By Morris Jones
Our search for extraterrestrial intelligence employs as many methodologies as possible. It makes sense. The more you look, the greater the chances of discovering ETI. There’s another issue. We are not really sure of how extraterrestrials would communicate with us. Would they use radio waves, lasers, or something more exotic? Perhaps the universe is awash in extraterrestrial signals that we cannot even receive. SETI and METI practitioners spend a lot of time wondering how a message would be encoded in terms of language and content. It’s also important to consider the medium of transmission.
How do we listen for ET right now? Mostly, it’s done with radio telescopes. Radio waves are used extensively on Earth for communications, and it seems rational to assume that extraterrestrials would discover this too. Radio astronomy was practically the only way that modern SETI was performed for decades, since Frank Drake made his legendary first search.
For more than a couple of decades, SETI practitioners have also used optical telescopes to search for laser signals beamed across space. This also makes a lot of sense. Lasers are used extensively for telecommunications by humans. They can propagate across interstellar distances just like radio waves. METI International has its own affiliation with optical SETI searches, as reported in this blog.
Another search branch is artefacts. We look for physical infrastructure that could have been constructed by extraterrestrials. In 2015, there was considerable excitement about strange occultation patterns around a star, which some people hoped were caused by large artificial structures blocking the star’s light. SETI practitioners do not believe that this is true, and suggest that the strange effects were produced by natural phenomena. Again, METI International has covered this particular incident in earlier blog postings.
Right now, that’s basically how SETI is practiced. But could there be other ways of searching for ETI?
There are still some exotic channels in physics that have yet to be properly explored. One is neutrinos. These are strange, ghostly subatomic particles that travel vast distances and pass through solid matter. Detecting them is difficult but possible. Neutrinos are generated in nuclear reactions. The Sun spews them out in copious quantities. They stream in from other natural sources in deep space. We can also make neutrinos on Earth. Could extraterrestrials communicate with us through neutrino beams?
It’s plausible, but we haven’t really looked yet. One problem is getting the right equipment. SETI is under-resourced and struggles to maintain the world’s small number of radio and optical searches. We will hopefully get around to neutrino searches one day, but it probably won’t happen soon.
Now to gravitational waves. In February 2016, the first confirmed detection of gravitational waves astounded the world. Space and time could be rippled and warped, just as Einstein predicted. Gravitational wave observatories will be the next major revolution in astronomy. Some will be deployed in space. We will be able to see things that are beyond the vision of other telescopes. But could extraterrestrials really use gravitational waves for communication? It’s hard to conceive with our current grasp of physics. They are extremely difficult to generate at a detectable level. You would need abilities similar to those of superheroes, and be able to smash neutron stars and black holes together at will. There are probably easier ways to get a message across the stars.
Can we get even more exotic? Could there be ways of communicating that use physics we don’t even understand? It’s hard to say, but we can’t rule it out. SETI scientists love to speak of “Zeta Rays”, a tag for unknown physics, when they consider this suggestion. Is it possible to transmit with something better than we already have? Until we know a lot more physics, we just won’t know. Humanity in the twenty-first century could be like an isolated tribe in the Amazon jungle a century ago, unaware that the air around them was filled with radio signals.
SETI uses the science and technology provided to us by other disciplines. Thus, we must wait until physics itself makes some more major breakthroughs. Only then can we consider such exotic methods of searching. We think a lot about the message. But we should also think about the medium.
Artículo en español: http://meti.org/es/blog/los-extraterrestres-se-comunican-con-rayos-zeta