Finding signs of life elsewhere in the universe will not be easy

The story in "A for Andromeda", a book by Fred Hoyle and John Eliot, starts with the last-minute tests before the opening of a new radio telescope.

During those tests a signal from an extraterrestrial civilization is picked up. The signal was coming from the Andromeda Galaxy. The movie "Contact" is also about the detection of alien radio signals. Both these stories rather understate how poor the odds are of detecting radio signals from alien civilizations, providing there are signals to detect.

Imagine if you heard there was a good television program on tonight, but somehow you could not remember when, or on which channel.

With possibly hundreds or even thousands of channels available, spending the night flipping would be a nightmare. Now add a few more complications. Instead of thousands of channels, imagine billions.

Another complication is that we have to be pointing our antenna at the right object in the sky at a time the extraterrestrial signals might be arriving.

Then, in addition, even if the transmitter producing the signals is very powerful, by the time the signals have crossed interstellar or intergalactic distances they will be extremely weak. We will almost certainly have to stay on that frequency channel for a while, allowing time to collect a detectable amount of signal.

Then of course, what sort of signal are we looking for? We cannot assume those alien civilizations do things exactly as we do.

There are two sorts of signals we could look for. One kind is the complex mix of signals we use to pass information to or entertain each other. Most of this signal power goes blasting off into space. If you were on an alien spaceship arriving in the Solar System you would immediately detect the cacophony of radio signals coming from Earth. You would almost certainly not be able to make sense of what you are detecting, although the signals would clearly not be natural.

Our main use of radio is as a means to move information. We generate a radio wave, imprint our information on it and then send it out to recipients. They receive it, extract the information and discard the radio wave. There are many different ways to imprint information on radio waves, and unless you know how that was done, you won't be able to make sense of the signals.

If we really want to communicate with aliens, a different approach is needed. The information imprinted on the signal we send will have to be very simple and easy to extract. For example, turning the signal on and off in a recognizable pattern. In addition, we will need very high power transmitters, and large antennas to focus that power in the desired direction.

At the receiving end we still have the problem of where to look, when, and which of the billions of frequency channels to tune to. Luckily, we now have digital receiving systems that can observe at millions of frequency channels simultaneously, and radio telescopes such as CHIME, the Allen Telescope Array and the Low Frequency Array Radio telescope (LOFAR), which can observe large patches of sky at the same time. This greatly improves the odds. However, even millions of frequency channels covers only a fraction of the radio frequency spectrum.

Finally, we need to be monitoring the right patch of sky at the right time.

Even if we get a signal, and then send a reply immediately, we cannot expect to have much of a conversation. If the signal comes from a star 10 light years away, which is very close, that signal took 10 years to get to us and our reply will take 10 years to get to the aliens.

With each interchange taking 20 years we are unlikely to get beyond letting each other know we are here.

In "A for Andromeda,” the signal came from the Andromeda Galaxy, over two million light years away. Not surprisingly, in the story, nobody bothered to send a reply. However, just knowing we are not alone will make history.

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Venus, Saturn and Mars lie close together low in the dawn glow. Venus is the brightest and Saturn the faintest. The Moon will be new on April 1.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.