|
SETI is the
This note will briefly explore |  |
INTRODUCTION
|
SETI is the
This note will briefly explore | |
Humans have been asking this question for as long as they have been around.
For all of recorded history we have indications of a belief in life beyond the Earth.
The earliest humans had a strong belief in gods – usually in humanoid form - that lived in the heavens and watched over the planet.
COSMIC PLURALITY
A belief in other worlds like our own populated by creatures similar to us is often termed ‘cosmic plurality’. The first historical indications of secular cosmic plurality are from India in the 8th century BCE and from Greece in the 6th century BCE. A group of Greeks known as atomists – because they believed in ‘atoms’ as the smallest constituents of matter – espoused the idea of cosmic pluralism. Leucippus, Democritus, and Epicurus were the leading proponents of this group.
The philosopher Aristotle opposed this view and unfortunately for human progress his ideas held sway for well over a millennium. It is interesting that the early Greeks before Aristotle held many ideas about the Universe that we now believe are correct (eg a round Earth, a heliocentric solar system). This all vanished with Aristotle.
The next we hear of cosmic plurality is in medieval Islamic thought. Many medieval Muslim scholars endorsed the idea of cosmic pluralism. Imam Muhammad al-Baqir (676–733) wrote "Maybe you see that Allah created only this single world and that He did not create humans besides you. Well, I swear by Allah that He created thousands and thousands of worlds and thousands and thousands of humankind.“ Cosmic pluralism was depicted in fictional Arabic literature. "The Adventures of Bulukiya", a tale from the One Thousand and One Nights (Arabian Nights), depicted a cosmos consisting of different worlds, some larger than Earth and each with their own inhabitants.
The first person to seriously raise the idea of cosmic pluralism in the West was Giordano Bruno who introduced the idea of multiple worlds in a dialogue from the mouth of his character Philotheo in his work “De l'infinito universo et mondi’” (1584). Dialogue was a standard device in these times to introduce new ideas. Philotheo claims that "innumerable celestial bodies, stars, globes, suns and earths may be sensibly perceived therein by us and an infinite number of them may be inferred by our own reason.“ For this heresy of cosmic plurality and other anti-Aristotelian ideas he was charged by the Inquisition and burnt at the stake in 1600.
In 1686 preceding the period of the Enlightenment the French philosopher Bernard Le Bovier de Fontenelle wrote a foundational work entitled “Entretiens sur la pluralité des mondes” (Conversations on the Plurality of Worlds) . This definitive work, speculating on ideas arising from the new Copernican cosmology, resulted in cosmic pluralism entering into the mainstream of scientific thought during the Scientific Revolution. It was rapidly adopted by many others of the time.
The current interest in SETI probably started with a paper written in 1959 Gieseppe Cocconi and Philip Morrison showing that telescopes then used by radio astronomers had the potential to detect radio signals from interstellar sources.
Frank Drake, a radio astronomer, was the first person to actually attempt to listen for extraterrestrial signals with a 26m radio telescope at the National Radio Astronomical Observatory in Greenbank, West Virginia, USA.
Drake also proposed an equation, now bearing his name, to tray and compute how many civilisations might exist in our galaxy that had the technology to communicate by radio signals. The Drake Equation
The physicist Enrico Fermi also proposed a paradox which now bears his name, by making the statement "“If there are extraterrestrials, where are they?”. The Fermi Paradox.
Many searches have now been made at various frequencies in the radio spectrum and some in the optical spectrum. All searches have so far produced a null result.
R-SETI
Most SETI researchers believe that the radio spectrum is the best spectral region in which to search for extraterrestrial intelligence – because of low background noise.
Most people think that Frank Drake’s Project Ozma was the first attempt to detect extraterrestrial signals. But in 1929 the US Army had several radio operators listen for signals from Mars.
COMMUNICATING WITH ETI
If we detect an extraterrestrial civilisation should we try and communicate with it (CETI) or send it a message (METI)?
Some people think we should. Some people, including some scientists think the risk is too great and we should not.
