It was less than a month ago that Chinese astronomers and scientists using the Five-hundred-meter Aperture Spherical Telescope (FAST) announced they had picked up strange signals that they believed showed all of the signs that they were from an intelligent civilization. That announcement was quickly taken down, leading some to believe it was being covered up by the Chinese government, while scientists in other countries, and a few in China as well, believed the analysis of the signal was mistaken and its source was actually from radio interference and radio pollution created by earthlings. That means the best known “I want to believe it's aliens” signal is still the famous Wow! signal recorded on August 15, 1977, by The Ohio State University's Big Ear radio telescope while scanning part of the constellation Sagittarius.
WOW! has been debated ever since, and the needle has constantly moved back and forth between alien signal and something else without ever creeping to the “it’s aliens” edge of the “What is it” meter. However, another group of scientists say they’re very close to nudging that needle – and they think they may be able to pick it up again because it’s something called a “stochastic repeater.” Is that a great name for a band or proof of WOW! ending the search for extraterrestrial intelligence?
“Big Ear was also a passive telescope. Astronomers simply set it up, and it would run on its own, recording the strength of signals as it goes. Because of this, the signal was only discovered days after the event when recorded observations were reviewed. By the time astronomers could go back to observe the source, the event was long over.”
In a recent study, “Could the "Wow" signal have originated from a stochastic repeating beacon?”, published in the preprint journal arXiv and accepted for future publication in the science journal Monthly Notices of the Royal Astronomical Society, David Kipping, an Assistant Professor of Astronomy at Columbia University, and the late Robert Gray, author of “The Elusive Wow: Searching for Extraterrestrial Intelligence,” explain the idea of stochastic repeating and why WOW! signal could be one. Many signals detected in space are regular repeaters – a simple example is an emission from a star that is blocked every time a planet passes between it and Earth. Many fast radio bursts are repeaters and their period can be measured. Because astronomers knew the general area the WOW! signal came from, it was hoped that pointing telescopes at it would picked it up again.
That hasn’t worked, so Kipping and Gray picked a different wall to bang their heads against. “Stochastic” means having a random probability distribution or pattern that may be analyzed statistically but may not be predicted precisely. So, a ’stochastic repeater’ is a random repeating signal that gives signs it will repeat but not enough to accurately predict it. Universe Today gives the example of earthquakes as stochastic repeaters – seismologists know where they happen, but not when.
“However, a recent Bayesian formulation of one-oﬀ events showed that at least an order-of-magnitude more data than that used in the original discovery is often required to place statistically signiﬁcant tension on a signal’s credibility. Motivated by that work, we here explore a rigorous statistical approach to address: i) how likely is it that Wow repeats but has simply been missed by follow-up eﬀorts to date, and ii) if so, what are the most likely properties of the signal under this scenario.”
Bayesian statistics or Bayesian formulation is the perfect statistics theory for the WOW! signal because it stretches the definition of ‘probability’ to include a degree of belief in an event. Going back to the earthquake example, scientists can’t pinpoint exactly when one will occur but they have a high degree of belief that an earthquake will happen along a fault based prior knowledge of past earthquakes and faults – thus avoiding the need to base statistical probability on the relative frequency of events that have happened before. Since there has been only one WOW! event, Bayesian statistics seems to make sense as a tool to find another. In this case, Kipping and Gray used it to first eliminate the most likely places where another WOW! signal WON’T likely occur – thus narrowing the field down to the best places it could repeat.
“Here, we employ a likelihood emulator using the Big Ear observing logs to infer the probable signal properties under this hypothesis.”
Proving that astronomers (and many other scientists) should never throw anything away, Kipping and Gray used data logs from The Ohio State University's Big Ear radio telescope which first picked up the WOW! signal. According to the study, Kipping believes it won’t take long to find a second one or eliminate it. As he explains to The Daily Beast:
“I think it’s worth chasing down for a couple more months to get to the point where we could say with confidence that the field isn’t worth pursuing anymore. Either we spend two months on the Wow! field and see nothing and can then move on, or we see a recurrence—and that would change the whole story.”
Specifically, Kipping and Gray estimated “62 days of accumulated additional observations” using today’s telescopes, which have vastly better technology as the Big Ear, to find another stochastically repeating WOW! signal. That seems reasonable, doesn’t it? Unfortunately, there are long lines of astronomers waiting to use the most powerful telescopes, and the time spent on them is expensive. Assuming Kipping can raise the funds and schedule the time (Gray died on December 6, 2021, from complications from lung cancer), the definition of ‘stochastic repetition’ does not limit the frequency of repeats to 62 days. What of WOW!’s frequency is years or decades or perhaps even centuries? Would the agencies that control access to the telescopes look at that and turn down Kipping’s request? The researchers believe they would get the opportunity because, even if they didn’t find a repat of the WOW! signal, they would show the benefit of Bayesian statistics for tracking down sparse, irregular observations of SETI signals of interest. In fact, they propose that “such an approach could also be used for targets without any signals detected, in order to derive robust upper limits on a hypothesized signal’s properties (be it periodic or not).”
Nearly 50 years later, the WOW! signal is still the best candidate to be the first detected and proven signal from another intelligent civilization. It would be a fitting tribute to the late Robert Gray if it’s proven to be a stochastic repeater and the needle moves from ‘probable’ to ‘WOW!’.