SETI is a rather simple acronym that deals with one of humanity's biggest questions: are we alone in the universe?
The Search for Extraterrestrial Intelligence (SETI) is looking for advanced civilisations. It's not interested in tiny microbes or any such simplistic lifeforms.
Most SETI searches hunt for radio and optical signals to indicate intelligent life.
Radio astronomy is used to hunt for radio signals that an intelligent civilisation could produce. These tend to look for narrow-band signals, which are radio emissions that only cover a tiny part of the radio spectrum. This is because natural objects will emit radio waves across the spectrum, but if you find a signal that just uses a small region of the radio spectrum, it could have an artificial source. Scientists also use optical searches to look for brief flashes of light in the search for intelligent life.
Such optical and radio signals could be deliberately beamed out of a planet, or they could be picked up accidentally. Earth has unintentionally broadcast radio and radar signals since World War 2. We also purposefully transmitted a simple message from the Arecibo Observatory in Puerto Rico in 1974.
This radio message (shown above) carried basic information about the human race and was fired at the globular star cluster M13 in the hope that extraterrestrial intelligence might receive and decipher it.
Our closest star, Alpha Centauri, is 4.3 light-years away. So, if the Joker tried to talk to an advanced civilisation on a (yet-unseen) planet (where Batman is) around that star, it would take more than 8 years for that signal to travel from Earth, to that world, and back again.
The SETI Institute
The SETI Institute is the largest player in the hunt for advanced civilisations in our cosmos.
Set up in 1988, it is now a not-for-profit organisation (after its funding was withdrawn after a year) and is made up of scientists, engineers, teachers and other staff.
The Institute has more than 100 active projects. And, in a joint project with the University of California, Berkeley it built the Allen Telescope Array - a 42-strong radio telescope array to examine one million stars in the next two decades.
Has SETI found anything?
Despite hopes being raised just over a year ago, SETI hasn't found any evidence of intelligent extraterrestrial life.
We'll just have to wait a little bit longer for ET to phone home.
There's so much information on the SETI Institute's website and the FAQ section is particularly useful.
You can also analyse the light from an exoplanet (a planet outside of our own Solar System) to work out what its atmosphere is made up of. If the atmosphere is made up of oxygen, nitrous oxide and methane, then this could indicate life is present. If you'd like to find out more about exoplanets - NASA's Kepler space telescope has found dozens of potentially habitable worlds, including this mysterious "alien megastructure".
And here's a list of the seven most likely places in the universe where intelligent life could exist.
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