Researchers at SETI are using radio telescopes to listen specifically for signals that are “obviously engineered”—something that nature, at least as far as we know, can’t produce.

Question: How has the search for intelligent life evolved over the past 25 years? 

Jill Tarter: It’s really all about computing. It’s all about speed. How much of this really vast universe, how many of the 400 billion stars in our Milky Way galaxy can we explore, looking for someone else’s technology? And today the tools I use are 14 orders of magnitude, 14 factors of 10 better than Frank Drake was able to use in 1960 and that improvement is going to continue, and continue at a faster and faster pace, because our computing capabilities are improving exponentially. For anyone who has ever studied an exponent, things double and then they double again and that doesn’t seem very much, but after you get through a number of doublings in fact you’re making changes at an enormous rate, so everything kind of happens at the end. We’ve recently built a brand new telescope to do SETI and radio astronomy all the time and simultaneously, and with that telescope in the next 10 years we expect to be able to observe at least a million stars, maybe 10 million stars over a wider range of frequencies simply because the compute power is there and it is getting better every day. 

Question: What signal is the radio telescope looking for? 

Jill Tarter: Well what we’re looking for with our radio telescope is a signal that doesn’t look like the kinds of signals that nature produces, so when natural sources of emission like pulsars or molecular clouds or hydrogen gas emit radio signals they spread it across the spectrum... Sometimes it’s relatively limited. Sometimes it’s completely broadband, but we have the ability with our technology to create a radio signal that is a single tone, a single channel on the radio dial if you wish and it’s very detectable against the background noise if you have the right detectors, so that is what we’ve been looking for, something that is obviously engineered, something that nature, at least as far as we know, can’t produce. Now that may be the wrong thing. We might have guessed wrong. We might... as we get more computational capability we might be able to look for other kinds of signals that occupy more of the spectrum, but still appear different than the signals that natural sources emit. So if you can imagine a two-dimensional screen and it’s full of snow and static like an old analog television set, which wasn’t getting good reception. But on that two-dimensional display imagine a line that is drawn and it can be straight up and down or it can be slanted and if that screen is displaying two dimensions, one of frequency and one of time that line would be a signal at a single frequency and if it was straight up and down that frequency would be constant. If the line has a slant to it the frequency is changing in time and that might well happen because the transmitter is accelerating with respect to the earth. 

We’re also now beginning to look in the optical part of the spectrum, not just the radio. Whereas in the radio we look for frequency compression, we look for narrow signals, in the optical what we’re looking for is time compression. We’re looking for really bright flashes that last a nanosecond or less. Now as far as we know, again, that is the kind of thing that nature can’t do. But with the right detectors even when you’re looking directly at a star you can see a bunch of photons showing up in a single nanosecond against the background and if you found such a thing it would certainly suggest a technology, an engineered signal. 

Question: Are we broadcasting any signals that would help extraterrestrials find us? 

Jill Tarter: On earth we currently leak a lot of signals, broadcast television for example, radio. The signals are intended for our local neighborhoods, but in fact, many of those signals go on beyond the earth and travel and spread out in a bubble around the earth that gets bigger one light year per year, so we’re announcing our presence inadvertently. That is going to change in the future as we change our means of broadcast technology and go to direct TV kinds of deliveries and digital, but actually even the satellites that are delivering the signals have some leakage out the backside of them, so we’ll never go completely radio quiet, but we’re not actually deliberately transmitting signals to different planets. We now know about 455 planets around other stars, so we’re now beginning to know about some of the places we might decide to transmit to, but we’re not doing that and the reason is we’re actually too young. We’re a very young technology in a very old galaxy, so with respect to interstellar communication we’ve had appropriate technology for maybe 100 years. The galaxy is 10 billion years old, so we don’t know whether there are any other technologies out there, but we do know that we’re the youngest that could participate in interstellar communication. Anyone younger than we are with less technical capabilities than we have can’t yet be part of a conversation. And the odds are in a 10 billion year-old galaxy that anyone else’s technology is a lot older than ours, so right now it seems to me that it’s appropriate to let the older technology do the heavy lifting. Transmitting is harder than receiving, so we’ll put that job on them. Then if we ourselves get to be an old technology, if we grow up, if we in fact can get ourselves organized to be able to take on projects that last not 2 years or 5 years, but 10,000 years or 100,000 years, which is really what you need to do if you’re thinking about transmitting purposefully, then when we’re older it would be appropriate for us to begin to transmit. Of course, by then I hope that we could answer the question about who should speak for Earth and what should they say.