Receiving Radio Signals

Can we listen to ETs?

"Wisdom is the reward you get for a lifetime of listening when you'd have preferred to talk."

—Doug Larson

Is listening for alien radio signals in space better?

There is presumably a better alternative. Instead of transmitting signals into space, some scientists believe it is much more sensible to search and listen for artificial signals emanating from space. As the old Russian proverb says,. "Don't hurry to reply, but hurry to listen." (1)

A more sensible idea? Let us see.

Probably the earliest suggestion for listening to alien radio signals came from the electrical engineer eccentric and inventor Nikola Tesla. In 1896, Tesla suggested that a more sophisticated and powerful version of his wireless electrical transmission system could have the power to contact aliens living on Mars(2)

In 1899, Tesla believed that he may have detected artificial signals emanating from Mars while it remained in the sky. In experiments he conducted at his Colorado Springs experimental station, the signals reminded him of something artificial because they were coming from the planet as a repetitive static signal. It would suddenly stop as soon as the planet set in the night sky. Today, scientists think Tesla may have heard the signals from the powerful magnetic field influencing ionised particles around the planet Jupiter, or he may have been hearing signals coming from Marconi's European radio experiments.

Speaking of the Marconi experiment, the inventor Guglielmo Marconi, together with Lord Kelvin and David Peck Todd gave their belief that radio signals could be used to contact people living on Mars. Interestingly, even Marconi stated that his stations had also picked up potential Martian signals.

With talk of possible Martians possibly communicating with the Earth, it seemed natural that by 1924, with Mars at its closest approach to Earth for more than 80 years, program director David Peck Todd at the United States Naval Observatory with military assistance from Admiral Edward W. Eberle (Chief of Naval Operations) was inspired enough to send up a radio-camera system attached to a high-altitude balloon. When it returned to Earth after reaching a height of 3 kilometres, it was hoped the radio receiver could have detected strong radio signals from Mars. Even with William J. Friedman, a chief cryptographer of the United States Army at the helm of this innovative and broad-minded project, nothing has detected, or at least not something that can be translated into a form of intelligence.

Then the scientific community took more seriously the idea of searching for radio signals in a scientific paper published in 1959

American physicists, Dr Guiseppe Cocconi of Cornell University and Dr Philip Morrison, both former professors in the physics faculty of Cornell University in Ithaca, New York, USA, and now at the Massachusetts Institute of Technology, gave support for this approach in an article that started the entire modern scientific search for ETs (or SETI for short) movement using radio telescopes as the preferred listening device. The article titled, "Search for Interstellar Communications", as published in the pages of the highly respected Nature magazine on 19 September 1959, stated that:

"Few will deny the profound importance, practical and philosophical, which the detection of interstellar communications would have. We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chance of success is zero." (3)

But again any form of listening of this sort must assume extraterrestrial civilizations are not aware of the various problems associated with transmitting radio signals into space. Either that, or we must assume there are civilizations out there willing to spuriously send out signals without any expectation of a reply (perhaps they are really lonely, have no understanding of limited resources and what a budget is, and/or have nothing else to do in the vastness of space and time — the alien equivalent of being bored). Even if ETs are purposefully sending messages into space on a continuous basis without any expectation of a reply (they have to be dumber than us in our attempts to send radio signals into space just for the sake of showing its desire to communicate with anyone in the cosmos), there is still the problem of establishing what form the alien message will take. Of greater concern is the problem of not knowing exactly where to look for such messages — that is, to which sun-like stars should we be pointing our receivers, and at what frequency? Radio telescopes can only pick up signals that are precisely directed to them and tuned in properly, otherwise the signal is far too faint to be noticed.

To put it succinctly, scientists are hoping extraterrestrial civilizations will continuously send out radio signals into space of which at least one of them is directed to the Earth at a specific frequency, and we are at the right time to notice the signals.

This is all that's keeping some SETI scientists listening for alien radio signals.

As Dr James Rick Forster, an American astronomer and dedicated SETI scientist with a radio observatory at Hat Creek in California, said:

"What we're looking for is something like a radio broadcast which has been in outer space and pretty much aimed at us. So what's required here is an intelligent civilization with technology advanced enough to be able to produce such a radio tone. What's furthermore required is that they are actively trying to contact us."

