MeerKAT picks up mid-frequency radio waves, including the part of the spectrum traditionally targeted by SETI searches. As part of its commissioning phase, MeerKAT will conduct sky surveys, mapping the structure of the galaxy while hunting for pulsars and FRBs. Pete Worden said Breakthrough Listen is "deep in discussions" with the MeerKAT team, hoping to run piggyback SETI searches at the same time.

"These are next-generation facilities in terms of their sensitivities, and their field of view, and also in terms of the way that we can access them digitally," said Andrew Siemion. "So it's incredibly easy for us to plug instrumentation into them, and that makes it possible for us to use them for SETI very easily."

MWA is a low-frequency array. Low frequencies are not typically targeted by SETI searches because longer wavelengths constrain how much information can be transmitted over any given period of time.

Low-frequency arrays can, however, cover the entire sky all at once. For this reason, scientists like Dan Werthimer are increasingly interested in conducting SETI searches with arrays like MWA, "not necessarily because we think E.T. might be broadcasting there," but because the experience could be used to build higher-wavelength all-sky arrays like Horowitz envisioned.

"The microwave part of the spectrum that most people think about for SETI experiments—that will be a little harder," said Werthimer.

The second phase of the Square Kilometer Array, SKA-2, includes a mid-frequency array called MFAA. One of its proposed precursors, MANTIS, would use 250,000 antennas to cover 200 square degrees of sky at once—the equivalent of 1,000 Moons. Its frequency range is 450 to 1,450 megahertz—a large chunk of the water hole, making it a good tool for SETI research.

Though the U.S. did not help fund SKA, the National Radio Astronomy Observatory is considering its own ambitious, SKA-like facility called the next-generation Very Large Array, or ngVLA. Should it be built, the ngVLA would consist of 214, 28-meter high-frequency radio dishes in the southwestern U.S. capable of receiving signals from 1,200 megahertz to 116 gigahertz. Jill Tarter said SETI researchers are making the case that the search for life should be part of the ngVLA's science justification, should it be built.

Big data

In an era where the term "big data" dominates the technology landscape, many SETI scientists are eyeing improvements to the way telescope signals are stored and processed.

At Parkes, Breakthrough stores up to 100 times more data than a typical telescope user—down to individual voltage levels bouncing off the dish itself. The team currently stores a petabyte, or 1,000 terabytes, of those data. "But they quickly get through that," said Jimi Green, the Parkes scientist.

New algorithms and machine learning could help rule out spurious signals while finding hidden ones scientists don't know to look for. Pete Worden hopes to bring in help, perhaps on a volunteer basis, from unique places like the intelligence community.

"We'd really kind of like to get somebody that may work in the daytime for a three-letter agency, who goes home at night, downloads the data says 'Hey, I found something interesting,'" Worden said.

About a year ago, the SETI Institute teamed up with IBM to start using machine learning to sift through the 54 terabytes of data per day the Allen Array captures. Bill Diamond said IBM was interested in placing the data in "a gymnasium for software" to test new computing algorithms. In return, the SETI Institute gets access to cloud computing resources and tools.

"It's almost like building a new instrument, or building a new telescope," Diamond said.

The big picture

During his 1978 Tonight Show appearance, Carl Sagan theorized about what it might mean to establish two-way communication with another civilization.

"We are at a very dangerous moment in human history," he said. "We have weapons of mass destruction, we are in the process of inadvertently altering our climate—exhaustion of fossil fuels and minerals—all kinds of problems that come with technology. We are not certain that we will be able to survive this period of what I like to call technological adolescence. Were we to receive a message from somewhere else, it would show that it's possible to survive this kind of period. And that's a useful bit of information to have."

Humans have only had radio technology for a century—just a blip on the galactic timescale. If we do find intelligent beings, it would be "awfully unusual to find them where they just discovered radio a hundred years ago," Werthimer said. Odds are they'll be much more advanced than us, and potentially able to offer the kind of guidance Sagan envisioned.

Hearing nothing won't necessarily mean no one is out there; perhaps we aren't looking the right way. What if intelligent beings communicate using a form of energy stronger than gamma rays? Or chat via subspace, like on Star Trek?

"We have to reserve the right to get smarter," Tarter said. "We may be doing a fantastic, excellent job at just the wrong thing."

Or, we could truly be alone in the cosmos. Paraphrasing Arthur C. Clarke, Siemion said the non-detection of intelligent life would be just as profound as detecting it.

"The only thing weirder than there being intelligent life out there is that there is not intelligent life out there," he said. "These ideas are kind of equally compelling—equally strange and amazing."

At a Breakthrough Initiatives meeting just before the Listen project was announced, each team member predicted the odds the effort would find intelligent life, Worden said.

"The numbers ranged from a percent or two, to ten to the minus fifth," he said. Milner was among the low end of the estimates.

"I was just thinking at the time, if I had gone to the U.S. government and said I want a hundred million bucks to do something, and they asked me what I thought the probability of success was, even if I had said two percent, they would have said, 'you must be nuts,'" he said.

Even negative results help define the boundaries of where and how to look. And the only way to know for sure whether there's anybody out there is to keep searching.

"I think most people in the public think we're always looking, which is totally not true," said Shelley Wright. "We've barely looked, contrary to all of our sci-fi movies."

Acknowledgements

Parkes Observatory story header timelapse and imagery by Angelo Papakostas and John Cassimatis.

Many thanks to Amir Alexander, who previously published a Planetary Society SETI overview, which was enormously helpful while researching this story.

To support The Planetary Society's feature reporting, or our science and technology projects that bolster the search for life, consider becoming a member today.