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takyon writes:

Smart aliens might live within 33,000 light-years of Earth. A new study explains why we haven't found them yet.

[An] upcoming study in The Astronomical Journal, which we learned about from MIT Technology Review, suggests humanity has barely sampled the skies, and thus has no grounds to be cynical. According to the paper, all searches for extraterrestrial intelligence, or SETI, have examined barely a swimming pool's worth of water from a figurative ocean of signal space. "We haven't really looked much," Shubham Kanodia, a graduate student in astronomy who co-wrote the study, said during a NASA "technosignatures" workshop in Houston, Texas on September 26.

[...] In their study, Kanodia and his colleagues built a mathematical model of what they consider a reasonably sized cosmic haystack.
Their haystack is a sphere of space nearly 33,000 light-years in diameter, centered around Earth. This region captures the Milky Way's bustling core, as well as many giant globular clusters of stars above and below our home galaxy.

They also picked eight dimensions of a search for aliens — factors like signal transmission frequency, bandwidth, power, location, repetition, polarization, and modulation (i.e. complexity) — and defined reasonable limits for each one. "This leads to a total 8D haystack volume of 6.4 × 10¹¹⁶m⁵Hz²s/W," the authors wrote. That is 6.4 followed by 115 zeros — as MIT Technology review described it, "a space of truly gargantuan proportions."

Kanodia and his colleagues then examined the past 60 years' worth of SETI projects and reconciled them against their haystack. The researchers determined that humanity's collective search for extraterrestrials adds up to about 0.00000000000000058% of the haystack's volume. "This is about a bathtub of water in all of Earth's oceans," Kanodia said. "Or about a five-centimeter-by-five-centimeter patch of land on all of Earth's surface area."

Those numbers make humanity's search efforts seem feeble. But Kanodia views it as an opportunity — especially because modern telescopes are getting better at scanning more objects with greater sensitivity and speed. For example, he said, a 150-minute search this year by the Murchison Widefield Array covered a larger percentage of the haystack than any other SETI project in history.

Related: Stephen Hawking and Yuri Milner Announce $100 Million "Breakthrough Listen" SETI Project
Narrow SETI Targets by Looking at Places Where Earth Transits can be Seen
Either Stars Are Strange, or There Are 234 Aliens Trying to Contact Us
New Theory Suggests Radio Bursts Beyond Our Galaxy Are Powering Alien Starships
A New Theory on Why We Haven't Found Aliens Yet
Russian Physicist Proposes New Solution to the Fermi Paradox
Are We Alone? The Question is Worthy of Serious Scientific Study

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