Communication with Another Civilizationphysics.wm.edu/~hancock/171/notes/interlude2_wed.pdfphysical object that far is very unlikely and would take extremely long periods of time …

Communication with Another Civilization

On Pioneer 10 and 11 was a plaque designed by Carl Sagan. The plaque shows a schematic of the hydrogen hyperfine transition (21 cm line), a figure of a man and a women, the relative position of the Sun and 14 pulsars and the solar system.


Pioneer 10 will pass near the star Altair in about ¼ million years.


Voyager 1 and 2 each had a golden 'phonograph' record. The record contained sounds and photographs encoded in an analog format. Voyager 1 will pass near a star is about 40,000 years


So do we wait for many thousands of years for a return message? The odds are minuscule that any of our spacecraft will even come remotely near to being discovered by another civilization. Sending a physical object that far is very unlikely and would take extremely long periods of time … longer than our civilization may last.

We can wait to detect the radio signals from another civilization or send our radio signals to them. But what might their radio signals look like and what would we send? It would probably be something to do with math and/or physical knowledge of the universe.


Something related to math is probably the most obvious way to distinguish your signal from a naturally produced signal. But math is something that is intrinsically related to the human brain. Would a human 'math' radio signal be something an alien civilization understand?


Math is heavily dependent on symbols. Even our Hindu–Arabic numeral system we use today was only introduced into Europe in 1202 by Fibonacci. Until the last couple of hundred years the idea of the square of a number was primarily a geometrical concept (as in the area of a square figure). Math is only as powerful as the its symbols. It might all look like gibberish to an alien unless they learned the math alphabet.


The most basic way to communicate integer numbers to an alien with a radio beam would sending binary numbers. This would be encoded as 1 and 0. These would be simple 'on' and 'off' of a 'carrier' wave e.g., 1.42 GHz hydrogen spin flip frequency.


You could not send many basic math constants like π and e because they are irrational numbers. Irrational numbers are numbers that can not be expressed as the ratio of two integers. As a decimal number they continue for every without a repeated pattern i.e., π = 3.14159 …You can encode an approximation but not with a simple binary number.

Even scientific notation is difficult without knowing the encoding. If you want to express the size of Earth as the number of side by side hydrogen atoms (a very large number) and alien would have to know the encoding.Your computer does this all the time with 'floating' point numbers but the computer knows the encoding.


A long sequence of integers can be be a way to send information. The Fibonacci sequence would be one sequence you could send as a series of integers.

Another might be simply a sequence of powers of two:1,2,4,8, 16, 32, 64, 128, 256 etc.

However both of these occur in nature but not in radio noise.


Carl Sagan proposed sending a sequence of prime numbers. Prime numbers are integers. Of course, they would have to be transmitted as binary numbers (1 and 0). Sending the first 220 prime number would tell an alien where are a technically sophisticated civilization. The 1.42 GHz hydrogen spin flip frequency would be a natural if you have enough directed power for the radio beam.


Question: What 'math' radio message could we send that might convince an alien civilization that we are intelligent beings?


Question: What other type of non-math radio message could could we send?


Question: Are we smart enough to 'decode' a radio message from an alien civilization?


Question: So we send a message and receive a reply many years later. What would be the next step? What message would be our next message? Who would decide what we send or if we send.

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Communication with Another Civilizationphysics.wm.edu/~hancock/171/notes/interlude2_wed.pdfphysical object that far is very unlikely and would take extremely long periods of time …