We have been searching for signs of extra-terrestrial life for over 100 years, and so far, we have found no evidence of anything beyond our planet.
Out of all the billions of stars just in our own galaxy, the Milkyway, with all the billions of associated planets, let alone the billions of galaxies in the rest of the universe, we haven’t seen or heard of anything that we would consider as proof of intelligence.
But what are we searching for, and how are we searching for it?. We are framed by our own human expectations, our current technology and understanding of the universe and the physics that we believe make it up.
In other words, we are looking for what we might expect to see based on our current situation, if beings are using more advanced technologies, we might never find them. A bit like showing a Victorian a smartphone, only just over 120 years difference but a world away in technology.
So let’s look at what we have done to try and find proof of intelligent life beyond planet Earth.
Before we go any further, we have to preface this with a couple of assumptions.
Firstly that there is intelligent life out there, because if there aint any then it seems like an awful waste of space, to quote from Carl Sagen’s “Contact”
Secondly, what intelligent life is out there has reached the point where they can broadcast their existence beyond the confines of their own planet, be that intentionally or as a by-product of communication among themselves.
Also that any intelligent beings are active at the same time as us. If they reached the same ability to transmit using radio as we have now, even as little as a thousand years ago, an infinitesimally small time difference in cosmic terms, we could have missed them. Just look at how our politics and attitudes flip-flop almost from year to year, maybe they decided to keep radio silent after a time or moved on with tech we don’t yet know about.
Sounds obvious but don’t forget that it was just at the turn of the 20th century, 120 years ago that we learned how to send signals by radio, and these were only meant to be received by other humans.
Ever since, we have been leaking radio waves into space, from the most basic spark transmissions of Marconi’s first tests to high-speed data communications with satellites and space probes of today and everything else in between.
By now, these signals will have reached over 1000 nearby stars, and if there were intelligent life in this area, they could have deciphered it and sent a reply back to us, providing that after seeing our TV content, they hadn’t deemed us too mad, bad and dangerous to know.
Back in 1877, Italian astronomer Giovanni Schiaparelli whilst studying Mars, saw features which he called canale or lines connecting darker patches on the surface that would change with the seasons.
The word canai was mistranslated into English as canals, and soon, people began to think that these canals were an irrigation system linking the dark areas, which might be lakes and vegetation built by Martians to irrigate the planet’s surface.
In 1896 Nicola Tesla thought that an extreme version of his wireless electrical transmission system could be used to contact these intelligent beings.
Even though the canals of Mars were later proven to be an optical illusion, the thought that Mars could be a world like Earth populated by intelligent beings took off and was boosted by one of the first Sci-fi novels, H.G. Wells’s War of the Worlds.
This portrayed the Martians as an alien species coming to colonise and take over the Earth, which some believed it to be a play on our own colonisation of the new world and its more primitive peoples. This trope has been with us ever since and has led some to advocate not sending out signals to potentially hostile ET’s but it did begin the search for signs of life outside of our planet.
In 1899 Tesla thought that he had picked up odd repetitive static signals which seemed to cut off when Mars set in the night sky. Later analysis of his data later pointed to possibly picking up Marconi’s early transmissions or even naturally occurring noise from Jupiter’s moon IO as it moved through the magnetosphere of Jupiter.
In the early 1900s, Telsa, Marconi and Lord Kelvin thought that radio could be used to contact Mars and Marconi said that he thought he had picked up Martian signals with his equipment.
On August 21st to the 23rd 1924, Mars came closer to earth than at any time in the previous century or the next 80 years. In the US, a 36-hour period of radio silence was promoted for 5 minutes on the hour every hour. During this time, the United States Naval Observatory used an airship to lift a receiver to 3000 meters to listen for signals coming from Mars and try and translate anything they received but nothing was picked up.
In 1959 Giuseppe Cocconi and Philip Morrison wrote a paper proposing searching the microwave spectrum centred around the Hydrogen line at 21cm wavelength or 1.42Ghz for signals. Cocconi wrote “The probability of success is difficult to estimate; but if we never search, the chance of success is zero.”
The reason for using the Hydrogen line is that at this wavelength, signals pass through cosmic dust and gas clouds much better than visible light as well as our atmosphere and the universal nature of hydrogen, would make it the best place to send and receive modulated signals over the vast distances of space.
Using microwaves for communication also means that the antenna used are small as they are a product of the wavelength, 1.42ghz is just 21cm, so spacecraft can use small antennae.
In 1960, Frank Drake later of the Drake equation, a probabilistic argument used to estimate the number of active, communicative extra-terrestrial civilizations in our own Galaxy, started SETI or the “Search for extra-terrestrial intelligence” with Project Ozma using the 26m National Radio Astronomy Observatory, Green Bank, West Virginia.
Drake scanned a 400kHz band around the marker frequency using a single-channel receiver but found nothing of interest. This also highlighted the problem that they were only able to analysis a tiny fraction of the frequencies.
In 1965 Dr John D. Kraus at the Ohio State University Radio Observatory created the “Big Ear”, a flat Reflector in a remote location to search for extra-terrestrial radio transmissions. Big ear was the first to be used to map the sky for radio sources from 1965 to 1971.
In 1971 NASA funded a SETI study including Frank Drake that concluded with a proposal for Project Cyclopes. This was a suggested earth-based radio telescope array with 1500 dishes but a price tag of $10 Billion. Needless to say it wasn’t built, but it laid the groundwork for modern SETI works.
In 1977, Big Ear detected what is now known as the “WOW!” signal, the first signal that looked like it could have been sent by an artificial source.
Many people have misinterpreted the character string “6EQUJ5“ highlighted on the printout as an encoded signal, but this is just a method of showing the signal strength.