And if that is what we hope will be happening out there, then someone has to be listening right? In which case, it might as well be us doing the listening if no one else in the cosmos has done it yet. Because without listening, there is no chance of ever picking up the signal. Just as Cocconi and Morrison pointed out in their article. As Dr Carl Sagan said:

"The chance of success in picking up messages directed our way depends in large part on how serious we are at investigating such possible signals."

So long as ETs are serious about sending radio signals into space and do not mind how long it takes and have no expectations of receiving a reply or at least don't expect to receive anything useful in the reply to transform their understanding of the universe, then this would have to be the cheapest and most efficient way to communicate with ETs.

The only thing is, is this truly the smartest way to communicate between civilisations separated by the vastness of space and time?

Indeed, how likely is it that we can detect an alien radio signal in our cosmic neck of the woods using the technology of radio telescopes? And will we be able to recognise it as such (i.e., alien and something artificial)? To the SETI scientist, the answer to these questions will depend very much on where we can find such signals, how long we have to spend to listen and find this right radio signal when it finally arrives, and to hope the aliens will make it easy for us to find it. Of course, what the signal will look like is anyone's guess, but hopefully it will be easy to recognise for the scientists.

SETI scientists are certainly hoping that there are enough civilisations out there willing to send radio signals into space with simple messages, and we do not have to wait long before we can pick up one of them.

Between the 1960s and the turn of the 21st century, various short-term SETI searches were conducted, and there are plans to build larger and more dedicated radio telescopes (but likely will never be built due to their multi-billion dollar price tags).

In 2015, the most serious international effort is underway to search for the pesky signal following the announcement from Stephen Hawking and Russian billionaire Yuri Milner to fund the Breakthrough Initiatives. This is considered the most powerful attempt by humans to search for alien radio signals, using an array of radio telescopes dedicated to the search.

Where to find the pesky signal?

To make the horrendous task of searching for this proverbial "needle-in-the-cosmic-haystack" a little easier for the scientists, Cocconi and Morrison have proposed that we should carefully search in the frequency range between 1GHz and 60GHz where the background radiation noise from the universe, the Earth's atmosphere and the Milky Way is at its minimum in this range and it also includes the neutral hydrogen (H2) and hydroxyl radical (OH-) spectral lines of 1.420GHz and 1.720GHz, respectively, first pointed out by Morrison and Cocconi in 1959, which signify water (H2O) in the minds of scientists. For these reasons, scientists assume an alien civilization will recognise all these properties and transmit a radio signal somewhere within this "waterhole" band.

The frequency range chosen by SETI scientists is still very narrow compared with the rest of the electromagnetic spectrum. Despite this, it is still quite a massive task to scan the entire band in the hope of stumbling across an alien signal. Indeed, it has been said that if a narrow, single-channel receiver was made to scan this entire microwave band, and at the same time look at all the possible directions where an extraterrestrial signal might come, it would take thousands of millions of years for the search to be completed.

Good news! The search has been made a little more manageable owing to recent advancements in integrated electronics, which have seen the development of sophisticated radio receivers capable of scanning billions of channels simultaneously. Combine this with new mathematical algorithms developed by physicist Dr Kent Cullers to more quickly sift out the distinctive tones of television and radar signals from the radio noise and some scientists are feeling they could have an unprecedented opportunity of detecting alien radio signals in space.

In terms of the frequency of the alien signal, scientists are assuming aliens are using television and radar technology for their communication.

Beyond that, scientists just have to find a way to solve the problem of how to interpret and understand the content of the alien message when we recognize it, assuming, of course, we can intercept it. For this reason, scientists are crossing their fingers that an alien civilization will make it as easy for us to understand as they possibly can, just as we have tried to make it easy for the alien who may pick up our innocent little message sent by the Arecibo radio telescope in 1974.

The general scientific feeling (nothing like a bit of feelings in all this good scientific work!) is that the message will be nothing more than a way of saying "hello" in the symbolic language of science — perhaps as enlightening as sending a list of prime numbers in binary form (so much for asking ETs to help us solve our world problems)!

