SETI: Search for Extraterrestrial Intelligence

It can be shown that the cheapest thing to send across interstellar space is radio waves, and that there is a convenient window of observations between frequences 1 GHz and 10 GHz. Lower frequencies have interference from galactic synchrotron radiation from electrons orbiting in our Galaxy's magnetic fields. Higher frequencies have interferences from the Earth's atmosphere and quantum effects. To date, most SETI efforts have involved searches for interstellar radio broadcasts. These searches have all failed, though they have examined only a few stars and/or a few bits of the spectrum.

A variation of this approach is searches for flashes of visible light: "optical SETI" or OSETI. These efforts have only recently started.

Another approach is searches for evidence of large engineering projects. The best-known example of that has been the canals of Mars, but those have turned out to be figments of the imagination of their observers. Searches for galaxy-scale engineering have also failed, though such engineering projects are very difficult.

So declaring SETI a failure is rather grossly premature.

METI: Messages for Extraterrestrial Intelligence

Also called "active SETI" or ASETI. It involves broadcasting messages to various stars, and also putting messages on spacecraft headed out to interstellar space. The messages so far have been diagrams intended to describe us and our Solar System, though the Voyager spacecraft have also included lots of pictures and sounds from us.

So far, our messages have not gotten any responses, and the spacecraft are still not very far from the Sun by interstellar standards.

CETI: Communication with Extraterrestrial Intelligence

That's an alternative name for SETI that was popular around 1970. It is the goal of SETI and METI efforts.

It must be pointed out that many SETI supporters hope to discover ET's that are as as friendly, as helpful, and as talkative as the ET's reported by UFO contactees, even if across interstellar space.

IETI: Invitation to Extraterrestrial Intelligence

Proposed at this site: Invitation to ExtraTerrestrial Intelligence, a project of the late Allen Tough. It invites ET's to contact us. That is a commendable ambition, and I agree with it myself.

To any extraterrestrial visitors who might be reading this page, please consider contacting us Earthlings, even if not necessarily me.

But an over-the-Internet invitation has a great difficulty. It is difficult to reverse-engineer Internet transmissions, especially satellite Internet transmissions, for reasons that I explain here. So one has to be covertly present on our planet to do so, complete with using Internet-client end nodes, the desktop and laptop computers, the smartphones, and the tablets that Internet users access the Internet with. Server nodes and telecom-company hardware are usually less accessible.

Internet communication works by sending messages in packets, and these packets have a layered structure:

The link layer is for the specific hardware that the packet is being transmitted over. A packet may be sent across many different sets of hardware, and the link-layer header and footer may be different for each one.

The internet layer is for specifying which end node will get the packet. It can be either for the familiar Internet or for inside some Local Area Network (LAN).

The transport layer is for specifying which end-node receiver software will get the packet, something done with a port number. It can also handle various other tasks, like ensuring reliability and correct arrival order.

The application layer is for the software inside the end nodes, software like web servers, web browsers, and the like, software that is the purpose of the networking. This layer has protocols specific to applications, either published ones, like for web browsers and servers, or proprietary ones, like for networked games.

Satellite Internet service adds further difficulties. Satellite transmissions typically have error-correcting coding and they are often encrypted. So without knowledge of the protocol details, they would be very hard to reverse-engineer.

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