Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message. Active SETI is also known as METI (Messaging to Extra-Terrestrial Intelligence). The term METI was coined by Russian scientist Alexander Zaitsev, who proposed a subtle distinction between Active SETI and METI:
The science known as SETI deals with searching for messages from aliens. METI deals with the creation and transmission of messages to aliens. Thus, SETI and METI proponents have quite different perspectives. SETI scientists are in a position to address only the local question “does Active SETI make sense?” In other words, would it be reasonable, for SETI success, to transmit with the object of attracting ETI’s attention? In contrast to Active SETI, METI pursues not a local, but a more global purpose – to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation “You are not alone!”
In 2010, Douglas A. Vakoch from SETI Institute, addressed concerns about the validity of Active SETI alone as an experimental science by proposing the integration of Active SETI and Passive SETI programs to engage in a clearly articulated, ongoing, and evolving set of experiments to test various versions of the Zoo Hypothesis, including specific dates at which a first response to messages sent to particular stars could be expected.
On 13 February 2015, scientists (including Douglas Vakoch, David Grinspoon, Seth Shostak, and David Brin) at an annual meeting of the American Association for the Advancement of Science discussed Active SETI, and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea. That same week, a statement was released, signed by many in the SETI community including Berkeley SETI Research Center director Andrew Siemion, advocating that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent". On 28 March 2015, an essay with a different point of view was written by Seth Shostak and published in The New York Times.