"Wouldn't it be lovely to make contact with another civilisation that has arisen and evolved independently."
—Dr Carl Sagan
Is it best to send radio signals into space?
The Arecibo Ionospheric Observatory, located in the tropical jungles of Puerto Rico, is the world's largest, single radio and radar telescope, with a staggering dish diameter of 305 metres. The massive mechanical listening device of the Arecibo telescope is so powerful that it can communicate with a similar telescope situated anywhere in our galaxy.
At 1.30 p.m. on Saturday, 16 November 1974, a brief interstellar message of 169 seconds duration was transmitted from this facility at radio frequency 2380MHz toward a great cluster of stars known as Messier 13 (M13) or Hercules Globular Cluster, which lies about 25,000 light years away from Earth. (1)
M13 is a concentration of 300,000 stars confined to a radius of about 18 light years and is situated just on the outskirts of our galaxy.
The Arecibo message was the brainchild of Professor Frank Donald Drake, then Director of the Arecibo Observatory, with assistance from members of the National Astronomy and Ionosphere Center of Cornell University. The narrow-beam radio signal carrying the message gave an average power output of 3,000,000,000,000 watts and is the strongest radio signal yet sent out into space by humans.
If any technical extraterrestrial civilization having a radio telescope should be lucky enough to detect the Arecibo signal in roughly 25,000 years time, let alone stumble upon the technology of radio communication, they must have even greater luck to work out the following set of enigmatic procedures:
Step 1: Start listening, and listening, and…
They must listen on a frequency close to 2380MHz and somehow record the entire 1,679 bits of binary information (i.e., on-and-off pulses) lasting only about three minutes.
Step 2: Remember your prime numbers!
Assuming the aliens have not made the mistake of considering these pulses as coming from a pulsar or some other natural object in the universe, they must then realise that the number 1,679 in itself is the product of two prime numbers (23 and 73).
Not sure what a prime number is? In case you were dying to know a mathematical fact or two in your life, a prime number can only be divided by 1 and itself. No other number can be divided into a prime number in order to give a whole integer amount.
Step 3: Try arranging the bits of binary information into a rectangular grid of dimensions corresponding to the prime numbers
They must then hit upon the idea of arranging the "bits of binary information" into a rectangular grid with dimensions 73 rows and 23 columns.
Step 4: Visualise and see the patterns lying in the message
Then miraculously they should notice within all those binary digits the crude shape of a human figure, a "map" of the solar system, structure of our DNA molecule, a radio telescope, and other kinds of information! For a clue, download this document.
What would the chances be for an alien civilization to achieve all of this and to recognise the message for what it is? In all probability we should not hang around for the reply!
Sending a message closer to Earth
The chances of receiving a reply from ETs may have improved somewhat in 2009 following the decision by scientists to send a much longer message to a star much closer to the Earth.
On 28 August 2009, scientists at the Tidbinbilla Tracking Station in Canberra, Australia, sent a 2-hour long message to a red dwarf lying 20.3 light years away where it is thought any life on the planet Gliese 581D might be able to pick up and reply to our message.
Unfortunately advanced life, if any, on this highly watery world would need to have developed the equivalent of hands to extract the metals and develop a radio telescope to detect the message. And if that is not enough, the message just so happens to be in English in case the aliens aren't challenged enough by their own language and environmental difficulties.
Oh well, at least it is better than nothing. The message was merely to encourage youngsters to see the value of a career in science (i.e., sending messages to distant stars even if there is virtually no chance of a reply). A nice job if you can get it. On the positive side, at least we only have to hang around for a little over 40 years to see how successful we were. And then it will be our turn to be seriously challenged by a possible reply on top of all the environmental, political and social problems of the day we must grapple with.
Surely there must be an easier way.
The problems with sending radio signals into space
Transmitting radio signals into the ubiquitous emptiness of space certainly brings out a few teething problems associated with this form of communication. Firstly, we have not the faintest idea how much time is required to broadcast a radio signal to the stars so as to assist any unsuspecting extraterrestrial civilization to take serious notice of our message. Secondly, only a technological society could intercept and reply to a radio signal directed at them. And thirdly, we have no way of knowing whether a technological society will receive our message and has understood it unless we hear from them. But that may take many years, perhaps thousands or even millions of years before we receive their reply, and there is no guarantee of a reply anyway.
Another problem worth considering is this: Do we really need to make ourselves known to others?
Incidentally, ever since the great U.S. electrical engineer Nikola Tesla invented the radio in 1893, humans have been unintentionally leaking out into space radio, television and powerful military radar waves. The consequences of our action has been an ever-expanding shell of strong radio emissions from Earth over the past century. Many of the more powerful earthly signals can be detected on any of the dozen or so Sun-like stars lying within 100 light years away by any civilization technologically equivalent to ours. So perhaps we are already making ourselves known to others.
Would it be better for us to listen for alien radio signals? As Robert Baden-Powell once said:
"If you make listening and observation your occupation, you will gain much more than you can by talk."