Laser SETI will look for signals that radio and optical telescopes cannot see

Laser SETI intends to search the sky for a variety of pulsed light signals that might have been overlooked before.

Until now, SETI (Search for Extraterrestrial Intelligence) experiments, whether listening for a radio transmitter or searching for a high-powered laser, have assumed that ET is on-the-air all the time, so that wherever the instrument is pointed, the signal will be there. Laser SETI is the first experiment to circumvent this assumption. (Image credit: SETI)
Until now, SETI (Search for Extraterrestrial Intelligence) experiments, whether listening for a radio transmitter or searching for a high-powered laser, have assumed that ET is on-the-air all the time, so that wherever the instrument is pointed, the signal will be there. Laser SETI is the first experiment to circumvent this assumption. (Image credit: SETI)

IMAGE:Until now, SETI (Search for Extraterrestrial Intelligence) experiments, whether listening for a radio transmitter or searching for a high-powered laser, have assumed that ET is on-the-air all the time, so that wherever the instrument is pointed, the signal will be there. Laser SETI is the first experiment to circumvent this assumption.(Image credit: SETI)

Laser SETI intends to search the sky for a variety of pulsed light signals that might have been overlooked before. Nearly $55,000 has been raised by SETI (Mountain View, CA) for the project on Indiegogo; see https://www.indiegogo.com/projects/laser-seti-first-ever-all-sky-all-the-time-search-science#/.

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SETI scientists spend most of their time looking for the kinds of radio or light signals that we generate on Earth. For example, when Frank Drake began the first SETI observations in 1960, he chose to look for signals similar to those for AM radio broadcasting. It seemed to make sense that if humans use AM radio to communicate, then ET (extraterrestrials) might do the same. But there is a vast menagerie of methods to encode sound into a radio signal, for example, using pulses. Drake did not look for short pulses. If he had he might have discovered a kind of neutron star called a pulsar discovered in 1967 by Jocelyn Bell and earning a Nobel Prize for her postdoctoral advisor, Anthony Hewish.

You might imagine that after the first 70 years of radio astronomy we would have noticed all the types of radio signals that nature has to offer. But you would be wrong. In 2008 Duncan Lorimer and coworkers discovered a completely new kind of radio signal we now call the fast radio burst or FRB. Ironically, FRBs are among the brightest astronomical radio sources in the universe and detectable bursts appear hundreds of times every day.

Why did it take so long for someone to discover FRBs? Because no one had guessed that enormously bright singleton radio pulses that last only a millisecond were even possible in nature. Hence, no one had designed a telescope capable of detecting them until the twenty-first century. Their discovery required a radio telescope with an appropriate response time (milliseconds) and exploration of a very large fraction of the sky.

Switching gears now to optical SETI, until now searches have been designed to find either continuous laser signals lasting hours at a time, or extremely short laser pulses lasting only one billionth of a second (one nanosecond). These searches have a simple motivation; since the most powerful lasers on Earth operate either continuously or by generating nanosecond pulses, we suppose that ET will communicate with those types of signals. But isn’t this anthropocentrism? These searches are good as far as they go, but they are blind to pulse durations lasting one millionth or one thousandth of a second.

At the SETI Institute, we are mindful of anthropocentrism. We believe in the necessity of exploring all kinds of electromagnetic signal types, and particularly, all possible light pulse durations. And generally speaking, most optical telescopes examine only a tiny fraction of the sky at a time. Even the so-called wide field of view optical telescopes used in the Sloan Digital Sky Survey or the Large Synoptic Survey can probe only about 1 part in 5,000 of the sky at any given time.

That is where Laser SETI comes in. Laser SETI will observe all of the sky, all of the time so even relatively rare events can be found. Laser SETI can discover pulses over a wide range of pulse durations, and is especially sensitive to millisecond singleton pulses which may have been overlooked in previous astronomical surveys. There are good reasons to imagine that ET might produce millisecond laser pulses (hint: light-sail spaceships). But equally exciting is the fact that by exploring new territory our chances of finding something completely unexpected are not zero.

SETI invites you to become a part of this scientific endeavor. Preliminary designs and proofs of principle are complete. When we meet our fundraising goal of $100,000, we can install the first of several optical telescopes around the world and begin searching in this new way. We hope you will join us.

SOURCE: SETI Institute; http://www.seti.org/node/3280

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