As Morrison remarked:

"Messages will be anticryptic and the transmitting civilization will want to be as easily understood as possible." (4)

Or what if aliens don't want to make it easy for us? Is it possible aliens are already aware of our existence and are choosing to keep quiet? And what if aliens have already solved the problem of interstellar travel? This last question could be particularly pertinent when we realise the greater benefits of physically visiting other worlds and making the communication. So much more can be exchanged in one hour's worth of conversation than many years of waiting for a message to reach the home of an alien civilisation, and an equally long period of time to wait for a reply. A bugger if by any chance you have to ask the ETs, "Sorry mate! We just missed one part of the message. Can you re-send it again?" And if we start this conversation with a greeting like, "Hello!", we are going to have to wait a whole lot longer.

Despite the overwhelming problems scientists must overcome to find the all-important alien signal in space, many are still pursuing the issue. There is a belief that by building bigger and more sophisticated instruments, it will increase the chances of ferreting out that elusive and tenuous signal in the vastness of space, time and frequency. It is as if scientists believe the problem of finding ETs will be solved, and only solved, by building a big enough radio telescope.

Or why not engage more radio telescopes separated over a great distance and with new equipment to handle the task? For example, on 20 July 2015, Russian billionaire entrepreneur Yuri Milner has announced that he will spend US$100 million to fund a new 10-year search for ETs. To show he is genuine in his aims, he invited several superstars of the scientific world — Professor Stephen Hawking, among other scientists — to join him on stage as a show of scientific support to the ambitious businessman. The project, known as Breakthrough Listen, will bring together a number of worldwide researchers to scan the skies for evidence of alien life via an artificial electromagnetic signal emanating into space. This will not be a "pussyfooting" and quick focus on a few of the closest and older variety of sun-like stars to our Sun and listen over several years to see if anything has emerged from them to reach the sensitive electronic ears of current radio telescope technology. Milner expects the search (costing approximately $66 million to build the equipment and hire astronomers, and the remainder to rent out two of the largest radio telescopes in the world in West Virginia and Australia) to cover 1 billion stars closest to Earth and 100 galaxies outside the Milky Way. By grouping together such vast numbers of stars in a concentrated search, Milner believes the probability of finding an alien radio signal should increase dramatically.

Milner confirms the effort will scan 10 times more of the sky, process data 100 times faster, and increase the range of radio frequencies to scan than any previous search scientists have ever conducted.

Yet despite all this effort, and with so much effort being poured into building bigger and better radio telescopes and covering more of the sky, are the scientists having any luck in finding the elusive radio signals?

Project Ozma

The first serious search for extraterrestrial signals began in April 1960 by Dr Frank Donald Drake. He exploited the listening power of the National Radio Astronomy Observatory located in the Blue Ridge Mountains in Green Bank, West Virginia, USA. The project, named Ozma, used the single-channel 185-metre radio telescope as a listening device directed at hundreds of stars nearest to Earth, especially two of the most favourable candidates for extraterrestrial life, Tau Ceti and Epsilon Eridani.(5)

After 200 hours of listening spread out over a period of three months, nothing was detected in the neighbourhood of frequency 1420MHz. The only exception was a strong, pulsed signal in the direction of Tau Ceti that faded out soon after commencement of the project on 3 April 1960. When Drake broke news of the mysterious pulsed signal, U.S. officials from the Pentagon in Washington, USA, quickly issued an explanation for the signal as emanating from a highly secret U.S. military experiment on radar countermeasure. (6)

Today, the search for alien signals has been given the equivalent of a steroid injection thanks to the financial generosity of Yuri Milner in July 2015. Why the ambitious effort? As Milner said to a reporter from The New York Times:

"We have a responsibility to not stop searching. It should always be happening in the background. This is the biggest question. We should be listening."

The status of listening for alien radio signals today

To this day, scientists have had no such luck despite tremendous efforts to increase the probability of success through improved radio telescope technology. This lack of clear-cut evidence is surprising (7) a few scientists, including the late Dr Carl Edward Sagan, former astrophysicist and professor of astronomy at Cornell University, USA, and Dr Paul Horowitz, a professor of physics at Harvard University, USA. Does this mean we are alone in the universe? Highly unlikely according to observations and arguments presented so far. As Dr Wolfram Thiemann of the University of Breman, West Germany, said:

"Chemical evolution is definitely growing on other planets and in interstellar material. There is more and more evidence that there are other planets like Earth in outer space." (8)

If the universe is quietly humming with the sounds of life, then why haven't we heard from them by now?

