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NOVA ScienceNOW

The Search for ET: Expert Q&A

  • Posted 07.29.08
  • NOVA scienceNOW

On July 29, 2008, Seth Shostak answered questions about searching for signals from extraterrestrial civilizations, whether ETs have visited us already, worm holes, and more.

Seth Shostak

Seth Shostak

Seth Shostak is Senior Astronomer at the SETI Institute. Full Bio

Photo credit: Courtesy Seth Shostak

Seth Shostak

Seth Shostak is Senior Astronomer at the SETI Institute. He earned a B.A. in physics from Princeton and a Ph.D. in astronomy from Caltech and helps to guide the Institute's scientific research. But he's also responsible for much of the Institute's outreach activities. Shostak has written hundreds of articles for newspapers, magazines, and the SPACE.com Web site, as well as three books, including a popular textbook on astrobiology. He currently hosts the SETI Institute's weekly radio program Are We Alone? Shostak also is the inventor of the electrical banana, an achievement he claims has had little positive effect on his life.

Q: Could we find ourselves? If there were an alien civilization equivalent to ours in the Milky Way, could we find it? Or do we overestimate the length of time technological civilizations are producing, by accident, radio signals that escape into space? The NOVA segment seemed to intimate that with advances in technology we may significantly reduce our radio fingerprint, so to speak, and eventually "go dark" even though we are still here. Gordon Lampley, 7th grade teacher, Norwood, North Carolina

Seth Shostak: Dear Gordon,
Although Earth is inadvertently broadcasting radio, television, and other signals into space 24/7, the facts are that most of these signals wouldn't be detectable by our SETI experiments at distances greater than about one light-year, which is not even the distance of the nearest star beyond the Sun. Of course, the aliens might have much larger antennas than we do, so this doesn't rule out someone finding us. However, Earth's strongest signals-mostly military and research radar-are strong enough to be found dozens or even hundreds of light-years away, even with equipment that's no better than our own. Will such strong signals be emitted by an advanced civilization? Who knows, but having a few powerful radar transmitters might help avoid an asteroid hit that could ruin an alien's entire day.

Q: What are some of the technical details involved in your search, such as: what is the width of each frequency band you analyze, what is the total range of frequencies that you look at, how often do you look at each frequency band, what are some of the signal characteristics you look for when you find a signal, etc.?

Also, what operating system and software language(s) are used in the front-end analysis of all of the incoming data? Anonymous

Shostak: We try to examine as much of the radio dial as we can, although the best of our previous searches (Project Phoenix) only covered from about 1.2 to 3.0 GHz. These days we can do better. The bandwidth of the individual channels we scrutinize for alien signals is typically 1 Hz-which is gosh-darn narrow. The presence of a narrow-band component to any signal would tell us that we'd found a deliberately built transmitter, and not just some astrophysical phenomenon.

Our observatory computers generally run Unix, and the code is usually constructed in C++.

Q: Traditionally, radio-based SETI concentrated on the hydrogen line with the idea that it would be used as an intentional interstellar beacon. Now that more computing resources are available, are there programs or plans to look at different frequency ranges, using the logic that any unnatural radio signal, regardless of intention, would be evidence of ET intelligence? Greg Shreve, San Pedro, California

Shostak: Dear Greg,
You bet your footwear! The new Allen Telescope Array can cover frequencies from 0.5 to 11.5 GHz, which is an enormously greater range than any previous SETI experiment. As you suggest, looking at more of the dial should increase our chances of picking up ET's broadcast.

Q: What salient characteristic will convince SETI searchers that a signal is from intelligent beings? Simplicity? Complexity? Patterns? What? Rick Freeman, Louisville, Kentucky

Shostak: Dear Rick,
A narrow-band signal is the thing we look for-something 1 Hz wide in the radio spectrum (or narrower). This is the type of emission that transmitters make, but interstellar gas clouds, quasars, and pulsars don't. As for the "message"-well, we'll worry about that after we've found a transmitter that's on the air.

Q: According to some astronomers, electronic signals from Earth will dissipate to static even before they reach the ort cloud, and will be completely indistinguishable from background radiation by the time they reach Alpha Centari. If we are to apply these physics to alien life on other planets, wouldn't they have the same difficulty? If not, then are we to assume that they have achieved interstellar communication. How close do you feel we are to achieving interstellar communication? I believe in life on other planets, but I also believe it is folly to attempt to communicate with them due to the huge expanse of space and time. James Grant, Phoenix, Arizona

Shostak: Dear James,
This is, alas, wrong, as I suggested in my answer to Gordon Lampley above. The strongest of our signals (for instance, the radar signal from the Arecibo antenna in Puerto Rico) could be detected by a similar-sized antenna at hundreds of light-years distance. And indeed, any signal-at any distance-would be detectable if you had a large enough antenna. Radio astronomers routinely study natural cosmic static from galaxies that are billions of light-years away, after all.

