0 x 10) + (5 x 1) •7205 = (7 x 103) + (2 x 102) + (0 x 10) + (5 x 1)

IN BINARY, AN EXAMPLE IS 10111011 = (1 x 8) + (0 x 4) + (1 x 2) + (1 x 1) 1011 = (1 x 23) + (0 x 22) + (1 x 2) + (1 x 1)

1011 IN BINARY IS THE NUMBER ELEVEN. IT IS WRITTEN AS 11 IN DECIMAL

BINARY NUMBERS SIMPLEST SYSTEM – ONLY TWO SYMBOLS (0 AND 1)

NEEDED EACH SYMBOL (0 OR 1) IS A BIT USED BY MOST COMPUTERS A MESSAGE CONSISTING OF A SEQUENCE OF BITS

COULD BE ENCODED IN SEVERAL WAYS:– A PULSE COULD BE A “1” AND A GAP (NO SIGNAL) COULD

BE A “0” (OR VICE VERSA)– A LONGER-DURATION PULSE COULD BE A “1” AND A

SHORTER-DURATION PULSE COULD BE A “0” (OR VICE VERSA)

– TWO DIFFERENT FREQUENCIES COULD BE USED – A PULSE AT ONE FREQUENCY COULD BE A “1”, AND A PULSE AT THE OTHER FREQUENCY COULD BE A “0”

BINARY NUMBERS A SEQUENCE OF BITS CAN ENCODE A PICTURE – LET 0

BE A WHITE DOT AND 1 BE A BLACK DOT (OR VICE VERSA).

THE DOTS MUST BE ARRANGED TO MAKE A PICTURE. IF WE START STRINGING TOGETHER THE DOTS IN ONE

LONG ROW (OR COLUMN), IT WON'T LOOK LIKE A PICTURE.•IT WILL BE LONG AND THIN, WHEREAS A PICTURE WOULD BE CLOSER TO SQUARE.

INSTEAD, WE MUST STRING TOGETHER DOTS UNTIL WE REACH THE END OF A ROW (OR COLUMN), THEN START ANOTHER ROW (OR COLUMN).

HOW DO WE KNOW WHEN WE REACH THE END OF A ROW (OR COLUMN)?

BINARY NUMBERS WE MUST ARRANGE BITS INTO ROWS AND

COLUMNS IN AN UNAMBIGUOUS WAY.– IF A MESSAGE CONTAINS 1200 BITS, THE DOTS COULD BE

ARRANGED IN:• 30 ROWS, 40 COLUMNS (OR VICE VERSA)• 50 ROWS, 24 COLUMNS (OR VICE VERSA)• 60 ROWS, 20 COLUMNS (OR VICE VERSA)• 120 ROWS, 10 COLUMNS (OR VICE VERSA)

• WE'D HAVE TO CHECK ALL THESE POSSIBILITIES TO SEE IF ANY OF THEM RESULTED IN SOMETHING THAT LOOKED LIKE A PICTURE.

CHOOSE TOTAL NUMBER OF BITS IN THE MESSAGE TO BE THE PRODUCT OF TWO PRIME NUMBERS. – FOR EXAMPLE, 551 = 19 x 29– BUT IS THIS 19 ROWS AND 29 COLUMNS, OR 29 ROWS AND

19 COLUMNS?

111100001010010000110010000000100000101001000001100101100111100000110000110100000000100000100001000010001010100001000000000000000000010001000000000010110000000000000000000100011101101011010100000000000000000001001000011101010101000000000101010101000000000111010101011101011000000010000000000000000010000000000000100010011111100000111010000010110000011100000001000000000100000000100000001111100000010110001011100000000000011111000000101100011111110000010000011000001100001000011000000011000101001000111100101111

WHAT COULD IMPROVE THIS MESSAGE?

MORE INFORMATION - INCREASE THE NUMBER OF BITS.– WOULD MAKE THE PICTURE LOOK MORE “NATURAL” -

OBJECTS COULD BE GENTLY CURVED RATHER THAN POINTY – WOULD SPREAD OBJECTS FURTHER APART, MAKING IT MORE

OBVIOUS WHAT EACH ONE IS SUPPOSED TO BE

COULD USE MULTIPLE PICTURES TO INDICATE MOTION (WITH A LONGER GAP BETWEEN “FRAMES”).

ONCE SOME INFORMATION IS EXCHANGED, WE COULD PROBABLY EVENTUALLY AGREE WITH THEM ON OTHER WAYS TO ENCODE INFORMATION MORE EFFICIENTLY.

FIRST CONTACT

ANY EVIDENCE, WHETHER THROUGH COMMUNICATION OR DIRECT ENCOUNTER, THAT EXTRATERRESTRIAL INTELLIGENCE EXISTS

HOWEVER, KEEP IN MIND SAGAN’S CAUTION:

“AN EXTRAORDINARY CLAIM REQUIRES EXTRAORDINARY EVIDENCE” (Sagan, date unknown)

FIRST CONTACTU.N. DECLARATION OF PRINCIPLES

2. INFORM OTHER RESEARCHERS OF THE DISCOVERY AND WAIT FOR THEIR CONFIRMATION.

1. BE CERTAIN THAT THE SIGNAL CANNOT BE EXPLAINED BY NATURAL OR TERRESTRIAL PHENOMENA.

3. MAKE AN ANNOUNCEMENT TO THE INTERNATIONAL SCIENTIFIC COMMUNITY.

4. MAKE ALL DATA AVAILABLE TO THE SCIENTIFIC COMMUNITY.

5. CONTINUE TO OBSERVE AND RECORD EVERYTHING.

6. OFFICIALLY PROTECT THE FREQUENCIES USED. STOP USING THEM FOR ANYTHING ELSE.

8. DO NOT RESPOND UNTIL WE DECIDE WHAT TO DO. THE DECISION SHOULD BE MADE BY A DIVERSE GROUP OF SCIENTISTS, GOVERNMENT OFFICIALS, AND ORDINARY PEOPLE FROM MANY PARTS OF THE WORLD.

7. THE PUBLIC SHOULD BE INFORMED THROUGH RESPONSIBLE SCIENTIFIC ORGANIZATIONS.

RESPONSE TO FIRST CONTACT? PANIC?

– FEAR OF INVASION OR WAR – INTERSTELLAR INVASION OR WAR IS PROBABLY

NOT FEASIBLE GIVEN THE DIFFICULTIES OF INTERSTELLAR SPACE TRAVEL (NEXT TIME)

JOY?– KNOWLEDGE THAT WE ARE NOT ALONE– PERHAPS WE CAN LEARN SOMETHING USEFUL

FROM THE ALIENS

SIGNIFICANT EFFECTS ON RELIGION, PHILOSOPHY, ETC.?

•AS PEOPLE RE-EVALUATE THE HUMAN SPECIES' PLACE IN THE UNIVERSE