Perhaps the aliens are out there, but are listening for evidence of other lifeforms just as our scientists are doing right now with their "you beaut" radio telescopes. Could everybody be listening and nobody sending? As CSIRO astronomer Dr Kelvin Wellington said:

"There's a joke around that everybody might be listening, nobody sending." (9)

If this is true, then surely someone must have realised this fact and started sending signals out into space to begin the whole communication process, considering how old the Milky Way galaxy is, let alone the universe. Yet our scientists have detected nothing.

Or could it be that we are the "new kids on the block" so to speak and that other, possibly more advanced, civilizations in our interstellar neighbourhood are simply not all that interested in us?

"Just another fly on the wall," as an alien might say. "Once you've seen one fly, you've seen them all."

If so, then perhaps we need to be a little more proactive in finding radio signals from an alien civilization. For example, could we eavesdrop on the radio and TV signals emanating from an alien civilization? Again it depends on whether aliens are using the same kind of technology as we are for transmitting radio and TV signals. If aliens are sending the signals through cables or narrow, high-frequency laser beams, we are in big trouble.

Or is the universe teeming with life but have not reached the point of developing radio telescopes? Perhaps life is still struggling on other planets in the Milky Way and need more time to evolve and develop the necessary brain and manipulative limbs needed to build a technology. If so, only a few truly advanced civilisations exist and are spread out to great distances. Seems unlikely considering it has taken 6 billion years to create the Sun, Earth, life on Earth, and eventually a humanoid creature capable of developing the require technology. Surely this must be the run of the mill timeframes and knowing there are plenty of sun-like stars to provide this amount of time.

Or is there another explanation?

Despite these possibilities, it hasn't deterred the imagination of astronomers by mid-2006 with their grand visions of building the world's most powerful radio telescope called the Square Kilometer Array (SKA). When in operation by 2020, SKA with its 1,500 radio antennas will be 10,000 times more sensitive than any other radio telescope (including the Arecibo) and would be used to study the universe in the radio wave region of the electromagnetic spectrum between 0.1 and 32GHz to an unprecedented level of detail. It would be well within the frequency range for humans to pick up the potential for alien radio and TV signals being leaked by distant planets assuming their technology is on par with our own. Such sensitivity should be enough to pick up unintentional or leakage radio signals at the power equivalent to present-day human radio and TV transmissions for the four closest stars to the Sun. Or if the transmissions are from more powerful pulses of radiation known as radar like those used in our airports, SKA could detect them up to a range of 500 stars.

As Joseph Lazio of the U.S. Naval Research Laboratory said:

"Combined with other bioastronomical facilities, on the ground, in space, and on other planets in the solar system, the SKA will play a key role in finding life elsewhere in the Universe."

Further details about the project can be found at

The SKA project, when it finally gets going, is a nice idea for those scientists searching for ETs. But what if the aliens have already progressed to cable transmissions using light waves instead of radio waves? A rather sobering possibility! Unless there are plenty of civilizations of the same technological capabilities as our own and are deliberately choosing to spuriously emit radio waves into space, the chances are that most other civilizations in our interstellar neighbourhood have already technologically progressed to the stage of using low-powered, narrow beam transmissions such as satellite dishes, fibre optics and cable television. If aliens are using low-powered narrow-beam transmissions, then our chances of success in eavesdropping is negligible. Otherwise life on other planets must be so primitive as to be not so concerned about radio communication (understandable if a predator is about to bite your ass).

Even if other civilizations are more advanced, it still does not explain why they had not had the courtesy of saying "Hello" to us, just to let us know they are out there. We have been spuriously sending radio signals from Earth to a distance of well over 100 light years away. And you don't need an SKA telescope to detect this. Even the one in Arecibo is more than adequate to detect the Earthly signals. And there are plenty of sun-like stars in this region of space. Surely there must be at least one advanced civilization within this range to have noticed our activities.

Nevertheless, the search continues.