Q: What percentage of stars is of a size comparable to our sun that could provide for a solar (planetary) system that had planets that could support life? Irving Schnirman, Petaluma, California

Shostak: Dear Irving,
Well, roughly one in eight stars is approximately the same size (and brightness) as the Sun. Most stars are smaller. But even these runty guys could conceivably host planets on which life could develop. The planets would just have to be in smaller orbits (to get more heat from their star) than if they were around a solar cousin. When you add it all up, roughly 98 percent of all stars could, in principle, host planets with life (the other 2 percent don't burn long enough for life on orbiting planets to arise and develop).

Q: Hi Dr. Shostak,
Perhaps telescopes and radio broadcasts are not going to be effective in finding intelligent life and Earth-like planets in the Milky Way galaxy. Is physically traveling far distances across the galaxy possible through worm holes? James, California

Shostak: Dear James,
I wish I knew! Worm holes seem to work on physicists' blackboards, but could you actually make one and use it for travel? At this point, you'll have to ask the worms.

Q: How do you think humanity would react if tomorrow we discovered other intelligent life in the universe? Would it change for the better how we view ourselves, would there be mass paranoia or would most people just not even care. Thanks! Jon, Lawrenceville, Georgia

Q: Do you think that confirmation of ET advanced societies will affect peoples' religious beliefs? Anonymous

Shostak: Dear Jon and Anonymous,
Call me naïve, but I don't think that finding a signal would cause people to radically change their beliefs. At least, not in the short run. After all, the public is already comfortable with the idea of aliens-they see them every night on TV and in the movies. About one-third of them think aliens are visiting Earth (although I don't). However, if we were to get understandable information from any contact, that might change things in the long run.

Q: How do I download the software for my Mac to watch for ET life? Anonymous

Q: What about the SETI@home project-what does it do? Does it accomplish anything? Dennis Emanuel, Raytown, Missouri

Shostak: Dear Dennis and Anonymous,
You can find the SETI@home screen saver by simply doing a Web search. This software is free, and is provided by the University of California at Berkeley's SETI group. You'll be joining a few million people who are combing through some SETI data, looking for a signal-and who knows? You might be the first to find one. In which case, you'll probably be on the cover of Time Magazine.

Q: Seth...we are bathed in galactic noise with an average temperature of 20K (or thereabouts). Knowing that signals weaken by the square of the distance puts some serious bandwidth limits maximum distance before signals are lost in the 20K noise. It doesn't take many light years of distance to diminish ET signals to below the noise level. So how can we possibly detect ET intelligence say 50 light years away? It seems like Boltzman's constant is not on our side!
-Charlie Charlie Thompson, Buda, Texas

Shostak: Hi Charlie,
Well, not to worry. You can always increase the signal-to-noise of a deliberate signal by wielding a larger antenna. The natural noise tends to average out, but the signal just gets stronger as you use a bigger and bigger receiving setup.

Q: Hello, Dr. Shostak,
Thanks for this opportunity! Regarding the search for ETI in the vastness of space, would one be correct in viewing any possible communications with ETI in terms of sending/receiving letters every 60 years or so since even light is limited to how far and fast it can travel?

Again, thanks for this chance to talk with you! Mark Knockemus, Cheraw, South Carolina

Shostak: Dear Mark,
Well, 60 years might be optimistic! If there are 10 thousand broadcasting societies in our Galaxy, then the nearest one is 500 to 1,000 light-years from South Carolina. So that will be communication that's slower than molasses in Greenland. Don't count on conversation-it will all be one-way communication.

Q: Dr. Shostak,
When we look for ET life, why do we always look for signs of water, carbon, oxygen etc.? We are assuming that all 'life' is only carbon-based life similar to life as we know it on Earth. Is it not possible, or is too preposterous, to even consider non-carbon based life forms or intelligence?
Regards, Rajnish Kelkar, Vancouver B.C., Canada

Q: Surely there is intelligent life elsewhere. But what are the odds that intelligence would resemble human life on Earth? Anonymous

Shostak: Dear Rajnish and Anonymous,
It's true that most researchers are highly terracentric-which is to say, we look for life "as we know it." But even though that's probably 'way too conservative, it at least allows us to formulate a plan of action. It's pretty tough to look for life-as-we-don't-know-it, after all: just ask the folks who design spacecraft to search for microbial Martians. But there's also this to be said: carbon is the best element around for making complex molecules at the temperatures at which water is liquid. So it seems a good bet that a lot of alien life is carbon-based, too. This is not just a conceit of "Star Trek," it makes good biochemical sense. But would intelligent aliens resemble us? I doubt it. Dolphins don't look much like us, even though they're Earthlings. But they're said to be pretty clever.