The numbers 1-9 indicate a signal-to-noise ratio strength compared to the average background noise measured a few minutes earlier. So the number 3 would be a signal 3 times the average background noise.
For higher signal intensities, the letters A-Z are used. A, being 10-11, B 12-13, C 14-15 and so on. The letter U equals 30 to 31 or 30 to 31 times that of the background noise.
The signal was an unmodulated continuous wave, although any modulation with a period of less than 10 seconds or longer than 72 seconds would not have been detectable.
That was 40 years ago, and although the patch of sky around Sagittarius where the signal was picked up has the checked many times, nothing like it has been found since.
Over the years, there have been many theories about the WOW! Signal and that it could have been created by a star or a comet, there were two comets passing through that area of sky at the time, and the signal was blue-shifted, indicating that it was travelling towards the earth at about 10km/s, however, the comet theory has since been discredited because they produce a much broader spectral content amongst other things.
The main problem with trying to detect a signal is that you don’t when it could be coming, where from in the sky and on what frequency. This is assuming that it being sent via radio and not by some other technology which we have not yet discovered. Maybe using radio to other intelligent beings out there is like us trying to receive an email with two cans and a piece of string.
But until we know better, we have to scan as much of the sky as possible and as many likely radio frequencies as possible.
When we scan the sky for artificial signals, it’s like tuning radio to find a station.
Normally you start at one end of the scale turning the dial and listening for something of interest but instead of listening for stations, astronomers are looking for signals from space that are not naturally occurring noise, quasars, pulsars etc but signals that could have been made by intelligent beings.
This is how they used to look for signals, slowly scanning through the frequencies but it is very slow when you need to scan a range of frequencies that could be millions of times greater than the AM or FM band on domestic radio.
To speed up, the process astronomers use a spectrum analyser which allows you to see a range or a spectrum of frequencies all at once. Using modern digital signal processing using Fast Fourier Analysis a spectrum covering millions of frequencies can be scanned in one go, greatly speeding up the process to find a signal with the right kind of characteristics.
In the 1980, when Carl Sagen, Bruce Murray, and Louis Friedman founded the U.S. Planetary Society to carry on SETI work there were only analogue spectrum analysers available. These had a limited number of frequency filter channels which greatly limited the search.
By the early 80s and with the advancement in digital electronics and digital signal processing, it was possible to build a portable analyser with 131,000 channels called the “Suitcase SETI” for project Sentinel and used with the 26M Harvard/Smithsonian radio telescope at Oak Ridge Observatory in Harvard, Massachusetts.
By 1985 this had been replaced by META or the “Megachannel Extra-Terrestrial Assay” which could scan 8.4 million channels and used frequency Doppler shift to distinguish between signals coming from earth and those from space.
In 1995, META was replaced by BETA or the “Billion-channel Extraterrestrial Assay” which could receive 250 million simultaneous channels with a 0.5 Hz resolution per channel from 1.400 Ghz to 1.720 Ghz. A new feature of BETA was the rapid and automatic re-observation of candidate signals.
On March 23rd, 1999 the telescope that Sentinel, META and BETA had used was blown over in strong winds and servely damaged forcing the closure of BETA.
Since then our processing ability has increased exponentially, and dedicated arrays have been setup to scan the skies like the Allen Telescope Array, named after the project’s main benefactor and Microsoft co-founder Paul Allen.
This was to be a mini cyclopes array but with 350 6-meter dishes with an Offset Gregorian Design and advanced design features which could instantaneously image an area of sky 17 times more than that obtainable by the Very Large Array telescope in New Mexico which has been featured in several movies, including the 1997 Contact.
Using many more smaller antennas its able to gather many times the data compared to traditional large dish telescopes of comparable size. The issue in the past was that all the separate signals had to be combined, which was not commercially viable until the advent of low-cost high power computing.
So far just 42 of the 350 dishes have been built, but most of the hard work and development has been done and the rest of the 308 dishes was estimated to cost $42 million in 2007, about half the price of a traditional telescope array using large dishes with a similar collection area.
From 2007 to 2015 the ATA has been searching for 12 hours a day 7 days a week and found hundreds of millions of technological signals. However, all have been put down to earth-based interference, noise or too short a duration, less than one hour to be classified.
In 2015 The ATA was used to investigate tabby’s star with its unusual light fluctuations of up to 22%, which some thought could be evidence of a Dyson sphere and In 2017, the interstellar asteroid ‘Oumuamua was investigated for signs of technology but no unusual radio emissions on either occasion.
If the ATA could be finished, it would be one of the largest and fastest radio telescopes in the world, this also highlights the problem that funding is still difficult to find for SETI projects, even when companies like Mark Zuckerberg’s Meta can spend $10 Billion on a VR world where legs on the avatars seem to have been an afterthought and Elon Musk can spend $44 billion to buy Twitter when it valued at a quarter of the price and every scientist and his dog is begging for government research grants.
Telescope time is very limited, and too many scientists are chasing too few time slots.
Searching for signals for extraterrestrial sources, be they intensionally sent or not, requires dedicated telescopes like the ATA searching for as close to 24/7 365 days of the year as possible because you never if or when these signals could arrive, and like the WOW signal in 1977 never re-appear again.
Piggybacking onto the largest radio telescopes like the VLA in new Mexico or the Arecibo observatory when its running again or the 500m FAST newly built in China when there is a bit of free time maybe better than nothing but far from the best solution.
There are other SETI-like projects around the world but compared to mainstream science, the importance we place on searching for intelligent life out there which could be the biggest discovery in history, makes you wonder if we should be looking for intelligent life on this planet before looking elsewhere.