In human quest for life beyond Earth, distance acts as a barrier

A recent paper, “Estimating the prevalence of malicious extraterrestrial civilisations”, from Alberto Caballero of Vigo University (Spain) has generated interest across social media. The paper estimates there may be four “malicious extraterrestrial civilisations” in the Milky Way.

Caballero is doing a PhD in Conflict Resolution at Vigo and calls himself a criminologist. The paper, which he calls a thought experiment, hasn’t been peer-reviewed. It’s a follow-up on a paper (peer-reviewed), which he published in Cambridge’s International Journal of Astrobiology: “An approximation to determine the source of the WOW! Signal.”

A patents clerk called Albert Einstein based the Theory of Relativity on “thought experiments” as he himself called them. So we can’t denigrate the paper on those grounds. Researchers have for decades been chasing leads that may pinpoint alien activity. Some hypotheses are crackpot; others are rational “thought experiments”.

In 1961, Frank Drake, an astrophysicist, formulated a thought experiment that estimated the possible number of active, extraterrestrial civilisations in the Milky Way, which could possibly communicate with Earth. Drake was among the founders of the SETI — the Search for Extraterrestrial Intelligence, which uses crowd-sourced computing resources to analyse radio signals from space.

Drake didn’t actually put a number down. Instead he challenged everybody to combine what’s known about the number of stars with planets; the fraction of planets likely to have conditions supporting life; the fraction which would actually develop life; the few species that develop intelligence; the few intelligent species that develop detectable communications; and the length of time such a civilisation may need to exist before any signals become detectable from Earth.

There’re at least 100 billion stars in the Milky Way and a large proportion are likely to have planets. Even if a very small percentage of planets can harbour life, and a very, very small percentage of life is intelligent, and capable of long-distance communication, that may still aggregate to a very large number of possible civilisations with detectable communications.

But distance is a barrier. Humans have been spewing out radio signals for 120 years. Radio signals are electromagnetic waves travelling at light speed. Our civilisation is thus detectable by some alien that can monitor radio signals only if that alien is located within 120 light years of Earth. That’s a comparatively tiny sphere of space. Any civilisation more distant would have to wait until the first transmissions arrived.  

This brings us to SETI, which analyses radio data. Stars and other astronomical objects spit out loads of radio signals — indeed, radio telescopes are commonly used to observe space. SETI looks for possibly non-natural signals buried in radio telescope data.  

One of SETI’s promising transmissions was the so-called WOW! signal, which Caballero tried to locate. In 1977, the Big Ear Radio telescope at Ohio State University recorded 72 seconds of radio signals, which didn’t seem to have natural causes. The researcher analysing this, the astronomer Jerry R Ehman, called it the “WoW!” and the name stuck.

There’s a “Nikolai Kardashev scale” for alien technology. Numbered 1-7 (he originally proposed three levels), the Kardashev type 1 civilisation would be capable of using the entire energy of its home planet; a type 2 could use all the energy of its solar system; while a Type 7 would be capable of using the energy of multiple galaxies. Kardashev (another SETI pioneer) reckoned humans were perhaps at 0.7 — capable of using most of the Earth’s energy.  

If civilised aliens exist and if they could reach Earth, they would be far more technologically advanced. As Stephen Hawking pointed out, when technologically advanced societies meet primitives, our colonial history indicates that the primitives always get badly hurt.

If aliens have been monitoring us, they would be aware we have a destructive streak, and we use nuclear power to blow up things. Therefore, those aliens might decide to get rid of us before we became a threat to them. That leads to the Cixin Liu “Dark Forest” hypothesis – in a dark forest (like space), you hide yourself, and assume anybody else is a hostile predator out to get you.

Caballero has looked at wars and invasions since 1915 to figure out how likely it is that an alien civilisation would be malicious. Intuitively, this methodology seems about as irrelevant as trying to figure out the chances of being hit by a meteorite by studying the number of bird droppings that land on people’s heads. What Caballero has done that’s useful is focused some attention on space exploration, and even if much of that interest is ephemeral and driven by an oddball concept, that cannot be a bad thing.

Nikolai Kardashev scale for alien tech

• Numbered 1-7
• Type 1 civilisation would be capable of using the energy of its home planet
• Type 7 would be capable of using the energy of multiple galaxies
• Kardashev, a SETI pioneer, reckoned humans were perhaps at 0.7