With no luck so far in a six-decade search for signals from aliens, you’d be forgiven for thinking, “Where is everyone?”
A new calculation shows that if space is an ocean, we’ve barely dipped in a toe. The volume of observable space combed so far for E.T. is comparable to searching the volume of a large hot tub for evidence of fish in Earth’s oceans, astronomer Jason Wright at Penn State and colleagues say in a paper posted online September 19 at arXiv.org.
“If you looked at a random hot tub’s worth of water in the ocean, you wouldn’t always expect a fish,” Wright says.
Still, that’s far more space searched than calculated in 2010 for the 50th anniversary of the search for extraterrestrial intelligence, or SETI. In that work, SETI pioneer Jill Tarter and colleagues imagined a “cosmic haystack” of naturally occurring radio waves she could sift through for the proverbial needle of an artificial, alien beacon (SN Online: 5/29/12). Her haystack went beyond physical space to include factors such as a possible signal’s duration, frequency, variations and strength, as well as the sensitivity of radio telescopes on Earth that would presumably detect a signal.
She concluded that searches had covered about a drinking glass’s worth of seawater — hardly enough to conclude the ocean is fishless.
Wright and colleagues Shubham Kanodia and Emily Lubar updated Tarter’s calculation by devising a slightly different haystack, including factors like the frequency and bandwidth aliens might broadcast in. It also included more recent SETI searches such as the Breakthrough Listen project (SN Online: 7/20/15).
Converting the volume to liters for the sake of analogy, the researchers concluded that SETI has covered the equivalent of 7,700 liters out of 1.335 billion trillion liters of water in Earth’s oceans.
“We’re finally getting to the point today … that we have a chance of finding something, depending on how much there is to find,” Wright says.