August 2017

Actually, the fact that anyone with an Arecibo telescope can detect our Earthly signals has got some scientists wondering, "Why is it that we have not found the alien radio signal?" It seems the telescopes themselves are no the problem. The sensitiveity of the existing radio telescopes should be enough to detect a similar burst of artificial radio energy from our planet. There must be another reason. Now people are thinking, it could be because the speed at which we can sift out the alien radio signal from the noise is just not fast enough.

Now, the latest computing power and new software is making it possible to number crunch huge amounts of data in radio signals received by radio telescopes. Combined with the knowledge of how common planets and sun-like stars are in the Milky Way and throughout the universe, a number of scientists think this should be more than enough to reinvigorate the search for ETs with a new project and find the evidence. It is called Breakthrough Listen Telescopes. It will be the biggest, most expensive, and most serious search for ETs ever conducted. Costing $100 million, the project will last for 10-years to give scientists enough time to see if anything can be found.

The to the success of this project is threefold:

  1. Only narrow-band signals have the highest probability of being artificial in nature (or it could represent a new natural phenomenon).
  2. The software and computing power needed to find this type of signal is now available.
  3. Data on which stars have planets is not sufficient to make highly targeted SETI searches.

Because of these reasons, scientists are confident the answer should come in the next few years thanks to this advancement.

Should we be listening higher up in the electromagnetic spectrum?

Unfortunately, all this work to find ETs using radio telescopes is still going to be limited toi the radio wave frequency band. What if ETs are already communicating with us using visible or infra-red light? Radio telescopes trained to look at radio waves could easily miss the signal if the frequency is much higher up.

Certainly, the frequency of communication on Earth have significantly changed over the past 150 years. Before the advent of technology, humans use their vocal chords to generate sound with frequencies below 30kHz to relay information to others over a very short distance. When the first radio voice transmitter was built using a simple frequency oscillator circuit, it generated radio waves between 1 and 100Mhz and the information transmitted to a receiver tuned to the same frequency could be picked up at a greater distance. Today, television and satellite equipment can transmit information much further away using ultra-high and microwave frequencies ranging from 150Mhz to 40GHz. Having said that, could advanced alien civilizations be using frequencies even higher up near the infra-red, visible and ultraviolet region of the electromagnetic spectrum?

Then again, you might be wondering, "Why such high frequencies? Don't the aliens want to make it easy for us?"

Well, why would they? The aliens might be looking to have an intelligent conversation with a similarly intelligent and advanced civilization that has developed the same very high-frequency transmissions instead of the radio wave kind. Otherwise it would be like asking India's former political and religious leader, Mohandras Karamchand Gandhi (1869-1948), also known as Mahatma Gandhi, if he was alive today, to have an intelligent conversation with former U.S. President George W. Bush.

Has anyone considered searching for ETs in the infra-red, visible and/or ultraviolet end of the spectrum? Surprisingly not that many.

Project Mania, a soviet SETI project conducted by Victorij Shvartsman, was aimed at searching for strange artificial pulses in the optical range which could be construed to an alien civilization. Shwartsman used Russia's six-metre optical telescope at Zelenchukskaya to do all his observations. However, in 1987, Shwartsman died, and the project was abandoned. (10)>

Professor Michael Papagiannis of Boston University, USA, began a search for signs of possible extraterrestrial activity. Using the one-tonne 'super cool" satellite IRAS, he had hoped to detect unusual infra-red sources within our solar system that might be evidence for artificial bodies emitting heat signatures. The project, held at Infra-Red Processing and Analysis Center at Caltech, was in operation for only a short while until it suddenly had to stop. The reason, Papagiannis says, is a lack of sufficient funds. (11)

Maybe we will never know. However, as Morrison pointed out, if an alien civilization really wanted to communicate with us, they would have made it easy for us to pick up their message in the radio wave region of the electromagnetic spectrum by now. But it seems as if the aliens do not want to make it quite that easy for us.

Or are the ETs being rude to us? If that is so, we can be sure scientists would be more than happy to hear a cosmic fart heading their way just to prove the existence of an alien civilization.

But still we have heard nothing.

Is it time to broaden our search to include other extraterrestrial hotspots?

Or could it be that we have overlooked something critical in this ET debate? For example, how about UFO reports? For a clue, check this out.