Detecting Alien Signals Based on Lasers: A Variant on Optical-SETI

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Are They Out There?

The search for Extraterrestrial Intelligence (SETI) project has been ongoing for some time; so far nothing tangible has come forward. But how do you go about finding a needle in a cosmic haystack? The universe is a vast place, where is the best place to look and what do we look for? Indeed valid questions. Some cynics say that it is the only science with nothing to study - the same might have been said about Galileo or Copernicus in their eras.

The primary research conducted by SETI involves scanning the sky for radio wave signals. The universe produces an abundance of radio waves in all frequencies - a sort of galactic static. With new advances in computing, coupled with sophisticated software filtering out the static, the chances of extracting useful signals have increased.

Granted, the scope of scanning billions of frequencies in the hope of finding a useful signal and then deciphering its meaning and content is bit daunting but within the realm of possibility, but it also has its problems. Transmitting a radio signal in all frequencies is not only impractical but a waste of energy, therefore why not use a more efficient and directional medium like a high energy light laser source?

Detecting Alien Laser Signals

Theoretically there must be some form of intelligent beings other than humans in the universe. And if there are, at what stage of technological evolution are they at. Do they possess the technology and knowhow to broadcast signals that can convey meaning and understanding at a universal level? Were there beings out there that have just simply died off eons ago with technology similar to ours?

There is relevant logic to the notion that we are not the only beings with advance technological resources. There may well be far superior beings that are thousands of years ahead of us possessing superior forms of technology for communication that we know nothing about.

Radio is not the only avenue for searching the universe for intelligence. Lasers are much more efficient at sending signals over vast distances. While radio transmissions can be broadcast in all directions, lasers are highly directional.

We should spending more time looking for external laser activity, looking for distant beacons of pulsating light not unlike a Morse code signal. I use the term “galactic semaphore”. The SETI institute have conducted simple optical SETI searches using a telescope and a photon pulse detection system.

Methods of Laser Detection

The mechanics of sending and receiving laser signals is relatively straight forward.

The transmitter located on Earth consists of high energy laser attached to a ten-meter focus mirror acting as an interstellar beacon. Such a system could be set up to automatically steer itself through a target list of distant stars, sending a pulse to each target at a rate, say, one pulse a second. This would allow targeting of all Sun-like stars within a distance of 100 light-years form Earth..

The receiver uses a laser pulse detector or camera system mounted on a two-meter mirror, with the light from distant stars focusing on an array of light detectors specifically sensitized to detect high energy light pulses. This automatic detector system could perform sky surveys to detect laser flashes from civilizations attempting to contact us.

SETI has already adopted the optical laser techniques in some of its programs. A Harvard-Smithsonian group that includes Paul Horowitz, designed a laser detector and mounted it on Harvard’s 155 centimeter optical telescope. This telescope was being used for conventional star surveys. The light from the telescope was diverted to the laser detector “piggy-backed” to the telescope. Between October 1998 and November 1999, the survey inspected about 2,500 stars. Nothing that resembled an intentional laser signal was detected, the search is still ongoing. [For more on the Planetary Society’s Optical Seti program, click here.]

You can even build a simple laser detector; it is the realm of the hobbyist to construct a detector using just a few off-the-self electronic components. (I have built a few laser detectors with reasonable success and attached them to the telescope’s eyepiece. It is not as sensitive or sophisticated and it’s much larger cousins but it’s a start.)

The Search for Extraterrestrial Life Continues

There is no way to know what frequencies aliens might be using. Trying to transmit a powerful signal over a wide range of wavelengths is impractical, and so it is likely that such a signal would be transmitted on a relatively narrow spectrum for example high energy light waves.

Finding a civilization with some form of language structure could be possible by using a technique called information theory. Originally information theory was developed to find fundamental limits on compressing signals on a phone line. The same algorithm can be used to calculate the complexity of a language.

The greater the number of words or sounds that can be strung together that are dependant on the first word or sounds in a sequence the more complex the language. The English language has a complexity factor of 9 while the Humpback whale has a language complexity of 12. This raises a few more questions, if an Alien called on us who would they talk too? Us or the humpback whales? And if we do happen to get a message, would we be able to understand its meaning?