The Message from Arecibo
In 1974 the giant 300m radiotelescope at Arecibo on the island of Puerto Rica sent out a short radio message in the direction of the globular star cluster M13. It was a digital message of zeroes and ones and contained basic information about humanity and Earth. It was sent in the hope that extraterrestrial intelligence might receive and decipher it. As the distance to M13 is 25,000 light years, it will be at least 50,000 years before we might expect a reply. Part of the message is shown below.
0000001010101000000000000101000001010000000100100010001000100 1011001010101010101010100100100000000000000000000000000000000 0000011000000000000000000011010000000000000000000110100000000 0000000000101010000000000000000001111100000000000000000000000 0000000001100001110001100001100010000000000000110010000110100 0110001100001101011111011111011111011111000000000000000000000 0000010000000000000000010000000000000000000000000000100000000 0000000001111110000000000000111110000000000000000000000011000 0110000111000110001000000010000000001000011010000110001110011 0101111101111101111101111100000000000000000000000000100000011 0000000001000000000001100000000000000010000011000000000011111 1000001100000011111000000000011000000000000010000000010000000
The length of the message was the product of two prime numbers, and it is thus possible to form an image from the message. The result is shown below. (The colour version is an artificial enhancement to show the various parts of the message).
Australian METI
COSMOS magazine, the Australian Department of Innovation, Industry, Science and Research, CSIRO and NASA cooperated to send a message toward the planet Gliese 581d on 28 August 2009. The star Gliese 581 is a red dwarf in the constellation of Libra. This stellar system was chosen because it is believed that the planet Gleise 581d lies in the habitable zone of its primary.
The project was titled "Hello From Earth" and received 25,878 messages that were bundled together and transmitted in the direction of the planet by the 70m radio communication dish at the NASA Deep Space Communication Station at Tidbinbilla near Canberra. The messages transmitted were collected from a wide range of Australians including high-level politicians and primary school children.
Before transmission the messages were sent as text files to the NASA JPL facility in California where they were encoded into binary, packaged and tested before their transmission from a 60 kW transmitter feeding the large dish at Tidbinbilla.
SPACECRAFT MESSAGES
A plaque was placed on the side of the Pioneer 10 and 11 spacecraft, in case they are ever intercepted by ETI. They are supposed to be self decoding and contain information about us and where we live. Launch was in 1972.
The two Voyager spacecraft carried a phonograph record, a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth. They were launched in 1977.
BREAKTHROUGH LISTEN
With $100M in funding from Russian Oligarch Yuri Milner, Breakthrough Listen is a project to search for intelligent extraterrestrial communications in the universe. It began in 2016 and will continue for 10 years. Using the Australian Parkes radiotelescope and the Greenbank (West Virginia) radiotelescope as well as the Automated Planet Finder (optical) in California, it will search the radio (1 to 10 GHz) and visible light bands of one million nearby stars and the centres of 100 galaxies. All the data is available to the public.
QUESTIONS
RERERENCES
Steven J Dick, “Life on Other Worlds”, (Cambridge University Press, 1998)
Giuseppe Cocconi & Philip Morrison, “Searching for Interstellar Communications”, Nature, 184, 844- (1959)
AGW Cameron, “Interstellar Communication”, (Benjamin, 1963)
Ron N Bracewell, “The Galactic Club”, (Freeman, 1975)
NASA, “The Search for Extraterrestrial Intelligence”, (Dover, 1977)
Reinhard Breuer, “Contact with the Stars”, (Freeman, 1982)
Paul Davies, “Are We Alone? Philosophical Implications of the Discovery of Extraterrestrial Life”, (Basic Books, 1995)
Stephen Webb, “Where Is Everybody?”, (Praxis, 2002)
Paul Davies, “The Eerie Silence”, (Houghton Mifflin Harcourt, 2010)
An Overview of SETI in Australia
FICTION
James Gunn, “The Listeners”, (Charles Scribner’s Sons, 1972)
Carl Sagan, “Contact”, (Simon & Schuster, 1985)
Australian Space Academy