Guest blog: Answers to your Laser SETI questions

Posted by Alison Klesman
on Thursday, August 17, 2017

By Eliot Gillum

Image credit: SETI Institute

The Search for Extraterrestrial Intelligence (SETI) is a humbling process, to be sure. It’s difficult in the extreme to find something when we don’t know where to look for it, or what it will look like when it appears.

More on that shortly but, before I get any further, I’d like to thank three groups of people. This article wouldn’t exist without those who asked great questions: Tom Scarnati, Richard Hammer, Bartlomiej Król and daughter, Don Schmidt, Dr. Muhsin Sheriff, Michael J. Sloboda, Cormac McKay, Crystal Robin, Roshan Vemula. Because of the overlap and connectedness of their questions, I’ve aggregated my answers rather than addressing them one-by-one. Second, I want to share my deep personal gratitude to the over 500 people who’ve contributed and/or shared their support for the Laser SETI Indiegogo campaign. And of course, I’d be remiss if I didn’t thank my team and colleagues at the SETI Institute, who have moved this project forward in countless ways and constantly demonstrate the highest levels of scientific expertise and integrity.

Now, how can we search when we don’t know what we’re looking for? The answer is easy to define as “an indication of something non-natural and not human.” Each SETI project refines this definition for their particular approach. In radio SETI, it’s traditionally a narrower signal than we’ve ever seen in nature, which is exactly what we always do to tune our communications to be more efficient. Optical SETI has historically looked for a clustering of photons on a very short timescale--nanoseconds. The SETI Institute’s latest project, Laser SETI, is also an optical SETI project but uses a broader definition of a single-color point source of light that comes from beyond the moon and starts and ends at a definite time, whether lasting nanoseconds or minutes. None of these systems are intended to immediately decipher and understand a signal, but really just detect its presence. This is different than communication systems we’re familiar with in everyday life, like WiFi, whose job it is to communicate lots of information, like pictures of cats.

The Allen Telescope Array // Image credit: Seth Shostak, SETI Institute

SETI has been carried out in various ways for nearly 60 years, what more is there to search? The short answer and understatement of the year is “a lot.” The sum total of SETI experiments thus far haven’t yet covered even a tiny fraction of the space-time-frequency domain, and that’s looking for signals we can currently conceive of and detect. Clearly, the first thing to do is cover more of what we understand, starting with the most economical, then as we gain access to new technologies, like gravitational waves, we can search them too someday.

Just which frequency (or color of radiation) to look for is a big problem. Project Ozma in 1960 searched two stars using a single-channel receiver over a miniscule portion of the radio dial. Today, the SETI Institute’s purpose-built Allen Telescope Array searches over 1000 times that amount of radio spectrum using 70 million channels, but there’s another million-fold increase required to cover the full radio dial. And with the reasonable budgetary assumption that we’ll be conducting these experiments from the surface of the Earth, there’s another spectral “window” in our atmosphere that we colloquially refer to as light—from ultraviolet, through the visible, into the deep infrared. Infrared might be an ideal choice if someone is intentionally trying to signal us, for instance, as it passes through interstellar dust much better because of its longer wavelength, but our detectors for it are less suitable and more expensive. And remember that they’ll be moving with respect to us, and may or may not have measured our atmosphere, so we’ll see whatever signal is sent as a different color/frequency than it was sent.

Earth's atmosphere has specific "windows" that allow radiation (light, radio waves, etc.) to reach the ground. // Image credit: NASA

Then there’s the number of places to search. If we limit ourselves to stars—which may not be valid if ET has much brighter transmitters than we do, or spaceships—then there’s 18 million within 1000 light years, which is about 1% of the diameter of our galaxy, and contains over 100 billion stars and is itself just one of billions of galaxies. And the sum total of all searches thus far haven’t even examined 1% of those 18 million stars.

Finally, there’s the issue of time. Whatever signal we receive, it will have travelled across exactly as many light years as it took years to get here. It’s wonderful to see into the past, but we don’t know if signals are washing across us every second, every century, or never. An intriguing possibility, enabled by our newfound knowledge of exoplanets, is to look for a signal when two exoplanets line up along our line of sight. We’re just starting to study such opportunities. And, hoping the signal repeats so we can study it better, how often will that happen, if ever? What if the signal arrives while we’re looking at another part of the sky?

Image credit: SETI Institute

Fortunately, as I alluded to before, technology has been improving consistently, decade over decade. This was anticipated by the SETI community when, 20 years ago, they set three goals. One was to build what became the Allen Telescope Array. Another was to monitor the whole sky all the time. This is where Laser SETI comes in. It is the first economical project to take the spatial and time dimensions off the table, by observing the whole sky all the time—and across the entire optical band. Its unique design allows for 4 cameras to observe any potential signal, in order to produce compelling evidence of its origin or easily discard it as a false positive. It may or may not be the last SETI project ever, but it’s a major step forward and an achievement if we complete it. 

Through Aug 18th, everyone has a unique opportunity to contribute to its success via the Indiegogo campaign we’ve setup. If you’re still reading this, you’re clearly interested enough in SETI that you should definitely take a look and see how you can help!

Moving on, many people ask what would happen if we discovered a signal. First, we would check and double-check ourselves. SETI must exclude all natural and human sources, instrumentation is complex, and nobody wants to embarrass themselves with a false alarm. Next, because this is science, it requires peer review and independent verification, wherever possible. We would ask other astronomers to examine the source, and bring their expertise to bear on both its apparent origin as well as our instrument and data. The SETI community is working on a system to quantify the confidence in a received signal, call the Rio Scale. Previous potentially interesting signals have demonstrated that this process includes the press and is necessarily international.

This radio message was transmitted toward the globular cluster M13 using the Arecibo telescope in 1979. // Image Credit: Arne Nordmann (norro); Wikipedia

Another aspect of contact many people ask about is if we would respond and what would we say. Speaking for myself and my discussions with every other SETI scientist I’ve discussed this with, listening is completely separate from transmitting. In most cases the equipment is different but, more importantly, if and how we respond is a decision for the whole planet, not any small group. I’ve even heard the argument that we shouldn’t listen for signals for fear of who would respond or what they’d say. That strikes me as simply enabling whoever you think might respond to do so in secret and guarantee you don’t have a say in the matter!

I’ve spent a lot more time thinking about how to send a self-explanatory (“anti-cryptographic”) message, than the words to put into it. Efforts along these lines are referred to as METI (Messaging to Extra Terrestrial Intelligence) but are not formal or prescriptive. However, not to dodge the question and assuming the original signal didn’t have an obvious reply e.g. “Do you want to chat?” or “Can we eat all the humans?”, I would simply want to express greetings, thanks, and the hope that we could learn from each other. Since the round-trip time will likely be years, maybe millennia, that gives us a long time to think about it and probably include a lot more in response, perhaps even the sum of human knowledge—despite the guarantee that it would be out of date by the time it arrived.

SETI is enthralling and empowering. It offers answers to questions we’ve had since the dawn of civilization, and the hope to unify all inhabitants of Spaceship Earth with the knowledge that we’re not alone. Contact would demonstrate to us that it’s possible to survive our technological adolescence. In today’s modern age, we all have a chance to participate in this thrilling process, whether via science and engineering, funding, or sharing our excitement with others. Thank you for your interest and please share your passion with others!

ABOUT THE AUTHOR: Eliot Gillum is a Laser SETI project scientist and director of the Optical SETI program.

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