Q: How certain are you of the search methods for finding ET in the first place? From my point of view there have been plenty of well documented sightings of UFOs over the years that suggest that some (at least one) would be a genuine ET come to visit for reasons unknown. That suggests to me that our science may not fully appreciate how aliens do communicate and generate electromagnetic fields for their own use in a way that we can detect in the first place. Isn't it possible that our own methods of research are biased and perhaps incapable of finding what is right under our collective and terrestrial noses? Jay MacVean, Columbus Ohio

Q: Have we been visited by extra-terrestrials? Dave, Eureka, Missouri

Shostak: Dear Dave and Jay,
Well, it's true that SETI assumes that at least some aliens are using radio or light to send information around. That might be wrong, at least if there's some physics that allows faster (or cheaper) communication. But it doesn't really help to make that argument, because we can't set up any experiments using physics we don't know. Are we being visited? I don't think so, although plenty of people do. The evidence-even after more than 60 years of claimed alien presence-is still not good enough to stack up in a museum or intrigue many scientists. It's like ghosts: lots of people believe they exist, and there are sightings all the time. But rather few scientists are convinced by the evidence presented to date that such spectral beings are really living rent-free in the attic.

Q: Wouldn't alien intelligent life only want to exploit our planet rather than make friends with us? Therefore, advertising our location is dangerous: not in our best interest? Anonymous

Shostak: I have no idea what would interest aliens about our planet, but I somehow doubt it would be to exploit its resources. They could find those much, much closer to home. As for advertising our presence: well, given the distances to the stars, I don't think there's much reason to be paranoid. If you disagree, then we should petition to shut down all airport radars and TV stations.

Q: Hello Seth,
In all the years that we have been looking for life on other planets via the radio spectrum, have we come across any credible evidence of intelligent extra terrestrial life? Do the results so far, contribute to the accuracy of the Drake Equation and if so, how?

Thanks for any response. John Gilmour, Fort Erie, Ontario, Canada

Shostak: Dear John,
Well, there's no evidence so far for intelligent aliens that a scientist would consider convincing. But we've barely begun the search which, fortunately, will get much faster in the next decades. I can't say that SETI efforts thus far have helped to put limits on the numbers computed by the Drake Equation, however.

Q: If I am not mistaking, at the time SETI was instituted we really only had radio waves as a feasible option for an attempt at communicating or searching for other life. Now that we seemed to have advanced in light wave and it is a viable, quicker means of transmitting and receiving information, has SETI implemented this technology or plans to in the future?

If life exists elsewhere, and they where searching for us what are the odds that they would use a the means of radio for communication, being so fundamentally basic considering all other options of communication? What about means of communicating we haven't even discovered yet?

Or am I simply mistaking SETI's method of searching for life elsewhere? Glen Hutchinson, Longview, Texas

Shostak: Dear Glen,
In fact we do look for light signals (it's called "optical SETI"). There are several telescopes in California and Massachusetts that are outfitted with high-speed photomultiplier tubes looking for very short (one-billionth of a second) flashes from alien lasers. As for means of communicating that we haven't discovered so far ... well, we haven't discovered them so far!

Q: Since any contact will be very newsworthy, do you anticipate any government censorship when such a contact is received by SETI? Dick Stacy, Montrose, Colorado

Shostak: Dear Dick,
No, I don't. The government shows zero interest in even the most exciting of our false alarms. And there's no secrecy in the SETI enterprise, so everyone knows when we find signals.

Q: Hello,
If the actual missions on Mars discovered just one single organism there, how that will affect our search of life? And, will it change the Drake Equation?
Thanks, Anonymous

Shostak: Well, assuming that the organism is not related to us (which could happen thanks to mutual contamination of Earth and Mars by itinerant rocks), this would greatly encourage our search for life. After all, if the next planet out from the Sun also developed life, you can bet that life is all over the universe. It would be a big, big news story. It wouldn't change the estimates in the Drake Equation by very much, however, since the "guesses" that are usually used for that formula are already pretty optimistic.

Related Links

  • SETI: The Search for ET

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  • Aliens in the Milky Way?

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  • Will We Ever Find ET?

    What are the odds that smart aliens exist in the universe?

  • The Drake Equation

    Try your hand at calculating how many intelligent, communicating civilizations might be in our galaxy.